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So been confused by this so I thought id try the cerebral might of stw.
Compare a bikes on flat road and rollers. Assuming rolling resistance is the same and the road had a tailwind that negates air resistance perfectly. They will be doing the same amount of work.
So same scenario on a gradient (hill for road and angled rollers) are they both working the same?
Nope, you are working against gravity in the real world, not on the rollers.
Although if you replace the rollers with a conveyor belt you will be doing the same work as on the road.
No you won't, that doesn't introduce gravity. You could potentially replicate the additional effort required, not the same though.
I think it will be exactly the same though. Imagine first that you have a completely friction free set of rollers. No matter how fast you pedal you won't be able to stop yourself rolling backwards as otherwise you would have to continually accelerate to keep at the same heightYou could potentially replicate the additional effort required, not the same though.
The only way to stay at the same height is to introduce enough friction in the rollers to counteract the force of gravity pulling you downwards. Then instead of the work increasing your potential energy as you get higher the work is used against the friction. It is the same amount though
or I may be talking bollocks
The issue is that on the road you are moving upwards as well as along - so you are inputting more power to work against gravitational potential energy. If you add more resistance to the rollers you could replicate but it wouldn't be identical.
But it is identical, it has to beIf you add more resistance to the rollers you could replicate but it wouldn't be identical.
Some numbers (as I'm sitting waiting for a delivery)
Imagine you are 80kg (with bike), travelling up a 10deg hill at 10km/hr (at least thats as fast as I can manage 🙂 )
Your speed in m/s is 2.78m/s
Your height increase per second is 0.48 m/s
So your increase in potential energy per second is 378 J/s - roughly what you would expect
Ok, on the rollers set at 10deg
Force straight down due to gravity is 9.8N/kg
Force pulling you back on the rollers is 136N (remember you are 80kg)
Now you need to produce that same force on your wheels to stay at the same point and not slip back
Work done per second = F * distance traveled by wheel in one second
= 136 * 2.77
= 378 J
The problem of course is whether or not you believe the wheel does any work by rotating rather than moving forwards - but my legs say that it does and I believe them
Inclining a set of rollers wont add resistance, it's more like wheelieing on flat ground.
On rollers the wheel is chocked in place by the rollers, if it weren't you'd jump out of them so the concept of pedalling to stay on the roller is flawed.
Inclining a set of rollers wont add resistance, it's more like wheelieing on flat ground
If thats the case then why do all the turbo manufacturers make front wheel blocks that elevate the front wheel and therefore allow a turbo session to replicate a climb?
Not saying I agree with either side, I genuinely don't know....
The wheel block is to level the bike up as the rear wheel is raised by the turbo.
If thats the case then why do all the turbo manufacturers make front wheel blocks that elevate the front wheel and therefore allow a turbo session to replicate a climb?
Because that replicates body position and allows you to engage the muscles you would actually use in climbing rather than sitting there in a "cruise along a flat road" position while pedalling a climbing resistance.
Whereas rollers aren't designed for that sort of workout; they're more for warm-up, spinning drills, light core work.
The front wheel block is just to replicate the position, so you aren't pointing downhill all the time.
The block just keeps the bike level for comfort and goes some way to stopping the bars twisting.
It's probably clearer to picture if you reverse the situation. Incline the rear wheel and imagine if you could free wheel. If you cant then there's no change in load.
A conveyor belt would free wheel so can change the resistance.
Leffeboy,
Where is the energy going? On the bike going up a hill you're converting kinetic in to potential by raising the load against gravity.
On the rollers you're not accounting for that at all (friction free rollers, no sound, heat etc)
you need to add resistance to the rollers to stop you going backwards and falling off the back. That resistance has to be exactly the same. If it is more then you will start to ride up the rollers, if it is less then you will move back
Ok...fair points
My front block is adjustable though and goes much higher than putting the bike level.
Rollers have three rollers, with the back wheel sitting in the trough made by two of them. For small inclines, gravity keeps the wheel in the trough and you won't slide off backwards.
That's true. For small inclines nothing will happen other than changing your position on the bike. For larger inclines the above appliesRollers have three rollers, with the back wheel sitting in the trough made by two of them. For small inclines, gravity keeps the wheel in the trough and you won't slide off backwards
Inclining a set of rollers wont add resistance,
It will if the back roller is rubbing on the carpet when you tip it up. 🙂 Different carpets can be used to replicate different gradients. Contract felt is equivalent to riding in Lincolnshire. Shagpile is roughly equal to Applecross
Friend of mine gave up on his running treadmill as however he set the resistance he couldn't run on it properly. Whne he went to put it in its box and two little bolt-on feet fell out of the packaging. Picked up the treadmill and he'd worn a groove in the floor. 🙂
for larger inclines I'm pretty sure you'd just fall off the back (assuming minimal friction rollers)For larger inclines the above applies
For a running machine style conveyer belt I still don't think inclining it will make it a proper climb. Yes it's harder when you are running on a treadmill but you're accelerating/decelerating your legs constantly, incline means lifting your feet/knees/legs higher, afaik still not equivalent to running up a proper hill tho as you aren't shifting your whole body weight up the incline.
On the flat a running machine would be almost useless as you could just hold onto the side bars and freewheel, inclining it will introduce effort but still not proper climbing, bet it would be a bugger to keep on the thing aswell.
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guy agrees[/url]
You'd roll straight off the back no matter how fast you're pedalling. When you're climbing a hill you can't accelerate the earth, there's not much limiting the acceleration on a set of rollers.
At about 1:30 in
For larger inclines the above applies
for larger inclines I'm pretty sure you'd just fall off the back (assuming minimal friction rollers)
Yes, I said that at the start. Without the friction you will fall off the back and the amount of friction needed is the same as if you were climbing the same incline
(some of those treadmill fails are rather funny as well)
Dont forget the temperature, fan required
If you were riding on a treadmill or conveyor belt set at a constant speed, and somebody increased the incline, you'd have to ride faster to stop you going off the back, the force of gravity really does come into play in this situation.
if you elevate your front wheel on rollers, all you achieve apart from perhaps more comort, is having to move the back rollers forward a bit.
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Hmm.
See, when modelling things in Physics, one way to do it is look at the energy paths.
When you cycle up hill, you are increasing your gravitational potential energy. You are doing work with your legs and converting it into potential energy. This is the energy that does work against wind resistance on the downhill, and becomes your kinetic energy as you zip down.
On the treadmill, you aren't giving yourself any extra potential energy. It would certainly feel exactly like climbing a hill, because the forces in your frame of reference would be the same, but I don't think you'd slow the belt down because the energy transfer isn't there. Assuming constant speed.. might be different if you are surging forward and slowing, as if on a super steep climb.
I don't think you'd slow the belt down because the energy transfer isn't there
Once you add incline it's effectively speeding up the belt, it's more about trigonometry than energy diagrams.
Still not going to be too difnified when you roll off the back of the belt, whatever the reason.
[quote=molgrips ]On the treadmill, you aren't giving yourself any extra potential energy. It would certainly feel exactly like climbing a hill, because the forces in your frame of reference would be the same, but I don't think you'd slow the belt down because the energy transfer isn't there. Assuming constant speed.. might be different if you are surging forward and slowing, as if on a super steep climb.
I'm not quite sure what you're agreeing or disagreeing with - but as you write, from the rider's reference frame the forces are all exactly the same as if riding up a real hill (apart from wind resistance, but we're presumably ignoring that). Therefore energy is being applied to the belt by the rider, energy which must go somewhere - the only place it can go is into friction (or something equivalent - on a normal belt it will have motor generators providing resistance, which convert the motion into electricity/heat). So the rider is effectively trying to accelerate the belt through their pedalling and is the resistance in the belt which slows it down.
In order for all this to work and balance properly the belt must be set on a gradient, so that the bike would roll backwards off the end if the rider didn't pedal - this enables the bike to exert a force on the belt.