Can wheels be too light? Whats the optimum weight?

Nick Fitt

I was reading a wheel review and the reviewer stated they were light but that "speed isnt quite as easily maintained as with a heavier rim" (Cycling weekly 9-20th ZIPP202, 1370gms).

I'd never really thought of wheels being able to be so light they don't hold speed, if so, that means there must be an optimum weight, anyone know what it is?

Might save a fortune if its 1700gms :shock:

ugo.santalucia

I wouldn't give much relevance to magazines reviews... they are not made by experts, they are not made by real journalists either... they have to fill the pages and sometimes in addition to the photos, some words are needed... when they make sense, take it as a coincidence

geebee2

It's nonsense - wheels cannot be too light.

I'm a heavy rider - which means I come down hills very fast. But any advantage from that is of course more than compensated by the extra effort I have to make when climbing a hill.

Similarly, if I stop pedalling on the flat, I will keep going for longer than a light rider, but I have to expend more energy to get up to speed.

Now, for a rider, there is a trade off - more weight can mean more muscle, and more power output. But for a wheel, it's dead weight, it makes no contribution.

All this is assuming similar mechanical and aerodynamic properties for the two wheels being compared. If the heavier wheel is more aerodynamic or stiffer, the extra weight could be justified.

Grill

Less rotational mass a bad thing? Hardly. Speed is more easily maintained in certain conditions with aero wheels which are generally heavier than their non-aero counterparts, but crosswinds can always ruin that plan.

turnerjohn

Grill wrote:

Less rotational mass a bad thing? Hardly. Speed is more easily maintained in certain conditions with aero wheels which are generally lighter than their non-aero counterparts, but crosswinds can always ruin that plan.

...aero wheel generally heavier didn't you mean ?!
Agree with you...heavier wheels have that rotational effect which once your up to speed is faster then a lighter wheel. Add in aero benefits and your on a winner. Not all wheels are created equally tho so some heavy wheels actually ride far lighter then they actually are. Obviously there is some balance of the two...Pro's change the wheels to suit the course.

Grill

turnerjohn wrote:

Grill wrote:

Less rotational mass a bad thing? Hardly. Speed is more easily maintained in certain conditions with aero wheels which are generally lighter than their non-aero counterparts, but crosswinds can always ruin that plan.

...aero wheel generally heavier didn't you mean ?!
Agree with you...heavier wheels have that rotational effect which once your up to speed is faster then a lighter wheel. Add in aero benefits and your on a winner. Not all wheels are created equally tho so some heavy wheels actually ride far lighter then they actually are. Obviously there is some balance of the two...Pro's change the wheels to suit the course.

Yup, fixed! :oops:
A bit early for a Sunday...

thiscocks

Optimum weight is 2,150g

MichaelW

geebee2 wrote:

I'm a heavy rider - which means I come down hills very fast. But any advantage from that is of course more than compensated by the extra effort I have to make when climbing a hill.

Do heavier riders descend faster than lighter weight riders? I recall an experiment filmed on the moon where a feather fell at the same rate as a hammer.

Grill

Yup. I've lost speed on descents since I've lost a lot of weight. I cane the uphills only to be reeled in on the way down by the bigger guys.

ugo.santalucia

MichaelW wrote:

geebee2 wrote:

I'm a heavy rider - which means I come down hills very fast. But any advantage from that is of course more than compensated by the extra effort I have to make when climbing a hill.

Do heavier riders descend faster than lighter weight riders? I recall an experiment filmed on the moon where a feather fell at the same rate as a hammer.

Shame the experiment only works in the absence of air... heavier objects have a higher momentum (or kinetic energy if you prefer to see it this way) and are more efficient at displacing the fluid (air). That is counteracted by their size and exposed surface, but as the body scales in a fashion that a heavy guy is not much larger than a normal one (but significantly heavier), then heavier riders have an advantage going downhill (or keeping the momentum going).
In the case of wheels the same might apply, but 200 grams difference won't make any difference in the real world as the rider+ bike combo weighs easily 100 Kg... hence you are talking a 0.2% increase. There is the flywheel effect, but even so...

Nick Fitt

ugo.santalucia wrote:

MichaelW wrote:

geebee2 wrote:

I'm a heavy rider - which means I come down hills very fast. But any advantage from that is of course more than compensated by the extra effort I have to make when climbing a hill.

Do heavier riders descend faster than lighter weight riders? I recall an experiment filmed on the moon where a feather fell at the same rate as a hammer.

Shame the experiment only works in the absence of air... heavier objects have a higher momentum (or kinetic energy if you prefer to see it this way) and are more efficient at displacing the fluid (air). That is counteracted by their size and exposed surface, but as the body scales in a fashion that a heavy guy is not much larger than a normal one (but significantly heavier), then heavier riders have an advantage going downhill (or keeping the momentum going).
In the case of wheels the same might apply, but 200 grams difference won't make any difference in the real world as the rider+ bike combo weighs easily 100 Kg... hence you are talking a 0.2% increase. There is the flywheel effect, but even so...

On a bike, where the engine is the human (arguably!) the flywheel effect would matter at the cranks wouldn't it? I cant see how lighter wheels can lose speed tbh. I think even more so in a group of riders or, on a climb. I can see aero wheels easily maintaining a constant for longer. The loss of speed surely is down to aero and quality of rotating bits, bearings etc?...

mallorcajeff

is there any correlation on the subject when you look at turbo trainers the cheaper ones have a 1k fly wheel weight the more exp ones have a 2k weight for a more realistic feel?

Valy

Lighter wheels require less force to get up to the same rotational speed - so they feel snappier.

As for an ideal weight - yeah hear d a few things on some wheels feeling too light but it's probably entirely subjective - could be caused by going from say a 1500g wheelset to a 1000g one - it may feel like they accelerate too quickly for the rider to keep constant pressure on the pedals or something.

drlodge

Nick Fitt wrote:

I was reading a wheel review and the reviewer stated they were light but that "speed isnt quite as easily maintained as with a heavier rim" (Cycling weekly 9-20th ZIPP202, 1370gms).

That would be true if you're a heavy rider on ultra light wheels..they'd buckle and stop you dead in your tracks!

styxd

You cant really have a wheel thats too light.

But you can have a light wheel that might be too flexy or have the wrong aerodynamics or a poor ride quality etc. etc.

Nick Fitt

There is a new cycling mag out called Cycling(!), this has some interesting views on weight v performance. It seems that mainly aerodynamics seems to be the big earner. On flat at a constant speed, weight is not relevant, least not as relevant as aerodynamics

Grill

Yeah, that's been mentioned many times. Ever tried climbing with a disc wheel?

jibberjim

MichaelW wrote:

Do heavier riders descend faster than lighter weight riders? I recall an experiment filmed on the moon where a feather fell at the same rate as a hammer.

Heavier riders do generally descend faster than lighter riders given the same skill levels etc. in real world situations. Yes where the only force is gravity on an inclined plane the weight is irrelevant.

However, in the real world, there are places where the road flattens or goes uphill, where there are corners you need to accellerate out of etc. If the road flattens then the higher inertia of the heavier rider will mean less speed is lost by the time the descent is resumed, also, because the heavier rider has more power (in general of course) then with aerodynamics being the dominant resistence and w/cda scaling differently to w/kg when they are pedalling the heavier rider will almost certainly be accellerating more than the lighter.

Against that of course you have to look at the cornering forces and the larger amount of braking needed and the extra power needed to accellerate the heavier mass (which will be the same from gravity but most people pedal)

So it's not as simple as your experiment.

geebee2

MichaelW wrote:

geebee2 wrote:

I'm a heavy rider - which means I come down hills very fast. But any advantage from that is of course more than compensated by the extra effort I have to make when climbing a hill.

Do heavier riders descend faster than lighter weight riders? I recall an experiment filmed on the moon where a feather fell at the same rate as a hammer.

Basically yes, because extra weight means extra downward force, which makes you go faster (when going downhill).

The extra weight will mean a slightly bulkier body (= more air resistance) but this is not very significant compared to the extra force.

Take it from me - on club rides, I can be free-wheeling away from a light rider on a downhill, even though he is pedalling furiously to try and keep up!

But of course, I have to work much harder when going uphill, and here the extra weight loses me much more than I gain on the downhills. I'm trying hard to lose weight!

deadfall

geebee2 wrote:

MichaelW wrote:

geebee2 wrote:

I'm a heavy rider - which means I come down hills very fast. But any advantage from that is of course more than compensated by the extra effort I have to make when climbing a hill.

Do heavier riders descend faster than lighter weight riders? I recall an experiment filmed on the moon where a feather fell at the same rate as a hammer.

Basically yes, because extra weight means extra downward force, which makes you go faster (when going downhill).

Wrong. The acceleration due to gravity will be the same for two different masses. F= mg, and g is constant. The extra downward force goes into kinetic energy, not velocity.

The kinetic energy will serve a heavier rider when he/she encounters a new negative force as it's effect will retard their velocity less than a lighter rider. But over the full course, both riders power being equal, the lighter rider will be faster.

sungod

deadfall wrote:

Wrong. The acceleration due to gravity will be the same for two different masses. F= mg, and g is constant. The extra downward force goes into kinetic energy, not velocity.

The kinetic energy will serve a heavier rider when he/she encounters a new negative force as it's effect will retard their velocity less than a lighter rider. But over the full course, both riders power being equal, the lighter rider will be faster.

wrong

you are not allowing for aerodynamic drag

in a vacuum, two spheres, each 1 metre diameter, one with mass 1g and one with mass 100kg, will roll down an inclined plane at the same speed

but at normal atmospheric pressure, the heavier sphere will roll down a *lot* faster

same applies to people on bikes

geebee2

deadfall wrote:

geebee2 wrote:

MichaelW wrote:

geebee2 wrote:

I'm a heavy rider - which means I come down hills very fast. But any advantage from that is of course more than compensated by the extra effort I have to make when climbing a hill.

Do heavier riders descend faster than lighter weight riders? I recall an experiment filmed on the moon where a feather fell at the same rate as a hammer.

Basically yes, because extra weight means extra downward force, which makes you go faster (when going downhill).

Wrong. The acceleration due to gravity will be the same for two different masses. F= mg, and g is constant. The extra downward force goes into kinetic energy, not velocity.

The kinetic energy will serve a heavier rider when he/she encounters a new negative force as it's effect will retard their velocity less than a lighter rider. But over the full course, both riders power being equal, the lighter rider will be faster.

When a rider is going fast downhill, the two main forces are gravity and air resistance.

Terminal velocity is reached when these forces are equal.

Air resistance is largely independent of the weight of bike and rider ( a lighter rider or bike may be slightly more aerodynamic, but the difference is marginal ).

Therefore terminal velocity for the heavier bike/rider combination will be greater - so the heavy bike/rider will go down hill faster.

Nick Fitt

Grill wrote:

Yeah, that's been mentioned many times. Ever tried climbing with a disc wheel?

Good point, but, it depends on what you mean by climbing. Assuming Alps then course not, assuming a sporting 10 or 25 then the value of a disc on the flat will out run the negatives of 'climbing' on the hills. Looking at all round race wheels, weight is less on an issue if the wheel is aero tuned, and lets be honest most of our UK 2,3,4 racing is not exactly on mountainous circuits! so surely aero bias is better than weight bias (within reason, mainly cost versus reality)

Interestingly on the aero theme the introduction of disc brakes is down to getting breaks off of the rims so the rims can be lighter and more aero. Which makes sense but, I wonder if the disc itself which is not aero tuned is nullifying the aero improvements at the rim? This all going to get well out of hand! :shock:

Ron Stuart

I guess this post was always going to throw up a huge amount of pseudo science and it sure has