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Rivian's TM-B electric bike

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188 points hasheddan | 2 comments | 22 Oct 25 18:00 UTC | HN request time: 0s | source
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soco ◴[22 Oct 25 18:48 UTC] No.45673474[source]▶
Bear with me I don't know much about bikes but I have this honest question: why does it need a chain, and won't place the engine (or whatever gear box it has) directly on the wheel?
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STKFLT ◴[22 Oct 25 19:02 UTC] No.45673640[source]▶
The biggest reason is minimizing unsprung mass, the performance of the rear suspension would be much worse with a hub motor.
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1. Groxx ◴[22 Oct 25 19:09 UTC] No.45673727[source]▶
does that actually matter much on anything except dirt-bike tracks, or trying to go 40mph on a horrifically bumpy track? minus some comfort advantage, of course.

like technically, sure, it's obviously true. but for performance it only really matters when you would get air time with higher mass, and the lower mass stays in contact more. commuter e-biking generally doesn't get anywhere near those speeds or bump-sizes. (trail biking: sure! I 100% believe it's a sizable consideration there)

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2. STKFLT ◴[22 Oct 25 19:50 UTC] No.45674251[source]▶
I've never ridden a full suspension with a hub motor so I can't say, but my guess is that yes, it would make a pretty big difference with an aggressive rider or poor quality streets. It's not just keeping contact that matters, its the consistency and quality of contact, especially with a super torquey motor ready to jump at a twitch of your thumb. Its of course not necessary for commuter biking, but neither is basically anything on this premium product aside from the wheels and pedals.

Also to note, they are very much marketing it as a trail bike in addition to a commuter so it's not surprising they would spend a bit to optimize for ride quality and traction.