why clincher more pricey???

[Christie]

Isn't it the other way round - heavier bike needs 18w more to get the same acceleration over 30s?  Sounds a small but noticeable number over hours' date=' but with maybe 10-15 minutes maximum accelerating over a 2.5 hour race, it is neglible.
[/quote']

 

Fixed it - the the difference is 5w.

 

I can't see from quickly scanning JB's post is bike A weighs the same as bike B, with only different wheels, or if bike A is 400 grams heavier in total.

[Jules]

JB's calc shows the difference in power needed to accelerate a bike and rider weighing 91,2kg and one weighing 91,6kg.

 

 

 

It does not distinguish where the weight is saved.

 

 

 

Kiwi is arguing weight saved at the perimeter of the wheel is more important. The key question is: how much more important?

 

 

[Johan Bornman]

I think we have lost track of what the original question was: <?: prefix = o ns = "urn:schemas-microsoft-com:office:office" />

 

just a quick Q...why are most carbon clinchers so much more expensive than the tubbies??? i want clinchers but the price differences between them and tubbies get me wondrin if it worth it gettin tubbies rather than clinch...anyone know why exactly??

 

And I was say it is because they are more complicated to make and weigh less. I'm saying the 100 grams saved on each wheel at the rim (carbon rim with alloy braking surface vs. full carbon rim and braking surface) is significant and will make a difference to your ride.

 

I totally agree that the weight savings of lighter or fewer nipples or nipples moved to the hub end of the spoke is negligible.

 

 

 

Kiwi, you dance and sidestep like a politician outside a courthouse.

 

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.

 

Wheels with fancy designs to avoid nipples at the rim are bogus. They also complicate things unnecessarilly. It usually means proprietary components and difficulty in repair.

 

Not every "innovation" we see actually innovates. Some of them are a step backwards.

 

I've put together a Wheel Appreciation talk that I'll still find an audience for. The industry is full of silly innovations and a few of real innovations.

 

 

 

 

[Johan Bornman]

Easy calculate average power: P(ave)=dW/dt

So if the units of energy in JB's extreme calc of accelerating 30km/h in 30 seconds is Joule' date=' the average power over the 30s for bike A is 1350w [edit'] 1373w, and for bike B (with 200 grams less on each wheel) is 1368w.

Sorry, my bad, took 40500 for bike A, instead of 40500+720

 

 

Yes, that's right.  A difference of 5 watts. How much does five watts cost us? If we consider that a watt is one joule of energy per second, we're talking of 5 joules per second of the accelleraton. Lets say that the total accelleration time in the race was 10 minutes, then we have 60 x 10 x5 = 3000  joules or in food terms, 3 Kj.  A Windhoek Lite provides 125 Kjoules and a chocolate bar 3000 Kjoules. 

 

 

[Johan Bornman]

JB's calc shows the difference in power needed to accelerate a bike and rider weighing 91' date='2kg and one weighing 91,6kg.

It does not distinguish where the weight is saved.

Kiwi is arguing weight saved at the perimeter of the wheel is more important. The key question is: how much more important?
[/quote']

 

The weight is saved on the wheel.  

 

I think I must build a spreadsheet to let people play with different combinations. Problem is to post it and still make it work. I don't know how.

 

Jules, we'll talk about this tomorrow, but the point is that the energy required to spin up a wheel is only a small fraction of the energy required to accellerate the rider and bike.

 

And like Christie points out, that energy isn't lost, it is returned when you freewheel.

 

 

[Jules]

We all seem to agree that moving weight away from the perimeter will improve acceleration slightly. We also seem to agree, except for perhaps Kiwi, that this improvement is not worth paying silly money for.

 

 

 

However, none of us has been able to quantify exactly how much the saving is. JB, I look forward to the discussion tomorrow.

[Kiwi]

We all seem to agree that moving weight away from the perimeter will improve acceleration slightly. We also seem to agree' date=' except for perhaps Kiwi, that this improvement is not worth paying silly money for.

However, none of us has been able to quantify exactly how much the saving is. JB, I look forward to the discussion tomorrow. [/quote'] <?: prefix = o ns = "urn:schemas-microsoft-com:office:office" />

 

I assume that Eclipse is talking about wheels like Planet X's Pro Carbon 50 tubbies R7,221.00 (1604 grams actual weight) vs. the Pro Carbon clinchers R9,515.00 (1769 grams actual weight) which is R2,294.00 extra.

 

There were some new 50mm deep carbon/alloy clinchers (1960 grams a set) going for R7,500 on The Hub recently.

 

In my opinion and experience, I don?t think that an extra R2,015.00 is silly money for full carbon 50mm deep clinchers vs. 50mm deep carbon clinchers with alloy rims.  I don?t feel R2,015.00 is excessive money to save 191 grams of rotating weight at the part of the wheel which has the most effect, i.e. the rim. I also don?t think R9,515.00 is silly money for full carbon aero clinchers, when you see how much are the other brands are selling for eg 17,000.00 a pair

 

Good wheels are the most effective way to improve the performance of a bicycle.

 

I stand by my offer for an interested buyer take a set of Planet X carbon clinchers out and race them then compare them against an alloy rimmed version to see for them selves.

[butafly]

the difference between top cyclists is not in the weight of the equipment or the best training methods as they all have access to that , the difference is in their mental capacity to suffer (brain) and i suppose PD's. butafly2008-11-29 12:56:45

[linnega]

 

the difference between top cyclists is not in the weight of the equipment or the best training methods as they all have access to that ' date=' the difference is in their mental capacity to suffer (brain) and i suppose PD's. [/quote']

 

That applies to all riders and in a roundabout way supports what Kiwi is saying.  Slap on a pair of "performance" wheels and feel the difference.  Well, it seems the difference is 99.95% is your head, but since that is where the difference is made, if the wheels improve your headspace then they'll improve your performance. 

 

Kiwi - I think everyone should buy a pair of your alloy wheels - they llok like good value.

 

[GoLefty!!]

if light wheel does not help save energy during acceleratrion then a heavier wheel does not assist in conservation of momentum since it is a small component of the total weight.

 

However the point is not that the science is bogus, the point is that the science is overplayed in order to support a unique attribute which catches your attention>

 

 

The inertia mostly comes from the rider and the rest of the bike.

In an engine, the massof the flywheel is greater than the mass of reciprocating parts...

 

SO in short, buy the blingest whels you can afford.

Gold Rims nd Gold Hubs with carbon spokes.

 

Remember, there are no half measures of bling.

 

 

signed

 

Sultan of Bling

[bruce]

I think I must build a spreadsheet to let people play with different combinations. Problem is to post it and still make it work. I don't know how.

 

 

docs.google.com

 

 

[Thug]

Ok, we did try and get Johan to prove his theory this morning whilst we were cycling up a 9% gradient but he left his scientific calculator at home. 

[jmaccelari]

 

Jules has asked me to look at this problem. I am a physicist and applied

mathematician so it's right up my alley.

 

The bottom line is that taking mass (weight) off the wheel is more

effective than just taking it off the frame (my example shows it is twice

as effective).

 

This is because we need to add translational and rotational kinetic

energy when accelerating a bicycle - they are separate systems

and have their own conservation laws. If we reduce the frame or cyclist

mass we only reduce the translational kinetic energy, whereas if we

reduce the wheel mass, we reduce both the required translational and the

required rotational energy - a double whammy.

 

The mistake in the thread was to ignore the rotational component! It is

small compared to the total energy equation, but is comparable to the

 translational energy saving so cannot be ignored if we are looking at

energy savings!

 

I have attached a document with the problem detailed and a worked

example at the end.

 

I hope it is clear to all and sundry - if not ask me for an explanation!

 

The thread then ambled on to power calculations which are merely energy

equations differentiated with respect to time, so the same conclusions

will hold if we look at power.

 

The document can be found at:

www.cyclesafe.co.za/wheel_physics.pdf

 

Just to prempt those who are going to fly off without reading the

document:

- the effect is SMALL. At best in a perfect world taking weight off the

extreme outside of the rim is only twice as effective!

- it's probably better for most of us to leave our socks at home than

try to shave a couple of grams off our wheels. It'll be cheaper...

 

jmaccelari2010-01-04 09:27:06

[jmaccelari]

 

Jules has made the following comments:

 

C: Christie pointed out in that thread that an acceleration from

30kph to 60kph is extreme and is unlikely to occur more than once

or twice each race.

A: This is true, but as I show, a mass change makes no difference

to energy change if you are accelerating from 0 to 30 or 30 to 60.

They have the same energy requirement (if we ignore air and other

resistances). Air resistance does, but that is outside the scope

of the question.

However, if we have lots of little accelerations (10kph or so)

during the race, they do start adding up to a lot of extra energy

required to spin the wheels up. This energy is not recoverable

as it it lost to heat (breaking) or wind resistance. I do not know

of a racing bike with a KERS system!

 

C: He is of the opinion that the rotational mass story is

over-hyped.

A: Agreed. It's less than a 1% difference if you lose 400g on the

RIM (the best scenario).

However, if you're at the level where a 1% difference makes the

difference between winning or losing...

 

C: A saving of 400g is much easier to achieve on the frame than at

the perimeter of the wheel.

Yep - remember the "frame" includes the cyclist!

 

C: It's also probably worth pointing out that one doesn't

accelerate much on steep hills, where weight saving is going to be

most important.

A: Agreed. Here we are looking at potential energy and it doesn't

matter where the mass is lost from (frame, wheels, cyclist, ...).

Potential energy is recoverable - as we find out on free wheeling

on the downhills...

 

C: In the absence of acceleration, the weight saving is the same,

no matter where it is on the bike.

A: Not well put. With no acceleration, mass has no effect on

energy usage (under ideal circumstances) on a flat surface.

 

C: I reckon aerodynamics is a far more important concern than mass

at the perimeter of a wheel.

A: I dare not go into aerodynamical calculations (they are

horrific and usually non-linear and only solvable by numerical

means), but I would tend to agree with you here.

 

jmaccelari2010-01-04 09:19:56

[Spinnekop]

I'll get the popcorn.....

[Jules]

I'll get the popcorn.....

 

 

 

Spidey, I thought you said earlier that popcorn was inappropriate for this thread We need beer and biltong

 

 

 

Thanks Jeremy for doing all the calculations . Your answers have come the closest to helping me understand how much of a difference rotational mass makes to cycling performance.