What size rear sprocket for racing?

[Guest]

To make sure I have enough clearance at the pivot point on my 80 gs1100 with a Bandit swingarm, I run an 18 tooth countershaft sprocket with a 530 chain. I wanted lower rpm's on the highway so I'm using a 42 tooth rear, works great. However, I drag raced last week & found I was just shifting into 4th about 200 feet before the lights, so obviously I need to go to a larger rear. Any idea what size I would need to at least get me into 5th gear? Maybe 48 or 50?

 

[Steve]

I have no experience with changing sprockets for racing, so will have to give it a mathematical approach until a racer chimes in.

Look up the transmission ratios for third and fifth gears and apply that difference to your current sprocket ratio. Maybe subtract one tooth from the result.

As I understand it, you will want to be approaching redline (or peak power) as you cross the finish line, that should get you close.

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[redstedman]

Properly hooked you may run 124 mph. Try this chart. Gear it for 135 top speed. Now you realize you will be buying another chain s you will need a longer one. Countershaft sprockets are cheaper than rears but I suggest you buy both. You can go too small on the c sprocket and wear out a chain. 14 or 15 teeth, 13 may be too much. You'll end up having multiple set ups. I'm sure the pro dragracers here will set you straight.

http://www.gearingcommander.com/

 

[Guest]

Please re-read my original post. I'm keeping the 18 tooth front sprocket for clearance issues. It's the rear I want to change for racing.

 

[Steve]

Please re-read my reply. Have you bothered to look up your transmission ratios?

Evidently not, since you are still asking, so I looked them up for you. :-\\\

Your third gear ratio is 1.38, your fifth gear ratio is .961, your current rear sprocket has 42 teeth.

If you want to go as fast in fifth gear as you currently do in third, you need a 60 tooth sprocket.

Since performance might improve a bit, and to leave a little bit in reserve, you might want about a 55 tooth sprocket.

Of course, that's 55 teeth, American, not sure what the Canadian equivalent would be.

EDIT: the stock ratio with the 630 chain is 15/42. The equivalent ratio with your 530 would be 18/50,
so the 55-tooth sprocket is about 10% shorter gearing than stock.


.

 

[Guest]

Please re-read my reply. Have you bothered to look up your transmission ratios?

Evidently not, since you are still asking, so I looked them up for you. :-\\\

Your third gear ratio is 1.38, your fifth gear ratio is .961, your current rear sprocket has 42 teeth.

If you want to go as fast in fifth gear as you currently do in third, you need a 60 tooth sprocket.

Since performance might improve a bit, and to leave a little bit in reserve, you might want about a 55 tooth sprocket.

Of course, that's 55 teeth, American, not sure what the Canadian equivalent would be.

EDIT: the stock ratio with the 630 chain is 15/42. The equivalent ratio with your 530 would be 18/50,
so the 55-tooth sprocket is about 10% shorter gearing than stock.


.

Actually, I was referring to redstedman when I said that but thanks for looking it up.

 

[redstedman]

I understand it costs more $. You will still need a longer chain. Why not have multiple gearing options while you are at it?. Do some gear ratio calculations & buy a front sprocket too. Please fill us in on the details & et/mph.