Help I've got the wobbles

baggies2354

Hi Guys,

i'm in need of some help and inspiration, today I decided to use my road bike on my 9 mile commute as I had to drop it in the LBS. On a hill I travel down every day and wind permitting get up to around 30mph, at the bottom there is a seam running along the road where two sets of tarmac don't quite match up since a bus lane was put in. Today I hit that seam and it induced a serious case of the wobbles, scary indeed, but then only a mile later on a cycle path doing 19mph I encountered an even worse case that started as I crossed one of these sections of concrete that they put on cycle paths just before junctions where there are grooves. Now I had encountered the dreaded speed wobble on 3 previous occasions once on a hill in Worcestershire and the second time on a local 10% hill which resulted in a badly broken collar bone (2 operations) and wrecked bike. After this I had new forks and wheels put on and changed make of tyres but still had it happen again and then today. All occasions have been on poor road surfaces or triggered by riding over things like today, LBS think that today may have been caused by some of the spokes in my front wheel having twisted and not be aligned with the others. For the tech minded my bike is a Felt F55 which is an Aluminium frame with carbon chainstays, seatstays, forks and seatpost. The original set up was Mavic Aksium wheels, Continental tyres and Felt forks, the new set up is Fulcrum Racing 3 wheels, Vittoria Diamante Pro tyres and Easton EC90 fork but both set ups have resulted in wobbles. I had read how to deal with it if it happens and it works but I'd rather find a cure as I am losing all confidence in descending.

If anyone has any ideas as to the cause and how it can be prevented I would be most grateful.

Thanks

MountainMonster

It could purely be down to poor technique for going across these parts on your bike. You say you read up on what to do when it happens, but can't prevent it. Alot of the problem may be you see it coming, and automatically stiffen up a bit to try to reduce the shock, which is exactly what you don't want to do. You want to be very loose when going over rough terrain.

sungod

19mph seems slow for speed wobble, worth checking that there's not something loose/amiss with the bike, but is it possible you were giving the bars the 'death grip' after the earlier scare?

at 30mph it's more likely, depending on conditions it could probably happen with any bike, so it's more about avoidance - pressing knee against the top tube, not gripping the bars too tight, unloading weight from the saddle

baggies2354

Thanks Guys,

I've ridden this route for 5 years on my hybrid, MTB and the Felt and until yesterday had never experienced this problem on this stretch of road or cycle path. Maybe the LBS are right about the spokes as on Fulcrum 3's they are flat blades and there was a strong crosswind. I've been quite happy previously going in excess of 40mph on the same bike without problems, both the surfaces that started the problem ran parallel not across the path so I went along them rather than over them and when coming out of them the wobble started. Went down the same road today on my Scott Sub 20 Hybrid same speed no problems.

stevec205gti

Do you have a bike computer fitted? Sometimes the size/position of the magnet can upset the balance of the front wheel.

MountainMonster

stevec205gti wrote:

Do you have a bike computer fitted? Sometimes the size/position of the magnet can upset the balance of the front wheel.

The place of a 5g odd magnet on a wheel is in no way ever going to upset the balance of a wheel enough to cause wobbles.

Dumbest thing i've ever heard.

To the OP, it probably was just the spoke design. With a crosswind and flat spokes it'll be quite a bit harder to keep going well.

dag_on_a_bike

Tis was an entry made by me in an earlier thread:

Been there and hit the deck at 38mph!

See http://www.bikeradar.com/road/fitness/a ... bble-14776

and

http://www.bikeradar.com/road/forums/viewtopic.php?t=12585336

also

http://www.bikeradar.com/road/forums/viewtopic.php?t=12591241

Body's 'fixed' and bike's fixed (arguably better) but to this day, 18 months later, I still don't have the same confidence when descending.

Now, almost 2 1/2 years later I still have not regained my confidence in descending. I have experienced wheel wobble since but not to the same extent and it's scary - I'm getting too old to break bits again.

Here's the link to the thread:

http://www.bikeradar.com/road/forums/viewtopic.php?t=12696809

Peddle Up!

Yep! Been there and done that too. It's very depressing and has spoiled my enjoyment of cycling (a little). I now descend with caution and I can't see that changing unless someone develops an Ironman suit to protect my bones from harm.

stevec205gti

MountainMonster wrote:

stevec205gti wrote:

Do you have a bike computer fitted? Sometimes the size/position of the magnet can upset the balance of the front wheel.

The place of a 5g odd magnet on a wheel is in no way ever going to upset the balance of a wheel enough to cause wobbles.

Dumbest thing i've ever heard.

To the OP, it probably was just the spoke design. With a crosswind and flat spokes it'll be quite a bit harder to keep going well.

So, if the system (in this case the OP's bike) is right on the border line of being rideable and throwing a literal wobbly, a small thing could be enough to tip the balance. You do not know the size of a magnet that may be fitted, how it is fitted, or where it is fitted. Could be next to the valve. Could be out of a fridge motor and glued to the rim for all you know. However, simply removing the magnet could be the end of his woes, so I considered it an easy and simple thing to check.

As for how much it can throw a wheel off, ever been in a car or on a motorbike with an out of balance wheel? Ever seen how little weight it can take to smooth the running back out again? Ever wondered why some bike wheel manufacturers even try using different spokes around the valve to balance a wheel out? Ever seen a model helicopter grenade itself as it's rotors are a fraction out of balance? It may not do much, but it could be enough to throw the OP's bike out of balance.

Koopa91

everything has a resonant frequency. this includes bike frames.

to put it basically, when a bike starts to vibrate at a certain rate it will amplify the vibration. it isnt a major problem, just a minor pain. i dont think there is much you can do about it tho.