Now offering 20T 415 front sprockets as well

Formula390

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PacMan wanted a 20T 415 sprocket... and what the PacMan wants, PacMan gets!
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Figured I'd let others know as well, in case they wanted to have a chance of keeping him in reach, or want to give those N400's a run for their money! :D

Formula390 Sprockets

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kostean

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Hi! What are the benefits of running 20 teeth in front?
I have used only 19T so far and in general, needed to admit 19/57T combo is the usual one to go at tracks with longer straights, but where does the 20T front one give any benefit?
 

Formula390

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Hi! What are the benefits of running 20 teeth in front?
I have used only 19T so far and in general, needed to admit 19/57T combo is the usual one to go at tracks with longer straights, but where does the 20T front one give any benefit?
Taller gearing for higher speed. Because peak power is just below 9k RPM, having taller gearing is necessary for bikes that make higher HP numbers and want to utilize that power.

My spreadsheet for gearing details how the 20T changes things which can be found at: Gearing Options
 

kostean

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Great. Heads up @Formula390 , will place an order for some sprockets now toward you.

Another one from past season I were wondering of. Does anyone know to refer how to overcome the problem of KTM rear sprocket cush drive being susceptible for allowing the sprocket carrier to bend too much and I suspect several cases on where it has caused the 415 chain to roll off from the sprocket?

I saw at duke forum someone had even produced improved cush drive inserts for that purpose, but I wonder if anyone knows where such could be purchased or @Formula390 , as you have the machinery, how difficult would you create some for sale?

https://www.ktmduke390forum.com/threads/upgraded-cush-drives.25425/


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Formula390

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for a racing application, I would think the OEM ones would be more than sufficient and if you are inspecting your drive and keeping your chain tension correct, the chain should never jump off the sprocket. The teeth on a 415 sprocket are smaller, due to the thinner width (0.165" for 415 and 0.250" for 520) and smaller roller pitch (0.500" for 415 vs 0.675" for 520) so you DO need to make sure your chain is tensioned properly. I've only heard of one person having their chain derail while running 415 sprockets, and it's suspected that he had not checked his chain tension or his rear wheel alignment wasn't correct, as he took those sprockets off and then continued to run the rest of the season a different set of my sprockets for slightly different gearing, and he'd run that sprocket set for the entire season previously.

Which I suppose is a long way of going about saying I don't believe "upgraded cush drives" are a thing one needs to worry about in the slightest. In my life, I have never once had a cush drive go bad on me. I've put down somewhere around 2 million miles on bikes in my life, and that was from doing a rough estimate of miles ridden about 10 years ago. I think "failed cush drive" is a way of explaining a failure of attention to chain tension and wheel alignment... I just don't see that being a real problem with the 390... claims about a failed cush drive on the duke forum are even MORE suspect, as 99% of the duke 390 owners are first time bike owners and first bike riders who in my previous interactions, don't have the experience of doing motorcycle maintenance to know what they are talking about so reach for explanations outside of their having made a mistake... but I've been wrong before, and I'm sure I'll be wrong again.

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kostean

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@Formula390 - you are right, and I think the situation where the chain has come off have been mostly caused by the chain wear and least likely due to cush drives.

My observation on 390 cush drives inferior design has been mainly by the comparison of Yamaha R3. R3 rear hub setup looks to be way more sturdy and does not allow any sort of angular movement of the rear sprocket- the cushions are way larger and provide more side support for the sprocket carrier. While I can get the rear sprocket to move sideways some 3-4 mm with hand on 390 then the R3 one feels like welded.
 

Formula390

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@Formula390 - you are right, and I think the situation where the chain has come off have been mostly caused by the chain wear and least likely due to cush drives.

My observation on 390 cush drives inferior design has been mainly by the comparison of Yamaha R3. R3 rear hub setup looks to be way more sturdy and does not allow any sort of angular movement of the rear sprocket- the cushions are way larger and provide more side support for the sprocket carrier. While I can get the rear sprocket to move sideways some 3-4 mm with hand on 390 then the R3 one feels like welded.
Do you mean you can push the entire sprocket in and out, or do you mean you are able to deflect the sprocket by making it cock to one side? Are you SURE you have all of your spacers in place and that your axle is tightened to spec? The rear axle should be tightened to 90nm (66ft lbs) so if that's loose, it could also result in problems like you are describing, as well as many more...
Rear_Axle-Torque.jpg

I had one customer mount his rear wheel, and omitted the center spacer that fits in the wheel. He saw it, but couldn't figure out what it was or where it went on his bike. That caused quite a few problems for him. Also, what shape are your wheel bearings in? Sounds like they might need to be replaced as well. The OEM ones are garbage, which is why most racers swap them out for some high quality Koyo bearings, or similar.
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So, you might want to consider bearings and spacers, before trying to blame the cush drive. I've got them in stock as well and ready to ship:
http://formula390.com/parts.pl?D=rearsets
Part number: TPER-0003ORANGE or TPER-0003SILVER

I just tried grabbing the edge of my rear sprocket on the shop mule RC390, and damn if I was able to get it to deflect anywhere NEAR 4mm! I wouldn't call it welded, as I could move it a thousandths of an inch and that was me leaning into it pretty heavy. That's probably deflection of the sprocket itself, but that's also an amount that could only be measured by a machinist indicator or experienced eye for incredibly small amounts of movement. When I REALLY leaned on it, the most I could get it to deflect was not more than 0.003" (aka 0.075mm). Tops. If you can move it 3-4mm, you've got a serious problem as there is NO way it should be able to move THAT far! It sounds to me like you have a problem with your wheel bearings, spacers, or axle torque... and NOT your cush drive. $0.02.
 
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