running a longer trvel fork on my frame

mr.helius

Hi there, I have a Nicolai Helius ac frame. Now I get a new fork which has a 550mm ATC length, but the tech sheet on the Nicolai website indicates that the max fork length is 542. Can I still run the new fork on my frame? I the geometry will change, and will it cause any other problem if I run this new fork on my frame. tks in advance.

steve_sordy

Yes it will change the geometry by making the bike a bit slacker (easier down, harder up). It will raise the BB height by 3-4 mm (more pedal clearance but higher centre of gravity).
It will increase the leverage on the headtube by 1.5% (more stress on the bearings and the frame welds).

All these are small changes, and you may decide to ignore them.

thistle_

Might be used against you if you make a warranty claim on the frame...if the manufacturer finds out.

mr.helius

steve_sordy said:

Yes it will change the geometry by making the bike a bit slacker (easier down, harder up). It will raise the BB height by 3-4 mm (more pedal clearance but higher centre of gravity).
It will increase the leverage on the headtube by 1.5% (more stress on the bearings and the frame welds).

All these are small changes, and you may decide to ignore them.

How come the change of AC length will stress the headtube and bearings? The new fork has same travel as old one just longer ATC length. Let's say, if travel increase, the fork will take more impact which will stress the headtube. But for same travel changing ATC length, I don't understand.

steve_sordy

A longer ATC makes the whole fork longer.

robertpb

A longer travel fork is not the problem, it's longer fork which creates more leaverage on the headtube and welds. In this case I don't think it's going to make a hapeth of difference.

mr.helius

robertpb said:

A longer travel fork is not the problem, it's longer fork which creates more leaverage on the headtube and welds. In this case I don't think it's going to make a hapeth of difference.

Is it because of the longer travel change the headtube angle, so the leverage change also? If so when bikes are running on the terrain the leverage should chnage also. Since then how is the leverage really affect the frame?

robertpb

The fork is a lever, so the longer the fork the greater the lever, the end of the lever is in the headtube.
Back in the mid Eighties I lent one of my MTB's to a lad who worked for me, he rode it into the back of a car, it deformed the downtube with the level of leverage on the headtube, one expensive frame destroyed.
So the longer the fork the more likely the frame will damaged, bikes that are designed with longer forks have more robust toptubes and downtubes to stop this.