Can an MTB+700c's compete with a road bike??
Comments
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Sorry, to be clear, the point I was making about old timers stems back to the original comment about it being overall rider and bike weight that is important for climbing, not just the bike.0
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So there's no loss of speed by the downward force (weight) on a flat piece of road then? If you had two materials with the same contact area and same co-efficient of friction but a different mass moving over the same surface in a vacuum would one be easier to move than the other with the same force being applied?0
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I commuted for 2 years on a Cannondale F1000 with a variety of thin slicks and a large chainring, now I commute on a roadbike. The roadbike accelerates and maintains it's speed with less effort and the climb on the way home is easier on the roadbike. Chalk and cheese for me. That is without all the scientific handbag waving
Colnago C60 SRAM eTap, Colnago C40, Milani 107E, BMC Pro Machine, Trek Madone, Viner Gladius,
Bizango 29er0 -
Pross wrote:So there's no loss of speed by the downward force (weight) on a flat piece of road then? If you had two materials with the same contact area and same co-efficient of friction but a different mass moving over the same surface in a vacuum would one be easier to move than the other with the same force being applied?
A rather strange and totally theoretical question unrelated to rela life cycling.
To answer your question, using newtonian mechanics then the downwards force applied by gravity acting upon the rider could not be resolved directly into a restraining horizontal force.
I guess where you are trying to lead the question is whether frictional losses are increased with increased masses, which is true however their magnitude is negligible in comparison to the other forces applied to the rider. Especially at higher speeds as aerodynamic drag increases with the square of speed, unlike frictional losses.
Bicycling Science has several chapters about the various forces that a rider experiences and produces lots of empirical evidence to back this up.
A quick google brought up
http://en.wikipedia.org/wiki/Bicycle_performance
Which, in a brief skip through, looks like it covers much the same ground as me. Perhaps that is hardly surprising given that one of its principle references is ‘Bicycling Science’!0 -
Chris James wrote:turnerjohn wrote:
Weight doesn't effect speed except up hills; even then it's not "28lb vs 18lb", but something like "228lb vs 218lb".
hum yes it does ! weight hampers acceleration for a start, also a lighter bike is easier to keep at speed then a heavy one...its simple physics.
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You didn't study physics did you?
A lighter bike is more difficult to keep at speed than a heavy one, as the heavy one has greater momentum and better resists the slowing effects of aerodynamic drag, rolling resistance etc.
I have an A-Level in it and it was part of my degree !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
A lighter bike is easier to accelerate and KEEP at speed, true a heavy bike is better with momentum (as it has more mass) BUT as its heavier it needs MORE power to do anything with in ... it really is simple physics !
As for "slowing effects of aero drag...." er so a solid steel tube is less prone to wind resistance then an equally sized / shaped hollow lighter one?...hum no !
If a heavy bike is faster then why dont all the Pro riders ride them? and why has the UCI put a weight limit on light weight bikes?!!!!!!!!0 -
youd have to travel a very very long way with a spirit level to find a totally flat route to limit the effects of extra weight. more weight has more momentum, but other than crashing into something its of no use.the momentum has to be put back equally as difficult so theres no free ride with momentum. the statement that heavier is easier to keep at higher speed is false over any meaningfull time span. more weight = more drag from tyres as well.turnerjohn wrote:Chris James wrote:turnerjohn wrote:
Weight doesn't effect speed except up hills; even then it's not "28lb vs 18lb", but something like "228lb vs 218lb".
hum yes it does ! weight hampers acceleration for a start, also a lighter bike is easier to keep at speed then a heavy one...its simple physics.
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You didn't study physics did you?
A lighter bike is more difficult to keep at speed than a heavy one, as the heavy one has greater momentum and better resists the slowing effects of aerodynamic drag, rolling resistance etc.
I have an A-Level in it and it was part of my degree !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
A lighter bike is easier to accelerate and KEEP at speed, true a heavy bike is better with momentum (as it has more mass) BUT as its heavier it needs MORE power to do anything with in ... it really is simple physics !
As for "slowing effects of aero drag...." er so a solid steel tube is less prone to wind resistance then an equally sized / shaped hollow lighter one?...hum no !
If a heavy bike is faster then why dont all the Pro riders ride them? and why has the UCI put a weight limit on light weight bikes?!!!!!!!!0 -
Chris James wrote:Pross wrote:So there's no loss of speed by the downward force (weight) on a flat piece of road then? If you had two materials with the same contact area and same co-efficient of friction but a different mass moving over the same surface in a vacuum would one be easier to move than the other with the same force being applied?
A rather strange and totally theoretical question unrelated to rela life cycling.
To answer your question, using newtonian mechanics then the downwards force applied by gravity acting upon the rider could not be resolved directly into a restraining horizontal force.
I guess where you are trying to lead the question is whether frictional losses are increased with increased masses, which is true however their magnitude is negligible in comparison to the other forces applied to the rider. Especially at higher speeds as aerodynamic drag increases with the square of speed, unlike frictional losses.
Bicycling Science has several chapters about the various forces that a rider experiences and produces lots of empirical evidence to back this up.
A quick google brought up
http://en.wikipedia.org/wiki/Bicycle_performance
Which, in a brief skip through, looks like it covers much the same ground as me. Perhaps that is hardly surprising given that one of its principle references is ‘Bicycling Science’!
Of course it was theoretical, I was using an extreme to demonstrate a point. I realise that kinetic energy means that (theoretically) an object will keep moving with no further work once acceleration is complete but that in reality there are external forces acting with or against the moving object plus the fact that nothing is 100% efficient (I'm not sure how efficient a bike is but suspect nowhere near 100%!).
However, you dismiss weight as only being relevant for climbing and acceleration. In reality most commutes will involve quite a lot of acceleration and deceleration due to traffic queues, lights or junctions and each one of these will require more energy to be expended by the rider. Added to that there is no such thing as a flat road other than an instantaneous point at the crest or trough of a curve. The generally accepted minimum gradient of a road is 0.8% to allow it to drain sufficiently. So the theoretical advantage of a heavier bike is just that. In the real world a bike with lower mass will require less energy to power it (all other things being equal).0 -
Pross wrote:In the real world a bike with lower mass will require less energy to power it (all other things being equal).
But the record books - real world examples - quite clearly show that is not the case!
There isn't a lot of point repeating myself, if anyone has read the link I provided it covers the maths well.
Incidentally regarding the heavy bike = more drag from tyres comment, rolling resistance relates to tyre pressure, tyre section and diameter and energy losses in deformation of the tyre (so relating to threads per inch of carcase).
http://en.wikipedia.org/wiki/Rolling_resistance
The resistive FORCE is proportional to weight, but for a heavier bike, this greater force is acting upon a proportionately greater mass thus producing the same decelleration for a heavy or light bike. In any case, it is a gnat's cock in comparison to aerodynamic drag - as described in the link in my previous post.
Heavy bike shaped objects are invariably fitted with cheap tyres so that would make a difference. But comparing liek with like, if you fitted the seat tube of the same bike with lead then it wouldn't make any difference to your overall speed over a flattish (including rolling) course.
It truly is a case of the Emperor's new clothes when people disbelieve a professional mechanical engineer, or the content of the seminal text book on the subject Bicycling Science (I've got a copy and have read it - has anyone else?)0 -
Yeah, anyway, back to the OP's question.
If you really want a faster road bike, wait until next years C2W and get a new road bike. In the meantime have a lot of fun on your mtb, and just use the old roadie.
Slicking up a mountain bike just isn't the same.0 -
Getting back to the topic at hand- when _not climbing_ I would suggest that weight is far less significant than rider position. The rider position on a mountain bike is simply very unaerodynamic, you can really "feel" the wind resistance on a purely subjective level. I would be straight down in the drops if I had them.
To extend that I would suggest that on a typical, non-mountainous course, the lack of aero on the MTB is more the factor than the weight.
My experience comes from cycling a ~7kg road bike, ~10kg MTB and ~12.5kg tourer... the tourer although heavier is certainly faster than the MTB on road. I'd go so far as to say it is faster even with 10kg on the back, on a flat road.
Would you all agree with this?0 -
blorg wrote:Would you all agree with this?
Yes. That and increased rolling resistance of lower presure tyres on the MTB.0 -
Indeed, although I was considering here that the MTB was on slicks.Chris James wrote:blorg wrote:Would you all agree with this?
Yes. That and increased rolling resistance of lower presure tyres on the MTB.
There is a simple calculator here that lets you play with various inputs (there is a numeric version if you want to plug in your own values for frontal area and RR.)
What is clear from that at least is that weight on a flat road makes F all difference compared to rider position and rolling resistance. And the latter only really makes a big difference if you are comparing road tyres at full pressure to MTB knobblies at low pressure. If both tyres are high-pressure slicks it will all be about rider position.
You can put in an absurdly heavy bike and it will still be faster than a UCI-minimum one in a drops vs bartops comparison. Example, changing power to 200w, set A to 6.8kg on bartops and set B to 21kg in drops and we get the bikes going the same speed up a 2% gradient. Flat road and the 21kg bike is going 3.5km/h faster.
Worth bearing in mind too that the grips on a MTB bar are MUCH further apart compared to a road bar, you are looking at 58-60cm wide rather than 40-44cm wide. This basically turns you into a sail. Rider position is generally higher up at the front too.0 -
Chris James wrote:Pross wrote:In the real world a bike with lower mass will require less energy to power it (all other things being equal).
But the record books - real world examples - quite clearly show that is not the case!
There isn't a lot of point repeating myself, if anyone has read the link I provided it covers the maths well.
Incidentally regarding the heavy bike = more drag from tyres comment, rolling resistance relates to tyre pressure, tyre section and diameter and energy losses in deformation of the tyre (so relating to threads per inch of carcase).
http://en.wikipedia.org/wiki/Rolling_resistance
The resistive FORCE is proportional to weight, but for a heavier bike, this greater force is acting upon a proportionately greater mass thus producing the same decelleration for a heavy or light bike. In any case, it is a gnat's fool in comparison to aerodynamic drag - as described in the link in my previous post.
Heavy bike shaped objects are invariably fitted with cheap tyres so that would make a difference. But comparing liek with like, if you fitted the seat tube of the same bike with lead then it wouldn't make any difference to your overall speed over a flattish (including rolling) course.
It truly is a case of the Emperor's new clothes when people disbelieve a professional mechanical engineer, or the content of the seminal text book on the subject Bicycling Science (I've got a copy and have read it - has anyone else?)
take it you've ridden many bikes in your time then!
tell you what get to identical bikes, fill the tubes / frame with lead then find out which is fastest .... no Emperors clothes needed!
hum as for your quoting you do know weight is not the same as mass?..you do refer to them in the same context! weight is subject to gravity whereas mass isn't0 -
blorg wrote:Worth bearing in mind too that the grips on a MTB bar are MUCH further apart compared to a road bar, you are looking at 58-60cm wide rather than 40-44cm wide. This basically turns you into a sail. Rider position is generally higher up at the front too.
Don't know what kind of jey boy mincing xc biek you ride but real mountain bikes have man sized bars, nothing less than 685mm wide is the order of the day he hee
Anyway, slicked up MTB is faster than knobblie tyred MTB simplez.
I've gone form a geared (compact & 11-32 cassette) 700x28mm slicked up 24lb hybrid to a single speed (42:16) 700x28mm 22lb slicked up hipster wagon and over my 9mile commute there just as fast as one another.
However when I rode my 17lb 700x23mm slicked up road bike it was faster, probably cos it's red though 8)0 -
Weight does make a difference. But it is minimal compared to air resistance on a flat course.turnerjohn wrote:tell you what get to identical bikes, fill the tubes / frame with lead then find out which is fastest .... no Emperors clothes needed!
You could do more than fill the tubes with lead. Using the calculator above, again with 200W output and everything else at the default, a bike weighing 130kg (over 20 stone) would beat a 9kg bike over 30km if the rider on the heavy bike stayed in the drops while the other rider remained on the tops.
Mass is not subject to gravity, interesting.hum as for your quoting you do know weight is not the same as mass?..you do refer to them in the same context! weight is subject to gravity whereas mass isn't
@Steve- my MTB is indeed limited to XC as a roadie I would be too frightened to try anything else (no joke!)0 -
@ blorg - it's good to hear people talking sense with regard to frontal area as opposed to bike weight. Kinda brings the whole "how do I loose a pound off my bike into context"
No offense intended on the the MTB front, hope none was taken 0
