Seatpost clamp size for a ‘531 tandem’ Reynolds tube set?

[Dynamite_funk]

The seatpost clamp on our tandem has finally gone and I need a replacement. Does anyone happen to know the correct diameter seatpost clamp I would need? The seatpost is 27.0mm.

Thank you

[rjb]

531 tandem tubing. The seat tube will be a standard size so 28.6mm
Assuming it's a broken external seat clamp not a failed braze on clamp.

[Dynamite_funk]

Many thanks!

[Dynamite_funk]

Hi all. Afraid it is not 28.6. Callipers say 32.6 so 33 seems nearest. I’ll go with that.

[rjb]

32.6mm are you sure it's 531?, Check with a magnet to see if it's an aluminium frame.

Could it be oversize tubing like 531 Magnum.
In which case the seat tube will be 31.8mm. (0.7+0.7+30.35)

[peetee]

I would seek recommendation from the likes of Spa or St Johns Street Cycles on a suitably strong aftermarket clamp. If it is for the front it has an awful lot to support. With the weight of one rider and the upper body forces of the other you don’t want a sub-standard clamp snapping mid-ride. On the subject of diameter, the front post almost certainly will be sleeved with a lug of some description for the reason I have already given so the clamp diameter will not be directly related to the external diameter of the seat tube and should be measured accurately making any allowance for any pre-existing distortion as a result of incorrectly fitted posts in the past.