Chevy Colorado & GMC Canyon banner

1 - 2 of 2 Posts

·
Registered
Joined
·
17 Posts
Discussion Starter #1
Sorry if it has been answered already, but i couldnt find it.

On my 2004 gmc canyon crew cab 4 wd I-5 i want to go from the 235/75 R 15 to a larger tire, maby a 31" or whatever the Z-71's have on them. First, will they fit on the stock rims for my Z-85. Second, will it help, hurt or not affect fuel milage, prob 95% highway 65-70 mph.

Thanks,
Brian
 

·
Registered
Joined
·
1,345 Posts
2nd question first: It will decrease the mileage. The question for you will be whether it will decrease the mileage an appreciable amount. The factory tires on the Z71 are 265/75R15s which are essentially 31x10.50/15s. So you're probably not going to lose much on size alone, but you will lose some. Another issue will be what tire you choose. The more aggressive the tread, the more rolling resistance, and wind resistance it will have. Any good offroad tire will be much heavier than the factory Z71 tires also. As memory serves, the factory Generals (265s) were about 36 lbs. each. You can go to General Tire's website to verify. A heavier tire, together with larger diameter, means more inertia, which means it takes more energy to remove it from it's state of rest, which means you burn more gas getting the job done. Then, the rolling resistance and wind resistance (friction) kick in requiring more energy (gas) to keep them rolling. Again, no more difference than you're talking about, that may not be an excessive decrease in mileage. What you have going for you is that your decrease in mileage will be less noticeable at cruising speeds because acceleration is where you burn the vast majority of your fuel. That's why city mileage is always less than highway. And remember, too, that your Speedo and Odo will be off when you change tire diameters, so any mileage computations will need to take into account the Odo error. Incidentally, your tires are the same size as the factory spare on the Z71s.

As for whether they will fit on the factory rims, I believe the rims on the Z85s are 15x6.5" Please correct me if I'm wrong. That's a little narrow for a 10.5" wide tire. I think most 10.5s recommend a 7" minimum. However, that said, it's a 4" difference which is actually less difference than running a 12.5" wide tire on an 8" rim. That's what I'm running, and most 12.5s spec an 8" minimum rim width. I'd say it'd be worth a try. You might just have to run a pretty low pressure to keep from wearing off the middle of the tires first. You'd just have to experiment to see what pressure works. But check the specs on whatever tires you're interested in. They'll tell you the minimum recommended rim width.

Edit: You might be interested in this thread http://coloradofans.com/forum/viewtopic ... highlight= Then again, maybe not. I see he's in Ft. Worth and will not ship. :roll:
 
1 - 2 of 2 Posts
Top