Tube recommendations for stiff touring/commuting bike
Hi All!,
Im looking for thoughts and recommendation on tube selection for my first (technically second) frame build. I am a fairly accomplished metal worker so am 100% confidant in my ability to fabricate the frame but dont have any experience designing frames. This frame will replace my current bike (1st gen Salsa Vaya Ti) as mostly a commuter bike. My main gripe with the Vaya is when loaded with 5+ pounds in a front rack bag and rear panniers with 10-15 pounds its WAY too flexy. Im about 195 pounds and 6'-2" and ride a 58-60cm frame so am on the larger size. The Vaya flexes has so much torsional flex that its jumps around when hammering out of the saddle and is a little uncontroable. If I am not careful it will shimmy when riding with no hands. I can get the bike to wiggle all over the road with a little shake of the bars. I would like this new frame to not flex in the same way so am thinking of building the frame with Nova's 38mm DT 8-5-8 29er tubeset. Is this a good choice? Should I jump up to the 42MM set or will 38mm be too much and I should go do down to 35mm DT? I have 38mm tires on the bike and will be using that to smooth out the ride. Any thoughts or recommendations on tubing choices would be greatly appreciated!
Re: Tube recommendations for stiff touring/commuting bike
Hello Isaac!
You are asking the BIG QUESTION in frame design. one that I have been doing my best to answer for 20-some years. My approach is to go for lateral stiffness and a reasonable measure of vertical compliance. The heart of the frame is the seat tube and chainstay - that's where you need stiffness the most. For a person your size and strength I would build a 1.25" butted seat tube, and look for very stiff chainstays. The old Reynolds track chainstays are nice but hard to find; mostly I bend my own out of 3/4 x .035" aircraft grade tubing. The next most important tube for lateral stiffness is the DT - the TT and seatstays aren't really in the picture that much.
The culprit in your Salsa's wimpy ride may be the chainstays - give them the squeeze test in your hand.
For the main triangle I use an OS (28.6/31.7) tubeset and have had good luck with a .7-.4-.7/8.-.5-.8 TT/DT combo. That gives me a bike that I can ride all day without getting beat up too badly. For a little more stiffness you could bump it up to .8-.5-.8/.9-.6-.9 or go up to 31.7/35 and use the lighter butt profile.
Be careful of "short butt" tube sets!
Good luck
jn
Re: Tube recommendations for stiff touring/commuting bike
Quote:
Originally Posted by
jon_norstog
Hello Isaac!
You are asking the BIG QUESTION in frame design. one that I have been doing my best to answer for 20-some years. My approach is to go for lateral stiffness and a reasonable measure of vertical compliance. The heart of the frame is the seat tube and chainstay - that's where you need stiffness the most. For a person your size and strength I would build a 1.25" butted seat tube, and look for very stiff chainstays. The old Reynolds track chainstays are nice but hard to find; mostly I bend my own out of 3/4 x .035" aircraft grade tubing. The next most important tube for lateral stiffness is the DT - the TT and seatstays aren't really in the picture that much.
The culprit in your Salsa's wimpy ride may be the chainstays - give them the squeeze test in your hand.
For the main triangle I use an OS (28.6/31.7) tubeset and have had good luck with a .7-.4-.7/8.-.5-.8 TT/DT combo. That gives me a bike that I can ride all day without getting beat up too badly. For a little more stiffness you could bump it up to .8-.5-.8/.9-.6-.9 or go up to 31.7/35 and use the lighter butt profile.
Be careful of "short butt" tube sets!
Good luck
jn
Thanks Jon,
Ive been thinking of bending my own chain stays from 3/4" tube, I have a full mandrel bender with tooling for 1.5" and 2.25" CLR with ID mandrels for 0.20, 0.035 and 0.042 wall tube and a wiper die. I was thinking 3/4 x 0.035 would be best. Would chainstays built from 3/4 x 035 be stiffer than basic NOVA 29er chainstays? While I dont want this bike to ride like shit it will only be used on a 20 mile round trip commute everyday and I have 26 x 2" tires to soak up some harshness.
