42 mph?

Larger battery and more powerful motor. I think the new cutoff point for the regular(non-Prime) Prius is around 60mph, maybe 65. Granted, EV mode doesn't last long at those speeds since you're burning through electricity at a pretty brisk pace, but you might get a minute or three of EV before the ICE kicks in, depending on the slope and wind conditions. For me, the conditions have been pretty rare for it to happen, but I've had the ICE shut off at 55mph a handful of times on a flat road when I had a decent tailwind.

 

The change is a much bigger hybrid battery pack and a much bigger electric motor...

 

and also MG1 can spin higher RPMs without flying apart, which was the original reason the engine had to start spinning above 41 MPH.

 

Coincidentally the 42 MPH speed was likely to have been selected as the cut off point for EV running because it is equal to 65 KPH in the Japanese market.

The owner's manual for the 1st Gen Prius advised that you should drive below 63 MPH during the break in period. That's an odd speed till you convert it to it's metric equivalence... 100 KPH.

 

older or newer model, don't be deceived by your info screen showing motor not "running". The ICE still has to spin up at 'SPEED' - at some MPH point. It took older Prius owners a bit of time to determine what MPH necessitated ICE being spun up - but I'm sure someone is already working on determining the newer model's mph spin-up speeds as well. I'm looking forward to reading up on what the new Gen5 MPH parameters are for "heretical mode" as well.

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That's part of it, but the other part is the changes in gear ratios. Since G3 there's been a reduction gear in-between MG2 and the planetary gearset, and that allowed the final drive ratio between the planetary gearset and the wheels to be reduced. Which means that with the ICE off, MG1 spins less fast for any given wheel speed.

G3 actually had a lower MG1 rev limit, but still a slightly higher ICE-off speed.

The no-ICE limit for the G5 plug-in is 84mph, same as the G4 plug-in. Don't think it's been determined for the G5 non-plug-in, but for G4 that was 74mph, so probably at least that.

 

Thanks for catching that; yes, my notes have final drive ratios around 3.905 for gen 1, 4.113 for gen 2, and 3.268 for gen 3.

So even if the specs for MG1 had stayed exactly constant, if the limit was 41 MPH for gen 1, it would have been 39 for gen 2 and 49 for gen 3.

Gen 4 by my own calculations (using the tooth counts shown at 25:02 in the Weber P610 deep dive video) comes out at 2.834, or 3.218 for the Prime (different numbers are shown over at openinverter.org, which they call "ring to pinion gear ratio" and which don't include the counter driven/drive tooth counts). My numbers would correspond to 56 MPH (50 for Prime) even if nothing about MG1 had ever changed since gen 1.

I haven't gathered those specs for gen 5 yet.

 

I agree with all your G1-G4 numbers for what I've got down as the "(planetary) ring to wheel ratio".

And the G5 values I have are:

3.017 for the 1.8 HEV (74/20 final drive, 53/65 counter)
3.390 for the 2.0 HEV (77/21 final drive, 49/53 counter)
3.606 for the 2.0 PHEV (78/20 final drive, 49/53 counter)