Cycling UK Forum

531colin wrote: ↑21 Aug 2024, 7:55am

stevegreen wrote: ↑20 Aug 2024, 9:44pm On the Paris frame, does the loop of tube joining the down tube to the laterals add much/any stiffness?

I think the question before that would be “ Do the laterals add much stiffness?”
I’m guessing they are even thinner than some other laterals, maybe closer to 10mm than 12mm? Tubus carriers are 10mm steel tube, for comparison.
“Paris” by the way was a London frame builder with “form” for some odd designs; Paris Galibier for one, and they were also responsible for “Harry Rensch” tandem frames with 2 sets of twin laterals. ..OK with a child stoker….

I take your point, therefore I will ask the question that I should have asked in the first place!
Does that loop of tube add any of the stiffness lost by using twin laterals?

531colin wrote: ↑20 Aug 2024, 4:05pm 1. Is the stiffness shown by the "foot on BB axle end and push" test any sort of reflection of how quickly a bike accelerates with that first harder push on the pedal?

2...If a seat tube is going to fail due to fatigue, it will (usually?) fail a bit above the bottom bracket shell; even on bikes made of plain (un-butted) tubing. I think I remember Brucey posting something like "displacement of the BB due to pedalling forces is reacted almost exclusively in the seat tube".

1) I think it as good an ad hoc test as you can expect to do, and it can tell you a lot. If the BB moves too easily it could be the rear wheel/chainstays or the down tube/forks which are flexing. IME the three things that make a frame 'responsive' when you pedal are stiffness, efficiency, and absence of weight. Great bikes/frames have all three, two is a good bike, and if a bike has 1/3 it is probably good enough to ride down the shops on, or perhaps go training. 'Efficiency' is a bit of a catch-all for a lot of things, including how effective the frame is as a spring.

2) One can pedal 'forcefully' whilst seated, without working the handlebars. In this case one of the reaction forces is a side thrust in the saddle. This force is not very high, but it is on the end of a long lever, the seat tube. Most folk that have an efficient style don't work the handlebars whilst seated, so the seat tube takes a pasting and that is why they sometimes fail via fatigue. Riding out of the saddle stresses the down tube via the handlebars; a few people work the handlebars (and the down tube) when seated. I don't think this is terribly efficient.

So overall, any time you increase the stiffness of the chainstays or the seat tube, the bike should feel more responsive. Also if the frame becomes a better spring, the bike should feel more responsive. However, I think you can have too much stiffness; not only does the law of diminishing returns come into play, but I believe that you only get any good feedback from the pedals if the frame flexes slightly. The amount of flex that is optimal will vary with the rider.

thanks, Brucey, i think I'm getting there!

daddyduca wrote: ↑3 Aug 2024, 12:10pm I would like to have a mixte frame built for my wife, but no one can source the necessary lateral tubes. Framebuildersupply.com had the lugs needed, but they don’t seem to have the tubes. Does anyone know where I can get some?

Btw, this will be a 70th birthday present for my wife. Right now she has an anglais frame, but it sometimes sways in curves and she fell recently when we hit a small patch of sand. I’ve tried for decades, but she can’t be convinced to get a men’s frame.

As a few weeks have elapsed since your original post I wonder what you have decided to do?

It’s been an interesting thread, thank you for starting it.

I'm here in the US and am enjoying this thread.
I have plans to build 2 lighter weight touring frames this winter. I have built a few frames with 1 being a twin lateral mixte.
My wife has a Dutch touring frame that is a step through that we bought in The Netherlands. But it is made for handling 4 panniers and it has 26" wheels. Really quite a touring rig.
So keep the comments coming!