Handling problems

KevinDrinkell

Hello all, I was hoping you might be able to help with a problem I have when going down some slopes (not even hills, I live in Norfolk!!). The problem is when I'm starting to build up speed and on two particular roads, every time i ride them my back wheel starts shaking and feels like it's going to fall off the bike followed by me. I become gripped with fear, tensing and reaching for the brakes which only seems to make things worse. Eventually I have to stop, collect my thoughts and then start again. I've started going down it at about10mph which is very frustrating as other roads I can do 30+ without a second thought so I don't think it's so much a problem with the speed but something which just keeps happening on these two roads though it's starting to affect my confidence on other slopes. I can't understand though why the shaking of the wheel starts. I have a Giant SCR2, XL bike frame, I'm 6ft5 and a fit (!) 16stone if this is relevant at all. Any advice would be much appreciated as this is really ruining my enjoyment of riding.

This panic I have when descending these slopes also occurs when going round bends. I can't take them at any speed and if I try, I daren't turn sharp enough to guide myself round because I feel my bike is going to skid out from under me and so I again become gripped by panic and start veering towards the kerb unable to steer away from it. Once again I have to brake to a halt though a few times I've just gone straight on to the grass verge as I've been unable to make myself steer. I think I need a bike psychologist because I don't know what's going on in my mind!!! Regards

Gerry Attrick

Assuming your bike is set up right, I reckon you must be a new convert to cycling and need to gain confidence. Years ago, I had a bad crash rounding a right-hand bend on a motorcycle, whch for months afterwards meant I could ride round right-handers only at walking pace. If you are not familiar with bike geometry, get your local bike shop to check out frame and wheel alignments.

Some road surfaces on a cycle seem to match with the natural frequency of the frame and cause the whole plot to go haywire.

Practice on the same familiar bends at gradually increasing speeds until you become more confident of you and your bike's abilities. It will take time, but you will get the hang of it. Start by rounding bends at a speed you definitely know you can get round safely, and do that a good few times.

Best of luck.

Fab Foodie

http://www.sheldonbrown.com/brandt/shimmy.html

Zendog1

Shimmey scares the shit out of me too. If you want to ride the hills at full speed you could try griping the top bar between your thights but I just slow down on the one hill that produces the resonance that causes it.

topdude

Hi, first look at the bike -
I suggest you have your wheels checked and if necessary adjusted, for no play in the bearings, minimal wobble at the rim (1mm or less) and fairly even spoke tension.
What tyres are you using ? if they are narrow ie 700 x 23 or 25 it might be worth fitting some wider 700 x 28 tyres, these will have slightly more rotating mass and should change any tendency for the bike to vibrate / shimmy. Also wider tyres might make you feel more confident about going downhill and cornering. You can always go back to narrow tyres as you gain confidence.
Second, the way you ride -
When going downhill at speed i find it best to sit further back on the saddle or even slightly off the back of the saddle and grip the sides with my thighs. Hold the handlebars lightly so you are in control but not gripping tightly. The bike can move around beneath you but you are still in control.
Let us know how you get on.

jellybellywmb

I encountered the same sensation when I got my SCR 3.
I checked the bike and noticed that the front wheel was not in the middle of the forks but pushed over to one side.
I took the bike back and the set the wheel up correctly and the problem has gone.

jellybellywmb

http://www.bikeradar.com/forum/viewtopi ... highlight=

Like this

John.T

Are you certain that it is the back wheel that is at fault. More often 'shimmy' comes from the front and is felt as a shaking of the handle bars and the front of the frame.

KevinDrinkell

Hello all,

Many thanks to you all for your replies and tips and techniques. I didn't realise there was a term (shimmy) that covered this area and if nothing else it's a some relief not just me who experiences this!

To the questions asked:
- I have always cycled but am fairly new to road biking but so I would agree I need to gain more confidence on cornering definately!
-The wheels/tyres are 25s.
- When I hand turn the wheels there does appear to be some limited wobble but they have been like this since I've had the bike. I did query this with my the bike shop but they said it was more likely to be slight uneveness in the tyre rather than any buckling of the wheel. I do seem to suffer with rattling spokes on my front wheel though which have been tightened at the shop a couple of times since I've had the bike (6 months)
- The vibration/wobble does feel as though it's coming from my back wheel
- It is only on two roads were I have experienced this so maybe there could be something in the point about wheels resonating with the road surface. I look closely at the surface when I go over it for any obvious signs of deterioration but it doesn't look any different to other parts of the road though there must be some reason why it doesn't happen on all slopes? Having to slow down so much to go over this stretch I couldn't imagine descending at 40 odd mph over roads I don't know!

I only do this commute on a Friday so will see how it goes this week buit the suggestions about getting the wheels/bearings checked out seem very sensible and then I might try the thicker tyres if this doesn't do the trick. Could tyre pressure have any impact BTW?

Thanks to you all again, this is a brilliant forum

feel

Might be worth checking that the rear tyre is seated properly, sometimes they aren't evenly positioned all the way round. It is possible that the rear tyre isn't balanced ie the weight of it isn't uniform all the way round, you could try swapping front and back tyres around and seeing if this has any effect. Is there a rotation direction marked on the tyre?

grayo59

These roads don't cross a ley-line do they?

O/K!

heavymental

I'd just google shimmy and speed wobble and go through the suggestions you find but certainly you need to relax. Take a deep breath and relax your body but make sure your in the right position too. Good luck, shimmy can be a real pain and take a while to get over.