Re: Formula for tire size conversions and Dunlop Sport 8000 tires in 195 55 14 for '86 Coupe GT (fwd)

[Robert Phillips <r3rfp@dax.cc.uakron.edu>]

This didn't go through the first time, so I'll re-post it.

On Tue, 25 Jul 1995, gkaufman wrote:

> Can anyone supply me with the formula to calculate the wheel circumference 
> so that I can see the differences in the two tire sizes?

Don't bother.  Technically, the 195 is the width, the sidewall is 55 
percent of the width.  Since tires differ significantly in overall 
circumference, it is best to obtain a chart from each tire manufacturer 
that lists each individual circumference for each specific tire.  As 
manufacturing tolerances, as well as tread design influence the actual 
circumference of the tire, this is the only way to find out how big it 
really is.

> What would be the difference between the 205 55 and the 195 55 sizes?  I 
> guess the 205 would provide greater grip in the dry and less grip in the 

It's not really that simple.  Tread design and compound have a much
 greater effect on the way tire reacts to wet and dry conditions, it's 
not always realistic to say that a wider one will grip less in the rain.

Not to sound like a guru or anything, but I have run all of the tire 
sizes that you have mentioned on my 4KS.

I have a set of all-season 185/70-14 that I use for the winter.  They are 
very smooth over bumps, grip well in the snow, but have way too much 
sidewall flex to be used in serious corners.  For reference, they are 
Kelly Metric radials.

I have a set of 205/55-14 Yokohama A008RS soft compound race tires for 
use at the track.  They work better than anything else I have ever driven 
in the dry or the wet.  The wet performance, however, is due to the soft 
compound, as the tires are moulded at 6/32" tread depth.  They probably 
would hydroplane quite easily, but I don't use them for the street.

My street tires are Dunlop D40M2 Sports, 195/55-14.  They work excellent 
in the wet and the dry, but due to the short sidewalls, they have quite a 
bit of impact harshness on small bumps.  I will continue to live with a 
little harshness to get the increased cornering grip from a great set of 
street tires.  You might not be as tolerant.

I am told that the SP8000 work even better than the D40's.  They are 
about the same price, and are also avail. in 195/55-14.  This is the only 
14" size offered in either the D40 or the SP8000.

I also ran a set of 195/60-14 last summer for street tires.  They offer 
a little less grip in the corners than the 195/55's, but offer a much 
softer ride.

This all means:

If you don't mind a few bumps, and want the ultimate street tire, go with 
the Dunlop D40 or SP8000 in 195/55.

If you want a really soft ride, and don't mind compromising some grip, 
get the 185/70-14.

If you want a softer ride, but want good grip, get the 195/60-14.

Don't bother with the 205/55 unless you are really serious, and want some 
really wide tires.

Sorry the response is so long, but these are not simple questions,

Robert Phillips
The University of Akron Sociology Department-------Akron, Ohio
1987 Audi 4000S, 1.8L 4-cyl, FWD-----SOLO II D-Street Prepared