TOPIC:

Hello everyone, My old 750 4cylinders has a 13-33 sprocket (original).. I want to down low my Rpm at 100km/h and more…  does 14-33 or 13-30 seems to be a good compromise?! What are you suggest me to not lose my low Torque.. and does the 14 teeths can fit with the stock 630 chain without cutting the engine case !!!!!?? Thank you so much 

What is the current rpm's at that km/h? How much lower do you want rpm's to be? With a little math you can find what final ratio would drop it to where you want it. 

For example; lets say your bike cruises at 100 km/h / 4,000 rpm and has a final drive ratio of (33/13) = 2.54:1 - if you change to 33/14 = 2.36:1 or if change to 30/13 = 2.31:1 
Divide your current rpm at that km/h with the current final ratio.  Then multiply by the new ratio to get how much drop in rpm it will produce.
4000/2.54 = 1575  
1575 x 2.36 = 3715 rpm
1575 x 2.31 = 3638 rpm




 

Thank you.. I have difficulty to count that..  In my memory, the rpm was 6000 at 100km/h!!  My ratio in the manual says 2:53 

Maxbou92 wrote:

Thank you.. I have difficulty to count that..  In my memory, the rpm was 6000 at 100km/h!!  My ratio in the manual says 2:53 

6000rpm seem's high for 100kmh (62.5mph) so on that basis at 9000rpm it would max out at 150kmh (93.75mph) assuming it could pull the revs in top gear - is that all the 750's are good for ? 

Yes I know thats high.. im pretty sure that the rpm at 100km looks like that..  I don’t really understand the rpm calculations 

Have you counted the teeth on both the front and rear sprockets?  Or are you obtaining the 13/33 count from the manual?  It is not unusual for previous owners to change sprocket ratios.  You always want to confirm what is on the bike before changing ratios.

Yes they are 13/33 sprockets!!!
 

If you have the original sprockets and chain, you might want to upgrade to modern 530 parts.  They are better than the old 630 stuff in almost every way.

Can you tell me why the 530 are better than 630 parts ?

Lighter, smoother power transmission, from the smaller space between rollers, quieter, and a modern 530 chain will be far more durable than the old 40 year old 630.

All right, and what lenght I need if my 630 is 120 links?! Same thing ?

Are you sure your 630 chain have 120 links or do you have a extended swing arm?!

rbracing-rsr.com/chainlength.html offers a chain length calculator.