Gearing questions

[lundracing]

Looking to get the gearing right on my Kx 500. I have a 17 lt SE kit. 14 tooth on bike. It runs 45 mph on top end. I am always in 4th and 5th gear. I would like it to run 60 mph on top. What will be the easiest and cheapest way to get me there.


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[cbc76am]

Not the counter shaft sprocket. moving to a 15 or 16 will leave a chain length that won't align with the amount of play in the chain tensioner. Might be looking at dropping a tooth on the rear and going up 1 or 2 on the front.

 

[lundracing]

Would changing gears under the cover on the kit be fastest. I think they are both 17 tooth. Could I do a 19/15 with those?


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[cbc76am]

I don't think a larger than 17 will fit under the cover... without modding the chain case cover also. Maybe an 18T would squeeze in there.

 

[highflyernick]

What's your track rollout at right now? I'm running a KX500 w/16 SX120. Running 13/16-18/16. Track rollout 16.75"

Bike rips!!! 18-16 in the chain case is the easiest way to gain some track speed.

Also the splined sprockets are super cheap.

 

[cbc76am]

Great info, thanks nick. Only issue with that is the 16.75 sounds like too much for out lower HP motors. Most folks seem to recommend 13.50 - 14.25 on 450/500 4 strokes. I have to admin though... this 5th gear required to go 35Mph is horse ****. So i'll try getting the 18/16 gears. You get those at the dealer? Can't find TS parts any where else these days it seems.

 

[highflyernick]

ya my 500 is a 2 stroke. But I can climb all day in 3rd and I'm carrying a ton of momentum when I go flying by the 450s haha

Ya those gears came from a TS dealer. Innerspace watersports in BC. Should be standard gears for any dealer

 

[cbc76am]

I'm running the keyway gears, so that will complicate things a bit. I measured my run out... 14.50 in 13-17, 17-17.. so yeah I'm hunting 16+ for sure. Thanks for the help.

 

[lundracing]

What's your track rollout at right now? I'm running a KX500 w/16 SX120. Running 13/16-18/16. Track rollout 16.75"

Bike rips!!! 18-16 in the chain case is the easiest way to gain some track speed.

Also the splined sprockets are super cheap.

I don't understand rollout ? What is that and how do you measure it.


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[snowbikekits.com]

http://www.snowest.com/forum/showthread.php?t=352628&highlight=rollout

search tool still works!

 

[cbc76am]

I just discovered the half link thread also... That would be a cheap way to test before investing in the new chain case gears to replicate the ratio with less "failure prone" parts in the mix.

 

[cbc76am]

Here's what I got for ya. Grab the half link kit to test but I think you'll end up in a similar place as me. grab a 15-16 counter shaft sprocket to test the ratios with. There are calculators on the thread that sbk shared with you. You can customize from there. What I have is 14.5 roll out on my stock 13-16 / 17-17 setup. This shows the math - adding a tooth gives me a bit more than an inch additional. I get another 1.2 for the 2 teeth more on the counter shaft. My HOPES are that one is a bit short, and the other a bit tall - which is when I'll buy the 18-16 gears for the chain case and go back to the 13-16 primary drive. That splits the difference at 16.31 - hopefully spot on for 45Hp or so at 8K RPM. It's a cheap way to test and find the right ultimate gearing for your bike and riding style / conditions. Good luck, I'll need some too.

STOCK GEARING Sprocket RPM
Counter Shaft Inner Jackshaft Outer Jackshaft Drive
Gear Trans Ratio Engine RPM Speed 13 16 17 17
1st 0.500 9000 28 4500 3656 3656 3656 Roll out: 14.5
2nd 0.600 9000 34 5400 4388 4388 4388
3rd 0.714 9000 40 6429 5223 5223 5223
4th 0.846 9000 48 7615 6188 6188 6188
5th 1.000 9000 57 9000 7313 7313 7313
6th 1.238 9000 70 11143 9054 9054 9054

Test 1 Sprocket RPM
Track Speed Change 7.7% Counter Shaft Inner Jackshaft Outer Jackshaft Drive
Gear Trans Ratio Engine RPM Speed 14 16 17 17
1st 0.500 9000 30 4500 3938 3938 3938 Roll out: 15.615
2nd 0.600 9000 37 5400 4725 4725 4725
3rd 0.714 9000 43 6429 5625 5625 5625
4th 0.846 9000 52 7615 6663 6663 6663
5th 1.000 9000 61 9000 7875 7875 7875
6th 1.238 9000 75 11143 9750 9750 9750

Test 2 Sprocket RPM
Track Speed Change 15.4% Counter Shaft Inner Jackshaft Outer Jackshaft Drive
Trans Ratio Engine RPM Speed 15 16 17 17
1st 0.500 9000 33 4500 4219 4219 4219 Roll out: 16.731
2nd 0.600 9000 39 5400 5063 5063 5063
3rd 0.714 9000 47 6429 6027 6027 6027
4th 0.846 9000 55 7615 7139 7139 7139
5th 1.000 9000 65 9000 8438 8438 8438
6th 1.238 9000 81 11143 10446 10446 10446

Test 3 Sprocket RPM
Track Speed Change 12.5% Counter Shaft Inner Jackshaft Outer Jackshaft Drive
Trans Ratio Engine RPM Speed 13 16 18 16
1st 0.500 9000 32 4500 3656 3656 4113 Roll out: 16.313
2nd 0.600 9000 38 5400 4388 4388 4936
3rd 0.714 9000 45 6429 5223 5223 5876
4th 0.846 9000 54 7615 6188 6188 6961
5th 1.000 9000 64 9000 7313 7313 8227
6th 1.238 9000 79 11143 9054 9054 10185