OK...Let me see if I got this...If I purchase a 20" rim, I can only place a tire with the following specs on the rim Size: 275/55-20....If I want it to run properly and be compatable with spare...Is this correct?

 

mine are 275/65R 20 and have no problem

 

Now I am really confused!!!!!(LOL)

 

as long as the overall tire size is not larger then 35 it will fit.
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but what about the "revolutions per mile"?? any validity to this from the Tire Kingdom guy

 

I am looking at maybe getting all black rims... does anyone know if they pit or chip... they would be exposed to heavy beachsand and salt...

(I am not meaning to hi-jack the forum, but this is somewhat relevant)

 

To machines. I don't know what the hell the tire kingdom guy is talking about. I had a 2 wheel drive dodge truck that came with some 29 inch or so michilens from factory, lifted it and put on 35's w/o ever changing anything. Worst case seems to me is it will be slightly sluggish if they're a little big, and your speedo will read slower (just a little) But you can se your actual speed thru one of those drive by radar trailer things. And your odometer will read a lil less miles! Ha! Stick it to the man.

 

Another way to say this is "what is the circumference of the tire" as compared with stock (or the spare). Not to sound too basic here, but the circumference is the distance around the outside of the tire. This is relevant for two main reasons: 1. presumably, the manufacturer has optimized the gear ratio of the t-case, transmission and differentials based on the tire size, and 2. the speedometer is "tuned" to this tire size. The only way the speedo knows how fast you're going is "counting" how many times the wheel has gone around in a given amount of time.

Each tire's circumference will dictate how many times it will go around in one mile. A mile is 5280 feet and a tire that has a 35" diameter (height) is about 109.9" circumference. (pi X diameter = 3.14 * 35 = 109.9). This means that a 35" tire would go around approximately 576.52 times (63360" per mile / 109.9' = 576.52).

On the other hand, the stock tires (I think they're 31" tall / diameter), would go around 650.91 times per mile (63360" per mile / 97.34" circumference = 650.91).

The difference is about an 11% reduction in rotations per mile between the stock 31" tire and a 35" tire. Obviously, the closer the size is to stock, the less difference you'll experience in final drive ratio and speedo results. So, back to your question, is the Tire Kingdom guy making a fair statement? Yes. If your goal is to change your tire/wheel combination but maintain the stock final drive ratio and speedo accuracy, then his question is valid. The reality is that you can alter the final drive ratio within these ranges without impacting drivability very much at all. I just changed the stock wheels/tires and moved to a tire that's a 305/50/20 (about a 32" tire) and it rides great...The speedo should be within a few % of accurate. So feel free to go up in total size if that's the appearance you're looking for, just remember that the speedo will be off a bit.

I'm not sure what compelled me to go through this exercise. Is this as clear as mud?

 

Tires bthat are larger can engage the Stabilitrac too if you have it. I speak from experience on that one.

 

Spoke with Hummer of the Palm Beaches (Service)....was told to put on 275/60R/20....(that is the tire they use on 20" rims)...
Machines