Been searching the web to find info but I'm not having much luck.  Can you guys help me out?  I have a 2007 2500HD (new style) duramax that I pull a travel trailer and jetski for camping trips in the summer.  I also use it for deer hunting in the fall.

I love this truck, but it came with the puniest donuts I could've imagined, and to top it off, the dealer threw some really cheesy looking Firestones on it.  So it definitely needs a wheel/tire upgrade.

So, can I put 20" on this truck?  I know I'll have to have a mechanic recalibrate it if I change the tires, but is it recommended/not recommended to upsize?  Will 20" fit?   I had an F-150 supercrew before this that had stock rims, but I put 275/85s on it and it looked pretty mean, I liked it.   Want the same type of look here, but I don't want to bother with a lift.

Second question, since I tow, is it an issue to change tire sizes?   Would it be dangerous at all?

Thanks for any help you can give guys!

Hi Folske - first off, welcome to the forums! Secondly, congratulations on your truck purchase. I own an '05 Duramax and love it!

I'll try and answer each of your questions here...

So, can I put 20" on this truck?  
The 20" you're talking about is referencing the rims, not the tires. So, yes, you can put 20" rims on this truck. Ensure that the backspacing is equal to or better than the stock wheels, so that they won't rub when you are turning the wheel full lock.

Also, you should strongly consider staying with the same tire size, otherwise you're going to lose fuel economy, and power. You see, as you effectively increase the tire diameter, you decrease the overall gearing efficiency of the truck, which makes the engine work harder and puts your truck out of it's peak power band.

I know I'll have to have a mechanic recalibrate it if I change the tires, but is it recommended/not recommended to upsize?  Will 20" fit?   I had an F-150 supercrew before this that had stock rims, but I put 275/85s on it and it looked pretty mean, I liked it.   Want the same type of look here, but I don't want to bother with a lift.

Couple points here... First, the recalibration; this is done electronically now, and any 4-wheel drive shop can do this for you much cheaper.

20" rims will fit, see above.

Bigger ties - I too, like the look of bigger tires, they fill the wheel wells nicely. I took my truck and effectively added a mear 1.5" in tire size (from roughly a 30.5" tire to a 32" tire) and saw about 4 mpg drop in city driving and 1-2 mpg drop in highway driving (a regrettable action, now). If you do insist on bigger tires, make SURE you upgrade your axle gears. That'll add about $1,000 to your tire/rim purchase though, as gears and setup are not cheap.

Second question, since I tow, is it an issue to change tire sizes?   Would it be dangerous at all?

Nope, not an issue, if you consider a few things:

1. There is such a thing as too big of a tire when towing... in my humble opinion, I would steer away from anything bigger than a 33" tire.
2. Above a 33" tire, you'll need more lift at that point, and then you're talking about a serious drop-hitch, as well as deeper gears.
3. Bigger tires equals more weight, which affects braking too. 
4. Be sure to get an appropriate load range tire too

Hope that helps,

Rick