Gearing with stock chain - 16T front

acruhl

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I have a 2020 RC390.

I found this message: https://www.rc390-forum.com/threads/front-sprocket.2664/#post-31673

This is very useful. My question is more about practical experience. This bike feels geared too short. 1st gear is just too low, even for the street. Then there's the problem of a long straight at my track where I will probably top out in 6th. So I was going to go to 16T front.

The thread says this can cause rubbing on the front sprocket cover, but maybe not always. Maybe it's not a problem on newer bikes?

If anyone has gone to just a 16T front sprocket, I'd like to hear about it. Plenty of chain adjustment? Does it clear? How does it work on the street?

Thanks.
 

acruhl

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Answering my own question.

The 16T has enough clearance in the countershaft area. There is a case protector but it clears it just fine.

Unfortunately the stock chain is too short. I suspect if it was worn out a bit more it would be fine, but that would be a nice easter egg waiting for me when I replace the chain.

The answer is going to be either a 44T rear sprocket or a longer chain, not sure yet. Depends on what I can find locally 2 days before my track day.
 

acruhl

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A friend of mine with an RC cup bike had an aluminum 44t rear sprocket. So now I'm at 16/44 rather than the stock 15/45.

To me the transmission feels a little bit like a dirt bike. Low 1st, gear, lots of change in RPM between gears. So I think KTM geared it pretty short so you're using all the gears on a normal street ride. Nothing really wrong with that for the street.

Unfortunately I think most racetracks will put you on the limiter on the straightaway, which is never pleasant.

16/44 feels pretty tall on the street to me (I only tested it in my neighborhood) but not out of line. The engine has enough torque to pull it off just fine I think.

If I don't actually need 16/44, the next test will be a longer chain and 16/45. I'm hoping there's enough adjustment for a 114 link chain.
 

Alibee071290

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Hi

where did you get your 16t sprocket from ? what make is it ?

I can't seem to find a 16t here in the UK and it would help a lot with adjustability on track.

Thanks
 

acruhl

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Sprocket center in California. Driven also has them but they are out of stock for about a month. Formula 390 has the expensive chrome moly ones which look good.

Just to remind - 16T with the stock 45T rear will not work with the stock chain unless it's worn out a little bit. If one "modified" the chain adjusters it might work but that doesn't seem like a good idea.

I rode around the track yesterday and 16/44 was definitely too tall. I went back to 15/44 and it's closer to right, but that's very specific for my conditions.

Luckily I haven't had to put on a different chain yet.
 

acruhl

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More info.

In my particular situation I'm between 3rd and 4th for most of the infield of the track with 15/44. I could go taller to carry 3rd a little longer but then I might lose on some straightaway speed. I'm shifting into 6th right when there is a slight downhill so it's pretty good. 15/44 is probably close enough to right for now.

For the street, 16/44 is really nice. 1st doesn't feel so low and cruising at higher speed isn't so busy. The bike feels plenty fast for it. And you can keep the stock chain!
 

acruhl

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I'm still really happy with 16/44 on the street. The real benefit can be felt at 40mph and up. Even 1st gear feels more usable.
 
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