Dangerous Speed Wobble - whats the cause

yespsb

I have a serious problem when I get to circa 30mph, my front wheel starts to wobble and in a matter of seconds the wobble increases to the point where there is a serious danger of me being thrown off the bike.

So far I have managed to get away with it by reducing my speed slowly and holding on to the bars with an iron grip but its only a matter of time before my look runs out.

I cannot work out what the cause it and that's why I am asking for help.

Every thing on the bike appears to be tight, tyre pressure is circa 100psi, wheels are true, headset bearings feel good. The bike is a 2007 Specialised Roubaix Pro and the only mods are lighter, better brakes and a pair of Campy Shamal Ultra 2 way fit wheels with Hutchsion Fusion tubeless tyres.

Any ideas welcome, I really don't fancy another bike related trip to A&E, thanks Paul

andrewjoseph

Do a search here or Google for it, generally, if bike is not the issue, it's the rider. Relax, unweight saddle, put knees against toptube, relax.

yespsb

Relaxing as your front wheel has the equivalent of an epileptic fit at 30 mph is a whole lot easier to say than it is to do ;-)

6wheels

Have you put any tubeless sealant in the tyres? If you can , try some other wheels.

6wheels

Should have added, that they may be badly out of balance.

diamonddog

viewtopic.php?f=40013&t=12919056

Have a look at this thread.

Mikey23

I've had this a couple of times and is well scary... My bike is a spesh roubaix too

andrewjoseph

yespsb wrote:

Relaxing as your front wheel has the equivalent of an epileptic fit at 30 mph is a whole lot easier to say than it is to do ;-)

Yes, I do know, I have experienced a few myself.

slowbike

try a different wheel ...

you could also spin the wheel up on a workstand - or just holding it - that should show if there is an imbalance.
An imbalance could be caused by a tube - possibly twisted or a tyre - or the wheel itself.

Escher303

yespsb wrote:

... and holding on to the bars with an iron grip but its only a matter of time before my look runs out....

It's possible that this may be the cause or at least making it worse. Of course it is difficult to relax when it happens but if gripping on really hard makes the problem a whole lot worse then you need to be aware of that fact!

I had a big stack at 35mph after a speed wobble, lost my descending mojo completely, to the point where I could involuntarily make my bike wobble at 12 mph downhill, it took me a while to work out but it was because I was very tense and mistakenly believed that holding on tight would stop the wobble.

Eventually I worked out that both times I've had it really bad I was hit by a strong side gust descending at 40mph and tensed, gripping the bars too tight and this brought on the wobble, gripping hard as the wobble started made it worse. Vicious circle.

So I practised and practised, increasing speed and descent distance makign sure I was relaxed and concious of what I was doing especially in cross winds. I needed to think to relax my position even if my natural reaction was not to. BY being aware of what I was doing and forcing myself to not tense I got there eventually and now I'm happy and relaxed descending at 45+ mph again.

So yes it isn't easy but tensing up even if that is not the original cause will make a speed wobble a whole lot worse, so what choice do you have?! Practice descending relaxed on hills you feel safe on and build up. It is much, much better to avoid the wobble in the first place than to correct it when it happens. You can help with this by being relaxed when you go downhill.

morstar

Escher303 wrote:

Practice descending relaxed on hills you feel safe on and build up.

I think this is absolutely key, not just practice, practice, practice, but practice WHERE YOU FEEL COMFORTABLE.

30mph feels scary fast on some steep local twisting hills whilst doing 40+ on a smooth wide road is as relaxed as anything.

The first thing is to trust the bike. Learn to build up your speed on a big, wide and smooth road. If you still get a wobble where you're totally relaxed, you know it's mechanical. Conversely, when you're experienced going 30+ in a comfortable environment but experience a wobble at the same speed on a trickier descent, you know it's rider induced.

One thing I will say is get your weight forward so that the steering system has good contact under load. Nervous descents frequently involve leaning back away from the slope but this makes the bike more like an unguided missile. Very easy to see in skiers who lean back.

slowbike

morstar wrote:

Escher303 wrote:

Practice descending relaxed on hills you feel safe on and build up.

I think this is absolutely key, not just practice, practice, practice, but practice WHERE YOU FEEL COMFORTABLE.

I've got several choices of routes home - a couple have long descents that I will avoid in the wet - they're straight enough roads, but in the wet doing 35-40mph with cars passing it just doesn't feel safe ... so yes - practice, as has been said - on roads where you feel comfortable!

Bar Shaker

There has to be something mechanically wrong here, though.

I occasionally get to high 40mphs and a friend recent did 59mph, all wobble free. 30mph is not fast and there is no way you should be getting a speed wobble at that speed.

I would look for play in wheel bearings and headsets. Remember, the problem could be on the back wheel, as much as the front wheel.

Shuggy76

As has been mentioned, keep a relaxed but good position on your handlebars, and ensure that there is enough weight distribution over the front wheel, not enough can lead to a nervous front end.

essexeagle

When going downhill hang your ar5e behind the saddle and over the back wheel leaving a space of no more than .5cm between it and the rear tyre. You may still crash but you will look good doing it

Gary D

I have had it happen to me twice. The first time was going down Fish Hill near Evesham and was terrifying :shock: . At first I thought I had punctured, but hadn't.
In the end, it was the rear wheel bearing that had a very small amount of play in it. The wheels are Mavic Aksiums, and although they have cartridge bearings, they are still pre-loaded and can have play. Once I adjusted them, the problem never re-occurred on those wheels.
The second time it happened with another set of wheels, I knew exactly where to look and sure enough there was slight play again.

So, the moral of the story is - check your wheel bearings!!

Gary.

unixnerd

Had this once and it was down to low tyre pressure. Yours sounds worse, I'd remove and refit the tyre in case it's not seated properly.

Nairnster

I have started experiencing this on my Giant Defy 2. Getting it on any hill,.

Nothing on the bike has been changed, from when it was working fine and not doing this on the very same hills. Its happened in all conditions too, and I keep my tyres inflated to the same pressures (I check before every ride)

Its scared the hell out of me several times, and at the moment I am too scared to ride the bike as it kicks in so violently, I am worried it will throw me off before I get the chance to do anything.

Anyway, had the rear wheel off today, and noticed the rear QR skewer is slightly bent on the drive side. Cant remember it being like this when I got the bike, so not sure how its happened.

Am going to replace it and see if that makes any difference, Cant see it doing so, but I cant fond anything else wrong with the bike.

pearceygy

I had this problem myself on speeds over 30+ on my giant defy it was really annoying and i posted on here about it, anyway I was advised to have a bike fit and i found that my bike size 58 was to big for me.
I have since bought a new bike 56 frame and I now regularly do speeds of 40+ on dissents without the slightest bit of wobble.

kayakerchris

Have a look at this thread for some help. https://yacf.co.uk/forum/index.php?topic=74617.50

Wheels can be part of the problem. I have run hutchisons for the last couple of years and have no problems with them. I would be surprised if it was the sealant as that will evenly distribute fairly quickly unless it has all congealed in one place.

try and borrow some wheels and try them out. I would get a reliable sensible LBS to look at your bearings to make sure that they are all trued.

It may be you, but it is unlikely.

nweststeyn

Had this happen once. It was the front wheel bearings, made worse by me getting the fear and tensing up on the bike.

vichanby

It's not caused by the rider. It's a mechanical instability that has been well known for years e.g. as a 'tank slapper' by motorcyclists and a lot of research has been done on this in the last decade. I've a Trek which threw a scary wobble descending the Crimea Pass in Wales at 83 kph and I had a repeat in a club freewheel competition. In both cases it happened on gusty days. I also have a Donohue which is rock steady at all times under similar conditions, no change in rider input.

kayakerchris

But if you can't tell us what that 'mechanical instability' is then you're just crying wolf

No he isn't. He is saying as everybody has said that there are a multitude of mechanical causes that can cause a harmonic disturbance which is in the right frequency to build into a dangerous wobble. Some bikes by the shape and length of the tubes will do it easily, others will need something odd to happen, such as a specific speed on a certain tyre with a gusty side wind. some you will be able to easily diagnose, others will be impossible.