Bicycle Mechanics - Question about 1 1/8" headsets

Lets say you have a 1 1/8" headset. What would be the diameter of the steerer tube?

Similarly, if a headset is 1", what would be the diameter of the steerer tube?

Thanks in advance.

Digger

1" for the 1" equation.

Thus 1 1/8 is the steerer tube.

1" for the 1" equation.

Thus 1 1/8 is the steerer tube.


I realize it may sound like a stupid question, but I have a good reason. :-)

I sold a fork and headset to a guy on Ebay, I measured the steerer tube to be 1 inch. I advertised it on ebay as 1 inch. He gets the fork and headset, tells me he brought it to 2 bike shops each one says it's 1 1/8th.

Well, I measured the thing with my calipers that measures to 1/100th of a mm (i.e. 2 decimal places) and I got 25.4mm.

Soooo, I was thinkin, jeez it's not something like the steerer tube is a tad smaller or something crazy like that. I mean, a 1 inch headset takes a steerer tube that HAS to be 1 inch. Similarly, a 1 1/8" headset takes a steerer tube that is 1 1/8".

But, I had to ask to make sure my brain was workin good and something didn't change with the law of physics and space/time when I wasn't lookin.

I find it hard to accept I got that wrong. I am a survey engineer I measure for a living for God's sake!! But I guess I have been known to make mistakes. :eek:

Heh :o

Digger

25.4mm is an inch. you were right the first time.

25.4mm is an inch. you were right the first time.


Yes, I know that 25.4mm is an inch.

BUT since this guy told me that the bike shop said it was 1 1/8" (28.58mm) and I am damn sure I did not measure it improperly, I was reaching for an explanation as to why my measurement of the steerer tube (1 inch) did not agree with both bike shops.

I was thinking (for some crazy reason) that just MAYBE the steerer tube had to be a tad smaller than the headset. Yup, sounds stupid I know. But I was reaching.

ANYWAY, since 2 bike shops assessed it I guess I DID measure it improperly. But jeez I was so sure....

Or maybe I got mixed up in a 1 inch stem i was selling at the time...... Ah I dunno. Somethings screwy...

Digger

What did the headset say (labeled/engraved) the size was? If you took it off your bike, what size is the headtube on your bike?

Maybe if you give specifics on what headset and fork we can be more helpful?

Try to find out what problem the bike shops had... If you measured the steerer to be 1", you're probably right. Question is why do the bike shops think the steerer is 1 1/8". Perhaps the fork race is sized differently or the bearing cups are sized differently.

I had a situation where the fork and headset were both 1" but the bearing cups were 32.7mm (BMX) instead of 30.2mm (Road). Who'd have guessed unless you've dealt with both types of bikes.

Says so on any fork manufacturer's site, fork manufacturers don't make headsets, the do make the steerer tubes though which are the actual measurement. When 1_1/8 steertube is mentioned, it means the width is 1_1/8, if it say 1, then it measures out to be an inch.

I advertised it on ebay as 1 inch. He gets the fork and headset, tells me he brought it to 2 bike shops each one says it's 1 1/8th.

Well, I measured the thing with my calipers that measures to 1/100th of a mm (i.e. 2 decimal places) and I got 25.4mm.

DiggerSomething wrong with the buyer or your caliper..... most likely the buyer...

What did the headset say (labeled/engraved) the size was? If you took it off your bike, what size is the headtube on your bike?

Maybe if you give specifics on what headset and fork we can be more helpful?


The fork has a threaded steerer tube and was made by Marinoni, frame builders in Montreal. Bought the bike in 1999. See this - http://cgi.ebay.ca/ws/eBayISAPI.dll?ViewItem&item=3664006247&ed=1078672976

The headset is an STX. See this - http://cgi.ebay.ca/ws/eBayISAPI.dll?ViewItem&item=3663997582&ed=1078668571

I have a quill stem which is marked as 25.4mm (1 inch). This stem will fit and tighten perfectly inside the steerer tube.

After having read this by Sheldon Brown http://www.sheldonbrown.com/gloss_h.html#headset I am now thinking it is a 1 1/8". Scroll to bottom and see headset sizing.

So if the stem is 1 inch and fits down inside the steerer tube, that means the steerer tube has an INSIDE diameter of 1 inch. So, could it be possible that the outside diameter is 1 1/8 inch?

I was so positive that I measured that outside diameter to be 1 inch.

Digger

I realize it may sound like a stupid question, but I have a good reason. :-)

I sold a fork and headset to a guy on Ebay, I measured the steerer tube to be 1 inch. I advertised it on ebay as 1 inch. He gets the fork and headset, tells me he brought it to 2 bike shops each one says it's 1 1/8th.

Well, I measured the thing with my calipers that measures to 1/100th of a mm (i.e. 2 decimal places) and I got 25.4mm.

Soooo, I was thinkin, jeez it's not something like the steerer tube is a tad smaller or something crazy like that. I mean, a 1 inch headset takes a steerer tube that HAS to be 1 inch. Similarly, a 1 1/8" headset takes a steerer tube that is 1 1/8".

But, I had to ask to make sure my brain was workin good and something didn't change with the law of physics and space/time when I wasn't lookin.

I find it hard to accept I got that wrong. I am a survey engineer I measure for a living for God's sake!! But I guess I have been known to make mistakes. :eek:

Heh :o

Digger

I'm thinking that this is probably a crown race diameter issue. There are two different crown race diameters commonly used on 1" forks. Most higher end stuff is 26.4mm diameter. Some OEM forks use a JIS standard 27.0mm crown race. For what it's worth, a 1 1/8" fork would have a 30.0mm crown race. Good luck!

I'm thinking that this is probably a crown race diameter issue. There are two different crown race diameters commonly used on 1" forks. Most higher end stuff is 26.4mm diameter. Some OEM forks use a JIS standard 27.0mm crown race. For what it's worth, a 1 1/8" fork would have a 30.0mm crown race. Good luck!


Well, it looks like it is a 1 1/8". The buyer measured the inside diamter (ID) and outside diameter (OD) of the fork and here's what he found:

Fork steerer tube: OD 28mm, ID 24.5
Headset Cup: OD 34mm
Frame: ID of headset tube, 29mm

So der it tis and it ain't no tiser.....

I am truly a bonehead.....I must got mixed up with something else I sold on Ebay.....

Digger