Does weight really matter

dhk2 said:

5 kg certainly is a big drop. If you and your old bike weighed 100 kg, you've dropped 5%. On a steep climb at 10 mph, 5% faster means 10.5 mph...that's a big deal.

Regardless of numbers, the 7 kg bike is going to feel a lot more responsive underneath you; like it's ready to jump whenever you step down on the gas.

Yeah it is a big drop, probably an exaggerated example for most people trying to get some weight of their bikes but none the less I certainly can vouch for weight making a difference. I think though it has to be somewhat substantial unless of course you are at the elite level where it all counts.

And your right about the responsiveness, its awesome in comparison. It just goes!

TrekDedicated said:

Yes it does.

I have lost 23 lbs thanks to my jaw surgey, and have now started riding again. HUGE DIFFERENCE.

Add some lighter wheels, lighter brakes, and I am one fast mo-fo (even after 3 months of no riding)

Ha, congrats. Must have sucked not being able to ride for so long... Better get yourself training for racing season though, PartisanRanger is gonna tear up the C's! :P

this is my anecdote:

I'm no weight weeny -- my lightest bike is probably 8.5kg -- and I prefer strong, stiff stuff over light, floppy stuff, especially wheels.

I notice a difference in "feel" when the weight difference of the bike is approach 2kg (in other words, my old 531 bikes feel slower than my lighter alu bikes) but I can't honestly say this translates to a 'real speed' difference on flat or rolling roads

alienator said:

The difference that a wheel's moment of inertia makes on acceleration is almost nothing. Human's--including McEwen, Boonen, or whoever--don't accelerate fast enough for the difference to be noticeable.

Even when climbing, a "heavy" wheel does not cause any significant performance difference until the slope gets very steep.

But still, it's an area that's easier to shave a significant amount of weight. Recently I managed to trim off around 600g in a combined wheel and tyre change, along with improved bearing (reduced frictional resistance). Now I have two sets of wheels for different purposes and neither is put to waste.

sogood said:

But still, it's an area that's easier to shave a significant amount of weight. Recently I managed to trim off around 600g in a combined wheel and tyre change, along with improved bearing (reduced frictional resistance). Now I have two sets of wheels for different purposes and neither is put to waste.

Yup, you're right. If a person wants to shave weight off his bike, the first place to go is the wheels because that's where the biggest gains....er, weight losses.....are. In my recent wheel history, I went from Bontrager Race X Lites (veritable [censored] wheels) to a custom set with White Ind's new hubs, CX Ray spokes, and Alex Crostini 3.1/3.2 rims. In the process, I shaved about 250g off the bike weight. Then I bought a set of Reynolds Stratus DV tubies and shaved another 120g off. So in total, I lost 0.8 lbs. The only real performance difference that I notice is that once the pace gets goin' I can maintain a slightly higher speed w/ the Stratus DV's. Of course, that's an aero thing, not a weight thing.

The one place everyone notices weight loss on a bike is when they're climbing out of the saddle or sprinting. In both cases, you can feel the difference as you throw the bike back and forth. Of course, that means squat for goin' faster.

There's naught wrong with wanting to shave weight off the bike. I'm a gearhead/tech geek, and making my bike lighter while keeping it everyday useable was/is fun in a weird way. It's important though to keep in mind that any performance gains from dropping your bike's weight will be very small, at best.

alienator said:

So in total, I lost 0.8 lbs. The only real performance difference that I notice is that once the pace gets goin' I can maintain a slightly higher speed w/ the Stratus DV's. Of course, that's an aero thing, not a weight thing.

The one place everyone notices weight loss on a bike is when they're climbing out of the saddle or sprinting. In both cases, you can feel the difference as you throw the bike back and forth. Of course, that means squat for goin' faster.

Not sure the basis of perceived improvement, but after I changed the wheel, I definitely felt the bike is more lively on acceleration. It could be the weight reduction, it could also be the stiffer wheel. At the end of the day, it's good to be able to perceive an improvement in the bike after all the expenditure. As to whether it's scientific or not, that's for another day. 😄

rotational mass is a bit of a myth.

"dominant factor in wheel performance is aerodynamics. Wheel mass is a second order effect (nearly 10 times less significant) and wheel inertia is a third order effect (nearly 100 times less significant). http://www.biketechreview.com/archive/wheel_theory.htm

fast wheels are those that are rigid and aero, like these: 🙂
[img]epinions.compr Bike Parts Accessories Mavic Comete Rear Wheel Road Clincher resized200.jpgOpen ↗[/img]

1250g for one wheel!!!!

and let's not forget the heavy track bikes that are stiff and aero, weigh 18 to 20 pounds, yet have to be accelerated from 0 to 60kph as quickly as possible!
None of the bikes at the recent Track World Champs came close to the UCI's minimum weight of 6.8kg
http://www.cyclingnews.com/track/2006/apr06/wtc06/tech/?id=/tech/2006/features/track_worlds_bikes

If a lighter wheels flexes more, then it is slower in all situations, with the exception of big mountains. Some light wheels flex so much that they rub on the brakes!! Brake-rubbing aren't very fast! 🙂

as far as weight on hills goes, isn't it simple physics?
I guess the point is how much weight will be noticeable.

As far as accelerating a mass a flat ground goes, I guess that's slightly less simple physics. 🙂 Then I suppose there's a difference between accelerating from zero kph to a given speed, or from (say) 30kph to a given speed.

there's a well known coach around here who puts weighted vets on his athletes to let them feel how much a few kg of blubber slows them down.

Weight does matter. But only if it is lost in the right places. If you get a lighter frame which is much flexier than your old one (or wheels for that matter) alot of power will be lost making them flex, so even though it is lighter, you lose speed on a hill or in a sprint where it really matters. Also, if you get a light bike (i know this is negligible) which isn't aero, it will be harder to maintain a speed in real world conditions. If you want to lose weight where it matters, get lighter shoes or a tyre/tube set. I count the weight of my shoes when i am weighing my bike out of curiosity, as I believe they are a part of it, as it is very very difficult to ride without them on. I lost 300g from the shoes, 60g from the pedals, 130g from tyres/tubes for only $430, plus gaining stiffness and losing rolling resistance. That is the best value.

dhk2 said:

Believe you've got an error in the drag portion of your calculations. Drag force is a factor of cdA and v**2, not a constant. As a result, power to overcome drag is a function of the v**3, the cube of the velocity.

I know, don't pick on me too much! I seriously messed up friction by a factor of v there ... 😄

Anyway, you seem to be right, the approximation that a small percentage decrease in weight equals the same percentage increase in climbing speed is really good.

So out of all of the discussions of physics and flex and such.

The way to loose the most weight and thus gain the most speed is jaw surgery?

My copay on the surgury would be $125. Loose 23 pounds.
Upgrade bike $400. Loose 12 ounces.

alienator said:

Yup, you're right. If a person wants to shave weight off his bike, the first place to go is the wheels because that's where the biggest gains....er, weight losses.....are. In my recent wheel history, I went from Bontrager Race X Lites (veritable [censored] wheels) to a custom set with White Ind's new hubs, CX Ray spokes, and Alex Crostini 3.1/3.2 rims. In the process, I shaved about 250g off the bike weight. Then I bought a set of Reynolds Stratus DV tubies and shaved another 120g off. So in total, I lost 0.8 lbs. The only real performance difference that I notice is that once the pace gets goin' I can maintain a slightly higher speed w/ the Stratus DV's. Of course, that's an aero thing, not a weight thing.

The one place everyone notices weight loss on a bike is when they're climbing out of the saddle or sprinting. In both cases, you can feel the difference as you throw the bike back and forth. Of course, that means squat for goin' faster.

There's naught wrong with wanting to shave weight off the bike. I'm a gearhead/tech geek, and making my bike lighter while keeping it everyday useable was/is fun in a weird way. It's important though to keep in mind that any performance gains from dropping your bike's weight will be very small, at best.

+1 for Alienator

Having started this thread.....the bottom line is if you want to be a better climber have jaw surgery. 😄 LMAO!

bladegeek said:

Having started this thread.....the bottom line is if you want to be a better climber have jaw surgery. 😄 LMAO!

Or get chemotherapy.
I know one guy swear that was the best thing happened to him. He's pretty famous too.

Strid said:

One thing I don't know to make this more correct, what is a typical power output (watts) at, say, 40 km/h for a cyclist?

I think there is too much variation for there to be a typical power requirement but this page should give you something to work with. For the same cyclist and conditions it gives a range between 75 and 622 watts depending on the type of bike and body position.

I've gotta get this off my chest 🙂

I blame triathletes for introducing all this 'weight weeny' stuff. When i was racing in the late '80s, apart from the odd mention of Tour riders drilling out components for mountain stages, most of the chat about good equipment centered around stiffness, never weight. It was 'stiff this' and 'stiff that', or the 'smoothest and fastest hubs'. We even tied and soldered out wheels for more stiffness (I dunno if it worked). Then the flower pot heads came along (triathletes were smart enough to wear helmets before we did 🙂), and they were the first dudes I heard obsessing about bike weight.

531Aussie said:

I've gotta get this off my chest 🙂

I blame triathletes for introducing all this 'weight weeny' stuff. When i was racing in the late '80s, apart from the odd mention of Tour riders drilling out components for mountain stages, most of the chat about good equipment centered around stiffness, never weight. It was 'stiff this' and 'stiff that', or the 'smoothest and fastest hubs'. We even tied and soldered out wheels for more stiffness (I dunno if it worked). Then the flower pot heads came along (triathletes were smart enough to wear helmets before we did 🙂), and they were the first dudes I heard obsessing about bike weight.

I put stiffness and durability long before weight. I'd rather have a stiff, well fitting traditional geometry frame, than a cheap, ill fitting compact carbon thing that weighs 400g less. I could lose that 400g in a week with a little effort.

If you want to test it try this:
1) Get a heart rate monitor.
2) Do a hill course for 1 hr keeping your heart rate constant.
3) Record how far you got

4) Repeat 1 to 3 above with a weight on your bike.

Compare the results. The theory is heart rate is a proxy for energy consumption.

BTW, the extra 10lb probably means little if you already weigh alot say over 200lb. In that case spend the extra money on hubs/BB/tires/rims.

bobbyOCR said:

I put stiffness and durability long before weight. I'd rather have a stiff, well fitting traditional geometry frame, than a cheap, ill fitting compact carbon thing that weighs 400g less. I could lose that 400g in a week with a little effort.

yeah, that's why Columbus starting taking over Relynolds in the lates 80s, because riders wanted the stiffness of SLX and MAX, etc; even though this stuff was usually heavier than 531

geo8rge said:

If you want to test it try this:
1) Get a heart rate monitor.
2) Do a hill course for 1 hr keeping your heart rate constant.
3) Record how far you got

4) Repeat 1 to 3 above with a weight on your bike.

Compare the results. The theory is heart rate is a proxy for energy consumption.

BTW, the extra 10lb probably means little if you already weigh alot say over 200lb. In that case spend the extra money on hubs/BB/tires/rims.

Sounds kind of complicated. I'd trust the math... F = ma, E = Fd, and P = E/t. In other words, it takes x% more force to accelerate x% more mass. It takes x% more energy to lift x% more mass up a hill. And if your power output doesn't change, it'll take you x% less time to climb a hill.

Just remember that the mass (and change of mass) is for the whole system which includes you, your bike, the water bottles, the clothes you're wearing, etc, etc.

All this neglects air resistance of course, but it is much, much better than an order of magnitude calculation and way more accurate than that heart rate thingy.

John Swanson
www.bikephysics.com

ScienceIsCool said:

Sounds kind of complicated. I'd trust the math... F = ma, E = Fd, and P = E/t. In other words, it takes x% more force to accelerate x% more mass. It takes x% more energy to lift x% more mass up a hill. And if your power output doesn't change, it'll take you x% less time to climb a hill.

Just remember that the mass (and change of mass) is for the whole system which includes you, your bike, the water bottles, the clothes you're wearing, etc, etc.

All this neglects air resistance of course, but it is much, much better than an order of magnitude calculation and way more accurate than that heart rate thingy.

John Swanson
www.bikephysics.com

+1

Measuring heart rate with that method has way too many uncontrollable veriables which render the results inaccurate. The maths is more accurate,