Confused about gearing

[black5]

I fitted a 15 tooth front sprocket to my DRZ last night.

The chain & rear sprocket are part worn and I had a 14 tooth front on it (that was knackered).

The 15 is temporary as I wanted to see what gearing would be best to buy.

Now I went for a ride after fitting it and it didn't feel much different. Top end might have been slightly more (about 3 mph), but acceleration seemed just as swift (if not quiker). The only thing I can think is different is that the chain is correctly adjusted now.

What should have adding 1 tooth to the fronthave done to the acceleration / speed etc?

BTW I didn't count the rear teeth, but guess it is a standard sprocket.

[s7paul]

In general, adding 1 tooth to the front sprocket should marginally take the edge off acceleration, but if the bike is fairly low geared anyway it may not be that noticeable. It may allow a higher top speed, but only if the engine has enough power at the top end of the rev range to pull the higher gearing. If it feels OK to you, there would be no harm in leaving it as is. You may also see a slight improvement in fuel consumption (if you're bothered about such things!).

[chilli]

As I understand it, dropping teeth on the front and adding to the rear will result in faster acceleration, but this has a negative impact on top speed.

Am I right people?

[black-k1]

Moving from a 14 to 15 tooth front will increase the gearing but only by about 8%. This should reduce acceleration by reducing the revs for any given gear at any given speed. May also slightly increase top speed IF your bike can red line in top.

All of this is theory but occasionally practice can be different. Increasing the overall gearing may have allowed you to “hold gears for longer” during the bits of acceleration you actually use on a regular basis. It may also mean that in the lower gears you are now able to get the throttle fully open before the requirement to change up where, with lower gearing, this would have caused the front wheel to lift.

Either way, you are only talking about an 8% change so whatever happens, it’s not going to be dramatic.

[black5]

So when I change the C&S I want more low down acceleration. I don't mind loss of top end. 90mph is more than enough. Geared to 75-80mph would be find.

I use the bike (Drz400) both off road and commuting. On my commute I only every get above 60mph for about 5 miles (of 25) and am more concerned about off road ability.

So I guess it will be a 14 front and a lower tooth rear (than I have).

Is there a way of working out what the top end will be? And poss the difference in acceleration?

[black-k1]

black5 said:

So when I change the C&S I want more low down acceleration. I don't mind loss of top end. 90mph is more than enough. Geared to 75-80mph would be find.

I use the bike (Drz400) both off road and commuting. On my commute I only every get above 60mph for about 5 miles (of 25) and am more concerned about off road ability.

So I guess it will be a 14 front and a lower tooth rear (than I have).

Is there a way of working out what the top end will be? And poss the difference in acceleration?

Note that to lower the gearing you can either reduce the number of teeth on the front or increase the number of teeth on the back. As the back sprocket has more teeth the addition of an extra tooth will have less impact than the removal of 1 tooth on the front.

If your speedo is driven from the gearbox then remember that changing the gearing mean that the speedo is wrong. (Reduce the gearing and the speedo will be even more optimistic!) Likewise, you may also have a slight impact on fuel consumption. Reducing the gearing will tend to mean you use slightly more fuel.

Top speed calculations will all depend on you being able to hit max revs in top gear. The higher the gearing the less likely that will be! If you assume you can always reach max revs in top then adding the tooth to the front will increase top speed from 90 to about 97 (8% increase) where reducing the front to 13 teeth would give a top speed of about 83 (8% decrease).

[hobo]

chilli said:

As I understand it, dropping teeth on the front and adding to the rear will result in faster acceleration, but this has a negative impact on top speed.

Am I right people?

Basically YES.