front & back size differential

[oasis]

Hi,

I would like to know what you think about different size wheels and tires for the front and back. I am really asking about handling characteristics more than anything.

I have always thought I would have the same size at all four corners but it seems some GL'ers prefer differing sizes front and back -- although not to the same extent as the typical Cal-Look treatment.

Thanks,
René

[Tim]

I read an article about suspension/wheels tuning for racing. It said that increasing the wheels and tyres width at the rear will reduce oversteer and increase understeer.

I am using 15x6 fuchs at all four corners on my standard Beetle but the front tyres are 185/65 and the rear are 205/65.

I am building another super beetle for racing and I plan to use 15x6 front with 195/55 tyres and 15x7 rear with 205 or 225 tyres.

Tim

[chigger]

From what I understand about it which is probably misunder stood especially by me is that the tire size should match the weight balance of the car. For example if the weight is 40/60 front to rear, the tires should be narrower on the front to achieve a balanced tire loading on all four corners. If all four tires have the same loading or lbs of weight per square inch of footprint you should have neutral handling. While looking for tires and wheels on ebay I noticed that the tire sizes on the porsch rims were always different from the front to rear. They run something like this 205/55 on the front and 215/50 on the rear. The tires should be about the same diameter. I think this is because of the aspect ratio. As the tire gets wider to retain the ratio the sidewall has to be taller.
Once you get this all sorted out then you have to worry about sway bars, springs, shocks, etc. All these items have similar effects on the handling.

[factman]

they do do it for handling purposes but i think mainly for traction. the front wheels dont have 400+ hp trying to brake traction on them and to prove it look at the american Dodge Viper. huge V10 motor in the front but the tires are 305 in the front and 335 in the back so that the tires wont brake loose from all the hp's it has. those are just my 2 cents on the matter. i think spring rate and sway bars have more to do with cornering then anything.

[Tim]

That's true. There are many factors affecting the handling. This link explains everything.

http://www.rennsportsystems.com/1-e.html

Tim

[oasis]

I know it has been over a month since the last post but I am still digesting the information.

While trying to decide on my plans for brakes, I searched the 944 articles and posts. Subsequent to that, I searched The Tire Rack on wheels and tires for Porsche 944s. They had BBSs which were 18x8 with 225/40-18 tires on the front and 18x10 with 255/35-18 tires on the back. I really liked those wheels, but my goodness, US$3000 just for wheels is not exactly what I had budgeted even though I planned new car money for the overall project. I don't even know if I could use these wheels/tires if money were no object.

The RS article is fascinating but I must admit, some of it is a bit over my head at the moment. But, I am learning.

Thanks Tim, chigger, and factman.

[MattKab]

My 1303 has 17*7.5" wheels front and rear, with 215/40ZR17 on the front and 225/45ZR17 on the rear.

I spent a great deal of time deciding on that combo, in fact 5 out my 6 past Bugs had lower profile tyres upfront.

Wheel diameter differential has a great influence on braking bias too, as a smaller wheel turns quicker/has longer to roll with respect to the rear.

In my case, this helps as my brakes are 4pot Brembo and the bias could possibly be too far forward, if I did not have front tyres that are 95% of the hieght of the rear tyres.

It's also a matter of taste, 205/40x17's look lost on the back of a Bug IMO