Wheels

500g is a fairly substantial weight savings, especially when you consider that it's rotating mass. You will definitely notice ability to spin up the lighter wheels much more quickly. Obviously, the more quick accelerations you do (e.g., crits, short sprints) and/or the more hills you do, the more you will notice and benefit from this weight reduction. Someone else will have to offer opinion in Spynergy wheelset. I do not have informed opinion on these wheels.

Based on the very good model at analyticcycling.com, reducing wheel weight by 500 gm will put you 0.02 sec (0.24m) ahead after 100m jumping out of a corner. You might be able to feel that; I can't.

asgelle said:

Based on the very good model at analyticcycling.com, reducing wheel weight by 500 gm will put you 0.02 sec (0.24m) ahead after 100m jumping out of a corner. You might be able to feel that; I can't.

I bet you could feel that 500 grams going up a 6% grade. Try the equation with the uphill grade and you will be sold on the lighter wheels...

I'd say if the lighter wheels are flexier, they'd be slower.

500g is a nice chunk of weight to drop when you're going up up hills, but if rigidity is sacrificed, I wouldn't be taking the lighter wheels to your local criterium 🙂

tonyzackery said:

I bet you could feel that 500 grams going up a 6% grade. Try the equation with the uphill grade and you will be sold on the lighter wheels...

Kreuzotter provides such a calculator

http://www.kreuzotter.de/english/espeed.htm

I bet the 24cm benefit mentioned above was from the overall mass of the rider and bike being reduced

I reckon the "external rotating mass" myth is the biggest in cycling, especially the suggestion (I've read elsewhere) that acceleration is improved if weight is moved from the rims to the hub, with no drop in overall mass.

Firstly, the friction on a bike tyre is JINORMOUS!! External mass accelerating equations may be apt for a fly-wheel, or a bike up on a stand (both with ZERO external friction), or a racecar generating hundreds of thousands of watts, but bike wheels are stuck down so firmly on the road by so much weight that a couple of hundred grams isn't gunna make the wheel start spinning freely.

Think about it: how is 250g off a rim gunna make any difference to a wheel that's stuck to the road by 80,000g of rider and bike? Is the wheel gunna suddenly start spinning at great speed. It's so minute it's ridiculous 🙂

Secondly, a cyclist has a power to weight ratio of a farm tractor!🙂
Even Tom Boonen, at 80kg, "only" generates 1600w in a sprint; and that's his all-out effort, not something he'd be generating out of every corner of a crit. So, including an 8kg bike, Big Tom has a power to weight ratio of ~18w/kg. That's like a 1700kg sedan dropping from a 200kw engine (117.6w/kg) to a 30kw engine. So, if I'm trying to 'slug' my MASSIVE 1700kg sedan out of corners with a PISSY 30kw (0.9 cyl) engine, how the heck is a few kg off the tyres gunna make any difference?

How about a 70kg club rider (with an 8kg bike) who may only generate 900w out of a corner? That's only a power to weight ratio of 11.5w/kg: same as the 200kw engine on the 1700kg car being reduced to a 20kw engine. Imagine trying to haul a 1700kg sedan out of a corner with a 0.58 cyl engine! With such horrible acceleration, lighter rims would make such little difference it couldn't be measured.

🙂

A single gram of rim weight is multiplied 34 times at just 25mph and it goes exponentially up from there. Thus sayeth the almighty computer at Boeing.

Mercian said:

A single gram of rim weight is multiplied 34 times at just 25mph and it goes exponentially up from there.

but the forces generated by cyclists are so small that it's meaningless, especially relative to the overall mass of the rider and bike which has to be overcome.

Then there's the friction of the tyre stuck on the road. That tyre and rim ain't spinning nowhere until the very large (and relatively massive) weight on top of it gets moving, and the relatively weak engine moving that lard only generates a measly several hundred watts

Mercian said:

A single gram of rim weight is multiplied 34 times at just 25mph and it goes exponentially up from there.

such numbers are probably applicable to a Boeing engine, spinning turbines at a zillion mph, at a billion watts, and with virtually no external friction, but I'd suggest it means nothing on a bike.

Mercian said:

A single gram of rim weight is multiplied 34 times at just 25mph and it goes exponentially up from there. Thus sayeth the almighty computer at Boeing.

Uh, no. The almighty Boeing computer must have a hangover or something... It's important to know the moment of inertia when trying to figure out how "tough" it is to accelerate a wheel. The total energy required to bring a wheel to speed is equal to:

Energy = 1/2 mv^2 + 1/2 I(v/r)^2

The first term is the amount of energy required to accelerate the wheel's mass forwards. The second term is the amount of energy required to spin up the wheel. I've measured a lot of wheels now and it's fairly consistent that the second term is about 20% as big as the first term.

Overall, the wheels are about 4% of the total kinetic energy of a cyclist... So a 500 gram change in the wheels means that the total kinetc energy of the bike and rider has changed less than 1%. In other words, it will take 1% longer to get up to speed, or 1% more power. And that's only when accelerating.

Aerodynamics on the other hand... At 40 km/hr it takes about 1.2 Watts more power to keep a Ksyrium ES wheelset moving than a Shimano WH-540 wheelset. That's all the time. Not just when accelerating.

I'd conclude that the aerodynamics is much, much more important than 500 grams.

John Swanson
www.bikephysics.com

ScienceIsCool said:

Overall, the wheels are about 4% of the total kinetic energy of a cyclist... So a 500 gram change in the wheels means that the total kinetc energy of the bike and rider has changed less than 1%. url]

so, any benefit would be from the reduced total mass of the bike and rider?

531Aussie said:

so, any benefit would be from the reduced total mass of the bike and rider?

Yes, absolutely. The wheels are just one part of an entire system (rider, frame, wheels, pump, etc, etc). When you ride, you are accelerating that entire system so it's helpful to think of it in those terms.

John Swanson
www.bikephysics.com

ScienceIsCool said:

Yes, absolutely. The wheels are just one part of an entire system (rider, frame, wheels, pump, etc, etc). When you ride, you are accelerating that entire system so it's helpful to think of it in those terms.

John Swanson
www.bikephysics.com

You both are Correct, but so was the Boeing computer. The 34 X mass at 25mph is only applicable to an imbalance in the wheel. However, it does point out that mass is important in a wheel. The old rule of thumb is that a mass reduction in the wheels was worth 2X on the frame or rider is relatively accurate, esp. in perceived exertion.

As far as it being insignificant, I disagree with you. Lightweight wheels are extremely important, esp when accelerating. After all, the amt of watts that are available to be expended by the rider are not infinite.

Also, I find an error in the assumption that once a wheel is up to speed, energy used is no longer significant. A heavier wheel not only takes more energy to accelerate, it takes more energy to keep it at speed. Wheels are not effective flywheels, which your equation is assuming. While a heavy wheel may spin longer, it still requires more energy to keep at that speed becuz it does slow down, and must be accelerated again to get it up to speed. This is the reason Tour de France winners and whiners ride the lightest wheels they can ride for their weight and conditions. Every little bit helps. Just try to be the designated team chaser with a heavy set of wheels.

Cheers

Mercian said:

The old rule of thumb is that a mass reduction in the wheels was worth 2X on the frame or rider is relatively accurate, esp. in perceived exertion.

Cheers

Sorry, but I still disagree with you. I have taken direct measurements and this old rule of thumb is not true. Mass on the wheels is worth less than 20% extra on the frame, so to speak. So a drop of 500 grams on the wheels feels like you've lost 600 grams (Not 1000 grams as you claim). But only when accelerating. Not when going at a constant speed - even uphill.

If you are interested, I explain this in a bit more detail on my website. Or I can answer any questions you have in this forum.

John Swanson
www.bikephysics.com

ScienceIsCool said:

Sorry, but I still disagree with you. I have taken direct measurements and this old rule of thumb is not true. Mass on the wheels is worth less than 20% extra on the frame, so to speak. So a drop of 500 grams on the wheels feels like you've lost 600 grams (Not 1000 grams as you claim). But only when accelerating. Not when going at a constant speed - even uphill.

If you are interested, I explain this in a bit more detail on my website. Or I can answer any questions you have in this forum.

John Swanson
www.bikephysics.com

You will notice that I stated, "perceived" as well as fact. It is and was the perceived value and the actual value. Or as national caliber cyclists have stated to me: "I want that extra 1%". You have stated that there is an advantage, and that is true. By how much is irrelevant, becuz it IS an advantage. You can throw out an any advantage if you want to, but it is at your peril in the peloton.

I also am forced to ask, what exactly is your point with all this math? Do you mean to imply that the "perceived" advantage with either aero or low mass wheels is exactly that, and is of no consequence in a race? If so, maybe you should discuss this with sprinters or Tour competitors, etc. I'm sure that they will welcome your mathmatical formulas.

For me, in competition, I will ride the light wheels and sewups anyday.

Cheers

two things i would note:

1. less weight is less that NEEDS to be accelerated, also less that needs to be slowed down in a panic stop. aerodynamics does matter, esp. as they pertain to the spokes -- i had an old set of spinergys that would create drag above 18-19mph because, mainly, of the PBO spokes. they're currently on their fifth owner since 1999.

2. the ADvantage of the spinergys would be better bearings, which have as much effect as anything else on the efficiency of the wheelset.

i'd personally look at rolfs.

Mercian said:

I also am forced to ask, what exactly is your point with all this math? Do you mean to imply that the "perceived" advantage with either aero or low mass wheels is exactly that, and is of no consequence in a race? If so, maybe you should discuss this with sprinters or Tour competitors, etc. I'm sure that they will welcome your mathmatical formulas.

For me, in competition, I will ride the light wheels and sewups anyday.

Cheers

The point of the math, is to show except for that less than 1% difference; the major difference is in your head and your confidence. If you had the same confidence and forward thinking on a set of Shimano 550's or whatever vs a set of Zipp 303's you are going to have the same result. The point is you feel better on the Zipp 303's because of pedigree, because of mental thought that you *SHOULD* win on Zipps.

You shouldn't win because of the Zipp's, you'll win because of your mental edge.

Thats my evaluation of it anyway.

Mercian said:

A single gram of rim weight is multiplied 34 times at just 25mph and it goes exponentially up from there. Thus sayeth the almighty computer at Boeing.

At a steady speed of 25mph a gram is a gram wherever it is.

artemidorus said:

At a steady speed of 25mph a gram is a gram wherever it is.

So, then you agree with me that light wheels do make a difference?

Mercian said:

So, then you agree with me that light wheels do make a difference?

I'm in the "yes, but not very much" camp on this one.