33s vs 35s: weight or diameter?

[89grand]

This got me thinking, the diameter itself shouldn't make a huge difference from a 33 to a 35" as far as axle strength and braking strength. Of course you need more clearance for the bigger tire, and gearing needs are different, but the general consensus is that you are usually fine with a 33's, with stock brakes and even a stock Dana 35 (no locker), but not with 35's.

Is that based off of simply the diameter difference, or the assumed increase in weight?

I ask this because there are some stupid heavy 33's, like the Toyo M/T, and Falken M/T, that weigh more in a 33", than say the Cooper STT Pro does in a 35". As an example, the 33" Falken weighs 75 pounds, whereas the 35" Cooper weighs 67 pounds.

Thoughts?

 

[Jerry Bransford]

It's the diameter that makes the biggest difference. The diameter changes the effective gear ratios. And at least as important is a larger diameter tire has a longer radius which gives it more leverage against the axle shafts, gears, drivetrain, engine, and brakes. The increased leverage of larger diameter tires gives them more ability to break axle shafts, require more power to turn, more leverage against the brakes making it harder to stop, etc. This is why we regear axles according to tire diameter, not weight, and why we need better brakes to cope with the increased leverage larger tires have against the brakes.

 

[89grand]

See that's what I always thought, was that diameter was the difference, but my mind works in weird ways, sometimes I solve problems, sometimes I look at the absurd, which at times helps me solve problems, and what I'm about to say is absurd, and not likely in the real world, and I know that.

What made me post this, was I was thinking if a 27" tire and wheel package somehow weighed 200 pounds each, that would have to be harder to get going, stop, and have the momentum to break axles vs a 35" wooden wagon wheel.

Of course those two things will never be used, but it suggested to me that weight is very important, and diameter less so. Again though, taking gearing, tire clearance and practicality out of the equation.

But yeah, in real world applications, I can see the diamter of the tire being the issue, if all other things are equal.

 

[jjvw]

That extra inch of clearance that only a larger tire can give matters when it matters.

 

[mrblaine]

See that's what I always thought, was that diameter was the difference, but my mind works in weird ways, sometimes I solve problems, sometimes I look at the absurd, which at times helps me solve problems, and what I'm about to say is absurd, and not likely in the real world, and I know that.

What made me post this, was I was thinking if a 27" tire and wheel package somehow weighed 200 pounds each, that would have to be harder to get going, stop, and have the momentum to break axles vs a 35" wooden wagon wheel.

Of course those two things will never be used, but it suggested to me that weight is very important, and diameter less so. Again though, taking gearing, tire clearance and practicality out of the equation.

But yeah, in real world applications, I can see the diamter of the tire being the issue, if all other things are equal.

I view things the same way in the extreme. Generally it works. Easier is to consider your 27" 200 lb tire and a 30 lb bicycle type wheel and tire that is 5 feet in diameter with the same brakes close to the centerline for both.

Weight and diameter both matter but leverage will be more important for our uses.

 

[-T.]

Interesting discussion. I'd agree that diameter is probably the biggest consideration off road, but when you also throw highway driving into the mix, it is certainly worth considering overall tire/wheel weight. Dabbling in autocross, and following car builds in that hobby, the additional unsprung weight and rotating mass of heavier wheels, even when the overall diameter of the tire/wheel combination doesn't change, does affect handling, braking and acceleration enough that it is worth keep in mind when choosing a wheel/tire package for a Jeep too. Just after purchasing my Jeep, I swapped some particularly heavy 305/70r16 tires for 255/85r16s and the difference was pronounced.

 

[TJDaveX]

I also agree with the leverage issue, which is why I never ran 35's on my Dana 35.
Although, when I did swap in a rear Dana 44, I also went from heavy ass 33" Toyos on steel wheels to Pro-Crap 35" MT's on alloys. The mounted 35's were considerably lighter just lifting them. Braking was much better also. Adding Black Magic pads and new Centric rotors made them even better.
Did I mention I'm not a fan of Pro-Crap tires? I'm running 35" MTR's now.