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Old 02-02-2003, 06:36 AM   #1
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Default One-ways and efficiency Q

From time to time, I read that a one-way adds extra effiency to the drivetrain. Once upon a time, I read that it is because at a certain speed, the front wheels want to spin faster than the rear wheels.

Can someone please explain if this is true? If so, whats the reason for this behavior? (because I dont understand it )
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Old 02-02-2003, 06:44 AM   #2
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In a straight line it's a bit more efficient, because the driven rear wheels will end up not slipping so the front wheels will just end up freewheeling (as the axles turn at the same speed).

When the wheels are slipping, the car will switch to full-time 4wd.

Also, because 4wd touring cars don't have a centre differential, the one-way helps to stop differences in wheel speed at different corners of the car from slowing the car down.

Last edited by sosidge; 02-02-2003 at 06:46 AM.
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Old 02-02-2003, 12:13 PM   #3
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Quote:
Originally posted by sosidge
In a straight line it's a bit more efficient, because the driven rear wheels will end up not slipping so the front wheels will just end up freewheeling (as the axles turn at the same speed).
This is exactly the part, that I dont get; If the axles turns at the same speed - and they will, since they are connected in the ratio 1:1 - then why should one end of the car wants to spin faster?
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Old 02-02-2003, 04:13 PM   #4
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A one way should make no difference to efficiency in a straight line unless you are over/under driving one axle of the car.

The reason a 1 way adds efficiency is because the front wheels travel further than the rears in cornering (assuming you're not hanging the rear out in the corners). The easiest way to demonstrate this is to ride a bike through a puddle and then make a sharp turn. If you look at the tracks you can clearly see that the front wheel follows a much longer path than the rear.
Cars behave in the same way. This means that without a 1 way fitted you are forcing one end of the car to slide and is the reason why 1/8 scale off roaders and many full size cars have 3 diffs.

In reality though the efficiency gains are questionable.
Firstly the car is usually sliding at racing speed anyway so the rear tyres travel further than they would at slow speeds and the one way has little effect.
Secondly Most of the gain in efficiency will be on corner entry when you are braking anyway. On corner exit the one way won't be freewheeling because the power applied is more than sufficient to start the rear tyres slipping.
Most of the gains in speed from a 1 way differential come from the fact that you have no differential effect when you put the power down hard so the car pulls more out of the corners, and if you are putting more power down the car is in fact less efficient.
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Old 02-02-2003, 04:43 PM   #5
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dw, you've got that backwards. The more power you can put down to the track, the more drivetrain efficiency you have, think about it. Oneways will give more on-power and corner exit steering because the front is acting like a solid axle on power. This causes you to scrub much less speed than you would with a diff. Because you are srubbing less speed and putting all the power you feed from the motor to the drivetrain onto the track, you have a more efficient drivetrain. The motor is not wasting extra power trying to make up for scrubbed speed like it would with a diff in. Since the drivetrain is more efficient, it's a little easier on batteries
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Old 02-02-2003, 05:09 PM   #6
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How about cars that run a centre one-way pulley as well as a front one way unit?
Does the centre one way make a difference?
Would it be better to replace it with a fixed pulley or leave it and replace the front with a regular diff unit?
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Old 02-02-2003, 05:18 PM   #7
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Default Info i got from mpowered-racing

During off power steering:
Center 1 way have more than no one ways.
Front 1 way have more than center one way.

On power steering:
Center 1 way same as no 1 ways.
Front 1 way have more than center 1 way.

Acceleration while cornering
Center 1 way same as no 1 way.
Front 1 way more than center 1 way.


Hope this info helps.
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Old 02-02-2003, 10:46 PM   #8
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Quote:
Originally posted by Mort
How about cars that run a centre one-way pulley as well as a front one way unit?
Does the centre one way make a difference?
Straigth line: If the front actually freewhell at some point , then the use of two one-ways should result in a front belt, which dont turn. Meaning more efficiency and better top-speed. But only if the rear wheels spins faster than the front wheels, thus the front-wheels freewheeling.....
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Old 02-03-2003, 02:58 AM   #9
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Axiom

No it wasn't backwards. ( Badly phrased though) Efficiency is the ratio of power in to useful power out. It is not the same as power output. For example if you put a really low turn modified in your car you will get lots more power out but the car will be less efficient.
It is a similar sort of analogy with the 1 way diff (or spool). Anything that increases traction on acceleration increases power output (and input) but decreases efficiency.
This is why formula 1 cars use much less fuel in the wet, and why people dump more on high grip tracks.
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Old 02-04-2003, 02:38 AM   #10
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dw,

Basically. You are saying, the higher the load you apply to the motor, the less efficient it is. Correct? This is what I thought you meant. I thought what Axiom is talking about is totally different, but he's not incorrect though.

I am curious about this whole one way deal as well. I've heard many different explanations but I could never really figure it out.

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Old 02-04-2003, 03:06 PM   #11
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dw,
you keep believing that and you'll have plenty of rear bumpers to look at .
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Old 02-05-2003, 11:56 PM   #12
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Okay, so no one have tried installing both a one-way pulley and a one-way diff ?
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Old 02-06-2003, 12:05 AM   #13
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I know people who run both or just one or the other. They use the differnet combinations of them as a tuning tool.
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Old 02-06-2003, 12:12 AM   #14
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Default Very interesting

Quote:
Originally posted by Leon
I know people who run both or just one or the other. They use the differnet combinations of them as a tuning tool.
Do they use different combinations for handling purposes only, or might there also be more top-speed, while using both in combination?
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Old 02-06-2003, 02:56 AM   #15
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Quote:
Okay, so no one have tried installing both a one-way pulley and a one-way diff ?
I have a MR4TC Worlds Edition, they come with both one way pulley and front diff.
Putting in a regular diff this weekend because on small tracks i found i had a lot of off power steering and quite a bit of oversteer as well.
One thing i would like to know is there any advantage to leaving the one way pulley in there or should i get a fixed one as well?
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