Quote:
Originally Posted by fcatwo
Bill
mtnguy
It's not a big deal but I think the 225s are only 0.3 wider than the 215s and not 0.8 (8.8 vs 8.5). They are significantly taller however and the lift kit is probably mandatory for their us. For info: I recall that RMR asked the TM factory at one time about using 225 tires on their 3500lb axles and was told they had not tested that combination and could not recommend it. IMO Bill has thoroughly tested the 215s on the 3500lb axle and found them wanting so it's time for the factory to get with the program. I can't answer the question about any possible offset difference between the 215 and 225 5X4&1/2 wheels. I was going to take one of my 14s to Camping World and compare them to make sure they are the same before switching but never reached that point.
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FCATWO, let me give you a tire conversion formula we use everyday, to tell the difference between heights for tires. On a metric size tire Ex:215/75 15, the 215 is the section width in millimeters(215 millimeters), the 75 is the aspect ratio(which is the height of one sidewall from the rim to tread, or easier to remember as a percentage, 75% in this case), the 15 is the rim diameter. Ok, let's convert it to inches and get the approx diameter of the tire.
section width X aspect ratio X 2 (you have to include both sidewalls from the center of the rim)=?
Take the result and divide it by 2540. This is how you convert it over to inches. They're are 25.40 mm to an inch. If we take out the decimal at the last step, it saves on the next one.
Take this result and add it back to whatever the rim diameter is. In this case 15. Everything before this had just gave us the measurements of the sidewall (x 2), now we need to add the diameter of the middle of the tire or rim. The rim is already in inches, so we don't do any conversions, just straight adding.
If I punched my calculator right, then I got a 215/75 15 tire is appro. 27.70 inches tall. If I want to know the width, all I do is divide 215 by 25.40. Remember I said there were 25.40 mm to an inch.
Another thing to remember in comparing the differences between 2 tires (circles) is overall diameter difference is half of what difference you get in lift. Say there is a 1 inch difference in total diameter for two tires. This works out to be a half inch from the center to the top and a half inch from the center to the bottom. To visualize this, stand a penny beside a quarter, and notice how much difference. Now place the center(the hub) of the penny on the center of the quarter. You see it's only half to the bottom and top. A 1 inch difference in tire diameter, gives you a half inch difference in total lift of the trailer.
Here it is again
section width X aspect ratio X 2
------------------------------- + rim diameter =appr diameter (height)
2540
I say approx. because different tire manufacturers calculate their section width and/or aspect ratio at different points. Supposedly, the section width is the distance between the two bulging sidewalls at loaded status, but different tires have more bulge than others when loaded. The above formula will give you accurate results if you use the same brand and model to compare with. It'll be close when comparing two different brands, but not as accurate.
After you practice with this a few times, you can do it quickly. Here it is as per example
215 X 75 X 2
------------- = 12.70 + 15 = 27.70 diameter
2540