front sprocket

cachidril01

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Hello Guys, I am trying to find a 16T or 17T front sprocket, but looks like nobody have anything.

any idea where to buy it?

thank you
 

vulgr

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Maybe just go a smaller rear sprocket?
Vortex rear sprockets on eBay from 38T upwards

Edit: driven have 16T front sprockets
 
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Formula390

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Hello Guys, I am trying to find a 16T or 17T front sprocket, but looks like nobody have anything.

So there are a few problems with swapping out the front sprocket:
- Going smaller, and you are going to rub on the swingarm

- Going larger end up rubbing through your front sprocket safety cover. Yes, it's only plastic (or Carbon Fiber if you buy the Tyga replacement) but most people who have tried running a larger front sprocket have run into problems here. There is also the problem of chain and sprocket wear.

- The front sprocket NEEDS to be steel. Aluminum front sprockets will wear out FAST!!! In my younger years racing we would run aluminum front and rear sprockets with a 520 chain with no o-rings... the chain would stretch so much it would need to be replaced every 3rd session out on the track, and I always needed to fit a new chain prior to any race. The front sprocket would usually only last a weekend. This was when I was chasing a championship so every fraction of a HP counted... so even the meager gains offered by the aluminum front sprocket and no o-rings helped. It was costly tho. It's not something I recommend to anyone without them having a full understanding as to what the ramifications are with running an aluminum front sprocket.

- You can't NOT run a front sprocket cover unless you plug the rear bolt hole as this is a through hole and goes directly to your transmission. Leaving this bolt out, and you aren't going to have any problems with chain wear, but might have an issue with keeping your foot on the peg or the black flag from being pointed at you as you go by. :) LOL

With the RC390, generally "the thing to do" is to swap out the rear sprocket. You aren't finding a wide offering of front sprocket choices for the RC because of the clearance issues with changing that out. I have a full range of sizes from 39T to 48T.

Anyway, hop that helps you with understanding the sprocket wonkiness in selections for the RC.
 

CDN Duke

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I've been running a Driven 16T front sprocket for several thousand KMs with zero issues, very happy with it.
 

green_bread

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So there are a few problems with swapping out the front sprocket:
- Going smaller, and you are going to rub on the swingarm

- Going larger end up rubbing through your front sprocket safety cover. Yes, it's only plastic (or Carbon Fiber if you buy the Tyga replacement) but most people who have tried running a larger front sprocket have run into problems here. There is also the problem of chain and sprocket wear.

I have run 14T, 15T, and 16T sprockets for the last 3 years of racing and I have not had any of those issues.

Agree with pretty much everything else you said. I personally would rather swap just the front sprocket than have to take the wheel off... but the reality is that I usually end up doing both front and rear to dial in the gearing I need.
 

Formula390

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I have run 14T, 15T, and 16T sprockets for the last 3 years of racing and I have not had any of those issues.

Agree with pretty much everything else you said. I personally would rather swap just the front sprocket than have to take the wheel off... but the reality is that I usually end up doing both front and rear to dial in the gearing I need.

It could be the guys who had issues with the 16T front were running with a chain which was too loose or something, but there were 3 different guys (2 racers, 1 street) who reported issues with the larger front sprocket. If we've got 2 racers here reporting that the haven't had problems, then might be either a difference in the sprocket cover, chain, chain adjustment, etc etc etc... who knows! If we've got reports of success tho, then that changes the arrhythmic on gear ratio setup possibilities. Hrmmmm. Now I'm going to have to investigate this further!
 

Solidwire

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Any updates in the front 14 tooth causing the chain to rub the swing arm? Thinking about playing with a front 14 tooth.
 

Formula390

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Any updates in the front 14 tooth causing the chain to rub the swing arm? Thinking about playing with a front 14 tooth.

In short, it will likely rub. This somewhat depends on what your rear sprocket is, and how much your suspension travels, so I strongly advise against it. It's also pretty brutal to the chain. That's a pretty tight loop!
 

Solidwire

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I was planning on running the stock rear 45 tooth. The rear travel depends on how hot the rear shock gets. Lol

What your suggestion for a 114 link chain if I buy a 48 tooth rear sprocket from you?
 

Formula390

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I was planning on running the stock rear 45 tooth. The rear travel depends on how hot the rear shock gets. Lol

What your suggestion for a 114 link chain if I buy a 48 tooth rear sprocket from you?

Yeah, the problem with that rear shock and heat isn't a small concern either. If you are still running the stock shock, honestly, you need to seriously look at different options there. I so wish that I could talk JRi into producing their RC shock again. :( I have tried and tried, begged and pleaded, to no avail. Never the less, I just sent JRi an email asking (again) if they will reconsider bringing the RC shock back into production. Who knows, maybe they will! Baring there not being a JRi option, the next two I recommend are the Bitubo and K-Tech shocks. Both are excellent shocks, and there are a lot of guys running those shocks that love them, both on the street, as well as racing/trackday riders.

As for gearing, I produced a spreadsheet which shows various gearing options, and the corresponding (new) chain length and "theoretical" top speed.
The caveats here are:
  • Chain Length: The calculated chain lengths are using a new chains length. In theory, as a chain stretches with wear one might be able to get the chain to fit
  • The "theoretical" top speed you obviously would need to have the HP to pull the higher speeds, and there are always potential issues like clutch slip which could also prevent hitting the higher speeds. You can find the spreadsheet here: https://docs.google.com/spreadsheets/d/1T42Kjs53Xbad4d_krrIw5OPAEve9NntuLEwNRPkrnOY/
  • None of the calculated options make reference to tire size choices, which can also have an impact on gearing as well.

So, for a 114 link chain, you would be looking at options of:
  • 14:48
  • 15:47
  • 15:48
  • 16:46
  • 16:47
  • 16:48
You also need to keep in mind that a 14:48 option would run out of a adjustment pretty quickly as well!

To make a recommendation, I would really need more information. Is this a streetbike or track bike? Are you after more top speed, or looking for more "grunt" out of the corners? Are you currently hitting redline in top gear? What HP is your bike putting down to the rear wheel?

Gearing choices are a complicated subject, and there is no single or "correct" answer for all riders! Gearing choices are ultimately left to the rider, their riding style, and setup preferences. You could have the same top speed even, but end up with different characteristics with the lower gears.

Say we take a top speed for 109.3MPH using the 15:45 stock gearing setup. Well, you can get the same top speed with a 14:42 and a 16:48 (as well as a 19:57 415 chain setup) but... we could run thought experiment where we take four different racers, each with the same HP to the rear wheel and rider weight. and put these four bikes side by side. Which bike will accelerate faster? Will all four bikes accelerate at the same speed? Nope! While the gear ratio is the same, the mechanical advantage will go to the rider with the larger front sprocket and smaller rear. This is what's called "Roll Out", and it can have a dramatic impact on acceleration.

Basically, like any tunable characteristic... "It's Complicated" is an understatement. :)
 
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