kurt M

Keep in mind that wider wheels tend to wider to the outside as most stock setups are close to the struts to start with.

It all depends. I was asked to drive test a 911 with some real issues. Tramlining, darty, and changed from over to under to over steer with little excuse. They had been playing with sways and the toe settings and were in full chase the tail mode.
We put the sways in the middle front and back and it was a little better but still a real turd of a drive. Skip shuffel, 2 hands firmly on the wheel. We tried a set of corect stock wheels with right sized tires loaned by another car and all the issues went away. Wrong wheels and spacers were used to make fit.

trackjunky

OK, so I think this thread basically brought me right back to a point I've always believed. I'm no Mechanical engineer here so I may get some things wrong. But, I always believed that you want to keep the center of the wheel over the center of the hub. My reasoning is that you spread the forces evenly over the hub. Once you upset this balance/positioning, you screw up the calculations the original engineers made. If you were to add spacer and move the center line outward, you would basically need to re-engineer the suspension to change how forces are exerted at the hub +/- the change in the distance of the spacer/offset.

Soooo, I've also thought that increased camber (derived from moving the shock towers inward) changes this relationship as well, to some degree. Right? Wrong?

Why then, would anyone add spacers? I'm just following along as the Happy Idot here, but I still don't get the spacer thing.

My original plan was to look at the orientation of the wheel to the hub and see if a spacer would center the tire more, but I changed that approach by reading too many posts.

Now, let's talk professional race cars in Koni, WC, BTC and Grand AM (loosely). The wheels seem to be pushed outward to fill out the wheel wells. Spacers?

mark kibort

spacers will change the cars road handling capability, like lowering the car. in fact, in general, lowering the car .5' is like widening the car like 1". (something like that). now, the geometric changes are a entirely different story. With the 928s, we have no downside by moving the tire outward, by wheel offset or spacers. generally, the 928 racers do a little of each with no ill effects. one thing about the prior post regarding the car that wasnt fun to drive, is that when you move the wheel and tire outward, you basically increase its lever distance, which can make the system much softer. (how much depends on a bunch of factors). this would explain how the car handled better when the proper or stock wheels and tires were used, however, if the suspension was set up right, you would probably want the widest system possible. I bet if you look around the race paddock, you will find a huge difference in this aspect of most racers. (that is spacer vs wheel offset) and I bet most that have race a while have it to where their car handles best for them.

mark kibort

Thanks for posting the chart. Its different for each car and car's geometry. some cars get better by using spacers and others get worse. However, I think you can deal with the trade offs in set up to a certain extent. I think the 7mm spacer is going to be a rounding error in most cases, but playing with 14mm spacers, (1/2") , and you might see some ill effects or benefits.
In my experience with all sorts of ofset combinations on my race car, i didnt notice too much of the "Heavy steering " feel, until I put Huge tires up front. the same overall width with a smaller tire vs the narrow set up, didnt change things at all, but handling was better due to the wider foot print. Quite possibly, when you have front tires between 275 and 305, vs 225s, it might be something that the size of the tire masks. (tramlining, bumpsteer, etc)

onefastviking

Not with a 23mm spacer.

onefastviking

It's like you thinking you could run the car as low as the Cups do, you don't have the same subframes and by radically changing the geometry you add other issues into the handling. Some of those might be ok compromises, some not, but what the hell do I know.

Ok, lets look at the basics. You want to bring the wheel further out to increase track width. By adding the spacer it will bring the centerline of the wheel out. You do also have adjustible camber plates and adjustible lower gt3 arms to play with.
What is the car doing, or not doing, that we are trying to make these changes for ? Does it have a handling issue ? Just not fast enough ?

With the power steering of the street 996 I seriously doubt you will notice the heavier steering even with a huge scrub. Unless of course you are pushing it around.

bobt993

Is he really running a 23mm spacer on the front or is this a typo??

trackjunky

No, I'm not. I put the post because the front spacer would be 23mm and that just seemed way to big to me.

The post is "what's the overall effect?" Which means I want to know what effect the spacers would have. Cory gave the best scientific answer, but I was hoping to find some practical applications and experience with both pro's and con's that might give me a little bit of direction on what I could tune in or out of the car's handling.

I like experimenting with set ups to see what happens, that way I'll know more about how to fix problems if/when they pop up.