Something I've half picked up on is quite a few recent eMTB launches being mixed wheel sizes. Specialized's Turbo Levo SL and the Ethic by Bird are the only ones I can name, but a cursory look at Tredz (just because they have some working filters on their website) shows that 20% of eMTBs are mixed wheel whereas only 5% of non-assisted MTBs are.
Is this a thing, and if so what reasons are there behind it?
Restoring a bit of agility to a heavier bike? More space for a motor without an excessively long motor (although I see Specialized managed 432mm in mixed mode and 442mm in 29er mode).
It works for MX bikes, right? Most of the criticism I see of mullet is the extra slackness making climbing a bit harder and that's not an issue on ebikes.
The motor does eat into chainstay space a bit. Comparing my Vitus e-Sommet with the non-e Sommet it's about the same chainstay length for the mullet e as the 29er non-e.
Conservatism? I think ebike buyers are probably more inclined to try the latest thing wheras non-e buyers might stick with what they know.
Ebikes are what people buy these days so they get the new innovations.
Old style pedal bikes are pretty much dead so not worth manufacturers spending development money on.
Most non-XC bikes will be launching as MX-able for the forseeable I would say as it offers versatility for low downsides. On an Eeb its about chainstay length, wheel strength and reducing the already crushing weight of them. Efficiency doesn't really matter.
There seems to be a lot of consensus from the likes of PB, ST, Vital and NSMB that MX/mullet suits e-bikes well.
Pinkbike did say they'd comment on the Turbo Levo SL in both modes when the long term test report comes out.
Looking at the lightweight options, everyone apart from Orbea do a 440mm chainstay in 29er mode, and Pivot even do 430mm. But I appreciate it probably makes packaging more difficult, probably varyingly so with different motors.
Weight example, the saving by sizing down an XM481 rim exactly pays for upgrading to an EX511, and the same applies with a DHR2 from EXO+ to DD. You can choose to save 40+75g and have a more durable setup due to its smaller size, or have an even more durable one for no net weight gain.
An ideal scenario would be to demo one in both modes then be able to order from one of the custom assembly brands with your preferred option.
My main personal bike (not E) is a mullet. The other day I borrowed a Specialized Kenevo SL (29er) and we rode a double black Trail near Pemberton BC. The only time I thought about the wheel size was when someone mentioned it after the ride.
I've also borrowed a Levo (mullet) and didn't think about the wheel size on that ride either.
I think that people over-think these things to justify purchases.
I agree with bikeandroots weight / strength comment though.
My first ebike was a mullet some six years ago. It seems to work ok, so when my second 29er ebike broke it's rear XT microspline hub I decided to mullet it. I honestly don't notice much difference. Slightly better downhill maybe? The bike is designed for either wheel size with a flip chip on the shock. Mustache game 8 if that matters!