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Circuit Suspension set up

Wed Feb 11, 2009 10:14 pm

To all the circuit racers out there. I am finally getting to the point of my car being track ready. I will now be setting up my suspension and need to know where to start with for the suspension settings. I am currently running Tein HA and 17x7.5 wheels with 215x40x17 tires. I think I will start off with a -2 degree front camber and 0 rear along with a slight rear toe out. The car pushes a lot through the corner and quick transitions. Any suggestions would help me out. Thanks.
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Thu Feb 12, 2009 1:53 pm

Get a temperture probe, track it then get in pits as quick as possible and check for event temp accross width of tyre. and adjust camber as necessary until its even all accross. Its the only way to check if camber is correct for race applications....

Thu Feb 12, 2009 2:28 pm

Have you seen the whiteline specs for the GT4? They're posted here on the site. I think its all zero toe with -1.5 up front and -1 in the rear. I tried to get that with stock hardware and managed -0.5 up front and -1 rear with all zero toe. I've had it for solosprint (Time attack), driving school, autoX, and DD and have liked it. I'd like to try a little more camber up front. The car is not completely neutral with that but I've had it worse before those specs. I'll try to dig up the numbers but I think I had toe out front and back which had me pushing in corners pretty bad. The -2 up front sounds like a good compromise. You might want to look at a little camber for the back though. How come you are looking for toe out on the rear?

I agree with the temperature test too once you have a starting point. I've used an IR thermometer before with decent success. Not as accurate as a probe since it is only surface temperature and you have to be quick but it does show up some differences that I used to adjust tire pressures for slalom and sprints. Slight pressure differences were making a BIG difference in my lap times.

Thu Feb 12, 2009 3:36 pm

Thanks for the replies. The reason I was looking for a little rear toe out was to help the car rotate as it does not like to now. What I will try is your combination plus the -2 front and keep rear toe at zero. I may try to enter the Redline Buttonwillow event coming up so I will be dialing in my suspension until then. I hope to have the new custom suspension coming to me before then but if I don't I will stick with the HA. I am still new to the AWD drivetrain so I am still learning about how to drive this car fast. What I have learned is that I have to drive it more like a front wheel drive car than anything. Yet, it's still a little different. The car pushes on power through the corner without rotating. I seriously don't know how you guys auto cross this car because it just does not like to change direction. :(

Thu Feb 12, 2009 6:52 pm

So how serious are you about this? What custom suspension do you have coming?

If you just want to do the occasional track day then I'd just go with whiteline specs and adjust as you feel from there.

If you really want to push the platform and be competitive at Time Attacks, study this guy's tech articles: http://farnorthracing.com/tech.html
That may be more involved than you really want to get in to as his approach involves a lot of datalogging etc. But it's what I would do if I was going to seriously track a 'trac.

Also pick the brain of gtfour77. He is by far our board's most serious twisty racer.

I expect pics and vids if you do the redline event!


Thu Feb 12, 2009 8:08 pm

I have the same suspension you do and I feel like the rear rotates a bit better with the rear struts dialed up a couple clicks harder than the suggested settings.

What all suspension work do you have? Have you gotten the whiteline sway bar yet? It really helps a lot.

And yes, we need more pics & vids of alltracs in action.

Fri Feb 13, 2009 1:21 pm

If you REALLY want it to rotate some tire pressure changes should be able to get the car to power off over steer to the point of needing to be careful not to spin it (Which is where I run into problems, I have an unfortunate reputation of spinning out a lot at events but it is fun).

While still learning the car I would run through slaloms by hitting the gas and letting off when I want to turn (big oversteer situation) then mashing it to straighten out the car once it was pointed where I want to go (Understeer to get it going straight again), let off, mash, let off, mash. Not elegant or fast but it was exciting. Do it right and you can get some AWD drift going for a moment, which doesn't get you there faster on pavement really.

I think to get it to rotate in a controlled manner I want to try still letting off the gas or light braking to shift the weight forward but not so abruptly as to get the car sliding.

I've seen the link to that DSM page before too and it is a really good read. I compete against a Talon locally who is very fast and prepared. I think they are a comparable car when setting up for track events at least for driving style.

I'd focus on getting it to stick, even with stock hardware you can get rid of most of that nasty understeer with very slight alignment and tire changes. This season I was thinking of trying stiffer shocks and springs to eliminate the body roll which is making me pickup the rear inside tire or at least have that tire go light and causing me to slide a lot when the outside tire loses traction. I thought I might go ever so slightly more for the camber 2 or 2.5 front, and no more than 1.5 rear this season. Any thoughts?

Fri Feb 13, 2009 1:34 pm

Oh another thing I've played with is spacers on the back wheels. I've found a big difference in understeer vs oversteer with big spacers on the back. Having them on there makes the car look good but handle poorly. Toyota made the back end narrower for a reason, to make the car understeer less. What I haven't tried is putting spacers on the front to widen the front track. That is something I want to do this season as an experiment.

Fri Feb 13, 2009 2:53 pm

I have messed with small spacers on the front, and there was a slight improvement. A 25mm spacer on the rear increases the rear track more than the front track by a few mm (I think 10mm). I forget specs but we have a thread on it. I put a 8mm spacer on the front and the car did seem to react well to it (I think it made the front track 6mm wider than the rear total). I think as long as the rear track is not wider than the front track you are fine.
I do not mind understeer. I just do not like having so much understeer at such low limits.

I currently run 2 degrees in the front and a little over 2 in the rear. I do need a new alignment since I put the new axles in. I will be running a more conservative setup though. I am thinking 1.5 for the front and ~1 in the rear. If I do any race days, I will likely change the front to the 2.5-3.

My only real opinion on alignment is to try running the car with stock alignment. And once you fully experience the car's characteristics then start turning bolts.

I still have some push on corner entry if I enter too fast but it is rare that I see that limit. Back from the gtfour yahoo list there was a tip given to me by a rally driver to get the most out of this car. Slow in, fast out. I tested this out on at an autox and knocked about 4 to 5 second off my time. I reduced my corner entry speed to keep the car more stable and as I got to mid turn I was able to floor it and have a much faster exit speed. I really think it is related to the center dif being a VC and slow to react. It isn't doing much for us on corner entry and is finally transferring power as we are already in the turn. I would like to experiment with it more with my new tires.

Another driving concept I picked up recently was left foot braking. Last time I went to the dragon I decided to experiment. I would brake with the left foot and keep my right foot on the gas and I was able to make the rear end throw itself out. I wanted to play with it more, but it turns out my rear control arm was unbolted and might have been affecting this. Now that everything is installed correctly I would like to see if I could still simulate this. I felt like I was able to get on the power earlier in the turn. I felt like I have to modulate the the throttle more on corner exit and correct with the steering since the rear was so apt to go out on me. I think I might be able to use this as part of my corner entry and maybe make some adjustments by apex then full throttle on corner exit.

I would like to experiment with caster on these cars. I have heard since I owned the car that the caster needs to be adjusted. From what I have studied on some other cars, the caster adjustment has helped their steering, which may affect your slalom speed.

I feel like one mod that helped me was going with a smaller steering wheel. Since you can not get the short rack for these cars anymore I went with a much smaller steering wheel. I felt like before I could not turn the wheel fast enough the distance it needed to go to get through the turns.

Now that my car is done, I want to get more seat time in it so I can rethink my suspension and such.

Fri Feb 13, 2009 3:15 pm

another good way to get the car to rotate is to stagger the rim width front to back. i remember reading a scc article a few years back where they tested a bozz speed evo that had 9 inch wide front rims and 8.5 in rear. tire widths were the same but the narrower rim allowed the sidewall to flex slightly and thus allowed predictable breakaway and rotation. obviously this is an expensive option but judging by the 997 it might be viable. besides 17x7.5 and 215's are a pretty narrow and smallish choice. they will most likely overheat very quickly. a spec miata runs 205's and they weigh 1,000 lbs less.

Fri Feb 13, 2009 6:04 pm

I have seen reverse staggered run on two gtfours. The garage cruise 185 is one.

Wheels were 17x9.5 35et and the tires were: F 255/40/17, R 235/45/17

Fri Feb 13, 2009 6:15 pm

Again I thought the same but the information is coming from Papa Gushi himself so I figured I'd give it a shot. He has a 165 himself and is running narrow tires as well. I'll see how it goes. If it doesn't I will definately go with the larger wheels and tires as I had planned in the first place. I run 25mm spacers front and rear in order to keep the same difference in track between front and rear. Doesn't look good in the rear but I'm trying for better handling than I am worried about looks.

I left foot brake as well to rotate the car but it's not how I would like to drive if I can help it and it only works for faster corners. Slower corners I have to deal with a great amount of understeer. It's understeer heaven.lol Understeer in entry, understeer mid, understeer exit. Hahaha.

I just lost my wheel bearing last week so I will have to replace that before I get my alignment done. I'll let you guys know how everything goes. We're planning on running Big Willow after it's done to get some idea on what the car is doing.

CMS-GT4 what settings are you running on your shocks for track? It may be a good starting point for me. After reading that article on the Talon I was happy about the choice in suspension that I have coming my way. Sorry to hear about the HAs though since I do like them.

Fri Feb 13, 2009 6:30 pm

When I would autox, I think I ran 8 clicks from hardest in the front and 10 in the rear. If I remember correctly. I ran the recommended height then too. The car is a little lower now but I also have a rear lsd now too. When I used to run at autox I had 205/40/17s. It was not near enough tire for the car. Now I run 255/40. While I love the grip, I really notice the difference in the heavier tires.

I will likely go down to 245 for my next tire.

Do you know your springs rates on the HAs? I have the 10kg F and 7kg rear. They offered up to 12kg for the front.
Last edited by CMS-GT4 on Fri Feb 13, 2009 6:32 pm, edited 1 time in total.

Fri Feb 13, 2009 6:31 pm

i was always opposed to using staggered tires on an awd car for driveline sake. unfortunately st165's have to run narrow tires by design unless you are willing to butcher the fenders and use coilovers. good luck and keep us posted!

Fri Feb 13, 2009 6:58 pm

I'm running 10KG front and 6KG rear. Actually I didn't even know that they offered higher spring rates. What I have coming is a 12KG front and 8KG rear. I may need to increase the rear spring rate some more but I won't know until I try it. How are the 225s doing on the track? What wheel width do you run? As for my suspension I run 6 from the top in the front and 4 from the top on the track, 8 and 8 in the canyons, and softest on the street.
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