Replacement seat clamp - which size are they referring to

[TonyEnjoyD]

I know this sounds like a numpty question but never had to buy one before...

I want to replace my roadie seat clamp with a lever (quick release) type.
The seat stem is approx 28mm and the post/downtube is 34mm (+/- 1.5mm)

Do I buy a 28.2mm clamp or 34.8mm?????

Cheers
Tony

 

[TheDoctor]

It's the downtube size you go on, not the seat post.
Generally, there's three sizes IIRC - one for steel frames (the smallest) one for aluminium (the one in the middle) and one for carbon (the biggest).

 

[srw]

I've just had to replace a clamp (the bolt sheared as I was tightening it). There was a useful number stamped on the clamp housing.

 

[TonyEnjoyD]

It's the downtube size you go on, not the seat post.
Generally, there's three sizes IIRC - one for steel frames (the smallest) one for aluminium (the one in the middle) and one for carbon (the biggest).

Hi TheDoctor,
Are you referring to the inner diameter of the downtube or outer?
When I said 34mm I was referring to the outer as the inner is about 2mm wider than the seatpost at 30mm I assume to allow for getting it in and out.

So, my seatpost (the bit between the seat and the downtube) is 28mm diameter

Sorry - I'm not being pedantic - just didn't want to order one online just to have to return it.