Author Topic: Ideal bike weight as a percentage of body weight?  (Read 4773 times)

Ideal bike weight as a percentage of body weight?
« on: June 05, 2017, 11:13:34 pm »
As a tall and lean but relatively heavy rider of 185lbs I was wondering if there is any wisdom, perceived or proven, on the ideal percentage weight of a bike with respect to that of the rider? 
Most of the stuff I say is true because I saw it in a dream and I don't have the presence of mind to make up lies when I'm asleep.   Bryan Andreas

Re: Ideal bike weight as a percentage of body weight?
« Reply #1 on: June 05, 2017, 11:17:21 pm »
Perceived wisdom is lower is better. At 178lbs a 16lb bike feels different to a 19.4lb bike, but not sure the weight actually makes any real speed difference. Riding position does however.

Re: Ideal bike weight as a percentage of body weight?
« Reply #2 on: June 05, 2017, 11:42:57 pm »
Perceived wisdom is lower is better. At 178lbs a 16lb bike feels different to a 19.4lb bike, but not sure the weight actually makes any real speed difference. Riding position does however.
Thanks, that's reassuring in that my position is good but less so in that my all up bike weight is ~36lbs :o
Most of the stuff I say is true because I saw it in a dream and I don't have the presence of mind to make up lies when I'm asleep.   Bryan Andreas

T42

  • Gaulois réfractaire
Re: Ideal bike weight as a percentage of body weight?
« Reply #3 on: June 06, 2017, 10:13:13 am »
Total weight matters - take it ad absurdum and imagine pedalling a 100 kg bike up a 20% hill. But it's more the strength of the bike that matters. The rider-weight limit for my carbon bike is 100 kilos, which is something like 220 lb.

From the weight, I'd guess that your current bike would be a steel tourer or MTB. You'd probably be fine on a carbon butterfly weighing half as much.

There is a rule of thumb re rider weight vs tyre pressure, which goes pressure in bars = 1/10 rider weight in kilos, to the limit of the manufacturer's spec.
I dare eat all that may become a man.

But hold the oysters.

Re: Ideal bike weight as a percentage of body weight?
« Reply #4 on: June 06, 2017, 10:22:53 am »
There is a rule of thumb re rider weight vs tyre pressure, which goes pressure in bars = 1/10 rider weight in kilos, to the limit of the manufacturer's spec.
15% deflection is a much better rule of thumb, if a tad difficult to measure.
<i>Marmite slave</i>

citoyen

  • Cat 6 Racer
Re: Ideal bike weight as a percentage of body weight?
« Reply #5 on: June 06, 2017, 10:58:50 am »
Based on the 6.8kg lower bike weight limit for pro racers, and the reported weights of riders:

For Dumoulin (71kg) the bike is a bit over 9% of overall weight.
For Quintana (58kg), it's under 11%.

How much of a difference does that make? Is Quintana unfairly penalised by the UCI bike weight limit? Or does that actually work in his favour?

Re: Ideal bike weight as a percentage of body weight?
« Reply #6 on: July 07, 2017, 07:33:50 am »
 
Perceived wisdom is lower is better. At 178lbs a 16lb bike feels different to a 19.4lb bike, but not sure the weight actually makes any real speed difference. Riding position does however.
Thanks, that's reassuring in that my position is good but less so in that my all up bike weight is ~36lbs :o

That's some bike. My Dutch (Gazelle Impala) upright was 39lbs



I used it to commute through York (flat) - it was good training especially with a strong headwind.


Sic transit and all that..

Re: Ideal bike weight as a percentage of body weight?
« Reply #7 on: July 07, 2017, 09:53:23 am »
What advantages derive from greater bike weight as opposed to greater stiffness, strength? I can't think of any, apart from training.
The earth is vast and beautiful and contains many miraculous places. (Chekhov)

Re: Ideal bike weight as a percentage of body weight?
« Reply #8 on: July 07, 2017, 10:02:08 am »
Perceived wisdom is lower is better. At 178lbs a 16lb bike feels different to a 19.4lb bike, but not sure the weight actually makes any real speed difference. Riding position does however.

My bike weight as a percentage of body weight is reducing at an all too alarming rate.

 :'(

What advantages derive from greater bike weight as opposed to greater stiffness, strength? I can't think of any, apart from training.

Momentum? I think the benefits come more for utility cycling... I find a heavier bike much more pleasant in windy conditions - lighter bikes (even with similar geometry) always feel a bit skittish.

As long as the distances are relatively small and there are no bastard hills, heavy bikes can be quite pleasing.

I'm not sure for 'proper' cycling there are any particular advantages beyond stiffness, strength, durability and training.

Re: Ideal bike weight as a percentage of body weight?
« Reply #9 on: July 07, 2017, 10:11:32 am »
Stability in wind is a good point. I'm not sure about momentum, as inevitably you never gain quite as much on the downhill as you lose on the uphill.

I'm not sure for 'proper' cycling there are any particular advantages beyond stiffness, strength, durability and training.
I'm trying to isolate stiffness, strength, durability from weight. They depend on materials and construction too. So if you have two bikes of identical stiffness etc but one weighs say 9kg and the other 14.
The earth is vast and beautiful and contains many miraculous places. (Chekhov)

Re: Ideal bike weight as a percentage of body weight?
« Reply #10 on: July 07, 2017, 11:24:58 am »
What advantages derive from greater bike weight as opposed to greater stiffness, strength? I can't think of any, apart from training.

Lower cost?

Samuel D

Re: Ideal bike weight as a percentage of body weight?
« Reply #11 on: July 07, 2017, 10:29:38 pm »
Based on the 6.8kg lower bike weight limit for pro racers

Most bicycles in the pro peloton are well over the UCI weight limit (here’s an 8 kg example before adding computers, transponders, etc.). That’s because grams that avocational riders obsess over do not matter even to pro racers.

If you do the calculations, even rotational mass at the periphery of the wheel (that counts double during accelerations) makes a typically trivial difference. The energies involved are negligible compared to a typical cyclist’s power. Nonetheless, people convince themselves that ‘light’ wheels, that weigh maybe 200 g less than ‘heavy’ wheels, are nothing less than transformative. I think this happens because there is a noticeable difference in inertia when the handlebars are quickly rotated through a large arc at walking speeds. In this unconscious test, the lighter wheel feels more nimble, responsive, agile, quick, etc. – all those words that bicycle reviewers use when they should be saying something important.

The magic of the wheel is that it takes the work out of carrying weight.

I don’t think a bicycle should weigh some proportion of its owner’s weight. Rather, it should be built for its intended purpose. If that is a lifetime of being thrown around bike racks and left outdoors in the rain with maintenance every decade whether needed or not, you end up with Dutch-bike weights. If it’s one season of racing, you end up with something pretty light.

But even if you’re racing, a comfortable saddle will probably make more difference than saving 100 g. And 400 g pedals with ball bearings are certainly faster over most courses than ultra-light pedals with plain bearings, despite the latter (plastic bushings) being the default choice on road bikes these days.

When I chose a set of components for a long life of solo rides, enjoyable blasts in fast groups, and a bit of practical transport, I ended up with something around 10 kg. For me, that’s a benchmark of sorts. Much below 10 kg leads to compromises I’m unwilling to make, and even the lightest machines are not usefully faster. Much above 10 kg gains me little in function and makes carrying the bicycle up the five flights of stairs to my flat needlessly hard work.

Some interesting weights are quoted here.

Re: Ideal bike weight as a percentage of body weight?
« Reply #12 on: July 08, 2017, 12:18:14 am »
Samuel, thanks for these wise words that help articulate the relationship between between weight, function, reliability and speed.  Since my original post I felt compelled to reduce the weight of my bike following during a 5 day tour in preparation for LEL where every other rider told me I was mad for riding such a heavy bike, even though I was able to complete every climb and finish each day's ride in comfort when others riding modern lightweight road bikes were not.  The "unconscious" improvements following the 1.2kg weight reduction are exactly as you describe whereas the coincidental improvements that have been made through the use of better pedals, forks, tyres and riding position are measurably significant at the expense of a small amount of comfort.  The only thing left to consider now having watched the video you linked on Marcel Kittel's bike is whether to swap out my 31.8 seatpost for a 27.2 , is the difference in comfort really noticeable?
Most of the stuff I say is true because I saw it in a dream and I don't have the presence of mind to make up lies when I'm asleep.   Bryan Andreas

Samuel D

Re: Ideal bike weight as a percentage of body weight?
« Reply #13 on: July 08, 2017, 09:34:12 am »
Differences in seatposts have not made any difference in comfort to me, although I only weigh 66 kg. I’ve tried narrow and fat, carbon and aluminium, all with no perceptible difference (different forks or cranks, on the other hand, have made a clear difference). Anyway, how can you change the seatpost diameter without buying a new frame?

Cyclists believe extraordinary things about bicycle weight. Like you, I’ve been told I’m hampering myself by riding a heavy bicycle – except in my case, mine was about 10 kg and theirs was about 8 kg! (But theirs were carbon, with all the alleged magical properties of that material.) This was shortly before a long climb out of a café where I put in an effort to make a point, dropping three-quarters of the commentators, all of whom were racers.

For steep climbs, the maths is simple: speed equals power divided by all-up weight. In your case, the all-up weight was around 220 lb. Therefore each pound lost (around that weight) produces a speed increase of less than half of one percent. It doesn’t matter where the pound is lost from: belly, frame, or wheel rim. On most hills, where aerodynamic drag and rolling resistance still play a role, the difference is even less than that. And on the flat, the difference is for all practical purposes exactly nil.

Re: Ideal bike weight as a percentage of body weight?
« Reply #14 on: July 08, 2017, 09:50:41 am »
What advantages derive from greater bike weight as opposed to greater stiffness, strength? I can't think of any, apart from training.

Greater momentum == easier to keep a constant speed on the flat ?  I'm just trying to guess something, without the slightest bit of a scientific evidence!

Re: Ideal bike weight as a percentage of body weight?
« Reply #15 on: July 08, 2017, 08:14:14 pm »
Anyway, how can you change the seatpost diameter without buying a new frame?
I've actually shimmed in a 27.2 seatpost previously when I've been trying out different saddles but never considered that it might introduce a bit more comfort, I certainly didn't notice any difference.  Having got my saddle set up perfectly now I'm reluctant to swap the seatpost especially as  saddle comfort is extremely good.
Most of the stuff I say is true because I saw it in a dream and I don't have the presence of mind to make up lies when I'm asleep.   Bryan Andreas

Re: Ideal bike weight as a percentage of body weight?
« Reply #16 on: July 08, 2017, 08:34:34 pm »
I'd no qualms about doing the Raid Pyrennean on a 23lb steel bike with saddle bag and mudguards. 

They laughed at my set up but at least the mudguards meant I was able to descend the Tourmalet in a freezing torrential downpour when the others were walking.  Apparently there was no hot water left at the hotel by the time they arrived.   
Sic transit and all that..

Re: Ideal bike weight as a percentage of body weight?
« Reply #17 on: July 10, 2017, 06:51:30 pm »
lighter feels much nicer and is a bit faster uphill. every time i set off for a long ride with all the luggage/electronics/bottles attached it feels demoralising initially - so heavy, unresponsive and road irregularities are more jarring with almost double unsprung weight!! setting off for a training ride with all the bits removed it just floats over the road and feels like an extension of myself - pure joy.
as long as the bike is well put together from reliable components i don't see why heavier could be better - it's very easy to add weight.

dim

Re: Ideal bike weight as a percentage of body weight?
« Reply #18 on: October 02, 2017, 09:20:46 am »
I'm busy building a 1981 steel framed Koga Miyata Full Pro that I am using as my daily commuter and which I will use for some shorter Audax rides

It should weigh approx 8.5kg when it's completed (currently weighs 10kg but the wheels are close to 1.9kg) .... I'm changing the groupset to Dura Ace 7800 with the Dura Ace 7900 compact crankset and will possibly fit carbon forks

from what I have read, if a steel framed bike with steel forks weighs less than 8kg, chances are that the frame will be very flexi ....

Carbon on the other hand is different

so, I would not say that bike weiht should be a percentage of body weight .... what does matter is the wheels though .... heavier rider needs more spokes
“No great mind has ever existed without a touch of madness.” - Aristotle

Karla

  • car(e) free
    • Lost Byway - a Pacific bike ride
Re: Ideal bike weight as a percentage of body weight?
« Reply #19 on: October 02, 2017, 09:50:28 am »
Based on the 6.8kg lower bike weight limit for pro racers

Most bicycles in the pro peloton are well over the UCI weight limit (here’s an 8 kg example before adding computers, transponders, etc.). That’s because grams that avocational riders obsess over do not matter even to pro racers.

That's Marcel Kittel's bike.  He's an 86kg power sprinter FFS.  A less weight-focussed rider you could hardly have picked. 

Samuel D

Re: Ideal bike weight as a percentage of body weight?
« Reply #20 on: October 02, 2017, 10:44:59 am »
I think you’re mistaken. Sprinting is all about the ‘jump’, i.e. acceleration. A good jump gets you on the right wheel or prevents your opponent from getting on yours. Races are very often lost by less than half a bicycle length.

Of the various categories of cyclist, only climbers should be more concerned than sprinters about weight.

However, pro racers labour under the same misconceptions about weight as the rest of us. Abrupt steering movements feel light, ergo the bicycle is quick. It’s an easy one to fall for if you don’t understand the physics to put the numbers in perspective.

Besides, plenty of weekend cyclists weigh 86 kg and think a lighter bicycle would help them keep up with their group. When you tell them they could save 50 watts by wearing a jersey two sizes smaller and drafting on the leeward side, they think you’re exaggerating! People believe the funniest things.

Karla

  • car(e) free
    • Lost Byway - a Pacific bike ride
Re: Ideal bike weight as a percentage of body weight?
« Reply #21 on: October 02, 2017, 11:20:44 am »
No I'm not mistaken. 

Marcel Kittel puts out 4 figure powers during his sprints, so he needs a bike built to cope with that.  He rides a Specialized Venge, which was originally designed with another sprinter - Mark Cavendish - in mind.  On any mountain stages, Kittel isn't vastly concerned with weight because he he's not contesting for a win or even a placing, just to get round within the cutoff. 

Quickstep's GC man Dan Martin doesn't ride the Venge, he rides Specialized's lightweight bike, the Tarmac.
 
An 86 kg weekend warrior will be putting out a tenth of the power, and doesn't need a Venge, but does need all the help they can get from a light bike. 

citoyen

  • Cat 6 Racer
Re: Ideal bike weight as a percentage of body weight?
« Reply #22 on: October 02, 2017, 11:30:29 am »
In Kittel's case, the rationale will be that stiffer and more aerodynamically efficient frame and wheels are of more benefit in a sprint than lower weight - the thinking will be that the 'jump' can be more effectively achieved by more efficient power transfer and reduced drag than by reducing the overall bike weight. (I make no claims as to the correctness or otherwise of this way of thinking.)

If you weigh under 60kg and can put out ~400 watts on a ~10% climb for several km, the difference between a 6.8kg bike and an 8kg+ bike might be noticeable. I would wholly agree that for a typical Sunday rider weighing 86kg, a lighter bike will make no practical difference at all.

quixoticgeek

  • Mostly Harmless
Re: Ideal bike weight as a percentage of body weight?
« Reply #23 on: October 02, 2017, 11:43:39 am »
In theory it's pretty simple, for a given input of power, speed will be directly proportional to all up weight (rider+bike). Assuming that friction (air and road) remains constant between the two. So if you are putting out 200W, and you plus bike == 100kg, then you will have a speed of x, if you plus bike =80kg and you're putting out 200w, then your speed will be proportionally greater than x.

Where this becomes more complex tho is that aero drag represents a far bigger factor about your speed than bike weight. I often see Dutch bikes with clip on aero bars. They may weigh 25kg, with a 80kg Dutchman on, but in the Omnidirectional headwind, those bars make a significant difference. It's also worth noting that aero drag effects things based on a cube root or some such (no doubt Kim will be long shortly to correct me), so an improvement in your frontal area by x, will have a much more significant impact as a proportion, than a similar change in weight...

Then of course we get to the fun of rotating mass. On my Brompton riding next to a friend on an Omafiets, I notice that my small wheels have less inertia than hers, meaning that if I stop pedaling and coast, I slow much faster than she does. Useful as I'm a faster rider so I can moderate my speed by lifting off for a second...

For anything other than a city bike, I'd question how exactly you get to something that weighs over 15kg. Even an all steel Genesis Croix De Fer is only 11.5kg. Add on a pair of mud guards and racks, and you're still gonna be under the 14kg mark...

Will a lighter bike be faster/easier to ride? Probably. Are there other things you can do that are cheaper and with better gains, probably. Does this mean you shouldn't treat yourself to a lighter bike? Only if you can afford it...

J

PS Conversion of metric to funny units is left as an exercise for the reader.
--
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Re: Ideal bike weight as a percentage of body weight?
« Reply #24 on: October 02, 2017, 12:01:58 pm »
In theory it's pretty simple, for a given input of power, speed will be directly proportional to all up weight (rider+bike). Assuming that friction (air and road) remains constant between the two.

No. With that assumption that air/road friction is the same between the two then the speed would be the same. It would just take the heavier rider slightly longer to get up to same speed.

On the flat you stop accelerating when the input power is being used completely to overcome friction (air and road), so if that friction is the same between two riders then the same input power will result in the same terminal speed. It's only on the way up to that speed (accelerating) when the mass of the rider is relevant and means more work (power * time) is required to get the heavier rider up to that speed.

So if you are putting out 200W, and you plus bike == 100kg, then you will have a speed of x, if you plus bike =80kg and you're putting out 200w, then your speed will be proportionally greater than x.

Again, not on the flat. And talking about "proportionally greater" doesn't really make sense here, you'd probably say "speed would be inversely proportional to weight" but that's still not accurate given the complexities involved.

Where this becomes more complex tho is that aero drag represents a far bigger factor about your speed than bike weight.

Yes, and aero drag will be significantly higher for a typical 100kg rider than for a typical 86kg rider.

So, on the flat, an 86kg rider putting in 200W will generally go faster than a 100kg rider putting in 200W if they have a similar approach to aerodynamics (clothing/setup/equipment/etc).

However, a 100kg rider will typically be able to put in more power at a certain exertion level than a 86kg rider at the same exertion level, purely because the heavier rider weighs more and their muscles are used to supporting that heavier bodyweight. (Again, it's possible for lighter riders to be more efficient and more powerful than heavier riders, etc).
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