I have a road bike, a Taiwanese alloy frame (Avanti - probably only Australasian people will know the brand) with Tiagra components and when I try to ride no hands at speed above 30km/h it gets violent death wobbles. Everything's OK when I put my hands back on the bars but it's a little disconcerting (to say the least) to have this happen. THe bike is about 1 1/2 years old and done (guestimate) 8000km.

I can ride my cheapo heavy mild steel framed rigid mountain bike with out-of-true backwheel no handed for miles at virtually any speed without any problems.

Any comments (apart from don't ride with no hands )?

It really could be any of many things. Frame alignment, fork alignment, ball bearing missing in headset, headset not tight, poor geometry/design(head angle/fork/trail combination-when you sit up and take your hands off the bars, you also take weight off the front end. If the trail is not correct this could result in a tendency to dive or oversteer, corrected by gyroscopic forces, a tendency to dive , corrected by gyroscopic forces, repeat, repeat, aka a "wobble".), frt wheel alignment, etc... If I were you, I'd start with whatever seemed easiest and work through them in a process of elimination.

Avantis generally have a good reputation here, and I've not heard of severe problems like this before, so it might not be frame geometry per se, but more mechanical.

Like don d said, check the front end and everything in the elimination process.

Wheel truness is a good starting point. Have you replaced the tyre or fixed a puncture lately to bring this on -- a tyre may be out of round, or not the not seated properly? Is the axle properly in the drop-out and the quick release done up firmly.

Check the headset bearings as a priority... I just checked my randon bike's the night before last, and it was slightly looser than it should have been. So they can loosen off on you without you knowing. The headset bearings are the least thought about on a bike.

Are the hub bearings from and rear adjusted properly? Can you move the wheels back and forth laterally? Check rear wheel dish, as that can throw the alignment off, as the rear wheel not being centred in the drop-outs (even vertical ones), and hence between the chainstays. If you have doubts about frame alignment, remove the rear wheel, tie a loop in a length of fine nylon fishing line, loop it around the head tube and back to the other drop out and pull tight so the line on both sides is in the same position (you'll know what I mean when you do it). Check the distance from the line on each side to the seat tube. Any more than 2-3mm difference, and your frame's probably out of alignment.

I have an Apollo MTB (Falchoon will know the make) that was heavy as all hell that was sound at any speed except when fron suspension forks wore out the seals (resulting in the legs moving around). Then very serious speed wobbles would start. Very tiring to hang on to all day, too.

FWIW

R

I can't imagine metal fatigue causing the problems you have described, unless you have a weld which has completely broken. Since you haven't described a broken frame, my first inclination is to tell you to look at the condition of the headset.

Sounds like you need a new bike to me.

Here's a very simple check and I had a similar problem to your and this was the cause.

My front wheel wasn't all the way in the drop-outs. I replaced it while it was in the rack and it must have fallen slightly as I secured the quick release. Undo your quick release while the bike is on the ground a make sure the wheel seats all the way down!

L8R

In the motocross world this is known as headshake. This is most common under deceleration and when you are are the brakes. HONDA CR'S were bad for this in the 90's. It is due to frame geometry. I once had bad armpump and crashed hard on a CR500 beacuse I could not keep the front wheel from swapping out from underneath me.

You probably know this but for others benefit, what happens to a motorcycle decelerating or braking is the front end dives down because the weight is shifted to the front. This causes the forks to compress, which steepens(changes) the the head angle, which affects the amount of trail which is responsible for the stability of the front end.

This dynamic is more subtle on a road bike which has no suspension fork. But, just the change in weight of sitting up and taking ones hands off the bars is enough to affect the way the trail (that is fixed into the design) acts.

This does not have anything to do with any individual design feature, but is a combination of head angle, fork rake, and weight distribution. For example, My Bianchi track bike has 28mm(very short) of fork rake, but I can ride it hands off forever because the headangle was designed with this fork rake in mind to make the bike stable and the alignment is spot on.

If I took that same fork and put it on another bike with a different head angle, I may be fighting to keep the bike upright with my hands on the bars. These subtle differences can make the difference between whether a bike tires you out over a 100mile ride or seems easy and comfortable to ride.

"Maico Breako"

I like the maico breako comment! M

I liked the maico breako comment! My dad and uncle used to race those. Dad still owns a PENTON,HODAKA & HUSKY. I agree with the forks diving down also will affect the handling ,what you explained is what I should have.

My brother raced a maico 250, I raced a Dunstall Norton. Same parents, different genes. Born and raised in Ohio, Penton country.