How to figure out sprocket size/chain drive

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How to figure out sprocket size/chain drive

Postby AFRd_CJ5 » Mon May 23, 2011 4:36 pm

Ok, here's my issue......
Changed dad to a chain drive last year. His gearing was 5.13 rear and 4.88 in the front. We ran a 23 tooth sprocket at both ends because we wanted the gears staggered. Running 32x14 scoops in the rear, and 14.50 DT's in the front. Putting a 9" rear in and going to a 5.43 gear.
So....how do I figure out my sprocket I need so I can get the staggered gearing so it's the same as it was with the 5.13/4.88? How do you figure out the tooth count?
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Re: How to figure out sprocket size/chain drive

Postby JustaJeepII » Mon May 23, 2011 6:22 pm

Excel spreadsheet, compliments of Mike Ellington.

Let me know your email address and I'll send you a copy.
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Re: How to figure out sprocket size/chain drive

Postby sandaltered » Mon May 23, 2011 9:42 pm

I'm on a business trip. I don't have my personal laptop with me. I may have the spreadsheet on here, but I'll have to look.

Remember, you want your tires to travel the same distance. So if you have shorter tires in front, it's going to take a little more revolution to go the same distance than the rear. Remember from Math Class: Circ = Pi * Dia.

You're much better off to measure the rollout (circumference of your tire). Set it to your running pressure and measure around the tire with a sewing tape. Just saying it's a 32 is kinda meaningless. Since that is just the printed size of the tire.

If you can give me the exact rollouts of your tires I'll figure it out.

It's funny, a group of us were just talking about this on Saturday night.
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Re: How to figure out sprocket size/chain drive

Postby Inkahoots » Tue May 24, 2011 12:25 pm

Send me your Email and when I get home I will send it to you.

Guy
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Re: How to figure out sprocket size/chain drive

Postby AFRd_CJ5 » Thu May 26, 2011 5:36 am

Thanks guys! I'll get some information out later today hopefully. Been trying to get mine back together!
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Re: How to figure out sprocket size/chain drive

Postby sandaltered » Thu May 26, 2011 6:45 am

AFRd_CJ5 wrote:Ok, here's my issue......
Changed dad to a chain drive last year. His gearing was 5.13 rear and 4.88 in the front. We ran a 23 tooth sprocket at both ends because we wanted the gears staggered. Running 32x14 scoops in the rear, and 14.50 DT's in the front. Putting a 9" rear in and going to a 5.43 gear.
So....how do I figure out my sprocket I need so I can get the staggered gearing so it's the same as it was with the 5.13/4.88? How do you figure out the tooth count?


OK, I have a second. This is purely and example since I don't know the rollouts of your tires.

Rear Tire Rollout / Rear Gear = Front Tire Rollout / X
or Reararranged: X = (Front Tire Rollout*Rear Gear) / Rear Tire Rollout

X = Needed front gear Ratio. So if you have a 4.88 and you need a 5.13 you need to slow down the front. That would be a gear ratio for the chain drive of: 5.13/4.88 = 1.05

So in your case you would need a 1.05 Chain Drive Ratio. So if you have a 23 sprocket at the trans you would need a 24 on the front driveshaft. (24 / 23) = 1.04 That would make you about 1% overdriven on the front. Always be a little overdriven so you don't end up in big trouble in the shutdown area.

Hopefully everybody else that figures these agrees with me.
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Re: How to figure out sprocket size/chain drive

Postby AFRd_CJ5 » Sun Jul 03, 2011 2:28 pm

Thanks a ton for sandaltered for helping me get this figured out!! Everything is working now!
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Re: How to figure out sprocket size/chain drive

Postby sandaltered » Tue Jul 05, 2011 10:41 am

Glad I could help. :D Hope it's running good.
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Re: How to figure out sprocket size/chain drive

Postby hayshakerracing » Tue Aug 12, 2014 8:45 pm

Going to bring back an old thread here and hope to get some help. With my numbers by Mikes math I get 0.99 sprocket offset

Rear tire is 119.75 rear gear 6.17
Front tire 97 front 3.73
I have a 16 tooth sprocket on trans.

My math says to run a 16 tooth on front drive as well. Anyone care to add this up for me to have another view on it? If I am correct on the .99 is that close enough to 0 to not be under driven on the front? From my math the exact number I got was actually .997........ so that'd pretty much be 1?...

Am I correct that anything greater than 1 is over and anything less than .99 is under driven?

Edit: after posting I re-did the math again and I come up with needing a 17 tooth front "driven" sprocket to work with the 16 tooth "drive" gear. And I think this would be rather close to 0% under or over driven
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Re: How to figure out sprocket size/chain drive

Postby sandaltered » Wed Aug 13, 2014 4:27 pm

hayshakerracing wrote:Going to bring back an old thread here and hope to get some help. With my numbers by Mikes math I get 0.99 sprocket offset

Rear tire is 119.75 rear gear 6.17
Front tire 97 front 3.73
I have a 16 tooth sprocket on trans.

My math says to run a 16 tooth on front drive as well. Anyone care to add this up for me to have another view on it? If I am correct on the .99 is that close enough to 0 to not be under driven on the front? From my math the exact number I got was actually .997........ so that'd pretty much be 1?...

Am I correct that anything greater than 1 is over and anything less than .99 is under driven?

Edit: after posting I re-did the math again and I come up with needing a 17 tooth front "driven" sprocket to work with the 16 tooth "drive" gear. And I think this would be rather close to 0% under or over driven


Kyle,

I did the math and do not come up with 16 or 17.

(97*6.17) / 119.75 = 4.99 -----> That means you need a 5.00 gear in the front end if you were 1:1 at the chain drive. Since you have a 3.73 you need to slow down the front end with a different sprocket. Therefore you need a 5.00 / 3.73 = 1.3399 Chain Drive Ratio to be at 0% overdrive. So that would be a 16*1.3399 = 21.43. So if you put a 21 on the driven sprocket you would be 2% overdriven. So that seems pretty good.

I think I did it right. I did it with my spreadsheet and I did it by hand. Maybe people who actually race a 4WD can back me up. :lol:
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