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Why We Should STOP Our Obsession With Bike Weight

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Why We Should STOP Our Obsession With Bike Weight

Old 07-06-21, 07:38 AM
  #126  
The Chemist
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My bike is about 15kg and I've never once thought that I need a lighter bike. Prioritizing weight over durability just doesn't make a lot of sense to me.
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Old 07-06-21, 07:41 AM
  #127  
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Originally Posted by PeteHski View Post
For example I'm doing a 100 mile ride this weekend with around 4k elevation change. Predicted finishing time at my average endurance power is 7 hrs 35 mins. If I drop my bike weight by 2 kg the model predicts a saving of 4 mins. That's with 4k of vertical climbing! Running the same calculation on a much flatter 100 mile course, I would gain just over 30 seconds with the 2kg lighter bike. Basically nothing worth spending any money on.
I'm intrigued.. is there a bike calculator out there where you load a course/TCX and input an average wattage and bike weight characteristics to get an estimated time result specific to that course?
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Old 07-06-21, 08:07 AM
  #128  
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Originally Posted by The Chemist View Post
My bike is about 15kg and I've never once thought that I need a lighter bike. Prioritizing weight over durability just doesn't make a lot of sense to me.
What if the lighter bike is just as durable? Just because it's light, doesn't mean it's fragile. Just because it's heavy doesn't mean it's tougher.
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Old 07-06-21, 09:14 AM
  #129  
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Originally Posted by Sy Reene View Post
I'm intrigued.. is there a bike calculator out there where you load a course/TCX and input an average wattage and bike weight characteristics to get an estimated time result specific to that course?
Best Bike Splits. It's very accurate once you calibrate your aero drag against a few real life rides. Can also input precise weather data as a forecast before the event and in retrospect later. It typically predicts my finish times over 100 mile courses to within a minute or two when I go back and input my actual power figures and weather data. But I use it mainly for pacing as it shows live power targets on my Garmin during a ride.
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Old 07-06-21, 09:25 AM
  #130  
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Originally Posted by asgelle View Post
You need to adjust your mental model. Rolling resistance depends linearly on weight so even on flat ground, a lighter bike will be faster due to the decrease in rolling resistance. (Yes, the difference may be small, but conceptually, weight matters even on flat terrain.)
I'm not using a mental model. I'm using an accurate detailed physics model which takes into account rolling resistance with weight. This predicts that bike weight is only really significant when there is a lot of climbing involved and even then it's not a huge difference. So I don't worry about 1 or 2kg of bike weight. My current carbon endurance road bike is 8.8 kg with pedals, bottle cages, computer etc. A very expensive and more race focused bike would get me down to around 7 kg with pedals etc, but would probably sacrifice some of the comfort I prefer on longer rides. So the gains are very marginal at this level. Something like a Specialized Aethos would provide some realistic time gains on a long day of climbing in the Alps, but very little over my local routes.
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Old 07-06-21, 09:27 AM
  #131  
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Originally Posted by pgjackson View Post
What if the lighter bike is just as durable? Just because it's light, doesn't mean it's fragile. Just because it's heavy doesn't mean it's tougher.
Light, durable, cheap. You can only pick 2 of those 3 things on one bike.
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Old 07-06-21, 09:48 AM
  #132  
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Originally Posted by pgjackson View Post
All other things being equal, wouldn't you prefer a lighter bike than a heavier bike?
If you assume away the costs, then it's a no-brainer.
When are all other things equal, though? It doesn't really have anything to do with reality where weight choices will likely affect the prices and perhaps functionality of the bike and parts.
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Old 07-06-21, 10:00 AM
  #133  
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Originally Posted by asgelle View Post
You need to adjust your mental model. Rolling resistance depends linearly on weight so even on flat ground, a lighter bike will be faster due to the decrease in rolling resistance. (Yes, the difference may be small, but conceptually, weight matters even on flat terrain.)

I'm riding a bike, not a concept. How does that refute "the difference is too small for me to care about"?
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Old 07-06-21, 10:44 AM
  #134  
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Originally Posted by pgjackson View Post
All other things being equal, wouldn't you prefer a lighter bike than a heavier bike?
Depends on the bikes and the ride, though I suppose that's covered in "all other things being equal". I certainly wouldn't intentionally make my bike HEAVIER for no other reason than simply making it heavier.
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Old 07-06-21, 10:48 AM
  #135  
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My bike has effectively gotten lighter relative to the current crop with disc brakes, electronic shifting, big tires, etc..

The bicycle obesity epidemic...
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Old 07-06-21, 10:48 AM
  #136  
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Originally Posted by genejockey View Post
Depends on the bikes and the ride, though I suppose that's covered in "all other things being equal". I certainly wouldn't intentionally make my bike HEAVIER for no other reason than simply making it heavier.
Well, it has been suggested that a heavier bike is inherently more durable.
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Old 07-06-21, 11:02 AM
  #137  
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Originally Posted by pgjackson View Post
Well, it has been suggested that a heavier bike is inherently more durable.
No, it hasn't.

What is true is that a heavier bike can be made more durable, especially at a given price point.

Can be != Always is


​​​​​
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Old 07-06-21, 11:08 AM
  #138  
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Originally Posted by pgjackson View Post
Well, it has been suggested that a heavier bike is inherently more durable.
If you are a bike designer you will always be trading off weight vs durability within the constraints of your budget, however high or low that may be. So in that sense a heavier bike (of the same design and materials) will be more durable than a lighter bike. Obviously you can't say that any random heavier bike will be more durable than any random lightweight bike as there are so many other parameters affecting durability. But the light, durable, cheap trade-off is real.
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Old 07-06-21, 11:27 AM
  #139  
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A kilo less is about 1-ish % faster uphill, as a rule of thumb. It's both marginal and nice to have at the same time. If you can afford a nice lightweight race bike, why not?

The idea that it isn't comfortable seems very far fetched. ​Good saddle, good fit and some time in the saddle and I can sit on a race oriented bike all day.
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Old 07-06-21, 11:40 AM
  #140  
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Originally Posted by pgjackson View Post
Well, it has been suggested that a heavier bike is inherently more durable.

All other things being equal, there's probably some truth in that. But again, other things are never equal.

There's good reasons why a new bike that's light, cheap and durable is not a real-world thing.

You seem to be resistant to the idea that different people place different values on the qualities they're seeking in a bike.
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Old 07-06-21, 11:42 AM
  #141  
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Originally Posted by PeteHski View Post
I'm not using a mental model. I'm using an accurate detailed physics model which takes into account rolling resistance with weight. This predicts that bike weight is only really significant when there is a lot of climbing involved and even then it's not a huge difference.
Hold on, I had to dodge the moving goalposts.
Originally Posted by PeteHski View Post
Riding on nominally flat terrain I wouldn't expect to pick up any time on a lighter bike.
On flat ground, the lighter bike will have lower rolling resistance and so will be faster. Is the difference significant? That depends on each person's definition of significant. However one defines it though, the difference is there.
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Old 07-06-21, 11:43 AM
  #142  
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Originally Posted by livedarklions View Post
I'm riding a bike, not a concept. How does that refute "the difference is too small for me to care about"?
Where did I say it does? You might have noticed I wasn't responding to you.
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Old 07-06-21, 11:49 AM
  #143  
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Originally Posted by woodcraft View Post
My bike has effectively gotten lighter relative to the current crop with disc brakes, electronic shifting, big tires, etc..

The bicycle obesity epidemic...
My lightest bike has disc brakes and big tires. All my bikes with caliper brakes and skinnier tires are several pounds heavier.
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Old 07-06-21, 11:49 AM
  #144  
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Originally Posted by Branko D View Post
A kilo less is about 1-ish % faster uphill, as a rule of thumb. It's both marginal and nice to have at the same time. If you can afford a nice lightweight race bike, why not?

The idea that it isn't comfortable seems very far fetched. ​Good saddle, good fit and some time in the saddle and I can sit on a race oriented bike all day.

I'm on your end of the can sit on a race bike all day scale, but one thing I will never do is assume that's "normal". It's totally not far fetched at all that many if not most people would find it uncomfortable.

I don't buy lots of things I can afford because I think it would be a waste of money. Raising the price of the bikes I buy by a couple grand doesn't strike me as something I care to afford. I also don't mind that 1% of added effort on the hills I take. YMMV.
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Old 07-06-21, 12:03 PM
  #145  
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Originally Posted by asgelle View Post
Where did I say it does? You might have noticed I wasn't responding to you.

You might have noticed I was paraphrasing the comment that you said required the poster to "adjust" his "mental model". I happen to agree with the statement that you were quoting, so it's not a big stretch to assume you were saying I needed to adjust my mental model as well.

And if you're going to be this nitpicky, nowhere did I say or imply that you were responding to me. I just know a really bad "refutation" when I see it.

Literally no one is saying there's "no difference" on flat ground. A bunch of us are saying it's not a difference big enough for us to care about--on a flat ride, the time difference is going to be negligible. You may care about a couple minutes over a 100 mile ride, I don't. You're just making an argument against a strawman "there's NO difference".

To me this has always come down to a bang for the buck thing. I find spending exorbitant amounts of money to shave a couple grams off a bottle cage pretty funny, but if you want to do that, knock yourself out.
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Old 07-06-21, 12:13 PM
  #146  
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Originally Posted by asgelle View Post
To date, no such discrepancies have been found.
Not exactly. The Martin model is good enough to be very useful, but it's known to be incomplete. What is approximated as "crr" appears to be somewhat speed-variant, for instance, and it's not really clear how well suspension-related effects smush into the model. CdA for an airfoil also varies by Reynolds number, and that's an issue that largely gets ignored.

Originally Posted by asgelle View Post
Rolling resistance depends linearly on weight so even on flat ground, a lighter bike will be faster due to the decrease in rolling resistance. (Yes, the difference may be small, but conceptually, weight matters even on flat terrain.)
That's probably to a large degree counteracted by proper suspension tuning for the increased load (i.e. increase tire pressure).
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Old 07-06-21, 12:13 PM
  #147  
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Originally Posted by livedarklions View Post
Literally no one is saying there's "no difference" on flat ground.
That is literally what PeteHski wrote and to which I responded.
Originally Posted by PeteHski View Post
Riding on nominally flat terrain I wouldn't expect to pick up any time on a lighter bike.
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Old 07-06-21, 12:24 PM
  #148  
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Originally Posted by HTupolev View Post
Not exactly. The Martin model is good enough to be very useful, but it's known to be incomplete. What is approximated as "crr" appears to be somewhat speed-variant, for instance, and it's not really clear how well suspension-related effects smush into the model. CdA for an airfoil also varies by Reynolds number, and that's an issue that largely gets ignored.
No model is ever complete, but we know the Martin model agrees with experimental data to within 1-2%. So for all the things you listed and the ones you don't, the cumulative error must be less than that. Given the error in model parameter estimation (no road surface is perfectly uniform, wind is never constant in speed or direction, no one can hold a perfectly constant position, etc.), model form errors of the type you listed much be a very small component of the total 1-2% model error.
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Old 07-06-21, 12:39 PM
  #149  
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I've always been more concerned about the weight of my arse
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Old 07-06-21, 12:56 PM
  #150  
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Originally Posted by asgelle View Post
That is literally what PeteHski wrote and to which I responded.
And? You pulled the sentence out of context--in the same post, he actually showed his math and figured out he would gain 30 seconds over 100 miles of flat. You get no points for selectively quoting to make your straw man look real.

Here's what your quote left out, BTW:

"Running the same calculation on a much flatter 100 mile course, I would gain just over 30 seconds with the 2kg lighter bike. Basically nothing worth spending any money on."
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