Engineered / Warrantied for…

[TheManchot]

Hi all. I’ve been thinking about 37/35/33” tires on the Scouts (either). While I know we’re a ways away, I’m wondering what the factory/warranty stance will be on the 35” and especially the 37”s. It’s clear the vehicle (from a wheel cutout standpoint) can handle 37”s. But from an engineeering standpoint with the torque of electric, I wonder how the drivetrain itself can both handle and what Scout will warranty. The half-shafts and CV joints will be under serious stress with 1,000 lb-ft of EV torque (imagine being stuck and that torque is helping you get out). The stress of dislodging and spinning a heavy 37” tire seems like it would be exponentially higher than on a gas truck.

More of a discussion and curious what others think than looking for an answer from Scout unless they’re ready to talk about it.

EDIT: I mentioned the 37” (BTW I don’t think I want, 35s should be fine) because of seeing a Silo Green (is that the name?) Terra on video.

 

[THil08]

Hi all. I’ve been thinking about 37/35/33” tires on the Scouts (either). While I know we’re a ways away, I’m wondering what the factory/warranty stance will be on the 35” and especially the 37”s. It’s clear the vehicle (from a wheel cutout standpoint) can handle 37”s. But from an engineeering standpoint with the torque of electric, I wonder how the drivetrain itself can both handle and what Scout will warranty. The half-shafts and CV joints will be under serious stress with 1,000 lb-ft of EV torque (imagine being stuck and that torque is helping you get out). The stress of dislodging and spinning a heavy 37” tire seems like it would be exponentially higher than on a gas truck.

More of a discussion and curious what others think than looking for an answer from Scout unless they’re ready to talk about it.

I’m gonna let @Jamie@ScoutMotors take this question.

Everyone stand back. It’s uncle J’s time to shine.

 

[cyure]

Hi all. I’ve been thinking about 37/35/33” tires on the Scouts (either). While I know we’re a ways away, I’m wondering what the factory/warranty stance will be on the 35” and especially the 37”s. It’s clear the vehicle (from a wheel cutout standpoint) can handle 37”s. But from an engineeering standpoint with the torque of electric, I wonder how the drivetrain itself can both handle and what Scout will warranty. The half-shafts and CV joints will be under serious stress with 1,000 lb-ft of EV torque (imagine being stuck and that torque is helping you get out). The stress of dislodging and spinning a heavy 37” tire seems like it would be exponentially higher than on a gas truck.

More of a discussion and curious what others think than looking for an answer from Scout unless they’re ready to talk about it.

Okay I can’t speak to torque etc, but my understanding is the two options at the moment that they will be offered with are 33 and 35. The smallest wheel size will be an 18.

Scott specifically said in the reveal video that you would be able to get them on 35s.

The Traveler at Nats was on 20s with a 35 tire and I asked if it was “lifted”. The SM team members I spoke with said no not lifted in the traditional sense but a “offroad setup”.

Again, this is what we are aware of at the moment.

 

[J Alynn]

Hi all. I’ve been thinking about 37/35/33” tires on the Scouts (either). While I know we’re a ways away, I’m wondering what the factory/warranty stance will be on the 35” and especially the 37”s. It’s clear the vehicle (from a wheel cutout standpoint) can handle 37”s. But from an engineeering standpoint with the torque of electric, I wonder how the drivetrain itself can both handle and what Scout will warranty. The half-shafts and CV joints will be under serious stress with 1,000 lb-ft of EV torque (imagine being stuck and that torque is helping you get out). The stress of dislodging and spinning a heavy 37” tire seems like it would be exponentially higher than on a gas truck.

More of a discussion and curious what others think than looking for an answer from Scout unless they’re ready to talk about it.

They are displaying the Terra with 37’s and they said it clears the wheel well so gotta think if SM is showing and possibly offering them the warranty would cover things but SM probably has more info

 

[SpaceEVDriver]

tl;dr:
Back-of-the-envelope estimate: A 37” tire will increase stresses by about 20% relative to a 35” tire.

The moment of inertia of a cylinder like a wheel is proportional to the mass of the wheel and its radius squared. The moment of inertia of an object is its resistance to changing rotation rate. You can add in some resistance related to the ground-tire contact, but for a given pressure, that won’t change just because the diameter of the tire changes.

A 35” tire with a 20” wheel will have a mass of about 50 kg. Its diameter is about 0.9 meters, and radius is 0.45 meters.
The moment of inertia is I = 1/2 M * R^2 = 5 kgm^2.

For a 37” tire on a 20” wheel, the mass is about 53 kg and the diameter is about 0.94 meters, radius is 0.47 meters.
The moment of inertia is I = 1/2 M * R^2 = 5.9 kgm^2.

The torque required to cause a wheel to rotate is the moment of inertia multiplied by the change in rotational velocity.

For a similar change in rotational velocity, you can get the ratio of torques required to spin the 35” vs 37” tire up.

The increased stress going from 35” to 37” tires is proportional to the increased torque required to spin up to (whatever) speed:
5.9/5 = 1.18.

So, there will be an increase of about 18% stress in the system if you run 37” tires instead of 35” tires. Round it up to 20% to account for various unknowns. That stress will be distributed throughout the system unless there’s already a weak spot for the stress to become concentrated.

Most components will be resilient to that in single-instance cases. The real problem comes in when the stress is repeated and repeated and repeated. Eventually there will be a failure. Will it be on trail 20 or trail 200? That’ll be up to the engineering team and how much money the actuaries think you’re willing to pay for the 1/16th to 1/8th thicker pieces of steel where they’re needed and to pay for the heavier vehicles and higher rotational resistance due to the higher mass and higher diameter rotating pieces of steel. They would need to beef up the weakest components a fair amount and that would add mass and reduce efficiency.

I, for one, wouldn’t want Scout to overbuild the drivetrain components to protect against constant 37” use.

 

[cyure]

tl;dr:
Back-of-the-envelope estimate: A 37” tire will increase stresses by about 20% relative to a 35” tire.

The moment of inertia of a cylinder like a wheel is proportional to the mass of the wheel and its radius squared. The moment of inertia of an object is its resistance to changing rotation rate. You can add in some resistance related to the ground-tire contact, but for a given pressure, that won’t change just because the diameter of the tire changes.

A 35” tire with a 20” wheel will have a mass of about 50 kg. Its diameter is about 0.9 meters, and radius is 0.45 meters.
The moment of inertia is I = 1/2 M * R^2 = 5 kgm^2.

For a 37” tire on a 20” wheel, the mass is about 53 kg and the diameter is about 0.94 meters, radius is 0.47 meters.
The moment of inertia is I = 1/2 M * R^2 = 5.9 kgm^2.

The torque required to cause a wheel to rotate is the moment of inertia multiplied by the change in rotational velocity.

For a similar change in rotational velocity, you can get the ratio of torques required to spin the 35” vs 37” tire up.

The increased stress going from 35” to 37” tires is proportional to the increased torque required to spin up to (whatever) speed:
5.9/5 = 1.18.

So, there will be an increase of about 18% stress in the system if you run 37” tires instead of 35” tires. Round it up to 20% to account for various unknowns. That stress will be distributed throughout the system unless there’s already a weak spot for the stress to become concentrated.

Most components will be resilient to that in single-instance cases. The real problem comes in when the stress is repeated and repeated and repeated. Eventually there will be a failure. Will it be on trail 20 or trail 200? That’ll be up to the engineering team and how much money the actuaries think you’re willing to pay for the 1/16th to 1/8th thicker pieces of steel where they’re needed and to pay for the heavier vehicles and higher rotational resistance due to the higher mass and higher diameter rotating pieces of steel. They would need to beef up the weakest components a fair amount and that would add mass and reduce efficiency.

I, for one, wouldn’t want Scout to overbuild the drivetrain components to protect against constant 37” use.

I’ve missed your math.

 

[SpaceEVDriver]

A 33” tire on a 20” wheel will have a mass of about 43 kg and its diameter is about 0.84 meters (0.42 meters radius).
I = 0.5 * 43 kg * (0.42 meters)^2 = 3.8 kg m^2.

5/3.8 = 1.32

A 35” tire could increase stress on the system by about 32% compared with a 33” tire.

Note that these are very, very basic estimates. The engineers will be using finite element modeling and more advanced techniques to dial in the size, composition, shape, and mass of every piece of the drivetrain.

 

[J Alynn]

I’ve missed your math.

Was thinking the same thing. Wish I could wrap my head around math. I just draw pretty pictures

 

[SpaceEVDriver]

Was thinking the same thing. Wish I could wrap my head around math. I just draw pretty pictures

And I wish I had an artistic cell in my body...

 

[J Alynn]

And I wish I had an artistic cell in my body...

We all have our purpose!