Narrow D-Bolt Seat Clamp on 1957-58 Jaguars?

[Avanti]

I've recently noticed these narrow D-bolt seat clamps on 1957-58 Schwinn Jaguars. In some instances, the clamps are on bikes, which have the Sturmey-Archer shift cable pulley mounted above the top tube.

Does anyone know why Schwinn made this modification to the older wider D-bolt clamp and why they only seem to be found on 3 speed Jags? My suspicion is the clamp may have been re-engineered to give more room for a shift cable pulley to be mounted above the top tube so the cable could travel above the tank rather than through it.

 

[GTs58]

Interesting. I've never seen that set up before.

 

[sarmis]

That's gotta be the $1000 seatpost clamp !

 

[rustystone2112]

I've recently noticed these narrow D-bolt seat clamps on 1957-58 Schwinn Jaguars. In some instances, the clamps are on bikes, which have the Sturmey-Archer shift cable pulley mounted above the top tube.

Does anyone know why Schwinn made this modification to the older wider D-bolt clamp and why they only seem to be found on 3 speed Jags? My suspicion is the clamp may have been re-engineered to give more room for a shift cable pulley to be mounted above the top tube so the cable could travel above the tank rather than through it.

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looks like the early jags. like yours didn't have the notch in the front of the tank to pass the cables through and they ran it outside and used the modified post clamp to keep the cable aligned, later when the notch was added to the tank they dropped the pulley down lower

 

[rustystone2112]

Interesting. I've never seen that set up before.

i've seen several

 

[island schwinn]

I've seen those clamps,but never on a bike.cool stuff.

 

[Schwinn499]

Small framed/wheeled bikes

 

[Schwinn499]

 

[Avanti]

Interesting. I see the contours of the clamp almost perfectly follow the lines of the smaller frames. So I would assume instances where these clamps were installed on '56-57 middleweights was probably due to a factory worker just grabbing whatever clamp he had in the bin.

 

[GTs58]

Making the seat tube a fraction of an inch longer makes more sense to me.