I dusted off my very rusty Strength of Materials education and did some math(s)… I probably messed something up, but here’s what I came up with:
Assuming most of the compliance feel/noodleyness of the front triangle comes from torsion, I looked at the formula for twist angle of a thin tube. Here’s my math, note the assumptions about applied torque being equal, tube length being different, thin tubes, and shear modulus being equal. Also of course this assumes straight gauge tubing.
plugging it into excel, here’s what I got for needed 7/8" wall thickness to get an equivalent angle of twist to a slightly longer 0.035 1" tube if the same amount of torque is applied to both:
There are no issues with 25.4TT as far as I can tell, it was the right choice. The only issue is the availability of wall thicknesses and butt lengths. 25.4 tubes are getting rarer
Tell me about it. I’m making a ~45-46cm 25.4 top tube and even the tube with the shortest butting would leave 40mm of thicker butt on each end…Did you have to go with straight gauge for that example?
I have bikes for me (250lbs) with 1" top tube so that’s not an issue. Yeah, they are flexy but they have lasted thousands of miles. I used a 3/4" .035" (0.8mm) straight gauge tube for a top tube on a kids MTB bike and it held up great for the couple years he and another kid rode it. If you get 40mm butts on each end, you’ll be fine in terms of the joints but the braze-ons will be a challenge to get within that section.
I guess in my case it would mean to just avoid the cable stops and guides then…I think the only other concern is that it will be fillet brazed which might have more (longer) area that will be
*edit: will be affected
