Pardon my ignorance, but .... (suspension fork question)

Schnee80

I have just bought a new Vulcan XC MTB from Halfords (4.5 Stars on BikeRadar & What MTB Budget Bike 2007 he adds defensively).

On my first ride I noticed a rattling that I traced to the RH fork leg. I took it back to local Halfords and was told that it was the spring. I asked why the LH leg didn't rattle and was told that the LH leg is the 'oil side - one leg has a spring the other oil'.

Is this correct, how does that work? Please educate me.

Thanks

supersonic

What model of fork is it? The Suntour XCR? Are there adjusters on the top of each leg? I wasnt aware that the fork on the Vulcan had oil damping, and that there were two springs, one in each leg.

Anonymous

its the sort of thing oyu need to see really but it shouldnt rattle, maybe make a slight noise when its compressed, the sort of noise youd imagine a spring to make. Im not sure if those forks are even oil damped, wouldnt be surprised if the guy was wrong. even if it did it would make a squish noise. Could be the headset being loose either. Take it to a decent bike shop and have a see

dave_hill

Schnee80 wrote:

I have just bought a new Vulcan XC MTB from Halfords (4.5 Stars on BikeRadar & What MTB Budget Bike 2007 he adds defensively).

On my first ride I noticed a rattling that I traced to the RH fork leg. I took it back to local Halfords and was told that it was the spring. I asked why the LH leg didn't rattle and was told that the LH leg is the 'oil side - one leg has a spring the other oil'.

Is this correct, how does that work? Please educate me.

Thanks

Not sure about your particular fork but with most suspension forks that is how the system works. One leg of the fork will contain the spring (either a conventional coil spring or an air spring), and the other leg will contain the damping mechanism

Schnee80

Fork is SR Suntour

The bit I don't understand is how 1 leg would have a spring and the other 'oil'. It doesn't seem to make sense.

Or am I just an ignorant roadie??

Schnee80

Thanks dave_hill

Thanks, my mind is at rest - looks like I turned out to be an ignorant roadie!

PS - Should it rattle? Does it matter?

supersonic

Both legs dont have to contain the same medium - one can be a spring, the other have an oil damper to control the forks movement. Some forks without dampers will have a spring in each leg, and I am sure the fork on your bike is this way (the standard SR Suntour XCR). Springs can rattle a little. Try turning the adjsuter on he top of the fork leg a couple of turns.

Schnee80

supersonic

Thanks.

:oops:

dave_hill

Schnee80 wrote:

Fork is SR Suntour

The bit I don't understand is how 1 leg would have a spring and the other 'oil'. It doesn't seem to make sense.

Or am I just an ignorant roadie??

If you have a spring in each leg, you need to have both springs operating at the same rate (motorcycles with air-sprung forks have a balance pipe between to the two legs so the pressure is the same in both). Doing away with one spring solves this problem at a stroke, but you also need to make sure that fork crown and the lowers are stiff enough to cope with this.

Some forks have an oil damper. The fork leg has a measured amount of oil inside and a piston which fits tightly into the leg. As the fork is compressed, oil is forced through holes in the piston to control the rate at which the spring compresses. This is damping. The rate of damping can be controlled by varying the size of the holes or the weight (viscosity) of the oil.

To take this further, some forks have a damping circuit for compression (i.e. to control how fast the fork will compress for a given force) and a damping circuit for rebound, which controls how fast the fork extends having been compressed. Both are usually adjustable.

Just to confuse things even more, really high-performance forks have the ability to be tuned for high- and low-speed compression damping. This means that you can set the fork up to react differently for large and small "hits".

Unfortunately, as is often the case, lower budget forks may claim to have some of these features but very often the function of them is very limited or even non-existant.