Wierd vibration...

[sirroada]

So here is the story...
Bought a new S-works Tarmac off the shelf on clearance. It was a leftover 2015 that no one had purchased. Absolutely sweet ride, smooth, fast, matte black/white color, duraace, Roval Rapide 40 wheels...all the goodies. But after two weeks of pounding the pavement the matte finish started peeling on the rear chainstays. So, I took the bike back to my LBS and asked if there was any way to fix it. They took some pictures, called Specialized and the verdict was...we don't fix them, we replace them. So kudos to Specialized, they sent me a brand new 2017 S-works Tarmac frame. The LBS swapped all the parts from one bike to the the other.
Got the new ride back...its sweet BUT...The new bike has an annoying vibration that starts around 20mph and gets more noticable the faster you go. Its enough to make my hands go numb. It is definitely speed related as I don't notice it at any speeds under 20, it is always present, never intermittant and it happens whether I'm coasting or pedaling. It is NOT frame wobble, it is a vibration. It seems to lessen if I unload the rear wheel by leaning my weight forward onto the handlebars.
All the parts are tight on the bike. I did notice that when I hand pedal the bike in the bike stand there is a lot of up and down movement of the rear wheel, almost like its out of round...but it isn't. I pulled the tire and tube off the rear wheel put it back on the bike, spun it up and it still had that bounce in the bike stand. Could that be it? Otherwise...what are your thoughts?

[MesiJezi]

Sounds like a wheel bearing issue? If it continues even when you're not pedaling, that's where I would look. Or rubbing between some part of the wheel and another fixed component.

EDIT... I guess I didn't read the full post. Does the period of the vibration correspond to the RPM of the rear wheel? Maybe it is badly unbalanced?

[David Kirk]

Is it the same wheels on a new frameset or new wheels too?

dave

[Mark McM]

Well, the first easy test for a wheel issue is try a different wheel.

It is not uncommon for a small imbalance to make the bike vibrate when cranking the rear wheel when in a work stand. But half the equation for an imbalance vibration is the stiffness of the coupling - a work stand is much more flexible than a road surface or the bike frame, so an imbalanced wheel will create much less vibration when the bike is actually ridden. In my experience, a wheel imbalanced enough to cause a vertical vibration when riding will also create a noticeable forward/backward surge of the bike as the wheel rotates.

What is the approximate frequency of the vibration? At 20 miles an hour, the wheel rotates at about 4 revolutions per second - is that about the frequence of the vibration?

[Peter P.]

Can't be the rear wheel because the frequency of the vibration is too high for the wheel rpms, as you describe it.

As an aside, mount the wheel in the frame without the tire and verify the wheel hop is not in the rim. Then, switch tires front and rear to see if the hop appears on the front. If the hop is as bad as you say, it could be a bad tire regardless of whether it's part of your vibration problem.

As for the vibration, I don't know what tire pressures you're running or how much you weigh, but I'd suggest lowering the pressure 5psi. per ride to see if the vibration disappears. I'm thinking your tire pressure is too high and what would normally be considered road feel is being transmitted from the stiff frame to you.

Do you feel the vibration through your seat AND your handlebars, or just one?

[sirroada]

4 cycles per second sounds about right, hard to tell for sure. It is a higher frequency and increases with wheel speed, primarily in intensity.

Wheel still has "bounce" with tire and tube off it mounted in the frame.

I feel the vibration in both the saddle and the handlebars.

Same wheels that were on the previous frame (Roval Rapide 40's-full carbon, rim brake).

I just remembered that previous to moving the parts to the new frame I removed S-works tires and installed Continental Grand Prix 4000s ii tires. I did put 100 miles before moving them to the new frame and didn't notice any vibration on the old frame but those 100 miles weren't on smooth roads so I may not have noticed it.

I'm 185 lbs and am running 105 psi.

[shovelhd]

Originally Posted by sirroada

4 cycles per second sounds about right, hard to tell for sure. It is a higher frequency and increases with wheel speed, primarily in intensity.

Wheel still has "bounce" with tire and tube off it mounted in the frame.

I feel the vibration in both the saddle and the handlebars.

Same wheels that were on the previous frame (Roval Rapide 40's-full carbon, rim brake).

I just remembered that previous to moving the parts to the new frame I removed S-works tires and installed Continental Grand Prix 4000s ii tires. I did put 100 miles before moving them to the new frame and didn't notice any vibration on the old frame but those 100 miles weren't on smooth roads so I may not have noticed it.

I'm 185 lbs and am running 105 psi.

105psi is way too high. Try dropping them to 90psi. Also, GP4K tires can have a loose fit on some rims. The bead will seat but one side will be higher than the other, which will thump lightly at high speed. Spin the wheel and look for anomalies. If this is the case, deflate the tire, squeeze it all the way around the rim, and inflate slowly in steps, spinning the wheel to check for out of round.

[Peter P.]

I don't know what the tolerances are for carbon rims, but I would expect them to easily be as round as new, handbuilt aluminum rims.

Since carbon rims do not need a splice to hold the ends of the rim together, there should be no "hop" due to the weight of a spliced rim. I'm assuming the bounce you see is an out of round wheel and not the centrifugal force of a splice causing the bike to bounce up and down while in the stand.

You could have a faulty tire. Either borrow a set of tires to try, or as I suggested earlier, swap tires front to rear and see if the symptoms change.

You could also try putting the bike in a stand and cranking the rear wheel up to speed in the largest gear. Perform this test both with the tire ON and OFF. See if the bike bounces more in either case.

Tire tolerances are typically +/- 0.030" while typical rim tolerances are 1/10 of that.

[Mark McM]

You've described what you are feeling as a "vibration". But is it continuous oscillation, or is it more like a rapid "thumping"? For example, a tire that has a bulge will cause a quick "thump" at one particular point in the wheel revolution as the bulge reaches the ground contact point; whereas an out of balance wheels will cause a continuous up-and-down motion through out the entire wheel revolution.

[Fatty]

Try a different wheel tire combo. I had a wheel with a lot of shake in the stand. Used a long stem tube with the nut and a bullet valve cap and it took out most of the shake. And the bike did feel smoother afterwards.

[moobikes]

Could be something else but sure sounds like you are describing speed wobble.