Tire Advice Request - 986 Forum - The Community for Porsche Boxster & Cayman Owners

Hello, I have a 98 base with stock 17" wheels. Back tires are shot but fronts are great and of recent mfg date, so I'd prefer to only replace rears. I'm running BG Goodrich g-Force Sport Comp-2 tires which I love and would recommend. The specified 255/40ZR17 are backordered indefinitely. I located a pair of same tire sized 255/45ZR17 about 100 miles from me. Question is... Do I hold tight and wait for the correct size to go back into production (likely several months) or would the 45 aspect ratio be okay? 40 vs 45 aspect ratio. Of course the other more expensive option would be to scrap the good fronts and buy a full set of a new available in-stock tires. Thanks

I wouldn't use them, but you can use them if you don't mind having a taller tire in the rear, they are 1 inch taller than the 40's. You want to be within 1% percent of variance. It's not as important for a rwd car, but It's very important for an awd car, it will mess up your awd system if you are not within 1% variance. I assume that you have 205/50 r17 in the front? I have 17 inch wheels and I use 225/45r17 front and 255/40r17 in the rear. Use this tire calculator and you'll see if you are OK with the different height. https://tiresize.com/calculator/

Youre going to raise the rear a half of an inch by going with the 255/45. Probably OK but not ideal. From what I have read others describe, boxsters do not respond favorably to rake. If you're just mild street driving its no big deal. Otherwise I would be leary about it. You can always do a 245/40 instead. That would probably be a better setup than the 255/45. Be careful mismatching tires in terms of wear, I'm sure you already know this though.

Thanks for the input. I'll hold off for now and see if I can wait it out until production resumes.

have you checked online? can't imagine you couldn't find all 4 tires someone has in stock and you can just have a local place mount/balance & install.

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You can use 265/40r17 if they are available, that`s if the fronts are 205/50r17, it`s only 0.2" difference

Not sure how much difference is OK for ABS, though. While overall the car will behave fine, speed sensors may become more aggressive (it is only apparent behaviour as they will already be close to their tolerance for difference front/rear). You can change overall size all around, though. 205/50x17 and 255/40x17 have heights of 636.8 and 635.8 mm respectively. New rear (45 profile) would be 661.3 mm. the closest match for front would be 205/55x17 with 657.3 mm (only 4 mm difference - although OEM setup is at 1 mm). Yet this is within thread wear range... so should be fine. Here is a problem, though. Despite the tire being "specs" it will have a slightly different size on the rim. If the rim is wider the tire will sit a bit lower, while if it is narrower, it might push the tire out a bit. Take it with a grain of salt as it is tire and rim dependent... 205 50 17 636.8 205 55 17 657.3 215 55 17 668.3 255 45 17 661.3 255 40 17 635.8 245 45 17 652.3 265 40 17 643.8 Example: 155/70x16 is 623.4 mm 155*70/50+16*25.4=623.4 mm 155*70/100 = 108.5 mm side wall height

I burn through about two sets of rears for every set of fronts, and companies discontinuing the 255 size has been a constant problem. Hopefully this is just a backorder. I run the same tire and was pretty upset when the discontinued the original g-Force with the wave thread. I looked online and discount tire is showing 255/40/17 in stock for $140/each, TireRack is showing backorder, and Summit Racing is showing a backorder until 11/22, so a few months.

rick3000, I also go through two sets of rear to one set of front. I'm going to place a tirerack order so I'm in line when they are back in stock. My region discount tire show zero in stock and I checked the west coast and could only locate one.