Topic: sprocket ratios

[petercb750]

greetings from down under.
My head is starting to spin trying to work this out.  When I bought my 750K2 it had 17/47 front/rear sprockets. I'm putting new ones on (and new chain) and am going for the standard 18/48. What can I expect this to do to the ride? Will upping each sprocket by one tooth have no noticeable effect, as opposed to just upping one or the other? Is there a formula or calculation that you can do to work out what difference changing sprocket sizes will make to acceleration/top speed. I'm running standard transmission and wheel sizes etc.
Thanks in advance........
Peter.

[cb650]

Bigger front will lower rpms at any given speed but the bigger rear will raise rpms but not as much.
Generally 3 rear teeth are equal to 1 front. 
In your case it will lower rpm some.




             Terry

[cb(r)]

hopefully this is not in the realm of thread hijacking but this was the general question I was going to ask.  I was just told this weekend that for every 5 teeth you go up it was equal to one tooth down.  thought I would see if that was correct.  anyone?

[Jeff.Saunders]

It's fairly easy to calculate the impact - divide the rear teeth by the front teeth to get the ratios

17/47 = 2.765:1 ratio
18/48 = 2.667:1 ratio

Then is you take a given speed and rpm - say your bike cruises at 4500 at 65mph - divide the rpm by the old ratio and multiple by the new.

In this case:
4500 divided by 2.765 and multiplied by 2.667 = 4340 rpm - a small, but noticeable change - you would loose a small amount of acceleration, but gain on cruising.

[ofreen]

greetings from down under.
My head is starting to spin trying to work this out.  When I bought my 750K2 it had 17/47 front/rear sprockets. I'm putting new ones on (and new chain) and am going for the standard 18/48. What can I expect this to do to the ride? Will upping each sprocket by one tooth have no noticeable effect, as opposed to just upping one or the other? Is there a formula or calculation that you can do to work out what difference changing sprocket sizes will make to acceleration/top speed. I'm running standard transmission and wheel sizes etc.
Thanks in advance........
Peter.

It is a ratio, just as your topic title says.  A 47/17 combination gives you a 2.764 to 1 ratio (rounded off).  A 48/18 is 2.666 to 1.  That is roughly about a 3.5 percent difference.  At any given speed and gear with the 48/18 combo will give you about 3.5 percent lower RPM than the 47/17 combo.

[Sam Green Racing]

18/48 will gear the bike up to 2.66, you will cruise at a given speed for less revs.

if you want it to be as near as it was, you need to go 18/50 2.77 to 1 instead of your old set up of 17/47 2.76 to 1.

Sam.

[petercb750]

Thanks guys for all your help and responses  Good info and all makes sense.

Peter.

[eldar]

You could also do a 17/46 or 17/48
Dont need to do the 18 unless you really want to.