Tranny and rear end HP loss? December 04, 2010 04:40AM
So If I am building a new tranny and rear end setup is it better to gear the tranny high and the rear end low? Or the tranny low and the rear end high? There has to be some science on which way takes the least amount of power. Anybody have any insight on this?
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Re: Tranny and rear end HP loss? December 05, 2010 03:54AM
I know with over the road trucks a lot of the large companies are useing direct drive trannys (low) with high geared rears and claim 2 tenths better fuel milage. Is this realy true? Im not sure. I do know this puts a lot more stress on the drive shafts, the out put side of the trans, and the input side of the rear end. With pulling I would want to know how strong the trans out put shaft and pinion gear are. If you think either could break than gear the trans high and the rear low. As far as wich one takes more power Im not sure theirs a big differance as long as the overall gearing is the same.
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Re: Tranny and rear end HP loss? December 05, 2010 05:31AM
For pulling wouldn't the drag race mentality apply most are low rears. ?
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Re: Tranny and rear end HP loss? December 05, 2010 06:19AM
Well there is more to the science of all this than you think. Road trucks doing this for fuel mileage is WAY different than tractors trying to get the most out of HP to the track
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Re: Tranny and rear end HP loss? December 05, 2010 07:46AM
Keeping shaft speeds up reduces the torque load on them, thus adding reliability, but does it cost more hp? The low gearing still applies to pulling like in drag racing, plus the gears aren't in contact with each other as long which helps spread the stress over more teeth. You may find little difference in parasitic loss. I'm sure someone with alot more knowledge than me will chime in. Ed.
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Re: Tranny and rear end HP loss? December 05, 2010 10:05AM
Thanks for the input so far guys. My theory so far was to run the tranny fast and the rear end slow. My thinking on this is that it takes less power to run a straight cut tranny gear fast than an angular pinion shaft. Am I wrong? The final ratio will turn out the same way. Im just wondering if there is a better way to get to it.
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Re: Tranny and rear end HP loss? December 05, 2010 01:09PM
I was once told that you want to run your tranny as close to 1:1 as possible. This seems to go along with many of the responses already.
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Re: Tranny and rear end HP loss? December 06, 2010 05:16PM
If your tranny is 1 to 1 then it is straight thru, which means you dont have to turn a countershaft or other gears which should take less power
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Re: Tranny and rear end HP loss? December 07, 2010 01:19PM
I would have to assume that if you are putting power through the countershaft, rather than straight through there should be a siginificant loss of power. How to figure this difference??????
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Re: Tranny and rear end HP loss? December 07, 2010 02:26PM
You guys have good points. But what happens when I have to run a gear over direct? Is it better to overdrive the tranny or rearend?
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Re: Tranny and rear end HP loss? December 07, 2010 05:24PM
It takes less hp to turn a direct drive than an overdrive, so if you can speed the rearend up it would be better. THat may be hard to do if its an ag rear being limited on your ratios.
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