why clincher more pricey???

[MadScientist]

my brain eish she's burning now. so I would rather use the R2000 buy a fab diet and loose another 10kg's around my waist, that difference should be noticable

[GoLefty!!]

 

OK' date=' I think your averages vary far too much. If I work with these I have to ask you how much you accellerated for each attack from 1 to 24. Too much work. Give me an average attack speed and lets pretend on this race the attacks were all equal.

 

Scenarios (actual data)	Time (s)	Acc m/s2
Scenario One 33 to 63 in 30 sec	20	0.277778
Scenario Two  33 to 67 in 55 sec	25	0.171717
Scenario Three 36 to 72 in 55 sec	30	0.186869
Scenario Four  30 to 76 in 65 sec	35	0.324786

 

 

Have a look at the far right colum. This is accelleration for the said scenario in m/s/s or m/s2

 

Choose one and we go with that.

 

 

[/quote']

 

Just a little nit picking...

 

How the hell did a cyclist accelerate @ 200 m.s^2 when gravitational acceleration is but 9.8 m.s^2 ????

 

Your calculations are based on a load of bull Mr Wise Guy!

 

Using your most modest figure, this guy completed 90km in 30 sec

 

To clarify

 

s=ut+1/2at^2 (physics law of movement)

 

Say the guy does 0km/h and starts accelerating @ 200m.s^2

 

u = 0 (initial speed)

t = 30 (time)

a = 200 (acceleration)

 

Pop those into the equation and you end up with a total distance of wait for it

 

90 km in 30 seconds amazing!!!!

 

 

 

I think you take a deep breath bud and just read the relevant section a few times.

then you will realise it's a typo. it should read:

 

 Delta 20km/hr   0.277778m/s^2

 

 

gabbish!!

 

[GoLefty!!]

 

 

BTW' date=' I'm with Bornman on this one.

Even though differences in Ir and all that makes great calculation and keesp my HP48Gx busy, out on the road those little difference are lost in the total package on the road.

[/quote']

And I'd also agree with you. Maths ain't everything.

 

The energy saving really is less than 1%. What you probably noticed

was the inertia of the wheel. This (simplistically) is the resistance of

the wheel to changes in its rotational velocity (speed).

 

You took more energy (a very small amount) to spin them up and then

it felt more comfortable (like a flywheel) during the race since they

continued to roll more easily and smoothly.

 

The whole package is about more than just weight...

 

exactly J.

 

The statement weight at the wheels is worth twice on the frame is correct only when looking at each component from a non systemic point of view, without a rider. The whole point of view is of course incorrect from an on the road real world perspective where the rider is the most massive element in the equation.

 

Indeed it was perhaps partly the flywheel effect I felt but I think it was mostly due to the sound damping the AMC carbon 58's offered. The wheels feel stiff and don't transmit sound as much as the eastons do.

 

The subject of the aerodynamics of wheels is another pet project. The marketers of aero wheels like to tell us that their wheel is more aero than the nexts guys, yet they forget that the total drag of the wheel is again a very small percentage of the total package where the rider is bigger contributor to drag.

In fact there are studies that I have ead that show the riders head is something like x4 times greater contributor to drag than the wheels are and that a decent helmet makes a bigger contribution to drag reduction than the most aero wheels.

 

we cyclists love to justify our spend based on science when in fact all we really are chasing is a bit of vanity.. We all love pretty things is whatis really boils down too.

 

E.G I would buy the AMC Carbon 58 clincher because it looks nicer than the SRAM S40.

Someon else will opt for the SRAM S40 because it's more expensive

 

both puchase decisions are based on vanity but from a different perspective.

 

 

 

[jmaccelari]

 

Scenarios (actual data)	Time (s)	Acc m/s2
Scenario One 33 to 63 in 30 sec	20	0.277778

 

 

Just a little nit picking...

 

How the hell did a cyclist accelerate @ 200 m.s^2 when gravitational acceleration is but 9.8 m.s^2 ????

 

Your calculations are based on a load of bull Mr Wise Guy!

Wow! No need to get this personal! If you understand the table, it's

obviously a typo! "20 0.277778"

 

I disagree with Mr Bornman's physics, but as he's not trained for

it, it's a little harsh to start slagging him off for it!

 

His gut feel is on the right track, if not his methods and logic.

[TIMEprb]

Please accept my sincere apology for being so rude

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The error/typo was just too big not to be picked up by the author trying to prove a theory.

 

Indeed an interesting subject, way more complicated to calculate the net result, but I have to agree for a real world application the gain/loss will be negligible.

[Johan Bornman]

Oi guys! I accept responsibility for the typo. I did this a long time ago and vaguely remember having problems cutting and pasting a table into the editing space here. The type(s) dont affect the calculations at all. At a glance the decimals are clearly intoxicated since the first accellerations is out of kilter with the others and a second sanity check would have exposed the folly of the wandering decimal.

 

JMac, you say you disagree with my physics? Please point out where you disagree. What is wrong with my method and logic? Please spell it out. 

You talk about my gut feel as if it is something instictive and primitive that I couldn't back it up with figures. Perhaps you want to suggest an alternative approach to the problem?

 

Timeguy, yes it is way more complicated to calculate the absolute actual figures because we have to calculate the inertiall differences of two equally-sized wheels but with weight vaguely distributed in different (but undefined) places.

 

I wanted to simplify the problem and my objectes were to show that

 

a) We have to look at the whole package that needs to accellerate and

b) That the difference is insignificant.

 

I think I achieved it. I separated the moving bodies into two components - non rotating and rotating. I then calculated the energy required to accellerate those four bodies (two sets of humans and frames plus two different sets of wheels) from a given speed to a given speed in a realistic time supplied by one of the posters.

 

I expressed the answer in joules and then countered the argument of multiple accellerations by adding the total energy expenditure of multiple accellerations and proved that it was less than the energy supplied by one beer.

 

Why make it more complicated? Science should be simple and explainable.

 

If anyone else is still listening, do this little experiment:

 

Put your bike on a sturdy stand of sorts and shift to the hardest gear i.e. big in front, small at the back. Keep an eye on the computer and spin the bike up with your weak arm, from zero to 40kph.

 

Make a mental not of how many seconds it took to get there. No need for a stopwatch.

 

Now get on the bike and accellerate from zero to 40. Make another note of your time and compare the two.

 

This will show you just how insignificant the weight of the entire wheel is on accelleration. Now imaging saving 30grams by moving the nipples inboard. Still no difference.

 

Go ride.

 

[TNT1]

Whee! Nipples! Whee!

[Slowbee]

do these same assumptions and calculations apply to a mtn bike where there are alot more accelerations?

 

also at what point does a a weight difference on equipment become significant ? does 500g become significant to making a difference ... or 1000g ?

 

[TNT1]

 

a mtn bike where there are alot more accelerations?

 

 

 

 

What like Christoff's bike?

 

[Slowbee]

 

a mtn bike where there are alot more accelerations?

 

 

 

 

What like Christoff's bike?

 

no ... mine ...

 

[TNT1]

 

a mtn bike where there are alot more accelerations?

 

 

 

 

What like Christoff's bike?

 

no ... mine ...

 

No way... out of all the mtn guys, I reckon Christoff has the most acceleration.

 

[jmaccelari]

 

 

 

JMac' date=' you say you disagree with my physics? Please point out where you disagree. What is wrong with my method and logic? Please spell it out. 

You talk about my gut feel as if it is something instictive and primitive that I couldn't back it up with figures. Perhaps you want to suggest an alternative approach to the problem?

 [/quote']

Sorry - I was unclear. Your approach was correct, but I came across:

 

I've just shown you what a 200 gram difference makes. It doesn't

matter whether that is from nipples at the hub or from carbon instead

of aluminium at the perimeter. Accept it.

Which I will not accept as weight from the hub has a MUCH lesser effect*

on energy than carbon or aluminium at the rim. It makes me think you

don't really understand rotational inertia and have (correctly in your

example might I add) plugged some numbers into some formulae you

have found.

 

My opinion - not an attack on your person just in case you feel inclined

to blow up again!!!

 

As I stated, this does not detract from your general argument.

 

*The effect reduces as r^2 as you approach the hub, so at the hub

it has zero rotational effect! This is because the moment of inertia

I = Integral(r^2 dm), so as r tends to zero, so does I.

 

Remember the value of I you used (m r^2) is an approximation for

an infinitely thin hoop of radius r with no hub, spokes or depth - not at

all like a bicycle wheel (more like the iron rim on an ox wagon wheel).

The hoop approximation is a good one for our purposes though, in

that it gives us an upper bound for the effect.

jmaccelari2010-01-05 08:06:22

[Slowbee]

Bob, I didnt say the most acceleration ... I said the most accelerations .... I accelerate from about 15km/hr to about 16/17km/hr alot in a ride .....

[TNT1]

Oh, right, sorry slowone, I missed my afternoon nap...

[jmaccelari]

 

 

 

 

 

do these same assumptions and calculations apply to a mtn bike where there are alot more accelerations?

 

also at what point does a a weight difference on equipment become significant ? does 500g become significant to making a difference ... or 1000g ?

 

What will happen is that with a lot more accelerations the 16 or so Joules

saved will add up.

 

The significance is how much you feel.

 

What can be said is that if you want to save weight' date=' the best place is on

your wheels (the commonly accepted old wives tale that JB rubbished then

proved correct ).

 

This old old-wive's tale refuses to die. If you do the maths, and

believe me, it is not difficult stuff, you'll see that this story is

nonsense. The effect is negligible, so please stop perpetuating this

myth.

He is confused here. The old wive's tale (losing weight off the wheel

versus the frame) is TRUE. It is absolutely and completely TRUE. JB

has proved it himself. Just because the OVERALL effect is negligible

does not mean the actual rule of RELATIVE (frame versus wheel) weight

loss is false.

 

To reiterate:

100g on the wheels saves more energy than 100g on the frame.

 

JB's point of contention is (if I understand correctly) does it make any

difference in the real world?

 

The physics prove it does not have much of an effect for a single

acceleration, but for an entire race it adds up (if we have one 10kph

acceleration per minute in a 3 hour race we save about 600 Calories.

Plus for a fixed power output our accelerations will be faster, leading

to shaving about 16 seconds off our race time (at 300W output).

 

Does this mean we win the race?

 

As Berend pointed out, there's a lot more to worry about, but

it is another (slight) advantage.

And as GoLefty states, there can be an advantage to a heavier

wheel - he prefers the feel of it, how it rolls. This is due to the

extra inertia. This feeling outweighs the extra energy expense in

his opinion.

jmaccelari2010-01-05 08:29:54

[Eldron]

When looked at in isolation almost any "upgrade" is in/semi significant. Improving your cycling is a collection of in/emi significant improvements.

Losing 1kg in body weight:

Improving your cycling position/set up:

Lighter wheels:

Ceramic bearings:

Learning to draft better and sit closer to the rider in front of you:

Testing various energy drinks:

Better pedalling efficiency:

New tyres:

Playing with tyre pressure:

blah blah blah

 

Each of these when looked at in isolation have varying ratios based on:

The time to spend to acquire the improvement.

The amount of money you have to perform the improvement.

The amount of time in the race you'll actually save after the upgrade.

 

A lot of improvement are available without spending any money, some are available by throwing money at the problem, some are a combination.

 

Pick the ones best for you and when you start adding them up they start becoming meaningful!