Calculating stack height

[Nicko]

Hi Guys

 

So building up a new bike.

 

I've got a fork with a 175mm steerer length... And I'm fitting it to a frame with a 120mm headtube length, which leaves 55mm for headset and stem

 

I'm fitting a headset with a stack height of 20mm.

 

Which technically leaves 35mm for a stem right?

 

However, I've read that you should subtract 3mm from this stack height to allow for a gap between the top of the steerer column and the top of the stem...

http://www.parktool.com/blog/repair-help/fork-column-length-and-sizing

 

So that would mean I would need to fit a 3mm spacer if I'm using a 35mm stem right?

 

My question is if I bought a stem with a stack height of 40mm (which tends to be a lot cheaper), would it be ok to have a 5mm gap, or is this excessive??

[no calves]

depends where your bont clamp is located. ie clamping to the top then you can damage your steerer tube

[Nicko]

Yeah I'm just reading now on the spec sheet for the 40mm race face stem, they say do not exceed the 3mm clearance. I guess it could give an uneven clamping

 

Just gonna have to fork out the extra bucks, and do things properly rather than be a cheapo... haha

[Dicky DQ]

What is this stack height you talk of?

[droo]

You should be fine without a spacer, just going on the numbers. It's best to leave a spacer between your stem and topcap though, so you don't clamp to the end of the steerer tube.

 

The 3mm the Park Tool site speaks of is to allow space for the topcap to bear on the stem and preload the headset bearing.

[Nicko]

What is this stack height you talk of?

 

Check the link I posted

[Dicky DQ]

Check the link I posted

The reason I ask is I never knew it was so complicated.....

 

Put it all together mark, subtract 2-3mm done? I have never had an issue before, and most people add spaces above the clamp anyway in case they need to fit the fork to another bike etc. In this case just mix the correct spacers.

 

It was simple for me till now..... now I am going to have to scour the interweb each time.....

[Nicko]

The reason I ask is I never knew it was so complicated.....

 

Put it all together mark, subtract 2-3mm done? I have never had an issue before, and most people add spaces above the clamp anyway in case they need to fit the fork to another bike etc. In this case just mix the correct spacers.

 

It was simple for me till now..... now I am going to have to scour the interweb each time.....

 

Lol neither did I. I literally bought a fork, and figured it out afterwards. Was mission, had to find zero stack headsets, and low stack stem etc etc.

 

Busy with my first bike build, well buying components anyway... Learning a lot everyday