changing gear ratio?

[TerryMcC]

Hi Folks,

Not an expert so this is a newbie question, what would happen if you had a new set of front/rear gears cut that changed the 9:1 ratio to 12 or even 15:1. I know you would loose top speed but who uses that? Perhaps the power curve is already maximised at 9:1 and you would end up with less speed over the 1/4 mile due to losses at the higher rotation speed of the motors vs speed that this would cause. Perhaps also the stub axels would simply twist off :-0

Just a thought
Terry

 

[TBrownTX]

Hi Folks,

Not an expert so this is a newbie question, what would happen if you had a new set of front/rear gears cut that changed the 9:1 ratio to 12 or even 15:1. I know you would loose top speed but who uses that? Perhaps the power curve is already maximised at 9:1 and you would end up with less speed over the 1/4 mile due to losses at the higher rotation speed of the motors vs speed that this would cause. Perhaps also the stub axels would simply twist off :-0

Just a thought
Terry

Best Mustang mod I ever did was a set of 4:10 gears, I have been wondering the same thing.

Tim

 

[Gauss Guzzler]

Well first of all, there's no possibility of an affordable gear ratio increase. The large gear would have to get larger to make a higher ratio and you can see why that would require a new housing.

But if you could, increasing the gear reduction would shift the torque curve up/left as you'd expect but the power curve would only move to the left (not up). So the 475+hp power band seen here spanning 67-87 km/h would move left to lower speeds, meaning that you'd start feeling the power drop off ~1.5 seconds into a 0-100km/h sprint instead of 2+ seconds in.

TLDR: I suspect the peak torque at the wheels is pretty close to what the tires can deliver under the Model 3's weight so more gear reduction would only provide a small benefit before traction limitations at the low end and torque dropoff at the high end made it counterproductive.
Obviously it's not fully optimized since Tesla uses the same gear ratio F/R with a variety of tires and the same setup on the Y, but it's likely close enough to optimal that it wouldn't be worth the expense to change.

 

[bedoig]

Here's what you want:

 

[Gimmethecash]

Here's what you want:

View attachment 700783

…but will it clear the M3P’s calipers? LOL would barely clear the rotors.

 

[bedoig]

…but will it clear the M3P’s calipers? LOL would barely clear the rotors.

I would assume that's a negative, lol. Ultimate in rotating mass reduction... who even needs rotors and calipers when you've got regenerative breaking

 

[subieworx]

Smaller tires will do the same thing. That being said I have run tires that are over an inch smaller than stock and notice no appreciable change in acceleration.

 

[MountainPass]

Actually what most people want are longer gears to reduce the power loss at higher speeds. Any small increase in torque with shorter gears would be gone by the time you exceed ~46mph multiplied by your gear ratio change. So at 15:1, you'd have less output past 27mph.... !!!

A gear ratio change would also require electronics as the Drive Units compare the wheel speed with motor RPM, and if there is a big discrepancy I am quite sure the system would get quite upset!