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Old 04-20-2016, 05:07 PM   #1
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18" vs 20"

I am looking to get a new 3/4 ton TV soon. Can someone explain pluses/minuses of these two tire sizes? Vehicle will most likely be a GM product 6.0, maybe the Ram 6.4. I've done a 5 page search on this, but couldn't find anything. Thanks.
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Old 04-20-2016, 05:18 PM   #2
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Sorry, I can't really tell you what the difference would be. My 3/4 Ram came with 20" rims with Firestone Transforce AT's. I haven't been real happy with how the Firestone's have been wearing, as I only have just over 10k miles on my truck.
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Old 04-20-2016, 05:28 PM   #3
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Kevin,

The biggest difference between the two is the available replacement tire choices. A few more available in the 18" last I have looked. But I am also trying to go with a slightly larger tire than stock which limits choices without any t-bar cranking and or rubbing.

If the new GM trucks with the 20's still have the Goodyear SR-A's as the stock tires, they aren't the best. They didn't seem to bad the first 20k miles or so, but this last winter they seemed like they turned to junk as far as traction. I am only trying to get through this summer before replacing them.

Will you be buying off the lot, or ordering? Don't rule out a 3500 SRW regardless is ordering or off the lot. Price is usually about the same, and you will gain a fair amount more available payload.

Good luck!!!
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Old 04-20-2016, 05:35 PM   #4
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From what I've seen, smaller rim sizes on trucks (RAMs, at least) give the truck more tow (or payload) capacity. At least that was the case when I was doing comparisons when shopping for my truck.
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Old 04-20-2016, 07:02 PM   #5
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If the overall diameter is the same which I suspect it will be, with this 20 inch tire you will have a lower profile (less rubber between the rim and the road). The 18s will give you more capacity, better ride, and less expensive tires, they just won't look as cool! To help you make up your mind price out replacement tires in both sizes.
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Old 04-20-2016, 07:07 PM   #6
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If you're rocking a crew cab with a 6 or 8 foot bed then 20's will look more proportioned to that size of truck. Outside diameter and total wheel weight are two contributing factors to towing performance but with today's engines and transmissions the effect will be minimal. Having more rim and less rubber sidewall (as with a 20in) will provide a stiffer ride and more stable towing than an 18 with more rubber side wall to flex. I love my 20's wrapped in 33.5in mudders!
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Old 04-20-2016, 07:12 PM   #7
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I have new GM 2500HD on order and I went with the 18" rim/tire option in lieu of the OEM standard 17". I didn't put any do-diligence into considering the 20" rim/tire because I would be closing in on my garage door clearance height.

I'm somewhat old school in thinking, but I would think that GM has the 2500HD drivetrain (engine/transmission/axle ratio, etc.) optimized based on the "standard" components offered, i.e.; 17" rim/tires.

I remember back a few years Ford's publications stated that going from a 17" rim to a 20" rim reduced payload capacity by 500lbs....., I believe it was even reflected in their "build your own" tool. But since the start of the recent Big Three towing wars, I haven't run across this reduction statement.

I would assume that a 20" rim with a "larger tire diameter" (taller tire) then the OEM standard 17" tire diameter, the effective gear ratio would be reduced (IMO very little). I don't know the GM OEM 17" and OEM 20" tire diameter differences (if any).

Bob
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Old 04-20-2016, 07:25 PM   #8
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I agree with some of the others. I have the 19.5 inch wheels and the larger tires are VERY expensive. But, I have to disagree with load capacity comments.
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Old 04-20-2016, 07:29 PM   #9
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Quote:
Originally Posted by hoss10 View Post
If the overall diameter is the same which I suspect it will be, with this 20 inch tire you will have a lower profile (less rubber between the rim and the road). The 18s will give you more capacity, better ride, and less expensive tires, they just won't look as cool! To help you make up your mind price out replacement tires in both sizes.
I think we need to add this to the controversial posts list because looking "cooler" is definitely a personal preference. I've always thought low profile tires with big rims can look great on a sports car but I like rubber on my trucks. Still think it looks good, don't get me wrong but it falls into the category of low rider trucks. Not for me.
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Old 04-20-2016, 08:15 PM   #10
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I have 20 inch rims on my newer F250 and although the tires were more expensive and they are taller I don't believe they are much lower profile tires
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