How stiffer bike has less energy lost

[novetan]

I heard abt the stiffer the bike, the lesser the energy will be lost thru your effort in peddling.

Assuming all things being equal, same rider, same wind direction, same wheel size, same road, etc. Below an example:

Assuming peddling at 90 rpm at gear 7 on a less stiffer bike, wheel rotates “x” no. of revolution/min and bike travels a distance of 700m/min. As compare with similar peddling at 90 rpm on a stiffer bike at gear 7, can I assume wheel should also rotates the same “x” nos. of rev/min that will result in the same distance travel of 700m.

I like to know how energy lose comes into play.

 

[alienator]

First, there has been no study that has correlated improved performance with frame stiffness. That said, power applied to the pedals not only turns the rear wheel but also puts a torsional load on the frame at the bottom bracket, while the chain tries to pull the rear of the frame around to its side. Some measure of the loads but into the frame can be returned. How much is difficult to say. Far more important, though, than frame stiffness is fit and ride feel.

 

[jhuskey]

I would also add and advise anyone to concentrate on the most important part of the bike , the motor.

 

[dominikk85]

Gear 7?

You lose energy because you waste energy torquing your frame. for this especially stiffness at the bottom bracket counts.

I would guess this apllies mainly when you ride standing or accelerating, especially sprints. I don't know if it has any effect at a consistent pace,

 

[alienator]

You lose energy because you waste energy torquing your frame. for this especially stiffness at the bottom bracket counts. I would guess this apllies mainly when you ride standing or accelerating, especially sprints. I don't know if it has any effect at a consistent pace,

Unfortunately, it's yet to be shown that it has any substantive effect at any pace.

 

[gudujarlson]

The energy lost when a material bends is highly dependent on the type of material and metals tend to not lose very much, thus I am skeptical that frame stiffness causes any measurable energy loss. Your tires on the other hand definitely have measurable energy loss when deformed.

http://sheldonbrown.com/frame-materials.html

 

[alienator]

Your tires on the other hand definitely have measurable energy loss when deformed. http://sheldonbrown.com/frame-materials.html

Absolutely. Thus the source of rolling resistance.

 

[danfoz]

Makes for an interesting mathematical exercise but pro's are still winning bikes on less stiff bikes than other pro's. The folks in marketing departments fail to mention this tidbit. In fact one of the winningest sprinters of all time, Sean Kelly, rode what some consider to be one of the noodliest bikes around at the time... the skinny diameter aluminum tubed Vitus.

 

[dhk2]

Agree the frame doesn't "absorb" a significant amount of energy, but what about additional losses in the tires due to the loss of wheel alignment on a flexy frame? IE, in a strong sprint, the BB is flexing side-to-side while the tension in the chain is pulling hard on the drive-side of the rear axle. Particularly when the sprinters weight is on the DS pedal, wouldn't both these forces result in pulling the rear wheel out of alignment with the direction of travel, such that either the rear tire has to slip sideways, wasting energy, or the bike has to follow a "snaking", longer path to the finish line?

 

[CAMPYBOB]

Tire rubbing on the frame. Rim rubbing the brakes. Chain dragging on the derailleur. BB bounce and torquing during climbing/sprinting, rear triangle sway, head tube twisting, fork flex all suck IMO.

The new Vitus line is mainly carbon. I wonder if they made them uber flexy per Sean's fondly remembered specs? http://www.vitusbikes.com/ [Sean]Veetus have made da calculation and dees will coitaintly suceed![/Sean]

"with just the right balance of stiffness and vertical compliance."

Ah! I knew I could find the perfect marketing phrase in all their flowing prose and praise of their product. They even managed to work in the ever popular "reduced road buzz" phrase for those riders that buy bikes for their abilities to reduce road buzz. All market segments are covered. At least in print.

My guess is if you go back to the 1980's Vitus 979 catalog you'll find Sean describing the wet spaghetti 979 as having "just the right balance of stiffness and vertical compliance comfort."

Sadly, we can't buy wet spaghetti, el explodo 979's anymore. Not even Sean's successes and marketing wizards could convince folks that flexible racing bikes were efficient.

Their new Al road bike, the Zenium (Weird? I thought 'X' replaced 'Z' as the cool kid on the block?) is described as, "Our new 6061-T6 aluminium frame with custom-drawn aerospace tubing delivers a ride that is light, stiff and responsive."

Not, Heavy, flexible and dead"???

 

[danfoz]

Originally Posted by CAMPYBOB .

. Rim rubbing the brakes.

This is where I see flex killing the speed, and why I gots my rear calipers spread wide open. And the fork flex could definitely be a problemo making up time on the downside. I swapped back to my alu steerer tubed Columbus fork over it's full carbon counterpart for just this reason.

 

[CAMPYBOB]

Yeah. It's not a black/white equation, but flex...or at least excessive flex...does cost energy. I'm not going to qualify that statement with the usual heavier, powerful, sprinter/climber/racer, larger frame sizes, etc. Even at my modest power output and weight, I've experienced several flexible frames that had energy penalties that were made abundantly evident in everyday training. I parked a year-old Litespeed rather than put up with the frame AND fork flex (Easton EC-90-SLX fork walked around like it was paper mache).

Even some of the name steel framesets 'back in the day' were too flexible. A friend's Ciocc comes to mind. Under hard climbing and sprinting his front derailleur constantly made noise no matter how it was tuned. I had one that did that, too, but I can't for the life of me recall which bike that was.

 

[alienator]

Agree the frame doesn't "absorb" a significant amount of energy, but what about additional losses in the tires due to the loss of wheel alignment on a flexy frame?   IE, in a strong sprint, the BB is flexing side-to-side while the tension in the chain is pulling hard on the drive-side of the rear axle.  Particularly when the sprinters weight is on the DS pedal, wouldn't both these forces result in pulling the rear wheel out of alignment with the direction of travel, such that either the rear tire has to slip sideways, wasting energy, or the bike has to follow a "snaking", longer path to the finish line? 

I think the losses from such wheel movement will be on the order of rolling resistance or less. As for changes in path length, I think they would be exceedingly negligible. Over the course of the ride, path length changes due to rider steering input (no one steers a perfect path) would be much greater--I'd guess by a couple orders of magnitude or more--than any path length changes due to frame flex and the resulting change in wheel direction.

 

[oldbobcat]

Originally Posted by alienator .


I think the losses from such wheel movement will be on the order of rolling resistance or less. As for changes in path length, I think they would be exceedingly negligible. Over the course of the ride, path length changes due to rider steering input (no one steers a perfect path) would be much greater--I'd guess by a couple orders of magnitude or more--than any path length changes due to frame flex and the resulting change in wheel direction.

My feeling is that it's more about the energy expended keeping the bike on its intended path. A squirmy front end can be an energy pit, which is why I'm happy to see tapered head tubes and steerers. On the other hand, you can neutralize any gains made up front with a long head tube and a 3.5 cm stem spacer stack.

In my totally impressionistic experience, there are noodles and coal carts. Most bikes fall somewhere in the middle, and the noodle threshold depends on the rider's mass, the size of the frame, and the rider's finesse at making the cranks go around fast.

 

[alienator]

A squirmy front end can be an energy pit, which is why I'm happy to see tapered head tubes and steerers.

I'm not sold on the idea that tapered steerers provide a significant performance benefit. My Look 595 has a tapered steerer and descends very well, but it falls a bit short of well my Moots Compact with its 1.125" steerer and Reynolds Ouzo fork The Moots just felt planted in corners on descents.

 

[oldbobcat]

There are all sorts of ways to make a bike stiffer up front, and I meant to point to tapered steerers and head tubes as an example of how the brands are giving the front end the attention it needs. After a certain level of stiffness, I think other factors might be more significant, anyway--head angle and trail, first, and then lateral stiffness of the fork and front wheel.

I do believe that in climbing and normal hard pedaling that a loose front end can take out as much energy as an overly loose drive section. And I believe that super-stiff drive sections are generally over-rated.

 

[WillemJM]

Originally Posted by CAMPYBOB .

Tire rubbing on the frame. Rim rubbing the brakes. Chain dragging on the derailleur. BB bounce and torquing during climbing/sprinting, rear triangle sway, head tube twisting, fork flex all suck IMO.

The new Vitus line is mainly carbon. I wonder if they made them uber flexy per Sean's fondly remembered specs? http://www.vitusbikes.com/ [Sean]Veetus have made da calculation and dees will coitaintly suceed![/Sean]

"with just the right balance of stiffness and vertical compliance."

Ah! I knew I could find the perfect marketing phrase in all their flowing prose and praise of their product. They even managed to work in the ever popular "reduced road buzz" phrase for those riders that buy bikes for their abilities to reduce road buzz. All market segments are covered. At least in print.

My guess is if you go back to the 1980's Vitus 979 catalog you'll find Sean describing the wet spaghetti 979 as having "just the right balance of stiffness and vertical compliance comfort."

Sadly, we can't buy wet spaghetti, el explodo 979's anymore. Not even Sean's successes and marketing wizards could convince folks that flexible racing bikes were efficient.

Their new Al road bike, the Zenium (Weird? I thought 'X' replaced 'Z' as the cool kid on the block?) is described as, "Our new 6061-T6 aluminium frame with custom-drawn aerospace tubing delivers a ride that is light, stiff and responsive."

Not, Heavy, flexible and dead"???

LOL

Amongst my stable of classics, I still have two silver 979's, one that I have trained on and still often do since 1983 and the other is a Sunday bike. The first has done more races than I can remember and back in the day I had to try hard not to have the back wheel jump three inches side to side in a flat out sprint.

In short it takes a bit of getting used to the spaghetti, which would not be tolerated by todays standards, but I believe there is no energy loss. To put energy into the aluminum tubing, one has to exceed the elastic limit of the material, which would deform it permanently and lose heat energy in the process. Within the elastic limit, any bend or deflection becomes potential energy, which comes back as soon as the bending force is removed.

 

[CAMPYBOB]

"... back in the day I had to try hard not to have the back wheel jump three inches side to side in a flat out sprint."

Now THAT'S flexible!!!

I keed! I keed!

I always found wheel skipping/jumping was not the result of stiffness, but from pulling the rear end off the ground and/or running those Clements at 125 PSI.

Sadly, in all the years I've ridden no frame has given me enough energy back!

 

[danfoz]

Oh jeez, it's the old timers lamenting the giddy snap of their Criterium Seta's at high pressure.

Oh wait, I guess that means I'm in good company.

Carry on /img/vbsmilies/smilies/biggrin.gif

 

[CAMPYBOB]

Hey you kids! Get off my lawn!

Hell, I'ld be happy if the legs still turned over like they did when I still HAD something that could remotely be described as a sprint! Town sign training has become...er...somewhat less fullfilling these days.

Columbus tubing dimension list from the days of yore, when men were men and bikes gave back more energy than the rider put in!

http://equusbicycle.com/bike/columbus/columbuschart.htm