Perineum discomfort, numbness and so on...

[roubaixtuesday]

I was pointed in the direction of this thread by @slowster, being rather tall myself, though a mere 192cm.

I'm lucky enough to have a custom build frame from Swallows, which features the longest top tube done on 953. I expect 531 has the same max length, a frame builder could advise I guess. On that bike I have an average length stem, not sure exactly what.

I also have a tandem, which has been far more tricky to get to fit. I had similar issues to you on that. I now have one of these stems:

20220827_210314.jpg

Ergotech do a range of similar. I tried an adjustable one before buying a fixed (the adjustable ones have some play in use and are a PITA IMO).

I don't know what would work for you, but my best guess would be:

1. Saddle all the way back
2. A long and rising stem.
3. And longest top tube you can get (if a different bike is an option)

Good luck, and you're not alone!

Current 953 tube listing is rather disappointing, there are only 2 top tubes listed, both 28.6mm diameter, length 625 or 635mm, with different wall gauges. Down tubes similarly, only 34.9mm diameter, both 680mm long, different wall gauges.https://www.torchandfile.com/953-MAR-AG ... c_131.html....so a frame for a 5' rider uses the same diameter tubes as a frame for a 6' 4" rider?
The 2016 listing has many more tubes, including 31.75mm diameter 650mm long with various butting profiles and wall gauges..... I would be happy to specify something like that as top tube for a really big frame .... and 36.4mm diameter tubing for down tubes for big frames, as well as exotica like tapered and bi-oval tubes.

Thats some stem on the tandem.
I am quite concerned at the amount of leverage exerted on the quill/ahead adapter. Failure is hopefully unlikely, but the consequences of failure don't bear thinking about.
I have been having a conversation here about tandem headsets viewtopic.php?t=152743.... hopefully the problem is solved with my strange headset designed for forks with damaged threads.
I guess your tandem has inch and eighth threaded headset?
If that was mine, I would be exploring possibilities.....if current inch and eighth threadless headsets will fit the frame, I would be looking at going threadless with a very long steerer; a framebuilder could replace the existing steerer, or it could be extended like this...

005 by 531colin, on Flickr

Thats an inch steerer I extended. Its sleeved internally using a bit of quill stem, with silver solder run in holes drilled at intervals..

003 by 531colin, on Flickr

Inch and eighth steerer can be extended similarly by sleeving internally with inch steerer which fits closely enough to be silver soldered; the join needs to be away from where the headset will go.
Its a lot of messing about, but you won't break a solid inch and eighth steerer, and it gives you much more choice in stems.

I wouldn't put a stem like your tandem stem on a carbon steerer.

My downtube on the Swallow is what you refer to as bi-oval. I don't know the top tube length, but I recall it was mentioned its was the longest available.

I'm afraid my knowledge of forks and headsets isn't sufficient to comment on the rest, but be assured there's nothing carbon on the machine anywhere!

[531colin]

...........
I'm afraid my knowledge of forks and headsets isn't sufficient to comment on the rest, but be assured there's nothing carbon on the machine anywhere!

Ok, so to be crystal clear; I don't know that your quill / ahead adapter and your long high rise stem are designed to be safe to be used together. I think there is an outside chance that the handlebars could come off in your hands.
You might like to show the bike to somebody, or even just post that picture in the technical section here.