Cycling UK Forum

There are clearly more physicists on this forum than cyclists........

There are clearly more physicists on this forum than cyclists........

Am I not allowed to be both?

You don't have to be a physicist to know that moving mass, once up to speed ,does't need energy to keep moving.

Keezx wrote:You don't have to be a physicist to know that moving mass, once up to speed ,does't need energy to keep moving.

Not in a vacuum with no friction it doesn't, no.

Leeflatz wrote:Does 2 mm make that much difference?
Bemused by all the debate I keep coming across.

Has this thread helped...? [emoji23][emoji23][emoji23]

I reckon I can sum it up as 'a smidgen comfier, but otherwise it makes near as dammit no difference in general riding'.

But we should never let that get in the way of a good discussion, of course. [emoji6]

I'm a trendy consumer. Just look at my wobbly using hovercraft full of eels.

Leeflatz wrote:Is there honestly that much difference between 25mm and 23mm tyres?
Been using 23s for years in all weather's, even on tracks and canal bank, no problem.
On these tracks you can manage as long as you don't sit on the bike like a sack of spuds.
Just wondering.
Does 2 mm make that much difference?
Bemused by all the debate I keep coming across.

I've only just seen this. I tried 23mm for a couple of years, and reverted to 25mm. This is just my feeling, based on that experience - and it does depend on which brand/make of tyres, but I've found no noticeable advantage in rolling resistance and no noticeable advantage in lively feel with the 23mm tyres, and marginal (although it may be all in the mind) more comfort with the 25mm tyres.

23 vs 25 vs 28 Conti GP4000sII

https://www.bicyclerollingresistance.co ... i-23-25-28

Alan O wrote:

Keezx wrote:You don't have to be a physicist to know that moving mass, once up to speed ,does't need energy to keep moving.

Not in a vacuum with no friction it doesn't, no.

Still, air resistance and friction is independent from mass.

Mr Evil wrote:A lot of unsubstantiated talk about the detriment to performance from the increased weight and drag. Let's put some numbers to that:

http://www.slowtwitch.com/Tech/Why_Wheel_Aerodynamics_Can_Outweigh_Wheel_Weight_and_Inertia_2106.html
http://www.biketechreview.com/index.php/reviews/wheels/63-wheel-performance

In summary, the effect of increased wheel weight is approximately nothing. Aerodynamic drag from the wheels is potentially more significant, but it's still small (and tyre width only contributes part of that). Even if you're a racer who cares about these things, the reduced rolling resistance and increased comfort of wider tyres may still be worth it. For normal folk there should be no contest - does it really make sense to use less comfortable tyres just because you're worried that your journey might be a couple of seconds slower?

But if I run lower pressures and fatter tyres it's like riding through porridge! I don't like riding through porridge. And you keep perpetuating the myth that narrow hard tyres are less comfortable to ride on - they are not, now if you factor in RW roads, maybe and only maybe, there might be an advantage running low and fat, we at least know the Pro's think so for stuff like Roubaix. But generally they are on 22c tubulars so clearly riding for 200 plus kilometres at a time can't be so bad on narrow tyres.

On a blind test I reckon I can identify tyre widths fairly consistently just from how they ride. And with the aid of technology I can tell everyone that on a similar ride I need to put out 25-50w more on the bike shod with 28c than I do on the 23c's. Some of that is bike weight but as apparently that makes no difference I can only put the extra effort down to the tyres.

At the end of the day, who cares? I ride what I like, you ride what you like and we're all happy bunnies!

Keezx wrote:You don't have to be a physicist to know that moving mass, once up to speed ,does't need energy to keep moving.

Until you come to a hill.

foxyrider wrote:

Mr Evil wrote:A lot of unsubstantiated talk about the detriment to performance from the increased weight and drag. Let's put some numbers to that:

http://www.slowtwitch.com/Tech/Why_Wheel_Aerodynamics_Can_Outweigh_Wheel_Weight_and_Inertia_2106.html
http://www.biketechreview.com/index.php/reviews/wheels/63-wheel-performance

In summary, the effect of increased wheel weight is approximately nothing. Aerodynamic drag from the wheels is potentially more significant, but it's still small (and tyre width only contributes part of that). Even if you're a racer who cares about these things, the reduced rolling resistance and increased comfort of wider tyres may still be worth it. For normal folk there should be no contest - does it really make sense to use less comfortable tyres just because you're worried that your journey might be a couple of seconds slower?

But if I run lower pressures and fatter tyres it's like riding through porridge! I don't like riding through porridge. And you keep perpetuating the myth that narrow hard tyres are less comfortable to ride on - they are not, now if you factor in RW roads, maybe and only maybe, there might be an advantage running low and fat, we at least know the Pro's think so for stuff like Roubaix. But generally they are on 22c tubulars so clearly riding for 200 plus kilometres at a time can't be so bad on narrow tyres.

On a blind test I reckon I can identify tyre widths fairly consistently just from how they ride. And with the aid of technology I can tell everyone that on a similar ride I need to put out 25-50w more on the bike shod with 28c than I do on the 23c's. Some of that is bike weight but as apparently that makes no difference I can only put the extra effort down to the tyres.

At the end of the day, who cares? I ride what I like, you ride what you like and we're all happy bunnies!

What he said.

+1 from me too.

Mick F wrote:

Keezx wrote:You don't have to be a physicist to know that moving mass, once up to speed ,does't need energy to keep moving.

Until you come to a hill.

Still no energy needed for moving/turning the wheel, only for bringing the mass up against gravity.

just to add a further dimension to this discussion....

Under high torque conditions the sidewall of a rear tyre will start to wrinkle. This happens nearly all the time with many MTB tyres and often causes the carcasses to fall to bits. Low tyre pressures, high loads and a slightly 'stabby' pedal stroke aid and abet this type of behaviour.

It is very probable that this is also associated with much higher hysteresis losses in the tyre, i.e. greater rolling resistance. There is also some slippage (always) between the rear wheel tread and the road. Both these things will never be seen on a typical tyre test because the tyres are simply rolled around a drum with no torque other than the tiny torque of pure rolling being transmitted.

In other words the fact that the rear wheel is being used to drive the bike along is completely ignored in such tests; the tests only represent what is going on at the front wheel.

I think that fatter tyres can be very much more lossy under high torque conditions, i.e. whenever you are climbing, or whenever you are laying down a large amount of power, or you have a high peak force in the pedal stroke. By contrast a less powerful rider and/or with a smoother pedal stroke will never see the same loads at the tyre and therefore will never see the same losses either.

This could help to explain why it is that Foxyrider reports such a power increase is required with wider tyres, and why it feels like you are pedalling in porridge. I don't have an accurate tool to measure my power output but I definitely do not climb as well or sprint as well on fatter lower pressure tyres, so I would broadly go along with both sentiments that he expresses.

If this is so, and it applies more widely to lots of other riders (which I would expect it does) it also means that until a better test is devised, the Crr measurements that so many people set so much store by really only apply to front wheels, not rears, and the whole subject of drag and real losses in tyres is still up for grabs.

Remember that for a touring cyclist (with typical output of power, aerodynamics, tyres and net speed on a flat road) about 50% of the drag might be aero drag but for a racing cyclist this often goes up to 90% or more. This means that there is a significant discrepancy between the power transmitted by the rear tyre and the pure rolling resistance in the case of a touring cyclist but there will be a truly massive one for a more powerful, faster rider. Whatever errors are introduced because the rear wheel is not just rolling are magnified very greatly for riders that are powerful and fast.

cheers

Keezx wrote:

Mick F wrote:

Keezx wrote:You don't have to be a physicist to know that moving mass, once up to speed ,does't need energy to keep moving.

Until you come to a hill.

Still no energy needed for moving/turning the wheel, only for bringing the mass up against gravity.

Yes, but not quite correct.

Examples:

Climb a very steep hill on a normal 700c or 27" wheel bike.
You weave a bit, and if you can only manage 2mph, you weave a lot.

Do the same hill with a heavy wheel bike and compare that to a light wheel bike.
The lighter the (front) wheel, the easier it is to weave as it's easier to move left and right. Less weight to turn the steering, not absolute weight, but weight to turn the steering.

Try it again on a bike with small wheels.
The weaving is too easy and almost frightening! Believe me, the Moulton and the Mercian are very different beasts when climbing a 25% hill.