Front end wobble / Anti - AT Crime wave!!

[johntaylor]

If i release grip on the bars slighltly whilst riding along the front end starts to move from side to side as I decelerate and depending on how quick I am going it gets quite violent. I noticed this happening on my first ride on the bike having just found it on its side as it had been knocked off its stand (by a london bus I suspect). Any suggestions of what this could be or tests I could do to make sure everything is aligned correctly would be much appreciated.

I am gutted - this week the bike got knocked over, last week someone lifted my top-box and all in it when it was parked in East Dulwich (ok, ok, it was in peckam!), The week before some knicked my parket permit and my cover. This is all in between getting repeated tickets from zombie-esque parking attendants who failed to see my tax disc or permit (Before they were knicked!!!) Arrrrrggghhhhh!!!

[GSPD750]

Loose spokes will cause the shimmy you describe.

[xrv_jim]

Possibly your front forks/wheel out of alignment John. No point in checking it as the fix is simple.

Slightly slacken the top yoke pinch bolts, mudguard/forkbrace and the four nuts on the axle clamp - just loosen them a bit mind. Push the bike forward fairly sharply into a London bus (a wall or tree would do aswell) so the front suspension compresses. Repeat a few times and the bits should be untwisted. Don't forget to tighten up all the bolts.

Oh, yes. Check your tyre pressures too. Too low can also cause a wobble

Best of luck

[Larry Biskit]

Know how you feel about the f ing thieves . Whilst living with the @ and another bike on the street in the West End, the buggars nicked the Number plate off and the courier who used it racked up 35 tickets in 4 months, tearing through bus lanes and speeding , sometimes 3 or 4 tickets per day. Lots of writing to various council's with Police incident numbers etc... to protest my innocence. Some of them disputed my claims, meaning I had to write with pictures of the bike, showing the difference between bikes, photocopies of Log book etc... Man soo much messing around.

The bstards also cut my cover off, (£75) and then ripped off the tool cover flap (£60) the replacement is a different colour due to Honda having discontinued making them for the 90 model. Just the little things that start to really piss you off. I finally lost it one day and caught one little street rat pinching someones bicycle outside Starbucks. Ran up and got him before he escaped, he was 14, so couldnt really justify laying into him. Just tried to scare the crap of him and told him where to go. I filmed the little sods and gave the video to the police, not that will achieve much, they seem to be so damn bold, hoods up, caps on, nicking stuff in broad daylight... with the d*@kheadds in Starbucks watching from literally 2 metres away.

Deep breath and relax.... ahhh. Sorry, just had to rant.

My bike wobbled a bit with panniers and a load on. Hows the front wheel, is it buckled slightly, my front wheel got nudged by passing cars who didnt realise their own width. The @ sticks out into the street quite far unless you can angle park a bit (or the twats are blind).

Good luck.

[Lumiya]

Wobbles, Can be caused by the following

• Camber on the road
• Uneven wear on tyre caused by road camber
• Wheel not balanced properly
• Steering head bearings worn or not tightened properly
• Wheel out of alignment
• Bike out of balance (more weight on one side)
• Spokes loose
• Riding style
• Tyre problem
• Innertube problem
• Wheel bearings worns
• and the list could go on

I thought that I had a problem recently with my GPz doing the same thing when riding down the local roads, if I released my hands the bars would start wobbling building up to a mightly tank slapper. I thought I had a problem till I tried it again on a recently layed car park (no cars or people about) and on this level ground never had any wobble at all.

Kymmy

[YEN_POWELL]

Weight on the back of the bike, like luggage or a passenger can make the bike handlebars shake if you take your hands off the bars, it obviously lightens the front end a little. Worse at low speeds.

[loftyjohn]

Hi
Mine does the same, as the tyres wear. Especially semi offroad tyres on spoked rims the balance changes. Spoke move, tred wears uneven. Get the front rebalanced it generally cures it

[Yeti]

Don't quote me on this but just a thought. From personal experience I got curious when I first found this happening on my TA. I have subsequently tried it out on any bike I ride to check out the differing effects. (Q all the physics buffs that can be arsed to divulge properly the gyroscopic technicalities of the whole affair!!)

http://en.wikipedia.org/wiki/Gyroscope and http://en.wikipedia.org/wiki/Precession head mess enjoy!.

Think you will find that most undamped steering on bikes will do this within a particular speed range as different variables come into play, often as the bike decelerates with engine braking and the weight moves forward. My 02 transalp was hideous for it. The Africa seem a lot less affected but is more dependent on how much fuel there is in the tank.

Basically the gist is that any 'body' (crank etc.) rotating about its spin axis, when moved (on the bike a seesaw motion) about the longitudinal axis (imagine a broom handle through from left to right) caused by following any (even the slightest) deviations in the road or weight shift and suspension compression, will try and spin the whole bike left to right about a precession axis vertically through the bike.

to simulate the effect, if you imagine the bike pinned to the floor by a nail through the front tyre where it is in contact with the road, and imagine trying to twist the bike left and right between your legs. Because the headstock is a (not quite central but try and imagine it as such) pivot and the front wheel is pivoting about that nail, as you twist the bike left the front wheel will turn to the right and vice versa, and there is the start of your slapper.

Once this is kicked off it is then simply a bit more science as to why the frequency of oscillations involved and additional gyroscopic effects of the wheels and other moving parts develop it so easily into a right slapper (chavette technology!! ) There are so many variables involved it doesn't merrit worrying about, just damp out what you can .

Boats with a screw propeller suffer the same problem. As you go down the face of a wave the boat turns to the right and as you go back up the face of the next wave it turns left (is that correct?? using the right hand rule?!?! ). Normally the net effect is the boat goes in a straight line but if the chop in the water is 'all over the shop' and uneven then so is the boat and keeping a straight line is a pig!

If you get up to speed and knock the bike down into neutral and let go you will normally find it doesn't slap or not as badly. If it does then see all the previous posts and i'll shut up n get back in me box!!

[johntaylor]

Thanks for the above guys and girls - a really great help. A fantastic rant and an extremely scientific explanation for what I am experiencing on my bike. I no longer believe that the said bus squashed my wheel making it wobble but Newton wants it to wobble - which makes me feel better....I think!

Thanks again,

John.

[Yeti]

ney bother! I could just be full of sh!t though and talkin nonsense! thats what her in doors always tells me.

Who's this Newton anyway!