Gearing with Grudgebox?

[Nastytls]

If you want to maintain near stock final gearing, what rear sprocket size would you use on an M8 FLH chain conversion?

[kd]

If you go to the Big Boyz drive train calculator you can enter the OEM ratio and any available options from the assorted chain drive sources.  That way you can choose a ratio close to OEM "or" one that may suit your riding circumstances better than OEM. One of the advantages of chain conversions is the ability to quick change the rear sprocket for local or touring, two up and loaded or solo fun riding.  I have 4 ratios to do just that.  Presently I am stuck on the fun ratio. 


http://www.bigboyzheadporting.com/Gearratio.htm

[Ohio HD]

So easy even a cave man can do it.......


Stock
(46/34)*(68/32) = 2.875


Stock with GB
(46/34)*(68/32)*0.92 = 2.645


Chain drive with GB
(46/34)*(55/24)*0.92 = 2.852


Chain drive with GB
(46/34)*(56/24)*0.92 = 2.904


You can get just above it, or just below it.

[rigidthumper]

RB racing offers a 26 tooth transmission sprocket, so there's another option.

[kd]

RB racing offers a 26 tooth transmission sprocket, so there's another option.

We discussed that option in earlier threads.  There is a risk of damage due to the extra sprocket diameter for contact to the inner primary chain case if the chain adjustment is too loose.  Centrifugal force lifts the chain and increases the working circle it runs in as speed increases. I used to experience it with my earlier bike.  Loading and suspension sag can do something similar on bumps and road heaves.  That isn't to say you can't do it.  It's just too iffy for me after having to replace a near unobtainable 66 to 69 inner chain case.  (I welded it and the starter housing instead and dropped a couple of teeth on the trans sprocket before reassembling.  )

[Nastytls]

Great, thank you!

[Nastytls]

Most of the chain drive kits say "at least" 120 link chain. Does that leave you with enough room for adjustment, or should I buy a larger chain and cut it down? If 120 is truly enough to have adequate adjustment, I'd rather go that way, because it's a lot more for a 150 link and that's a lot to cut off and throw away.

[scotman623]

120 definitely works for stock gearing or going up in the rear sprocket...