FAQ: Gear ratios and sprocket selection
 

Question:
How do I determine the gear ratio based on my front and rear sprockets?
What sprockets do I use for more torque and better acceleration?
I want more top speed... what sprockets should I change to for road use?

Answer:
The best way to explain gear ratios is to see them in tabular format. As shown below, the same gear ratio can be obtained by several combinations of front and rear sprockets. The gear ratio is calculated by dividing the "rear sprocket number of teeth" by the "front sprocket number of teeth". Lower gear ratios provide more top speed but less torque and acceleration. Whereas, higher gear ratios provide more torque and acceleration but less top speed.

An example is shown below to help interpret the table. It may be seen that a reduction/addition of 1 tooth on the front sprocket is equivalent to approximately 4 teeth on the rear sprocket. It should be noted that smaller front sprockets (such as 12T) can cause more chain wear. While swapping front sprockets may offer convenient setups between road and tight singletrack, this does result in a larger jump. By changing the rear sprocket, fine increments in gear ratio can be obtained with each tooth.

http://i45.photobucket.com/albums/f7...ear_ratios.jpg

Gear ratios and sprocket selection
 

Thanks Matt. Very handy. My FSE450 came with 13t front and 48t rear. I'm thinking I'll drop one tooth in front for tight technical stuff, keep the 13t for some dualsport stuff, and go with a 14t for most dualsport and commuting to work etc. I just hope I don't have to change my stock chain length. It'll be close.
It's very easy and much less time consuming to change your front sprocket for different types of riding. Works great if your on a long trip and U want to go explore some interesting terrain. Takes about 5 minutes.

Thanks for posting but his is only part of the picture Matt. Whats more important than final drive numbers are the inter gear ratios.

Here is the influence of the internal and final gear ratios relative to speed. I only made plots of several gear ratios. This is good for "visual" purposes. If your looking for a particular one, I can post up others as needed.

All of these were calculated using the GasGas internal gear ratios posted in their manual. I used the stock gear ratio (13T front/48T rear) for reference in all comparison plots

Here is a screenshot of my Excel spreadsheet. The information is entered in the pink column.

http://i45.photobucket.com/albums/f7...cs_example.jpg

Here is a comparison between (13/48) and (13/52):

http://i45.photobucket.com/albums/f7...C25048vs52.jpg

Here is a comparison between (13/48) and (13/50):

http://i45.photobucket.com/albums/f7...C25048vs50.jpg

Here is a comparison between (13/48) and (13/46):

http://i45.photobucket.com/albums/f7...C25048vs46.jpg

sweeet! Thanks, now if we find out what a 250 really revs you could extropolate the numbers to reflect this and we could settle once and for all the theoretical top speed debate

A lot of variables there between years and diffferent components. I think the '07 revs the highest by far compared to my '00 and '03. I've seen over 70 MPH on my ICO with 13/52 several times.

Help me figure this out
 

Ok I have read the above discussion but I am really in need of some specific help. I understand the sprocket changes that I can do but I want to know what to expect and maybe somebody could help me out.

First, My bike is: 2004 GASGAS FSE450 Supermoto

- I dont know what size the stock sprockets are. Hopefully one of you out there will know. I dont know if it is the same as a FSE non sumo. I want to change the sprockets. My top (cruising) speed is around 60. 60 allows me to go for a few miles without the bike complaining and reving out too high. 70 is too high to do for more than 30 seconds and ive only gotten it up to 80 once.

-What I want to do is gear it so where is basically turn my 60mph into 70 or 75mph. I want to gear my bike where 70-75 is at the same rpm as maybe say 60 or so. I plan on riding my bike on a few trips that are 70 miles more or less and I am not going to be able to do 55-60 the whole way without pulling my hair out. I mostly ride the bike around town, but I want to be able to cruise at at least the speed limit on the freeway for god sakes! Im afraid though, that in doing this sprocket change, I will significantly reduce my power and acceleration to the point where the bike sucks to ride.

Ok. The question now is that when or if I gear my bike for a better higher cruising speed of say 70-75 will I SIGNIFICANTLY reduce my power and acceleration factor? If I do this am i going to hate it basically is what im asking? So for example purposes I can compare my bike to a DRZ400SM. The DRZ has 35 horsepower stock and weighs 300lbs dry. My bike has aprox 50hp and weighs 260 Dry. The DRZ can cruise at like 70 or 80 without straining itself and has plenty of power. My bike has plenty of power and acceleration (so it feels) but my top speed sucks for what I want. Im not saying I like the DRZ better AT ALL!! But I want to be able to cruise with one if I have a buddy with a DRZ. The way my bike is geared right now I cant even ride with buddies with streetbikes because I cant go past 60-70 really. I dont like that.

What should I do? I need help with this topic. Any suggestions are welcome.

MattR Can you email me your excell spreadsheets?

adpartain if yours is like mine I think its is a 13 or 14 front and a 48 rear. And mine with 17" wheels tops out at like 90mph!

Doesnt anyone know how large a front I can go and it still fit?

Nice article. Just what I was looking for.

I have the same question....wonder if he ever figured it out ?
 

I would love to know the answer to this ?? Anyone ??