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Comment by ErroneousBosh | Hacker News Reader

> BYD builds a unit with an integrated motor, differential, axle, and wheel hubs

So wait, the whole axle is solid then? Like a 1960s pickup truck but with all the weight of the motor and gearbox hanging off it too?

That must give it ridiculous unsprung weight.

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it's not really like a 'live axle' from an older truck, it's more like a de-Dion style suspension (or dead axle).

https://en.wikipedia.org/wiki/De_Dion_suspension

you still see these in velocipede-style vehicles commonly.

and to your point : a dead axle is an effort to reduce unsprung weight compared to a live axle; it also lets you actually use alignment as a remediation for asymmetry issues rather than just pre-delivery straightening.

Ah, like on my old Volvo 340 ;-) They were fun, all that weight at the back (the diff and gearbox were bolted together under the rear floor) gave it excellent balance. Bit of a shame all that 50/50 weight distribution was only pushed along by a 1.4 Renault engine then, I guess.

Have you ever seen the Jaguar IRS setup? It's more like a twin-wishbone suspension *but the driveshaft is the upper link!* It's in compression and stops the hub tilting out, and the rear brakes are inboard to reduce weight even further.

On the platforms I've worked with, the weight isn't the issue so much as the quantity of expensive and vibe sensitive parts that are unsprung.

Looks like they do in-hub motor for buses and in-differential(like everyone else) for passenger cars?

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