Rivian Top Speed - Using Math to understand Why top speed is limited

[the long way downunder]

Munro Live says they were identical. Whether or not they actually did a tooth count and part comparison, I couldn't say.

Munro is not prone to guesstimation. They said the parts are identical … that means they did everything short of a metallurgical study of the hardening of the tooth faces … : ) … and that study is in their report for sale to paying customers … : )

What I find impressive about this teardown is the casual comparison of the ludicrously beefy Rivian drive train with the Tesla Plaid drive unit … which looks like it's out of a freight train … : )

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[Nix]

It leaves the door open for an OTA update for a less conservative, higher top speed if real world reliability is high (low warranty repair rates).

 

[iansriv]

My Rugby brain interpreted all that as-the parts don't sum to more than 125mph. Fine by me. I've been living in the fast lane too long. Time to slow down and smell the fern. Cheers.

 

[usofrob]

Very interesting. I've read to new dual motor uses different gearing in the rear. We'll see if that's true this time.

But, I'm also wondering if the top speed will be different because of the different motors.

 

[tplociniak]

So happy someone put this out there. This has been my general response to so many of these threads on FB groups. I was trying to find the RPM data for the motors from Bosch but couldn't find anything. Thanks

 

[sub]

It leaves the door open for an OTA update for a less conservative, higher top speed if real world reliability is high (low warranty repair rates).

I do not believe that the top end limitations are due to warranty concerns from a slightly higher risk of motor damange.

Very, very, few people would spend enough time driving faster than 110 to burn out the motors even if the risk was 100x higher than driving at normal freeway speeds. And for the handful of people who would spend a bunch of time over 110, Rivian can make a very strong argument that driving faster than 110 MPH was a warranty voiding activity.

The warranty excludes racing, negligent use, criminal activity and "unusual" stress.

• Driving 110 MPH on a public road is both a negligent and a criminal activity in most if not all circumstances.
  
  
• Driving 110 MPH on a race track - would be racing.
  
  
• And if you found some other way to spend enough time over 110 MPH to burn out the motors without landing into one of the buckets above, they could pretty easily toss that into the category of an unusual stress.

 

[SamDoe1]

Uhh...pretty sure the top speed rating is to make sure you're within a reasonable safety margin for the tires that have a 130mph max limit more so than the motor speed. A 10% margin for the drivetrain is painfully small and would likely result in a lot of failures in the long run, definitely within the warranty period. That's running way too close to the limit.

 

[mudito]

There has been a lot of threads over the months and years about why the speed is limited, and claiming it's "Nanny" speed limiting, tire specifications, etc. I decided to pull together various spec data that is available online and see what the math says. TLDR if math scares you - the speed limit is almost certainly a function of the maximum motor RPM specs, with Rivian possibly derating it a bit to ensure they don't have people blowing up motors. As an engineer and Rivian shareholder, I understand and agree with that, lol.

The calculations:

Rivian uses 400 volt Bosch electric motors. We don't know the exact RPM specs from RIvian, but Bosch has specs calling out 16,000 RPM @ 400 volts (and 18,500 RPM @ 800 volts) on their web site for their E-Axle product. It's safe to assume that Rivian's 400 volt motor is similar, perhaps identical.

Rivian documented in their EPA filing that the gear ratio is 12.6:1 on the front and back drive units.

We know the diameter of the wheels and tires, and therefore we can calculate the circumference of the tire.

With that information, we can calculate the theoretical mechanical speed of the truck. Calculate the maximum wheel RPM, and then calculate the distance traveled per revolution, and then how far the vehicle traveled in one minute and convert to MPH.

The second column (400 volt 16,000 RPM motor) shows that the calculated speed is 124.7 mph.

Perhaps not coincidentally, Rivian was quoted early on as saying that the top speed was 125 mph.

It's a pretty common practice to derate products below their maximum design spec to ensure reliability. In the first column, I derated the RPM by 10% to 14,400 RPM and arrived at a speed of 112.2 mph. Coincidence or not?

I think this pretty much sums up that the speed limitation is based on engineering and design limits of components used by Rivian, and not "Nanny Rivian", tire specifications, etc. I can't really find fault with Rivian for derating by 10% - that's how they can feel comfortable providing a 7 year warranty. That 7 year warranty sells a lot more vehicles than a 125 mph top speed spec with a 3 year warranty.

Also of interest is the specs on the 800 volt motor - in theory it could run at 144 mph, so perhaps a future R1 or the R2 will have a higher speed limit.

As a new owner of a '22 R1T that just found out today that I couldn't go faster than 110mph (and now reading this) the only thing as I got as a conclusion is "I need bigger tires" ?

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