I can't see much of a point fiting knobblies to e-bikes TBH.
I get 24 mph with a15A controller quite easilly
to qualify the skidding bit, for me road surface has a great deal to do with it, on one long steep descent on very smooth tarmac in the mornings 38mph feels fine and solid, later on the way home there's very rough tarmac where the tyre seems to vibrate/bounce above 30 mph in ways that cause the front wheel to drift slightly in ways that feel terminal
That's not because of the width of the tyres, that's because of the type of tyre. Marathon Pluses, whilst they have many favourable assets, aren't great on grip. I have significantly more grip on 40mm Vittoria Voyager Hyper semi-slicks than I do on 25mm Bontragers, both on 700C wheels.
Perhaps counterintuitively it's actually the opposite - with identical types of tyre wider ones are quicker. Schwalbe have a good article on the topic here, I find Off The Beaten Path's pioneering tests and articles on the matter here good reading and Continental have a useful diagram below (their copyright):
Yes,, but on his old bike that had Schwalbe City Jets on, i could always beat him in a rolling contest. Also, he always seems to be able to roll halfway up the next hill, while I have to pedal from the bottom. There's no doubt that it's a better rolling bike: As soon as you start pedalling, you can feel how easily it goes, even without the motor.
Nice theory, but logic says that if that were true, everybody in the Tour de France would have 2 inch wide tyres!
And Off The Beaten Track address exactly that point in this article here! It's more than theory which is why both Schwalbe's and Continental's input is linked to in the post above, as is Off The Beaten Track's extensive testing on the matter.
I read a very good article in atob by mole (will find and paste it) about this - and why schwalbe big apples have such low rolling resistance (it has to do with the footprint being round) - and indeed they do (I've tried them, it's astonishing how easy they roll at around 15mph), but idiosyncratically I find they don't do that well at high speed - anything above twenty mph and they feel sluggish (in my experience only of course)
Knobblies don't have that much contact area so they do have less grip on road. Try a wide fast touring / commuting tyre though and the confidence they provide is amazing. They don't immediately feel as fast because they are heavier to spin up and you don't get as much handlebar buzz.
At that speed the vibration may be your wheel out of balance or slightly out of round. Something is generating the resonance and the vibrating fork is the result rather than the cause. Balance is not usually a problem at normal bike speeds but the tyre valve can generate quite a force at 30 + as can one of those spoke reflectors.
Oh dear more legal issues...
French road code requires a yellow reflector in each wheel for night time riding, white tyre reflector is not enough. Of course the lycras don't have reflectors which they get away with by not going out at night. seemed true and balanced when I mounted it.
