why clincher more pricey???

[CaptainDura]

cant wait for the outcome of this

 

 

[CaptainDura]

"Pick me, Pick me!!"  o sorry that is a different movie altogether.

 

Johan just pick scenario one and run with it.

 

O ja, en maak gou!!

 

 

 

[Jules]

Ja, my beer is getting cold and the cat's eyeing my biltong!

 

 

 

Also, there is some vital information missing from your calculations such as whether the day is overcast or not, the wind speed and direction and whether the nipples are plain silver or anodized pink

[CaptainDura]

Ja' date=' my beer is getting cold and the cat's eyeing my biltong!
[/quote']

 

Jules Pick one scenario:

 

Scenario 1) If your beer is getting cold then your airconditioning is worth every cent you paid for it.

 

OR

 

Scenario 2) It is still in the fridge and you need to get it out and start drinking asap.

 

Pick one and let us know

[CaptainDura]

Scenario 3) You MEANT to say "your popcorns getting cold and your mate is eyeing your beer" ?

 

 

[Jules]

I'm of pommy descent: I drink warm beer

 

 

 

Actually what I meant to say is my acceleration should be good because I always ride with my nipples tucked away. Jules2008-11-28 05:58:59

[Wyatt Earp]

 

I think the answer to this is either 42

 

 

I agree, seeing that the ultimate question has not been posed yet it could be C.

 

[Johan Bornman]

I calculated this using a weight saving of a large 200 grams per wheel and my hypothesis was that weight saved on the wheel is no more important than a similar weight saving on the bicycle and rider combo.  <?: prefix = o ns = "urn:schemas-microsoft-com:office:office" />

In order to avoid semantics, my term ?no more important? means that the energy saving in accelerating the two differently equipped bodies (but with same overall weight) is negligible compared to the total energy input.

 

From now on I shall refer to the package of bike and rider simply as ?the bike?. Bike A has the heavier wheels.

 

I assume that 200 grams per wheel is reasonable, but if not, we can simply plug in another figure. I weighed a naked rim and tyre, but did not include a tube. Since both wheels need tubes (or <?: prefix = st1 ns = "urn:schemas:contacts" />Stan?s or whatever), it will simply cancel out in anyway.

 

I simplified the process by calculating the total energy stored (i.e. required to get it to that point) in two similar bikes with different wheels.

 

I start off by stating that the total energy stored in a bike travelling at speed is equal to its linear kinetic energy plus its rotational kinetic energy.

 

And by looking at the bike's total stored energy at the end of a constantly-accelerating run, we know how much energy was put in. The one who requires the least energy to get there wins.

 

The total package?s linear energy is calculated thus:  1/2 M*V^2.  

 

The wheel?s rotational energy is also 1/2M*V^2.   We have to add these to get the total.

 

Assumptions:

The bike weighs 90kgs.

We measure the energy at 30 kph.

The heavy wheel weighs 800 grams.

The light wheel weighs 600 grams.

The bike has two wheels.

All the wheel?s weight is concentrated in the rim/tyre combo.

The hubs and spokes weigh nothing. ? but don?t break your head on these two statements, they simply take a bunch of calculations out of the equation that would have cancelled each other in anyway.

The two bikes reached 30 kph under exactly the same conditions in terms of wind, road, gradient etc.

I?m not converting to standard units since we?re only after a ratio. I do the same for both bikes and the effect is therefore nil.

 

Now for Bike A?s total kinetic energy at say 30 kph.

 

We know that it is 1/2 MV*^2  (one half mvsquared)

 

Plus  1/2 M*V^2. for wheels only.

 

Thus

 

1/2 x 90 x 30squared   Plus 1/2 x 1.6 x 30squared

 

= 40 500 units Plus 720

 

= 41220 units of energy.

 

Bike B?s total kinetic energy at 30 kph.

 

1/2 x 90 x 30squared Plus  1/2 x 1.2 x 30squared

= 40500 Plus  540

= 41040 Units of energy. 

 

The summary:

 

***************************************************************************************************************

 

Bike A has 41220 units of energy stored after an acceleration from 0 to 30kph and

Bike B has 41040 units of energy stored after an acceleration from 0 to 30 kph.

 

***************************************************************************************************************

 

The difference is 180 units of energy or 0,43 percent and that for an all-out acceleration from zero to 30kph.

 

Conclusion: it requires 0,4 percent less energy to accelerate a bike with tyres/wheels weighing 400 grams less (at the rim) than a bike of equal weight but with heavier tyres.

 

400 grams is of course an outrageous weight for a few nipples, but I've used an absurd example to make my point. 

 

Now you have to go and contemplate how often in a ride or race you accellerate flat-out so that your speed increases by 30kph. Using the above data, you can also calculate how much energy you use to do that say ten times per race. Your conculsion is that the energy is less than one Windhoek Lite can provide.

 

Comments welcome 

 

[linnega]

400 grams may be a ridiculous amount for nipples, but it is a reasonable difference between a pair of handbuilt 32 spoke wheels with Record hubs and lets say Open Pro's, and a set of R20k carbon super duper wheels.

[Spinnekop]

Assumptions:

The bike weighs 90kgs.

 

Comments welcome 

 

 

 

No comment.........

[Johan Bornman]

400 grams may be a ridiculous amount for nipples' date=' but it is a reasonable difference between a pair of handbuilt 32 spoke wheels with Record hubs and lets say Open Pro's, and a set of R20k carbon super duper wheels.[/quote']

 

 

I suppose one could find all sorts of reasons for a 200 gram saving at the rim to be a reasonable difference. That's why I conservatively went for an upper end thumbsuck.

[Johan Bornman]

Assumptions:

The bike weighs 90kgs.

 

Comments welcome 

 

 

 

No comment.........

 

No place for poofter bikes here.....

 

That's obviously bike plus engine plus camelback plus four energy bars plus a cellphone, fllicknife, some coins, a leatherman and a peppermint from the last restaurant.

 

 

[Jules]

Thanks for this Johan. Any engineer hubbers able to confirm/refute the calculations? It's a looong time since I was in physics class

[Decado]

 

Most embarrasing moment ever:-

 

Getting a stomach bug and throwing up outside constantia village, then being offered a peppermint from a restaurant by a bergie to clear the taste up.

 

Sorry, jb's peppermint comment set me off.

 

Decado2008-11-28 06:27:57

[Tumbleweed]

Thanks for this Johan. Any engineer hubbers able to confirm/refute the calculations? It's a looong time since I was in physics class

 

can't remember what i had on my sandwiches at break?

[linnega]

You left out the sawn-off shotgun

 

It is always an interesting discussion when it comes to wheels.  The fact is lighter wheels feel a bit faster and the cool sound that deep section wheels make is probably also part of that sensation.  However, I find it really difficult to justify paying 10x more for a set of wheels simply for an actual improvement (as demonstrated) of nothing and a marginal improvement in the wheel "feeling" faster.