front to back tire size ( stagger ) again

slow arnie · Post by **slow arnie** » Fri Feb 09, 2007 4:20 pm

The word I'm getting is it should not be a lot. Maybe just one jump, say 195 and 205 ( for a street car ) otherwise there's understeer. But looking at pictures of race cars I see a lot and certainly they wouldn't tolerate bad handling balance. Also didn't porsche do it on some cars?

It only makes sense. The front sees braking and cornering loads. Certainly you'd want the smallest, lightest tire that can do the job. The rear is heavier, it sees an additional load: driving traction, wouldn't you want quite a bit more rubber for that?

Ozzie · Post by **Ozzie** » Mon Feb 12, 2007 3:07 am

It depends on what you are doing. Autocross? You will exaggerate an existing inherrent problem.
IOW: My problems were getting the front to stick (understeer) and rotation. It took a lot of stiffening up the rear to finally get rotation.

kdf · Post by **kdf** » Mon Feb 12, 2007 4:26 am

We ran 205 at the front and 225 at the rear. But our class has a tire width limit (225 for our weight), and the 205 tires at the front were probably chosen for other reasons than performance (budget). Handling with different sized tires is a question hard to answer, because we haven't tested the same car with different tire width distribution.

When optimizing the chassis usually tire width is dictated by the weight distribution if the formula is free.

An example I found was a 2007 Porsche GT3, with 235/35 ZR19 - 305/30 ZR19 tires from the factory.

helowrench · Post by **helowrench** » Mon Feb 12, 2007 6:37 am

let me look through my links and see if I can find the page I ran across way back when..

Rob

helowrench · Post by **helowrench** » Mon Feb 12, 2007 6:49 am

most of these go through much more than just tire....;

http://www.turnfast.com/tech_handling/h ... able.shtml
https://www.rsracing.com/tech-tire.htm#hipochrt
(easy to see charts)

Long read on theory and some application, even has a section about changing some issues in completed vehicles
http://www.rqriley.com/suspensn.htm

and of course
http://www.aircooled.net/gnrlsite/resou ... ndling.htm

happy reading

rob

Ozzie · Post by **Ozzie** » Mon Feb 12, 2007 7:38 am

Here's another...
http://rogerkrausracing.com/overundr.html

helowrench · Post by **helowrench** » Mon Feb 12, 2007 11:25 am

very nice Ozzie,
It is now bookmarked for me .

Thanks
Rob

slow arnie · Post by **slow arnie** » Tue Feb 13, 2007 12:37 pm

Thanks very much for the replies.
Lots of good info to chew on.
I'm just a street car guy looking for the magic formula for my 71 SB (before I make a move), but I guess it's not that easy. I'm not surprised.

Ozzie · Post by **Ozzie** » Wed Feb 14, 2007 3:21 am

slow arnie wrote:I'm just a guy looking for the magic formula.

We all are. So get out there & try some stuff. Let us know how it goes.

ericsbracer · Post by **ericsbracer** » Thu Feb 15, 2007 1:02 pm

For "general handling" I think same size works well on a Super. The real key to handling is the suspension setup, and you can get some pretty respectable results for a small amount of money and time. I pulled .937 G's on a skid pad with all bolt stuff and some 205/50x15 G-Force radials on 5.5" Chromies. Switch back to a 195/60 and you can run with stock fenders and no rubbing, and still have above average handling.