brianrheffron

I believe older 928s had same section tyres front and rear and that this was changed to wider rear/ narrower front on later models even though the weight distribution front to rear was unchanged. My '89 928 S4 has 225X50X16 fronts on 7 inch rims and 245X45X16 rears on 8 inch rims. Was this done only to make the cars more "understeery" and stable or was there a more subtle technical reason.
I have read several threads on handling. Understeer (or push as the Americans say) seems to be the common complaint with alterations to the anti-roll bars being the usual remedy suggested.
I have got a spare pair of 8 inch rims and wondered if the car was on 8 inch rims with 245 section tyres all round would it make the car more neutral or would it tip the balance to just plain scarey. l would be interested in members comments both pro and con.

Vilhuer

Back when 928 was originally designed suitable 245 rubber didn't even exist I think. Pirelli P7 was latest high tech tire back then and only one Porsche had in mind when they decided original setup. 245's came to rear in response to raising hp and tq.

brianrheffron

I don't know if I am breaching Rennlist etiqette but I have replied just to move this query back up the list.
Surely there are more comments to come. Help me out here.

Alan

No problem - it is common to "bump" posts that didn't get much attention (OK as long as you don't do it too much - often a clarification may be needed to your question or more details).

However - in this case you got your answer - in the earliest years there were no wide range of large section tires... there were few alloy wheels either... huge changes over time...

Modern low profile tires on wider larger diameter wheels can transform the handling of older cars to much better than new. In general little happened to the weight balance or suspension over the years so newer wheel/tire/spring/shock set-ups can be used as a guideline.

Alan

James-man

I can just barely tell the difference between 225 and 245 on the rear.

8" on the front will have the wrong spacing. Offset will be wrong. That migh impact handling and fit more than the extra 20mm of rubber.

Alan

Well yes in any changes you need to keep the geometries the same - to the degree wider tires fit they will remain centered on the original rims. I was talking more about moving up to 17" or 18" wheels with lower profile, wider & better quality rubber.

The width is only one cosideration. Shorter & stiffer sidewalls & better rubber compounds make a huge difference too. 225 vs 245 will obviously not make as big a difference as moving from 225 to 275 which should be doable on all models. Expensive tires have much (much!) better traction than cheap ones - as always its a trade off - but when the car was first made these options didn't even exist.

Yes you have to get the right wheel offset and spacers for it to work right... but very doable on all models.

Alan