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Front Wheel Instability Enve 8.9
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Hi, during IMUK this month I experienced some front wheel stability issues that pretty much ruined my bike leg. I am riding a 2014 Cervelo P3, Enve 8.9 CC with Conti 4000s 25mm, 105 psi (at start - vittoria latex tubes). I weigh 90kgs and am 6'3".
I had completed a couple of fast descents, including coming off the back of Sheephouse Lane, which is both fast and slightly technical with bits of off-camber bends and not great road surface, and had no issues with my bike. Then coming off a further fast descent (30mph+) I hit a couple of big ruts in the road surface in quick succession. These were not potholes that could be avoided, just a generally poor road surface. After hitting these ruts my bike started to go into a speed wobble (something I have experienced before and know how to handle - grip the top tube with your knees, relax and ride it out when possible with a bit of 'feathering' of the back brake). This speed wobble very quickly escalated into what I can only describe as a 'tankslapper' (from my motorcycling days), were the front wheel felt like it was severely buckled. To say I was crapping my shorts would be an understatement. I was basically looking for somewhere to crash with the softest possible landing, whilst shouting f**k a lot.
I somehow managed to keep the bike upright and using the back brake brought the bike to a stop. I got off and checked the front wheel. All of the spoke tension seemed equal, the QR was looser than when I had checked it in the morning, so i tightened that up and the headset seemed fine. There was no lateral movement in the wheel either. I checked the back wheel and that seemed ok too. I got back on the bike and carried on. The same thing happened a further two times very quickly after, albeit not as bad as I was a bit wary of getting up to very high speeds. I decided to abandon the race on completion of the first lap, as I had to get back to Bolton anyway. After completion of the first lap, were i was on the brakes on every decent to avoid going over 20mph, my average speed was around 15mph. I changed my mind about sacking the race and continued on with riding the brakes on every descent. When I got off the bike my hands were really sore after riding on the bull horns pretty much the full distance.
I was trying to problem solve this issue all the way round and noticed that the bike felt solid when pedalling at load at good speeds (i.e. on a flat or slight incline), and the problem on occurred when freewheeling at high speed. I will be sending my wheels off to get the checked over, but they look totally fine by my untrained, but mechanically astute eye.
Has anyone else had an issue like this, or any experience that they can share please?
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Re: Front Wheel Instability Enve 8.9 [Xplombier] [ In reply to ]
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Bike shimmy can be caused by a few things, like a flexy toptube or poor weight distribution over the wheels. It is rarely caused by the wheels and by the spoke tension being too low. I would look elsewhere on your bike.

Have a read:

http://cyclingtips.com/2011/03/speed-wobble-when-the-bike-shakes-its-head/


http://davesbikeblog.squarespace.com/blog/2006/8/18/shimmy-re-visited.html


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


http://www.slowtwitch.com/Tech/Speed_Wobble_5033.html
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Re: Front Wheel Instability Enve 8.9 [Bdaghisallo] [ In reply to ]
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Thanks for the links. They make absolute sense and all of the info quoted is pretty much what happened to me and what i did incorrectly to try and correct the situation.
A light bulb moment if ever I had one!!
Many thanks
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Re: Front Wheel Instability Enve 8.9 [Xplombier] [ In reply to ]
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Good links had similar issues on different bike and different wheels. The thought of losing grip and taking hands off the bars is un-nerving, but since i get these on a monthly basis will give it a go.

2024: Bevoman, Galveston, Alcatraz, Marble Falls, Santa Cruz
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