Do you ever feel that you don't know what is going to happen next?

[Guest]

I was running 28f/36r on Eagle F1's with 224/45 and 255/40's on 17" cup alloys, and handling seemed OK, wet or dry, although don't really push it in the wet.
Last week got a nail in the sidewall of one rear so replaced both rears. Fronts still have 5mm of tread and wear on all 4 tyres is even. Anyway, got a great deal through a friend of a pair of new Avon ZZ1's fitted and balanced for 150 the pair. Too good eh? Well since they were fitted, the rear feels a bit dicey to say the least. Same route to work, which involves a couple of roundabouts, means a far more cautious approach than I would like. I know the Avons are not exactly top of the range, but would they make that much difference or is it the fact that front and back are now miss-matched. Worth changing the pressures on the back?
TIA

 

[Melv]

"but would they make that much difference or is it the fact that front and back are now miss-matched"

In one -how many times do I have to tell you guys -DON'T MIX MAKES OF TYRES OR 'N' RATINGS!!!

Replace the fronts..................

Melv

 

[Jamie Summers]

ZZ1s are pretty horrible - the compound is just way too hard for a car that is tail happy in the first place. I had a set on my car when I bought it and replaced them with Toyo Proxes T1-S which made a dramatic difference. I suggest you just ditch the ZZ1's or trash them on a track day.

 

[Guest]

In one -how many times do I have to tell you guys -DON'T MIX MAKES OF TYRES OR 'N' RATINGS!!!

I have to agree with Jamie, the ZZ1s are your problem. Having different tyres front and rear is not necessarily a problem - so while Melv is kind of technically correct, his statement isn't perhaps very useful. You need to take a more holistic approach. This is what I have said previously:

"I know its stating the obvious, but the front and back of a 911 are, of course, not equal "" the front is lightly loaded and the rear heavily loaded. With different inputs of steering and throttle and in differing conditions your car will understeer or oversteer. Having different tyres front and rear will only change these characteristics to a degree. If the tyres are fairly closely matched the change in handling characteristics will not be great. Porsche designed your car with smaller front wheels and tyres in order to decrease the oversteer characteristics that are inherent in a rear engine design. Consider this example, using a tyre with slightly less grip on the front of your 911 will further decrease any tendency to oversteer. It will also increase understeer and may slightly decrease braking ability as a less grippy tyre may lock slightly more easily. So, not really a catastrophe, just something to be aware of.

I have from time to time run different front and rear tyres with no problem at all. One time, I even did a set of 10 laps at Oulton Park with mismatched tyres front and rear (I didn't have time to change to my track tyres and didn't want to miss out on my session!). Admittedly, not best practice but no real problems, just a slightly greater tendency to understeer as the front tyres had slightly less grip. This is exactly the same effect as might have been achieved by altering tyre pressures, running a bigger rear tyre or altering an anti-roll bar setting "" all perfectly normal methods that people use to tune the handling characteristics of a 911.

One thing I would not do is run different tyres on either side of the car. I think that the possible mismatch in grip and performance could have adverse consequences under severe or panic braking.

A further point to consider is relative tread depth. If your rear tyres only have a millimetre or two of tread left but your front tyres are new, for example, you are again effectively changing your handling balance "" particularly in the wet. Your car will become an oversteer meister!

Conclusion "" replacing just the front or rear tyres of your car is not necessarily a recipe for disaster, just beware that it may alter the handling balance of your car. "

You can see this whole thread and learn all about tyres here:

http://www.porscheclubgbforum.com/tm.asp?m=1895&p=2&tmode=1&smode=1

RB