Seat Clamps (although The Post Is Sorted Now)

[Tommy d]

Right, topic recycled, I've ordered a seat post and a saddle, now I just need to know about clamp diameters.

If my seat post diameter is 25.4mm, do I also need a 25.4mm seat clamp?

Or do I need a larger seat clamp to take into account measuring the outside rather than the inside of the seat tube of the frame?

Anybody?

Cheers

Edited March 28, 2007 by Tommy d

[Brian Bleech]

I'm buying a saddle, a seat post and a clamp for my new frame and I'm not sure about sizes and stuff.

The only thing I know so far is that the frame takes a seat post with a diameter of 25.4mm.

Does this mean I also need a 25.4mm seat clamp, or will the clamp be a larger size cos of the outside rather than inside measurement?

Also, is it correct that most seats use 7mm rails, and therefore a DMR Expert seat (8mm rails) will not be compatible with most seat posts? (link below)

http://www.chainreactioncycles.com/Models.aspx?modelID=5606

Any advice appreciated. It's for my trials bike so I'm after lightish parts...

Thanks

if you are after a light seat & post go for macneil post with a macneil sl seat - try bmx shops.

[Tommy d]

Ok I've got a seat and a post ordered now, just need to know about the clamp size (see above)

i.e. Do you buy the same size clamp as seat post or are they different sizes?

ps thanks anyway leedstrials

[RobinJI]

They are different sizes. I can't think off the top of my head what size will go with a 25.4 post. But I'd say around about a 27/28mm for a steel frame and a 30 for an aluminium one? Best bets to just get the calipers out and measure the size of the seat-tube at the top.

[Tommy d]

Ok, cheers, I will have to ask around in search of some calipers. It's steel by the way. Maybe I could just have a look and make a decent guess at the thickness of the tubing and times by 2 and add that on to 25.4? The clamp size is just the outside diameter of the seat tube yeah?

Thanks

[nmt_oli]

Yep.

be careful if your just guestemating though, dont want to end up with an ill fitting clamp.

[RobinJI]

Just realised your talking about an Iolo. So it might help to let you know mines a 30.0mm clamp. But my seat post isn't a 25.4, I think its a 26.8, or something around that. Had to do a load of filing to get any available size to go in right. haha.

[Tommy d]

Haha yes. I found out when my 25.4 post arrived... It was from Wiggle though so they just take it back if it doesn't fit. After a trip to a bike shop to use their calipers, it seemed like exactly what you're describing (which would make sense really) but I ordered a 26.8 seat post and a 28.6 clamp in the hope that they would fit, and that I'd be able to file them if they didn't.

I didn't manage to find a 30.0mm clamp anywhere though, which is why I ordered a 28.6. Is that definitely what you have? Where did you find it?! The measurement of the frame was like 28.9 I think so I'm just hoping it will fit... not sure how easy filing the inside of a clamp would be!

Cheers for the help. I'll do a bike pics thread when it's all sorted.

[RobinJI]

This seems the best bet: http://www.chainreactioncycles.com/Models.aspx?ModelID=6256

It is an unusual size and only seems to be used on a few modern steel frames, like 24seven, Revel and a few other steel jump frames. So it can be a bit of a bastered to get hold of, but it does exist. The one you've ordered should fit with a push though from the sound of it.

On mine I had to file out the inside of the seat-tube its self a little bit, because of where the heat had deformed it where the stays and top tube where brazed on.

[dave85]

Salsa make a 30.0 clamp (bolt or quick release) if you want something a little better.