Jump to content

Stanchion diameter


stewie911

Recommended Posts

What is the significance of fork stanchion diameter?

I see a lot of guys asking the diameter, but why does it matter?

Link to comment
Share on other sites

Bigger is better, up to a point.

 

In the old days most stanchions were 28mm and made of steel. Then they went to 32mm alu. By going bigger, you can make the walls of the tubes thinner, yet the tubes will still be stronger.

 

Most X-country bikes are 32mm.

 

For freeride some manufacturers have a 36mm (alu) or 32mm (steel) and downhill stancions by the king of forks, Marzocchi, are a whopping 40mm. They look like motorbike forks.

 

Manitou, always odd, has some odd sizes like 30mm.\

 

Speaking of Marzocchi, it died a sad death in this country. No agent, no spares, no hope.

Link to comment
Share on other sites

JB is correct.

 

It is about the EI value of a tube which is the bending stiffness. E is fixed for a specific material, while I (2nd moment of area, if I remember correctly from varsity) is dependant on the cross sectional geometry of the tube.

 

Since I is a function of (outer radius minus inner radius)^4 you can increase the stiffness of a tube by increasing the outer diameter and having a smaller wall thickness.

 

This will also result in less weight because the weight of the tube is a function of (outer radius minus inner radius)^2.

 

So the stiffnes increase by a x^4, the weight increase by x^2.

 

As JB said it only works up to a certain point, because with thin wall thickness comes problems like fatigue strength and weldability etc.

Link to comment
Share on other sites

 

Speaking of Marzocchi, it died a sad death in this country. No agent, no spares, no hope.

A gap in the market perhaps?

Link to comment
Share on other sites

What Stephan explained is correct, and I also believe that "bigger is better" up to a point. Other than the strenght / weight issue, there's also more surface area = larger wear surface = less wear / pressure on stanchions and seals. However, I've been in a cycle shop a few weeks ago and there was a top of the range KTM bike fitted with a DT Swiss Fork with 28mm stanchions.

 

Don't know the reason, but it seems that DT Swiss is going for 28mm stanchions on XC bikes while Rock Shox and Fox have pretty much standardized on 32mm.

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Settings My Forum Content My Followed Content Forum Settings Ad Messages My Ads My Favourites My Saved Alerts My Pay Deals Help Logout