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Need help with chain drive ratio.


Post Wed Apr 01, 2009 10:27 pm

Posts: 92
Location: Taos, New Mexico

First time chain drive user, running cut 44 Boggers on rear with 7.16 ratio and 35 cut Hawgs on front with 4.10 ratio. Have a 15 tooth drive gear on the output shaft and want to overdrive the front diff about 10 mph. How many teeth on the driven side of the chain drive? Thanks in advance.
Norbert Mondragon
(575) 770-7144
www.batcaveracing.com
NMMRA

Post Wed Apr 01, 2009 10:38 pm

Posts: 212
You need to first get the rollout of the tires on rims aired up.
Harry Mulnix
Prostock/outlaw prostock
MRA#112
www.thundershockmudracing.com

Post Wed Apr 01, 2009 10:41 pm

Posts: 212
I think you will need about a 18 or 19 tooth sprocket
Harry Mulnix
Prostock/outlaw prostock
MRA#112
www.thundershockmudracing.com

Post Wed Apr 01, 2009 11:10 pm

Posts: 92
Location: Taos, New Mexico

thundershock wrote:
You need to first get the rollout of the tires on rims aired up.
I can get that on unloaded tires, I guess that would be close enough. Will post tomorrow late after getting back from race shop.
Norbert Mondragon
(575) 770-7144
www.batcaveracing.com
NMMRA

Post Fri Apr 03, 2009 12:23 am

Posts: 92
Location: Taos, New Mexico

rollout on the rear tires is 135" with 7.16 ratio and 100" on front tires with 4.10 ratio.
Norbert Mondragon
(575) 770-7144
www.batcaveracing.com
NMMRA

Post Fri Apr 03, 2009 3:24 am

Posts: 719
Location: Warsaw IN
Norbert,
I am not sure where you want to end up with your chaindrive, but you are 29% overspun now, if it were straight up.
I would suggest the 5% - 8% is where you want to be. I hope this helps. Somebody else can tell you how to calculate what gear will get you there.
Brian Erne
Warsaw IN
MRA # 100
NMRO # 1456
574-268-7763
theernes@comcast.net

Post Fri Apr 03, 2009 5:42 am

Posts: 209
rollout on the rear tires is 135" with 7.16 ratio and 100" on front tires with 4.10 ratio




if you run 1:1 on the chain and use 4.88's in the front it will be about 4mph over

or a 19t bottom gear with 4.10's will give you about 2mph over

or a 18t Bottom gear with 4.10's will also give you 4 over...
Brent Foster
MRA Pro Stock
304-312-9283

Post Fri Apr 03, 2009 5:45 am

Posts: 209
a 16t bottom gear will give you your full 10, but I'm not so sure your going to like 10 over.
Brent Foster
MRA Pro Stock
304-312-9283

Post Fri Apr 03, 2009 4:03 pm

Posts: 1167
A friend told me how to do this a few years ago. Hope I remembered it right.

To find what gear / sprocket you will need try the following.

You will need to know the (1) roll out of the front tire. (2) roll out of the rear tire. (3) rear gear ratio. (You can use tire diameter - but roll out of the tire on the vehicle is best).

To find out what front gear ratio you need. (front tire dia. X rear gear ratio) divided by the rear tire dia. = front gear needed.
(example using tire Dia.) (35” (front tire Dia.) x 7.16 rear gear) /44”rear tire Dia. = 5.69 front gear. (35 x 7.16 = 250.6 / 44 = 5.695).

OR using roll out (109.9” x 7.16) / 138.16 = 5.648 front gear ratio needed. (if available for that front axle) - You would want a ratio as close as possible to that number. That does not mean you can swap in a 5.29 and make it work -it won’t.

To find what sprocket size is needed - You already know from the formula above you need a 5.64 gear set for the front. You already know you have a 4.10 gear set in the front. So - take the front gear ratio you need and divide it by the gear ratio you have (I.e.) 5.64/ 4.10 = 1.37 sprocket ratio. (If the number is more then 1 the big gear goes on the front or driven side. If the number is smaller then 1(i.e .87) the smaller gear would go on the driven side.

15 (tooth) drive sprocket (trans) X 1.37 (sprocket ratio) = 20.55 or for an overdrive number (20.55 x the % you want = number of teeth to subtract from the 20.55). (I.e.) 20.55 x 8% (overdrive) = 1.64 Then 20.55 -1.64 = 18.91 or 19 tooth would give you around a 8% overdrive to the front - if that is what you would like.

I hope that helps - it’s been a while and sometimes I get the sprocket positions backwards - but I think I have it right.
Last edited by traveler on Fri Apr 03, 2009 10:55 pm, edited 1 time in total.

Post Fri Apr 03, 2009 6:05 pm

Posts: 180
Norbert,

Put on a 20 tooth sprocket to slow down the front,
you will have 6% overdrive to the front end.
Back tires @ 100 mph Ft @ 106

a 19 tooth will give you 13% overdrive to the front,
back tires @ 100 mph ft @ 113
Gary Baker 865-856-0510
MRA, PROBADD
POWER PRO RACING PRODUCTS
http://powerproracingproducts.com/
http://www.probadd.com/
GaryBaker@PROBADD.COM

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