Fixed Wheel Speed Wobble

[sskelly]

Hello All,

I have been riding a fixed wheel for over a year now mostly on the flat. I have just started using it for more of a training machine rather than a commuting bike.

On some down hills I have noticed that the rear wheel feels like it is sliding away and occasionally I experience speed wobble. It is very unnerving and today I thought I was going to come off!!

I have a front and back brake and tend to use both down hills. Any advice greatfully appreciated.

Simon

 

[alfeng]

I have been riding a fixed wheel for over a year now mostly on the flat. I have just started using it for more of a training machine rather than a commuting bike.

On some down hills I have noticed that the rear wheel feels like it is sliding away and occasionally I experience speed wobble. It is very unnerving and today I thought I was going to come off!!

I have a front and back brake and tend to use both down hills. Any advice greatfully appreciated.

Check the rear wheel, first ... is the rear wheel true?

Are all of the spokes properly tensioned?

If you think the rear wheel is "okay" then either put it in another frame OR a different wheel in your bike's frame and see if you can replicate the "wobble."

Presuming the rear wheel is sound, then I suspect you may have a crack/broken-seam between one of the frame's stays & the BB shell ... or, even a problem with the seat stays.

Finally, is your rear brake caliper centered and does it apply pressure evenly (side-to-side) while you are braking OR is it possible that you are applying the rear brake so disproportionately to the front brake that you are causing the rear end to drift?

 

[sskelly]

Thanks for the very useful suggestions.

After posting I did wonder about the spokes and went down to the bike sheds to check. They are not as tight as maybe they should be, so that will be the starting point.

It was doing it again on the way in this morning down quite a steep hill, scares the hell out of me. I could not look down to the back wheel to see what was going but I could see the top tube moving left to right in relation to the steerer tube as the rear was swaying.

I will give it a good look over at the weekend and take a flat route home!

 

[sskelly]

I have had a good look at the bike tonight and trued the wheel (it was not too bad), tensioned the spoke a little and corrected the brake caliper position (it was pulling the rim slightly one way).

I have however noticed that there is some paint flaking around one of the welds - could this indicate a problem with the frame?

 

[alfeng]

I have however noticed that there is some paint flaking around one of the welds - could this indicate a problem with the frame?

It could, but there may be some unrelated reason for the paint flaking around the particular weld ...

I think that it would be a good idea if you had someone assess the frame if the "wobble" persists.

BTW. Check your frame's headset, too.

 

[alfeng]

I have however noticed that there is some paint flaking around one of the welds - could this indicate a problem with the frame?

BTW. My presumption has been that your bike's frame is made of steel ...

Regardless, clean & dry the area where the paint has flaked away ... and then, put a short piece of masking tape (e.g., 5cm/2") across the area ... smooth the tape down against the frame's surface as well as you can.

After the next wobbling episode, look at the tape AND if it is torn or pulled away from the frame then there is probably a crack at the weld.

If the frame is aluminum, stop riding it ASAP.

If it is steel, it will need to be repaired ... a gusset should be welded on AFTER the joint, itself, is re-welded.

 

[sskelly]

Hi,

It is an Aluminium farme (Felt Dispatch).

Simon

 

[alfeng]

It is an Aluminium farme (Felt Dispatch).

If you ascertain that there is a crack at the weld (particularly, by means of the broken "masking tape" test), even if it is out of warranty (FELT has only been around since the turn-of-the-Century/Millennium) I think you should be able to convince FELT to replace the frame because I presume there is no evidence of the bike being crashed at any point in time ... it is a premature fatigue failure.

Be very insistent about the replacement frame. FELT should want to retrieve the frame because they should want to have an opportunity to examine it.