So I took the beast out for a 15 mile cruise today and learned how the bike rides and handles. Did some hill climbs, flats and downhills.

Surprisingly, when I got up to 26 mph I noticed that I had a lot of vibration on the front end (forks)

I was wondering if this is normal , I should be worried , or stop riding right away !!! Mind you that this ride was on the city street (regular road with minimal potholes and cracks)

Perhaps this is what is occurring: https://sheldonbrown.com/brandt/shimmy.html

make sure your headset and wheel bearings aren't loose in any manner.

if they are all good, its a function of the steering geometry and your weight balance on the bike. some tires can aggravate it. changing your handlebar geometry can alleviate it, or riding with your weight in a different place. (maybe more tucked, maybe more upright?)

High speed front end shimmy is a resonance problem. As Pierce pointed out there are any number of input sources, including tires, minor wheel alignment issues, overall frame alignment. The cure is to address the input sources as best you can can and/or change the natural harmonic frequency of your bike. An old school trick is to put a knee against the top tube as a damper when coasting at high speed. Other things that can help is transferring some weight to the pedals, moving your body forward a bit to increase front wheel drag.

With a bit of experimenting you should be able to get a handle on managing the problem, though it may never go away completely. My old bike shimmied at about 35mph, but stopped above that, so I made it a point to either slow down or speed up a bit to stay away from the specific problem speed.

Just out of curiosity, what is the frame size?

A quick search of his other posts shows the bike to be a 1996 Trek 5200 with a 62cm frame.

So I was thinking maybe a couple things can be the problem but please, you guys be the judge.

1) The tires being 700 x 20

2) The road not being SUPER smooth

3) The wheel was not on tight enough? (How do you know what is too tight?)

4) The wheel not being true? (But when I was riding it, it looks straight and smooth riding down the hill)

5) Too much or not enough air?


But the most important question, is it SAFE for me to ride it?

20mm is pretty darn skinny for the road. you know they use up to x28's on the tour d'france these days? I'd give a good high thread count x25 a try.

as long as your wheel has no 'feelable' play from side to side, I'd think the axle and stuff was tight enough.

to check the rim for true, turn it slowly with a finger resting on a brake pad and grazing the rim....

I'd think you'd need like 140 PSI in a x20, any less and its pinch flat central

If you mean the bearings are loose, I've had that cause shimmy. Lift the bike (or put it on your car rack), and try to move the wheel side to side in the frame or fork. If there's appreciable wiggle, take it to the LBS's mechanic.

Hard to say, have the LBS check it out.

Read the shimmy article in dsbrantjr's post, #2, above. Re-read it, and again again, until you understand all the possible causes, and can eliminate them, or deal with the shimmy. Shimmy can cause a crash at high speed, which is unsafe (obviously). Sometimes it's a bike problem, sometimes it's a rider problem. Learn how to deal with it, or fix it, before you experience the crash.

Be sure to put in at least 100psi at that width. That's what you'd need if you're 140lbs. If you weigh more, adjust accordingly. Make damn sure your quick releases are as tight as you can get them without hurting yourself.

Sorry, but neither factor in the OPs problem.

It takes very little tension on a QR skewer to hold the axle faces fast to the fork. Play in the bearing may factor, so the hubs must be correctly adjusted, but in all fairness, I've seen front wheels with bearing play, and no shimmy, and dead on, no play hubs that do.

As far as tire pressure goes, lower pressure will generally tend to reduce shimmy, and higher pressure increase shimmy. That's because front wheels are stabilized by the caster effect, and increased tire drag increases the caster forces. I don't suggest lowering pressure as the best way to reduce shimmy, but often a slight reduction can yield a material improvement in shimmy, without a significant impact on total drag.

Not at all related the the Op's problem but the "coolest" shimmy i've ever had was from a seriously loose spoke tensioned front wheel, whenever the front brake was applied. Andy.

Was it shimmy, or what people now are calling a shudder?

I don't know what the difference is. I am new to the whole bike scene so I am learning as I go.

If anything, it made some sort of noise. I took it up to 28 mph today and noticed that the vibration still exists. My biggest fear is that it will cause a crash or even worse a major injury.

FB- Not sure I could tell the difference between a person shuddering and shimmying On the bike the loose spoke tension oscillation was very rythmic and dependent with the force of the brake application. On what i would call "speed man's wobble" (or shimmy as most say) the oscillations' aplatude vary with the speed but the frequency tends to saty stable. So perhaps what you suggest is shudder is what the loose spoke tension issue was. I could see the rim moving around under braking while the bars remained relitively stationary. Speed man's wobble, for me (and i have a lot of experience with it) can be damped with weight placement (fore/aft, high/low), leverage over the bars (hands by stem, by drops/levers), by cadence changes, by placing body parts against different points on the bike (knees on TT, heels on CS, thieghs on seat).

So tell me if what i call loose spoke tension oscillations is shudder. By the way simply tensioning the spokes up to what they should have been solved the wobbles. Andy.

Bad spelling... "rhythmic, amplitude, thighs, relatively" and probobly more. Andy.

These words don't have precise meanings. 40 years ago we called the high speed side to side vibration wobble, later that became shimmy. Many use the term shudder to refer specifically to the front/back pulsing vibration that front brakes can cause shudder. I prefer to keep the terms different and specific this way, because they're different problems with different causes, which is why I asked you if you thought it was one or the other.

Se my response to Andrew for the the difference between what I call shudder vs. your problem of high speed wobble or shimmy.

If you don't deal with, either cure or manage, your high speed shimmy it will cause handling problems and on long descents might get bad enough to cause a crash if you don't slow down out of it.

Try the various suggestions, such as making sure your headset is tight, lowering front tire pressure slightly (if going to 85-90psi doesn't help, don't bother going lower) shifting more weight forward, or to the BB, and/or bracing one knee against the top tube. Also check wheel alignment & play in hub bearings, especially front. Also spin your wheels while looking end on at your tires. If there's any wobble in the tire o tread either because of poor construction or poor seating, that will move the contact patch side to side as it rolls setting up the vibrations.

None of this involves spending money or replacing anything, so take your time and experiment. See what helps and what doesn't and see if you can cure the problem or at least get it manageable. Then if it's still a problem, come back and post what you did that helped, and that might point a direction for further investigation.

Sounds great! Sadly we are experiencing rain for the next three days but I will get the bike out sometime next week and post my findings.

Thanks everyone!

If you are seated way back like "10 feet" behind the rear wheel (bb shell), you will get the shimmy problem because the darn bike has the weight distribution wrong. Actually shifted to the back.

Do you have a picture of you riding the bike? Tall guys here in the US for some weird reason ride with like 90% of the weight at the back and like 5% in the front and obviously the bike will do weird things specially in the handling department that is where that bike have problems as well. Treks arent the best handling bikes over the planet anyways.

I do not have any pictures of me riding but I can get some if it would be helpful. I think the rains are suppose stop on Monday so I will try to get the picture by then.

When I am cruising I would say most of my weight is on the back but when I am speeding I'd say it's a solid 60/40 but then again I am VERY new to the sport so I can be wrong.

Is it worth taking it into a LBS to get it checked out or will they charge me an arm and a leg?!

It's worth talking to a shop because a decent mechanic can see what's happening and should be able to help resolve this faster that you would otherwise. The cost varies tremendously, based on the time involves, and whether you're a regular customer or someone who came in only for a hard to solve problem.

It's hard to assess your riding position, it's better to have an observer. That could be a shop mechanic, or a friend watching your position as you ride. Another way is to ride past store windows when the lighting is right and use them as mirrors to observe your own riding position.

I ride like this about 5% of the time

https://www.margrietkloppenburg.com/b...20bike%201.jpg


The rest is more like this...relaxed

https://www.velossimoracing.org/e107/...216_Blood_.jpg