The Chemist

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.

Sy Reene

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?

pgjackson

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.

PeteHski

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.

PeteHski

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.

PeteHski

Light, durable, cheap. You can only pick 2 of those 3 things on one bike.

livedarklions

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.

livedarklions

I'm riding a bike, not a concept. How does that refute "the difference is too small for me to care about"?

genejockey 

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.

woodcraft

My bike has effectively gotten lighter relative to the current crop with disc brakes, electronic shifting, big tires, etc..

The bicycle obesity epidemic...

pgjackson

Well, it has been suggested that a heavier bike is inherently more durable.

UniChris

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


​​​​​

PeteHski

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.

Branko D

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.

livedarklions

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.

asgelle

Hold on, I had to dodge the moving goalposts.
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.

asgelle

Where did I say it does? You might have noticed I wasn't responding to you.

genejockey 

My lightest bike has disc brakes and big tires. All my bikes with caliper brakes and skinnier tires are several pounds heavier.

livedarklions

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.

livedarklions

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.

HTupolev

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.

That's probably to a large degree counteracted by proper suspension tuning for the increased load (i.e. increase tire pressure).

asgelle

That is literally what PeteHski wrote and to which I responded.

asgelle

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.

fettsvenska 

I've always been more concerned about the weight of my arse

livedarklions

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."