langted

After 8 years, it's time for new tires at 72,000 miles. I currently have factory 265/60R20 Goodyear SR/A tires. They have been ok and trouble free, but they "look" small in those big wheel wells and I would like to upsize them a little. I drive 100% highway, often with a travel trailer, and I think I MAY have used 4WD once for less than a mile (other than cycling it occasionally to make sure it still works). Its a warm weather truck.

I am thinking of 10 ply Michelin Defender 285/60R20 LTX M/S. Not a big jump in diameter, but a LITTLE better. Will these fit my 2015 Z-71 2500HD (6L gas) without any modifications? Also, can the speedometer be corrected with a software update? What does that take?

Thanks
Ted

langted

Ok. No responses my 285/60R20 question yet but after more research, I found that one of the STOCK sizes on the 2020 (and a few years forward) for 2500HDs is 275/65/20. It does not appear that GM made any significant frame changes from 2015 through about 2022, and uses the same 6 speed transmission ratios. (although the engine was upgraded in 2020). The 275/65/20 tires are larger diameter than the 285/60/20 that I was contemplating, though a tad narrower. Also, I found a thread on a gmc truck forum (the originator there also thought the 2015 tires looked too small) with numerous respondents on that forum saying and via photos that the 275/65/20 size worked for them with no rubbing. Respondents had the Z71 package, same as mine, but I don't know if that makes a difference. So my conclusion is that the 275/65/20 is fine (for fit), and I will shift focus to that tire size.

I'll try to report back once I have them. Also, researching first how to correct the speedometer for the new tires since the change will make a 5% speed error, which I think is excessive.

langted

Still no outside responses, though this is a popular topic on truck forums....

What I found regarding the speedometer is that it is indeed software controlled, but it requires a plug in tuner with speedometer reset capability, typically costing $400-600. I did find one, "superchips flashcal" that will also reset the speedometer for different tire diameters, and it is currently a little over $200. Apparently, if you don't do this, you can get a number of drivability issues related to how the vehicle senses motion -- i.e. if wheels and transmission sensors are not calibrated together, it can affect anti-lock braking control, shifting, etc. and make coordination erratic. Per youtube videos (for whatever that is worth), you have to be careful that the tuner you use does everything completely and correctly. Apparently the unit I mentioned above does that, but its just something to be aware of. However, the tuners seem pretty specific to the car/truck model, so it may not be useful for other vehicles. I don't know anybody that has one I can borrow, the tire shop doesn't do this service, and it's just not that important for me to go to the bother and expense, so I'll stick to the tiny stock 265/60R20 E rated tires.

This is now a "dead" string with respect to me. Hope anybody reading finds some utility in it.