kikiturbo

sure, it all starts with the tires and I am looking at stock sized tires first and foremost. No front ARB might work for you as autocross is mostly slower speed stuff and shorter corner.. we use it when going driving on snow usually but not on the evo platform since we have ayc diffs and that throws a completely new set of possibilities..

EVOlutionary

iTrader: (38)

I get your point. But on the other hand that's like asking if Bullet Engines has a vested interest in the platform by developing a billet 4g63 block.

Regardless, looking forward to what you come up with for the rear. We may be digitizing the pick up points in the rear off the laser scan, so if that data is useful to you let me know.

Dallas J

iTrader: (1)

That would definitely be useful for me compared to manually measuring to ~1/16". Id probe it in the Haas but it doesnt fit

kikiturbo

I was involved in some discussion on MLR about roll centres so I pulled some graphs from my model on e9 suspension.. might be interesting

Stock e9 suspension, lowered 25mm vs same lowering on a suspension that has been modified by lowering the bottom ball joint 35 mm, with bumpsteer adjustment + increase in castor from 4 to 8 deg. Same initial camber (2 deg IIRC)

stock on the left


camber in roll, stock in red

you can see very small difference actually, maybe 1/3 degree on full roll

camber in bump, stock in red, again small difference actually but not to be sneezed at


castor change is good... this is camber change in steer, stock in red.. signifficant difference due to increase in castor, almost 1 deg change on full lock


however, I feel this is the point of roll centre correction.. With lowered stock geometry we get massive lateral movement of rollcentre... with 35 mm correction we are talking 4x less... from 2.2 meters movement on either side to something like 40 cm..

this will give more predictability to car behaviour among other things..

Dallas J

iTrader: (1)

Found your discussion there and tried to bring up some other suspension things I think are more important than RC (I find instant center more important on tarmac) though I dont see my response.. Maybe it has to be approved?

Dallas J

iTrader: (1)

Heres what I posted though,

"Upright discussions, I love upright discussions :smthumbup

Saw kikiturbo's measurement results which prompted me to come looking to see whats going on out on the other side of the pond.

One of the things Im seeing here is talk of roll center migration, my models all show an asymptotic relationship in migration as the RC approaches ground level. But there is one more odd issues I (and some other very knowelegable guys) don't really understand what it actually is the instant center the point the control arm vs slider axis reaches 90deg and instant center switches side.

I find this one more important to try and understand and at least avoid because its that tire thats doing 75+ % of the cornering. Combined RC though probably has more merrit in dirt than tarmac, but thats beyond my understanding.

Overall though, my models dont show what im hearing Vishnu (and others?) have claimed stock geometry is at the worst position. Im finding most things at the OEM level are very by the book good range other than a relatively low caster amount.

And not to try and advertise anything here, just a little justification for multi piece uprights. There were two major reasons, one is I can make the strut mount at different lengths or angles, or even an SLA adapted piece (still waiting for the person serious about working with me on that one). Steering arms I can make longer/shorter for instance a local guys challenging SCCA FP class and running 16" wheels. He can fit the 1.25" correction but needs a shorter arm. But the biggest reason, I'll add ~1lb back in to drop the cost significantly. Im not trying to target the big named guys who can afford 5k per end of the car, its the privateer grassroots guy I want to help. "

kikiturbo

yeah, dont see your response.. maybe try again..

minimising roll centre migration is something you can do on a double arm setup, not mcpherson. However I wonder what the difference will be as stock suspension when lowered by 25 mm or so (which is what we run ) tends to end with horizontal arms and huge roll centre movement in roll..
Personally I think that largest difference will be in going to 8 deg castor but roll centre correction (within reason) is another benefit.
Interesting experiment in any case..

Dallas J

iTrader: (1)

It is funny though, that 25mm lowering range is right in the bad spot that I think we're both agreeign on. Beyond that, at least everything is set to one side of instant center and RC movement so you can at least tune for their characteristic.

We run about 2-2.5" lower than stock, depending on the tire, which is very low. If I could go lower, I would. What seems common for the EU guys in more hardcore setups for spring rates? I've seen some hill climb cars that I thought were possibly too stiff, but then claimed rates of others see much softer than US Autocross guys tend to run.

kikiturbo

oh, I am more into rally, so I am dealing with 8 to 10 K range, maybe 12K for the track but I need slicks to use that. Actually, tarmac rally car will be in the sub 8K range. For our bumpy roads my target is something like 8K front 9K rear, 5K/5K set for winter and 10K/12K for track. No AX like you run in the US here. Since I am still on stock wheel size I dont have to lower as much as you do.

Since mitsubishi platfom is coming from rally, even the hillclimb guys will not run overly stiff springs. If you ask Reiger they will point you to some sub 10K springs. . I have no idea about cars with lots of aero though.

Dallas J

iTrader: (1)

Well thats making more sense. We run 14k/16k though have done every combo of 8k, 10k, 12k, 14k, and 16k with in 4k splits. And we've been high, gone back low, and new creeping back up on high. So stiffly sprung means very little actual suspension travel in roll, so we are now caring more about how the car rolls and in particular how it dives with inconsistent RC's F/R.

griceiv

iTrader: (2)

seems like Dallas is already on it, but lateral roll center migration is a completely useless metric to try to minimize. The 'best' suspensions are going to have crazy amounts of lateral RC migration (like +/- infinity) because the instant centers are near ground level (which is exactly what you want to minimize jacking forces).

Dallas J

iTrader: (1)

Seems to me their is some balance of outside jack force and inside dive force. Most articles I've read with regards to raised roll centers and jacking effect all seem to be making the assumption of excessively high without reference to what excessively high actually means. Is that above lower ball joint height, above wheel center, etc.

What I've been shooting for is living in that ~1-3" range above ground which keeps things on one side of above/below ground. Right now I know my car is above that and it does seem to do funny things. Im making a new ball joint stud (Will get extras for you marshal) that are OEM length instead of my current 10mm longer than stock joint.