Frame Stiffness

rollingscone · 25-11-2013 1:07pm #1

Having learned a valuable experiential lesson about the penalty you pay for an extremely flexible frame.

With having hoped to use my drop bar converted Giant escape as a touring bike I gave it a range test yesterday and found it far more draining than riding my roadbike for twice the distance.

Bearing this in mind, are touring bikes generally designed to be any less stiff than sportive style* roadbikes?

*Using this as shorthand for roadbikes that aren't particularly aggressive.

Morgan · 25-11-2013 1:11pm

I suspect that "stiffness" is not the only difference between the two bikes above.

Alek · 25-11-2013 1:12pm

I thought that touring bikes must be stiff enough to be able to carry the extra weight in panniers.

Lumen · 25-11-2013 1:13pm

I don't think one ride is enough to be definitive.

I find that when I switch to a new bike it takes me a while to adapt to slight differences in geometry. I think it's a neuromuscular thing.

If this is a real difference, why do you think stiffness is the culprit?

I believe that frame stiffness is in the same ballpark as fancy wheels in terms of "things which make bikes feel faster". I have never read a convincing technical explanation for how frame flex translates into significant losses which didn't at some stage degenerate into hand-waving.

rollingscone · 25-11-2013 1:14pm

Certainly not, the drivetrain makes a difference, but the thing I felt was the energy sapping effect of the frame.

ROK ON · 25-11-2013 1:40pm

There are pros & cons to stiffness in my experience.
I have three bikes that are each a bit more stiff than each other.

The stiffest is probably best for climbing, turbo training and racing (although I have rarely used this bike racing). It is a CF frame and fork.
I use some high end mavic clinchers.
On good roads (going up or down) it is a great bike.
On bad descents it is a nightmare. It doesn't cut through the poor road surface and instead is prone to rear wheel bounce and fishtailing.
Btw - I am not light - there is significant weight on the rear wheel.
Disconcerting - so much so, if I know I am taking certain routes I simply do not ride this bike. Too much vibration through front fork and too many suicidal moves by rear triangle/wheel combo. The bike is a Kuota Kebel.

Second bike is a Ti framed Van Nicolas Mistral. Semi-racy geometry. Flex when out of the saddle climbing, but is comfortable on all roads. I race and commute on this bike. But that is down to the geometry as opposed to stiffness.

Third bike is a CF Dolan Hercules frame on whatever wheels I have around at the time.
I have raced on this bike, I use it as a bad weather bike, but mostly it lives on the turbo machine.
It is flexy as fook - spongelike. On the turbo it is comical to see how much the BB sways from left to right.
Despite that I love this bike. It is reserved for some horribly dirty rides on bad roads. It works on these roads - much more so than the other bikes.

Stiffness is good - in some types of bikes. But that does not mean the flex is a negative in all situations.
I know of two guys that have gotten rid of a certain frame as it was way too stiff for our roads.

You need to find out what it is that you want and why.

rollingscone · 25-11-2013 1:55pm

Thanks for all the replies so far.

This is very much what I'm trying to investigate, what I found yesterday was that I was getting a lot less return on the energy I was putting into the bike, admittedly there's much that can be attributed to the fact that I was rolling on cheap wheels with 85psi as opposed to Aksiums running at 110 and the Ultegra BB and Tiagra cranks on my "proper bike".

Mostly it was something I physically felt, especially on sharp climbs like Knockmaroon hill and Captain's hill in Leixlip, the bike seemed to physically wobble under the strain, I suppose my main ponderance is whether such a performance might be punitive trying to do a relatively relaxed touring holiday of say 80km per day.

Geometry wise it's longer across the top tube yet more upright on the hoods.

Morrisseeee · 25-11-2013 3:15pm

I went from a hybrid to a Trek 1.2 to a Cervelo S1.
Some difference from one to the next.
Hybrid : grand for crooozing around.
Trek 1.2 : bit of an all-rounder, workhorse, good/ok for most applications.
Cervelo S1 : an animal, fast, stiff, and very responsive. It feels like 100% of my effort is translated into pushing the bike forward.

outfox · 25-11-2013 3:40pm

Rollingscone, a friend of mine did the same as you - put drop bars on a Giant hybrid. It might have been an Escape too. He says he doesn't notice any frame flex problems. But he does find that the long distance between saddle and handlebars forces him to stretch so much that he feels he can't get to full power. Reckons he's a bit slower than he would be on a proper road bike. He only has the one bike at the moment, so he's unable to give a direct comparison.
Personally, I think his modified bike is so ugly that it's sapping his strength.