Rolling resistance?

[reohn2]

Oh, and good luck

Or ask the Beach Boys.........I'm picking up Good......

[Brucey]

.....Alternatively use a nice (aka horribly expensive) high frequency handlebar test rig with measured data, but still a subjective ranking....

That is kind of what I feared!

I think that might have subconsciously lain behind my choice of wording; 'interpret data' rather than 'assess data'.

I guess one way of doing this would be to choose a few key frequencies (based on the kinds of road surface we ride over) and look at how they are transferred to the handlebars. My first shot at this would be something like;

a) the '10mm chipping @ 15mph' frequency
b) the cobblestone frequency (50-100mm pitch bumps)
c) the pothole effect frequency (bigger things that the wheel will drop into regardless of tyre section)

between a and b there would probably be another frequency, lets call it 'the gravel frequency' for 25mm pitch bumps.

I'd hope that the most important information about how a tyre feels at normal speeds would be captured in these frequencies, still subjectively of course in relation to comfort and how much it fatigues the rider.

[edit; I'd probably add a fifth frequency which would represent an 'excitation frequency'; this would be the resonant frequency of the handlebars; if this is excited by bumps in the road then comfort is definitely reduced.]

cheers

[Mick F]

I suppose my idea was to try and see what the difference was between a full suspension and big tyre bike, and a hard CF bike with hard narrow tyres.

Maybe they would be the extremes of the scale say 1 to 10 and we could then find what scale number our particular bike was.

If 10 was vibratory hard, and 1 a feather bed of a bike, mine would be 5 (or I'd like to think it would be!)

[reohn2]

Then you could do the same measurements with different handlebar tape,with and without under bar gel pads,different fork rakes and different fork bends,different head angles,different wheels,diffent spoke counts in each wheel,spoke tension?,rims?stem lengths?riding positions?saddles?chainstay lengths?seatstay thicknesses and bends? frame materials?(I didn't mention CF)
Ooooh, there's lots to play with there

Sorry,but I think we know it's a non starter and also highly subjective from rider to rider


Edit:- Oops,I forgot different tyres and tyre pressures

[Mick F]

Yes, of course it's subjective, but a fact is a fact, it's how we interpret those facts that counts.

Just say A's bike comes out at Vib5 and B's bike comes out as Vib8, it doesn't mean that either of them are unhappy with the vibrations, just that they are different.

The rest of us reading their Vib results will at least have something to compare A's and B's bikes.

[MartinC]

I'd be interested to see vibration test results. I'd also be interested too see how rolling resistance varies with the granularity of the road surface. The problem with all these type of tests is identifying the other factors and then controlling and testing them e.g. the vibration may vary with the pressure in the tyre but how does it vary with the suppleness of the casing and how do they both properties interact with each other?

[reohn2]

Yes, of course it's subjective, but a fact is a fact, it's how we interpret those facts that counts.

Just say A's bike comes out at Vib5 and B's bike comes out as Vib8, it doesn't mean that either of them are unhappy with the vibrations, just that they are different.

The rest of us reading their Vib results will at least have something to compare A's and B's bikes.

Consider the variables I've listed,you're in minefield territory,'difficult' doesn't begin to describe the variables there are.

[Mick F]

Yes, of course there would be a minefield of variables, but that doesn't mean the results would be meaningless.

The results would vary.
At any one time, you could read off the Vib unit. By continually monitoring it, you could find what was best for you at any single time.

I reckon if we all had a smart phone on our bikes with a software app, we could compare results. Just because I say I'm comfortable on my bike means nothing without numbers. No-one can compare my comfort to their comfort, but if I had a Vib5 on a particular ride on a particular day and they had a Vib2 on their ride on their day, at least they would know that their bike was less vibratory than mine at that time.

Maybe the next day the figures would be different, but at least you could put a figure to it.

Any road up, I'd find it interesting.

[reohn2]

I've not got a smart/i/android/?/phone and don't do 'apps' so I'll leave you enlightened beings to it

oh, for the love of numbers,eh?

[Brucey]

.....Ooooh, there's lots to play with there

Sorry, but I think we know it's a non starter and also highly subjective from rider to rider....

well if the objective is to get some kind of an idea how things change w.r.t to the use of different tyres I would not dismiss it out of hand. You don't need to look at many variables to test that.

If it is a case of identifying which is more important, tyres, frame/fork, or bar tape, I don't expect that question to be answered by such tests. But then I don't care; I'd suggest that most people know the answer to that anyway, and to a good approximation the beneficial effects of each are additive in any event.

BTW there is a real and unanswered question in this w.r.t. to the tyres; in theory the 'spring rate' of a narrow HP tyre could be the same as that of a wider tyre at lower pressure; what we don't know is how this pans out in reality (can you keep the same spring rate at the correct 'tyre drop'? Experience would suggest not...), and if the spectrum of transmitted vibrations is the same (again experience says not).

cheers

[Mick F]

Spring Rate.

Is there any mileage in lifting the front of a bike (say) 6" off the solid ground and dropping it and counting/assessing the bounces? Maybe do this for the rear as well?

Do bikes bounce differently depending on frame material and tyre design?

Would it tell us anything useful?

[reohn2]

.....Ooooh, there's lots to play with there

Sorry, but I think we know it's a non starter and also highly subjective from rider to rider....

well if the objective is to get some kind of an idea how things change w.r.t to the use of different tyres I would not dismiss it out of hand. You don't need to look at many variables to test that.

If it is a case of identifying which is more important, tyres, frame/fork, or bar tape, I don't expect that question to be answered by such tests. But then I don't care; I'd suggest that most people know the answer to that anyway, and to a good approximation the beneficial effects of each are additive in any event.

BTW there is a real and unanswered question in this w.r.t. to the tyres; in theory the 'spring rate' of a narrow HP tyre could be the same as that of a wider tyre at lower pressure; what we don't know is how this pans out in reality (can you keep the same spring rate at the correct 'tyre drop'? Experience would suggest not...), and if the spectrum of transmitted vibrations is the same (again experience says not).

cheers

Experience,there's no substitute

[Brucey]

Re the drop test; a good test is to drop a bare wheel (with no loose parts attached). If comparing different tyres/pressures a constant mass is a good idea.

The relative height of each bounce ( as well as the duration of all bounces net) tells you something about carcass/tread hysteresis (albeit it is not quite the same as a rolling contact, it says much about suspension losses in the tyre..), and the duration of each contact with the ground tells you something about the spring rate (for a bounce of a given height).

This test is tricky to do well; you need a straight bounce on a hard surface. I have had it in mind to use video recording to generate accurate timings and heights etc. but have not done this in a rigorous way as yet. I have even bought a video camera which shoots at several hundred frames per second to facilitate it, so I am indeed a proper dumbass for not getting on with it really, aren't I...?

Even without all this, you can very quickly compare two tyres of similar weight, and I've been doing this for years. In ad hoc tests with my chums we would sometimes whip out our front wheels (e.g. whilst waiting to go on a run) and have a play; we would very quickly identify which of half a dozen tyres would be likely to roll well and which were real stinkers this way. Even quite cheap 24mm cotton tubs (e.g. Wolber 'Internationals', remember them?) would do about x2 as well as an average HP training tyre for example.

cheers

[Mick F]

How much rebound can there be on the first drop?
50%?
25%?
No doubt the springier the tyre, the higher the percentage.

Quick non-scientific test with my front wheel - skewer out - is a tad under 50%.
80psi or thereabouts. Perhaps with a higher pressure the bounce would be higher?

[Brucey]

really nice-rolling tyres will normally bounce ~75% or so on a smooth hard surface. But remember that this is best used as a comparative test rather than an absolute one.

cheers