Simple mod for 0-60 <3.0 seconds?

[OrthoBlock]

Based on some simple math, related to an analysis I did for a different thread:

https://www.rivianforums.com/forum/threads/quad-motor-vs-locking-diff.12010/post-271827

it appears that the acceleration on the trucks appears to be purely power limed as opposed to traction limited. This helps explain the faster 0-60 times for the 21" and 22" wheels vs. 20" wheels, as the former have smaller diameter and thereby higher effective gearing (i.e., shorter torgue arm at the tire.)

This made me wonder if anyone had tried running the same aspect ratio tires as on the 22" wheels (275/50) on the 20" wheels, which would result in ~31" tire.

My understanding is that the stock diameters are approximately:

34" - for 20" wheels
33" - for 21" wheels
33 - for 22" wheels

So a 31" tire would result in creased force to the ground of anywhere from 9.5% to 6.5% (compared to 34" and 33" tires, respectively). Could this increase in available forward force be enough to get 0-60 in less than 3 seconds? Has anyone tried?

They seem to make plenty of tires in the 275/50R20 size...

p.s., I do realize this is a very simplified analysis, and I have no idea on the linearity of the torque curve on the motors with respect to RPM's (my expectations would be that immediate acceleration times would be faster, but longer times over distance, like the quarter mile, might even be slower -- not sure.)

p.p.s., I also realize that this is a completely silly question, as the acceleration speed of a pick-up truck over any distance is hardly worth losing sleep over. It's more of a fun mental curiosity on how first order physics might affect real-world vehicles...

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[Madsen203]

Speedo is off. Weight of tires is likely why 20” is slower. Put on light street tires and you’ll likely shave .15 seconds.

 

[kizamybute']

Going down to a 31" tire is the same as putting more "gear" in the car. For ICE cars, increased gear ratios generally resulted in quicker acceleration. The same would likely be true if such a small tire was put on the Rivian.

The handling would likely improve as well as it would lower the center of gravity and short sidewalls would result in less flex (rollover of the tire) for better stability.

Might look a little silly to have such a small tire on the truck, but if you wanted to do it just so you could go to your local drag strip and run 1/4 mile times, then why not.

If you're going to do that, might as well get down to a 35 series tire. Also, the 20 inch wheel would allow you to install a 295 width tire for better traction, which would be needed with that much more gearing. Would be a 28" diameter tire. Subtracting 5 inches from the 22" stock wheel / tire configuration, which are stated to be the ones that provide the best acceleration due to the higher grip of the tires used on the 22" wheels.

Just looked, a stock 20" tire is 48 lbs. A 295/35/20 is about 32 lbs. That's a whopping 16 lbs of rotating mass per corner. 64 lbs total. The 20" wheels are also the lightest of the three choices due to being the smallest.

Being that you likely wouldn't want to swap out tires on your regular wheels, could likely find a set of 20" wheels that are 10 lbs lighter per wheel than the stock wheels. That would be over 100 lbs saved in rotating mass. While you're at it, could get a wheel that's a little wider to allow for a 305 or 315 width tire for even better grip.

Again, would look silly as heck on the truck, but I would venture to guess that you'd likely be able to do a 2.8 second 0-60 run with such a setup, if not better.

I had to check on Youtube. Someone has probably already done something similar and I'm sure we'll see videos of someone that did it before too long. That setup, in the "lowest" suspension setting would put the truck notably lower to the ground. It's already one of the best handling trucks ever built, but would likely pick up a couple of seconds of lap time on a road course.

 

[Speedrye]

Going down to a 31" tire is the same as putting more "gear" in the car. For ICE cars, increased gear ratios generally resulted in quicker acceleration. The same would likely be true if such a small tire was put on the Rivian.

The handling would likely improve as well as it would lower the center of gravity and short sidewalls would result in less flex (rollover of the tire) for better stability.

Might look a little silly to have such a small tire on the truck, but if you wanted to do it just so you could go to your local drag strip and run 1/4 mile times, then why not.

If you're going to do that, might as well get down to a 35 series tire. Also, the 20 inch wheel would allow you to install a 295 width tire for better traction, which would be needed with that much more gearing. Would be a 28" diameter tire. Subtracting 5 inches from the 22" stock wheel / tire configuration, which are stated to be the ones that provide the best acceleration due to the higher grip of the tires used on the 22" wheels.

Just looked, a stock 20" tire is 48 lbs. A 295/35/20 is about 32 lbs. That's a whopping 16 lbs of rotating mass per corner. 64 lbs total. The 20" wheels are also the lightest of the three choices due to being the smallest.

Being that you likely wouldn't want to swap out tires on your regular wheels, could likely find a set of 20" wheels that are 10 lbs lighter per wheel than the stock wheels. That would be over 100 lbs saved in rotating mass. While you're at it, could get a wheel that's a little wider to allow for a 305 or 315 width tire for even better grip.

Again, would look silly as heck on the truck, but I would venture to guess that you'd likely be able to do a 2.8 second 0-60 run with such a setup, if not better.

I had to check on Youtube. Someone has probably already done something similar and I'm sure we'll see videos of someone that did it before too long. That setup, in the "lowest" suspension setting would put the truck notably lower to the ground. It's already one of the best handling trucks ever built, but would likely pick up a couple of seconds of lap time on a road course.

The 0-60 should be great, but the 1/4 mile would suck with the effective gearing change combined with the already-low speed limiter being dropped even further. My quick math shows going to a 28" tire would give you an effective top speed of 90mph.

 

[Dark-Fx]

There's at least 1000 lbs of *stuff* that could be removed off my truck to make it faster to 60 mph if that was the only thing I cared about.

 

[rivian_germany]

Just from a physics perspective, it takes a certain amount of force to accelerate a mass from zero to a certain velocity. If you are moving the same mass, whether the wheels are large or small, and you are limited by the amount of force, wouldn't the acceleration remain the same?

You are increasing the rotation speed of the wheels, but now that the wheels are smaller, they need more revolutions to travel the same distance. I think my head is going to explode.

 

[OrthoBlock]

Just from a physics perspective, it takes a certain amount of force to accelerate a mass from zero to a certain velocity. If you are moving the same mass, whether the wheels are large or small, and you are limited by the amount of force, wouldn't the acceleration remain the same?

You are increasing the rotation speed of the wheels, but now that the wheels are smaller, they need more revolutions to travel the same distance. I think my head is going to explode.

The issue at question is the torque arm length. The torgue at the wheel axle is the same in all cases, but the radius of the tire you mount to that wheel axel will determine how much tangential force the tire is able to apply to the ground. The smaller the radius of the tire, the higher then effective gearing becomes (yes, the axle will still always rotate at the same ratio to the motor, but the distance that a single revolution of the tire covers is a direct function of the radius of the tire.)

 

[kizamybute']

The 0-60 should be great, but the 1/4 mile would suck with the effective gearing change combined with the already-low speed limiter being dropped even further. My quick math shows going to a 28" tire would give you an effective top speed of 90mph.

Yes, you are correct, with the top speed limiter, you'd likely hit it well before the 1/4 mile. I guess you could go to the smaller 1/8th mile drag strips.

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