Dear Forum,

this is my first post here (apart from the one in the Boss 302 registry thread).

I have tried the search but found nothing on my question so I will be brief in case this has been answered before.

My problem is this: Depending on weather conditions and availability of transportation for my wheels, I either track my 2012 Boss 302 with Good Year Eagle street tires on the original Boss wheels or with a square setup of 265/35 R18 semi slicks (which I get for free in this dimension only, hence only 265 mm width).

While on the 265/35 R18 semis, the balance between under- and oversteer is just right for me. It is suprisingly agile but not prone to sudden oversteer.
But when on the original 19" wheels, I got massive understeer.

Since I do not want to re-adjust stabilizer bars or camber or whatever anytime I switch between tires, I thought that it should be possible to adjust understeer and oversteer balance by adding wheel spacers to the front wheels.

The question is: How many mm would be necessary to make a difference? Is it between say 5 mm and 15 mm per side or would more, like 30 mm per side, be necessary?

I would like to know that before I start changing to longer wheel studs and buying hundreds of wheel spacers.

Changing to a square set up on the original wheels as well is not an easy option since I would have to got though loads of paperwork to make another than the original tire dimensions road legal here in Germany.
Thank you very much for your input!

Regards

Oliver aka Tomcat0815

Bill Pemberton

Bill talked me through air pressure adjustments to adjust under/over steer. Unfortunately I am not 100% sure which way you go.

Bill you out there? Help a brother out. He is in a land where the government, großer Bruder knows best and he can’t simply add tire width to balance steering.

I don't think spacers will help with this issue. If I understand correctly.

Adding track width to the front will increase understeer. Imagine a toy model of a car that is just a center wood stick with two cross sticks representing each axle. If the axle sticks are the same length and you rotate the model against a solid surface, each axle will push the same. If you lengthen one stick, that one will push harder on the surface. This is weight transfer.

Your tire combination is not mutually supportable, look at it this way, the difference in 18 and 19s, let alone different sizes and compounds will affect the car far differently, as you have found out, to simply add spacers to change one of the other is not a good way to go about it. If you don't believe me, put the car on a set of scales with the 18s, then the 19s and you can measure the difference, especially if they are "live" scales that let you turn the steering wheel. You would be better off to pick a set of wheels and tires and just run them, and adjust to that setup, changing track messes with a lot of things, scrub radius, in particular. Changing wheel spacing to effect handling is something us kart racers do, only because we have a solid rear axle and no suspension.