Best tire rim size when towing

[dpam]

When I bought our 2008 GMC Sierra the tire size was 17 inch rims. At the time I was told that smaller tire rims tow better than 18 or 20 inch rims. I'm shopping around for a new 2011 tow vehicle and noticed that most of the 2011 Ford and GM trucks have 18 and 20 inch rims. I noticed that a number of MOC members have bought 2011 Fords and 2011 GM trucks. Therefore, I'm wondering what size rims you got with your trucks, and have you noticed anything both positive or negative about the size of your tire rims? I have very little knowledge about tire rim sizes, therefore I greatly appreciate your thoughts.

[8.1al]

If the height of the sidewall (from wheel to tread) is larger than stock then handling when towing may be affected as a taller sidewall is more flexible. From looking at tire sizes on 2011 - 2500HD GM trucks this doesn't seem to be the situation. The sidewalls on 17 & 18" tires look to be the same or less.

[dpam]

Sorry, I guess I should have mentioned that I was planning on buying a 2011 GMC 3500 or a Ford 350 (haven't decided on the brand at this time).

[thor]

the 2011 gm dually only comes with one size tires they are 17 inch tires.

[Delaine and Lindy]

thor is correct the our 2011 Chevy has 17" tires by Michelin. I'm hoping the 2012 has the same tires.. Happy Trails....

[Capt Kidd]

I think one of the reason for the 17 inch rim is to clear the bigger brake calipers.

[brenkco]

I have been shopping for a 11/12 Ford F350 SRW. I thought I'd want the 20's but I have been told that they don't wear as well. I did some research on the web and found the same feedback. Then I priced replacements, 18" were readily available where 20" were not and they were significantly more expensive.
I decided I wanted 18". Most, if not all of the remaining 2011 I could find were all equipped with 20". For that and other reasons, I decided to order a 2012 with 18".

Ken

[pineranch]

Ken,
Make darn sure the 18's will handle the weight vs the 20's. Find a tire expert rather than a truck salesman.
Mike

[Hooker]

quote:Originally posted by pineranch

Ken,
Make darn sure the 18's will handle the weight vs the 20's. Find a tire expert rather than a truck salesman.
Mike

...or check the capacity stamped on the tire.

[pbahlin]

Isn't the entire drive train designed for a particular diameter of tire (the outside diameter that is)? And isn't it true that changing the tire diameter changes the amount of torque you can deliver to the road surface? It seems to me that increasing the diameter of the tire would mean increasing your rear end ratio to keep the same delivered torque. Likewise reducing the tire diameter would require reducing the ratio to keep the same delivered torque.

I wouldn't mess with it because some sales guy talks about a rumor he got from his buddy who changed a tire once.

Why would you assume that the engineers who design these trucks are unaware of the optimal tire to put on their drive train? I'm not that smart I guess.

[mlh]

I have 20 inch rims on my 08 Ford. They are rated to carry over 3700 pounds. The 20s are about 1.3 inches in diameter larger than the 18s, so the side wall is a little narrower and a little stiffer. They should be a little more stable than the 18s. I have pulled with 16s 18s and 20 inch wheels. I much prefer the 20 inch wheels. They are more stable, almost as good as duel wheels. The big drawback is cost. My Michelins were over $1500, ouch.
Lynwood

[Art-n-Marge]

I had 17" rims on my Ford but went to 18" when I upgraded from the F-250 to the F-350 suspension. It is very difficult to find 17" tires with the proper weight rating. The E-rated 17" tires had much less weight rating than the E-rated 18" tires.

I think 20" tires are better if you need higher ratings but heard they are more expensive than 18" tires with the exact weight ratings.

I do think the 16" rim is going away on these more capable trucks because one way they increased ratings was to increase braking power too and the 16" rim is too small for the calipers. Then a large tire will hold more air and higher psi to support heavier weights.

Have fun with your search. I hope you post a description of your new TV.

[Art-n-Marge]

I forgot to mention regarding pbahlin's question. It is true the size of the tire is important for drivetrains. This is why tires should be the same size on the drive tires AND the same size per axle. You can have differing sizes front to back since a front wheel drive OR a rear wheel drive, the axles operate differently. On a four wheel drive they should all be the same size.

If you change the TIRE SIZE from what was previously on the axle and the axle is the drive axle then you must have the drivetrain adjusted to this new size. When I went from 17" wheels and tires to 18" wheels and tires I made an appointment at the Ford dealer to have this changed since the tire store where I bought the new tires did not do this. Driving to the dealership was surreal. The ride seemed strange and the shifting was terrible. After the service was done, things were back to normal. Size does matter and WILL affect the drivetrain is the adjustments are not made.

I could imagine if I did not do this adjustment I might get used to the "new" ride, but I can only imagine what harm I could have been doing and with the different shifting. Then at max loads or towing, this could be bad. I'm just thinking out loud, but I am glad I got this looked at. In my case it made that much different. Get larger or smaller tires, but adjust the drivetrain as needed.

[Carl n Susan]

Ford offers the buyer rims on three different sizes - 17", 18" and 20". They do not care which you order, nor do they change axles, gearboxes, or differentials to compensate for the differences in rim size. Why is that you ask? Because the tires they use are basically the same diameter.

The 17" rim comes with a 245/75/17 tire which has the following characteristics:
Sidewall: 7.2 in
Radius: 15.7 in
Diameter: 31.5 in
Circumference: 98.9 in
Revs/mile: 641.0


The 18" rim comes with a 275/70/18 tire which has the following characteristics:
Sidewall: 7.6 in
Radius: 16.6 in
Diameter: 32.2 in
Circumference: 104.2 in
Revs/mile: 608.0

The 20" rim comes with a 275/65/20 tire which has the following attributes:
Sidewall: 7.0 in
Radius: 17.0 in
Diameter: 34.1 in
Circumference: 107.0 in
Revs/mile: 592.0

The 18" rim/tires rotate 5.4% slower than the 17" ones. The 20" rims/tires rotate 8.3% slower than the 17" ones. The 20" rims/tires rotate 2.8% slower than the 18" ones.

If it were me, I would order the 3.31 rear end if I was planning on 17" rims. For 18" or 20", you are probably O.K. with the 3.31 rear end, but I would go for the 3.55 one. I doubt any of us can tell the difference in towing between 18" and 20" rims.

Given the power of current diesel engines, the gear box ratios don't have to be adjusted to accommodate the different tire sizes. Obviously, they do make some adjustments to the on-board computers as most of us would be unhappy with a speedo that was up to 8% off.