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A few questions...

Old 05-28-12, 07:46 PM
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A few questions...

Hello everybody,

I have a couple of questions regarding My seatpost size and my seat clamp size. I learned through bikepedia that my bicycle is meant to have a 30.6 seatpost. I am 95% sure this is the info on the correct bycle year. I then used a caliper to measure the ID of the seat tube and it came out at around 30.8. Should i go by the specs or by my caliper? I understand there is a margin of error that could leave me to blame so i am leaning twords the specs.

Also, i measured the OD of the seat tube and it came out at 36. I am aware that seatpost collars come in about 3 or 4 different sizes. If i get the 36.4 size clamp will it still work? I am assuming it doesnt have to be exact beacuse of the clamping it does wich changes or tight it gets.

I should also mention all of the above measurements are in millimeters.

One last question what is the peice of a headset that is equivillent to the crown race but on the top called? and is it possible to order one of these alone?

Any and all help will be much appreciated.

Sincerely,
Likesbikes36
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Old 05-28-12, 08:09 PM
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For the seatpost diameter and collar size, I'd take the bike to an LBS for a measurement using a seatpost gauge and try different collars. These things are hard to measure accurately and close enough isn't good enough.

I believe the headset part you are asking about is called the top race. Depending on the make and model, parts may be available from the manufacturer.
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Old 05-28-12, 08:51 PM
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Taking it to a shop and having them measure would really be the best option. But if you have no choice I would trust bikepedia before a rough measurement. I had to buy a post blind because some idiot had almost destroyed the seat tube of a steel bike I bought by crushing it around a tiny post. The specs on bikepedia were luckily correct.

Headset parts are not universal, so unless you can get exactly the part you need you're probably out of luck. Fortunately, headsets are not expensive so if you need to buy a whole new one it's really not that big of a deal.
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Old 05-29-12, 12:37 AM
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this is confusing. this is my understanding.....

a seatpost marked 27.2 should take a collar marked 31.8
if your seatpost is marked 30.8 or 31.6, then you'd use a collar marked 34.9 or 35.
(unless your frame material is >2mm thick)

if the ID was 30.6, it would be really hard to get a 30.6 to slide in. you also
need to consider that opening should close up some when you tighten the clamp.
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Old 05-29-12, 07:55 AM
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Originally Posted by saddlesores
a seatpost marked 27.2 should take a collar marked 31.8
if your seatpost is marked 30.8 or 31.6, then you'd use a collar marked 34.9 or 35.
(unless your frame material is >2mm thick)
~30mm post = aluminum/carbon frame which are generally much thicker than steel frames, especially up around the seatpost area even if they use a 34.9 clamp on front derailer.
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Old 05-29-12, 01:49 PM
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So besides going to my LBS to get measurements, which i may do if i have time. does anyone think the size collar size 36.4mm will work becuase of the clamping it does? I used both a vernier and digital caliper on the ID and OD of the seat tube and got 30.78mm for the ID and 35.97mm for the OD.
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Old 05-29-12, 02:15 PM
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Originally Posted by likesbikes36
So besides going to my LBS to get measurements, which i may do if i have time. does anyone think the size collar size 36.4mm will work becuase of the clamping it does? I used both a vernier and digital caliper on the ID and OD of the seat tube and got 30.78mm for the ID and 35.97mm for the OD.
Maybe it will and maybe it won't. That's why we recommended a trip to the bike shop to be sure. Othewise you are going to have to order the parts and try them yourself and be prepared to return them is they don't work.
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Old 05-29-12, 07:01 PM
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alright that sounds like what i need to do. thanks hill rider and everyone else for the help!
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