Going with 35s, stock height. Debate is to get a 18 inch wheel or 20 inch wheel. For those who have this setup can I get a few pro's and con's? Main thing for me I guess is it going to messup the speedometer and does that make a difference getting an 18 or 20 inch wheel. 2nd thing is what's the difference in mpg drop with these two different setups. Thanks again fellas.

 

No That make no difference. It is still a 35 inch will. Withe the 20 inch you have more rim and less side wall. That is what you trade off.If you do off road the 20 inch is not such a good idea. With off road you want flex. More sie wall is more flex and less chance that you will ruin the rim.

The speedo will be off since the 35 inch tire is taller, in other words it takes more distance to roll the wheel all the way aroung so the speedo will say a lower speed than you are actually going. Also the engine will have to work harder to turn the wheel around.
That is one of the reasons I am going down from 37 to 35 inch. Even though I like the looks on 37 better (on H2)

 

We had 35 on 18" wheel on my wifes Alpha, worked great.
The difference for the speedo is only 9% compared to stock.

 

You would expect the difference to be something like 8% to 10% difference, but on my H3T the speedo is only off by about 5%. Using a GPS my truck was around 5% off (faster than I was really going) with the original stock 33" tires - now it's 5% off the other way. I was able to confirm it with one of those "speedometer check" sections of the highway - accurately marked 5 miles vs. my trip meter.

I'm running 315/75/16s - ~35" tires on a 16" wheel - If I were buying a wheel/tire package from scratch I'd still go with ~35" tires, and 16" to 18" wheels. I couldn't tell you the mpg hit with 18" vs 20" wheels, but on a 16" wheel I'd say it's about 2 mpg.

 

Tire Dimensions Made Simple - Discount Tire

Hope this helps

 

I did a write-up on this a few years ago. See[URL="https://www.hummerforums.com/forum/hummer-h3-17/speed-distance-mpg-info-bigger-tires-18254/"]https://www.hummerforums.com/forum/hummer-h3-17/speed-distance-mpg-info-bigger-tires-18254/

I recently bought a H3x Alpha with the factory 18" wheels and put 295/70R18s on it. I went with the 295/70s (34.3") instead of the 325/65s (34.6") because the 295 is about 1" narrower. You'll notice with 315/75R16's or 325/65R18s that the tires will rub on the frame at full lock, and they'll stick out of the fenders about an inch or two.

That isn't that big of a deal and I admit it looks better, but you'll fling road debris all over the fender flare/back door and end up with a bunch of scratches and dings in the future... just speaking from experience.

 

Ours stick out about an inch from the fenders and the paint looks like brand new. No dings or scratches. On all the vehicles I've lifted and put larger tires on that we offroad with have done the same. No issues with scratches or dings. Yes, it will throw more mud on the side of the vehicle. Just always keep it clean and waxed and you should have no problem.

 

Not sure if a T is that much different, but my experience with Duratrac 315/75/16s are a little different. On stock wheels the tread sticks out ~1/4" on the front, and maybe 1/2" on the rear, with slight rubbing at full lock. I don't get rocks or debris banging the sides, even when going down gravel roads or through mud.

I test fit wider wheels with less offset, no rubbing even at full lock, but they did stick out 1" to 2". Here in UT that's a big no-no. Not only can you not pass safety inspection, but you will be pulled over and given a ticket. Easy solution, and what I plan to do so I can swap wheels, is add fender flares.

So basically, with 315/75/16 you either have slight rubbing with stock wheels, or you stick out an inch or two and no rubbing with non-stock wheels, but not both. I'm sure this is very much tire dependent - not all 315/75/16s are the same size. I can only guess, but perhaps what you describe is true for 325/65/R18.

 

The 285/75-16 Duratracs on my truck love to pick up rocks and throw them up on the rear fenders. Putting the nerf bars back on for on-road driving helped keep a lot of that from tearing up the fenders and thats with the OEM mudguards to boot. I cant imagine how bad 35" Duratracs would be!

 

I do have RR sliders, and they stick out far enough to be used as a small step, maybe that helps?

Here is a side view of my truck, stock wheels, 35" (315/75/16) duratracs. Again, wheel offset can make a huge difference. Some rocks and mud occasionally kick up, but no real problems as it sits. Maybe if I spent more time flying down loose gravel roads instead of mostly dirt or slow dirt/gravel climbs?