Odd seat tube diameter
06-14-18, 03:08 PM
#1
Senior Member
Thread Starter
Odd seat tube diameter
I usually change the seatpost collars (clamps) on my bikes mainly for cosmetic reasons. It’s never been a problem but my new MTB has an odd sized seat tube diameter. The seatpost is a standard 31.6mm in diameter. However, the seat tube appears to be 37.1mm in diameter. I’ve measured it using vernier calipers in several places as I was surprised by this measurement.
Because of this, I’ve been unable to locate a seatpost collar that would fit. Any ideas on whether a nearest one to 37.1mm would work, assuming the inside is for 31.6mm seatposts?
Because of this, I’ve been unable to locate a seatpost collar that would fit. Any ideas on whether a nearest one to 37.1mm would work, assuming the inside is for 31.6mm seatposts?
06-14-18, 04:23 PM
#4
Senior Member
Searching eBay it seems 37mm seatpost clamps are available commonly, but mostly they're quite garish ones from Hong Kong unfortunately 
06-14-18, 10:08 PM
#5
Senior Member
Have you checked the manufacturer's specs?. It seems odd that the seat post is standard, yet the tube is not
06-14-18, 11:40 PM
#6
Senior Member
Thread Starter
Yes I have, the seat post spec is listed but the seat tube one isn’t. I have found references to 37.1mm clamps on sites discussing Chinese carbon frames for road bikes,but my MTB is a German brand. I may email the manufacturer for clarification. I’m also going to triple-check the readings I took.
06-14-18, 11:52 PM
#7
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You need to find one of these. Probably not at this price, but it does exist. There is a part number and size in the pics.
https://m.ebay.com/itm/SPECIALIZED-s...wAAOSw~o5aXxmt
John
https://m.ebay.com/itm/SPECIALIZED-s...wAAOSw~o5aXxmt
John
06-15-18, 08:24 AM
#8
Senior Member
Thread Starter
I think I have to eat humble pie!
I went out earlier in much better weather and took the seat clamp off the bike. When I turned it over it had '35' stamped on it. I am assuming that this is the size I will need. The seat post is definitely 31.6mm. I am at a loss as to how I read 37.1mm for the seat tube diameter yesterday. I used the same Vernier calipers but measured the seat post itself slightly below where the collar was already mounted. Perhaps the very top of the seat post is a slightly different diameter?
I went out earlier in much better weather and took the seat clamp off the bike. When I turned it over it had '35' stamped on it. I am assuming that this is the size I will need. The seat post is definitely 31.6mm. I am at a loss as to how I read 37.1mm for the seat tube diameter yesterday. I used the same Vernier calipers but measured the seat post itself slightly below where the collar was already mounted. Perhaps the very top of the seat post is a slightly different diameter?
06-15-18, 09:44 AM
#9
Banned
Carbon? metal tubes used in bicycles tend to be fractional imperial outside diameters.. (except period French)
expressed in metric numbers 1" = 25.rmm, 1.25 " = 31.75mm..
expressed in metric numbers 1" = 25.rmm, 1.25 " = 31.75mm..
06-15-18, 10:43 AM
#10
Senior Member
Thread Starter
Hard to tell as there's so little detailed info on the bike on the 'Net. The frame is 100% alloy. The seat post, I'm pretty sure, is not carbon although I will try to compare it to one of my other bikes that does have a carbon seat post. However I think it's just powder-coated metal. Everything hooks together well - the fitting of the collar on the seat tube, the seat post within the frame, etc. The collar is a QR collar and isn't slipping under my considerable weight!
06-15-18, 12:00 PM
#11
Banned
Shim? add more aluminum under the next larger standard size
of seatpost band clamp. ?
FWIW I used a 2nd QR band around the seat post itself
to cure a slipping seat post..
Works well, on my folding bike.
...
of seatpost band clamp. ?
FWIW I used a 2nd QR band around the seat post itself
to cure a slipping seat post..
Works well, on my folding bike.
...
Last edited by fietsbob; 06-15-18 at 12:04 PM.
06-15-18, 12:45 PM
#12
Senior Member
Thread Starter
There's actually nothing wrong with the one I have and the bike is new. I just wanted a red one! I must have been drunk when I measured it last night and read 37mm. I've ordered a Hope QR one sized at 34.9mm. I'm pretty sure it'll fit fine.
06-16-18, 06:11 AM
#13
Senior Member
Thread Starter
Just to close off this thread. This picture illustrates how I made a mistake in measuring the seat tube diameter. Originally I did not remove the existing seat collar. I simply placed my calipers below it to measure the seat tube diameter.
As is shown in the picture, the seat tube diameter increases just below the top of the seat tube by a couple of millimetres. That's where I a made the mistake!
As is shown in the picture, the seat tube diameter increases just below the top of the seat tube by a couple of millimetres. That's where I a made the mistake!
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