285/65/18 Vs 275/70/18

johnnyz71 · August 15, 2011

I am looking at getting either 285/65/18 or 275/70/18 in BF GoodRich All Terrain KO's mounted on the 18" Z71 wheel. I have seen pics of the 275/70 here on the forum (it was the member with the black extended cab Silverado) and they looked good. I haven't really seen good pics of the 285/65/18 size with the 18" Z71 wheel. I also have the 2" RC Level Kit installed as well. Here are my questions:

What is the main difference?

Will these tire sizes throw off my speedo? If so, how much?

Will there be a difference in gas mileage?

I am under the impression that the 285 size will be wider but the 275 would be a little wider and taller? I appreciate any help and pics of these sizes.

Superperv23 · August 15, 2011

They are both basically 33 inch tires, the 285 is slightly less than 33 and the 275 is slightly more. Sometimes tires sizes that close to together have the same tread width but the sidewall distance is further apart so the tread might be the same but with less bulge to the sidewall with the 275 vs the 285. Your speedo will be showing slower than you are going by about 2 or 3 mph. Gas mileage shouldn't be that much worse, I didn't really see a difference going to bigger tires on mine.

mhenshaw · August 15, 2011

The main difference is price. 285s are high

Yes they will throw off your speedo by around 2-3 mph

The main difference in gas mileage will be caused by different tire weight.

285 are .4 inches wider but .3 inches shorter than the 275.

AgDoctor · August 16, 2011

True on the height difference and width difference. I had a set of the BFG 285sATKO and went back to the 275s and like them better. Taller and nearly as wide but alot cheaper. I think a little lighter as well. As for speedo difference it is not entirely try about the 3 mph. It will not be constant, which is to say while it may be 3the mph at say 50, it will be more incorrect at a higher speed. I got a blackbearperformance autocal to fix this. For fuel economy you can expect at least a 2 mpg difference. I have seen it on this '10 model and my last '07 model.

Doug_Scott · August 17, 2011

True on the height difference and width difference. I had a set of the BFG 285sATKO and went back to the 275s and like them better. Taller and nearly as wide but alot cheaper. I think a little lighter as well. As for speedo difference it is not entirely try about the 3 mph. It will not be constant, which is to say while it may be 3the mph at say 50, it will be more incorrect at a higher speed. I got a blackbearperformance autocal to fix this. For fuel economy you can expect at least a 2 mpg difference. I have seen it on this '10 model and my last '07 model.

The speedo will be off a constant 4%, assuming same air pressures in this case. Easiest way to figure this in the future (assuming same rim diameter), take the tire section width, multiply by aspect ratio (expressed as a percentage, so 65 would be .65) for both tires. then divide the smaller by the larger. Subtract the answer from 1.00 to get the percentage the speedo will be out. As for fuel mileage change, due not count on it. If the speedo is out by 4%, so is the odometer. A simple change in effective gear ratio does not always mean more mileage, if it did, the factory would simply do that to make CAFE numbers easier.

sic lsx · August 17, 2011

285/65r18 = 32.5x11.6

275/70r18 = 33.1x10.8

IMO 285s look much better.

nealsears · December 13, 2011

I am looking at getting either 285/65/18 or 275/70/18 in BF GoodRich All Terrain KO's mounted on the 18" Z71 wheel. I have seen pics of the 275/70 here on the forum (it was the member with the black extended cab Silverado) and they looked good. I haven't really seen good pics of the 285/65/18 size with the 18" Z71 wheel. I also have the 2" RC Level Kit installed as well. Here are my questions:

What is the main difference?

Will these tire sizes throw off my speedo? If so, how much?

Will there be a difference in gas mileage?

I am under the impression that the 285 size will be wider but the 275 would be a little wider and taller? I appreciate any help and pics of these sizes.

Which tire did you end up going with? I am looking at the exact same setup with a 2" RC kit and OEM 18" Z71 wheels. I am stuck between the 275's and 285's. Any pictures would help!

Thanks!

fixithud · December 14, 2011

I am looking at getting either 285/65/18 or 275/70/18 in BF GoodRich All Terrain KO's mounted on the 18" Z71 wheel. I have seen pics of the 275/70 here on the forum (it was the member with the black extended cab Silverado) and they looked good. I haven't really seen good pics of the 285/65/18 size with the 18" Z71 wheel. I also have the 2" RC Level Kit installed as well. Here are my questions: What is the main difference? Will these tire sizes throw off my speedo? If so, how much? Will there be a difference in gas mileage? I am under the impression that the 285 size will be wider but the 275 would be a little wider and taller? I appreciate any help and pics of these sizes.

try this http://www.miata.net/garage/tirecalc.html

Taylor Ginn · January 26, 2012

I have the 275/70/18's and like the way they look alot. I think the next time I buy tires though that I am going 305/60/18. I want to go for the wider look and I have seen alot of trucks with the 305's with the 2" lift and not had any trouble.

uh6tdrvr · January 29, 2012

^^ What he said ^^

gmctruck2018 · January 29, 2012

I agree i love my 305's no problems at all

NoMoreGM4Me · January 29, 2012

Load range "E" tires are HEAVY and expensive and WILL impact your gas mileage and performance significantly.

285/65/18 BFG A/T KO's are load E (10 ply) tires.

mmatthewman · March 13, 2012

I have a 2008 GMC Sierra 1500 All Terrain. I am looking to put larger tires on it, but dont want to do a lift or anything. I am looking at BF Goodrich All Terrain 275/70/18's. I have 18X9 KMC Rockstar wheels. I want to go as big as I can without doing anything to the truck and without rubbing. Are those 275/70/18's too big?

Any suggestions for sizes that are bigger than stock, but not too big?

Big Whiskey · March 13, 2012

Well, if you're not wanting to do anything to the truck, and don't want rubbing....then you're very limited on tire size. The 275/70/18 are way to big for that. A 275/65/18 works with stock height, and stock rims, but that's about the max. Those may even rub on your truck, depending on the offset/backspacing of your aftermarket rims. The 275/70/18 would fit with a 2" level kit.