Hey, I am looking to get new tires for my 99 HD 2500. I need a heavy load tire and want the best fuel mileage I can get. I am new at this so at the risk of sounding completely dumb. What does the sizing numbers mean, I know width, diameter, and rim size, but don't know which number is which would a 255/75/18 work well. stock is 245/75/16. I am not changing rim size. I would like a taller tire for higher end final gear ratio.

 

a 255/75/18 would not work with the stock size cuz the last number the 18 and the 16 are the rim sizes

 

Try Goodyear.com or Michelin.com, both websites have tools that show most every size of tire commonly made.

 

I just purchased the truck and what I have on there are 265/75/16. Does the first number show tire width or height? Would a 255/85/16 work?
thanks for the comments

 

No worries.

This is for metric tires. The first number (usually 265 or 245 for stock trucks) is the thread width in millimeters measured from sidewall to sidewall, the second number is the aspect ratio which tells you the height of the tire, from the bead to the top of the tread. This is described as a percentage of the tire width. If the aspect ratio is 75, the tire's height is 75 percent of its width (most tires are 75 %), and the last number is the width of the wheel. There should be a sticker on your drivers side cab pillar that shows what size of tires you truck came with.

That being said, if you haul or tow heavy, you will want to stick with a E rated (or 10 ply) tire. It will have the best load handling capability and wear better than a common 8 ply tire. That is assuming that you are staying stock and not stepping up to medium duty wheels and tires.

 

So with a stock 245/75/16 would be shorter than a 265/75/16. Correct? What would you recommend for a taller tire that would increase the end gear ratio? I am turning 2000rpm at 70mph right now and feel like I have plenty of power in the low end. I just want to drop the rpm at speed, or would you not recommend doing that?
Also off subject, but since I just bought the truck I would like to chip it. Is there one chip that ya'll would recommend, or is it a personal preference/ job orriented. I am looking to increase MPG. Thanks for the help.

 

Yes, a 265 would be taller and wider than a 245. You could go to a 285 but Im not sure what kind of weight you are talking about, so again, you might want to look for an E rated 285, which will give you better towing/hauling performance and wear. BFG A/T comes in this size and rating as does some many of the Toyos.

As for the chip - do you have guages installed in the truck? There are many chips out there but you need some guages (if the fuel box doesnt come with them), and a fuel pressure guage is an absolute MUST before doing any kind of performance mods to a 24V.

 

Thanks for the help, looks like it is time to go shopping. I will also have to get some gauges- do you recommend the fuel in the cab or electronic fuel gauge? Thanks for steering me in right direction.