Tire rotational mass vs actual tire weight

[sumguy75]

For starters, I blame this question on the cannabutter I consumed 2 hours ago.

I hear a lot about heavier tires being more stress on the driveline and making the motor/esc work harder. Is there a cutoff point between increases in tire weight and decreases in ballooning amount (due to belts) that makes it a wash? Rotational mass is what is responsible for rc's doing stunts and ballooning helps increase the rotational mass which should also be additional stress to the driveline. I guess there is the fact with added tire weight from belts, the extra mass is ALWAYS there, vs ballooning tires aren't ballooning 100% of the time.

I bought a set of 2.8 belted Trenchers for my Stampede, not worried about the weight because I've run my belted Duratrax 2.8MTs extensively without issue and they are within 10g of the Trenchers weight. I have non belted Badlands 2.8 that balloon huge because I run 4s. Seems like that would be around the same amount of stress as the heavier belted wheels that don't balloon at all.

Just wondering and no idea how to calculate the difference in use vs. sitting on a scale.

 

[Dan B.]

Why would ballooning increase rotational mass? I don’t believe it would, as the weight of the rotating tire/wheel does not change.
Ballooning most definitely increases the gyro effect, which is why it’s easier to control in the air as the diameter increases as RPM’s rise. It also increases top speed a bit as the wheels grow in circumference, just not in mass.
Belted tires definitely last longer on powerful rigs, but watch your temps and be prepared to drop a tooth or two on the pinion if, for example, you swapped out the stock Fortesses on your Mojave for some big assed heavy belted Trenchers.

 

[332_RC]

cannabutter heck yeah. Haven't thought about that in years. I dunno about the question but yeah I'm sure there is a point of no return with size. I bought 4s backflips for my Kraton build & my thinking is less overall weight, rotational mass, better acceleration & speed. If needed. I'm doing some other weight reduction items too. But think of this, I have a Redcat Kaiju EXT. The tires kinda look like Fireteam tires but smaller than 6s BF tires. I put them on my Notorious on 6s. They space out a little wider, the EXT is narrower. I also weighed the 6s tires & Kaiju tires. An exact one pound less difference. Halfway thru a pack, I completely exploded the center diff, blew into pieces, & let off a hell of a cloud. Catastrophic carnage. It was the stock plastic 100k. So I've never run them again. Maybe the less weight & smaller diameter was to much for the Notorious setup.

 

[sumguy75]

Why would ballooning increase rotational mass? I don’t believe it would, as the weight of the rotating tire/wheel does not change.
Ballooning most definitely increases the gyro effect, which is why it’s easier to control in the air as the diameter increases as RPM’s rise. It also increases top speed a bit as the wheels grow in circumference, just not in mass.
Belted tires definitely last longer on powerful rigs, but watch your temps and be prepared to drop a tooth or two on the pinion if, for example, you swapped out the stock Fortesses on your Mojave for some big assed heavy belted Trenchers.

Yeah, I definitely misworded it, lol. I'll try again...
Does the gyro effect generate extra forces on the axle that would increase drivetrain stress In a way similar to the added weight of belted tires.
Since belted tires don't balloon the added weight is a constant where IF gyro effect increases stress on driveline it would be variable so would it or would it not make a difference?
Seems like my Badlands wear out drive cups faster than my belted Duratrax that weigh 30g more per tire. But I also use the Badlands on rougher terrain.

 

[Bustedaw11]

Something else to consider- however small the effect.

A ballooned up tire tends to not stay 100% round and in doing so throws the balance off sometimes significantly. That out of balance tire may add extra stress that a belted tire of the same exact weight would due to the belted tire staying more true to balance..

Say.. 100g tire vs belted 100g tire. The non belted throwing its weight around in a ballooned/unbalanced state may actually show higher weights of say 120g. Adding extra stress.

I tried

 

[Dan B.]

Yeah, I definitely misworded it, lol. I'll try again...
Does the gyro effect generate extra forces on the axle that would increase drivetrain stress In a way similar to the added weight of belted tires.
Since belted tires don't balloon the added weight is a constant where IF gyro effect increases stress on driveline it would be variable so would it or would it not make a difference?
Seems like my Badlands wear out drive cups faster than my belted Duratrax that weigh 30g more per tire. But I also use the Badlands on rougher terrain.

Gotcha. I would only be surmising, but I would guess the added mass of a heavier tire would have more of an impact than a lighter ballooning tire. Ask AI. Or @Diem Turner

Something else to consider- however small the effect.

A ballooned up tire tends to not stay 100% round and in doing so throws the balance off sometimes significantly. That out of balance tire may add extra stress that a belted tire of the same exact weight would due to the belted tire staying more true to balance..

Say.. 100g tire vs belted 100g tire. The non belted throwing its weight around in a ballooned/unbalanced state may actually show higher weights of say 120g. Adding extra stress.

I tried

Very true. In my Mojave it routinely balloons the inside front tire when cornering hard. That increases its diameter and essentially re-gears that axle which the front diff can’t possibly be happy about. Like driving with two different sized tires on the front. But who knows what real-world effect that would really have. I normally destroy things due to impacts far sooner than any opposing laws of physics screw up my drivetrain.

 

[Bustedaw11]

Gotcha. I would only be surmising, but I would guess the added mass of a heavier tire would have more of an impact than a lighter ballooning tire. Ask AI. Or @Diem Turner

Very true. In my Mojave it routinely balloons the inside front tire when cornering hard. That increases its diameter and essentially re-gears that axle which the front diff can’t possibly be happy about. Like driving with two different sized tires on the front. But who knows what real-world effect that would really have. I normally destroy things due to impacts far sooner than any opposing laws of physics screw up my drivetrain.

If the diff were open to free spin and you had two different size tires you would technically go straight.
If you had a locked diff in the same situation you would constantly turn or be pulled toward the smaller diameter.

Look at 1:1 sprint cars that run a locker and two different sized rear tires. That is actually what drives them sideways around the track. It isn't purely on throttle drifting they're doin. Many dirt circle racing classes are actually staggered that way for that effect.

Your spider gears aren't actually meant to be spun at any significant rpm. When 1 tire is spinning at a different rpm then the other your spider gears are turning and quickly. This is why the pin they ride on is not bearinged or very significant in size. All you will do is wear the pin/gear by doing this.
In the rc world we use thicker diff fluid to act as a limited slip effect. To keep these gears from spinning opposite to easily. In doing so keeps 1 tire from Ballooning/ and or the diff from "diffing out.

Watch a slow mo vid of a ballooned tire and watch the shake they have. They shake and flex the suspension around hard due to that unbalanced tire. I still believe that force will surpass the force of the same weight belted tire that isn't ballooned/ out if balance.