Which tyre Size?

[Tigerfred]

Hi all,

Which size is correct for my 1990 S3?

At present on the front I have 205x55ZR15, on the rear 205x60ZR15, these have been on my car for the last five years.

Cheer
Fred

[phillpot]

From new it would of had the 60 profile, the 55's will do no harm, just sit a little lower and mess up speedo reading if you had them on the rear.

Mine had 55's all round when I bought it, reverting back to the 60's helps "fill the wheel arches" a bit

[Tigerfred]

Thanks, at least I know what was standard when car was new.

Fred

[Griffinr]

60 section are 627mm diameter, 55 section are 607mm diameter which is a difference of 20mm or 3.19%.
So at 70 mph actual your speedo on 55 section would show 72.2 (theoretically)

Rob

ps. I need to get out more.

[Longers]

55's all round on mine. My previous S had 60's which looked a lot nicer but the current car handles a lot better. The guy that built it told me the tyres help with this, although the suspension set up & roll bar also make a big difference.

I don't think with my driving the handling will be that different though, so when they need changing I'll be fitting 60's to fill the arches more.

Griffinr said:

60 section are 627mm diameter, 55 section are 607mm diameter which is a difference of 20mm or 3.19%.
So at 70 mph actual your speedo on 55 section would show 72.2 (theoretically)

Rob

ps. I need to get out more.

Rob, seeing as I've got 55's I must remember to quote the above if I ever get stopped by plod and asked how fast I was going

[phillpot]

Griffinr said:

60 section are 627mm diameter, 55 section are 607mm diameter which is a difference of 20mm or 3.19%.
So at 70 mph actual your speedo on 55 section would show 72.2 (theoretically)

Rob

ps. I need to get out more.

Ah, but at what pressure did you calculate diameter ? tyre will compress in contact with road proportional to pressure thus reducing radius and thereby the rolling circumference

[Rower]

I had 55's on mine and recently changed to 60's , big difference to clearance and no difference in handling , I have Bridgestones which do have stiffer sidewalls than others.

Rower