Drive Gear Ratio Help

[DiceCycles]

Sooo.. Im new here.. and thank you all for your help. I am a custom bike builder by profession..but in a completely different end of building .. and I am here seeking some help that pertains only to the XBs...

So were building a completely radical board tracker style bike and were using a 05 Buell Xb12r as the power plant.. The bike is going to have a 26 inch front wheel and a 26 inch rear wheel.. with a single sided swingarm front and back! This is what leads me to your help

The drive ratio is going to be all kinda wrong now.. so i am going to be running a chain instead of the belt..seeing the length is a problem when it comes to a belt.. I am just looking to under drive the sprockets enough to get me back to a stock ratio again. So basically you guys that are familiar changing your sprockets on these buells im sure you know what is base ratio should be in a chain conversion compared to what use to be there for a belt..

Stock tire i believe should be a 180/55/17 (total diameter is 24.8)
New tire size will be a 120/50/26 (total diameter will be 30.7)

1.24 Ratio from old to new

So the difference there is about 20% so thats me loosing 20% of power really.. so the big question isssss what sprockets so i need to basically zero me back to it stock..

Thank you for any help or input you have! (positive/constructive input preferred lol) and sorry if i left out any information you would need.. just ask

 

[mrlogix]

are you asking for the original final drive ratio for stock, or someone to do the math or what exactly. Sounds like you already have the answer (1.24 reduction in drive ratio) ????[confused]

 

[DiceCycles]

Well I do not know what the stock belt cogs would be if they were chain sprockets.. And also if someone knows how to do the math to correct my problem that would also be great...

Is it as easy as trying to subtract that difference from the tranny pulley/rear sprocket ratio?

I guess my question to start with would be what should be the tooth count be on sprockets instead of the cogs for the stock belt for a stock ratio chain set up.. Haha I'm probably over complicating it

 

[mrlogix]

whether you measure pulley diameter, number of teeth or cogs, etc., etc. the drive ratio is the drive ratio. Larger (diameter) tires change the circumference of the driven wheel surface feet per revolution. decrease the final drive ratio equivalently for the travel distance of the new wheel size per revolution. As far as actual sprocket size/ratios, what size sprocket are starting with for the drive sprocket (the one on the trans)? You have to nail down one of the variables to start the equation.

On another note;

I am a custom bike builder by profession..but in a completely different end of building ..

clarify please

 

[DiceCycles]

Ok well I understand the concepts of the teeth vs diameter all being relative and such.. But I do not have an original pulley on the trans or a rear wheel.. And I'm not a buell guy and that's why I'm asking these questions here.. So at the minimum I was asking was if this xb12r was converted to a chain drive what would the tooth count be front and back to replicate a stock ratio.. I just have an engine so I have nothing to go from on my end.. And I build custom Harley Baggers.. That's why I said on the other side of the spectrum..

 

[konarider94]

stock pulleys are 27/65 so with a 24% increase in diameter you would also have to change the ratio by the same amount. assuming you want the same front this would give you a 27/80.6 . Now obviously you cant have a partial number so rounding up it gives you a 27/81 ratio which reduces to 1/3 conveniently. So any multiple of that will work. 25/75 30/90 20/60 I think you get the idea.

If you want to play around with ratios a bit more and target certain speeds at certain rpms check out this site. There is a preset for buells. http://www.cryohold.com/bike/gears.html

Be sure to post up some pictures of the project[up]

 

[user_deleted]

this may also help if you want to consider ratios in relative terms to automotive differentials.
car: divide the tooth count of the pinion gear into the tooth count of the ring gear and gives you final drive ration
example: 45 tooth ring divided by 14 tooth pinion =3.21 final drive gear ratio.

in the cycle world you divide the tooth count of the rear sprocket by the tooth count of the front sprocket for the final drive ratio. works the same for belt pulleys.

 

[DiceCycles]

Hey guys thanks! That's exactly what I was looking for that's teeth for a 530 chain? And I will deff post pix soon.. Just finished powdercoated the engine

 

[mrlogix]

kona- nice link [cool]

 

[konarider94]

Hey guys thanks! That's exactly what I was looking for that's teeth for a 530 chain? And I will deff post pix soon.. Just finished powdercoated the engine

Chain size doesn't change anything with regards to ratio.