All 650's More front sprocket teeth to reduce vibration?

[EuroBadger]

I recently heard someone claiming that adding a teeth or two in the front sprocket reduces vibration and he has done it before.
While I believe the effect won't be dramatic, I thought it was interesting because it's like the only solution I know that actually deals with the cause of the vibration. As we all know the rest of the other methods i.e. handlebar weights, plusher throttle grip, etc. are just a way to hide the vib so you feel it less.
I can see the reasoning behind it and if I were ever to do it, I would reduce the rear sprocket teeth to match the gear ratio. Since the rear sprocket has way more teeth I doubt dropping a couple teeth in the rear will affect transmission's vibration.

What is your thoughts? I know some ppl here have tinkered with their sprockets so a feedback would be nice. Thanks!

 

[Atucker]

I guess I could see how adding tooth up front would reduce the RPM and the vibration associated with high rpm operation, but it seems that the effect would be mitigated if you're keeping the same ratio as stock with reduced teeth in the rear.

My personal findings and thoughts on vibration:
- Brand new odd vibration / strange noise at high RPM, but only at small window. Very disconcerting
- 3-500 miles still odd vibration, but worse using fuel with octane rating above 87 octane
- 500 - 1500 miles vibration smoothing. No odd / loud vibration at small high rpm window
- 1500 - 2500 miles occasional vibration - found fuel tank cover velcro loose. Minimal vibration again
- 2500 - 4500 miles no unusual or excessive vibration. Bike is now the smoothest operating vehicle I have ever owned. Its a complete turn around from when new.

The only thing that really seemed to help the vibration was breaking in the bike. I've only run 87 octane since the 4th fill up. I run this bike like its stolen and it has responded in ways that can't be described. It idles smooth as glass and if it wasn't for the Akra and sound of the exhaust I wouldn't even hear or feel a thing even when running it up to redline.

My advice would be to run the minimum octane fuel and break in the bike like it's been designed to run; i.e. high rpm 4cylinder. Changing the sprockets may have some effect, but only if keeping the RPM low which completely destroys the nature of the bike.

 

[EuroBadger]

I guess I could see how adding tooth up front would reduce the RPM and the vibration associated with high rpm operation, but it seems that the effect would be mitigated if you're keeping the same ratio as stock with reduced teeth in the rear.

My personal findings and thoughts on vibration:
- Brand new odd vibration / strange noise at high RPM, but only at small window. Very disconcerting
- 3-500 miles still odd vibration, but worse using fuel with octane rating above 87 octane
- 500 - 1500 miles vibration smoothing. No odd / loud vibration at small high rpm window
- 1500 - 2500 miles occasional vibration - found fuel tank cover velcro loose. Minimal vibration again
- 2500 - 4500 miles no unusual or excessive vibration. Bike is now the smoothest operating vehicle I have ever owned. Its a complete turn around from when new.

The only thing that really seemed to help the vibration was breaking in the bike. I've only run 87 octane since the 4th fill up. I run this bike like its stolen and it has responded in ways that can't be described. It idles smooth as glass and if it wasn't for the Akra and sound of the exhaust I wouldn't even hear or feel a thing even when running it up to redline.

My advice would be to run the minimum octane fuel and break in the bike like it's been designed to run; i.e. high rpm 4cylinder. Changing the sprockets may have some effect, but only if keeping the RPM low which completely destroys the nature of the bike.

The idea of + front teeth and - rear teeth was that since the rear sprocket is much bigger removing a couple teeth there won't have as much impact as adding a teeth in the front. And yes, just a couple less in the rear, because I will be deliberately altering the gear ratio to true the speedo (if I ever do it).

Good to hear our bikes can take abuse. Is there any reason for running minimum octane? Sounds very interesting.

 

[Atucker]

The idea of + front teeth and - rear teeth was that since the rear sprocket is much bigger removing a couple teeth there won't have as much impact as adding a teeth in the front. And yes, just a couple less in the rear, because I will be deliberately altering the gear ratio to true the speedo (if I ever do it).

Good to hear our bikes can take abuse. Is there any reason for running minimum octane? Sounds very interesting.

The bike is designed to run on 87. It can't take advantage of any higher octane so it's just a waste of money with zero benefit. People have the misconception that octane = power, but it's the exact opposite. 87 has more potential energy than 93.

 

[mikegml]

Hello. I just registered on the site an hour ago. Haven't even introduced myself yet but I will. Haven't even rode my my new (used) CBR650F yet!

Stumbled upon this thread by accident. Unless I misread you, your undersanding of adding/removing teeth is a bit off. I've had tons of bikes and changed the standard gearing on 4/5 of them. Adding teeth to the front does indeed gear UP. Removing teeth from the rear also gears UP. Rough rule of thumb, adding 1 tooth to the front is equal to removing 2/3 from the rear and is very noticable, for some it would be a bit too much. Adding 2 to the front would be a really big gear up, 1st would likely be closer to your 2nd gear as it is now. If you added teeth to the front AND removed teeth from the rear at the same time that would be a MASSIVE gear up. Removing 2 teeth from the rear only is usually a safer bet, a noticable gear up but not dramatic.

 

[EuroBadger]

Hello. I just registered on the site an hour ago. Haven't even introduced myself yet but I will. Haven't even rode my my new (used) CBR650F yet!

Stumbled upon this thread by accident. Unless I misread you, your undersanding of adding/removing teeth is a bit off. I've had tons of bikes and changed the standard gearing on 4/5 of them. Adding teeth to the front does indeed gear UP. Removing teeth from the rear also gears UP. Rough rule of thumb, adding 1 tooth to the front is equal to removing 2/3 from the rear and is very noticable, for some it would be a bit too much. Adding 2 to the front would be a really big gear up, 1st would likely be closer to your 2nd gear as it is now. If you added teeth to the front AND removed teeth from the rear at the same time that would be a MASSIVE gear up. Removing 2 teeth from the rear only is usually a safer bet, a noticable gear up but not dramatic.

You are right, I was mistsken when I'd said I would reduce the rear sprocket teeth. I clearly meant to increase, not reduce.
Just haven't done it yet because my sprockets are still very fresh.

 

[mikegml]

I'd try 2 teeth less on the rear to start with and see if that improves things. Best to do it before the sprockets become too worn.

 

[EuroBadger]

I'd try 2 teeth less on the rear to start with and see if that improves things. Best to do it before the sprockets become too worn.

Doesn't it make sense to do it when you replace the worn sprockets?

 

[mikegml]

Yeah, if you're willing to wait until they and the chain all need replacing. If not then change the rear now if the front and chain aren't worn too much.

 

[EuroBadger]

Yeah, if you're willing to wait until they and the chain all need replacing. If not then change the rear now if the front and chain aren't worn too much.

Well, the whole point of my experiment is to feel the benefit of larger front sprocket i.e. reduced vibration, so I won't be changing the rear before I swap the front. TBH I'm fine with the stock gearing (except for the fact that it overcalculates your mileage).

 

[trippy]

Well, the whole point of my experiment is to feel the benefit of larger front sprocket i.e. reduced vibration, so I won't be changing the rear before I swap the front. TBH I'm fine with the stock gearing (except for the fact that it overcalculates your mileage).

Higher gearing will only reduce RPM at any given speed. This is only useful if your cruising speed puts the bike at an RPM that makes it uncomfortable. The cost is lower acceleration.

 

[EuroBadger]

Higher gearing will only reduce RPM at any given speed. This is only useful if your cruising speed puts the bike at an RPM that makes it uncomfortable. The cost is lower acceleration.

That is the common knowledge.
Someone I stumbled upon said he could also feel the reduced vibration due to the larger radious of the front sprocket.
Not that I trust him 100%, I just want to try it out since it also helps with correcting the speedo.

 

[Cláudio Nogueira]

The bike is designed to run on 87. It can't take advantage of any higher octane so it's just a waste of money with zero benefit. People have the misconception that octane = power, but it's the exact opposite. 87 has more potential energy than 93.

Hello. Part of what you said is right, when you mention about people misconception of what octane level is.

But regarding not running on higher that 87 RON, allow me to inform you that in EU, particularly in Portugal where I am, the lowest RON we have is 95 E5. You can only choose between 95 or 98 with, premium (bulshit) or regular.

Never had or knew any car or motorcycle that justifies to use 98, but they sell it! There are people that swear that their engines sound like singing angels when running 98, and others believe them. I guess that´s why they sell so much 98 RON ;-)

Increased RON level is only justified for higher compression engines, to control detonation. With the level of compression os our CBs, the 95RON is more than enough to control detonation.

 

[wke002]

Hi All, time to try to up 1 tooth from 15 to 16. Anyone currently done it on Cb650r, and most important does it fit on current standard original chain fm factory.

 

[JDude]

Hi All, time to try to up 1 tooth from 15 to 16. Anyone currently done it on Cb650r, and most important does it fit on current standard original chain fm factory.

Yes and yes. I had enough slack in my chain, don’t see why your’s would be any different.