Ping: Blattus Slafaly

 

In response to my questions about the Yamaha TW200, on August 5 you
wrote: I have a TW200 and love it. Nice fat tires for sand and swamps.
I change the chain sprockets for better highway speeds. I get 100 to
120 miles per gallon if that interests you.
Blattus Slafaly

++A couple of questions about the sprocket change.

++What is the size/part number of the stock sprocket and what is the
size/part number of the one you put on your TW200?

++Did the sprocket change affect acceleration from a dead stop much?

++Did it increase your top speed?  To what figure?

++At what speed do you usually ride to get the great MPG figure you
mentioned?

++Sorry for all the questions but I'm new at this and if I go the
TW200 route (which I'm about 75% certain I will), 75% of the use will
be on-road and the sprocket change sounds like a good move.  Thanks
for any info you can provide.

++Bill

 

:


We discussed all this business of changing rear sprockets extensively
about a year ago, when another guy who kept changing his handle was
asking similar question.

He thought that the red marker on the speedo that indicated 55 mph was
some kind of red line.

Anyway, I pointed out that the TW200's transmission had increasingly
close ratios in the upper gears.

Motorcycle engineers will do that when the engine doesn't have much
power.

Most riders want to go the other way, they want to put a smaller front
sprocket or larger rear sprocket on the bike fore better acceleration.

The strategy is to calculate the percentage of RPM drop when shifting
from
4th into 5th gear, and then divide that in half when determing what
new sprockets you need.

The best compromise is to raise the overall gear ratio about 7.5% to
avoid having a situation where 5th gear becomes about the same as the
original 4th gear.

By the same token, when reducing the gearing for more top speed (or
putative fuel economy) you don't want to come out with a 5th gear that
acts like it's 7th gear, you will always be downshifting for every
slight grade or head wind.

Here are some links you may find helpful:

http://www.totalmotorcycle.com/photos/2006models/2006models-Yamaha-TW200.ht=
m

http://www.650ccnd.com/calc.htm

Just plug the TW200's gear ratios and tire size into the calculator
and work out what you think you need.

 



They'll also do it when a bike has lots of power but a very narrow power
band. Or just to keep a supersports engine on the boil.


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