Negative Camber at the rear wheels for a solid rear beam FWD car, how much would help handling?

Hi Everyone,

I'm getting close to having everything together to put the suspension back together on my 84 VW GTI and I'm debating if it's worth adding rear camber shims to my car. Factory specs supposedly are -1 degree for the rear and it's a solid rear beam in the back with bolt on stub axle spindles. There are multiple companies that make shims tailored to reaching a specific camber spec. You just place them between the beam and stub axle during installation.

Here's one for example:

rear camber shims

As for the car itself, I plan on running it for SCCA autocross in STS or FSP. I'm setting the suspension up with Ground Control Coilovers and Koni Yellow Adj. Sport shocks and 350 f/450 r spring rates with a larger 24mm solid 16v Scirocco rear sway bar. I will also be removing the front sway bar. I'm going to be running Dunlop Direzza ZII Star Spec tires on a 6.5" Wide 15" wheel. In short, I'm trying to get some rotation with this setup. I should also say that this isn't a "tow it to an event with a trailer track only race car", but it's also not a "drive it to work every day daily driver" either. Besides autocross events I want it to remain street able enough to take it to work or mess around on a weekend, and in the most extreme case do a 500 mile trip to a car show.

What I'm wondering is, is it worth investing in rear camber shims for what my intentions are?

And if it is, how much rear camber would be helpful without noticeably increasing rear tire wear?

I'm thinking a final spec of -2 Degrees (- 1 with the use of the shims) if it is helpful.

More grip is great, killing a set of tires in a short amount of time isn't. If isn't logical for my intentions and it would cause aggressive tire wear I would probably stick with stock specs.

The only sure way to know is to track tire temperatures across the face of the tire after runs and then adjust camber until the temperature is as even as possible.

It'll help a little but not as much as it would on an IRS car. The axle will "lean" in the corners as the outer tire is compressed and the inner one has weight taken off it and possibly lifts - so some negative camber will get you more grip on the outside wheel. You'll also lose more grip on the inside wheel than you would in an IRS car.

Edit: Of course this is assuming the car has a "tame" setting right now that's more optimized for tire wear and straight-line grip - if you want to be absolutely sure you'd need to test as turboswede pointed out.

Gameboy, keep in mind, twist beam FWD cars (and even some IRS FWD cars) will lift the inside rear tire, effectively lifting the inside edge of the outside tire. So some extra negative camber could be a very good thing, but only testing and documenting will tell for sure.

Biggest thing to do is to start with a known quantity of some sort and slowly test and adjust one thing at a time, re-testing after each change until the optimum setting is found and also what adjustments make what sort of change. That way if you need to make an adjustment due to a change in tires or surface, etc. you'll have an educated guess and data to use to help shorten that adjustment period.

I road race a 16V Scriocco and tried shims on the rear beam to increase neg. camber. I found that the beam had 1.5 deg. neg. to start so I removed the shims and tried that. The car handles very neutral, with some understeer on slow tight turns and a bit of over steer on faster turns if I give it a slight lift of the throttle.

I'm not saying you can't gain something with neg. rear camber but you can certainly tune the suspension so that you don't need more if it's neg. to start with.

If you do want to go with shims don't buy the plastic one. There are metal ones out there but their pricy. I used my lathe and made my own but as mentioned I never used them. I think their in some box of parts or another somewhere?

In theory, more negative camber would increase understeer.

Ford, in the Fiesta ST reduced the negative camber in the rear.

Most of them start at -1 to -1.5, that is plenty for your car. Dont know how stiff you built it but the inside tire probably won't be touching the ground or not much anyway.

I don't recall adjusting the rear camber much beyond spec on any of my A1 chassis VWs except to get it even as much as possible on both sides. YMMV.

A few of the guys who used to race/track/autocross Maximas would bend the rear beam to get about 1.5* negative camber, as I recall. I didn't do it to mine, but the word was that it substantially improved handling on those cars. Can't speak for other cars though.

iceracer wrote: In theory, more negative camber would increase understeer. Ford, in the Fiesta ST reduced the negative camber in the rear.

They'll increase rear grip which will shift the handling balance towards understeer, so you'd have to increase front grip to compensate.

You are really going to need to increase spring rate to get better rotation. I road raced EGT for several years and for the most part the rear tires were just along for the ride and to keep the bumper off the ground. Our testing showed that the rear tires were generally irrelevant and built very little pressure or temp racing at Road Atlanta.

The rear axle on the early SAABs was easy to bend.

Back in the day when most ice racers were 93/96's. Many had large amounts of POSITIVE camber caused by banging hard snow banks.

The best way to add negative camber to the rear of a VW is a stiffer front swaybar. That makes the inside rear tire hover closer to the ground and camber loss is reduced. Until all four wheels stay on the ground, changing roll stiffness doesn't affect handling because rear load transfer is 100%, so adding front stiffness actually reduces understeer. Don't be afraid of it.

Additionally, making the rear suspension as low as you dare also helps keep the rear tires close to the ground, CG lower means less three wheeling. It's incredible what an change of an inch in the rear ride height does for the ability to power out of a corner. Also means you don't need to run the front suspension so stiff.

I can't stress enough, once you're lifting a tire, traditional thoughts about spring rates and swaybars goes out the window. Those work by changing the ratio of load transfer at each end of the car. Once one end has a tire off the ground, further suspension changes do nothing but alter how far off the ground that tire is. One end is at 100% and you can't go more than 100% load transfer. So, personally, I'd NOT run the rear swaybar, and I WOULD run a front bar.

I have just a little Golf experience... The first thing when I got my A2 was plate the rear beam, which helped 3/10ths driving substantially but under more serious cornering, it did nothing because it just meant the inside rear was 8 inches off the ground instead of four. Adding front swaybar reduced high-lat understeer, putting Neuspeed ricer-slam springs in the rear took out an even bigger chunk.

Thanks everyone. Sounds like it's probably not worth experimenting with at this stage with the car. I think I'll pass for now.