Quote:
Originally Posted by jamesqf
Yes, that was the point: if the problem is tire folding due to sidewall height, then you could reduce or eliminate the problem by going to a larger rim with a shorter sidewall tire to keep the same diameter.(Assuming of course that you can find manufacturers that make the necessary sizes.) But if that causes other problems, then you either have to work out the optimum combination, or pick one over the other.
Then too, with a larger tire diameter, you'd get a larger contact patch. In the extreme, consider a tracked vehicle, which has the same contact patch as a tire many yards in diameter.
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The goal is to have a taller sidewall, decreasing the sidewall defeats the purpose of going with the taller skinnier tire. The large sidewall is what allows for airing down, it allows the rubber to flatten and conform to the substrate both front to back and side to side. "Tires with an aspect ratio of 50 or lower (like a 255/50 R 16) have very low volume of air and shouldn't be aired down much" (
http://4x4abc.com/jeep101/soft-sand-deflate.html)
Example:
Two tracks on sand, same size tire, one at 32psi a one at 10psi. Do you see the difference? One sinks and one floats. This is due to the ability to air down and increase surface area both in length and in width... With length being greater than width (you can see it's barely wider than the fully aired tire).
Another issue, is that a larger wheel often means more weight than a smaller wheel with a taller tire... At least when it comes to AT and MT tires on trucks. You also have to consider the greater cost of larger wheels and corresponding rubber. Here is a side by side comparison between 15" and 17" wheels with I believe 37" rubber... I tried to find one with more likely 33" tires, but I couldn't.
Quote:
Comparison
15-Inch............17-Inch
Ply Rating 6-ply (Load Range C) ...10-ply (Load Range E)
Load Rating (lb) 2,910 @ 35 psi... 4,080 @ 65 psi
Pit Bull Tire Weight (lb, ea.) 88... 90
Allied Rock8 Rim Weight (lb, ea.) 34... 46
Overall Weight Per Corner (lb) 122... 136
Pit Bull Tire Retail Cost (ea.) $399... $450
Allied Rock8 Retail Cost (ea.) $217... $308
Overall Retail Cost Per Corner $616... $758
From: Picking The Right Size Wheel For Your Truck - Rim Pickins
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As far as a comparison with a tracked vehicle, that's not even a remotely fair comparison. A tracked vehicle would be similar to having 4 or 5 smaller wheels on the vehicle, not having two larger wheels.
Lets take a look,
30psi
15psi
7psi
A tire capable of going to 10 or less PSI will most likely double it's contact patch, to accomplish that without airing down (or only airing down to about 20psi)... Well, you would need one seriously massive (tall) tire. I hope that shows that your tracked vehicle comparison is actually the reverse. An aired down tire is comparable to a track... A taller inflated tire is simply a taller tire.
The main issue, is choosing a tire which is capable of airing down and then also behaving as you would expect it to on the road. My statement about sidewalls folding over was a disclaimer regarding on road driving habits/techniques. If you drive your truck like a sports car, hitting twisty roads, death turns, etc, then you should get a lower aspect ration side wall and anticipate a reduced ability to air down on the trail (or so I would assume). Then again, if you are an ecomodder... You shouldn't be driving like a bat out of hell anyway
~C