on Sundays Road ride, I went down a Dual carriage way, I was going as fast as I could manage(not very) when the Bike started to wobble very violently, to the point I was looking for the softest landing spot to bail out, I relaxed my grip on the bars and gently applied the brakes, and it gradually disappeared.I carried on my ride without any further incident.
when I looked at the ride on Garmin, at the rough point it happened I was doing 45mph, a few things I have read mentioned it could be all sorts of variables,but I’m a little concerned that it will happen again.
Bike is a Planet X Pro Carbon, 38mm Carbon clinchers, 25mm tyres at about 100psi.
any tips on getting round this?

I vaguely recollect one doing something to my bike which caused something similar. Pannier on back with too much weight? Locked out front suspension doing 45mph along road going down hill in Wales?

I’ve had this, my arse was going like a rabbit’s nose I don’t mind telling you.

Says to stop it, well, I now always descend on the drops and make sure I have a reasonably relaxed grip, I also kind of grip my frame with my thighs if I’m not pedaling.

That seems to have stopped it for me, I’m sure a better cyclist will have a better was of stopping it mind you.

Wheel balance. I’ve had the 40+ mph wobble when I put spokey dokeys on my road bike. Throw in tired and slow reactions to help the wobble to amplify and your bouncing across a dualcariage way into a bush.

ive seen wheel balance issues before – its not that mad a theory …..

how ever mrs T-Rs friend had a px carbon pro – and it speed wobbled like mad

the headtube was not in alignment with the rear of the bike according to the string test.

same kit on a straight frame sorted the issue.

Yes, I had a similar Rabbits nose feeling, especially as there were cars all around.
No spokey dokeys fitted, although perhaps if i fit some this may counter the effect.

It’s probably the weight of the inner tube valves knocking your wheels out of balance. Turn your bike upside-down and spin the pedals fast in top gear and you can observe the effect while keeping your fingers clear!

Well, if ever there were an excuse for a new frame, I guess this is it!.
I have had this bike a couple of years and never had this, however the wheels are only on the second outing.

I had the mother of all tankslappers on once, turns out my wheel wasn’t in the rear dropouts correctly.

THe lighter the wheels the more pronounced the effect

Is that it?

[video]https://www.youtube.com/watch?v=xODNzyUbIHo[/video]

Could be incorrect weight distribution.

It’ll only happen at one speed. Hold on tight, pedal like buggery and get past it 😉

Yes, that video shows it quite well, very unnerving i can assure you.
I will try another day with the previous wheel set, to see if that makes a difference.

that video shows it quite well

Brave rider! Shows that the bike is still stable, though, even when resonating like Motorhead’s bassbins. Pretty cool.

Well, if ever there were an excuse for a new frame, I guess this is it!.
I have had this bike a couple of years and never had this, however the wheels are only on the second outing.

There’s a clue in there OP…

It’s probably not the frame, it’s probably your new wheels.

[Edit: ah I see you’re going to try the old ones, good call. 🙂 ]

Planet X Pro Carbons have a rep for this… (I own one and have never had it happen, though I know of others who have). I’ve often wondered if it’s a particular size frame that is prone to it?

Clamp the frame between your knees, preferably before it happens (now you know what speed it’s susceptible to it).

Mine would do it if I touched the brakes at 30. The only way to stop it was to get off the brakes and pedal. Made cornering exciting. Changing my cleat position and dropping the saddle 5mm fixed it. I still grab the frame with my knees while descending though…

Yup, I had this on my PX pro carbon on one of its earlier outings. Turns out my descending technique at the time was a bit too “MTB” as I read up a lot on this and the best way to prevent the dreaded speed wobble is to keep your weight low and forward. On the drops or leaning into the bars worked for me, I have never had the issue again.

I’m glad I’ve been through all the speeds/actions mentioned without issue on mine.

I did just raise my saddle by 4-5mm though. :S Fingers x’d

Only ever had oscillations from a lightweight steel frame when riding no handed around 20mph.