Street Touring Hatchback (STH) discussion/setup

[xXDavidCXx]

David, why do you say same camber front and rear when running ~2deg front?

Because lowering the rear camber is giving up grip.

Use the rear toe-out for rotation, not less grip via less rear camber.

 

[Oversteermybagel]

Are we though? A few things at play here, as you know:
* Front roll center is lower than the rear so there is more roll in the front
* Front tires have significantly more load so we would expect the front tires will have a harder time keeping up with centripetal force due to tire loading
* Rear camber curve is not the front camber curve

Basically, from your modeling, do you think 2 deg camber in the rear can be a grip limiter IF front is only set to 2 deg and spring rates/roll rates are something reasonable?

 

[JackRabbitSLIM]

The less rear camber you have, the faster the oversteer breakaway will be (if you can get oversteer).

Understeer = front slip angle > rear slip angle
Oversteer = front slip angle < rear slip angle
More rear toe out = more rear slip angle

 

[Oversteermybagel]

I don't know this for sure because I have not run the setup but I am going to put this out there as a hypothetical. Lets say you are doing high-G high-speed braking. The rear tires have less grip because of the negative camber and the suspension is going toe-out on its own (more so if you have compliance bushings). It seems like the combination of negative camber and toe-out here could make the car progressively more twitchy as you drive the car into the apex.

 

[bfury5]

I originally set my rear camber based on tire wear. At -1.9 I've had even wear across the the tread

 

[JackRabbitSLIM]

I don't know this for sure because I have not run the setup but I am going to put this out there as a hypothetical. Lets say you are doing high-G high-speed braking. The rear tires have less grip because of the negative camber and the suspension is going toe-out on its own (more so if you have compliance bushings). It seems like the combination of negative camber and toe-out here could make the car progressively more twitchy as you drive the car into the apex.

I don't know your track experience, I apologize if I'm talking down to you.

If you are newish: you want to error on the side of an understeering setup. Yes, it feels bad in slow corners, but you don't want to be surprised in the fast corners. I suggest running a healthy amount of rear camber (meaning more negative). Not crashing is more important than lap times.

If you are comfortable on track, I'm saying it's probably safer to balance your handling by incrementally increasing rear toe out. Don't go straight to .25". If you get yourself into a comfy place using toe, the breakaway will be slower than if you do it by decreasing camber. Snap oversteer is no good.

For autocross and street use, .25" rear toe out is no problem, send it.

In the words of Andy Hollis,
"So how do we make the car stop understeering? One way, is to decamber the rear, as you have been doing lately. But that is a fairly sudden breakaway, and actually doesn't make the car any faster (it just feels better than "riding out the push"). Here's another key point: Under steer is when the slip angle of the front tires is larger than the rear tires. One way to open up the effective slip angle of the rear tires (reducing understeer) is through toe-out in the rear. This "steers" the rear tire to a larger arc than it would otherwise be at."

 

[xXDavidCXx]

Also consider this is an autocross specific thread, I'm not concerned about high-speed braking. I need the rear to be a little twitchy to maneuver around the slower course elements.

 

[jmblur]

Well, the printer was broken so no printout, and he did another car after mine... Sigh.

He dialed in a bit more rear toe in than I wanted (factory spec toe in) but front was zeroed out, -2.1 degree camber each side front, -1.8 rear. I'll take it. Might play with toe a bit depending on understeer/oversteer behavior.

 

[xXDavidCXx]

Well, the printer was broken so no printout, and he did another car after mine... Sigh.

He dialed in a bit more rear toe in than I wanted (factory spec toe in) but front was zeroed out, -2.1 degree camber each side front, -1.8 rear. I'll take it. Might play with toe a bit depending on understeer/oversteer behavior.

With that toe in, you will understeer, no two ways about it.

 

[bfury5]

Well, the printer was broken so no printout, and he did another car after mine... Sigh.

He dialed in a bit more rear toe in than I wanted (factory spec toe in) but front was zeroed out, -2.1 degree camber each side front, -1.8 rear. I'll take it. Might play with toe a bit depending on understeer/oversteer behavior.

Good plan of attack. It's a solid starting point to make changes from

 

[GTIfan99]

Finally got everything buttoned up. Alignment tomorrow. R not GTI if that matters.

Assuming I'm at -2 camber front (hopefully!) I'm thinking -1.6-1.7 rear camber, zero toe front, slight (1/32") toe in rear to start, then maybe play games with rear toe later?

Start with at least 0 rear toe and go from there. -1.5 rear camber.

Just saw you already got it done.

 

[jmblur]

Need to set up a string box at home to make adjustments more reasonable. 3d printed string holders are in my future...

 

[odessa.filez]

those of you who set rear toe out for AX, do you set it back afterwards?

if so, would love to hear about an accurate, repeatable process. thanks

 

[jmblur]

those of you who set rear toe out for AX, do you set it back afterwards?

if so, would love to hear about an accurate, repeatable process. thanks

As far as repeatable, you can mark the bolt at both locations once you figure out where it goes. But a string box is definitely the most accurate way to go.

 

[JackRabbitSLIM]

those of you who set rear toe out for AX, do you set it back afterwards?

if so, would love to hear about an accurate, repeatable process. thanks

I had the shop mark where zero was, but I've never moved it from .25" out. I just drive around with rear toe. Front too.