Rolling resistance?

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Mick F
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Re: Rolling resistance?

Post by Mick F »

Right.
That sounds like a challenge. :D

Front wheels are easier and balanced side-to-side, so I'll pump it up to 120psi and try again.
Mick F. Cornwall
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Mick F
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Re: Rolling resistance?

Post by Mick F »

125psi. :shock:

60% bounce I reckon. Certainly more than 50%.
More pressure means more rebound, and the difference was quite marked from before.
Mick F. Cornwall
sreten
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Re: Rolling resistance?

Post by sreten »

Urticaria wrote:
sreten wrote:FWIW you'd need two accelerometers to pin down the dynamics.

Good job the accelerometers in smartphones and tablets are tri-axial e.g. ST LIS331DL


Hi,

No.

There is not remotely enough sufficient accuracy
compared to two. Say put at the seat and bars.

Even if the sensors gave enough detail you cannot assume the bike
is rigid, i.e. derive seat or bar readings from the opposite sensor.

rgds, sreten.
Scunnered
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Re: Rolling resistance?

Post by Scunnered »

It's been done using an iPhone here: http://slabtownrollers.files.wordpress.com/2013/01/pilot-study-bicycle-road-surface-roughness-final.pdf

The difference between smooth road and chipseal was very evident, using 25mm Gatorskins at 90psi and carbon forks.
Brucey
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Re: Rolling resistance?

Post by Brucey »



Nice. That is exactly the kind of thing that you would do as a first test. I had in mind that the data could be subjected to a Fourier analysis to pull out what kind of bumps there are in the road ('jolts vs buzz').

I don't think that (in the first instance) the lack of rotation axes is in any way significant for this kind of use BTW. Possibly of more concern is that the app. only samples at 100Hz, meaning that 'buzzy' frequencies over 50Hz are not collected. Maybe this isn't too important though.

I note with interest that instead of 90psi front and rear, a usual weight distribution would have been better met with something like 80f/100r. Thus in this case it could be argued that the test data was obtained using a front tyre that was slightly harder than some folk would have chosen.

cheers
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Dave W
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Re: Rolling resistance?

Post by Dave W »

You lot have totally lost me here. What exactly are you trying to prove apart from the obvious?
Higher the pressure the more bounce you'll get.
Lower pressures - smoother ride
Bigger the tyre the smoother the ride
Higher the pressures - harder the ride
Narrow tyres = harsher ride.
We know these things already.

The only important point on this whole post wasn't how fast the tour was in 1953 or what a bamboo bike looked like or how high your wheel can bounce but how fast tyres roll and whether the difference in speed (rolling resistance)was worthwhile between different brands and also different widths of the same tyre.
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Mick F
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Re: Rolling resistance?

Post by Mick F »

The point - despite a little thread drift :lol: - is that supple tyres roll better than rigid ones.
Also, that perhaps some "less wide" tyres roll better than some wider tyres.
Measuring this difference is problematical, and a vibration analysis could show up these differences, but that too is problematical.
Bounce test is useful, as it does show that some tyres are more lively than others.

All this is very subjective.
Mick F. Cornwall
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Re: Rolling resistance?

Post by squeaker »

Dave W wrote:The only important point on this whole post wasn't how fast the tour was in 1953 or what a bamboo bike looked like or how high your wheel can bounce but how fast tyres roll and whether the difference in speed (rolling resistance)was worthwhile between different brands and also different widths of the same tyre.

And what's wrong with a bit of thread drift :?: :lol:

You asked a tricky question, hence the drift - I'll ask one back: how do you define 'worthwhile'? What Mr Froome might regard as worthwhile might not interest me, and vice versa ;)

PS:I do not shave my legs....but I do have a beard :wink:

PPS: the i-phone work was a nice try: some comparative frequency analyses of the vibration measurements and the road surface roughness might be 'interesting' - but I'd need to see the frequency response of the i-phone and mount before getting too excited :roll: :lol:

PPPS: the i-phone approach would be useful as a comparative test between tyres, provided the inherent resonances in the road to phone transfer path did not swamp the tyre effects - fortunately I do not own an i-phone 8)
"42"
Brucey
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Re: Rolling resistance?

Post by Brucey »

Mick F wrote: Bounce test is useful, as it does show that some tyres are more lively than others...


exactly. At risk of stating the bloomin' obvious, the reason higher pressures give a higher bounce is very simply that at higher pressures, less of the carcass is deformed/flexed during the bounce.

The flexing is hysteretic (i.e. absorbs energy) and is (to a first approximation) likely to be dependent on the amount of flex, but not so much the pressure in the tyre (except inasmuch as how it affects the amount of flexing).

Which is why higher tyre pressures and narrower tyres always give lower Crr values on smooth surfaces.

However suspension losses increase with higher tyre pressures on anything other than a perfectly smooth surface and these can dominate overall Crr values on many 'normal' roads; this is difficult to quantify but it is likely that some kind of mean square acceleration value at the handlebar is going to correlate well with the suspension losses.

I don't have an I-phone either but there are similar accelerometers all over the place, e.g. buried inside a Wii controller. A bit of raspberry Pi action and perhaps you have a useful data logger....

cheers
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OnYourRight
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Re: Rolling resistance?

Post by OnYourRight »

Insomuch that the bounce test reveals rolling resistance, it only reveals the rolling resistance on a perfectly smooth surface (no matter how rough the surface it’s bounced off, of course!).

Perhaps that’s obvious to most of us, but I thought I’d mention it just in case.

Interesting idea for a test, though. But I suspect it’s very easy to misjudge the bounce height by eye. Best to record it on video (even an iPhone video would be fine) and analyse the frames one by one.
Dave W
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Re: Rolling resistance?

Post by Dave W »

Which would be faster - a bicycle with some suspension of some kind (Trek Madone, possibly Specialized Roubaix with Zertz inserts) on skinny tyres or fat tyres? A springy steel frame with skinny tyres or a stiff Carbon frame with fat tyres?
By the way not all carbon frames give a stiff ride.
reohn2
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Re: Rolling resistance?

Post by reohn2 »

squeaker wrote:............PS:I do not shave my legs....but I do have a beard :wink: ..........


I do shave my legs,sometimes my head and I always shave my face :wink:
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reohn2
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Re: Rolling resistance?

Post by reohn2 »

Brucey wrote:
The flexing is hysteretic.........

They should be burned at the stake,there's no place for such perverts in the CTC! :evil:

A bit of raspberry Pi....

Now we like that! :)
cheers

Never touch the stuff! :wink:
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"All we are not stares back at what we are"
W H Auden
brumster
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Re: Rolling resistance?

Post by brumster »

reohn2 wrote:
squeaker wrote:............PS:I do not shave my legs....but I do have a beard :wink: ..........


I do shave my legs,sometimes my head and I always shave my face :wink:



I've been following this thread with interest... I am now going to have to shave the palms of my hands ! :lol:
reohn2
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Re: Rolling resistance?

Post by reohn2 »

brumster wrote:
reohn2 wrote:
squeaker wrote:............PS:I do not shave my legs....but I do have a beard :wink: ..........


I do shave my legs,sometimes my head and I always shave my face :wink:



I've been following this thread with interest... I am now going to have to shave the palms of my hands ! :lol:


Dang! I just knew I'd forgotten something :(
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"All we are not stares back at what we are"
W H Auden
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