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There's one road on my commute that I only ride when commuting by road bike (the mtb route is through a forest & quarry 😉 )
But the roadie gets a shake on at 60-70 kph, quite scary. Have checked frame, forks, headset and wheel true. Changed tyres, and still got the shake.
Was playing with the bike today and spun the rear up to an indicated 100 kph (garmin, rear wheel sensor). Sure enough, shaking like mad between 60 and 70...
Wheel balance? Hubs loose on the cones?
You're probably hitting the resonant frequency of the frame. Try attaching a lead weight to it.
Clamping top tube with your knees can help. Deals with the symptom not the problem though.
Yep, it's resonance due to the wheel wobble. You can try getting the wheel more true but the chances are, it's the tyre. Try soaping the bead and then inflate to max pressure. Should hear the bead pop into place. Then let air out to desired pressure. Beyond this, it's tyre manufacture.
Remember to clean the soap off the rim if you're using rim brakes. Could always try adhesive wheel weights for cars. Or just ride faster when it starts.
Do you mean a head-shake tank-slapper type of wobble or a more vertical bounce kind of feel? You say you get it on the rear wheel in the stand - are both rims the same? Is it a skinny steel frame?
Taking a punt that it's a sleeve-joined rim F+R so off-centre balance, the front wheel creates a side-to-side wobble effect as you steer (even slighty, not on a corner necessarily) and this can set up a head-wobble on a flexible, springy frame.
Frame front-end stiffness and front trail seem to have a balance / resonance and it's felt most easily on skinny steel frames with short to middling trail ime. Bencooper's right, add a weight to the front of the frame (top tube) or try a different wheel in the front, to see if it still does it.
Some good suff there - ta!
Oversize steel frame, with a fairly steep head angle. Wheels are Mavic alloy rims. Shake doesn't happen under power, only on freewheel - so very dependent on gradient. The road mentioned above ^^^ is steep enough to get over 70kph, but not so steep that you [i]have[/i] to use the brakes...
However, it's quite twisty, so not easy to keep the power on without drifting wide. Come off the power, and the bike starts to shake - side to side wobble, tankslapper style. In the dry, confidence is there to go faster, and it's no problem. Wet and / or traffic, and I'm on the brakes, doing about 45 and clenching buttock....
Will have to play with the back wheel...
And today - it was fine.....?
Got up to 67kph - no wobble / shake
Different roads and better surfaces, but same speed ranges
PUZZLED ???