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Old 08-08-2003, 12:28 AM   #1
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Default Reduced rotating mass versus weight transfer

I've just reduced the weight of my transmission, in my Pro2.

In the rear, I went from steel diff outdrives, to the graphite version. On the layshaft, I changed a steel one-way pulley to a fixed graphite pulley. I also changed the other pulley from a alu to a graphite.

I havent put the parts on a weight, but I think it's around 25-30 grams.

First of, I'm impressed about how big an improvement it was. Faster acceleration, and longer runtime.

But it surpriced me, that it also affect the handling, I feel the car dont brake as much, when off-throttle. This suits me nice, but I supposed that a lower rotating mass, would result in more braking, since there's less energy stored in the rotating parts?
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Old 08-08-2003, 12:46 AM   #2
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Could it be that the molded parts distort a little and decrease efficiency slightly? It is an idea. Also, you switched from a one-way pulley to a fixed pulley, and I would think that a one-way equipped car would decelerate slower than a solid drive car.

Interesting....
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Old 08-08-2003, 05:54 AM   #3
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Quote:
Originally posted by Im2lazy
Could it be that the molded parts distort a little and decrease efficiency slightly? It is an idea. Also, you switched from a one-way pulley to a fixed pulley, and I would think that a one-way equipped car would decelerate slower than a solid drive car.

Interesting....
I got less braking by now, so I dont think there's a efficiency decrease.

I forgot to tell in the first post, that I still have mounted a front one-way diff.

The track I'm racing at, is small and tight, it's mainly around 2 meters wide and approx. 90 meters long. It's also quite technical, so regular bypassing another car is difficult. for the most, one have to stay behind and stress the other driver. When he make a mistake, you got the chance to pass. The track layout can be seen here: http://www.hillrace.dk/intrack2.jpg

So with my driving skills, I found it hard to handle the extra acceleration, that the ligther drivetrain gave me. I went from 27 laps to 26, when I igthend the drivetrain. I'll have to do some practicing, and see what I can do now. When I get used to it, I think I'll try and switch the front one-way to a graphite ball diff. Eventually combined with a one-way pulley.

But still, I dont quite understand, why the car has a little less brake effetc, while off-throttle, compared to the heavier drive train.
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Old 08-08-2003, 07:13 AM   #4
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hey cole, you are spot on! more rotating mass = more force needed to stop it (inertia). given all other variables unchanged, your car should stop faster. i'd be willing to bet that when you reassembled the car, something went toghther better, or cleaner. or your new pullies/outdrives are smaller (marginally). you do have a more efficient drivetrain if you are rolling longer with less weight. so that's good. that's also why your car will accellerate faster. not only is it lighter, but somewhere something freed up. usually i cannot tell an accelleration improvement due to dropping an ounce (28g) even if it's rotating mass. but that's just me.

btw- let me check on shipping. and i'll get back.

lata.
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Old 08-08-2003, 11:47 PM   #5
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You might have a point about better assembly.

However, I think I've mixed up my impressions. I doubt it was total off-throttle, I tend to believe it was at partial throttle. And THAT would make a difference with a ligther drivetrain. I'll have to re-check next time at the track.

About an ounce, so you dont find any acceleration difference between a leightwight diff versus a (heavy) one-way diff? I'm curious, beceause this will be one of my next experiments.
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