Tire Sizes on tow vehicle...is there a difference?

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WFD

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Joined
Feb 2, 2012
Posts
143
Location
Manitoba, Canada
I am looking at trading my tow vehicle and am wondering about tire size and their effect on towing and or ride... 2 trucks I am looking at are GMC 2500HD's...both have LT tires...one has 265/60/20's and the other has 265/70/18's. Just wondering if the 20in tires will have an adverse effect on towing and ride. I tow a 5th wheel so more weight on the rear axle and tires... Of the trucks I have been looking at, not many have had the 20 in wheels...

Any thoughts on this?

Thanks
Rick
 
About the only input I have is to suggest you price the 20" tire vs the 18" tire.  Looks like the 20" is $40-$50 more a piece.  So, if no one can testify to the superiority of the 20" over the 18" in your application, I'd look ahead at tire change time.
 
From Wikipedia on "Gear ratio":

The car?s tires can almost be thought of as a third type of gearing. This car is equipped with 295/35-18 tires, which have a circumference of 82.1 inches. This means that for every complete revolution of the wheel, the car travels 82.1 inches (209 cm). If the Corvette had larger tires, it would travel farther with each revolution of the wheel, which would be like a higher gear. If the car had smaller tires, it would be like a lower gear.

In other words, wider tires has the effect of lowering the numerical final gear ratio which will have the effect of lowering the torque at your wheels.  How much that would be depends on the outside diameters of the two set of tires.  By the way, we are not talking wheel ODs here but the OD of the mounted tires.
 
Carl L said:
In other words, wider tires has the effect of lowering the numerical final gear ratio which will have the effect of lowering the torque at your wheels. 

I think Carl meant to say taller tires instead of wider, but his thoughts are right on. However, if the manufacturer designed the truck with 20's then I am sure that the gear ratio will be correct for the truck as it was designed.  That being said, a lower gear ratio is usually better for towing as lower gears provide more low end torque.  The trade off is when you are running empty. Then the low range can be a killer to MPG.  That is unless the truck is equipped with enough gearing to handle freeway speeds without excessive RPM's. 

I would be curious to know what the load ranges were on the two vehicles tires.  Bigger tires may have a higher load capacity, but you have to check to verify that.
 
I think the main reason larger rim sizes are becoming more common is to reduce sidewall flex, lower profile tires should flex less side to side.  I doubt the difference between 18's and 20's on a truck is going to be noticeable.
 
Back when Dodge was the first/only truck to offer 20's, I remember seeing a footnote in the Trailer Life tow ratings that trucks with the larger rims had a slightly lower towing capacity due to their extra weight. It was not much - a couple hundred pounds maybe - but something to check out.
 
WFD said:
I am looking at trading my tow vehicle and am wondering about tire size and their effect on towing and or ride... 2 trucks I am looking at are GMC 2500HD's...both have LT tires...one has 265/60/20's and the other has 265/70/18's. Just wondering if the 20in tires will have an adverse effect on towing and ride. I tow a 5th wheel so more weight on the rear axle and tires... Of the trucks I have been looking at, not many have had the 20 in wheels...

Any thoughts on this?

Thanks
Rick


The LT265/70R18E has the greatest load capacity at 3525# at 80 psi  whereas the LT265/60R20E is rated at 3195# at 80 psi.

FastEagle
 
Fast Eagle is 100% correct 18 " has the heaviest load rating and personally I think they look the best as well.
 
Wow...I am surprised at the amount of difference in weight rating between those 2 sizes of tires.

Rick
 
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