Framebuilders - head tubes: mm to in

Bikeforums.net is a forum about nothing but bikes. Our community can help you find information about hard-to-find and localized information like bicycle tours, specialties like where in your area to have your recumbent bike serviced, or what are the best bicycle tires and seats for the activities you use your bike for.

View Full Version : head tubes: mm to in

seanchon
11-24-09, 04:21 PM
I'm looking through the Nova Cycles site and am feeling like a bit of a math dummy.

If the outside diameter of a head tube is 31.7mm with 1.0mm walls, I would imagine that's a 1 1/8 inch head tube based on the following.

Inside Diameter = (31.7mm - (2 * 1.0mm)) / (2.54 * 10) = 1.169in

Then you would ream out the head tube to get to 1.125. However, I am seeing this listed throughout the site under the 1" head tube categories. Is there something I'm missing?

jmichaeldesign
11-24-09, 06:07 PM
31.7 mm - 2 mm = 29.7mm a standard 1" threaded headset cup requires the headtube to be reamed to 30.2mm. So the 31.7 headtube is required for a 1" steerer. I've seem a 1-1/8" steertube run through a 1" headtube but it required a custom integrated headset that I believe was actually welded on. It was really just a show bike.

seanchon
11-24-09, 06:49 PM
Gotcha. I wasn't even considering the thickness of the headset cups. Thanks!

I think I just panicked when I started to convert metric to US. :P

KNEEL
11-24-09, 06:57 PM
Gotcha. I wasn't even considering the thickness of the headset cups. Thanks!

I think I just panicked when I started to convert metric to US. :P

Yeah , its kinda weird, it's all actually imperial sized and then converted to metric so the rest of the world can understand it. You will get used to looking at the numbers.

NoReg
11-24-09, 07:40 PM
They do categorize the tubes by steering tube size, so it ought to be easy to find what you want. Sometimes the walls vary in thickness so you have to go by the OD which isn't always listed, so back to the specified steering tube.

HMBAtrail
11-26-09, 08:27 AM
I'm looking through the Nova Cycles site and am feeling like a bit of a math dummy.

If the outside diameter of a head tube is 31.7mm with 1.0mm walls, I would imagine that's a 1 1/8 inch head tube based on the following.

Inside Diameter = (31.7mm - (2 * 1.0mm)) / (2.54 * 10) = 1.169in

Then you would ream out the head tube to get to 1.125. However, I am seeing this listed throughout the site under the 1" head tube categories. Is there something I'm missing?

32mm O.D. HT is for 1". 36 and 37mm O.D. HT is for 1 1/8". You will have to ream and face post-braze to the proper I.D. for the headset.