Ok, trawled the forums and I'm sure you'll already be shouting "31.8!!!", but...
Have a '98-ish P7 frame I'm rebuilding with nice stuff. Had components on it, so I have ref. Have a spare / basic 31.8 clamp. Tried to fit it. Nope, too small. So did some looking / measuring. A bunch of the threads kinda end in "just get a 31.8" and the OP does, and everything is fine, or the thread ends without a conclusion.
Here's my measurements...
The old clamp measures about 32.88
The seat tube OD at the top slot is 32.9
>> All good so far. Fits.
The seat tube ID (as confirmed by the shim) is 29.6 (to a 27.2 post)
The seat tube OD further down is a fairly consistent 32.2
>> OD seems to be consistently bigger than factory spec, just by a smidge.
The '98 seat tube was listed as 29.6 (or sometimes 30) ID, so I'm spot in there. This required a 31.8 clamp, so I'm out by over 1mm there. https://www.retrobike.co.uk/wiki/Orange. Even going by the Orange specs, this makes the wall thickness (31.8-29.6)/2 = 1.1mm with paint. Seems a bit thinner than reality, so I'm a bit iffy about the official specs.
The front mech is stated at 31.8 and the XT one fits mine just fine, so that's clearly within a 0.4mm wiggle room I have (31.8-32.2)
So, it all seems a bit out of whack but in reality, hey, that's reality, and I have all the numbers I need to just make it work for this frame. All I need is a 33mm seat clamp. Oh wait, they don't exist. Actually, there are a few but they're Johnny-no-name Ebay offerings. Choose 31.8 or 34.9...
So, yeah, tried the 31.8. Nope. Mainly as my seat tube OD is 1mm wider than 31.8 to start with.
Options seem to be:
1) Blame the current pain job thickness. I'm planning to repaint the frame anyways, so maybe less clear coat? Although it's really not that thick currently. Not sure this is a thing.
2) A Hope etc. clamp will work somehow magically where other no-name 31.8 clamps don't
3) Get a 34.9 clamp and clamp the heck out of it. I.e. take up 2mm of slack before it even starts gripping. Not sure I like that.
4) Flex the 31.8 clamp to "convince" it to fit. Although the existing "32.88" clamp doesn't have markings or seem to have been a 31.8 that has been massaged to fit. It's quite chunky.
5) Compress the slotted portion of the seat tube inwards a bit (by just over 1mm). But this would make the shim not fit. But I can get a smaller shim as they come in all sizes.
Literally no idea. Maybe 5 or 4? Maybe 1? 2 seems like an expensive experiment with little logic to back it up. 3 sounds sketchy. Any experts out there know what's going on... and even better, what the right path is?
Have a '98-ish P7 frame I'm rebuilding with nice stuff. Had components on it, so I have ref. Have a spare / basic 31.8 clamp. Tried to fit it. Nope, too small. So did some looking / measuring. A bunch of the threads kinda end in "just get a 31.8" and the OP does, and everything is fine, or the thread ends without a conclusion.
Here's my measurements...
The old clamp measures about 32.88
The seat tube OD at the top slot is 32.9
>> All good so far. Fits.
The seat tube ID (as confirmed by the shim) is 29.6 (to a 27.2 post)
The seat tube OD further down is a fairly consistent 32.2
>> OD seems to be consistently bigger than factory spec, just by a smidge.
The '98 seat tube was listed as 29.6 (or sometimes 30) ID, so I'm spot in there. This required a 31.8 clamp, so I'm out by over 1mm there. https://www.retrobike.co.uk/wiki/Orange. Even going by the Orange specs, this makes the wall thickness (31.8-29.6)/2 = 1.1mm with paint. Seems a bit thinner than reality, so I'm a bit iffy about the official specs.
The front mech is stated at 31.8 and the XT one fits mine just fine, so that's clearly within a 0.4mm wiggle room I have (31.8-32.2)
So, it all seems a bit out of whack but in reality, hey, that's reality, and I have all the numbers I need to just make it work for this frame. All I need is a 33mm seat clamp. Oh wait, they don't exist. Actually, there are a few but they're Johnny-no-name Ebay offerings. Choose 31.8 or 34.9...
So, yeah, tried the 31.8. Nope. Mainly as my seat tube OD is 1mm wider than 31.8 to start with.
Options seem to be:
1) Blame the current pain job thickness. I'm planning to repaint the frame anyways, so maybe less clear coat? Although it's really not that thick currently. Not sure this is a thing.
2) A Hope etc. clamp will work somehow magically where other no-name 31.8 clamps don't
3) Get a 34.9 clamp and clamp the heck out of it. I.e. take up 2mm of slack before it even starts gripping. Not sure I like that.
4) Flex the 31.8 clamp to "convince" it to fit. Although the existing "32.88" clamp doesn't have markings or seem to have been a 31.8 that has been massaged to fit. It's quite chunky.
5) Compress the slotted portion of the seat tube inwards a bit (by just over 1mm). But this would make the shim not fit. But I can get a smaller shim as they come in all sizes.
Literally no idea. Maybe 5 or 4? Maybe 1? 2 seems like an expensive experiment with little logic to back it up. 3 sounds sketchy. Any experts out there know what's going on... and even better, what the right path is?
