I thought I would just distract you from your considerations of the merits of 1.125" top tubed frames to bring to your attention some very very serious French bikes for sale on French Ebay..for collectors of the fine stuff! And I am certain that there will be quite a few oversized top-tubes on these machines. First off is an older NARCISSE touring tandem..possibly 40s. Narcisse is often rated in the very top rank of French builders..a constructeur's constructeur so to speakl! Item No 7242753627.
Coming up in second place is another tandem from another "constructeur", this time Pierre Perrin, who is still building quality mahcines in the fully artisanal way, at Arpajon about 45 minutes south of Paris. This looks like an earlier Perrin, possibly a 70s model..just built for someone to complete the Paris-Brest on it. Item No7243265477.
Bringing up thr third place is no less than ... yes! ..a 56cms 1971 Rene Herse bike in excellent order..with a starting price of 4000 euros. Item 4642405054. Trouble is is that there are no photos, but I am sure someone will ask for some to be placed on the ad.
I've no connection to any of the sellers, other than a fondness for French hand-built bikes.
Norris Lockley, Settle UK