Setting up ride height
10-31-2012, 04:54 PM
#31
The mk2 325 rear tire vs the mk1 305 rear tire basically accounts for the rear ride height difference of 133 vs 137.
What is more interesting is that in the front, the .2 RS running a 245/35 tire sits lower than the .1 with a 235/35 tire - so if I've done my math correctly, the big difference between the .1 RS and .2RS is that when you adjust for the taller front tire, the .2RS is actually lowered from the factory by basically 10mm at the front versus the .1RS - that is likely their setup difference to load the slightly wider front tire with additional weight - the rear is basically the same adjusted for the 325 tire.
If someone happens to have an as delivered factory spec car corner weighted, I'm guessing they have probably moved 50-100#s forward with the .2RSs vs the .1RS
As a total aside, there was a old video from a wind tunnel with a tuner that didn't seen to get a lot of respect around here comparing a mk1 gt1, mk1 gt3 with a cupfront lip and a few other aero tweaks, a cup car, and then the stock and tweaked street GT3s aero when they raised the rear end or sropped the whole car.
What was interesting from that video was if memory serves correctly, the biggest downforce effects were achieved my running the cup lip and then increasing the rake by raising the rear end - rasing the rear end, in combo with the cup lip, substantially increased front downforce for an mk1 gt3. Also surprising to me was while they could do this, the cup cars as delivered in a wind tunnel create almost no front downforce (997mk1s) but substantially more rear downforce than street cars - I thought that somewhat weird that a cup setup could be made so fast without substantial front downforce. I thought about this for a while but when you see how these cars are raced, they are really setup to carry as much speed into a corner for passing and then as much grip out of a corner for straight line speed - this while the heavy downforce prototypes fly by them in the corners with much higher downforce and mid corner speed.
10-31-2012, 05:10 PM
#32
Pro
If one were to shoot a laser @ 77 mm across the bottom of the car, parallel to the surface the car was sitting on, would the angle of the tub actually be raked, or is it just that the measurement point for the rear is offset up 38mm?
10-31-2012, 05:16 PM
#33
This means that when you measure on a flat surface the front suspension is 77mm from the flat floor and the rear suspension point is 115mm from the flat floor. This is on yokohama slicks that are 240/640/18 & 280/680/18 - cup spec tire in GTC and IMSA Cup in the USA.
Scrutineering uses a block that is as tall as the minimum ride height and sweeps it under the front and does the same for the rear. if the car does not clear the block, then you get dq'd
Scrutineering uses a block that is as tall as the minimum ride height and sweeps it under the front and does the same for the rear. if the car does not clear the block, then you get dq'd
10-31-2012, 06:07 PM
#35
Drifting
leave the front height alone, as-is... and LOWER the rear.
Grady had his GT3 setup with the rear all jacked up (from stock) at Sebring last winter, I told him something was wrong. With his new RS he LOWERED the rear from stock and now he loves it.
FWIW - if you lower the rear like I did then you cannot put the stock wheels/tires back on as they will rub the fenders. Stock wheels fit exactly without rubbing when sitting in the garage but as soon as you get in the car the left rear hits the fender.
couple of pictures of my low riders on 18" BBS:
10-31-2012, 06:37 PM
#37
Rennlist Member
Thread Starter
So would -10mm in rear be a good place to start on a .2?
10-31-2012, 06:47 PM
#38
Rennlist Member
FWIW, I run 245/40/18 Nitto's and 335/30/18 Toyo RA1 with these ride heights:
We checked trakcar 3.1 and 4.0 today and they are about the same at about with new tires mentioned above.
F 96
R 126
So I was lower then I thought. If you go lower, as I tried before the car gets bouncier over curbs and big bumps at Sebring, but it will be better on smooth tracks I suppose.
Kept rake a little less at 30mm.
Everyone like different setups, but this works well for me and the last 2 guys that bought my last 2 RS.
We checked trakcar 3.1 and 4.0 today and they are about the same at about with new tires mentioned above.
F 96
R 126
So I was lower then I thought. If you go lower, as I tried before the car gets bouncier over curbs and big bumps at Sebring, but it will be better on smooth tracks I suppose.
Kept rake a little less at 30mm.
Everyone like different setups, but this works well for me and the last 2 guys that bought my last 2 RS.
10-31-2012, 06:54 PM
#39
Burning Brakes
Join Date: Oct 2005
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I am at 94f and 125 rear. Both 19" stock and of course 18" BBS wheels with Nitto F and RA1 rear fit. It is low though. I am still debating if it is better or worse at Sebring for me.
10-31-2012, 07:12 PM
#40
Drifting
when the rear is lowered and the car feels bouncy at places like Sebring - then turn OFF the shock button on the dash. This will soften the suspension settings and feel much smoother on such a rough track,and upsets the car a lot less as well.
I run without hitting shock button (OFF) at all tracks as I like the car to be easy on the bumps - I seem to hit all of them.
I run without hitting shock button (OFF) at all tracks as I like the car to be easy on the bumps - I seem to hit all of them.
10-31-2012, 07:16 PM
#41
as a matter of fact that is not totally correct, as the car uses steering input, yaw sensors, throttle and different parameters and stiffs the suspension by itself even without the button being depressed.
10-31-2012, 08:01 PM
#42
I'm with Clarke and Mike Levitas - except I have also lowered the front
I got the same info from pro David Empringham who took me out in my car, a lowly mk1 at Mosport at a 1:30 - but my car is also lowered at the front but I run 600/900 springs and Mosport isn't Sebring bumpy.
Similar to what Clarke said, at my rear lowered height, the 2mm more aggressive offset just about touch even with 900# rear springs when I run the 315/30/19 R6.
I run, in my attempted curb-side measurement, about a 15mm rake with the front close to 90mm - but my springs allow this - stock mk1 springs would not.
The tracks I visit, Mosport, Calabogie, Tremblant, Watkins are all non-bumpy so this seems to work.
Based on driving in downtown Toronto, if I was at Sebring I would have crashed and died long ago. My setup works on average to smooth tracks.
I got the same info from pro David Empringham who took me out in my car, a lowly mk1 at Mosport at a 1:30 - but my car is also lowered at the front but I run 600/900 springs and Mosport isn't Sebring bumpy.
Similar to what Clarke said, at my rear lowered height, the 2mm more aggressive offset just about touch even with 900# rear springs when I run the 315/30/19 R6.
I run, in my attempted curb-side measurement, about a 15mm rake with the front close to 90mm - but my springs allow this - stock mk1 springs would not.
The tracks I visit, Mosport, Calabogie, Tremblant, Watkins are all non-bumpy so this seems to work.
Based on driving in downtown Toronto, if I was at Sebring I would have crashed and died long ago. My setup works on average to smooth tracks.
11-01-2012, 03:48 PM
#44
Race Car
Set of coilover wrenches and a level surface is all you really need.
It'll throw off your alignment though so plan a trip to the alignment rack shortly after making your changes.
It'll throw off your alignment though so plan a trip to the alignment rack shortly after making your changes.
