Sprocket Tooth Count Questions

[noahdog]

I need new sprockets and chain for the little Enduro 100 I picked up last weekend. The stock 1974 sprocket is 49 tooth which has since been discontinued and replaced with a 55 tooth which was also discontinued and now they're selling a 45 tooth replacement sprocket. That being said I also have to choose between a 13,14 & 15 tooth front sprocket. Can anyone easily explain what the tooth ratio does to top end speed vs quick starts? As it stands now 1st gear is basically a granny gear and I have to shift almost immediately. Hopefully I'm making some sort of sense and you guys can help me figure out which front sprocket to buy.

 

[Big R]

If you take the rear sprocket tooth count and divide it by the front, you will get the drive ratio. I've read before that +/- 10 percent is ideal. And fyi - a larger front sprocket is generally better because it puts less stress on the chain as it goes around.

Have you checked the chart on www.sprocketspecialists.com? I had to cross reference my rear sprocket and search ebay.

 

[Redbird]

As it was explained to me, many moons ago...

(this assumes you're starting out with stock gearing)
Going to a higher tooth count on the rear sprocket will increase your low end grunt, but top speed will suffer. Going to a lower tooth count will give you more top speed, but low end grunt will suffer.

The opposite is true with the front sprocket. Lower tooth count will increase low end, higher tooth count will increase top speed.

And one tooth front equals two teeth rear. For example: dropping one tooth on the front is the same as going up two teeth on the rear.

In your situation, I would guesstimate that you should try to go with a two teeth larger front sprocket to counteract the four teeth smaller rear sprocket. That should have you back (close) to stock specs.

 

[noahdog]

As it was explained to me, many moons ago...

(this assumes you're starting out with stock gearing)
Going to a higher tooth count on the rear sprocket will increase your low end grunt, but top speed will suffer. Going to a lower tooth count will give you more top speed, but low end grunt will suffer.

The opposite is true with the front sprocket. Lower tooth count will increase low end, higher tooth count will increase top speed.

And one tooth front equals two teeth rear. For example: dropping one tooth on the front is the same as going up two teeth on the rear.

In your situation, I would guesstimate that you should try to go with a two teeth larger front sprocket to counteract the four teeth smaller rear sprocket. That should have you back (close) to stock specs.

So by your logic my best bet for optimum low end grunt (which I'd assume would be better for off-roading) would be a 49 tooth on the rear and a 13 tooth on the front? Surprisingly the sprockets specialist site Big Rich posted has a 49 tooth rear for a decent price. I can't imagine a DT100 having that much top end speed to begin with even with the 2 stroke engine.

 

[Big R]

Be forewarned - when I tried to get a 40 tooth rear for mine, they said it was backordered for at least 4 weeks. It was in January, so it wasn't that big of a deal yet. I kept calling every couple weeks, and it was always BO'd. Finally the one girl told me "they are on back order from Asia, and we have to wait for the crate to be filled". Yes, the CRATE!

Call them and if they say it's not in stock, check ebay.

 

[drummershoes]

i know the thread's a lil old, BUT i do have a question and are welcome to any opinions and/or suggestions since I'm a total FNG at this still.

running stock sizes for front n rear sprockets on my 81 cb750F and would like to gear it for a lil more stretch for speed .
if I read the analogy right, and i'm looking to get more speed out per gear, I should get a SMALLER rear sprocket ? def not lookin to pop wheelies or anything, just wanting to get a lil more of a stretch between shifting gears and making it a lil more ideal for highway running/ longer hauls.

again, any suggestions or tips are completely welcome!

 

[Big R]

You got it - for lower rpm's at any given speed, you can get a "smaller" rear sprocket. Or a larger front sprocket.

 

[drummershoes]

sweet, now I've got that little detail straightened out, time to see what size(s) to get !