Toying with idea of taller Metro 5th gear (to go with the already taller final drive) - Page 5 - Fuel Economy, Hypermiling, EcoModding News and Forum

dcb · 09-12-2009, 12:44 PM

Probably completely impractical, but I do wonder if welding up custom axle halves (quarters?) and adapters and mounts so you can use a completely different gearbox (like out of a motorcycle or??) wouldn't be less expensive and more in reach of the diy. Does 1 wheel drive help efficiency by any chance?

dcb · 09-12-2009, 07:37 PM

or, pull the axle out of one wheel hub and lock it down so it can't turn, and the other wheel then turns twice as fast, aka quick and dirty super overdrive with one wheel drive. You did say you have a spare tranny?

Christ · 09-12-2009, 11:04 PM

Quote:

Originally Posted by dcb

or, pull the axle out of one wheel hub and lock it down so it can't turn, and the other wheel then turns twice as fast, aka quick and dirty super overdrive with one wheel drive. You did say you have a spare tranny?

You wanna explain how that would work?

dcb · 09-12-2009, 11:33 PM

same thing that happens when one wheel spins on the ice. If you removed an axle shaft from the car and replaced it with something to keep the associated transmission output shaft from turning, then the other output shaft would turn twice as fast (i.e. super overdrive

) and really give the cogs a workout too.

Christ · 09-12-2009, 11:38 PM

Quote:

Originally Posted by dcb

same thing that happens when one wheel spins on the ice. If you removed an axle shaft from the car and replaced it with something to keep the associated transmission output shaft from turning, then the other output shaft would turn twice as fast (i.e. super overdrive

) and really give the cogs a workout too.

But... it won't turn twice as fast.

If the final gear ratio is 2:1, it's 2:1 with both wheels turning, and it's still 2:1 even if only one wheel is turning.

Don't believe me, jack up the car, put it on stands, put it in 5th gear, and let it idle (it will stall instantly if it falls).

Once both tires get moving at the same speed, stop one. The other one won't be spinning any faster, because the engine's speed hasn't changed, and neither has the differential speed.

All that starts spinning faster are the spider gears in the differential, and you start wearing the pin that holds them together. Eventually, it will fail, shooting into the side of the diff case and grinding itself to oblivion... at least, that's what happens when you make 1-tire-fire in a Chrysler.

MadisonMPG · 09-12-2009, 11:43 PM

I think with a differential it would spin 2x faster, I have no idea what a FWD car has, so I can't answer the question.

Christ · 09-12-2009, 11:47 PM

Quote:

Originally Posted by MadisonMPG

I think with a differential it would spin 2x faster, I have no idea what a FWD car has, so I can't answer the question.

Jack up your truck and try it. The differential is geared the same no matter how many tires are spinning, no matter if it's FWD, RWD, locker, LSD, etc.

The only time you'll get 2x speed out of a tire in this case is when one was spinning backwards, as is the case with open differentials. If they're both spinning forward, or one is spinning and one isn't, the speed doesn't change.

dcb · 09-12-2009, 11:55 PM

Sorry Christ, but that just doesn't sound right. The only time the other wheel affects the rotational speed of the first is when it is spinning backwards you are saying?

Edit: no argument that there are plenty of examples of self destructing differentials though. This is not an entirely serious suggestion

Christ · 09-13-2009, 12:20 AM

Quote:

Originally Posted by dcb

Sorry Christ, but that just doesn't sound right. The only time the other wheel affects the rotational speed of the first is when it is spinning backwards you are saying?

Edit: no argument that there are plenty of examples of self destructing differentials though. This is not an entirely serious suggestion

Precisely. The differential's speed is based on it's input, not the wheel speed. The wheels' speeds are independent of each other.

This means that if the engine is coupled directly to the differential, and the differential's ratio is 2:1, when the engine speed is 2000 RPM, the output speed of the differential is 4000 RPM, regardless of which wheel it goes to. Neither wheel will spin any faster than 4000 RPM, regardless of the opposing wheel's speed.

If you are NOT driving the differential, you can spin one wheel either forward or backward, and the other wheel will spin 1:1 with it in the opposite direction, unless you have LSD engaged, or you have POSI or a welded diff.

MadisonMPG · 09-13-2009, 12:26 AM

Quote:

If you hold one side fixed, and continue to apply torque, the other side of the differential rotates at twice the speed it normally would (twice the speed of the ring gear and housing).

source:
Differentials (Open, LSD and so on)

I have a Lego Differential, but I can't find it I would demo it if I could.