HELP: Heavy vibrations!

[sixstring]

Hi all,

I just got by bike back from the shop yesterday. I had them put on a new set of 130 Pirelli Sport Demons and new rear brake pads. I bought some chain cleaner and headed home. Everything felt fine on the way home (or at least I didn't notice anything strange). When I got home, I washed the bike, cleaned the chain and lubed it.

This morning I took the bike to work and on the highway I noticed that the bike was vibrating more than usual. The problem seems to worsen as I reach higher speeds. However, at real high speeds the wind kinda cancels the effect. But riding at around 40-60km/h its REALLY noticable. The vibrations really get bad when your using engine braking and coming to a stop.

If I had to describe the vibrations, I'd say its more of a rapid thumping as opposed to buzzing; imagine you had a nail stuck to your wheel and riding on that.

Now, the guys at the shop couldn't had no reason to go near my engine so I'm wondering what could be causing this sudden increase in vibration? Maybe my chain cleaner took all the lube off my wheel bearings? Maybe I damaged something while washing?

I'd take the bike to the shop again but I'm not even sure what to say when they ask me what the problem is! Anyone else experience something similar?!

[OldGuy]

Given you put new tires on and your description of "thumping" it almost sounds like the tires; either not balanced properly or they are developing flat spots when the bike sits. Does the problem go away the longer you ride, stay the same, or get worse?

[sixstring]

The longest I've ridden the bike is to work which is only like 10 km away. I don't think it gets any better or worse.

I don't think its tire-related. It may just be my subconscious being more sensitive now that by bike fees weird, but I think the bike is vibrating harder than usual at idle too.... which reminds me: My bike usually idles at 1500rpms and today i found it idling at around 2000.... A twist of the idle knob solved that problem thou.

Maybe I should try changing the oil or something...

[CC Cowboy]

Go over all the bolts and nuts and make sure everything is tight. Maybe your fairing or windscreen has loosened up and is buzzing from the wind. I'd go over the entire bike and check everything for tightness. Run your hands over the tires and see if you picked up something in your tire. Check and see if there are weights (for balancing) on the wheels.

[BlueRaven]

My first thought is a belt in the tire that may be broken but i don't believe there's belts in bike tires, are there? Maybe the tire has defect like a flat spot.

[Snake]

It sounds very much like an unbalanced tire as OldGuy has said. Check to make sure there aren't any loose bolts. If none are loose then I would take it back to the shop and have them redo the balance.

[sixstring]

Hmmm... I'll definitely ask the shop to check the balancing. Is the bike even safe to ride? I guess I'll just have to take it REAL slow.

The funny thing is I didn't notice anything when I rode the bike home from the shop... Now it very well could have been just me not noticing it.... but is it possible for a balanced wheel to become unbalanced?

[kkim]

Originally Posted by sixstring

If I had to describe the vibrations, I'd say its more of a rapid thumping as opposed to buzzing; imagine you had a nail stuck to your wheel and riding on that.

is the thumping engine or speed related? try getting the bike up to a speed where the thumping is very noticeable, then pull in the clutch and let the bike glide. Does the thumping continue or does it go away even if the bike is still moving?

[kkim]

Originally Posted by sixstring

but is it possible for a balanced wheel to become unbalanced?

yes, a wheel balancing weight could have fallen off.

[sixstring]

Hey kkim. I tried to pull my clutch in and coast. While the quick vibrations from the engine goes away, the thumping is still there. So i guess this means the problem is not with my engine.

So now the rear tire is the suspect. However, the funny thing is the tumps seem heavier when I'm braking... which leads me to suspect the front tire (nothing was done to it, I just got my rear replaced). Do you have another trick to figure out which tire is the culprit?

[M-Oorb]

You also said you may be feeling it at idle...have you figured out if this is truely the case?
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[sixstring]

Well when I got the bike back from the garage, it was idling at around 2k when it normally idles around 1500. I adjusted the idle know and solved that problem.... Not sure how it got up to 2k to begin with.

[OldGuy]

Jerry I'd just take it back to the shop and have them check both tires. Hopefully it will be thumping on your way there so you can invite them to take a ride and feel for themselves.

Good luck.

[sixstring]

Well just got back from the garage. Got the rear tire balanced. Still having the vibrations. Bringing it back later to get the front tire checked out.

[greg737]

You can get "thumping/vibration" if the shop put the bike back together with the chain too tight. You should check to see if the chain has the manufacturer recommended amount of slack in it.

And remember that you have to check the chain at more than one place. Move the wheel, check the slack, move the wheel some more, check the slack again, repeat, repeat..... because the drive sprocket and countershaft sprocket are almost never perfectly centered and it takes several total rotations of the wheel to cover all the possible relative positions between them.

You have to take into account the fact that if both sprockets have very slight eccentricities (and they often do) then as the wheel rotates you'll get varied interactions between them because the countershaft sprocket rotates faster (about 3 to 1, I think) than the drive sprocket. This is why an overtight chain can create a very confusing "thumping" feel. It's confusing because the thumping doesn't correspond to wheel speed, it ususally has a slower frequency because the minor eccentricities in the drive and counter sprockets that create the tight spot only line up every second to third turn of the wheel.

[sixstring]

Well at this point both my tech and i are only speculating as to what the problem may be. We'll definitely check out the chain slack too. Thanks.

BTW,
Lots of fast and informative posts so far guys, very much appreciated. Thank you.

[kkim]

Originally Posted by sixstring

We'll definitely check out the chain slack too. Thanks.

what is the chain slack right now?

I like to set my slack measurement at the looser end of the tolerance window.