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head tube diameter deviations...(12 posts)

head tube diameter deviations...opencl
Nov 7, 2002 6:04 PM
Hi, is it normal for a 1" fork head tube to have an inside diameter than varies between 29mm and 30mm? thanks
re: head tube diameter deviations...mja
Nov 8, 2002 5:13 AM
What material: Is it steel, aluminum, titanium, swiss cheese?
It's foco steel nmopencl
Nov 8, 2002 9:16 AM
Nov 8, 2002 7:42 AM
What you are describing is called "butting". Very common in better bike frame tubing-as in "double-butted", or "triple-butted".
Ideally, it should be 30mm...opencl
Nov 8, 2002 9:21 AM
The inside diameter of the headtube should be 30mm ideally. But in my case, the diameter seem to be slightly "warped." Depending on where I measure it, the diameter is between 29-30mm. I guess my question is, will a 1" headset cup (30.2mm outside diameter) tolerate such "warped" headtube without damaging the frame? Or is it common to have such deviations in a frame?a

Butting is not what I am referring to.
1mm diff is oddCalvin
Nov 8, 2002 11:31 AM
That is quite a bit to be out in terms of ID. That is so much you should be able to look down on it and see it. You might try your measurements one more time. Make sure the calipers are held square to the axis of the headtube. Or, try this. Set the caliper to 29mm and lock it. Now stick it inside an see how it fits.

If it was a new bike I would recommend reaming without any question. However, if this bike has had a headset inside, then it is unlikely to come out and to spring back to 1mm off in tolerance. In terms of pressing, it is the frame that expands and gives to accept the head cup.
sure about that measurement??C-40
Nov 8, 2002 2:31 PM
1mm would be an an enormous out-of-round condition. One tenth of that amount would not be unusual, but much more would make it very difficult to get the headset cup to even start going into the head tube.
re: head tube diameter deviations...mja
Nov 8, 2002 2:51 PM
When replacing a headset on 853 steel, I encountered about 0.2 mm interference. (I'm estimating the deviation, as it was some time ago.) This put it out of spec according to the headset instruction sheet. (The spec was for no more than 0.1 mm.) And the deviation was not uniform -- the head tube was oval.

However the headset installed without any difficulty: My observation at the time was that the head tube easily conformed to the circular shape of the headset cups.

I agree with the others who suggest measuring again.
Yes, the HT is somewhat oval 29.4-29.8mmopencl
Nov 8, 2002 8:14 PM
I have remeasured it, it is around 29.5mm average. The thickness of the tubing was about 1.25mm. Is it safe to ream this headtube given that the thickness is 1.25mm? Thanks.
Yes, the HT is somewhat oval 29.4-29.8mmmja
Nov 9, 2002 4:38 AM
I won't answer the question about reaming. Just want to re-emphasize the significance of interference: It's the difference between the headset-cup OD and head-tube ID that is of significance. If in fact the head-tube ID is too small, Chris King may have an undersize headset available. But reaming would fix that problem once and for all.
Final outcome...opencl
Nov 10, 2002 6:23 AM
Thanks everyone. I tool the frame into the shop and the mehcanic have no problems at all in putting a standard iso 1" headset in. No reaming or facing was needed.
Still some confusion on my endCalvin
Nov 12, 2002 6:09 AM
There are two basic fit standards for the 1" steering column (ignoring a BMX standard). There is a JIS standard of 30.0mm cups, which need an ID of say 29.8mm. There is also a 30.2mm cup ("Euro" type standard) which uses a 30.0mm ID. The 0.2mm difference in press fit has been a commonly stated and used in the industry, but some manufacturers (such as Chris King) recommond only 0.1mm difference. Measuring ID can be tricky, which is why snap gauges can be handy.

If there was truely a 29.5mm ID, even the JIS cups of 30.0 would give a 0.5mm difference. This would be huge. Did the frame ever have cups installed? You may want to find out the OD of the cups pressed, it would be good for future reference. If they went in and the headtube did not crack, all is fine.

For more on headset fits, see the end of