tribanjules
Guru
- Location
- Birmingham
Good cure for constipation
Terrifying wobble under braking
- Thread starter winjim
- Start date
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Or lace up the ear flaps on your deerstalker.
raleighnut
Legendary Member
- Location
- One of the 'Elite'
It's a Peugeot, they're 5hit, they've always been crap but some folks won't believe it, bin the frame and get a Raleigh.
andrew_s
Legendary Member
- Location
- Gloucester
It's standard speed wobble, caused by the steering feedback into the bike matching the natural resonance frequency of the frame and forks.
One of the things that affects whether it happens is the weight distribution on the bike, which will be why it happened under braking and not whilst accelerating through the same speed.
I'd try experimenting with tyre pressure, or a different tyre, with more or less tread on it. I get a mild wobble riding no hands at about 18 mph, and tyre pressure changes will change the speed it happens at over a 5 or 6 mph range.
There also exist steering dampers for bicycles, though the ones I've seen are much simpler than the proper hydraulic dampers sometimes used on motorcycles to prevent tank slappers, so I've no idea how effective they may be.
One of the things that affects whether it happens is the weight distribution on the bike, which will be why it happened under braking and not whilst accelerating through the same speed.
I'd try experimenting with tyre pressure, or a different tyre, with more or less tread on it. I get a mild wobble riding no hands at about 18 mph, and tyre pressure changes will change the speed it happens at over a 5 or 6 mph range.
There also exist steering dampers for bicycles, though the ones I've seen are much simpler than the proper hydraulic dampers sometimes used on motorcycles to prevent tank slappers, so I've no idea how effective they may be.
Smokin Joe
Legendary Member
- Location
- Bare headed cyclist, Smoker
So how do you update your Facebook profile or type a text if you don't take your hands off the bars?
Facebook is, like, SO 2015.
You mean Instagram or Snapchat. I think the biggest problem is the mobile selfie
D
Deleted member 1258
Guest
Yes I still remember one from the early 1970's, on a Triumph Speed twin at 70mph.
Smokin Joe
Legendary Member
- Location
- Bare headed cyclist, Smoker
The only speed wobble I've experienced was on a Raleigh Dynatec at little more than walking pace. I'd just pulled away from home and before even clipping the left foot in the bars started snaking violently from side to side, I only just managed to stop before falling off.
If anyone can explain why that happened I'd love to hear it.
If anyone can explain why that happened I'd love to hear it.
OP
OP
winjim
Smash the cistern
Had a bit of a test ride this morning (my riding is currently limited to commuting two days a week). No descents but a good blast along the bottom of the valley and a chance to test the brakes.
There is a definite pulsing under braking, coming from the front. I imagine it's from either a buckle or a particularly clean/dirty/rough/smooth patch on the rim. As I brake harder this is making the bike oscillate back and forth. I'm guessing that once the frequency of this oscillation coincides with some harmonic of the resonant frequency of the frame/bike and rider/whatever, then it's inducing the violent side to side wobble. Braking doesn't help because it just increases the amplitude of the oscillation.
Next step, clean the rims and check for true.
There is a definite pulsing under braking, coming from the front. I imagine it's from either a buckle or a particularly clean/dirty/rough/smooth patch on the rim. As I brake harder this is making the bike oscillate back and forth. I'm guessing that once the frequency of this oscillation coincides with some harmonic of the resonant frequency of the frame/bike and rider/whatever, then it's inducing the violent side to side wobble. Braking doesn't help because it just increases the amplitude of the oscillation.
Next step, clean the rims and check for true.
Yellow Saddle
Guru
- Location
- Loch side.
I will be extremely surprised if unevenness in the brake track caused your shimmy.
OP
OP
winjim
Smash the cistern
Well there is definitely this pulsing/oscillation effect, which needs sorting out whether it's the cause or not, so it's a reasonable place to start.
raleighnut
Legendary Member
- Location
- One of the 'Elite'
I'd look for a 'ding' in the rim, can't really see anything else causing a pulsing, if it was contamination it would have 'evened out' after a short while.
I'd use the adjuster to reduce the pad clearance until you can tell where the 'grab' is on the rim.
OP
OP
winjim
Smash the cistern
I should get round to taking the thing apart and regreasing it anyway. So far I've only got as far as servicing the hubs and installing some new brake cables. The headset doesn't feel loose...
