30t rear trans + 70t rear sprocket on 07 bob... PLS ADVISE.
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Joined: Apr 2010
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From: Fort Worth, TX
30t rear trans + 70t rear sprocket on 07 bob... PLS ADVISE.
Hey, been reading threads (at least 30) and can't find much info on the double swap. My year has a 66t stock. Already have a 30t front sitting here. If I change both at once (im assuming) the overall belt length stays the same and I get around 16% more power.
Im pretty new to power pully's, so if im wrong let me know. Also, anybody whose done this please post. I'd love to get nice wheelies in 2nd and third.
HeltS
Im pretty new to power pully's, so if im wrong let me know. Also, anybody whose done this please post. I'd love to get nice wheelies in 2nd and third.
HeltS
Ultimate HDF Member
Joined: May 2008
Posts: 6,642
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From: Ogden, UT
First off it will not increase power, it will wind up through the RPMs faster making you shift quicker than you currently have to shift.
It will give you roughly 16-20% higher RPMs than a stock 32/66 setup.
It is possible you can keep the stock belt, but I doubt it with a 4 tooth change on the rear.
Each tooth change on the rear means about 1/8" change in the position of the rear axle, so 4 tooth means it should move about 1/2", if you can move that far and still have room for adjustment, then you may be OK.
It will give you roughly 16-20% higher RPMs than a stock 32/66 setup.
It is possible you can keep the stock belt, but I doubt it with a 4 tooth change on the rear.
Each tooth change on the rear means about 1/8" change in the position of the rear axle, so 4 tooth means it should move about 1/2", if you can move that far and still have room for adjustment, then you may be OK.
Thread Starter
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Advanced
Joined: Apr 2010
Posts: 94
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From: Fort Worth, TX
First off it will not increase power, it will wind up through the RPMs faster making you shift quicker than you currently have to shift.
It will give you roughly 16-20% higher RPMs than a stock 32/66 setup.
It is possible you can keep the stock belt, but I doubt it with a 4 tooth change on the rear.
Each tooth change on the rear means about 1/8" change in the position of the rear axle, so 4 tooth means it should move about 1/2", if you can move that far and still have room for adjustment, then you may be OK.
It will give you roughly 16-20% higher RPMs than a stock 32/66 setup.
It is possible you can keep the stock belt, but I doubt it with a 4 tooth change on the rear.
Each tooth change on the rear means about 1/8" change in the position of the rear axle, so 4 tooth means it should move about 1/2", if you can move that far and still have room for adjustment, then you may be OK.
Thanks for the reply.
The 30t I have here is 2 down in the front. A 70 would be 4 up in the back. combined, if I understand correctly the difference would offset each other.
As far as more power, if the bike has less to pull against (say the usable power band is 15% smaller) the rider will feel the bike has more power. With the same amount of motor, less to pull against = quicker throttle response.
Anybody else have some experience with this mod?
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Joined: May 2008
Posts: 6,642
Likes: 48
From: Ogden, UT
Thanks for the reply.
The 30t I have here is 2 down in the front. A 70 would be 4 up in the back. combined, if I understand correctly the difference would offset each other.
As far as more power, if the bike has less to pull against (say the usable power band is 15% smaller) the rider will feel the bike has more power. With the same amount of motor, less to pull against = quicker throttle response.
Anybody else have some experience with this mod?
The 30t I have here is 2 down in the front. A 70 would be 4 up in the back. combined, if I understand correctly the difference would offset each other.
As far as more power, if the bike has less to pull against (say the usable power band is 15% smaller) the rider will feel the bike has more power. With the same amount of motor, less to pull against = quicker throttle response.
Anybody else have some experience with this mod?
Yes it will feel like more torque, but that does not mean you have more power, you have the same power, it will just go through the gears faster.
I have played with pulleys and sprockets and currently run a 31 tooth up front, for a 5 speed it is a great compromise.
The difference you felt between a 32 and 30 Roth up front is almost identical to the difference between a 66 and 70 tooth in back.
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Joined: May 2010
Posts: 4,356
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From: san diego
First off it will not increase power, it will wind up through the RPMs faster making you shift quicker than you currently have to shift.
It will give you roughly 16-20% higher RPMs than a stock 32/66 setup.
It is possible you can keep the stock belt, but I doubt it with a 4 tooth change on the rear.
Each tooth change on the rear means about 1/8" change in the position of the rear axle, so 4 tooth means it should move about 1/2", if you can move that far and still have room for adjustment, then you may be OK.
It will give you roughly 16-20% higher RPMs than a stock 32/66 setup.
It is possible you can keep the stock belt, but I doubt it with a 4 tooth change on the rear.
Each tooth change on the rear means about 1/8" change in the position of the rear axle, so 4 tooth means it should move about 1/2", if you can move that far and still have room for adjustment, then you may be OK.
why do sportbike riders add tons of teeth dropping there top end mph, to gain the ability to wheelie when ever.
I am also interested in what a larger rear pully would actually do
take a gander of this page
http://www.thrustcompany.com/
Club Member
Joined: Jun 2007
Posts: 45,429
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From: Bedford UK
The change in gearing HeLtErSKeLtER refers to will increase torque at the rear wheel by about 13%, which is well worth doing. I changed the compensator on my TC88 Dyna from 25T to 21T, which gave increased torque of 19%, which is dramatic! Unfortunately TC96 owners can't make such big changes.
Ultimate HDF Member
Joined: May 2008
Posts: 6,642
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From: Ogden, UT
Read what I posted, I didn't say it doesn't do anything.
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From: Ashland Ore.
I have that on my bike. I used belt PN 40046-07 It definitely gears it down a bit. It rips off the line. It does throw your speedo off quite a bit too. I have a TTS Mastertune and calibrated my speedo with that.
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Road Master
Joined: Jun 2009
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From: Odessa Mo
More power = NO. More Torque = NO. More usable power lower in the RPM's = Yes. Lower Top end Speed = yes. FWIW I have a 09 bob, it also had the 32/66 combo. I added a 30t last year and it was well worth the expense. My bike was much more managable on the highway and around town, love it. I Do plan to ad a 70t rear sometime next year, Im going to put it on when I have to replace my tires/rotors/brakes. For what its worth I am 99% sure you can do the 30t and the 70t without changing belts....with the 30t and a 66 rear I am adjusted all the way out. There is a full 1" to 1 1/4" adjustment. The one down side is your speedo is going to be 3-5 mph off on the slow side....70 ='s 66 now. The rear pully shouldn't change the speed anymore, also I tach around 28-2900 @ 70. All in all it is WELL worth the time/money.
Last edited by jshull; Nov 12, 2011 at 06:18 PM.