Seatpost Clamp for a 29.8 seatpost !

You need to measure the Outside Diameter of the portion of the seat tube which the clamp will fit over ...

If 31.8mm is too small, then it must be close to 34.9mm/35.0mm which I think is the next size up from 31.8mm.

... and, 28.6mm (which would obviously be too small) is the next size down from 31.8mm.

Thanks for replying alfeng !

Yes I too feel that that the 34.9 should be good to go. Is there any table or chart that has the general compatibility. for eg the 27.2 seatpost would need a 31.8 clamp etc

Quoted post said:

Originally Posted by atlantis [IMG]/img/forum/go_quote.gif[/IMG]

Thanks for replying alfeng !

Yes I too feel that that the 34.9 should be good to go. Is there any table or chart that has the general compatibility. for eg the 27.2 seatpost would need a 31.8 clamp etc

It depends on the material used for the frame. Aluminum is usually thicker than steel or titanium, which necessitates a different clamp diameter. Salsa seatpost clamps cover most of the odd sizes, where the general clamp sizes are (as mentioned) 28.6, 31.8, and 34.9. Campy uses 32 and 35.

Salsa has: 28.6, 30, 30.6, 32, 35, 36.4

While there may be just such a compatibility chart, I am not aware of one.

I think you will always need to measure the actual OD of the seat tube to ensure that you buy the correct clamp size.

BTW. I have an aluminum bike frame which uses a 27.2mm seatpost & a 31.8mm clamp ...

I have a steel bike frame which also uses a 27.2mm seatpost & a 31.8mm clamp ...

So, the frame's material is not a factor in determining a clamp size ...

But, I guess that 'I' would always anticipate approximately a 4+ mm difference (2mm +/- thick walls -- maybe a litte more, maybe a litle less) between the seatpost size and the clamp size based on just the two, fore mentioned examples.

Quoted post said:

Originally Posted by alfeng [IMG]/img/forum/go_quote.gif[/IMG]

BTW. I have one aluminum bike frame which uses a 27.2mm seatpost & a 31.8mm clamp ...

I have a steel bike frame which also uses a 27.2mm seatpost & a 31.8mm clamp ...

So, the material is appaently not a factor in determining a clamp size ...

But, I guess that 'I' would always anticipate approximately a 4+ mm difference (2mm thick walls -- maybe a litte more, maybe a litle less) between the seatpost size and the clamp size based on just the two, fore menioned examples.

It depends on the quality of the tubing. A quality aluminum frame is going to have thin tubing. A cheap aluminum frame is going to have thick tubing. So thick, that I've seen Alu frames with a 27.2mm seatpost require a 35 seatpost clamp. Uncommon, but they do exist.

I've seen several steel frames with a 27.2 seatpost that need a 30mm clamp.