18 to 20 - Competing Shops and Data
 

OK, so here goes my quandry. No, I don't care what is the largest tire that will fit with or without a lift. What I am interested in is moving up from a 18" tire to a 20" tire, and what data is important in making that switch. Why do you ask? I like the look of 20" wheels and picked out a 20 x 9.5 with a 30 offset. So the wheels are set, now what tires do I pair them up with?

One shop tells me a 275/55/R20 would be the closest in overall size of my current setup. I agree. One shop tells me I need to go to a 275/60/R20 because the tires in the 55 category that I was looking at, don't have "enough capacity". The Michelin Defender LTX M/S in particular. So it got me to doing some research and seeing what I do know, and what I do not know, and hence, this post.

What I do know. Current tires are Michelin Primacy 275/65/R18 with a 116T rating. This gives me 5,512 weight rating per axle. My door sticker tells me my rear axle GAWR is 3,800.

https://cimg8.ibsrv.net/gimg/www.f15...f3a3c3ab87.jpg

So, if I were to replace my stock tires with the Michelin Defenders, I would go "down" in rating to a 113T, which "only" has a rating of 5,070 per axle. One shop is telling me, that because I have 116T on the truck now, we can't go down to a 113T. Now I'm not for lowering the capacity of my OEM truck here, but wouldn't a 113T still give me another 1,270 beyond the capacity of the truck itself?

I have had personal luck with both Michelin's and Coopers. Those are the brands I'm leaning towards, which is why my chart here focuses just on these two brands. I also do tow a travel trailer a couple times a year, total gross when loaded is about 6,500 lbs, with the tongue being about 800 lbs. I am looking for the best tires to give me the best ride when not towing, but make sure I have the capacity I need when I do.

https://cimg2.ibsrv.net/gimg/www.f15...c4aab698f4.jpg
I am leaning towards the Defender LTX M/S in the 275/55/R20, just because it keeps me in overall size close to stock, have had luck with this brand, they have great reviews, and does give me the weight rating that is more than the truck itself is rated at. If I wanted to stay in the 55 category, I could go to the Cooper's, which give me an even higher rating that what the stock tires came with.

Maybe I'm over complicating this, but is there an advantage to either buying too much rating, or upsizing to the 60s that I am not seeing here? I know, I spend too little time sometimes making rash decisions, and then some I over analyze.

You're definitely over-complicating it. I don't think there's a tire on the market that can't hold more weight than the truck itself can.

Some tire shops will avoid installing anything lower-spec'd for speed or load rating than OEM equipment because of liability concerns (and between our legal environment and the level of expertise generally available for tire-shop sales people, I can't really blame them).

With that said, are the Defenders P-metric or LT tires? You need to "de-rate" a P-metric tire by 10% for use on a truck (c.f. https://www.tirerack.com/tires/tiret....jsp?techid=70). You'd still be over the axle rating, but not by a whole lot.

Kbroderick, thanks so much for the information. I know I read about this before, but for some reason it just escaped me and didn't figure the de-rating when putting together my chart.

Now, according to the link you sent me, I should only use about 90% of the total weight rating for my calculations, because it would appear that each tire I have on the list are either P-Metric, Metric, or Euro. I couldn't find any information on whether the Michelin or Coopers were LT rated or not, but from what I could see, none of the tire sizes started with "LT". According to a different page on Tire Rack, if the tires are LT, they will start with LT, like LT275/60/r20. None of the tires I looked at started with LT, so Tire Rack says that means they are either Euro, or metric, in which case, for my calculations, I need to de-rate.

Using this data, I updated my chart to include a per axle "adjusted" number, and that feeds into the "Per Axle Adjusted" which is the total weight rating at 90%, minus my 3,800 axle capacity. You are correct, I am still over my truck's capacity, but only by 763 lbs. Tenx is also correct, none of the tires I am looking at will be under the rating of my truck.

https://cimg0.ibsrv.net/gimg/www.f15...c646b4aa5d.jpg

I know a lot of people may be reading this and thinking, "just pick a tire" already, but those that use data to make decisions are probably geeked out at the same time haha!

For me, now my decision point comes down to which size do I want to go with. The 55/20 or the 60/20. At this point it is a personal preference. I can say I'd skip the 275/55/20 Michelin Defenders. but could stay in the 55/20 with the Coopers. Or go up to the 60/20 size and be happy with any of those.