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Dustin B
Samba Member
Joined: March 29, 2007
Posts: 1017
Location: hesperia, Ca USA
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 Posted: Tue Jun 23, 2020 8:25 pm Post subject: Trying to figure out gear ratios for a big nut but I'm an idiot. |
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Hello, I'm getting ready to have a big nut rebuilt. I need to know what size 4th and r&p sizes needed for the build. I want to run at 60mph at around 3600rpm. My tire size is 195/70r15. Thanks
I did try searching but I get really confused with gearing.
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Wanted Victoria motors licence plate frame.
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Joey
Samba Member
Joined: August 12, 2005
Posts: 5366
Location: Nova Scotia - Canada
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| Posted: Wed Jun 24, 2020 4:17 am Post subject: Re: Trying to figure out gear ratios for a big nut but I'm an idiot. |
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The formula is:
MPH x final drive ratio x 336 ÷ tire diameter.
Read here for what the 336 number in the formula means.
A stock '66/'67 bus transmission will give you 3545 RPMs at 60 MPH.
The 4th gear is .82 and the r&p is 4.375. The reduction box ratio is 1.26.
.82 x 4.375 x 1.26 = 4.52
4.52 is the final drive ratio.
A 195/70R15 tire is 25.7" in diameter.
Soooooo...
60 x 4.52 x 336 ÷ 25.7 = 3545
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Joey
‘60 Kombi - '74 Bus - '79 Panel - '65 Beetle |
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Dustin B
Samba Member
Joined: March 29, 2007
Posts: 1017
Location: hesperia, Ca USA
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| Posted: Wed Jun 24, 2020 7:50 am Post subject: Re: Trying to figure out gear ratios for a big nut but I'm an idiot. |
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Thank you so much Joey. I appreciate it. I got pretty overwhelmed last night looking and im ordering it today.
_________________
Wanted Victoria motors licence plate frame.
62 og paint L469 type 1
61 og paint L31 DD panel type 2
64 heilite viscount tent trailer
71 sears clamshell trailer
I <3 Brazilian busses
Original paint and patina extravaganza http://www.thesamba.com/vw/forum/viewtopic.php?t=187156 |
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Clara 
Samba Member
Joined: June 14, 2003
Posts: 12401
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| Posted: Wed Jun 24, 2020 8:40 am Post subject: Re: Trying to figure out gear ratios for a big nut but I'm an idiot. |
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| Joey wrote: |
The formula is:
MPH x final drive ratio x 336 ÷ tire diameter.
Read here for what the 336 number in the formula means.
A stock '66/'67 bus transmission will give you 3545 RPMs at 60 MPH.
The 4th gear is .82 and the r&p is 4.375. The reduction box ratio is 1.26.
.82 x 4.375 x 1.26 = 4.52
4.52 is the final drive ratio.
A 195/70R15 tire is 25.7" in diameter.
Soooooo...
60 x 4.52 x 336 ÷ 25.7 = 3545 |
FWIW, That is the gear ratio I've had in my 61 with 1600 sp for over 20 years, about 60K miles.. It is perfectly matched to the engine size IMO.
I've used the 15" rims with 205 75 15 tires. The engine is due for a freshen up now.
Some people suggest higher gearing. My experience is only do that if you are using a bigger motor. Otherwise the engine feels gutless.
If you use a bigger motor with this gearing you just have more acceleration and pull hills better, even with lots of gear in your bus. |
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