Another change? 20" AT wheels no longer forged?

[crashmtb]

Thanks, this actually answered a thought I had in the EPA range thread. I'm hoping the 20" wheels get the aero inserts as an option going forward.

I think the biggest issue with the 20” wheels isn’t aero. It’s the increased rolling resistance of an all terrain tread pattern. Aero covers probably won’t help much. And theyd be just another thing to get damaged off-road.

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[brianmartin]

Perhaps it would help to take a step back and consider practical issues in this forged vs cast wheel weight discussion. A cast wheel is roughly 25% - 30% heavier than forged or perhaps 10-12 lbs each, so approx. 50 lbs total added weight.

That's equal to 4 bags of groceries, or two heavily loaded backpacks, or a child, or 1/2 to 1/5 of an adult. What you carry in your vehicle each day is going to affect your mileage more than cast vs. forged wheel weight. If you are going to obsess over wheel weight, then you should also be planning your daily cargo like a C130 Loadmaster, lol.

As DuckTruck mentioned, it's by far the tires that affect the mileage the most, not the wheels.

making an object rotate takes a lot more energy than moving a static object. im no physicist and i couldn't give you the exact calculations, but its well known that rotating mass has a much higher moment of inertia and takes significantly more energy than you would expect. It is quite common, in the sports car world to spend large amounts of money to cut weight from the wheels, regardless of tires. It is WELL worth the money to invest in a set of high quality, lightweight forged wheels. Same thing with offroading, except durability is more important so they aren't going to be as light as a sports car wheel. But the principle still stands.It's because, whether you know the physics or not, people realize that rotating mass has a large effect on energy required to move.
I know that when I had my Camaro, getting wheels that were 5 pounds lighter (same tires) produced a VERY noticeable effect. It made the car feel way faster. It also improved my gas mileage by about 2 mpg.

Lighter weight wheels (and tires) take much less energy to rotate. It's physics.
Tire compound matters too, but that doesn't mean the weight doesn't also matter.

 

[kneebuster]

Tire and wheel weight will only really matter when changing speed (as I said earlier but was misinterpreted). Tread compound will matter at all speeds. Aerodynamics becomes more important as speed increases.

 

[brianmartin]

Tire and wheel weight will only really matter when changing speed (as I said earlier but was misinterpreted). Tread compound will matter at all speeds. Aerodynamics becomes more important as speed increases.

yes aero definitely becomes more important as speed increases. but if you are changing speed a lot, accelerating and decelerating, for example, any city driving, or trail driving with a lot of elevation changes, you'll notice lighter wheels and tires very easily.

There is a reason there is a huge aftermarket for off-road forged wheels. It's because OEMs typically include strong and cheap wheels with their trucks. It's a situation where the choice is: "strong, cheap, light--pick two." OEM's want to keep costs down, and you can't really sacrifice strength (since users beat on their trucks), so everyone just accepts that OEM wheels are often very heavy. Hence, the aftermarket.

 

[kneebuster]

yes aero definitely becomes more important as speed increases. but if you are changing speed a lot, accelerating and decelerating, for example, any city driving, or trail driving with a lot of elevation changes, you'll notice lighter wheels and tires very easily.

There is a reason there is a huge aftermarket for off-road forged wheels. It's because OEMs typically include strong and cheap wheels with their trucks. It's a situation where the choice is: "strong, cheap, light--pick two." OEM's want to keep costs down, and you can't really sacrifice strength (since users beat on their trucks), so everyone just accepts that OEM wheels are often very heavy. Hence, the aftermarket.

For some reason you seem to want to correct me even though what I said was accurate, so here's some physics.

Rotational Energy = 0.5 * I * w^2
Where w is angular velocity (didn't want to try and post an omega).

Angular velocity squared is the dominant part of the equation since it's squared. Increasing angular velocity (the rate at which the wheel is spinning) dramatically increases the energy demand. Similarly, the faster the wheel is spinning, the more energy that will be required to slow it. In this case we recapture some of that energy via regenerative braking instead of wasting it as heat via brakes. We should also recognize that a larger diameter wheel/tire combo will have a lower angular velocity for a given vehicle speed, so from that perspective the bigger wheel/tire might have a slight advantage (it likely doesn't, but could).

The moment of inertia component is also important, but it's only loosely related to mass of the wheel and tire. You can have 2 wheel/tire combos with the same outer diameter and mass, but dramatically different moments of inertia. I used to run an experiment for my class when I taught dynamics where we rolled cylinders down and incline. Each cylinder had a series of holes inside it where we could reposition weights. Putting the mass near the outer edge (say, like with a heavier tread tire) slowed the roll down the incline compared to putting the weights near the axis of the cylinder (simulating a heavier wheel). You want bang for your buck? A lighter tire is more important than a lighter wheel, at least as far as energy goes. If we're offroading, then a durable tire is important, so the tire will be heavier, plus we're typically moving more slowly so the rotational energy is lower. We could also argue that increased moment of inertia is helpful in getting us over obstacles, but that's for another discussion.

We could also talk about the rolling resistance due to tread compound, tread shape, sidewall deflection, tire pressure, etc. but I think (hope) we're in agreement there.

 

[brianmartin]

you certainly know the physics better than i do, that's for sure. but there may be people lurking these forums who dont even realize rotating mass is different. I'm just trying to put it into simple terms for them. all else being equal, smaller, lighter wheels and tires take less energy to rotate. but nobody wants small tires so focus on the wheels. just KISSing..."keep it simple stupid"

 

[elas9000]

The wheels are either forged or cast. You seem to be confusing "cast" with "machined". Machining alters the surface shape/finish and has nothing to do with whether the material was forged or cast. Also, Rivian has indicated that their cast wheels use a higher end process known as flow-forming.

edit: I would not be surprised to learn that the 20s aren't forged but this isn't evidence of that.

Current configurator shows Machined aluminum for ALL wheel/tire options. No mention of cast/flow formed.

 

[crashmtb]

Current configurator shows Machined aluminum for ALL wheel/tire options. No mention of cast/flow formed.

Machined refers to the finish of the wheels. So they’re painted, with a second operation to make shiny machined areas.

The all-terrain 20” wheels are forged(all three styles)

The 21/22” wheels are tilt-cast with flow-formed(think metal spinning) barrels.
if you look at wheels on retail websites you will see the same terms used.

This has been discussed/mentioned many times. Search is your friend.
here is one such thread.
https://www.rivianforums.com/forum/threads/forged-vs-cast-wheels-weight-strength-longevity.943/

 

[electruck]

Current configurator shows Machined aluminum for ALL wheel/tire options. No mention of cast/flow formed.

While your observation is indeed correct, this does not change the definitions of words or facts established by Rivian. It just means the configurator doesn't address such concerns.

 

[elas9000]

While your observation is indeed correct, this does not change the definitions of words or facts established by Rivian. It just means the configurator doesn't address such concerns.

I concede.

While your observation is indeed correct, this does not change the definitions of words or facts established by Rivian. It just means the configurator doesn't address such concerns.

I concede. Was influenced by the identical wheel descriptions in the configurator. Seemed to me that one would would want a full and accurate wheel description in the configurator where one makes their wheel choice. Obviously it makes sense to have a stronger wheel in the ATs as more stresses are expected when off-roading

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