floppy steering ?

robinta

bought my fsr in Oct to replace my Hardrock and totally love it. The thing is, when I `straddle` the bike the steering will flop to either side. Which has caused a few comedy moments. Its not really a problem, I`m just intrigued why.

I did swap the stock Tora 100mm forks for 85-130mm revelations but this happens even wound down to 85mm so I dont think the fork is any longer physically. I`ve also changed the stem for a shorter one but this happened with the stock (longer)stem. It doesnt bother me when riding (so far) but as I said I`m just wondering why ?

supersonic

Hmmm, you'll have to explain the problem ina bit more detail. Too long a fork can cause low speed steering problems, where it will refuse to turn, then suddenly flop over, while to short a fork can cause the wheel to tuck under.

nicklouse

is the sag on the rear set correctly?

robinta

have messed about with the sag with no difference. The Rev fork is within 5mm axle to crown height of the Tora.

Its as if the wheel is trying to tuck under, but when I first rode the bike in its stock condition I couldnt believe how twitchy the steering felt. I`ve fitted the 85mm stem and wider Easton bars which have made it no better but no worse.

Maybe I need a 130mm stem !!

Could it just be a difference in head angle between the full suss and the hardtail ?

nicklouse

who fitted the fork?

robinta

local bike shop. Not the best with hindsight

Why ?

nicklouse

just making sure that all the bits should have been fitted.

it could just be the change of riding style and set up.

as set up on two springs requires a bit more thought on where the rider is in the riding position.

big_southern_jesse

If I understand this correctly, it's happening whilst stationary, just as you climb onto the bike.

The front wheel on a bike naturally tracks straight because of the head tube angle and the offset forward from the centreline of the head tube.

As with all these things, it's easier to see the forces if you exaggerate everything a little.

so imagine that your headtube slants at 45 degrees, and your front hub is held 6 inches in front of the forks. Now, if you twist the handlebars, the leverage operating at that angle and distance from hub, means that you actuall have to lift the forks up to the side, and this causes the bike to lift at the front. This happens normally on a bike but on a very small scale. Your weight on the bike helps to prevent this lifting, and hence allows you to ride along "no hands". This is why the bike will track straight much easier whilst you are riding than when you are pushing it. Once you're pushing it, you've removed about 75 or 80% of the weight, that creates the force to keep it straight.


As I said, on a normal set up, this is a very small force, otherwise you would not be able to steer at all. (It's why steering becomes slow or heavy if you put extra long forks on a bike!)

Whilst your bike is all straight and level, everything balances, but lean it to the side to get on and all that changes. Your handlebars are then unbalanced and have some turning force. With long bars and heavy levers/changers/ends/grips this weight is enough to overcome the other forces and the wheel will spin toward the side it's leaning. At this point, the bike doesn't normally have your body weight on it yet. Does this always happens just before you sit on the saddle but not after?

Happens to everyone. It will be worse for steep angled headtubes, and wider, heavier bars.

Hope this kind of makes sense. Not the best explanation, but have a play and see what happens in experiment!

Random Vince

my orange msisle with 130mm forks used to do a similar thing when i stopped riding and put my feet down, sat on the saddle.