Bouncing with 16T sprocket

[Easy Rider]

Somebody mentioned a bouncing sensation about 40 mph after installing the 16T sprocket.
I think it was in a thread on here but can't find it now.

Anyhow, I noticed the same thing.
I was able to get rid of it by tightening up the rear shock per-loads by one notch.
(At least I think it is gone. Haven't noticed it in 60 miles or so.)

[jonathan180iq]

Make sure that your chain is properly adjusted. I'm guessing I've had this sprocket longer than anyone and I haven't experienced that.

[Dirt_McGert]

It could be that you didn't align your rear axle/chain tensioner bolts correctly, so the rear wheel is uneven with the front, possibly causing shake. This would be my best guess. The chain tension bolts have an alignment marker metal tab thing, make sure they're at the same position.

[Easy Rider]

Originally Posted by Dirt_McGert

It could be that you didn't align your rear axle/chain tensioner bolts

Sorry I brought it up. It was not here where the original discussion took place.

It is NOT a shake. It is a bounce. Hard to describe if you haven't experienced it.
It feels like one of the tires is BADLY out of balance or out of round. Wierd.

Anyway it's gone now, with only a shock adjustment.

[Gadzooks Mike]

That was me that started this - the trotting horse affect.

I've still got it. I had changed from a setting of 4 to 5 for the trip to Michigan (loaded down pretty good) and it's still there with a setting of 5, although it does help quite a bit. I hadn't noticed it made a difference until you mentioned it, and then I realized that it did.

I'm pretty sure that just about any thumper will do this at certain RPMs unique to the machine. There just isn't anything to cancel out the sympathetic vibrations caused by that single cylinder moving up and down. I'd be curious to know if anyone riding as S40 has experienced this.

There are a couple of examples I could use, but since this is a family board, let's try this one: jumping up and down on a trampoline will get you the same sort of affect, and you don't notice it while jumping up and down on a wooden floor, although the floor is moving very slightly. Two people jumping on the trampoline in opposite directions (one going up with the other coming down) also dampens the vibration, just like a second cylinder will.

At least, that's my theory, and I'm sticking to it (until proven wrong, in which case I will blame it on space aliens and skunky beer).

[Easy Rider]

Originally Posted by Gadzooks Mike

At least, that's my theory, and I'm sticking to it (until proven wrong, in which case I will blame it on space aliens and skunky beer).

I'm sure you are probably right. The little beasts have a gear driven counter balance which is pretty good.....but not perfect.

Since adjusting my rear springs, I haven't noticed it at all and had forgotten about it actually. My last thought was that it might take some "trigger", like road joints at just the right distance coupled with just exactly the right speed.
Could be them little green men too! :cool:

[Sarris]

EZ, I mentioned it in my Nitrogen discission. Align the sidewall spot on your tire (the heavy spot) 90 degrees to the valve stem and use nitrogen. 95% of the sympathetic bounce will be gone. Don't be so damn cheap!! Nitrogen is only $10 a tire. Also, most people have no idea that the colored spot on their new tires sidewall indicates the heaviest spot in the tire.

[jonathan180iq]

If there truly a part of the tire that is heavier than the rest, then, obviously, the tire is not balanced.

Having the tire balanced, which is done by adding counter weights in the correct location, would offset any affect of a heavy spot in the tire, by design. Also, if the tire is balanced correctly, why would you need to roll it around to this magic point? You can't possibly blow the tire off the wheel. So, what's so strange about N that requires the tire to be filled in the HEAVY spot?

More importantly, as I've said before, a properly installed sprocket shouldn't change anything about the bike except the gearing. Since installing the sprocket requires loosening the rear axle nuts, it would make sense to check for proper rear wheel alignment. A misaligned rear tire would also lead some bouncy feelings.

Trying to fix a problem caused by improper installation by putting different air in the tires is like putting your pants on backwards and buying new shoes to correct the funny feeling.

-Jonathan

[Sarris]

It's more of a roundness issue, as the balance should have be done. As the slightly "thicker" heavier area rotates, it creates an out of round (very slight) sympathetic bounce usually only at one speed. This info comes from my local goodyear dealer, and it did eliminated my "bounce". Also, the bounce was more pronounced on my bike after the 16t sprocket change, mine being at 53 mph. Look, I don't purport to be an expert on anything. This is just how I solved the problem. Take it or leave it. I could care less.

[Gadzooks Mike]

jonathan180iq - it has nothing to do with the 16T sprocket or misalignment. The only thing the sproecket change did was change the SPEED when it happens. It used to happen at a slower speed with the stock sprocket, which leads me to believe it's the RPMs that's causing it. If it had something to do with the tires or alignment, it would happen at the same speed. Also, if it had something to do with a misaligned rear tire, it would seem to me that it would get worse, or at least more noticeable at higher speeds. But instead, it goes away. I can see where the nitrogen would help, as it would take away the mix of air and tend to dampen the bounce. I haven't used nitrogen in anything I drive, but I would imagine it would ride smoother. That, along with stiffer suspension, would make it all but disappear, I'd guess. And then I'd have to buy a rocking horse.