It's only a guess but because you're raising the gear ratio with the larger wheels the engine would be turning less rpm's so the mileage might be about the same.

My concern would be the added road noise from the more aggressive tread and that the speedometer would be off with the larger size wheels.

 

Mine came with 275/60R20 Trailrunners (115S load rating)
I run most miles in the 55 - 60 range.
Truck stays in 9th at these speeds.

8, 9 and 10 are all overdrives.

GM 10-Speed 10L90 vs. 8-speed Hydra-Matic Transmissions - Gear Ratios

Transmission:	10-speed 10L90	8-speed 8LXX
Gear ratios 1)
First:	4.70	4.56
Second:	2.99	2.97
Third:	2.15	2.08
Fourth:	1.80	1.69
Fifth:	1.52	1.27
Sixth:	1.28	1.00
Seventh:	1.00	0.85
Eighth:	0.85	0.65
Ninth:	0.69	–
Tenth:	0.64	–
Reverse:	4.87	3.82

 

I don't think the rim size/diameter will make any difference but the tire likely will depending on the tread pattern. I have the 18 alum rims on the Sierra with all season Goodyear road tires (ie: not aggressive lug/tread) and my overall mileage to date is 28.5 US MPG average (also dependent on how much of a lead right foot one has..). For what it's worth.

 

Ok so I’ve got stock 17” wheels and 255/70r17 tires on my 2020 1500 3.0.

Found a set of Trailboss 18” wheels and 275/65r18 tires at a good price $900. Usually sell for $1500+ in my area, I’ve been watching.

Only 10k miles on em. That said all the info I found is my wheels are 27lbs, trailboss 31lbs. So some unsprung weight, about 1” larger and more aggressive tire so add some rolling resistance.

They would look much nicer but not sure what kind of mileage penalty I’m gonna see. Anyone done this and have real world data with a 3.0Diesel 1500 on mileage loss

Maybe I should leave well enough alone at $5.xx gallon for Diesel.

Love the look but not sure I’d love the penalty. What say you?

The rotating mass of the wheel and tire as well as the probable increase in rolling resistance of the larger assembly will likely decrease your mileage but how much is anyone's guess. I've seen posts of a reduction in mileage of 2-4 mpg but depends a great deal on the driver, speed etc. FWIW.

I will be trying to buy a set of takeoffs with AT tires to reduce road noise and increase mpg for the spring/summer/fall and run the Duratracs in the winter only.

 

Found what I thought was an unusual thing about duratracs when looking for winter tires.

Strangely enough, the C load range duratracs GM has on the 1500's are not 3PMS snow rated -- even though the heavier E load range durtracs are 3PMS.

(R3O Tires, LT275/65R18C blackwall Goodyear Wrangler DuraTrac MT)


When I was looking, the duratrac made for GM was the only duratrac I found that wasn't 3PMS.

 

Found what I thought was an unusual thing about duratracs when looking for winter tires.

Strangely enough, the C load range duratracs GM has on the 1500's are not 3PMS snow rated -- even though the heavier E load range durtracs are 3PMS.

(R3O Tires, LT275/65R18C blackwall Goodyear Wrangler DuraTrac MT)


When I was looking, the duratrac made for GM was the only duratrac I found that wasn't 3PMS.

I believe these are TPC spec tires, made specifically to meet the manufacturer EPA ratings across the variety of tires/sizes they put on.
Usually they are sub-standard to actual product and wear out sooner too.
And the “LT-C” rating on TPC spec is a marketing ploy, they only have 5-6 plys and the load rating is same if not lower than a SL tire for the same make/model.

 

You are correct, mine were made in Mexico they do have a couple of sipes in the outer block but will not be ideal for ice and cold temperatures when they will be too hard.

 

Just going my Goodyear's info.

Not sure that where they were manufactured matters to Goodyear's formula and process.

 

My 21’ has the 20” wheels and 275/60r20 that equal 33”. I generally get 25-26 mpg so I wouldn’t think you going up would change your much, unless your over 30 mpg right now

 

My 21 gmc at4 came with the 20 in Bridgestone duallers on it. Swapped a guy with the 18 in duratracs. No noticeable change in mileage. Just added a little road noise.
I just hated the look of the 20’s rims.

 

Im leaning towards just painting the stockers black and rolling with what I’ve got. Sure it would look better with the Trailboss wheels and aggressive tires but it would be some sort of loss in mileage over the life of the vehicle. I drive 108 miles round trip to work at zero dark thirty and for the miles I’ve owned her, every tank hand calculated has been over 30. I have my Old Powerstroke F250 with MT tires for serious winter weather and real work.

Even a few % loss in mileage will add up over time as this is my DD for the next 6 years and 7 months till I can retire, but who’s counting lol.

Thinks I’ll pass. Thanks all for the info, be safe. Rye

 

Ok so I’ve got stock 17” wheels and 255/70r17 tires on my 2020 1500 3.0.

Found a set of Trailboss 18” wheels and 275/65r18 tires at a good price $900. Usually sell for $1500+ in my area, I’ve been watching.

Only 10k miles on em. That said all the info I found is my wheels are 27lbs, trailboss 31lbs. So some unsprung weight, about 1” larger and more aggressive tire so add some rolling resistance.

They would look much nicer but not sure what kind of mileage penalty I’m gonna see. Anyone done this and have real world data with a 3.0Diesel 1500 on mileage loss

Maybe I should leave well enough alone at $5.xx gallon for Diesel.

Love the look but not sure I’d love the penalty. What say you?

Looks like it will increase gearing about 5%, will that be an issue well it depends on what you use it for. It will certainly impact accelleration and towing capability not to mention speedo error. My biggest concern would be load rating on the tires, generally speaking the lower the profile the lower the load capability is.

 

Well the deal was too good to pass up, if anyones interested after a few weeks I can post some mileage results.

thus far a bit stiffer ride and far more road noise but that’s all to be expected with a MT tire.
Really happy with the look, I’m a blacked out guy. Now I have the annoyance of satin finish here, flat there, wrong center caps but hey I’m a disaster as well.

 

Keep us posted, would be good to hear the results after 2 or 3 fill ups And what difference if any it made.

 

Ok so after a bunch more research on the tires and wheels my final verdict is I gained 20lbs additional unsprung weight per wheel and tire (yikes). Extra rolling resistance is obviously up going MT vs Highway tread.
My Lie O Meter on the truck took a huge dive, I was super concerned. But numbers and hand calcs don’t lie.

the first number is my last hand calc with my Oem set up, meaning my 17” wheels and highway tires.

The second pic is my new 18” trailboss wheels and Goodyear MT tires at my first full fuel up. Now for the last # I added a 3% multiplier to the 609 mileage as the new tires are larger and the Speedo isn’t adjusted for the additional run out. So I’m at -1.65 mpg.
Crazy cause the lie o meter was much less so I was very concerned. I estimated -2-3mpg as a best guess when I purchased them.
I’m on a full tank and I’ll post up my next results. Really shocked and happy. Thought it was gonna be worse.

any questions shoot, Rye.

 

Looks good. Too bad they're not 8 lug. I have black Chevy center caps from a 2500 LTZ. I bought GMC caps for the All Terrain for about $25 each. I also got a great deal on the wheels.

 

So bringing this back because I couldn’t stand the road noise of the Duratrac tires on my quiet 1500 (if I want to hear noise I’ll drive the old Ford). So today I purchased new Michelin LTX M/S tires in 275/65/18.
So in a few weeks I’ll post up what moving to an 18” wheel but keeping a Highway tread tire looks like.

 

Install of 275/60 R20 Michelin LTX M/S MTP tires (Canada) vs stock 275/65/R18 Goodyear Duramtrac C (Mexico)

Michelins 33" vs Goodyear 32.3" so about 2.17% less rotation and a speedometer error of 61.3 mph vs 60 mph indicated.
I will be changing back to the Michelins soon and will update my build thread. I will have to try and see if I can get my tire pressure sensors to work on the AT4 or change them out? (22R has a newer sensor than the ones in the previous rims I bought)