...Ok, please excuse me for what might be a stupid question, but I'd like to understand...

...Why is it bad to have too heavy a wheel/tire combo?

...I don't see breakage as being related AT ALL to the weight of the unit, but far more to the length of the moment arm, ie radius of tire, and the traction present in & torque placed upon the system... I mean, I can't see the inertia from the weight of the tire being able to break the axle on its own (without HUGE torque), and I can't see it contributing to the breakage (unless it's considered an additional force to overcome when getting out of a jam, ie tire wedged in a hole)... All I can see is that it might contribute to maintaining rotation (like a heavier flywheel) when the tire becomes a little stuck, and also contributing to traction on a drooped tire due to its weight...

Maybe I'm missing something...?

...?

Best explanation I can see for tire/wheel weight having an effect on breakage is that the heavier the tire, the harder it is to turn both for steering and for power. If you get that thing bouncing, it can cause more windup in the drivetrain than a lighter tire. Of course, I don't mind heavy tires because they help to lower my center of gravity and stick my truck to the ground.

Lighter is also better for high speed because you don't have to overcome the inertia to move it up and down.

-John

Originally posted by Rover Addiction
Best explanation I can see for tire/wheel weight having an effect on breakage is that the heavier the tire, the harder it is to turn both for steering and for power. If you get that thing bouncing, it can cause more windup in the drivetrain than a lighter tire. Of course, I don't mind heavy tires because they help to lower my center of gravity and stick my truck to the ground.

Lighter is also better for high speed because you don't have to overcome the inertia to move it up and down.

-John

Totally understand the high-speed thing... Same reason IFS is better... less unsprung weight...

...But I would think for the hopping thing for example that having a heavier tire would be BETTER, since the heavier tire would be less likely to be stopped by the impact because of the higher momentum... Know what I mean? Or am I backwards?

...Steering, I can't see it either, at low speeds... Because steering it seems would be more affected by how big the contact area is, what kind of moment arm the steering setup has (relative to offset, etc), and the weight on the contact area, of which tire system weight is such a small portion...

?

Rotational Mass












111111111111111111:D :D :D :D :D

Originally posted by techguru73
Rotational Mass












111111111111111111:D :D :D :D :D

http://www.ssimicro.com/~warbler/temp/WTF.gif

Yes, it is... What's your point?

you mentioned moment arm (aka torque). The moment are is the same however the force applied to the moment arm is much higher

It doesn't matter as far as crawling except there is more unsprung weight (good in moderation). It really only makes a breakage difference on the street where you accelerate and decelerate rappidly (or attempt to). As far as turning goes rotational mass doeas make a difference but i doubt you would see a noticalbe difference (even at a high speed which is where it matters)

i've also been thinking about this.......
i'm mounting some 35 x 15.5 x 16.5 TSL SX's on some military Hummer wheels right not, (2 done, 2 left) anyway these bad boys are very HEAVY.....

i'm sure i'll have a lower center of gravity, and it will take more torque to get these moving, BUT as far as breakage??????? and how it's going to affect the my 44 axle shafts :nuke:

Coldnorth you are right about the radius of the tire having a greater affect than the weight but like TRD said, the force applied will be higher (force= :massey: MASSey * acceleration).

If you get those tires spinning at all or hopping, and then they come down and suddenly get traction, ALL that weight that you got moving has to come to a stop in a hurry. Think about the damage you can do swinging a sledge, then take the head off and swing the handle and see what you accomplish.

I think that it is a double-edged sword off road, you want unsprung weight to keep tires on the ground, keep you from rolling, and because typically they have tougher sidewalls, but all of that weight is a PITA to turn on the road (if that is a concern) and I do think that it is more likely to break parts.

Originally posted by ColdNorth
I mean, I can't see the inertia from the weight of the tire being able to break the axle on its own

Buddy of mine has 38.5X16 TSL's on the front of his mud racer (my old tires actually). His only braking system is a driveline disc on the rear pinion that locks everything up. Coming out of a pit he locked his brakes, stood it up on the front end slightly, & broke a front axle.

Now, I don't know if weight had anything to do with that, but I'm guessing it might have.

TEX

Originally posted by TEX


Buddy of mine has 38.5X16 TSL's on the front of his mud racer (my old tires actually). His only braking system is a driveline disc on the rear pinion that locks everything up. Coming out of a pit he locked his brakes, stood it up on the front end slightly, & broke a front axle.

Now, I don't know if weight had anything to do with that, but I'm guessing it might have.

TEX

...I think that's hard to compare to a standard truck... You couldn't duplicate that with wheel discs. In order to lock the front wheels, he's expecting the rear driveline, xcase, front driveline, front diff & axles to all take the stress... and since the front is where most braking takes place, it might be better having that driveline brake on the front (except for the mud-scoop factor, I guess)... But that's just my opinon.

And I think that breakage had a lot more to do with the radius of the tire and its traction, weight of the truck and setup than its weight...

...I guess to put it into context, explain how that situation would have been different if the rims weighed 30 lbs more... Know what I mean? I just don't think it would affect it.

Originally posted by Dirty Harry
Coldnorth you are right about the radius of the tire having a greater affect than the weight but like TRD said, the force applied will be higher (force= :massey: MASSey * acceleration).



I know that in a straight line, force=:massey:*acceleration, but that same formula doesn't apply in a rotational manner (or at least it takes different things into account...)

...Torque = Rotational-inertia*angular-acceleration...

...Rotational inertia for a solid cylinder = 1/2 mass * radius^2

...Rotational inertia for a ring = 1/2 mass *(radius inside^2 + radius outside^2)

...I actually figured it out for a tire 38" in diameter weighing 80 lbs, and a wheel 15" in diameter weighing either 20 and 50 lbs, and the increase of 30 lbs at the rim was the same as adding .9" of radius (17.5" to 18.4" radius, or 37" to 38.8" diameter) or 7.7 lbs to the tire. It's not that much, when you're talking about less than half way out the radius of the wheel/tire system... The 30 lbs is a 6% increase of rotational inertia in the system (+/- .5%)... Not much.

Originally posted by ColdNorth


And I think that breakage had a lot more to do with the radius of the tire and its traction, weight of the truck and setup than its weight...


Probably, now a BETTER example might be of a front axle breaking on acceleration. Two tires of equal diameter, but different weights will require different amounts of inertia to overcome rest. Because the heavier tire requires more umpff, you have to pour the coals on the axle/u-joint a lot more than you would if it were lighter. Therefore, breakage would be more likely to occur.

After all, traction is a function not only of the coefficient of friction, but also the amount of mass involved ;)

TEX

...And since in crawling the acceleration is usually nominal and usually steady (more or less), it lessens the effect even more.

On-road, in mud drags and in high-speed, it's TOTALLY different.

gravity.:flipoff2:

no, really.
bottom line at the end of the day i think, is the heavier something is, the more energy is needed to make it do something you want it to do. ('cept maybe sumo wrestling? haha) that extra energy is horsepower robbing/overheated brakes/lack of momentum going up hills/too much momentum going down hills/more fatigue on dampers and spring cycles and that twinge in your back when changing a 100 lb. tire instead of a 50 lb. one.:D

granted, i don't see much real world diff between a 65 lb. tire/wheel vs a 75 lb. tire/wheel taken individually, but all those little "doesn't make much of a difference's" add up to the negative side of the equation, i'm sure. imho.:p