Latest offering from JH.What doth ye thinketh?

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reohn2
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Latest offering from JH.What doth ye thinketh?

Post by reohn2 »

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Freddie
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Re: Latest offering from JH.What doth ye thinketh?

Post by Freddie »

I have to say, I take what Jan Heine says with a pinch of salt. He has postulated such wacky and pseudo-scientific ideas as "planing" (too hard to explain, look it up on his blog/site) and the idea that tyres with nail file patterns grip better than slicks, because these nail file patterns "lock" into microgrooves in the road. I find the latter idea in particular highly dubious, since any nail file design is likely to just deform on contact with the road and what road has consistent microgrooves that will align with the nail file tread pattern anyway? (none, is my assertion).

This said, I admire what he is doing and I do think there is probably merit in the idea that higher pressures are not necessarily more efficient. Low pressure, wider tyres will bob more under heavy exertion, which is no good for out of the saddle sprinting, which means they will never become a feature of racing bicycles.

I do sometimes think he is blinded by his own preferences, rather than approaching the subject from an unbiased standpoint. Nonetheless, it is nice to have some investigation into these things from a slightly different, non-racing angle.
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531colin
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Re: Latest offering from JH.What doth ye thinketh?

Post by 531colin »

He shows there is no point in running more than 80psi.......didn't we know that?

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pwa
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Re: Latest offering from JH.What doth ye thinketh?

Post by pwa »

Even if correct in principle, wider tyres will be heavier than narrower tyres made in a similar way, and the extra mass will slow you down in normal stop/start riding. I doubt the central conclusion though, because I think I can feel a sluggishness in a bike when tyre pressure has gone down from 90psi to 75psi.
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Si
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Re: Latest offering from JH.What doth ye thinketh?

Post by Si »

I think I can feel a sluggishness in a bike when tyre pressure has gone down from 90psi to 75psi.


I'm always wary of 'feel'. I think that many people (I don't necessarily mean you) associate a really hard, juddering ride with speed because we have had so many super stiff frames and 120psi tyres marketed to us as fast.
MartinC
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Re: Latest offering from JH.What doth ye thinketh?

Post by MartinC »

I too find JH's stuff interesting, thought provoking and useful. Long may he continue to do it, I love reading BQ. He's a great one for extrapolating a few data points in sweeping theories - I'm never sure whether the theory precedes the observations or not.

What his graph shows is that, for this rider, at this speed, on this road, with these 3 instances of tyres (or tires), in these conditions and for these 7 pressures (with this gauge) then that's how the power required varies. Even assuming you'd get the same results from another tyre of the same model needs validation - sample of one isn't much.

When you read the text you can see that "supple" is a big part of how he feels tyres perform - so he needs to define what it means, how you measure it and how it varies with speed, temperature, load, rim profile, etc. etc.

It's lovely stuff but it ain't science.
reohn2
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Re: Latest offering from JH.What doth ye thinketh?

Post by reohn2 »

pwa wrote:Even if correct in principle, wider tyres will be heavier than narrower tyres made in a similar way, and the extra mass will slow you down in normal stop/start riding.

The tests were all done on 25mm tyres.
That said,it's a given that wider and therefore heavier tyres slow you down,but that's not been my experience with wider tyres on flat to rolly terrain comparing 37mm(405g) to 28mm(350g) tyres,average speeds were within 1mph with and average of around 16mph.The plus being the bigger (supple)tyres were far more comfortable.

I doubt the central conclusion though, because I think I can feel a sluggishness in a bike when tyre pressure has gone down from 90psi to 75psi.

As Si says,feel can be a false reading,numbers don't lie.
When I first started experimenting with bigger rubber (37s)I had the impression the bike was going slower but after many test rides my opinion changed,I came to the conclusion it was the high frequency vibrations that gave the false feeling,and I reaped the comfort benefit the bigger volume tyre gave.When I began dropping tyre pressures comfort got better average speeds remained the same,though initially the lower pressures felt slower.
I also find grip much better at lower pressures,especially at speed ie;descending at over 40mph.
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"All we are not stares back at what we are"
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reohn2
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Re: Latest offering from JH.What doth ye thinketh?

Post by reohn2 »

MartinC wrote:I too find JH's stuff interesting, thought provoking and useful. Long may he continue to do it, I love reading BQ. He's a great one for extrapolating a few data points in sweeping theories - I'm never sure whether the theory precedes the observations or not.

What his graph shows is that, for this rider, at this speed, on this road, with these 3 instances of tyres (or tires), in these conditions and for these 7 pressures (with this gauge) then that's how the power required varies. Even assuming you'd get the same results from another tyre of the same model needs validation - sample of one isn't much.

When you read the text you can see that "supple" is a big part of how he feels tyres perform - so he needs to define what it means, how you measure it and how it varies with speed, temperature, load, rim profile, etc. etc.

It's lovely stuff but it ain't science.

I don't know if it's science or not and I'm no scientist.I've no doubt someone'll tell me how wrong/gulible I am :?
But the playing field is a level one,same track,following the white line,same conditions,or as near as can be,same tyre pressure gauge(I assume,though it'd be a pretty fundamental error if it weren't),same speed as near as a human can gauge it with the same computer(even if it's out a little it's out the same for the whole test)same indicated speed,same Powertap telling the same story even if it's slightly off everything's off by the same amount.
Four runs for each reading.
Is it or isn't it,I don't know,but it seems convincing.
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Brucey
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Re: Latest offering from JH.What doth ye thinketh?

Post by Brucey »

it is interesting but there are probably too many variables to draw a really safe conclusion. I'd have liked to have seen some coasting tests to back up the findings from the powertap, maybe runs using a different weight of rider, or stiffness of frame as well.

cheers
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MartinC
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Re: Latest offering from JH.What doth ye thinketh?

Post by MartinC »

The interesting thing about the graphs is that they don't show a direct relationship between tyre pressure and power (consumption). So taking his results at face value and speculating..............

I guess most people consider that rolling resistance is down to tyre deformation and tyre pressure is a proxy for this. So either deformation isn't directly related to pressure or rolling resistance depends on other variables.

Something else in the test (other than rolling resitance) is varying.

Either way his observations don't support the belief that there's a simple relationship between tyre width, pressure and rolling resistance.

Interestingly for the majority of values of pressure in his test increasing it leads to a reduction in power consumption which supports the view of those who say harder tyres feel faster.
reohn2
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Re: Latest offering from JH.What doth ye thinketh?

Post by reohn2 »

Brucey wrote:it is interesting but there are probably too many variables to draw a really safe conclusion. I'd have liked to have seen some coasting tests to back up the findings from the powertap, maybe runs using a different weight of rider, or stiffness of frame as well.

cheers


I'm struggling to see how the frame would alter the outcome as the same frame was used for each run in the test .
Rider weight difference I can understand would have an influence on outcome.
Coasting,do you mean a roll down test?
JH has done some roll down tests which I'm sure you're aware of:- https://janheine.wordpress.com/2014/01/ ... -too-wide/

JH defends his findings in the comments section and doesn't do to bad a job of it IMO.
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"All we are not stares back at what we are"
W H Auden
Brucey
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Re: Latest offering from JH.What doth ye thinketh?

Post by Brucey »

the reason the frame (/fork) stiffness may alter the results is because of resonant effects. Basically you have a big mass (the rider) some smaller masses (the bike, the wheels etc) coupled together with a load of 'springs' of various (and/or variable) stiffnesses, and some dampers. Then you are 'exciting' the system by riding it on a (bumpy) road. The road will inject a spectrum of frequencies into the system and if you alter the spring rate of any one part of the system the way it resonates (and therefore how much energy is sent to -and dissipated in- the damper elements) will vary.

So what do you learn by such tests? You find out something interesting about that rider, on that road, on that bike, on that day, sure. But if you are trying to find out something scientific about (say) tyres, past that there is 'something odd going on' you have not learned all that much.

You can see that altering the stiffness of the parts of the system will almost certainly change things but it isn't easy to say exactly how without having a really good system model or by actually trying it.

The reason coasting tests may be an interesting adjunct to such tests is that once there is a different power output (from the rider) the way the rider's body mass is coupled to the bike will change (because of the way weight is shared between bars, saddle and pedals), and this in turn will alter the way the bike both tracks the bumps and dissipates energy in the parts of the system that have a damping function. We have all experienced differences in the way a bike rides bumpy surfaces; sometimes bearing a little weight on the pedals helps, sometimes being sat in the saddle is a better idea. Similarly the grip on the handlebars makes a difference too. The same things make a difference on 'ordinarily bumpy roads' too, and it isn't anywhere near as obvious what (if anything) is going on.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
reohn2
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Re: Latest offering from JH.What doth ye thinketh?

Post by reohn2 »

MartinC wrote:The interesting thing about the graphs is that they don't show a direct relationship between tyre pressure and power (consumption). So taking his results at face value and speculating..............

Who's speculating?

I guess most people consider that rolling resistance is down to tyre deformation and tyre pressure is a proxy for this. So either deformation isn't directly related to pressure or rolling resistance depends on other variables.

My logical mind says to me that less air in a tyre=bigger contact patch=more drag.
My(unscientific)findings are that not to be the case at the speed levels I ride at,on the roads I ride,so convinced was I that now no longer own bikes with narrow tyres.
Also the comfort factor rocketed with bigger tyres and grip/roadholding similarly.

Something else in the test (other than rolling resitance) is varying.

What?

Either way his observations don't support the belief that there's a simple relationship between tyre width, pressure and rolling resistance.

But tyre width difference wasn't a factor in the test,as all tyres were the same(25mm)size from the same maker(Vittoria),two high end examples and one a training type tyre.

Interestingly for the majority of values of pressure in his test increasing it leads to a reduction in power consumption which supports the view of those who say harder tyres feel faster.

But the lowest power consumption is at 6 to 6.5 Bar and 8.5 to 9 Bar(other than the CX clincher which almost flatlines from 8 bar up) :?
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"All we are not stares back at what we are"
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reohn2
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Re: Latest offering from JH.What doth ye thinketh?

Post by reohn2 »

Brucey wrote:the reason the frame (/fork) stiffness may alter the results is because of resonant effects. Basically you have a big mass (the rider) some smaller masses (the bike, the wheels etc) coupled together with a load of 'springs' of various (and/or variable) stiffnesses, and some dampers. Then you are 'exciting' the system by riding it on a (bumpy) road. The road will inject a spectrum of frequencies into the system and if you alter the spring rate of any one part of the system the way it resonates (and therefore how much energy is sent to -and dissipated in- the damper elements) will vary.

So what do you learn by such tests? You find out something interesting about that rider, on that road, on that bike, on that day, sure. But if you are trying to find out something scientific about (say) tyres, past that there is 'something odd going on' you have not learned all that much.

You can see that altering the stiffness of the parts of the system will almost certainly change things but it isn't easy to say exactly how without having a really good system model or by actually trying it.

The reason coasting tests may be an interesting adjunct to such tests is that once there is a different power output (from the rider) the way the rider's body mass is coupled to the bike will change (because of the way weight is shared between bars, saddle and pedals), and this in turn will alter the way the bike both tracks the bumps and dissipates energy in the parts of the system that have a damping function. We have all experienced differences in the way a bike rides bumpy surfaces; sometimes bearing a little weight on the pedals helps, sometimes being sat in the saddle is a better idea. Similarly the grip on the handlebars makes a difference too. The same things make a difference on 'ordinarily bumpy roads' too, and it isn't anywhere near as obvious what (if anything) is going on.

cheers

I understand what you're saying but the tests were carried out on the smoothest surface available on the same bike by the same rider,trying to maintain the same riding position at the same speed so as to measure the power output.
The tests aren't exhaustive agreed but they're fairly level and honest AFAICT.
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"All we are not stares back at what we are"
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Brucey
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Re: Latest offering from JH.What doth ye thinketh?

Post by Brucey »

there is no such thing as a perfectly smooth surface! Certainly not one you can easily find and then ride a bike on.... :wink:

BTW one of the inputs into the spring/damper system is 'bobbing'. You can see this very clearly with some riders on suspension equipped bikes but on notionally rigid bikes it is less obvious. You can often see it happening if you look carefully at another rider's rear tyre when they are climbing; each pedal stroke squashes the tyre a bit more.

If the bobbing input is in sync with some other resonant frequency in the system then this will alter the way energy is used within the system (could be better, could be worse). The system frequency that is most likely to resonate is that of the primary mass (the rider) bouncing up and down on the tyre. Altering the tyre pressure changes the spring rate and therefore the resonant frequency.

Again, doing coast down tests would eliminate this input into the system. If the result change then this would give some direction to hypothesis concerning the observations and therefore direct any further testing.

cheers
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