New Front Tires - Question
 

I'll be ordering new front tires this week. My 2000 S came with 17 inch wheels and 205/50ZR17 tires. I am thinking of replacing with 225/45ZR17. The rears are 255/40ZR17.

What are the positive benefits ?

What are the negative drawbacks ?

Better front grip, shorter braking distance, less understeer are all positives.

Slightly more prone to hydroplane through standing water is a negative.

Here is my experience in switching from 205/50/ZR17 to 225/45/ZR17 on the fronts of my '99 (rears remain at 255/40/ZR17);

Pros:
- Much better overall grip
- Much less understeer
- No wheel, body or suspension fitment issues on stock wheels
- Speedo/ABS unaffected
- Looks better

Cons:
- Slightly slower turn-in
- Slightly more expensive

No Difference (that I can tell):
- Braking performance/distance
- Hydroplaning in the rain on the freeway

Overall, what I noticed the most was that the 205's would turn in quickly and then plow with understeer through the turn whereas the 225's turn in slower but are able to carve the turn much better. The 225's still understeer when pushed but not nearly as soon as the 205's did. Car is much better balanced with the 225's.

I'd highly recommend the 225's in front.

These are just physics 101. Braking distance is primarily a function of weight and tire grip. Any improvement in front tire grip where 80% of your braking forces happen and you will shorten your stopping distance. For a real eye opener, mount a pair of 255/40/17 R-comp tires to the front and compare your stopping distance... WOW!

Hydroplaning is the opposite effect. It is a function of speed, weight, and contact surface area for a given tire compound and tread pattern. All tires will hydroplane at some speed. Increasing tire contact surface area (wider tire) will result in hydroplaning at a lower speed through standing water. For a real eye opener again, mount those 255 R-comps to the front (very high contact surface area) and go out blasting through puddles on the next rainy day. WOW! Surf City!

My 205 PS2 street tires will hydroplane at around 65mph, 225 PS2s will hydroplane at around 57mph, my 255 R-comps will hydroplane at 40mph.

A good link:
http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=16

All I was saying is that I personally didn't notice any difference in braking or hydroplaning when the only change was going from 205 to 225 - everything else stayed the same (same tire mfg, model, compound, brakes, etc).

But you are absolutely correct that there should be (or is) an improvement in braking and some increase in hydroplaning due to increase in width of the 225.

The main point is that I've found the 225's to be a great improvement over the 205's.

Thank you Gentlemen.

Your answeres were exactly what I expected base on experiance with other vehicles. I beleived they would fit based on the allowed sizes for 18" wheels on the 986. But I really needed to hear someone say they have done it, the tires fit, they liked it, and with no real problems.

Tires are now on order. I ordered a new matching set of 255 for the rear too.

Thanks, Bill.

if 225 are better, how come they didn't come stock?

will 225 fit on 17" with only 7" width without any problems?

That is a good question. The new tires went on the car this morning. Fit is fine, no problems. Handling is much improved and car is rolling smother and the squirm is gone. I think it could be due to the less differance in the front to rear size. 205/255 is 50 milimeters differance and 225/255 is 30 milimeters. My '98 has 205/225 front/rear and is very steady, stable and smooth, even at over 150 mph. I haven't had the S over 125 mph becauase of the squirm. Its time to see what S can do.