Carbon frame on rollers

David1959

Have been given conflicting advice about using carbon frame bike for training on rollers. Some say it will crack frame while others say it won't cause any damage. Anyone got any experience or advice - good or bad ???

Lumen

Rollers is no different from the road, surely?

manwithaplan

Are you sure they weren't talking about a turbo?

Only chance of cracking a carbon frame on rollers is if you crash it into the coffee table.

Eamonnator

I may be wrong, but, I think, David is referring to Turbo trainers, where the bike is held in a rigid position. This might put more pressure on the frame and forks.

Hungrycol

Carbon is harder than you think. I would say you're exerting the same pressure on the frame as you would on the road. Pro's have no qualms about warming up on turbos pre race!

kumate_champ07

Pros will change their bikes often so thats different. Carbon on rollers is fine. Carbon could potentially get damaged using a turbo, the dropouts experience side to side stress which they dont recieve on the road. Carbon fibre doesnt have the same unidirectional strength as other materials

CheGuedara

Used my TCR C on the turbo don't know how many times - zero problems, zero damage, zero worries

kumate_champ07

drchuck72 wrote: »

Carbon could potentially get damaged using a turbo, the dropouts experience side to side stress which they dont recieve on the road. [snip]

spam profile^

kumate_champ07

rider weight and power output would also contribute to potential damage.

Popoutman

From an engineering viewpoint, it's not possible to have different stresses on the dropouts on a turbotrainer than on the road - as the axle is what's clamped when on the trainer - this means that the contact points are the exact same.
It may go against what you would expect, but the stresses will be exactly the same. The constraining of the bike laterally by the trainer is irrelevant. The magnitude and direction of the forces will be the same (relative to the frame). Anyone with a background in engineering should do up a pair of free body diagrams for the dropouts, one for a free wheel, and the other with the wheel in a trainer. The degrees of freedom are the same.

Next time you are on your bike, see how much flex is in the frame. Clip in on your right foot with the crankarm pointing forwards. Pull both brakes tight, gently balance on your left toe and shove hard down on the pedal with your right foot. Note the sideways deflection of the BB. When you are sprinting on the road or otherwise putting a lot of power down the BB will move laterally in the exact same way. You tend not to notice it when you are riding as you are not as constrained as when on a trainer, but that flexure is definitely present every time you put pressure on the pedals. Being on a trainer means that you'll see it more easily as you less free to move the wheels sideways - but the forces will be the same.

The only difference that I can see between forces on a trainer and forces on the road would be if you were hanging heavily off to one side, putting a twisting force onto the bike frame. You could still do this on a road session by keeping the bike tilted to the side while keeping your centre of gravity above the wheel contact patch but it'd be harder to keep it constant when on the road.

In essence, there's no difference between the forces on a bike frame when on a trainer with the axle clamped, and on the road.

kumate_champ07

Popoutman wrote: »

From an engineering viewpoint, it's not possible to have different stresses on the dropouts on a turbotrainer than on the road - as the axle is what's clamped when on the trainer - this means that the contact points are the exact same.
It may go against what you would expect, but the stresses will be exactly the same. The constraining of the bike laterally by the trainer is irrelevant. The magnitude and direction of the forces will be the same (relative to the frame). Anyone with a background in engineering should do up a pair of free body diagrams for the dropouts, one for a free wheel, and the other with the wheel in a trainer. The degrees of freedom are the same.

Next time you are on your bike, see how much flex is in the frame. Clip in on your right foot with the crankarm pointing forwards. Pull both brakes tight, gently balance on your left toe and shove hard down on the pedal with your right foot. Note the sideways deflection of the BB. When you are sprinting on the road or otherwise putting a lot of power down the BB will move laterally in the exact same way. You tend not to notice it when you are riding as you are not as constrained as when on a trainer, but that flexure is definitely present every time you put pressure on the pedals. Being on a trainer means that you'll see it more easily as you less free to move the wheels sideways - but the forces will be the same.

The only difference that I can see between forces on a trainer and forces on the road would be if you were hanging heavily off to one side, putting a twisting force onto the bike frame. You could still do this on a road session by keeping the bike tilted to the side while keeping your centre of gravity above the wheel contact patch but it'd be harder to keep it constant when on the road.

In essence, there's no difference between the forces on a bike frame when on a trainer with the axle clamped, and on the road.

road>rubber>air>rim>nipples>spokes>hub shell>axle>dropouts

with a turbo trainer the contact points dont have any variables because the virtual road surface is constant, the stress is costant, side to side flex at the clamping will cause the damage.

Im not an engineer but there is a reason why manufacturers dont recommend carbon for turbos, kurt kinetic has the rock n roll which will not damage carbon,
its the fact that the typical turbo trainer frame is stationary , the bike remains stationary and wont move with the riders motion that causes the extra stress on dropouts


*too mentally tired to explain properly and fix grammar, all ive had is a few slices of brown bread and strong coffee today..

Chips Lovell

My understanding is that the carbon frame on a turbo trainer thing is a bit of a myth. Will try dig out some links when I have time.

EDIT: Twas Tour Magazine in Germany who did a test and found the a bike is actually subject to more stress on the road. No link for it though I'm afraid. Mentioned on Weight Weenies here:

http://weightweenies.starbike.com/forum/viewtopic.php?f=6&t=26069

Popoutman

kumate_champ07 wrote: »

road>rubber>air>rim>nipples>spokes>hub shell>axle>dropouts

Go the other direction for the force directions, it may make it clearer to see what's going on.
Trainer: Rider -> Frame-> dropouts
Road: Rider -> Frame -> dropouts
No difference. All stresses go through the dropouts, in the same directions and pretty much the same magnitudes. There are 6 possible forces on each dropout when it is broken down and analysed. (the x,y,z axes, up is x, left right is y, and forwards backwards is z)

• Up/Down: weight of rider, bumps in the road
• left/right: forces from the rider's pedalling motion. Not that large actually.
• Forwards/backwards: braking forces, and acceleration from the pedals.
• Rotation around x: turning force from the handlebar, and a little bit from pedal stomping.
• Rotation about y: very small forces actually, road bumps will do a bit.
• Rotation about z: Fairly strong forces from the pedalling action especially if standing.

The largest forces are in the up-down direction generally, and the rotation about z when accelerating hard. The interesting scenario is if there are differences between the forces on each dropout, as that will be what can cause torsion on the bike frame, and bike frames (because they are thin) generall are poor at handling torsion forces - hence why some bikes feel noodley.

kumate_champ07 wrote: »

with a turbo trainer the contact points dont have any variables because the virtual road surface is constant, the stress is constant, side to side flex at the clamping will cause the damage.

It actually doesn't matter. If you isolate the frame and look at everything from the point of view of the frame, the stresses are the same. Take the frame as the "frame of reference", and allow the world to move around the bike (needed to do a proper visualisation of the forces involved). The stresses are changing with the same period and the same amplitudes - same pedal forces and the same bodyweight shifts relative to the bike. It feels very different to the rider for sure, as the bike is not moving, but as far as the bike knows, the forces are close enough for both situations not to be significant given the construction and material limits of the bike.

kumate_champ07 wrote: »

extra stress on dropouts

There just isn't any extra stress over what the dropouts are subjected to under normal cycling.
Examples that may help to explain it:
When you look from the rear of the bike to the front of the bike, when stamping down on the right pedal, there's a twisting motion where there is a rotation clockwise about the long axis of the bike when seen from the rear. On the road, this is transferred through the dropouts to the wheel axle, and the wheel has to deal with a force where the bottom of the tyre wants to move to the left of the bike.
On the trainer, that rotational force about the long axis of the bike is transferred from the frame through the dropouts to the trainer support. There's no difference as far as the dropouts can see.
Just because there is the possiblity for the bike to move relative to the world doesn't actually mean that there is any change in the forces involved on the bike components.

There are things going on in this scenario that may not make sense to people that have not had any engineering experience, but that do become easier to understand once you've had some exposure to the techniques and tools that engineers use. Check out free body diagrams if you can - it may help you to get a handle on why there isn't as much difference between the road and the trainer.

David1959

Thanks for all the replies, some interesting ideas. Think I'll give it a go on the turbo (said rollers but meant turbo). Again many thanks.

kenmc

There has to be a difference; when on the road the bike and frame is free to yaw underneath the rider as they apply power (look at a sprint finish, the bikes roll under the rider with each pedal stroke whereas the rider stays mostly upright) which must dissipate some of the forces applied through the frame. On the Turbo, this doesn't happen, unless you're on one of the class-looking rock-n-roll ones.

Now whether or not the majority of riders are capable of producing enough power for this to do damage to a carbon frame is not something I can answer, I suspect it'll be a case of "your milage may vary", depending on you, your frame and N other parameters.

MadHatter

The recommendation from the manufacturers of my carbon frame (Felt) is not to cycle out of the saddle while on the turbo. Stay seated and the bike should be fine.

petethedrummer

When you're on the road, momentum is keeping you upright. When you're on the turbo some other force must be keeping you upright. So there must be an extra force of some description through the rear dropouts where the bike is connected to the turbo. And most riders I presume will favour leaning to one side making the force larger in one dierction

Excuse any misuse of terms and concepts. Despite studying this stuff I was always rubbish at mechanics. I just want to know where this new holdy up force gets applied.

kumate_champ07

kenmc wrote: »

There has to be a difference; when on the road the bike and frame is free to yaw underneath the rider as they apply power (look at a sprint finish, the bikes roll under the rider with each pedal stroke whereas the rider stays mostly upright) which must dissipate some of the forces applied through the frame. On the Turbo, this doesn't happen, unless you're on one of the class-looking rock-n-roll ones.

Now whether or not the majority of riders are capable of producing enough power for this to do damage to a carbon frame is not something I can answer, I suspect it'll be a case of "your milage may vary", depending on you, your frame and N other parameters.

thats what I think

Lumen

petethedrummer wrote: »

Despite studying this stuff I was always rubbish at mechanics. I just want to know where this new holdy up force gets applied.

JUST PUSH YOUR BIKE BACKWARDS AND THEN PUSH IT FORWARDS

kumate_champ07

Popoutman wrote: »

Go the other direction for the force directions, it may make it clearer to see what's going on.
Trainer: Rider -> Frame-> dropouts
Road: Rider -> Frame -> dropouts
No difference. All stresses go through the dropouts, in the same directions and pretty much the same magnitudes. There are 6 possible forces on each dropout when it is broken down and analysed. (the x,y,z axes, up is x, left right is y, and forwards backwards is z)

• Up/Down: weight of rider, bumps in the road
• left/right: forces from the rider's pedalling motion. Not that large actually.
• Forwards/backwards: braking forces, and acceleration from the pedals.
• Rotation around x: turning force from the handlebar, and a little bit from pedal stomping.
• Rotation about y: very small forces actually, road bumps will do a bit.
• Rotation about z: Fairly strong forces from the pedalling action especially if standing.

The largest forces are in the up-down direction generally, and the rotation about z when accelerating hard. The interesting scenario is if there are differences between the forces on each dropout, as that will be what can cause torsion on the bike frame, and bike frames (because they are thin) generall are poor at handling torsion forces - hence why some bikes feel noodley.


It actually doesn't matter. If you isolate the frame and look at everything from the point of view of the frame, the stresses are the same. Take the frame as the "frame of reference", and allow the world to move around the bike (needed to do a proper visualisation of the forces involved). The stresses are changing with the same period and the same amplitudes - same pedal forces and the same bodyweight shifts relative to the bike. It feels very different to the rider for sure, as the bike is not moving, but as far as the bike knows, the forces are close enough for both situations not to be significant given the construction and material limits of the bike.


There just isn't any extra stress over what the dropouts are subjected to under normal cycling.
Examples that may help to explain it:
When you look from the rear of the bike to the front of the bike, when stamping down on the right pedal, there's a twisting motion where there is a rotation clockwise about the long axis of the bike when seen from the rear. On the road, this is transferred through the dropouts to the wheel axle, and the wheel has to deal with a force where the bottom of the tyre wants to move to the left of the bike.
On the trainer, that rotational force about the long axis of the bike is transferred from the frame through the dropouts to the trainer support. There's no difference as far as the dropouts can see.
Just because there is the possiblity for the bike to move relative to the world doesn't actually mean that there is any change in the forces involved on the bike components.

There are things going on in this scenario that may not make sense to people that have not had any engineering experience, but that do become easier to understand once you've had some exposure to the techniques and tools that engineers use. Check out free body diagrams if you can - it may help you to get a handle on why there isn't as much difference between the road and the trainer.

Ive tried to visualise what you described but I still think the stress caused is different and possibly harmful to the frame. maybe the majority of people wont have problems but I wouldnt chance it myself.

petethedrummer

Lumen wrote: »

JUST PUSH YOUR BIKE BACKWARDS AND THEN PUSH IT FORWARDS

I DON'T HAVE A TURBO.

kenmc

petethedrummer wrote: »

I DON'T HAVE A TURBO.

Get out of this thread so.

michael196

my carbon was on a turbo last year ( once only) I couldn't believe the flexing of the frame.... but that was probably my weight !!!!


would not be comfortable with excessive use of the carbon on a turbo...

setanta159

Bought a turbo a while back and absolutely no problems with Carbon frame thus far. To be honest I think people are nit picking. Any damage, if at all, will be minimal in the extreme and certainly far less than damage from cycling on Irish roads

Lumen

So...

On the "turbo does no damage" side we have engineering theory, free body diagrams and all that stuff. And on the same side we have scientific empiricism from Tour Magazine, who apparently "put lots of strain gauges on the frame, used the road and a TACX trainer and rode a 100-1000W range, finding the stress/distortion of the frame on the road more in all cases except the sprint, where it was equal."

And on the other side we have blind assertion, handwaving and fear for things made out of plastic.

kenmc

ah yeah but don't forget that science would have you believe that the world is NOT flat and that the Earth goes round the SUN!

ha.