QR seat clamp size

hainman

Im back again and needing more advice,Im looking for new seat post clamp(qr) and cant figure out what size i'd need for a seat post that is 29.8 on my Rockrider 9.1,
Your wisdom would be greatly appreciated AGAIN
CRAIG

cooldad

Look on the current one - they normally have the size on them or measure the seatube. Seat post size is irrelevent.
viewtopic.php?f=40073&t=12726337

hainman

Thanks,my old one is manky and rusty and didnt know it had the size on it
I'll take the post out and measure circumfirance of the seat tube,

nicklouse

why take the post out?

hainman

thought it easier to measure across the seat tube
Am i meant to measure round ??

cooldad

cooldad wrote:

Look on the current one - they normally have the size on them or measure the seatube. Seat post size is irrelevent.
viewtopic.php?f=40073&t=12726337

Yes.
That's why I posted a link. It's easier.

hainman

Thanks will drag my bike out and measure it
Now i can buy my shinny new red seat clamp and my qr skewers

hainman

So measured my seat post tube and its coming in at 36.3434
Is this right or have I botched it some how.dont see any clamps that measure 36 mm

cooldad

Whar circumference did you get? Chances are it's 34.9.

supersonic

It is the internal width of the seat tube, external width of the seat post.

hainman

So measured it with bit of string,marked it and it was 115mm and when I do the divide its 36.6which is mahoosive.there was a 35 marked under the bottom of the clamp,so does it mean I can order 34.9 or is it bigger?.
It's doing my head in,

supersonic

34.9 it is ;-)

hainman

Supersonic cheers I'll order that size and hopefully be right fit,just flung me abit when I got figures of over 36mm.all this for a shinny red seat clamp,better look good!!!!

cooldad

supersonic wrote:

It is the internal width of the seat tube, external width of the seat post.

Seriously? I think not. It's the external width of the seat tube.
The external width of the seat post would errrr be the seat post size.
Shirley?

hainman

So it's not 34.9 i need...... :roll:

cooldad

hainman wrote:

So it's not 34.9 i need...... :roll:

It is - what was stamped on your clamp.

hainman

Was 35 on the underside and other letters and numbers but I was just stumped when my measurement by tape was 36.something
I'll go with 34.9 and see how that goes might just get cheap one that way if its wrong I'm not faffing about returning stuff and trying to get money back for posting it
Cheers guys for all your help

cooldad

99% of the time it will be a common size, and 34.9/35 is common.

hainman

Cheers cooldad

supersonic

cooldad wrote:

supersonic wrote:

It is the internal width of the seat tube, external width of the seat post.

Seriously? I think not. It's the external width of the seat tube.
The external width of the seat post would errrr be the seat post size.
Shirley?

I thought he was clarifying the seat post size for some reason. All alu frames of 29.8 use a 34.9 seatclamp, so easy to tell from it.

Johnny_Cage

Hijack.

So, my seat post says 30.4 on it, I measured the outside of the seat tube, got 32mm

What size QR should I need?

There is a 31.8mm version of the QR I am looking at, is it outside of the seat tube you go by?

Thanks.

jimothy78

Forget the seatpost itself - the external diameter of the frame's seat tube is what's important. Very likely to be 31.8, but to double check, measure the circumference (around the tube) with a fabric tape measure (or a piece of string), then:

9cm seat tube circumference = 28.6mm clamp
10cm seat tube circumference = 31.8mm clamp
11cm seat tube circumference = 34.9mm clamp

nicklouse

jimothy78 wrote:

Forget the seatpost itself - the external diameter of the frame's seat tube is what's important. Very likely to be 31.8, but to double check, measure the circumference (around the tube) with a fabric tape measure (or a piece of string), then:

9cm seat tube circumference = 28.6mm clamp
10cm seat tube circumference = 31.8mm clamp
11cm seat tube circumference = 34.9mm clamp

0.6mm ain't enough wall thickness for clamping area more likely to be bigger.

But as we have no idea of the frame or even the material I will not guess the size as it could be anything.

Johnny_Cage

jimothy78 wrote:

Forget the seatpost itself - the external diameter of the frame's seat tube is what's important. Very likely to be 31.8, but to double check, measure the circumference (around the tube) with a fabric tape measure (or a piece of string), then:

9cm seat tube circumference = 28.6mm clamp
10cm seat tube circumference = 31.8mm clamp
11cm seat tube circumference = 34.9mm clamp

Yeah 10cmm, bang on.

Thanks.

rockmonkeysc

hainman wrote:

So measured my seat post tube and its coming in at 36.3434

How did you measure to one tenth of a micron?

coulddobetter

Really easy way. Take existing clamp into a shop and check with a human being who can match it.

Johnny_Cage

Are we not human beings?

I don't think you need to visit a shop for the simplest of things.

Pretty confident I've got the correct size.

Chunkers1980

Or just get some cotton wrap it around the outside, measure how long it is where the ends join and apply some maths.

Johnny_Cage

Already done that.

Don't see how visiting a shop is easier than that. Cause... it isn't.

The Rookie

nicklouse wrote:

0.6mm ain't enough wall thickness for clamping area more likely to be bigger.
.

Like 0.7mm?