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-   -   twitchy front end (http://www.bikeforums.net/track-cycling-velodrome-racing-training-area/951479-twitchy-front-end.html)

shrinkboy 06-02-14 01:59 PM

twitchy front end
 
i ride a 58cm Fuji 1.1 Track at Frisco Superdrome. it has a 120mm stem, and stock OEM wheels. when i am going full tilt in a sprint, the bike feels really twitchy at the front end. i think this causes me to instinctively dial back speed a minute amount. and when i put an 88mm rim tubular on the front, pressure at 130, this condition seems even more present.

any ideas about what might be going on?

Brian Ratliff 06-02-14 02:09 PM

You may need to shorten your stem. This seems to happen when the weight gets too far forward onto the front wheel. From Fuji's website, the geometry is 74.5 degree headtube and 30mm offset fork, which should translate into a pretty stable platform. It's what my Dolan Forza has and it rails nicely.

It could also simply be that you are tightening up really bad.

shrinkboy 06-02-14 02:27 PM

i'd considered the tightening up thing; i'm going to really pay attention to that. thanks for your reply

Pantani98 06-02-14 02:36 PM

Just to throw in my $.02, I had a problem in the beginning because of the same thing. It wasn't the bike. I was racing BMX bikes when I started track cycling. I had to break the habit of wanting to swing the bike shifting pull up on the front. Worst place to make the mistake: first time at the Giordana Velodrome and first flying 200. At the rain between Turns 3 and 4 when it happened. Luckily I saved it otherwise it wouldn't have been a pretty picture. Now I'm up on the bars and driving with the legs. Just a thought...

Kayce 06-02-14 06:09 PM

Sounds like you may not be used to riding at high RPMs. I would suggest that you do some low gear and high RPM flying 200s/ flying laps.

MarkWW 06-02-14 07:02 PM

Just to offer another opinion, also check your headset is properly preloaded. A loose headset can cause shimmy. Headsets on track bikes are also a little harder to check, since the standard procedure on a road bike is to lock the front brake and rock the bike back and forth feeling for play. On a track bike, try twisting the headset spacers or holding the wheel at the fork crown with your hand and try rocking back and forth that way.

Hida Yanra 06-02-14 10:30 PM

I don't know how long you've been riding a steep track, so it might not be the case but...

that long of a stem can load up the front wheel quite a bit (depending on how you are sitting on it)
I ride long/low on the road (54cm a/ 120 or 130mm stem), but get vastly better handling on steep tracks w/ longer TTs and shorter stems.

If you have ridden this position at the superdrome for a while and are used to it, it's probably something else, but if this is new for you, try less front/center weight.

shrinkboy 06-03-14 12:17 PM

i think the headset issue is a good venue to follow, will definitely check that. but also, the low gear/high rpm efforts seems good as well. although i'm about the size of many sprinters- 6'2", 200 lbs- i am most definitely an enduro. flying 200s definitely feel...unusual. thanks for all the good suggestions to this 3rd year, 63 year old cat 4 trackie

carleton 06-03-14 07:27 PM

Quote:

Originally Posted by shrinkboy (Post 16817708)
i think the headset issue is a good venue to follow, will definitely check that. but also, the low gear/high rpm efforts seems good as well. although i'm about the size of many sprinters- 6'2", 200 lbs- i am most definitely an enduro. flying 200s definitely feel...unusual. thanks for all the good suggestions to this 3rd year, 63 year old cat 4 trackie

Maybe get someone else at the track to do a lap on your bike to see if it feels weird to them.

A bad headset could be the problem, but a wonky headset would feel weird at any speed on a banked surface. It sorta feels like riding on deflated tires or if your wheel were in a crack in the road.

It could be a technique thing where you are tensing up when you go fast.

rensho3 06-04-14 10:34 AM

I had a similar issue, and it turned out that my seat was too far back. The wobble and shakes showed up after I sat down and was full gas to reach max rpm at the 200 start line. I ponied up for a professional fit by Nate Koch, moved the seat back, and the problem went away. Seems somewhat counterintuitive, but then I consider the forces on the bike and the extended reach when trying to put max horsepower (which for me is not that max) and I was probably lightening up the front wheel just enough, while pulling hard and tensely on the bars, to set up the wobble. Thank goodness I don't have to deal with that anymore. BTW, the fit gave me an instant .2 on my 200 time, which was probably a combination of better efficiency and more confidence (read that less fear of losing the front wheel at speed).

shrinkboy 06-04-14 01:51 PM

rensho, thanks. that's a good one. i run my saddle all the back on the rails, and what you describe is exactly what i've got going on- it seems the front end gets light, rather than staying planted. good feedback

Velocirapture 06-04-14 04:24 PM

Quote:

Originally Posted by shrinkboy (Post 16821292)
rensho, thanks. that's a good one. i run my saddle all the back on the rails, and what you describe is exactly what i've got going on- it seems the front end gets light, rather than staying planted. good feedback

Just a thought, to use or not use - if you are running your saddle all the way back, any chance your bike is slightly too small for you? That could leave you with more 'upright' arms than ideal, which can also translate into twitchy. Completely different angle to a light front end, so ignore if does not apply :-)

DanAVL 06-05-14 04:47 PM

This thread helped me quite a bit. Couldn't figure out why things were getting all wonky at the end of max efforts. Relaxed my upper body, boom, gone. And took time off my 500/1k.

Thanks!!

shrinkboy 06-09-14 09:39 AM

i found some slop in my headset, and tuned that out. i then experimented with moving the saddle forward ~1/2", maybe 3/4". this really seemed to help a lot. in my bike racing version 1.0 of the early to mid 80s, i habitually moved my saddle all the way back, and have resumed this habit until today. moved forward, i felt much more confident and in control of the bike. went to the track saturday, and all seemed much improved. good advice all around


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