Sprocket Changes

[Guest]

So this question is directed at chef1366 and posplayr, but anyone can obviously answer.

Bill is gonna be building my motor with these specifications:

http://www.thegsresources.com/_forum/showpost.php?p=2018105&postcount=9

My question is this: I use my bike as my daily driver/ touring bike. I don't have a car. As such, having better cruising mpg/top speed is more important to me than outright acceleration. I still corner carve. A lot. But I don't put so much emphasis on off the line acceleration. That said, I'd like to get a little bit more top speed and better cruising mileage by getting a different rear sprocket. What size do you recommend? I was looking at http://www.gearingcommander.com/ and it seems pretty cool, but my knowledge of sprocket math is 0. Anyone have a crash course on how to use this utility/have recommendations as to which sprocket/s I should get? Thanks.


-x01660

[Nessism]

Stock sprockets are 15/42 - 2.8 ratio. For more relaxed cruising rpm I'd go the equivalent of one tooth up on the front sprocket - 2.625 ratio.

[x01660]

Stock sprockets are 15/42 - 2.8 ratio. For more relaxed cruising rpm I'd go the equivalent of one tooth up on the front sprocket - 2.625 ratio.

I'm not sure. According to gearingcommander, its 15/42. And I do have the stock setup. The motor is an 83 1100 motor. So I think that's about right. Now if I do go one up on the front sprocket, how much will that kill my off the line acceleration?


-x01660

[tkent02]

I'd wait until the new engine is there and then ride it a bit before deciding. It might be quite a bit different than you are imagining.

What sprockets do the 1150s come with? That might be a good starting point.

[x01660]

I'd wait until the new engine is there and then ride it a bit before deciding. It might be quite a bit different than you are imagining.

What sprockets do the 1150s come with? That might be a good starting point.

hmmm... This is true.... So I guess the next logical question would be how much of a difference in oomph is there between the 1100 motor and the 1150 motor? I am asking for a subjective, set of the pants type of evaluation. Again, my main concern is mileage. I intend on going on long road trips, and I'd like to be able to cruise at 80 turning a low RPM...


-x01660

[tkent02]

Why the low RPM? Lugging is not conducive to good fuel efficiency.

[x01660]

Why the low RPM? Lugging is not conducive to good fuel efficiency.

Lower RPM, sorry. I figure I'd like to be at about 3K-4K RPM in 5th @ 80-85. You'll have to excuse my ignorance. I'm really unfamiliar with bike specifics... I'm still used to the RPMS on OHV V8's... Where you wanna turn 2.5k-3k for efficiency, lol...


-x01660

[tkent02]

Not so with bikes. MPG is much more dependant on speed than RPM. The RPM which will do the speed with the least open throttle is close to the most efficient, it is not a low RPM.

[tkent02]

I have an 800 with a gas mileage readout. At any given speed it doesn't really matter what gear you are in, until the RPM gets up around 7,000 RPM or more. Chugging under 4,000 is as bad as over 7,000. Going 70 - 80, third gear would be about the same mpg as sixth. Fifth woud probably be the best, but only sightly different. Going 50 mph, third would probably use the least fuel. 6th would be bad.

It is very much different than cars.

[posplayr]

530 gearing with dual range.

[storm 64]

Correct me if I'm wrong. But miles per gallon/fuel efficiency comes from aerodynamics, rolling resistance, proper air/fuel mixture. Changing your engine rpm will not necessarily change your mpg. You need X amount of horse power to go X miles per hour. Just a little food for thought.

[tkent02]

Exactly .

[x01660]

Correct me if I'm wrong. But miles per gallon/fuel efficiency comes from aerodynamics, rolling resistance, proper air/fuel mixture. Changing your engine rpm will not necessarily change your mpg. You need X amount of horse power to go X miles per hour. Just a little food for thought.

And it just hit me that the reason that cars are different is because they ALL have the HP to go X miles an hour, so the lower the RPM, the more fuel efficient they'll be.... Or am I off point here?


-x01660

[tkent02]

Cars have about the same wind resistance as bikes, five or six times the weight, bigger engines designed to be efficient at low RPM. Bike engines are mostly designed to make the most power at max RPM, or to sound cool at low RPM.

Everything is different.

[chuck hahn]

And remember the larger circumference of the sprockets gonna add 2 or 3 links to the needed chain length. Stock is like 96 so I would get a 100 and grind off a link if need be.