dbv1

I used to run the following setup:

#1 - 997.1 C2S, GT3 rear sway bar on softest, stock front bar, 71R 245mm on front, 305mm on rear, 30/35 psi. I liked this setup because it was almost neutral but I couldn't really get on the gas 100% because the rear was a little prone of coming around.

I switched to this:

#2 - all the same except rear sway went back to stock and the front is GT3 at 2/5 setting (second softest). Tires are now at 27/35 psi. I hate this setup with a passion. I can finally get on the gas but low speed corners are a pain as the car just won't turn in. Higher speed corners are fine. I am trail braking but it's not really helping.

What are my options? I could stiffen the front bar to say 3/5. Would that dial out some of the understeer? I could also put back the rear GT3 sway (at softest). That is certain to dial out some understeer but the on-gas behaviour could suffer. SpeedDem0n suggests to switch to 265mm front tires but that's not likely to happen this year as the season is almost over.

Any ideas?

sjfehr

Stiffer on the front bar at this point is likely to make your understeer worse. What's your alignment? More negative camber in the front will help reduce understeer. If you have adjustable dampers, you can use them as well.

Most cars will understeer on tight corners due to the difference in slip angle between front and rear tires at different radii; 981 GT3 fixes this with rear-wheel steering, but we're stuck picking a setup and driving around it. There are techniques to drive around mild understeer that might help (and some things you may be inadvertently doing that are making it worse)

dbv1

The camber is maximum that the car will allow on the front, -1.1. Rear is -1.5.

The car turned in a lot easier with setup #1. Should I then go to 1/5 (softest) on the front bar and put back the rear GT3, also on softest? Or just try the front bar alone at the softest?

jwr9152

I would do one thing at a time, so that you can see the difference it makes. Soften the front sway bar first and see if that helps the under steer. If not you could go back to set up one and maybe try some toe in on the rear to see if it calms the rear end down for you.

dbv1

I'm still hoping the bar isn't able to rotate somehow so I'll check that tomorrow. I'll bring a friend with a support vehicle for the next event so there's going to be lots of tweaking. I'll report back next weekend.

Just as I started to give the modified bunch a run for their money, this mess happened, pretty annoying. I was literally ~3 seconds slower last time.

Earlydays

Before you change anything else I would up the front pressures back up to say 31-32 (hot) and see if this improves your turn-in.....

dbv1

71R (extra load) has a pretty stiff sidewall and lowering the pressure should help turn in. Why do you think the higher pressure would help?

I ran today with both GT3 bars on softest and it's a lot better. I'm back to my usual performance although I'm missing that easy oversteer from when I only had the rear bar. I think I might go back to that.

Part of the problem is that the surface we run on is very smooth and dusty (low traction) and the courses are setup for Miatas so there are lots of sharp, low speed turns which don't suit my car. It's not an autocross you guys would be used to, judging by your videos.

jwr9152

if you feel like your close on your setup, I would stiffen just the rear bar for your normal auticrosses. It should help the car rotate. On bigger faster auticrosses you could then soften the rear again to make the rear end more stable at higher speeds.

dbv1

Good idea, thanks. I'll stiffen it up. It's easy enough to change that when needed.

kjchristopher

Y'all must get special miatas in Canada if they excel on sharp, low speed turns.

kjchristopher

Query, why did you switch setups? Is there an expectation that you could have the nice balance of setup 1 while being able to pin the throttle to 100%? We're you just testing? It sounds like your second step is to go backwards, more towards setup one and see how things react. Are you testing on the same course?

dbv1

Non-street legal, completely stripped Miatas with very few stock parts left, running 265 mm wide slicks on all 4 corners. These things weigh about a tonne or less after stripped. That kind. There are probably about 2 dozen of them in various stages of mods. And yes, they really turn on a dime.

I'm kind of surprised you don't see those. They're really popular here. Here's an example and they didn't really go all very far:

sjfehr

I'm pretty sure kjchristopher is familiar with the kind of miatas you're talking about.

The point is that miatas typically do best in tight speed maintenance courses, not sharp low speed turns or other deep digs. Miatas would probably not fare well on the type of course you described; if they did, it's more driver than car. (Unless you're talking about SSM or XP miatas in which case, yeah, they're fast everywhere!) And properly modified, no question they're quick!

Earlydays

I always play with tire pressures first and raising pressures will actually reduce understeer up to a point. Regardless of the sidewall stiffness, if the pressure is too low the contact patch will not uniformly stay in contact with the surface.
I have found this to be the case in my 964, which I have autocrossed for the last 18 years.

jwr9152

Here is an interesting read on autocross and tire pressures.

http://www.autocross.us/forums/topic...-in-autocross/