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Lowering 5th gear RPM's?

NCBILL

NCBILL

Active Member
Howdy All, .... I have an 06 Sportster, all stock. The rear mag wheel is the solid aluminum one, and 16". I recently purchased a set of spoke mag wheels that came off of an 06 Dyna (because I hate laced spokes and not being able to plug a flat tire and keep going on my way without having to be picked up for repairs). The rear mag wheel from the Dyna is a 17" wheel, with a 66 tooth belt sprocket. My intent is to lower the RPM's in 5th gear, and, I know the extra 1" taller wheel will do that to some degree. My question is, will keeping the 66 tooth sprocket on the rear 17" Dyna wheel also reduce RPM's even more than swapping out the stock rear sprocket (no idea how many teeth are on it) from my stock Sportster set-up? Thanks in advance for pointing me in the right direction.
 
If only things were that simple. Without me cross referencing parts comparability, some things you need to look at before proceeding. In no particular order: A 17" diameter wheel does not necessarily mean a taller tire. Does the rear Dyna pulley use the same width belt as your XL (aside from being on the opposite side)? Is the overall width of the wheel compatible with yours? More than a couple of teeth difference on rear pulley, may require a different belt length. I'm not pooh poohing your post, I just want you to be aware of the po$$ible roadblock$ you may face. Let us know how/what happens.
 
If the wheels came with tyres you will need to re mount the rear tyre to rotate in the correct direction
As Pete said a 17" wheel does not necessarily travel further in one rotation that depends on the profile of the tyre as a low profile tyre on a 17" wheel may travel less per rotation than a high profile tyre on a 16" wheel
If the 17" wheel is wider than stock 16" there may be alinement issues with everything

Brian
 
The wheels came with no tires on them, new take-offs when it was purchased by the original owner. My plan is to install a 160/80-17 tire. The measurements work out that shows me being left with 7/8" clearance on both sides of the rear fender. The original rear sprocket on my Sportster looks to match up with the one on the Dyna, and, it "appears" that I have enough "travel" to push the new set-up rearwards, if needed. I'll keep the board updated on my progress and final outcome. I know from prior ownership of a 1999 Honda Shadow VT1100T, that when I installed a car tire on the rear wheel, it brought my final RPM's down by 450 when running in 5th gear at 60 m.p.h. Hoping for the same results, or better. Got 38,000 miles of use out of that rear tire alone.
 
You never said if the Sporty was a 1200 or 883; primary and secondary drives could be different depending on the model. However, all things being equal, the basic change is a 66T wheel pulley in lieu of a 68; I think. Not sure of wheel tire diameter as mentioned in previous but if the tire is truly 1" taller, it will make a difference. I think you can expect about 100 rpm drop at cruise in 5th from the pulley change and, if the new wheel tire assembly is truly 1" taller, another 100 rpm drop. All within some margin of error but I wouldn't expect a total drop of more than 250rpms, probably a bit less.

A two tooth change, up or down, in sprocket size, trans or wheel can make belt fitment an issue by not having enough forward or rearward movement to put proper tension on the belt. Some get away with it, some don't. Good luck, let us know how it turns out.;)

DISCLAIMER: Not a Sporty guy. All comments above based on experience with TCs. I could not ride my bikes the way I do with a car tire. I remember a few years back when that trend was labeled " the dark side". It passed but obviously, there are still a few that like car tires on a motorcycle.:confused:
 
Since my last posting, I have made a paint-stick mark on the Sporty belt drive, and, after counting twice, spinning the wheel each time, I find that you are correct in it being a 2 tooth difference in the sprockets. Every little bit of RPM reduction matters to me, mostly because I end up knowing the motor isn't working as hard. The car tire I installed on the Honda was an "Austone Taxi Tire", purchased from E-bay. It worked out really well, had plenty of traction, and was never "squirrely" or anything far from normal feeling. I can only go by the 50+ years of bike riding I've accumulated over the years. Hope I'll still be riding 10 years from now, when I'm 75. :>)
 
As dolt said 200 maybe 250 RPM'S ,for me this isn't a big enough difference to warrant the size and expense of the job.

With that little of drop your engine will never know the difference. JMHO.
 
As I am still on old bikes my speedo works from the front wheel on all 3 bikes but on the later ones is it not driven from the gearbox with a sensor if so then the speedo may give a false reading

Brian
 
NCBILL said:
Being old and bored, it gives me something to tinker with. Recliners and rocking chairs don't excite me.
Click to expand...

You kinda sound like me. I just wanted to point out how little difference it's going to make.
Good luck and keep us updated on your results.
 
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