What is optimal strength and size for mtb?

[kwikee]

To brake, a heavier rider has to use more force at the levers, but his grip ( ie distance to stop) is the same because grip is a function of weight times co-efficient of friction ; the light rider carries less energy and therefore uses less energy to stop, but they both stop in the same distance.

Maybe.
Make the assumption that the 2 theoretical riders are using well bedded in Saints, and could lock the front wheel with maximum brake lever application, so they will modulate their braking to the maximum available traction to achieve the shortest braking distance.
The formula for kinetic energy (energy of motion) is E(kinetic)=1\2 mass x Velocity squared.
So also assume velocity is the same at the start of braking, then the mass is the only other factor. If mass of rider 1 is greater than the mass of 2, then the kinetic energy carried by 1 will be greater, by a factor of half their difference in mass.
The only other difference will apply where rider 1 is sending more Newtons per square mm of force through the contact patch of their tyres, than rider 2, and therefore can brake harder without locking up, providing greater resistance, and shedding slightly more kinetic energy per second.
Whether this equals the same distance would need to be calculated but it stands to reason.

 

[pharmaboy]

Maybe.
Make the assumption that the 2 theoretical riders are using well bedded in Saints, and could lock the front wheel with maximum brake lever application, so they will modulate their braking to the maximum available traction to achieve the shortest braking distance.
The formula for kinetic energy (energy of motion) is E(kinetic)=1\2 mass x Velocity squared.
So also assume velocity is the same at the start of braking, then the mass is the only other factor. If mass of rider 1 is greater than the mass of 2, then the kinetic energy carried by 1 will be greater, by a factor of half their difference in mass.
The only other difference will apply where rider 1 is sending more Newtons per square mm of force through the contact patch of their tyres, than rider 2, and therefore can brake harder without locking up, providing greater resistance, and shedding slightly more kinetic energy per second.
Whether this equals the same distance would need to be calculated but it stands to reason.

There's some inbuilt assumptions in there. 1 that contact patch will be the same (psi etc), and second and more importantly, that contact patch matters.

Apply known physics to the problem not assertions with inbuilt expectation.
Admontons law - friction in independant of the apparent contact area, AND, the force of friction is directly proportional to the applied load.

The only advantage contact patch gives you is more choices over the area to get good contact - important on a gravelly surface, absolutely pointless on a road - which is why, despite your massive contact patch on an Mtb, you can't out brake a road bike with decent tyres on. You can also test it in a car, 50psi versus 20psi produce the same stopping distance, strange but true.....

Back on topic - so MWI, I should be doing squats etc to increase muscle mass? ( not skinny - aerobic engine seems to have stopped responding much to training).

 

[driftking]

There's some inbuilt assumptions in there. 1 that contact patch will be the same (psi etc), and second and more importantly, that contact patch matters.

Apply known physics to the problem not assertions with inbuilt expectation.
Admontons law - friction in independant of the apparent contact area, AND, the force of friction is directly proportional to the applied load.

The only advantage contact patch gives you is more choices over the area to get good contact - important on a gravelly surface, absolutely pointless on a road - which is why, despite your massive contact patch on an Mtb, you can't out brake a road bike with decent tyres on. You can also test it in a car, 50psi versus 20psi produce the same stopping distance, strange but true.....

Does that assume a rigid tire? would a softer tire not give more grip due to the force dissipation and essential travel in the tire walls.

The physics assume the brakes are able to perform all the way to lock up. So XTs would work for both riders , but avid elixirs would give the featherweight 50 kg rider an advantage .

Friction relates to the surface and the tyre rubber x gravity x weight. There will be a point where the rider isn't strong enough to squeeze the levers hard enough or that the brakes simply aren't up to the task.

All that extra power to get the heavier rider up to speed, to accelerate and overcome greater rolling resistance has to be dealt with by the brakes and the tyres to slow him down - he will certainly wear out brake pads and tyres faster than the runt.

Is this something that becomes a practical issue for riding? Given today's brakes and riders is it likely there is a point where the brakes are actually not up to it?

Also given that weight increases traction, as I alluded to before though is there a point where the traction increase from the weight doesn't actually result in enough traction increase to make braking equal too. By is there that point where lock up will occur before the desired braking force is reached?

 

[pharmaboy]

Does that assume a rigid tire? would a softer tire not give more grip due to the force dissipation and essential travel in the tire walls.



Is this something that becomes a practical issue for riding? Given today's brakes and riders is it likely there is a point where the brakes are actually not up to it?

Also given that weight increases traction, as I alluded to before though is there a point where the traction increase from the weight doesn't actually result in enough traction increase to make braking equal too. By is there that point where lock up will occur before the desired braking force is reached?

No it doesn't assume a rigid tyre, and yes a softer tyre gives more grip - that's the co-efficient of friction bit. Eg a semi trailer tyre is about twice the hardness of a passenger car tyre - thus more economical and lasts waaaaay longer, but doesn't grip nearly as well ( so don't cut in front of a truck)

Heavier riders should use bigger rotors do dissipate heat - that kinetic energy goes somewhere, and much goes into heat in the braking system. 200mm rotors are made for 75kg whippets. ( unless they are on a 25kg downhill rig. )

Last para - the physics says no. In the real world (where surfaces are irregular and tyres are different with different wear points and riders have different weight biases etc etc), as a heavier rider racing xc I can brake and corner as well as the guy 20kg lighter - I just get left on the accelerating part ;(. And probably his tyres probably last longer than mine.

Read up on wiki DK, physics is interesting shit, and has more relevance to the real world than people give it credit for - eg try and figure out how it is that an F1 car can corner at over 4G at 300kmh but only 1g at 60kmh - the faster they go, the more group they have

 

[driftking]

No it doesn't assume a rigid tyre, and yes a softer tyre gives more grip - that's the co-efficient of friction bit. Eg a semi trailer tyre is about twice the hardness of a passenger car tyre - thus more economical and lasts waaaaay longer, but doesn't grip nearly as well ( so don't cut in front of a truck)

Heavier riders should use bigger rotors do dissipate heat - that kinetic energy goes somewhere, and much goes into heat in the braking system. 200mm rotors are made for 75kg whippets. ( unless they are on a 25kg downhill rig. )

Last para - the physics says no. In the real world (where surfaces are irregular and tyres are different with different wear points and riders have different weight biases etc etc), as a heavier rider racing xc I can brake and corner as well as the guy 20kg lighter - I just get left on the accelerating part ;(. And probably his tyres probably last longer than mine.

Read up on wiki DK, physics is interesting shit, and has more relevance to the real world than people give it credit for - eg try and figure out how it is that an F1 car can corner at over 4G at 300kmh but only 1g at 60kmh - the faster they go, the more group they have

I am highly intrigued by it, But I have never applied myself to really learn it. Although after watching a program on quantum mechanics the other night I'm a little more intrigued to actually take some real time to read up on physics.

 

[Dilstub]

does the F1 car generate its grip from the extra downforce created by high speed air over the spoiler/front fins etc. ?

 

[driftking]

does the F1 car generate its grip from the extra downforce created by high speed air over the spoiler/front fins etc. ?

At the risk of been wrong.

Yes, By directing air flow they can create positive and negative air pressures around the car, this manipulates the down force and aero to how they want it. Negative pressure is a big part of racing and is pretty cool when you lean about it. The wings are part of this, however, the under body plays a big roll in f1, teams are pretty secretive about their under body work. Traction is also dictated by chassis stiffness, axle stiffness, tires and suspension. They also use aero to improve braking, straight line speed, cornering.

 

[noddy]

Take away gravity, it acts on both heavy and light the same and proportionaly.
Its all about inertia, a heavy object has more and therefore requires more force to change that inertia, the maximal force a tyre can produce is limited by the track so for the same terrain the lighter rider will be able to change direction faster.

By same token, heavier riders will carry speed over rough terrain better, due to their higher inertia

 

[scblack]

does the F1 car generate its grip from the extra downforce created by high speed air over the spoiler/front fins etc. ?

Correct, F1 cars for years have had such powerful downforce they could drive upside down and stick themselves to the roof (at speed).

 

[Pastavore]

Vo2 max is all about long hours on the bike spent in the aerobic training zone, underpinning an increase in Vo2 is cellular respiration which requires more and larger mitochondria and the capillirisation to support this.

You sure about this one MWI?

I have been taught numerous times that training to increase your VO2 max is done by training at or around your current VO2 max, ie short (3m to 8m) intervals with something like a 1:1 work/rest ratio.


I am very aware that your knowledge of the literature is likely to be more up to date than mine, so happy to be corrected ( with references please!)

 

[driftking]

You sure about this one MWI?

I have been taught numerous times that training to increase your VO2 max is done by training at or around your current VO2 max, ie short (3m to 8m) intervals with something like a 1:1 work/rest ratio.


I am very aware that your knowledge of the literature is likely to be more up to date than mine, so happy to be corrected ( with references please!)

+1
Ill like the references to save for future reference.
My experience is like pasta's, Most things I read have always directed VO2 training to be max effort intervals. With aerobic and threshold training obviously improving the ability to utilize and be efficient with the bigger tank at a given effort.

Looking forward to it.

 

[Mywifesirrational]

You sure about this one MWI?

I have been taught numerous times that training to increase your VO2 max is done by training at or around your current VO2 max, ie short (3m to 8m) intervals with something like a 1:1 work/rest ratio.


I am very aware that your knowledge of the literature is likely to be more up to date than mine, so happy to be corrected ( with references please!)

+1
Ill like the references to save for future reference.
My experience is like pasta's, Most things I read have always directed VO2 training to be max effort intervals. With aerobic and threshold training obviously improving the ability to utilize and be efficient with the bigger tank at a given effort.

Looking forward to it.

I'm taking short cuts in answers and getting called out!

The simplest answer is you have to do both methods, both long endurance rides and also a progressve program of intervals at 85%> of VO2 or HHR. An athlete needs a periodised program that incorporates both methods - although an average bloke who's time poor - go high intensity.

Although from what I have been taught and sat through at sports performance conferences, skipping the long duration work and heading straight into high intensity training is putting the cart before the horse. While high intensity training certainly peaks Vo2Max over endurance training its volume dependant (endurance training times were limited) - and by default dependant on the training status of the athlete.

Here's one very heavily cited paper and one decently cited paper which both support high intensity intensity for improving Vo2max.

http://www.ncbi.nlm.nih.gov/pubmed/17414804
http://www.ncbi.nlm.nih.gov/pubmed/18580415

 

[Pastavore]

Thanks for that MWI.

 

[pharmaboy]

I'm taking short cuts in answers and getting called out!

You trained em to question!

Gotta wonder how these things effect mountain bikers where normal riding is all about short sharp hills and natural intervals anyway. Second thing, is the devil is in the detail of how trained the people are - ie do you need a certain base fitness to do well on intervals

 

[driftking]

Thanks MWI.
So the studies do support what we have already figured, That's good. It was about to flip my whole idea of training on its head.

 

[kurtis1984]

Thanks for all the interesting discussion so far. I'm going to take some time to sink my teeth into this one and come back a bit later.
Kurt