no1mad 

First post here in this forum, and probably only thread I'll participate in. Thinking about getting a Giant Via 2*. It's a cro-mo frame with a split top tube. From a structural integrity point of view, is this design something I should be wary of long term?

*I intentionally linked to the Via 1 model, due to it having an alternate view that shows the split tube.

Scooper

The top tube is under compression when riding, and that tubing looks awfully small to me even though there are two tubes. I'm not sure what purpose the split top tube serves.

unterhausen

there is nothing wrong with the design. You could make the argument that it doesn't use the material as efficiently as a single top tube, but that probably doesn't matter in this case. Was there a small framebuilder that made a bike like this so the big companies could all copy it? Trek also has a bike like this now.

thirdgenbird

origin 8 has a frameset with a split top tube as wel...


i prefer split seat tubes:

no1mad 

You must be referring to the Earl? I think that I like the geo on the Earl better than that Giant. I've been toying with the idea of going SS...

unterhausen

My LBS reports that the Earl has been selling well. The nice thing about the split top tube on that bike is that there is a u-lock mount.

Bezalel

These are targeted to different segments. The Via is a city bike and the Earl has a bottle opener. as far as aesthetics the seat cluster is much nicer on the Via (at least it looks like it from the photos).

Scooper

I agree; the twin top tubes on the Via are extended past the seat tube to the rear dropouts as seat stays similar to the 1939 Schwinn cantilever frames, simplifying the seat cluster. The big difference is that the Schwinn also has a beefy top tube and the smaller twin tubes carried forward to the down tube are to keep the head tube aligned in the same plane as the seat tube when the frame is subjected to dynamic twisting loads.

unterhausen

I'm trying to figure out how the Via has a cleaner seat cluster than the Earl. The only significant difference I see is that the Earl has a brazed on binder bolt.

Scooper

That's what I get for not looking at the Earl link.

fietsbob

Found a light thin Mixte frame's 2 tubes being thin wall and small diameter, Noodly. I could twist the head-tube and move the bars
and see the wheel move sideways .

I built up a loaded touring frame around a bent twin tube that comprised the rear triangle and top tubes.

They are 3/4" ..049" wall tube , Mandrel bent twice, 4130
Tig to BB shell , brazed to seat tube,

welded gusset behind the head tube
the tubes plugged solid and attached to the sides of the head tube by welding them ..

Human Powered Machines in Eugene was the shop I got to help building it ,
and a stainless welder in Killarney Eire, whose main trade was stainless A/C duct work

when the design sorted out some weak spots , the gussets were added there.
the joint was brazed on a hollow tube, originally ..

Now it's a solid working design.

I can put my pump in between the top tubes,
so It doesn't pop off when I lift the bike..

NoReg

The earl looks like a size larger on the tubing. Cheapness wise dropping 3 butted tubes sounds like a win. When it won't be stronger, is if any load bends the tube up or down like a fall or denting on a parking meter. That axis is sacrificed, which is probably ok in the use.

Doohickie

I have a bike with a similar design that was built in 1960, had the tar ridden out of it by a paperboy. When it got to me, the rims were trashed, the cranks were bent, but the frame is fine. I don't think it's a concern.

James_T

Double top tubes always remind me of the Torker BMX frame (similar to this one) that I rode in the early 80s. When I was a kid, I loved the double top tube design because it looked different and it served as a platform to stand on. I doubt many people are going be bike surfing on the Trek Earl or Giant Via, but I do think that aesthetics are the primary reason for both of those designs. They are just trying to make a simple steel city bike stand apart from the competitors.

Doohickie

Another thought... this is pretty much like every mixte in existence.

tuz

I agree that generally double tubes are less efficient. It seems you can have similar stiffness because of the triangulation (provided you have adequately sized tubes; the 1/2 tubes found in mixtes indeed are too small) but it'll be at the expense of extra weight and complicated fabrication. But a proper design is fine. For instance it seems having 2x 3/4 tubes instead of a single 1-1/8 DT is stronger (that's from my bicycle design book from 1896).

Doohickie

It depends on the wall thickness of the tubes, tuz.

CurbDestroyer