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 Post subject: Diff ratio question
PostPosted: April 26, 2016, 10:53 pm 
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Joined: March 17, 2007, 5:59 pm
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I recently discovered a 2.928 ratio differential. If used in a bike engine (liter bike) car roughly 1500 lbs for street use with 225/50/15 or 16 tires.
Would that be to long of a ratio or to much for the engine to move? I would love hear your thoughts or concerns.

Thanks,

Vince


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 Post subject: Re: Diff ratio question
PostPosted: April 27, 2016, 6:12 am 
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It depends on the bikes transmission ratios (including the primary reduction before the trans) and what the purpose of the car is.

It is good to select a diff where there are many different ratios to choose from, such as a Ford 7.5 which can have a ratio from 2 to 5:1 for a few hundred with many in between.

The higher the ratio numerically, the easier it is on the bike drive line for longevity. The trade off is higher rpm at cruising speed.

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 Post subject: Re: Diff ratio question
PostPosted: April 27, 2016, 9:03 am 
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Heres my dilemma, I want to make the car awd and turbo after I have it running. My idea is to turn the motor sideways like normal, send power to an electronically controlled transfer case then to both diffs. Power will be sent to the front when differing speed is sensed. I want to keep rpms down like you mentioned and if possible have a higher top speed, but finding a reverse rotation ring gear is a little harder to find. The shortest I can find is 3.31, would this be better option?

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Vince


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 Post subject: Re: Diff ratio question
PostPosted: April 27, 2016, 12:57 pm 
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Location: Pemberton, BC
Vince,
I'm not 100% sure, but I do believe that the 1L sport bikes (R1, GSXR etc.) are all very close in their final gearing. You can double check this here for your application.
http://www.gearingcommander.com/
My R1 had a final ratio of about 2.64, and by going with a 3.27 rear axle (94 Ford Mustang) and 15 inch wheels, I was able to get a decent reduction for the higher weight, while maintaining the cruising RPM to a manageable level (about 110km/h @ 6,000 RPM). It is not a stump puller, but very adequate. So a 3.31 would probably be right on, for that type of engine.

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 Post subject: Re: Diff ratio question
PostPosted: April 29, 2016, 8:34 am 
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Location: Falls Church, VA
I am looking at the RC51 engine and I concur with mgkluft. between 3 and 3.3 seems to be optimal for a decent highway cruz rpm and compensating for the shorter tires and heavier weight.

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 Post subject: Re: Diff ratio question
PostPosted: May 2, 2016, 4:12 am 
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Long time ago found a very simple and good gear calculator.. You have only to complete de magenta cells, with tire diameter, primary reduction of the engine, then on second drive ratio put your diff ratio( the gearcalc was made for chain final drive and automatic calculate, but you can simply put your number there) and simply fill the ratio for every gear ...very simple and practic.

Credits to Douglas Anderson from Westgarage Engineering for doing it, i was too lazy for.
It is archive because i can't upload the .xls directly.


You do not have the required permissions to view the files attached to this post.


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 Post subject: Re: Diff ratio question
PostPosted: May 3, 2016, 5:54 am 
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Thanks guys for the replies I will have to start shopping for diffs.

Vince


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 Post subject: Re: Diff ratio question
PostPosted: May 4, 2016, 1:20 am 
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I didn't check out the gear calculator above due to security settings but here is the one I use.

Good luck.https://drive.google.com/file/d/0B73zxBgu49hIQjRTd3NBY0ZVelk/view?usp=sharing

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 Post subject: Re: Diff ratio question
PostPosted: May 4, 2016, 11:52 am 
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You can check the gearcalc that i posted, it's only a .xls sheet but as i said, i'm not allowed to upload it in this format, that's why it's an archive
Yours is doing exaclty the same job, thanks for sharing.


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 Post subject: Re: Diff ratio question
PostPosted: May 4, 2016, 6:22 pm 
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Not much math. No need for a calc unless you want a spread sheet for all of it.

Related topic:
viewtopic.php?f=4&t=6314&p=61644&hilit=ratio+gear#p61644

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Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12


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 Post subject: Re: Diff ratio question
PostPosted: May 4, 2016, 8:12 pm 
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Joined: April 19, 2016, 1:03 pm
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Location: Falls Church, VA
m_a_e wrote:
You can check the gearcalc that i posted, it's only a .xls sheet but as i said, i'm not allowed to upload it in this format, that's why it's an archive
Yours is doing exaclty the same job, thanks for sharing.


Please don't misunderstand. I was on my work PC and it wouldn't allow me to download from an unsecure website because of security settings.

Not that I didn't want to look at what you posted, or thought mine was better, I just couldn't.

Yeah very similar. I have looked at a few different ones and keep evolving mine. A piece I have borrowed, very happily I might add, is the tire size converter on the side. Takes a step out of doing things.

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