ROLL OUTFOR TRACK....23mm Vs 20mm

[BernardG]

Looking at buying new tyres for my sons track bike......
Conti Supersonics.......
Come in 2 sizes 23mm & 20mm....

If i use the 23mm his rollout should be the same as he is not permitted to
exceed 6m.....

If i use 20mm his roll out would be reduced slightly....not sure how much
though....

Is the sacrifice for a faster 20mm tyre in roll out more beneficial as you
have a faster spinning tyre.....??????????????

Which one would be overall faster..

Bernard

 

[Server]

In article <[email protected]>, [email protected]
says...
> Looking at buying new tyres for my sons track bike......
> Conti Supersonics.......
> Come in 2 sizes 23mm & 20mm....
>
> If i use the 23mm his rollout should be the same as he is not permitted to
> exceed 6m.....
>
> If i use 20mm his roll out would be reduced slightly....not sure how much
> though....
>
> Is the sacrifice for a faster 20mm tyre in roll out more beneficial as you
> have a faster spinning tyre.....??????????????
>
> Which one would be overall faster..
>
> Bernard
>
>
>
Stay with the size that will give you the right rollout or change ring
and cog to suit. Also watch for the drop in track clearance with the
smaller bag. The 23's are faster at the same tyre pressure. You can go
for a 20 front and 23 rear.
My son is U15 too. He has clipped the banking with 23's in a derby - no
prob - so wouldn't like to go to 20's.
--
Mark Lee

 

[Etxy]

I heard a rumour that 23's have less rolling resistance then 20's? Of course, I heard this after I got myself a new pair of 20's. Would anyone care to verify/contradict this rumour?



--

 

[Andrew Swan]

Etxy wrote:
> I heard a rumour that 23's have less rolling resistance then 20's? Of course, I heard this after I got myself a new pair of 20's. Would anyone care to verify/contradict this rumour?

All other things being equal (N.B. on bikes, they rarely are), a larger
diameter wheel has lower RR than a smaller one. Don't ask me why, this
is just a general principle of physics. Anyone happen to know?

&roo

 

[Etxy]

Andrew Swan wrote:
> Etxy wrote:
> > I heard a rumour that 23's have less rolling resistance then 20's? Of
> > course, I heard this after I got myself a new pair of 20's. Would
> > anyone care to verify/contradict this rumour?
> All other things being equal (N.B. on bikes, they rarely are), a larger
> diameter wheel has lower RR than a smaller one. Don't ask me why, this
> is just a general principle of physics. Anyone happen to know?
> &roo



But by that logic wouldn't 25's be faster, 30's faster still... at what
point does this theory stop working? I know for a fact that when I moved
from 25's down to 23's my average went up, not down... we only see pro's
using 23's, sometimes down to 20's.



--

 

[rayner]

Etxy wrote:
> I heard a rumour that 23's have less rolling resistance then 20's? Of
> course, I heard this after I got myself a new pair of 20's. Would anyone
> care to verify/contradict this rumour?


20s should have a lower rolling resistance than 23s because of th
reduced contact area to the ground, which would reduce friction an
result in less resistance


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[rayner]

BernardG wrote:
> Looking at buying new tyres for my sons track bike...... Conti
> Supersonics....... Come in 2 sizes 23mm & 20mm....
> If i use the 23mm his rollout should be the same as he is not permitted
> to exceed 6m.....
> If i use 20mm his roll out would be reduced slightly....not sure how
> much though....
> Is the sacrifice for a faster 20mm tyre in roll out more beneficial as
> you have a faster spinning tyre.....??????????????
> Which one would be overall faster..
> Bernard


Forgot to write this in my last post. Had the same problem when i race
juniors. If i can remember right the difference is about fou
centimetres which wont make any difference whatsoever. I personally ra
the 20s after riding 23s in my first year and the difference wa
amazing not only in speed but also in the responsiveness of the bik
(probably was in my head tho!). The sacrifice in roll out is well wort
it With the supersonics be a little bit careful when moving slowly on
steeply banked veledrome as they dont stick too well at slow speeds
Hope that helped


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[Gemma Kernich]

"rayner" <[email protected]> wrote in message
news:[email protected]...
> Etxy wrote:
> > I heard a rumour that 23's have less rolling resistance then 20's? Of
> > course, I heard this after I got myself a new pair of 20's. Would
anyone
> > care to verify/contradict this rumour?
>
>
>
> 20s should have a lower rolling resistance than 23s because of the
> reduced contact area to the ground, which would reduce friction and
> result in less resistance.

Don't think so... rolling resustance isn't purely a function of contact
patch, rolling resistance is also affected by the stiffness of the sidewalls
in clinchers. As 23's are more flexible (generally) they come up better in
rolling resistance tests. You make your own judgement on how much the air
resistance increases with a fatter tyre though
Am sure there's plently about this one the web somewhere...
Gemma

 

[amirm]

Gemma Kernich wrote:
> "rayner" <[email protected]> wrote in message news:MVILb.7-
> [email protected]:[email protected]
> netserver.com...
> > Etxy wrote:
> > > I heard a rumour that 23's have less rolling resistance then 20's?
> > > Of course, I heard this after I got myself a new pair of 20's.
> > > Would
> anyone
> > > care to verify/contradict this rumour?
> >
> >
> >
> > 20s should have a lower rolling resistance than 23s because of the
> > reduced contact area to the ground, which would reduce friction and
> > result in less resistance.
> Don't think so... rolling resustance isn't purely a function of contact
> patch, rolling resistance is also affected by the stiffness of the
> sidewalls in clinchers. As 23's are more flexible (generally) they come
> up better in rolling resistance tests. You make your own judgement on
> how much the air resistance increases with a fatter tyre though Am
> sure there's plently about this one the web somewhere... Gemma

True. The higher the TPI, the lower the rolling resistance for the sam
given size. As the overall RR is the product of few factors, it's har
to rate tyres in this respect based on the diameter only

Besides, RR is effective during acceleration and not crusing. So thi
should not be confused with the speed. The larger tyre, giving large
circumference, will go faster at a set RPM, but if itsRR is greater, i
would take longer and more effort to accelerate with



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[stu]

l didnt want to get into this but here goes
> > > 20s should have a lower rolling resistance than 23s because of the
> > > reduced contact area to the ground, which would reduce friction and
> > > result in less resistance.
if the tyres have the same construction and
"if" the pressure is the same the the contact area will be the same, only
the shape of the contact area changes, the shape of the 20s being longer and
narrower(this mean more tyre deflection), so the 20 has a higher RR than the
23
> > Don't think so... rolling resustance isn't purely a function of
contact
> > patch, rolling resistance is also affected by the stiffness of the
> > sidewalls in clinchers. As 23's are more flexible (generally) they
come
> > up better in rolling resistance tests. You make your own judgement on
> > how much the air resistance increases with a fatter tyre though Am
> > sure there's plently about this one the web somewhere... Gemma
>
> True. The higher the TPI, the lower the rolling resistance for the same
> given size. As the overall RR is the product of few factors, it's hard
> to rate tyres in this respect based on the diameter only.
>
> Besides, RR is effective during acceleration and not crusing.
are you talking about roll out? or maybe the weight of the tyre?
because RR is always there
> So this
> should not be confused with the speed. The larger tyre, giving larger
> circumference, will go faster at a set RPM, but if itsRR is greater, it
> would take longer and more effort to accelerate with.
no its RR(at the same pressure) will be lower

how much difference it really makes is anyones guess

maybe l just didnt get what you were trying to say
and there is always the chance l am wrong

 

[amirm]

Stu wrote:
> l didnt want to get into this but here goes
> > > > 20s should have a lower rolling resistance than 23s because of
> > > > the reduced contact area to the ground, which would reduce
> > > > friction and result in less resistance.
> if the tyres have the same construction and "if" the pressure is the
> same the the contact area will be the same, only the shape of the
> contact area changes, the shape of the 20s being longer and
> narrower(this mean more tyre deflection), so the 20 has a higher RR
> than the 23
> > > Don't think so... rolling resustance isn't purely a function of
> contact
> > > patch, rolling resistance is also affected by the stiffness of the
> > > sidewalls in clinchers. As 23's are more flexible (generally) they
> come
> > > up better in rolling resistance tests. You make your own judgement
> > > on how much the air resistance increases with a fatter tyre though
> > > Am sure there's plently about this one the web somewhere...
> > > Gemma
> >
> > True. The higher the TPI, the lower the rolling resistance for the
> > same given size. As the overall RR is the product of few factors, it's
> > hard to rate tyres in this respect based on the diameter only.
> >
> > Besides, RR is effective during acceleration and not crusing.
> are you talking about roll out? or maybe the weight of the tyre? because
> RR is always there
> > So this should not be confused with the speed. The larger tyre, giving
> > larger circumference, will go faster at a set RPM, but if itsRR is
> > greater, it would take longer and more effort to accelerate with.
> no its RR(at the same pressure) will be lower
> how much difference it really makes is anyones guess
> maybe l just didnt get what you were trying to say and there is always
> the chance l am wrong

I'm confused now. Let's define the terms here. My understanding o
the rolling resistance comes from my motoring background, and by what
read here, it seems people are referring to a different concept unde
the same name. Or maybe I'm wrong

I guess one thing that can be easily confusing is the "rollin
resistance" and the amount of resistance caused by "friction"

I still cannot follow why the changed shape of deflected area going fro
23 to 20 (same construct; same pressure) can actually affect the rollin
resistance of the tyre. Unless the reason is "more threads involved i
the deflected area contributing to a higher resisting force"

About the effect of rolling resistance mainly during acceleration an
not during cruising, I was trying to say that the rolling resistanc
(and not friction force) is like inertia taking a considerable deal t
overcome at the time of speed alteration. Once the force is overcome
keeping the momentum requires a lot less energy. Friction, in contrast
is always there. By choosing a narrower tyre, we try to reduce frictio
drag mainly (of course with pressure adjustment). Rolling resistance o
the tyre is rather a product of its construct

This is my understanding which is in no way perfect. I'd like t
understand this concept right, so any further light is welcome



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[John Retchford]

amirm wrote:
> I'm confused now. Let's define the terms here. My understanding of
> the rolling resistance comes from my motoring background, and by what I
> read here, it seems people are referring to a different concept under
> the same name. Or maybe I'm wrong.
> I guess one thing that can be easily confusing is the "rolling
> resistance" and the amount of resistance caused by "friction".


Forget about friction (that involves sliding) and acceleratio
effects. The rolling resistance being discussed here stems from losse
within the tyre

The area of the contact patch of a weighted bicycle tyre equals th
downward force divided by the pressure in the tyre. This comes from th
definition of pressure. For a constant pressure the area does not depen
on the size of the tyre, but is smaller for higher pressure. For th
same pressure, the smaller tyre needs to deflect more to achieve th
required contact area. This deflection of the tyre walls and tread a
the wheel rotates is the primary cause of rolling resistance because
for practical tyre materials, it is a lossy process (hysteresis loss)

From the above it follows that a larger tyre (both wheel diameter an
tyre width) would deflect less and have a lower rolling resistance tha
a skinnier one all else being equal. But all else is not equal. For th
same pressure a fatter tyre will have higher forces in the tyre walls
The force in the wall is directly proportional to tyre width for th
same pressure. So, for a fatter tyre, you could opt for a thicker wall
which increases hysteresis loss, or for lower pressure, which als
increases hysteresis loss

In summary

Rolling resistance comes largely from hysteresis losses when the tyr
deflects. It can be minimized by: High pressure, which reduces th
flexing of the tyre Thin, flexible walls (needs high wall strength
Material choice (cotton has lower loss than nylon or Kevlar, but i
weaker) Large diameter (both wheel and cross-section) Absence o
patterned tread (tread squirms and increases losses

Several of these factors are mutually exclusive, so designers need t
seek the "best" compromise. At the moment this would seem to be a smoot
tyre with a thin wall and with a width of about 23 to 25 mm on a fairl
large wheel. Pretty much the sort of thing you see on most bikes! Not
that we are talking about rolling resistance here and not abou
aerodynamics

Does this help or just confuse

John Retchfor


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[stu]

> I'm confused now. Let's define the terms here. My understanding of
> the rolling resistance comes from my motoring background, and by what I
> read here, it seems people are referring to a different concept under
> the same name. Or maybe I'm wrong.
>
> I guess one thing that can be easily confusing is the "rolling
> resistance" and the amount of resistance caused by "friction".
>
> I still cannot follow why the changed shape of deflected area going from
> 23 to 20 (same construct; same pressure) can actually affect the rolling
> resistance of the tyre. Unless the reason is "more threads involved in
> the deflected area contributing to a higher resisting force".
yes thats it, they also have to deflect further
l have been trying to find some links but havent had a lot of luck
http://draco.acs.uci.edu/rbfaq/FAQ/8b.14.html
this is a start
> About the effect of rolling resistance mainly during acceleration and
> not during cruising, I was trying to say that the rolling resistance
> (and not friction force) is like inertia taking a considerable deal to
> overcome at the time of speed alteration. Once the force is overcome,
> keeping the momentum requires a lot less energy. Friction, in contrast,
> is always there. By choosing a narrower tyre, we try to reduce friction
> drag mainly (of course with pressure adjustment). Rolling resistance of
> the tyre is rather a product of its construct.
we sure are looking at RR from different points of view
the way l see it
RR=the energy use to deform the tyre
inertia=the resistance of the whole bike and rider to being accelrated

> This is my understanding which is in no way perfect. I'd like to
> understand this concept right, so any further light is welcome.
me to

 

[amirm]

John Retchford wrote:
> Forget about friction (that involves sliding) and acceleration
> effects. The rolling resistance being discussed here stems from losses
> within the tyre.
> The area of the contact patch of a weighted bicycle tyre equals the
> downward force divided by the pressure in the tyre. This comes from the
> definition of pressure. For a constant pressure the area does not depend
> on the size of the tyre, but is smaller for higher pressure. For the
> same pressure, the smaller tyre needs to deflect more to achieve the
> required contact area. This deflection of the tyre walls and tread as
> the wheel rotates is the primary cause of rolling resistance because,
> for practical tyre materials, it is a lossy process (hysteresis loss).
> From the above it follows that a larger tyre (both wheel diameter and
> tyre width) would deflect less and have a lower rolling resistance than
> a skinnier one all else being equal. But all else is not equal. For the
> same pressure a fatter tyre will have higher forces in the tyre walls.
> The force in the wall is directly proportional to tyre width for the
> same pressure. So, for a fatter tyre, you could opt for a thicker wall,
> which increases hysteresis loss, or for lower pressure, which also
> increases hysteresis loss.
> In summary:
> Rolling resistance comes largely from hysteresis losses when the tyre
> deflects. It can be minimized by: High pressure, which reduces the
> flexing of the tyre Thin, flexible walls (needs high wall strength)
> Material choice (cotton has lower loss than nylon or Kevlar, but is
> weaker) Large diameter (both wheel and cross-section) Absence of
> patterned tread (tread squirms and increases losses)
> Several of these factors are mutually exclusive, so designers need to
> seek the "best" compromise. At the moment this would seem to be a smooth
> tyre with a thin wall and with a width of about 23 to 25 mm on a fairly
> large wheel. Pretty much the sort of thing you see on most bikes! Note
> that we are talking about rolling resistance here and not about
> aerodynamics.
> Does this help or just confuse?
> John Retchford

John:

In the fact that your explanation deals with tyre construct, it is no
different from what I assumed first, except that you explained i
better. I learnt these when I was in the market to buy tyres for my 18
alloy wheels (for one of my previous cars) in year 2000. I mean al
about the interplay between thread pattern, side-wall stiffness, tyr
pressure, rubber material and the aspect ratio. In that business
choosing wheel/tyre combo requires attention to the weight of both tyr
and rim (as the main unsprung weight) and the rolling resistance of th
tyre. Here, talking about bikes, I usually hear people referring to th
weight of the wheel/tyre as a component of bike's overall weight rathe
than its effect on the acceleration

As you can see in the following post, RR can be used to refer to
technically different concept which explains the source of my confusion

Thanks for the explanation anyway. Cheers



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[John Retchford]

rayner wrote:

>wouldnt that make a 20mm tyre with recommended inflation of 170 ps
>have a smaller contact patch than its 23mm counterpart wit
>recommended inflation of 140 psi

Correct. That is what I said

> the original conversation was about two identical tyres in differen
> sizes. This means that the wall thickness is identical. With the 2
> being taller wouldnt this mean that the sidewall would deflect more

They both need to produce the same contact patch area if the pressure i
the same. This requires the narrower tyre to deflect more, whic
produces a smaller radius of curvature in the tyre wall. If other thing
are equal, the wider tyre with less flexure will have a lower rollin
resistance. But as you note (and as I noted in my previous post), th
narrower tyre can sustain a higher pressure and a higher pressure wil
reduce the contact patch area and thus the flexure in the wall an
tread. The narrower tyre can sustain a higher pressure because the forc
in the wall is proportional to the tyre radius for the same pressure
For the same wall construction, this means that the wall stress will b
higher for the wider tyre

All this is just basic physics. The problems come when we want t
quantify the effects. This requires experimental results and th
experiments are difficult to perform. The only ones that we (my son
actually) have done involved comparing the rolling resistance a
negligible speed (to eliminate aerodynamic drag) of bicycles fitted wit
23 mm tyres and with wide (about 40 mm) but smooth tyres, both inflate
to the maker's recommended pressure. The figures were about 2 newton
for the narrow tyres and about 4 newtons for the wide ones. Both thes
forces are very low and emphasise how efficient the bicycle is

John Retchfor


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[rayner]

Sorry if im a bit annoying but im trying to get my head around all
of this. So can it be safely said that a 20mm tyre inflated to 170
psi when compared to its 23mm counterpart inflated to 140 psi will
have less rolling resistance due to less deflection because of the
higher pressure?



--

 

[John Retchford]

rayner wrote:
> Sorry if im a bit annoying but im trying to get my head around all
> of this. So can it be safely said that a 20mm tyre inflated to 170
> psi when compared to its 23mm counterpart inflated to 140 psi will
> have less rolling resistance due to less deflection because of the
> higher pressure?


You are not being at all annoying. People should never be annoyed whe
yuou ask why - except with themselves when they feel they should be abl
to answer but can't. That is the position in which I find myself.
think we are all groping with these concepts together

I think the things I have written so far are sound and based solely o
th relationship between contact patch area and pressure and on th
properties of the materials involved (the hyrestesis loss). Now yo
want to vary both the width and the pressure! To answer your question
think we need to be able to predict the change in the radius o
curvature of the tyre wall as the piece we are considering goes fro
being above the contact patch to somewhere else on the tyre. It is no
obvious to what that is, although it is probably well known in the tyr
industry. Anyone know

What does seem apparent is that we can not keep reducing the rollin
resistance simply by increasing pressure, reducing the tyre diameter i
it is necessary to limit the force in the walls. (Remember that th
force in the wall is proportional to the tyre width.) The bi
breakthrough in Edward Dunlop's invention of the pneumatic tyre was th
use of the internal volume as an air spring, allowing the tyre to easil
roll over small obstacles and roughness in the road or track. Eventuall
this ability will be lost and the resistance will increase, although th
point at which this will happen will be different between a road and
smooth board track

As far as your question goes, this was a very long way of sayin
"Idon't know"

John Retchfor


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