Tire Width/Aspect Ratio

Opposite_Lock · 07-13-2009, 09:47 PM

I'm going to buy an 09 WRX to autocross in D Stock in our local street tire subclass. I've heard that the WRX is prone to serious understeer near the limit, so I've been throwing around the idea of running a wider tire in front than in the rear, to aid in bringing the rear end around a bit more. Just for background, the stock class rules say you have to use an OEM sized wheel with an offset within .25" of stock.

I've heard that if the overall diameter of the tire/wheel combo is different front to rear, it can play havoc with the electronic nannies (i.e. ABS, traction control, etc.). What I was considering is a 255/40 tire in front and a 225/45 tire in the rear. This works out to an overall diameter (theoretically) for the 225 of 634.23 mm and a circumference of 1992.3 mm. For the 255 it's 635.76 mm diameter and 1997.2 mm circumference.

Here's my question: does anyone know if this difference in overall diameter and circumference is enough to make the electronic nannies wig out?

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Opposite_Lock · 07-15-2009, 01:05 PM

Bump. Anyone? Bueller?

Badler · 07-15-2009, 01:09 PM

No, you will be fine. Plenty of people run wider/different offset in the front to help with understeer. Do you have any ACTUAL experience yet or is this just what you "heard"?

Opposite_Lock · 07-15-2009, 05:31 PM

Quote:

Originally Posted by aaronmsadler

No, you will be fine. Plenty of people run wider/different offset in the front to help with understeer. Do you have any ACTUAL experience yet or is this just what you "heard"?

Haven't bought the car yet, just "heard." I'm fantasizing about what I'm going to do to it once I sign the paperwork and drive off the lot. Just don't want to spend the $$$ for new rubber only to find out I've got the electronic gremlins breathing down my neck and have to spend more to fix the problem.

medamullet · 07-15-2009, 05:34 PM

sway bars would be cheaper than new rubber....

Crawdads · 07-15-2009, 06:02 PM

Quote:

Originally Posted by medamullet

sway bars would be cheaper than new rubber....

Unfortunately, in SCCA Stock class, the only the front swaybar can be changed.

Opposite_Lock · 07-15-2009, 08:23 PM

Quote:

Originally Posted by Crawdads

Unfortunately, in SCCA Stock class, the only the front swaybar can be changed.

Yeah, the SB that would actually have a positive affect on the understeer I can't use

07-13-2009, 09:47 PM	#1
Opposite_Lock Scooby Newbie Member#: 202925 Join Date: Feb 2009 Location: Pasadena, CA	Tire Width/Aspect Ratio I'm going to buy an 09 WRX to autocross in D Stock in our local street tire subclass. I've heard that the WRX is prone to serious understeer near the limit, so I've been throwing around the idea of running a wider tire in front than in the rear, to aid in bringing the rear end around a bit more. Just for background, the stock class rules say you have to use an OEM sized wheel with an offset within .25" of stock. I've heard that if the overall diameter of the tire/wheel combo is different front to rear, it can play havoc with the electronic nannies (i.e. ABS, traction control, etc.). What I was considering is a 255/40 tire in front and a 225/45 tire in the rear. This works out to an overall diameter (theoretically) for the 225 of 634.23 mm and a circumference of 1992.3 mm. For the 255 it's 635.76 mm diameter and 1997.2 mm circumference. Here's my question: does anyone know if this difference in overall diameter and circumference is enough to make the electronic nannies wig out? * Registered users of the site do not see these ads.

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07-15-2009, 01:05 PM	#2
Opposite_Lock Scooby Newbie Member#: 202925 Join Date: Feb 2009 Location: Pasadena, CA	Bump. Anyone? Bueller?

07-15-2009, 01:09 PM	#3
Badler Scooby Guru Member#: 133597 Join Date: Nov 2006 Chapter/Region: SCIC Location: Costa Mesa	No, you will be fine. Plenty of people run wider/different offset in the front to help with understeer. Do you have any ACTUAL experience yet or is this just what you "heard"?

07-15-2009, 05:34 PM	#5
medamullet Scooby Guru Member#: 99442 Join Date: Oct 2005 Chapter/Region: International Location: Man of Mystery Vehicle: 2006 SGM STI I'm on CORN YO!	sway bars would be cheaper than new rubber....