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Old 12-13-01, 05:13 AM   #1
stewartp
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I'm glad I'm not a toolmaker

I need to replace my bike's forks. So this morning I removed the headset & stem, dropped the forks out and put vernier calipers around the tube, at the threads. I measured outside, inside and the tube length. It's an italian bike (Olmo) so I assume measurements are in mm. I get 30mm for outside, 26mm for inside and 190mm for length.

So I'm feeling confident when I phone the bike shop to place the order. The guy asks me what diameter and tube length and there's a pause when I tell him "30mm"

"With respect" he says, "I think sir might be mistaken. Its most likeley to be 1 inch - 25.4 mm" I confirm that my headset is Campagnolo Mirage, so it definitley is 1 inch.

How could I be out by nearly 5mm on my measuring? I must have been looking at the wrong marker on the calipers or something. I can't wait to get home and check it again.

Like I say, it's a good thing I'm not a toolmaker or working for NASA! Nothing would ever fit together!

FWIW I bought clerance LOOK forks, a new Campag headset, the shop are going to press on the lower bearing for me.

Stew
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Old 12-13-01, 07:00 AM   #2
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You don't sound like you know very much about forks. If you did, you would know that threaded steer tubes for road bikes are nearly always 1" (except ancient English/French bikes).
Does the new fork have the same rake as the original? If you aren't careful, the wrong $200 fork can make a $1500 bike handle like a $100 Huffy.
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Old 12-13-01, 07:28 AM   #3
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You're right, all I know about forks are the pair I have on the bike now.

I never have been pleased with the way the thing handles, riding hands-free I always have to lean over to the right. The headset always gave a knock and would never tension quite right, which is why I replaced the headset about 2 months ago. This Campag Mirage replacement means there's only about 2 turns of thread left for the locknut. It keeps coming loose.

Hence the requirement for whole fork replacement.

I take your point about rake. Too steep could make the bike as twitchy as . . . a twitchy thing. But the fork cost is only £20 ($29USD) for my commuter/winter hack. Worst case I'll have to put the old forks back on.

Stew
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Old 12-13-01, 07:59 AM   #4
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I, on the other hand know a lot about forks. Have used them to eat almost all my life.

However, to your problem. Even though I had used calipers a lot in an earlier life, I fell prey to just such a mistake recently. What I did was to take my reading at the end of the moving carriage, and not at the zero mark on said carriage, which is some distance away. Even after I looked again, it took me a while to realize my error. Check to see if that is what you did.

Sixty years old, and I learn something new - often a lot - every day.

Cheers...Gary
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Old 12-13-01, 08:03 AM   #5
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I think I also should have been measuring the tube where there were no threads, Does the thread cutting splay things a teeny bit, or just cut into the tube?

Stew
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Old 12-13-01, 04:30 PM   #6
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You were only off by .6mm. Not bad, really, but every tenth of a millimeter counts.
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