quick question. is it worth going out to 285's in the rear of the FD over 275. i went to tire rack and glanced through the tire selections and there is a massive selection of 275's over 285. i know that there are better tires for better prices at the 275, but will the 1/2 inch or so make a big difference?
kris

 

10 mm is actually closer to 3/8ths of an inch, if that makes you feel any better.

 

well i didnt actually try and figure out the calculations, but to be exact here is the forumla i would use.
10/25.4=.39307
there is 10 mm to one cm. there is 2.54 cm to one inch. there for you would divide the mm's into 25.4. mm's and cm's cancel out and you are left with inches only. so .39307 would be in inches and in fraction would be closest to 25/64 keeping it as a somewhat reasonable number. 3/8=.375 which is still broad. okay just giving you are hard time. would it be worth while?
kris

 

Realistically, it depends on what you wanna do with the car. If you're big into track racing, then wider is almost always better (yes, just like that stupid Pontiac commercial). But, you'll be hard pressed to find a 285 for a 17 and I don't know that the tradeoff is worth it ... wider rubber vs. more upsprung weight. I guess it depends on your driving style. Personally speaking, I'm waiting for the right deal on 17x10's and going the 275 route. Race rubber is hard to come by (read: freakin' EXPENSIVE) for 18's.

 

The numbers don't always add up to wider tread on the ground, gotta look at the specs. Some 275 will have a wider contact patch than a 285.

 

I think its pretty commonly agreed that 275/40/17, or 275/35/18 (same diameter) are the tallest you wan to go (.7" more than stock). 285/40/17 are a whole inch larger (FYI, Bridgestone lists the diameter of the OEM 225/50/16 SO-1s as 25")

So, when folks want wider, they generall do to 18" size i.e: 285/30/18 to 295/30/18

This assumes you have a rim wide enough for them to work their best on. Most tire engineers will tell you that you won't get the best out of any size tire unless its mounted on rims that are towards the wide side of their published range.

 

285/40-17 results in 1 inch taller than stock overall diameter. This will change your rear end gearing and decrease acceleration, but will add to the top speed. You should also consider the extra weight of this tire size. This will be in the 30 to 33 lb range. FWIW this question has been discussed ad libitum. The search function is down at the moment, so you have an excuse

 

woo-hoo, thanks sleep R1. im innocent
kris

 

I'm with sleepR1, the 285/40-17 will be too tall (and cause other non-traction related problems), the contact patch difference is likely negligible.

K

 

well id like to say thank you for all that chimed in. these are just questions i like to get out of the way early. ill surely go with a 275(sticky tire) over the 285. id hate to change gearing as accelaration would still be a must. i plan to track my car with 17x9 1/2's in the rear. thanks again
kris

 

quick question... couldnt you just divide the tire size to get an overall size relationship in mm's. if you have a 225/50 tire(such as stock) then you would have 112.5 mm's. now if you go to an upsized stock, 245/45 you would have 110.25 mm's. if you go with a 275/40 (17" upgrade) you would have 110mm's and the 285/40 you would have 114 mm's which would be 1.5mm's taler than stock. does this actually make sense.
kris

 

To calculate overall tire diameter:

[(tire width in mm x aspect ratio as a decimal x 2)/25.4] + wheel diameter in inches

In your examples.

stock FD tire is 225/50-16
225 mm x 0.5 x 2/25.4 + 16 = 24.9 inches OD
275 mm x 0.4 x 2/25.4 + 17 = 25.7 inches OD
285 mm x 0.4 x 2/25.4 + 17 = 26 inches OD

Ideall you want tire widths with aspect ratios that yield stock tire ODs:

255 mm x 0.4 x 2/25.4 + 17 = 25 inches OD
285 mm x 0.3 x 2/25.4 + 18 = 24.7 inches OD
295 mm x 0.3 x 2/25.4 + 18 = 25 inches OD

FWIW you should choose rim widths that are 90% of the tire section width. For 255 you want at least 9 wide. For 285, 10 wide. For 295, 10.5 wide.

 

thanks sleepR1. makes total sense.
kris