Accident front wheel wobble

[cyclingthelanes]

I fell off my bike (Marin Larkspur ladies)on Saturday while cycling the lanes. There was a briar hanging out of the hedge on my way downhill, not cycling very fast. I didn't see it as a particular danger and I thought I would go through it/under it. However it may have caught on my handle bars and after that my front wheel went into a strange wobble and I went over the top. Could it be that the wheel wasn't completely true and this was a kind of perpetual motion wobble as suggested by a cycling friend? I have since noticed that one front brake block is much more worn that the other side. I have lost confidence in my bike unless I can find the reason why this happened. Any suggestions or thoughts very welcome. I NEED to get back on my bike asap- when my bruises heal.

 

[Mr Pig]

Hi there and welcome :0)

The brake block wear is down to poor setting of the brakes. One side has been rubbing/pressing harder than the other. Nothing to do with your crash.

The wobble might well have been down to muscle twitch on your part. Again, nothing to do with the bike. What to do is check your bike, which you should do anyway after a crash.

Spin the wheels and watch the wheel rims closely for any wobbles or bumps as they spin. If you see any, take the wheel to a good bike shop and ask them to true the wheel for you. When you refit the wheels make sure they are tight into the drop-outs, the slots they fit into, and lock them in as tight as you can.

Also look along the sides of the frame, forks etc to see if anything is bent. If you're in any doubt, ask the shop to do this too.

Buckled or bent wheels will give you a slight wobble or bobbing as you ride at speed on a smooth road, you'd see a bad buckle a mile off. If fact a wheel can be slightly bucked without you feeling anything at all.

Bike wheels act as gyroscopes. If the wheels are not tight in the drop-outs, or if the frame is not straight, the two will 'fight' each other. If you're going along at speed on a smooth road the bike will feel like it does not want to sit straight up, it'll want to pull slightly to the left and right.

However, none of the above faults will cause the kind of massive low-speed instability you describe. I don't think there was anything wrong with your bike, you just fell off ;0)

 

[cyclingthelanes]

Many thanks for taking the time to reply. A friend has had a good look and can find nothing wrong but yes I will take the bike to the bike shop and ask them to check it over. It's not the first time I've fallen off over the years but because I can't find an explanation for this fall, it has unnerved me.

 

[fossyant]

Riding bikes = you will fall off sometimes..... don't worry....

Probably nothing wrong with the bike, could have been poor/slippy surface that made the situation worse..

Jump back on and keep pedalling !!!

 

[cyclingthelanes]

Ideal weather conditions so can't blame the road surface. Probably the contact with the bramble had a bearing on the accident.

 

[PpPete]

take the bike to the bike shop and ask them to check it over.
.

It's all very well if you got the bike from a shop in the first place...

My dad (77 yrs) just fell off a bike I built about 25 years ago, now I've got to take it back and check it over for him...
GP says it could be down to his semi-circular canals, but I've not found any of those either on ebay or LBS?

 

[peanut]

what you experienced is the same phenomena as motorbikes get . Its called a `tank-slapper'. If you something suddenly knocks the front wheel off course at speed the bike forks are designed to auto correct or self centre. If that process is repeatedly quickly enough the motion becomes a fast occilation increasing in magnitude until you have a major off. All 2 wheeled vehicles are subject to it.

 

[Mr Pig]

Probably the contact with the bramble had a bearing on the accident.

Years ago I was pootling along a dirt track at diddley-squat miles an hour when I noticed a fly sitting on my left thigh. I moved to brush it off and the next thing I knew I was on the ground harbouring a strong suspicion that my left shoulder blade was broken. It wasn't, but to this day I have no idea why I went over the bars.

 

[Bigtallfatbloke]

I know how it feels after a bad fall. I came off in Meersburg on the bodensee this summer and it shock me up quite a bit. Luckily I had no choice but to get back on the bike again as the next day i had to ride to Basel to catch a plane.

I was very lucky as I hit my head on the concrete path and I was not wearing a helmet. I cut my knees and arms badly and had a graze on my head...I later found out (after I rode to Montpellier) that i also broke my wrist in that fall.

All i can say is that being shaken is very normal. Get back on the bike and do all you can to stay safe.

 

[Mr Pig]

Get back on the bike and do all you can to stay safe.

Isn't that a contradiction? ;0)

 

[cyclingthelanes]

Thank you all for taking the time to reply. The "tank slapper" sounds exactly what I experienced as I remember trying to hold on and the wobble just getting worse, until KLONK, the tarmac and I were making contact. Well I've booked the bike in for a check - up. My grazes and mega bruise are healing. The cracked helmet has gone in the bin. Don't know if I'll be on the bike next week for our holiday in the Yorkshire Dales as planned or if I'll take the return to cycling -the- lanes a bit more slowly. I really helps to know what happened. Thank you again.

 

[Mr Pig]

I remember trying to hold on and the wobble just getting worse, until KLONK

You probably fell off because you tried not to!

Much of riding a bike you obviously do subconsciously, you relax and just do it. Sometimes, if you panic, you can try too hard, it becomes something you're trying to do consciously, and it can't be done. You're over-correcting everything. The wheel goes one way, you pull it the other, but too far and the whole thing repeats itself. Until you fall off ;0)

You see it all the time when you're teaching kids. I remember years ago my son, who was about seven at the time, panicked as he was going down a hill. He was too scared to pull the brakes and was going faster and faster, heading for a bad crash. I was at the back of the group and I shot forward and caught up with him. I rode beside him telling him to relax and let the bike take care of itself. Once he'd loosened up a bit I told him to gently brake. Worked fine.

 

[02GF74]

could well be tank slapper; especailly if you have suspension front forks.

so question really is how to ensure it doesn't happen again? different tyres or bike would be a start but a lot depends on the rider.

wikipedia says:


Wobble, shimmy, tank-slapper, speed wobble, and death wobble are all words and phrases used to describe a rapid (4–10 Hz) oscillation of primarily just the front end (front wheel, fork, and handlebars). The rest of the bike remains essentially unaffected. This instability occurs mostly at high speed and is similar to that experienced by shopping cart wheels, airplane landing gear, and automobile front wheels. While wobble or shimmy can be easily remedied by adjusting speed, position, or grip on the handlebar, it can be fatal if left uncontrolled. This AVI movie shows wobble.
Wobble or shimmy begins when some otherwise minor irregularity accelerates the wheel to one side. The restoring force is applied in phase with the progress of the irregularity, and the wheel turns to the other side where the process is repeated. If there is insufficient damping in the steering the oscillation will increase until system failure occurs. The oscillation frequency can be changed by changing the forward speed, making the bike stiffer or lighter, or increasing the stiffness of the steering, of which the rider is a main component.[4]

 

[cyclingthelanes]

I don't have front suspension forks and yes you are right - how can I avoid it happening again?

 

[peanut]

could well be tank slapper; especailly if you have suspension front forks.

what do you mean the same sort of tank-slapper i spoke of on page 1 ?

what you experienced is the same phenomena as motorbikes get . Its called a `tank-slapper'. If you something suddenly knocks the front wheel off course at speed the bike forks are designed to auto correct or self centre. If that process is repeatedly quickly enough the motion becomes a fast occilation increasing in magnitude until you have a major off. All 2 wheeled vehicles are subject to it.