Alternative Tire Size For '07 Nbs 2wd

07Graystone · July 26, 2007

I have a '07 Silverado 1500 2wd with 17x7.5 factory aluminum wheels and P245/70R17 tires. I want to keep these wheels but change to a wider tire, like a P275/65R17. The difference in size are 1/2" greater overall diameter, 1.25" greater section width, and 1"-1.25" wider tread, depending on the brand.

Online tire size calculators indicate this size tire will change the speedo by 1.1 mph. Is that enough to require a tire size PCM adjustment?

If anyone has seen this wheel/tire size, especially if you have a picture, I'd love to hear from you before I spend the money.

Thanks! 07Greystone

rogerf · July 26, 2007

Not sure what it will do to your speedo but should consider the 265/70/17 factory size used on the 4X4's.

07Graystone · July 26, 2007

That tire has 1" more OD. I'm sure it would 'fill up the fender well' and look better than stock.

Paul58 · July 26, 2007

I swapped my 245/70-17's for 255/75-17's and they look considerably better. After the swap, my speedo was only off by 1 mph, according to my GPS, I was traveling at 71 mph when the cruise was set dead-on at 70 mph on the speedo. I still have about 1/2" of clearance when I turn the front tires. They ride better too. According to a tire/gear ratio caluclator I used, the swap essentially changed my rear gear ratio from 3.73 to 3.55, which I can live with.

07Graystone · July 26, 2007

I swapped my 245/70-17's for 255/75-17's and they look considerably better. After the swap, my speedo was only off by 1 mph, according to my GPS, I was traveling at 71 mph when the cruise was set dead-on at 70 mph on the speedo. I still have about 1/2" of clearance when I turn the front tires. They ride better too. According to a tire/gear ratio caluclator I used, the swap essentially changed my rear gear ratio from 3.73 to 3.55, which I can live with.

Those tires are way taller and slightly wider than our trucks came with, but your truck looks really good with less gap over the tire. Did you lower the back a little too? Also, was it necessary to reprogram your PCM for the new size?

Paul58 · July 26, 2007

I swapped my 245/70-17's for 255/75-17's and they look considerably better. After the swap, my speedo was only off by 1 mph, according to my GPS, I was traveling at 71 mph when the cruise was set dead-on at 70 mph on the speedo. I still have about 1/2" of clearance when I turn the front tires. They ride better too. According to a tire/gear ratio caluclator I used, the swap essentially changed my rear gear ratio from 3.73 to 3.55, which I can live with.

Those tires are way taller and slightly wider than our trucks came with, but your truck looks really good with less gap over the tire. Did you lower the back a little too? Also, was it necessary to reprogram your PCM for the new size?

My suspension is bone stock and the 1 mph difference is with no pcm reprogram. When running your stock tires your actually running about 68 mph when the speedo indicates 70 mph. Since I've gotten the Edge Evolution, I have adjusted it the pcm for the new tire size, so once again when I'm running an actual 68 mph (per my GPS) the speedo indicated 70 mph. I did it more to adjust the shift points for the new tire size. Also, when I was researching tires, I found the Bridgestone Alenza 255/75-17's were actually taller than the 265/70-17's, and the tread width was the same! My goal was to fill the huge gap above the rear tires!

The program that came with the Edge has a calculator that tells you what size to enter for any given tire size, and it will also calculate the new effective gear ratio that results from a different size tire. In my case it ended up being 3.55, which is a good all around gear ration for hauling and gas mileage!