MS6 Suspension Data & DIY Bilstein Coilovers

[phate]

From last weekend:

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First time on asphalt this year. Still not great on asphalt. I ended up 6/105 on PAX and 2nd on raw; and Johanna ended up 14/105 on PAX, and 5th on raw.

[zenit]

Originally Posted by zenit @phate; did you get a chance to look at whether water injection caused an overall decrease in airflow?

Bump?

[KevinK2]

Originally Posted by zenit @phate; did you get a chance to look at whether water injection caused an overall decrease in airflow? ...

Based on the dyno plots, there was a 13% loss of peak hp with the highest water inj setting. Even if he has the mass flow in g/sec, for flow comparison he would need to know the absolute temperatures and pressures to compare volume flow rates, at the Mass Flow Sensor. But the square root of the absolute temperature ratio is used, which becomes a small influence on flow. Phate mentioned this about BAT"s and water inj'n with small jets: "Saw BAT's upwards of 240° without water injection, and 200° with". I'm not sure that is at the MAF.

So his mass flow data, best corrected for temp and pressure changes with water inj'n, would be the best way to check the flow difference. But the power ratio should be close ... 13% loss.


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[phate]

We've been busy autocrossing nearly every weekend since the car has been running.

Currently hauling the car out to Lincoln, NE for SCCA Solo Nationals. We're running Tuesday/Wednesday, me in ESP and Johanna in ESPL (ladies have a full class of 7 for ESP!).

Picture from the last Autocross, taken by @burn813;

Sent from my SM-G935V using Tapatalk

[KevinK2]

Good luck to both of you. Your 1st gear starts have had low rpm shifts to 2nd ... easy on the trans-axle. Hope it holds up!

I'm sure you will turn a lot of heads with your performance in a Mazdaspeed6.


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[KevinK2]

I checked the SCCA Nationals results, and it appears Johanna placed 3rd ! Congrats !! Not sure, but looks like Phate (Clint) did well on one course ( well done! ) but had issues with the 2nd course, messing up his average.

2017 SCCA Nationals, partial results including E Street Prep'd

Results Files


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[Nliiitend1]

Yeah, his hot-pipe kept popping off the turbo, IIRC.

[KevinK2]

At least he ran well on one of the 2 courses, before that problem.
Better than the multiple transaxle failures and replacement ordeals that happened at a previous national/Pro event.

Last June Pro Event



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[phate]

Originally Posted by KevinK2 I checked the SCCA Nationals results, and it appears Johanna placed 3rd ! Congrats !! Not sure, but looks like Phate (Clint) did well on one course ( well done! ) but had issues with the 2nd course, messing up his average. 2017 SCCA Nationals, partial results including E Street Prep'd Results Files .

Nationals was full of highs and lows. Johanna did get 3rd in ESPL, which was awesome to see. She coned away a really quick run on the first day, which ended up costing her 1st place. But, a trophy at nationals the first time you go is nothing to be disappointed about - It was great.

For me, I drove, at best, mediocre on the first day and was 2s off pace. The second day was plagued by popping off the charge pipe to the turbo 3 runs in a row. We tried to save it, use a different clamp, etc, but it didn't hold. My 3rd run I DNF'd with a near-spin when it popped and killed power mid slalom. It came fully off near the end of the run. I think I would have been on pace the 2nd day seeing my time with near-spin and no power the last 1/4 of the course.




So, I've been looking towards next year. Several projects, but nothing as major as last year. These are the big ones:

• 315's on 18x12"
• Shock revalve with potentially stiffer springs

The car has changed drastically in the 3 years I've been running this setup. I've cut significant weight in both the sprung and unsprung masses, as well as changed the grip potential with the wide Hoosiers.

Attached a few pics








Johanna's cone:

[phate]

Going back to the event 2 weeks before nationals - I figured out the breaking up in long left handers that has been with us for a long time. It was really bad, and I happened to be data logging. I saw fuel pressure dropping slowly through a really long left handed section, so I did some investigating. I ruled out the high pressure side since it was a gradual decline, and @MATT DAMOND; sent me an old in-tank assembly they had lying around.

The basket design on the MS6 is bad. There's no backflow prevention (flapper valve) on the inlet port at the bottom of the basket. It's located at the front side (towards the front of the car), and it's oriented towards the passenger side of the vehicle...Take a look at this really terrible quality video:

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So, if it's low on fuel from running the tank low and/or being heavy on the throttle, braking and then turning left is a great way to evacuate all but a little bit. Makes total sense because after long sweepers I'm usually getting back on the throttle heavily and there's nothing for the pump to suck up.

Fix: Use an MS3 basket on both sides of the fuel tank. The MS3 basket is nearly identical, except for the crossover tube mount, and it has a flapper valve to prevent it from draining. [The 6 has what looks to be the same mounting point for the flapper valve, but it's too wide to fit the MS3 flapper.] The 6 has two openings for baskets, but the passenger side one is a crossover tube with a level sensor on it. My current configuration has the passenger side assembly simply pumping into the driver's side assembly. I did that so I didn't have to modify the stock plumbing that attaches externally to the pump/tank.

It takes some parts swapping between basket assemblies, but the pumps and connectors are identical. I used the original MS6 basket tops with a MS3 assembly in the tank. I kick on the passenger side pump by with a relay triggered by the primary pump's voltage. Fuel pumps and lines are completely unrestricted in my class, so I may refine it later on.

[KevinK2]

Originally Posted by phate Nationals was full of highs and lows. Johanna did get 3rd in ESPL, which was awesome to see. She .... So, I've been looking towards next year. Several projects, but nothing as major as last year. These are the big ones: 315's on 18x12" Shock revalve with potentially stiffer springs The car has changed drastically in the 3 years I've been running this setup. I've cut significant weight in both the sprung and unsprung masses, as well as changed the grip potential with the wide Hoosiers. Attached a few pics

Looking at the pics, I can see you could use a bit stiffer springs, based on lean due to the very high grip. You need some of that lean. In the hard corners, the tires look like all 4 have contact across the tire width, and you are not lifting any of them ... all that work payed off ! Great set-up and talent.

Fire the mechanic who made up the charge pipe to compressor hsg connection. Strange that it held up for Johanna's runs ???

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[phate]

Originally Posted by KevinK2 Looking at the pics, I can see you could use a bit stiffer springs, based on lean due to the very high grip. You need some of that lean. In the hard corners, the tires look like all 4 have contact across the tire width, and you are not lifting any of them ... all that work payed off ! Great set-up and talent. Fire the mechanic who made up the charge pipe to compressor hsg connection. Strange that it held up for Johanna's runs ??? .

I attached a couple high resolution pictures.

Cornering with little throttle or brake, both inside tires touch, but it's only on the inside 1/3-1/2 of the tread.


Heavy trail braking causes lift of the inside rear. I've seen it pull it off the ground 1-2".


I've seen the inside front catch air over slightly uneven surface on corner exit when we're heavy on the throttle. Lack of LSD in the front is pretty apparent when the inside front goes light.

[KevinK2]

Thanks for correcting my comment about all tires being in flat contact in a hard corner. The second original pic clearly showed edge contact on the inside tires, as you just noted and showed .. I should have picked that up.

"Heavy trail braking causes lift of the inside rear. I've seen it pull it off the ground 1-2""

In theory, I thought this raises the COG and limits the elastic roll resistance to just the front suspension, typically a bad thing. But for auto-x, I also thought it would be quicker around sharp corners. What is your experience, rear lift good or bad for tight corners?

"I've seen the inside front catch air over slightly uneven surface on corner exit when we're heavy on the throttle. Lack of LSD in the front is pretty apparent when the inside front goes light."

I assume you get wheel spin at the light side. I could see high spin with a center diff that is open, and a LS rear diff. But with the oem system, I can't see how high spin at the inside front can occur. Would you elaborate on this?

Thanks!

[phate]

Originally Posted by KevinK2 "Heavy trail braking causes lift of the inside rear. I've seen it pull it off the ground 1-2"" In theory, I thought this raises the COG and limits the elastic roll resistance to just the front suspension, typically a bad thing. But for auto-x, I also thought it would be quicker around sharp corners. What is your experience, rear lift good or bad for tight corners?

My opinion is that rear lift is bad. The more rear lift you have, the more load you put on the outside front tire. Hoosiers are really great at doing two things at once, but the more equally loaded tires you have the better.

Originally Posted by KevinK2 "I've seen the inside front catch air over slightly uneven surface on corner exit when we're heavy on the throttle. Lack of LSD in the front is pretty apparent when the inside front goes light." I assume you get wheel spin at the light side. I could see high spin with a center diff that is open, and a LS rear diff. But with the oem system, I can't see how high spin at the inside front can occur. Would you elaborate on this? Thanks!

There isn't an LSD up front, and the rear drive is a reactive system, you get wheel spin at the onset of power. I don't think I've ever tried to keep the inside front spinning to see if the rear drive would help things "catch up". I back off as soon as I feel the front starting to spin. Might be worth sacrificing a little rubber to find out, haha.

[KevinK2]

Originally Posted by phate My opinion is that rear lift is bad. The more rear lift you have, the more load you put on the outside front tire. Hoosiers are really great at doing two things at once, but the more equally loaded tires you have the better.....

That sounds right. Thinking it through, the rear sprung weight transfer has ended and the cars total roll stiffness decreases with loss of rear rate. When rear lift starts, the suspension now has excessive understeer, so with higher g's, the roll stiffness has decreased, and the once balanced condition of tire loads starts to build and increase an understeer condition .... I think.

Any idea why that charge pipe popped off 3 times in a row?


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[phate]

Originally Posted by KevinK2 That sounds right. Thinking it through, the rear sprung weight transfer has ended and the cars total roll stiffness decreases with loss of rear rate. When rear lift starts, the suspension now has excessive understeer, so with higher g's, the roll stiffness has decreased, and the once balanced condition of tire loads starts to build and increase an understeer condition .... I think. Any idea why that charge pipe popped off 3 times in a row? .

Yes, more load on the outside front should reduce its overall cornering ability at that high of load.

Charge pipe stayed on for both of us the first day, and Johanna's runs the second day. The car sat for a short while and it was back in grid for my runs. I didn't even open the hood before my runs. I don't have a good reason for it, and don't intend to worry about it much. I likely going to work with an intercooler setup over the winter, so it's all going to change, anyway.

Sent from my SM-G935V using Tapatalk

[zenit]

"Heavy trail braking causes lift of the inside rear. I've seen it pull it off the ground 1-2""

In theory, I thought this raises the COG and limits the elastic roll resistance to just the front suspension, typically a bad thing. But for auto-x, I also thought it would be quicker around sharp corners. What is your experience, rear lift good or bad for tight corners?
[/quote]
^this : raises the COG and limits the elastic roll resistance to just the front suspension

Regarding heavy bars for autocross use, big bars are great on initial turn in, but there's a mid-corner, maximum suspension travel penalty to pay. In particular, I was thinking about change in COG across the rear axle, and accelerated loading of the outside tire impacting the ultimate mid-corner grip.

It would be great to have a regressive rate/multi-rate swaybar that would provide high roll resistance on initial turn-in, and then with increased suspension travel, the bar rate reduces and the lateral suspension members decouple enough to allow the rear to roll (versus lift).

Or add some stiff rebound springs inside the shocks, such that you could effectively reduce the spring rate of of the suspension members under extension, and through the magic of swaybars, reduces the outside's wheel rate as well- allowing the rear to squat (and lower the COG).

I don't think just upping the spring rates and bars is the most measured solution.

"I've seen the inside front catch air over slightly uneven surface on corner exit when we're heavy on the throttle. Lack of LSD in the front is pretty apparent when the inside front goes light."

Been noticing this for a while. A wavetrac LSD system would be awesome, but they want $20-30k for the first 20 units. I'm not sure there are 20 people who would buy LSD's for an MS6.

Also, are you now convinced that the VT defeat for SWAS works?

[phate]

Originally Posted by zenit "Heavy trail braking causes lift of the inside rear. I've seen it pull it off the ground 1-2"" In theory, I thought this raises the COG and limits the elastic roll resistance to just the front suspension, typically a bad thing. But for auto-x, I also thought it would be quicker around sharp corners. What is your experience, rear lift good or bad for tight corners? ^this : raises the COG and limits the elastic roll resistance to just the front suspension Regarding heavy bars for autocross use, big bars are great on initial turn in, but there's a mid-corner, maximum suspension travel penalty to pay. In particular, I was thinking about change in COG across the rear axle, and accelerated loading of the outside tire impacting the ultimate mid-corner grip. It would be great to have a regressive rate/multi-rate swaybar that would provide high roll resistance on initial turn-in, and then with increased suspension travel, the bar rate reduces and the lateral suspension members decouple enough to allow the rear to roll (versus lift). Or add some stiff rebound springs inside the shocks, such that you could effectively reduce the spring rate of of the suspension members under extension, and through the magic of swaybars, reduces the outside's wheel rate as well- allowing the rear to squat (and lower the COG). I don't think just upping the spring rates and bars is the most measured solution.

Steady state cornering, without braking or accel, the car doesn't lift either wheel. It's only when you get into the brakes or gas that they lift.

Dive and squat resistance need increased to combat this. I don't want to decrease roll resistance at any point. You'll end up increasing load on the front end by decreasing rear roll resistance, as well as increasing roll in the corner. More roll + more load = unhappy tire.


Car needs more dive/squat resistance, or decreased load transfer.

• Lower the car more to decrease load transfer - that's pretty realistic and easy to accomplish.
• Increase spring rates to increase dive/squat resistance - as long as the dampers are valved appropriately, I think this is going to happen.
• Add z-bars to front and rear suspension - not going to happen, but z-bars are really cool.

Originally Posted by zenit Been noticing this for a while. A wavetrac LSD system would be awesome, but they want $20-30k for the first 20 units. I'm not sure there are 20 people who would buy LSD's for an MS6.

I bet you're right. Have you measured the diff from the 6, or talked to wavetrac about measuring one?

Originally Posted by zenit Also, are you now convinced that the VT defeat for SWAS works?

Pretty convinced, yes.

[Fstrnyou]

I can see that there would be loads of inside front wheel spin if kept hard in the gas on corner exit. Bad for acceleration, but can help limit understeer. Imagine an LSD putting power down to the outside front that may already be at its traction limit.

[KevinK2]

Originally Posted by Fstrnyou I can see that there would be loads of inside front wheel spin if kept hard in the gas on corner exit. Bad for acceleration, but can help limit understeer. Imagine an LSD putting power down to the outside front that may already be at its traction limit.

Me: "I assume you get wheel spin at the light side. I could see high spin with a center diff that is open, and a LS rear diff. But with the oem system, I can't see how high spin at the inside front can occur. Would you elaborate on this?"

Phate's answer: "There isn't an LSD up front, and the rear drive is a reactive system, you get wheel spin at the onset of power. I don't think I've ever tried to keep the inside front spinning to see if the rear drive would help things "catch up". I back off as soon as I feel the front starting to spin. Might be worth sacrificing a little rubber to find out, haha."

The thought is that the center coupling should lock when excessive wheel spin on a front tire initiates. Then the inside tire should be limited to the outside tire speed, thanks to the "locked" center coupling and the limited slip rear diff.

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[Fstrnyou]

He also said he's never stayed in it to see what happens with the "reactive" OEM system. He's always let off as soon as the inside front started to spin.

What I'm telling you is, the inside front will continue to spin until you get some load on it...or let off the gas.

The electronics that engage the rear clutch is amazingly quick. It's engaged before you feel the front spinning.

[KevinK2]

Originally Posted by Fstrnyou ... What I'm telling you is, the inside front will continue to spin until you get some load on it...or let off the gas. ...

and previously:

I can see that there would be loads of inside front wheel spin if kept hard in the gas on corner exit.

It sounds like both you and Phate wisely back off the throttle when you detect inside front tire spin in this tight corner situation.

My problem is that the "loads of inside front tire spin" can only occur if the center coupling is open, leaving you with FWD and an open front diff, with the inside tire off the ground or very lightly loaded.

If the center coupling is effectively locked, both front and rear differential pinion gears are at the same speed. This means the average front half shaft speed is the same as the rear's. In this case, the inside front tire can't be spinning significantly faster than the outside tire.

To me, it sounds like either there is a bit of lag before the center coupling gets the command to tighten up, or the ecu has selected an intermediate duty cycle that allows some slip at the center coupling, and more average half shaft speed at the front.

It is a confusing situation for the ecu, going quickly from heavy trail braking to throttle as you exit.

[zenit]

Originally Posted by phate More roll + more load = unhappy tire.

Sure, but the same is true for a rising COG. More lift, more unhappy tire.
I think roll is the lesser evil, here, especially if you have a steep enough camber curve.

Originally Posted by phate Car needs more dive/squat resistance, or decreased load transfer.

Does it? I feel like further restricting the car's motion even further in an effort to fight load transfer is a game of diminishing returns, much like a FWD drag car.
There's got to be a more creative solution out there for this platform.

Originally Posted by phate Lower the car more to decrease load transfer - that's pretty realistic and easy to accomplish.

Sure, I like this idea the best, but what's the impact on bump travel? Can you sacrifice the travel?
Not to mention, how much more body saw are you going to have to use to make sure the body doesn't turn your 3xx x 18" hoosiers into cheater slicks?

Originally Posted by phate [*]Increase spring rates to increase dive/squat resistance - as long as the dampers are valved appropriately, I think this is going to happen.[/LIST]

Meh, for the reasons above.

Originally Posted by phate [*]Add z-bars to front and rear suspension - not going to happen, but z-bars are really cool.[/LIST]

fuck yes. @xfeejayx; and I occasionally talk about custom tubular subframes. Wanna play in SM?

Originally Posted by phate I bet you're right. Have you measured the diff from the 6, or talked to wavetrac about measuring one?

I did, and talked to wavetrac about it 1.5 years ago and even offered to send them a diff for further inspection.
There weren't interested unless there was financial backing for the project. However, I wouldn't discourage anyone from calling them, they're nice, knowledgeable people.

Originally Posted by phate Pretty convinced, yes.

@Steve@VersaTune;

[phate]

G-G frequency charts from Lincoln. I removed the idle time so I could have a visual of how often we were at high cornering/braking force. It contains ~86,000 data points, so I think it accurately shows our ability to push the car, and to show the capability of the car.

Red is low occurrence, green is high occurrence. Read them as if you're looking from above the car, front end towards the top of the screen. So, up is braking, left side of your screen is turning right.

This is from all of our runs, combined:


This is from all of my runs, combined:


This is all of Johanna's runs, combined:

[Fstrnyou]

Originally Posted by KevinK2 If the center coupling is effectively locked, both front and rear differential pinion gears are at the same speed. This means the average front half shaft speed is the same as the rear's.

I see what you're saying now, and I agree.
I was playing around in an empty wet parking lot a while back. While driving somewhat slow, I turned the wheel then punched it. Inside tire spun, rear tires hooked, and it pretty much drove straight. Per your explanation, the pinion carriers were spinning at the same rate (which is correct). With my inside front spinning like crazy, this therefore means my outer front tire was spinning slower than my vehicle speed. This might explain the severe understeer. Both front tires were slipping. One overspeed, the other underspeed.

Wet or dry, there is a traction limit. And at that limit, I'd expect the same results. A severe understeer if inner front wheelspin is present.

[phate]

Originally Posted by zenit Sure, but the same is true for a rising COG. More lift, more unhappy tire. I think roll is the lesser evil, here, especially if you have a steep enough camber curve.

The front regains ~42% of roll angle in camber gain, the rear regains ~28%. Not enough.

Originally Posted by zenit Does it? I feel like further restricting the car's motion even further in an effort to fight load transfer is a game of diminishing returns, much like a FWD drag car. There's got to be a more creative solution out there for this platform.

Design something that isn't heavy, simple enough that it won't break all the time, and is within the rules. That third part is what I'll have trouble with, I think. More spring is easy and it helps both roll and pitch motions. I don't see any reason not to.

Originally Posted by zenit Sure, I like this idea the best, but what's the impact on bump travel? Can you sacrifice the travel? Not to mention, how much more body saw are you going to have to use to make sure the body doesn't turn your 3xx x 18" hoosiers into cheater slicks?

Yes. It will be overall less roll from lowering CG and increasing spring rate. There's hopefully some offset by going with wider tires (more grip = more roll), but I think I'll overcome it with a 10-20% increase in spring rate.

Fenders were cut so 26" tall tires will clear. 315's are only 25.6" I think there will be plenty of room.

Originally Posted by zenit fuck yes. xfeejayx and I occasionally talk about custom tubular subframes. Wanna play in SM?

No. The car would need to be at least 4-5s faster around a 60s course moving to SM from its current state. I don't think this car is a good candidate for that class.

[zenit]

Originally Posted by phate The front regains ~42% of roll angle in camber gain, the rear regains ~28%. Not enough.

Do you happen to have a copy of the camber v suspension travel graphs that escaped the photobucket apocalypse?

[KevinK2]

Originally Posted by zenit .... Regarding heavy bars for autocross use, big bars are great on initial turn in, but there's a mid-corner, maximum suspension travel penalty to pay. In particular, I was thinking about change in COG across the rear axle, and accelerated loading of the outside tire impacting the ultimate mid-corner grip. It would be great to have a regressive rate/multi-rate swaybar that would provide high roll resistance on initial turn-in, and then with increased suspension travel, the bar rate reduces and the lateral suspension members decouple enough to allow the rear to roll (versus lift). ....

I don't think Phate was suggesting heavier sway bars, fwiw. But you have some very creative ideas. It would be difficult to lower the rear (or front) CG with them in a corner, by their nature of equal torque at each end of the strait bar in torsion. You can get one end of the car to lower in a corner, by having a shorter lever arm setting on the inside wheel, but for an opposite corner, that end would jack the end up instead.

At an Auto Show, I saw a top end SUV prototype, that used hydraulic endlinks, so they could decouple them with a switch on the dash for hard core off-roading, with increased wheel travel. I could see a version of this to stiffen them like steel endlinks, and also allow a softer rate under a combination signal of high g's and tight steering angle. These endlinks would be similar to very small shocks.

As Phate later mentioned, a pair of Z-bars would be ideal in keeping the car level during braking and acceleration. I effectively had one in the rear of the Triumph pictured on the left. It was incorporated in the rear transverse leaf spring, by way of a hinged connection to the top of the rear diff housing. Very stiff vertical support, with minimal roll resistance.

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[zenit]

Originally Posted by KevinK2 At an Auto Show, I saw a top end SUV prototype, that used hydraulic endlinks, so they could decouple them with a switch on the dash for hard core off-roading, with increased wheel travel. I could see a version of this to stiffen them like steel endlinks, and also allow a softer rate under a combination signal of high g's and tight steering angle. These endlinks would be similar to very small shocks.

Apparently those hydraulic endlinks are very effective and very banned from several racing groups.

A couple other ideas are cross-linked shocks, similar to the system used by the MP412c, or position-dependent damping shock absorbers.

Or a third spring/heave spring system.
A the moment, the most feasible solution would be a shock internal rebound spring (which I know are open/unrestricted in the AX rulebook). It would also not be hard to do, even with existing shock-valving.

I'm rusty on the specifics of the AX rules, I'll review.

[KevinK2]

Originally Posted by phate I attached a couple high resolution pictures. Heavy trail braking causes lift of the inside rear. I've seen it pull it off the ground 1-2". ....

I'm a bit puzzled by the pic on the right (post 932). The front wheels suggest a moderate corner, but the rear inside wheel lift is significant. So this must be hard braking from a high speed, on a moderate corner? I know you have stiffened the rear springs, vs the FCM recommended balance. Any chance there is too much roll stiffness in the rear?


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[phate]

Originally Posted by zenit Do you happen to have a copy of the camber v suspension travel graphs that escaped the photobucket apocalypse?

Right click on the icon, open in new tab. If that doesn't work, I'll upload directly later.

Originally Posted by KevinK2 I don't think Phate was suggesting heavier sway bars, fwiw. But you have some very creative ideas. It would be difficult to lower the rear (or front) CG with them in a corner, by their nature of equal torque at each end of the strait bar in torsion. You can get one end of the car to lower in a corner, by having a shorter lever arm setting on the inside wheel, but for an opposite corner, that end would jack the end up instead. At an Auto Show, I saw a top end SUV prototype, that used hydraulic endlinks, so they could decouple them with a switch on the dash for hard core off-roading, with increased wheel travel. I could see a version of this to stiffen them like steel endlinks, and also allow a softer rate under a combination signal of high g's and tight steering angle. These endlinks would be similar to very small shocks. As Phate later mentioned, a pair of Z-bars would be ideal in keeping the car level during braking and acceleration. I effectively had one in the rear of the Triumph pictured on the left. It was incorporated in the rear transverse leaf spring, by way of a hinged connection to the top of the rear diff housing. Very stiff vertical support, with minimal roll resistance. .

I'm trying to strike the balance between bars and springs. I'm right at the edge of too much bar, so more spring is where I'm headed.

Originally Posted by zenit Apparently those hydraulic endlinks are very effective and very banned from several racing groups. A couple other ideas are cross-linked shocks, similar to the system used by the MP412c, or position-dependent damping shock absorbers. Or a third spring/heave spring system. A the moment, the most feasible solution would be a shock internal rebound spring (which I know are open/unrestricted in the AX rulebook). It would also not be hard to do, even with existing shock-valving. I'm rusty on the specifics of the AX rules, I'll review.

The big thing in SP is that stock mounting locations and type must be used for springs:

Ride height may only be altered by suspension adjustments, the use of spacing blocks, leaf spring shackles, torsion bar levers, or change or modification of springs or coil spring perches. This does not allow the use of spacers which alter suspension geometry such as those between the hub carrier and lower suspension arm. Springs must be of the same type as the original (coil, leaf, torsion bar, etc.) and except as noted herein, must use the original spring attachment points. This permits multiple springs as long as they use the original mount locations. Coil spring perches originally attached to struts or shock absorber bodies may be changed or altered and their position may be adjustable. Spacers are allowed above or below the spring.

And sway bars are specifically called out as anti-roll bars...so a z-bar for pitch motion would not be allowed, imo:

Vehicles may only exceed the allowances of Section 13.7 as specified herein. Substitution, addition, or removal of any anti-roll bar(s) is permitted. Bushing material, method of attachment, and locating points are unrestricted. This does not authorize removal of a welded-on part of a subframe to accommodate the installation, or the cutting of holes to route the bar or links. Non-standard lateral members which connect between the brackets for the bar, including allowed strut bars per Section 15.2.C, are permitted. The bar may serve no other purpose which is not explicitly permitted elsewhere herein. Components such as anti-roll bars and strut housings which 84 — 2017 SCCA® National Solo® Rules 15. Street Prepared serve dual purposes by also functioning as suspension locators may not be modified or substituted in ways which change the suspension geometry or steering geometry, and may not be installed in positions (e.g., upside down) other than that of the original configuration.

Originally Posted by KevinK2 I'm a bit puzzled by the pic on the right (post 932). The front wheels suggest a moderate corner, but the rear inside wheel lift is significant. So this must be hard braking from a high speed, on a moderate corner? I know you have stiffened the rear springs, vs the FCM recommended balance. Any chance there is too much roll stiffness in the rear? .

Just looking at how close the bottom of the front bumper is to the ground, I'd say heavy braking/moderate corner. There's still quite a bit of tire deflection both front and rear in that pic.

Increasing rear stiffness via bars and springs to the current rates have only yielded faster times.

[KevinK2]

Originally Posted by phate Originally Posted by KevinK2: I'm a bit puzzled by the pic on the right (post 932). The front wheels suggest a moderate corner, but the rear inside wheel lift is significant. So this must be hard braking from a high speed, on a moderate corner? I know you have stiffened the rear springs, vs the FCM recommended balance. Any chance there is too much roll stiffness in the rear? Just looking at how close the bottom of the front bumper is to the ground, I'd say heavy braking/moderate corner. There's still quite a bit of tire deflection both front and rear in that pic. Increasing rear stiffness via bars and springs to the current rates have only yielded faster times.

I agree with your results. Thinking again about my FCM comment, I was the one who pushed you to rely on physics for spec'ing the rear motion ratio, using the .57 we agreed on, vs his preferred .75" iirc, thus increasing the rear roll stiffness more than he suggested.

We agreed that rear lift is bad, so I was trying to see why it occured in that pic, vs the other pic to the left, with more lean in a tight corner. Another possibility is if the droop was limited by the shock travel ... just a guess.

[phate]

Originally Posted by KevinK2 I agree with your results. Thinking again about my FCM comment, I was the one who pushed you to rely on physics for spec'ing the rear motion ratio, using the .57 we agreed on, vs his preferred .75" iirc, thus increasing the rear roll stiffness more than he suggested. We agreed that rear lift is bad, so I was trying to see why it occured in that pic, vs the other pic to the left, with more lean in a tight corner. Another possibility is if the droop was limited by the shock travel ... just a guess.

I went back on that at some point. I agree on his assessment that backtracking to an MR from frequency yields his number based on how the car rides.

For stiffness and roll bias calcs, I use the mechanical MR of .57.

[thrasher1992]

Following for epic wisdom.

[KevinK2]

(ref: pic in post 932) Rear Wheel Lift

Originally Posted by phate ... Just looking at how close the bottom of the front bumper is to the ground, I'd say heavy braking/moderate corner. There's still quite a bit of tire deflection both front and rear in that pic.

Originally Posted by KevinK2 We agreed that rear lift is bad, so I was trying to see why it occurred in that pic, vs the other pic to the left, with more lean in a tight corner. Another possibility is if the droop was limited by the shock travel ... just a guess.

I think the heavy braking that you mentioned explains why rear wheel lift occurred in the right pic, vs the tight corner in the left pic.

But I'm still trying to rationalize why the rear inside tire lifted in this case, and if stiffer springs would help. As you noted, anti pitch hardware would help, if it existed. A lot of the sprung weight has transferred to the front end, perhaps about 20% based on a high braking g load, CG height, and wheelbase. But for a similar lateral g load, the narrower track vs wheelbase transfers more sprung weight from inside to outside tires.

Both braking and cornering lighten the inside rear tire load.

It doesn't look like a lot of body roll, and my initial thought was lift was due to high rear roll stiffness. Another possibility is lack of droop travel in the shocks, which is easier to check. Stiffer springs would reduce deflections at the wheels, but the impact of rates this high is reduced by the tire spring rates that are in series with coil spring rates at the wheel. I'm not sure if the g-load point of tire lift would change significantly. Lower ride height would delay tire lift, in this case.


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[KevinK2]

Phate, could you run this case with your excel type model? You could move the CG forward to reflect the typcal braking g load in this case, and the forward weight transfer. The roll moment lever arm would need to be corrected. Then based on lateral g load look for negative forces at the inboard rear tire that would indicate lift. You could "dial in" variables to show the current condition of lift, then see the effect of stiffer springs, with the same roll stiffness balance. I recall you had a very accurate model.


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[phate]

Originally Posted by KevinK2 Phate, could you run this case with your excel type model? You could move the CG forward to reflect the typcal braking g load in this case, and the forward weight transfer. The roll moment lever arm would need to be corrected. Then based on lateral g load look for negative forces at the inboard rear tire that would indicate lift. You could "dial in" variables to show the current condition of lift, then see the effect of stiffer springs, with the same roll stiffness balance. I recall you had a very accurate model. .

I haven't gotten around to redoing this, yet. Working out of state is eating up my free time, and I'm working on winter projects whenever I'm home.



Things I have going on right now:

1) Engine and trans are out. I pulled it to replace the clutch, mostly. Turns out I have a leaky rear main seal, so I'll replace it while it's all out.

2) Investigate front diff options...we don't really have any options except for the phantom grip. I saved the diff from my last trans, and checked out how everything works together, today. The front diff is open, and the diff is splined directly to the PTO. So, the PTO turns at the average of the front wheel speeds (edited to correct operation of diff), which makes me think my inside front wheel spin is a sign of a worn clutch pack in the rear diff. I'll probably go ahead and get a low mile rear diff clutch pack this winter while I'm at it. It's about time I start to stockpile some of these things.

YouTube Short

YouTube Short

3) Shocks are out and I'm working out the final details with Shaikh for a revalve.

[KevinK2]

Originally Posted by phate .... The front diff is open, and the diff is splined directly to the PTO. So, the PTO turns just as fast as the fastest front wheel, which makes me think my inside front wheel spin is a sign of a worn clutch pack in the rear diff. ....

I see it a bit differently. The front diff carrier spins proportional to gears in the PTO, and that carrier spins at the average of the two front wheels.

Edit:

It is true the diff (carrier) has an extended tubular splined portion that carries the drive gear for the transfer case. This makes the main drive shaft spin proportional to the diff at all times.

During your test, the carrier (that holds the spider gears) did not turn, it had zero rpms. The front half shafts spun in equal and opposite directions, for an average of Zero rpms.


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[phate]

Originally Posted by KevinK2 I see it a bit differently. The front diff carrier spins proportional to gears in the PTO, and that carrier spins at the average of the two front wheels. .

The carrier can't spin at the average, because one wheel can't spin faster than the diff.

[KevinK2]

By "diff" you you mean the carrier that the ring gear is attached to, in this case ? If so:

For any diff, front or rear, when you turn the outer wheel spins faster than the inside wheel. The outer half shaft spins faster than the inside one. This applies to the side gears in the diff too. The diff can not be at the same speed as either side gear. If the car speed does not change in the turn, I believe the average rpm of the wheels is the diff rpm.

Your demo proved the average rpm of the wheels is the diff rpm.

A quick google should help out here.

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