21 replies to this topic

[Andy69]

I've been workign on a write up but I keep having to go back and revisit things to get it straight in my head.  It's been 4 years since I last looked at this.  I'm currently working on other aspects of the car, and suspension setup will be the last thing.  I'm just going to leave it where it stands for now

 

Based on the work I've done so far with the various models and calculators, when I get to that point I'm going with the following setup

 

27mm front bars

550# rear springs

front and rear ARBs

front height set to -3 degrees on the LCAs (slope up toward the wheel)

no aero

 

Once I get it set up this way I'll take some measurements off the car such as initial camber to see how it compares to the models.  I'll also pick up a pyrometer to check tire temps as I have a hunch that the initial camber, if it matches the model, will be enough, and I'll be able to swap out the camber plates for the strut bar.

 

I expect this to be neutral handling with the least amount of body roll.  If I need to tame any understeer I can add more rear spring.

 

aero will come later

Edited by Andy69, 20 June 2024 - 07:46 PM.

[CSPCRX]

In for results.  I’m running 30mm bars and 600lb springs with 3 degrees of camber up front.  My pyro analysis showed good temps across the tire surface.

 

im considering upping rear spring rate as I’m not getting as much rotation as I would like.  Tires impact this so much as well, but for my setup I feel I need a bit more in the back.

[Andy69]

In for results.  I’m running 30mm bars and 600lb springs with 3 degrees of camber up front.  My pyro analysis showed good temps across the tire surface.

 

im considering upping rear spring rate as I’m not getting as much rotation as I would like.  Tires impact this so much as well, but for my setup I feel I need a bit more in the back.

 

If it's just a little bit you need, try a little toe out in the rear.  You can add some shims \around the four  bearing assembly bolts.  Adding a like 1/32" to the front two would give you maybe 1/16 toe out, or adding to the bottom you can get some neg camber.  I had it set up with a little toe in but I'm going to leave the shims out and add later if I need to tune

Edited by Andy69, Yesterday, 09:21 AM.

[Andy69]

In for results.  I’m running 30mm bars and 600lb springs with 3 degrees of camber up front.  My pyro analysis showed good temps across the tire surface.

 

im considering upping rear spring rate as I’m not getting as much rotation as I would like.  Tires impact this so much as well, but for my setup I feel I need a bit more in the back.

 

 

I plugged your spring rates into my model just for grins and came up with frequencies of 2.94 and 3.17 which is higher than most seem to recommend for autocross but more or less the same spread f to r in terms of frequency.  Mine with 27.5 and 550 is 2.55 and 3.03 which gives the rear more spring relative to the front than your setup so I would expect maybe neutral or oversteer but it all depends on driving style.

 

All that is going to change once I add the aero and start messing with it.  I wish I could find a good online calculator or at least a guru of sorts to kind of point me to a ballpark initial setup.  I have a pretty good idea how much more rear grip I can expect from a spoiler but I'm completely in the dark as to the effects of a front splitter and air dam.  An air dam doesn't just make downforce in the front, it changes the entire car by restricting air entering the underside of the car from the front.  I'm limited as to the size of the front splitter, and actually the spoiler too but the spoiler can be 9" tall and angle is unrestricted so I'm envisioning maybe making a series of test mules of different heights.

Edited by Andy69, Yesterday, 09:44 AM.

[CSPCRX]

I was figuring based on your data my rate was a little low in the rear.  Mine is setup for time attack, but these larger tires and stager setup have really played with things.  I do not like running a tone of bar, always feel like it makes the car more twitchy.

[Andy69]

I was figuring based on your data my rate was a little low in the rear.  Mine is setup for time attack, but these larger tires and stager setup have really played with things.  I do not like running a tone of bar, always feel like it makes the car more twitchy.

I think it depends on driving style.  I've seen autocross setups on these cars with a ton of front spring - like 31mm bars plus two ARBs and relatively light rear springs.  Seems to me it would understeer hopelessly but the car was quick.

[Andy69]

I was just thinking on my way to the liquor store, I think the biggest reason it's taken me so long to get this car straightened out is that the weight I removed changed the balance considerably.  

 

The car was well set up when I got it.  My aunt didn't know the setup as my uncle handled all the mechanical stuff and he'd passed a few years earlier.  Whoever did it knew what they were doing.  It was fast.

 

But I took 250+ lbs off it including removing the roll cage.  But I didn't do any kind of baseline model.  I should have but I was learning all this.  I'd do it differently now.

 

Anyway, I'll get it.  It's taken me so long because I just got burned out after it broke the last time.