Home
What the? Flexible down tubes can be changed on this commuter bike

Here’s a bike, debuted at Interbike in Las Vegas this week, to file under curious. It’s from new company Alter Cycles, and is their first bike that has been two years in development, a flat-barred commuter with an interchangeable down tube. Yes, an interchangeable downtube.

The curved downtube can be removed and changed for another, to tune how much comfort the bike provides. It's deisgned to flex you see. Alter Cycles describe it as an “adjustable suspension bike that can be dialed into the weight of the rider.”

That’s the theory anyway. Quite why a commuter would want to alter the comfort of a bike designed for whizzing across town, or why you’d want to make a key structural element of the frame interchangeable is beyond us. The down tube is available in three levels of flexiness, from soft to medium and hard. In a double diamond frame a down tube provides a huge chunk of the stiffness of the frame, so what impact this bow-shaped flexible element has on the handling remains to be seen. It'll also be interesting to see how much deflection the down tube provides. It also looks like there's going to be little compliance come through the back wheel, regardless of what down tube you have installed.

You can do wonderful things with materials these days though. It’s not exactly new territory for bicycle design. The famous Slingshot, a bike first conceived in the 80s, replaced the conventional down tube with a steel cable, spring and fibreglass hinge. The idea was to use the flex in this arrangement to produce a bike that could better handle rough terrain, softening bumps and holes. There was also something about the design ‘storing’ pedal energy and released at the dead spot.

Judging by their Facebook page, they’re riding and testing samples so it must work. We can't wait to ride it ourselves to find out how it performs. No idea whether this bike will see the light of day in the UK, but over in the US it will cost $799, with down tubes costing $99. Excitingly, they’re working on similar designs for road, mountain and cyclocross models too. Check out their website at http://altercycles.com/

David has worked on the road.cc tech team since July 2012. Previously he was editor of Bikemagic.com and before that staff writer at RCUK. He's a seasoned cyclist of all disciplines, from road to mountain biking, touring to cyclo-cross, he only wishes he had time to ride them all. He's mildly competitive, though he'll never admit it, and is a frequent road racer but is too lazy to do really well. He currently resides in the Cotswolds.

13 comments

Avatar
arrieredupeleton [581 posts] 3 years ago
0 likes

Call me old fashioned but you'd probably get better results by changing those completely inappropriate 29er MTB tyres for something a bit narrower/smoother/higher pressured.

How do they deal with security? 1.) you wouldn't put a lock in the main triangle and 2.) someone might just nick the downtube anyway.

Why don't they invest in a bike that transforms from a roadbike to an MTB? Fast uphill and fast down. That would be utopia.

Avatar
BBB [454 posts] 3 years ago
0 likes
arrieredupeleton wrote:

Call me old fashioned but you'd probably get better results by changing those completely inappropriate 29er MTB tyres for something a bit narrower/smoother/higher pressured.

It depends on the tyres.
High end MTB tyres with minimal tread and thin and flexible high TPI casing like Furious Fred will beat most of clinchers and commuting/touring tyres on rolling resistance at much lower, comfier pressure, especially when run tubeless.
To me popular "fast" tyres like e.g. Gatorskins at around 100PSI ride like carriage wheels (or at best like hosepipes) in comparison  16

Avatar
KiwiMike [1297 posts] 3 years ago
0 likes
BBB wrote:

To me popular "fast" tyres like e.g. Gatorskins at around 100PSI ride like carriage wheels (or at best like hosepipes) in comparison  16

I run 28c Gatorskins at 80 back, 50 front. Comfy as hell. Nary a flat in 4,000km either.

Agreed, 100psi is a stupid pressure for people who haven't got with the low-rolling-resistance-low-vertical-mass-shift times.

Avatar
Ad Hynkel [156 posts] 3 years ago
0 likes

Just looked them up: "Furious Fred is not an allrounder, its grip is limited and risk of punctures is high.", say Schwalbe. The people who make the tubeless Furious Fred. Not the people who make the highly puncture resistant Gatorskin clincher carriage wheel. So, get friendly with the latex you commuters if you are following BBBs advice.

Avatar
Veedubba [4 posts] 3 years ago
0 likes

You mention Slingshot, but did you mention it's by the same designer/ inventor of the Slingshot - Mark Groendal?

Avatar
Steve Worland [28 posts] 3 years ago
0 likes

If his Slingshot designs are anything to go by, the ride will be better than you'd imagine by looking at it.

Avatar
DrJDog [413 posts] 3 years ago
0 likes

The downtube on my Marin commuter almost completely snapped a few weeks ago - I can say with some authority that having a remotely flexible downtube is not something that you want on a bike.

Avatar
Bez [612 posts] 3 years ago
0 likes
DrJDog wrote:

The downtube on my Marin commuter almost completely snapped a few weeks ago - I can say with some authority that having a remotely flexible downtube is not something that you want on a bike.

You know how Ryvita is stiff, but snaps really easily? And you know how Hovis is flexible, but takes more effort to tear?

Well, that.

Avatar
BBB [454 posts] 3 years ago
0 likes
Ad Hynkel wrote:

Just looked them up: "Furious Fred is not an allrounder, its grip is limited and risk of punctures is high.", say Schwalbe...

...as a mountain bike, not road/commuting tyre.

When run tubeless with a sealant, they are virtually puncture free, have excellent grip on tarmac and are roll better than most of theoretically faster tyres, e.g. Conti Grand Prix 28mm.

It's just an example, anyway.
They are other, more robust (can be run with tubes) fast rolling MTB tyres available that make perfect sense for commuting and offer similar speeds to that of narrower slicks.

Ad Hynkel wrote:

...Not the people who make the highly puncture resistant Gatorskin clincher carriage wheel. So, get friendly with the latex you commuters if you are following BBBs advice.

I'm not offering advice. I simply disagree that one needs narrow tyres at high pressure to ride fast on the road, as suggested by arrieredupeleton. (backed by actual riding experience, not just looking tyres up on the internet  3 )

Owners of Big Apples or Supermotos probably know what I mean.

Avatar
joebee9870 [73 posts] 3 years ago
0 likes

pointless............

Avatar
DrJDog [413 posts] 3 years ago
0 likes
Bez wrote:
DrJDog wrote:

The downtube on my Marin commuter almost completely snapped a few weeks ago - I can say with some authority that having a remotely flexible downtube is not something that you want on a bike.

You know how Ryvita is stiff, but snaps really easily? And you know how Hovis is flexible, but takes more effort to tear?

Well, that.

Good for you.

I'm saying that the resultant broken, very flexible downtube made for a quite terrifying bicycle.

Avatar
bikeylikey [223 posts] 3 years ago
0 likes

'It'll also be interesting to see how much deflection the down tube provides. It also looks like there's going to be little compliance come through the back wheel, regardless of what down tube you have installed.'

It 'looks like' lots of things would happen. They must have tested and researched it a lot in two years though, so maybe it doesn't just perform like you'd think it would. I'd have thought that the down tube flexing would put too much strain on the seat cluster weld or lug, as the seat tube will be acting like a lever, moving back and forth as the down tube flexes. This would provide rear wheel compliance, but looks like it would bend or crack the top tube.

The developers must know better than someone who's just looked a picture for five seconds.

Avatar
behemothprocycling [41 posts] 3 years ago
0 likes

I had a Slingshot BMX about 17-18 years ago.
Another bike I should never have sold (got out of BMX and into MTB).