←back to thread

Rivian's TM-B electric bike

(www.theverge.com)
190 points hasheddan | 1 comments | 22 Oct 25 18:00 UTC | HN request time: 0.201s | source
Show context
legitster ◴[22 Oct 25 21:25 UTC] No.45675359[source]▶
So the interesting thing about this is the ... peddle-by-wire drivetrain? So unlike a normal e-bike, when its battery dies it turns into a stationary bike.

I love ebikes and generally like what Rivian does, but in a very competitive market it's hard to see the appeal of this.

replies(12): >>45675455 #>>45675507 #>>45676159 #>>45676241 #>>45676253 #>>45676285 #>>45676419 #>>45676560 #>>45676810 #>>45677043 #>>45678041 #>>45678340 #
_carbyau_ ◴[22 Oct 25 23:06 UTC] No.45676285[source]▶
In the next sentence:

"It features a new pedal-by-wire drivetrain called “DreamRide” developed in-house. The rider pedals a generator, which replenishes the battery,"

So uh, keep peddling?

Yes, the motion->electric->motion circuit is not as efficient as direct pedal but you are explicitly not stranded.

replies(1): >>45676468 #
blacksmith_tb ◴[22 Oct 25 23:29 UTC] No.45676468[source]▶
If that worked well though, why pack a large battery in the first place? My suspicion is that pedaling provides a small percentage of the energy needed to move you and the bike and your cargo.
replies(7): >>45676520 #>>45676524 #>>45676528 #>>45676538 #>>45676949 #>>45677047 #>>45678059 #
1. tree_enjoyer ◴[22 Oct 25 23:37 UTC] No.45676520[source]▶
A traditional bicycle chain drive is something around 98% efficient - particularly if you're using internally geared hubs or a single speed with the chain line perfectly straight. What's a typical consumer alternator efficiency? Maybe 85%? And then a few steps for losses in the charging circuit and then again at the motor.

Not even napkin math, but ballpark I would think you're looking at having to pedal about 20-25% harder to accelerate the same rate compared to a chain, with no supplemental energy directed towards charging the battery (though I would assume al the energy goes through the power management system anyways).

However you get some gain in that you don't have to select a gear ratio, and that the electric motor provides torque efficiently at any rpm you can realistically expect on a bicycle. If it has an adaptive resistance level it will probably be more work (energy) but for many non-cyclists feel much more intuitive and simple