2000 KTM250exc sprocket sizes? I am totally confused!

[dmitrikinaev]

Hi guys,

Currently the bike has 14 on the front and I think 52 on the back. (is said renthal then a few number finished by t52)

With the bike came a new 15 fron and a new 40 back.

To make the bike more street friendly, do I just put the 40 on the back? Or both the 40 and 15?

I perfectly understand that by putting a smaller sprocket on the back will equal to more top end speed (which I am searching for - the bike being a 5spd), but the front one confuses me, because I think "why put a bigger one on the front as well - would not that cancel the back out" or is there deeper underlying meanings - gearbox ratios etc...

I dont get it.

Anyway not sure what to put on? just 40 on back, or both 40 and 15? Instead of right now it has 14 - 52.

-cheers,
Dmitri

 

[dmitrikinaev]

PLease anyone?

 

[oldgoat]

Smaller on the back equals higher top speed

Bigger on the front also equals higher top speed

 

[elf]

1 Tooth larger in front = about 3.5 less teeth in the rear
Put the 15 on the front and see how you like it, if you use the 40 out back you will have to use a shorter chain.

 

[OldTimer]

52(rear) divided by 14(front) = about 3.7
That means you have a 3.7 to 1 final drive ratio or ... the front sprocket has to turn 3.7 times for each revolution of the rear sprocket/wheel. :think:
40 divided by 14 = about 2.9, so.. the front sprocket only has to turn 2.9 times for each revolution of the rear sprocket/wheel. :think:
40 divided by 15 = 2.7 and so on...
The lower the ratio, the faster the top speed.
Smaller on the back has the same effect as bigger on the front, but, since the front sprocket is only about 1/3 the size of the rear sprocket, each tooth change on the front will have triple the effect of a tooth on the back. :think:
Let that bounce around for awhile. :cool:

 

[dmitrikinaev]

Thankyou so much guys, the haze of ambiguity is clearing!!

 

[Jaybird]

Also consider that you can obtain similar ratios with differing sprockets.
In other words, if you want a 4:1 ratio...you can obtain it by using a 12/48, 13/52, 14/56

When we choose a ratio, we must consider that due to the "chordal action" and the dynamics of chain pull, the largest front sprocket you can use to obtain the desired ratio will net a longer lasting chain drive.

Inversely, the smaller the front sprocket used to obtain a desired ratio, the faster the set-up will wear the chain out, and consequentially the sprockets.

 

[dmitrikinaev]

I put the 15 on the front and noticed that the chain would have about 1 - 2mm clearance! between it and the hydrolic clutch thing. I dont know why its that close, but 14 is the only one that can fit, the 15 will definately hit I rekon. I mean, you need at least 2mm just in case. I guess, I have to buy a smaller rear sproket. BTW, If I get say a 45 tooth, would I have to get a shorter chain (hopefull not) or could I just move the wheel back a little and stretch it out a bit?

-cheers.