Mark_12345

255/50/16 tire has a diameter of 25.65"
225/50/16 stock tire diameter is 24.86"

According to http://www.miata.net/garage/tirecalc.html

legalrep

But how does the apparent fact that the stock tires really don't measure as true 225/50/16 effect all these measurements?

shingles

[QUOTE]Originally posted by Mark_12345
[B]255/50/16 tire has a diameter of 25.65"

STL

Keep in mind that:
1) the OEM S-02s treadwidth is not typical
2) keeping the tread width ratio (between front and rear tires) very close to the same as the OEM tires is very important
3) the more rubber you have touching the road, the better the dry handling BUT the worse the wet handling will be (generally speaking)

More details about 1
The rear 225/50/16 OEM tires have quite a bit wider tread width than most any aftermarket 225/50/16 tire. This has been confirmed by several people (as well as with published specs). Also the fact the rear tires have don't have a lot of grooves (and those it has are narrow) means this tire probably has as much rubber touching the road as most 245s or maybe even 255s

It is also rumored that the front 205/55/16 OEM tires are slightly more narrow (tread width wise) than a typical aftermarket 205/50/16 tires.

ALSO, keep in mind the S-02 PPs are inherently more narrow (tread width wise) than most all tires. I bet their replacements, the S-03 PPs, will be the same way! Also these tires have much wider grooves which means even less rubber touching the road -- thus they handle well in the rain (as they were designed to do).

More details about 2
If you go to aftermarket tires and change the tread width ratio (actually it's the actual contact patch area ratio, but that's a lot harder to calculate) then the cars handling will change. If your new ratio is more weighted to the front tires then you car will likely be more tail happy!

STL

Actually the OEM tires do measure 225/50/16. It is just that the measurement (225mm) is NOT the tread width -- it's the widest part of the tire (that's how all tires are measured for that spec). This tire is more squared-off thus it's tread width is wider than most all other aftermarket 225s, but the tire is not being mis-labeled.

legalrep

STL

So, if I plan to go to Michelin Pilot Sports as replacements due to the improved wet handling, but want to stay as close to original size so won't change speedometer, or odometer (unless it records less miles than driven) and is close to original on handling, what sizes should I get?

WhataRide

I've always been told that size doesn't matter.

STL

I must say that since I only drive my car on fair weather days (or at least that's the plan) that I haven't researched foul weather tires very much...thus I'm not sure what the best setup might be. Guessing, I'd say to keep a 205/55/16 on the front and put a 245/45/16 on the rear. I tried to take a look at the Mich Sport specs (on Tirerack and the Mich site) but tread width was blank or no specs were given. Without this data it's hard to make an informed decision -- thanks Michelin!


[Edited by STL on 04-25-2001 at 03:13 PM]

STL

Just for grins, I looked at the Dunlop SP9000 specs and found this:
205/55/16 have a tread width of 7.2
245/45/16 have a tread width of 8.8

Our OEM S-02s:
205/55/16 have a tread width of 7.1
225/50/16 have a tread width of 8.5

Some things must be kept in mind that tread width measurements cannot be directly compared between different manufacturers for the same reason you cannot compare treadwear ratings directly (because each company has unique/different testing techniques because there is not standard)! But ratios can be directly compared. So looking at the numbers above it appears the SP9000 setup has too much rear tire width....but if we take into account that the OEM tires are drastically different tread designs (with the rear tire having smaller grooves and more rubber touching the road -- and remember it really all goes back to the ratio of rubber touching the road but that area is much harder to measure) then it appears this SP9000 might be very close to the stock ratio!! Even if the this SP9000 setup has a little more rear rubber (ratio wise) then it would only make the car less tail happy.

legalrep

So, can we probably assume that most tires are like those and we should stay with 205/55/16 on front and 245/45/16 for rears? Anyone else try Michelins or Goodyears on S2K?