Question for those who think bike weight doesn't matter ...

[bpsmith]

Do people put maximum effort in on the commute, without ever slowing down in traffic and lights, etc, though? My guess is that the commute is not the best scenario to compare speeds between bikes.

 

[Joshua Plumtree]

My best guess is that the lighter/fitter you are then the more performance gains you're likely to see from a lighter bike.

But it's not all about the lightness of the frame. Aero bikes are generally heavier, but more than make up for this - given the right topography - by bring more er..... aerodynamic.

Then there's all that stuff about being horizontally stiff but vertically compliant which I only half understand!

 

[Shut Up Legs]

Bike weight matters. I weigh about 82kg myself, my touring/commuting bike 15kg and my road bike 8kg. I can definitely notice the difference between the 2 bikes when riding uphill, because the road bike makes the combined weight of myself and the bike about 9% less.

 

[mustang1]

My best guess is that the lighter/fitter you are then the more performance gains you're likely to see from a lighter bike.

But it's not all about the lightness of the frame. Aero bikes are generally heavier, but more than make up for this - given the right topography - by bring more er..... aerodynamic.

Then there's all that stuff about being horizontally stiff but vertically compliant which I only half understand!

I fully understand but only half believe it.

 

[Pumpkin the robot]

Do people put maximum effort in on the commute, without ever slowing down in traffic and lights, etc, though? My guess is that the commute is not the best scenario to compare speeds between bikes.

It is the best to compare for me as I was doing it every day. The only variable that made a difference over 6 months was the wind.

 

[bpsmith]

It is the best to compare for me as I was doing it every day. The only variable that made a difference over 6 months was the wind.

That's fair enough. No issue there. I was just pointing out that this comparison would likely have a different answer when considering the commute as opposed to recreational rides.

 

[Piemaster]

I've got bikes that are at the opposite ends of the weight range. A carbon road bike and a mtb based hybrid with an xtracycle conversion.The xtracycle conversion alone probably weighs more than the complete road bike and I'm not sure I could pick it up. Indeed I've carried the road bike on it and the extra weight was barely noticeable.
Weight makes a difference.

 

[Rohloff_Brompton_Rider]

My steel bike is 4.5kg more than my carbon bike, but I only get 0.5mph difference in my average speed over the 20 mile commute. (only 1000ft of climbing in it)

This is interesting, you don't live far from me. I do however have those pesky 3 mile long hills. But, my Brompton is a very sit up and beg H type with a double IGH friction loss.

So I'm now wondering if it's more the flexy-ness and IGH's more than the weight I'm feeling (the aero effects being nullified by my less than 12mph average).

 

[Pumpkin the robot]

I was slower on a hybrid by about 2mph on equivalent weight bikes, so aero makes more difference than a few KGs.

 

[fossyant]

My steel bike is 4.5kg more than my carbon bike, but I only get 0.5mph difference in my average speed over the 20 mile commute. (only 1000ft of climbing in it)

You have the wrong steel bike ! LOL !!

 

[Fab Foodie]

From time to time, someone mentions that bike weight doesn't matter for general cycling or commuting. Then a bunch of others who think the same will chime in solidifying the argument through repetition.

So what are those heavy e-bikes like when not using electric assist?

I heard on The Bike Show podcast they are reviewing the Smart e bike and the users said it was a great bike but really heavy. Hence they had a concern going up hill if the battery was discharged.

Does the bike weight matter in this case?

OK, I'll bite ....

Firstly as Smokin Joe mentions, the laws of physics are not immutable here. All things being equal a heavier bike will be slower than a lighter bike. But in the real world such pure differences might not be clear, significant or so realisable as simple maths suggest.

I'm assuming that the question comes from threads here where people say bike X is 700g lighter than bike Y for the basis of a purchasing decision, or an upgrade from a heavier to a lighter groupset for example.

So here's my quick rambling to add to the debate ....

Weight matters when either accelerating or climbing.
It also stands to reason that 1kg extra bike weight for me at 90kg on a 10kg bike is about 1% of the total mass whereas somebody 60kg on a 7kg bike it will representa a greater percentage and hence bigger impact.
In the case with bikes that are equal apart from weight, the lighter bike has a benefit in relation to the weight benefit, how much I'll let the mathematicians calculate and determine the significance. However as speed increases, wind resistance is by far the biggest user of power rather than weight at which point relatively small differences diminishes to virtually nil.
In theory and seemingly in practice, once moving on a flat surface wight difference become virtually negligible in the face of other factors such as wind resistance, Weight also provides inertia which helps maintain momentum too, this can also be beneficial on rolling routes.
Weight distribution might also have an impact - does anyone know if you have a 10kg total weight bike with 2kg wheels or a 10kg total weight bike with 1kg wheels which is faster? Both weigh the same but less rotating mass is said to accelerate faster so Weight=Speed is skewed.

Often, people are not comparing alike situations and this is where the saving a few hundred grams here and there is debatable. And the benefits of a lower weight depend where and how you ride. The benefit is less on long flat open wind-blown roads of say the fens that the hills of the Peak district.

But there are also other less quantifiable factors.
In my own world, I have a light stiff alu/carbon TCR and an 80s 531 Holdsworth. Clearly the Holdsworth is heavier and by maths slower. But it doesn't seem that way (anecdata alert!).
The fit of both bikes is the same, so I can discount that and the effects of aerodynamics. The TCR is stiffer and twitchier and absorbs less vibrations than the heavier Holdsworth on normal roads. Over short fast rides I reckon the TCR has a very slim benefit, but as the distance increases, I reckon more energy is expanded keeping her in a straight line and absorbing and dealing the with road shock and discomfort than on the heavier Holdsworth, which is smooth and stable and one can concentrate on sitting in a good position and just turning the pedals. Over distance, the heavier bike might be quicker. This is much the same deal with TT bikes, that are very efficient over short distances, but would be hell over a regular road stage.
It's interesting that rider comfort in the carbon age has suddenly become very important in relation to performance.

So my thinking is that in most real-world applications, debates over bike weights need to be tempered by more pragmatic thoughts about the rider and the use of the bike rather than the scales.
That's whey when discussing the virtues of bike X over bike Y some of us might discard the wight differences as a bit of a red herring .... but good marketing.

And by the way .... we're not all interested in outright speed

 

[Dogtrousers]

And by the way .... we're not all interested in outright speed

This.

If I had a much lighter bike it's probable that I'd be a wee bit less knackered at the end of a hilly 100 or 150km, but it's not likely that I'd finish much sooner because that's governed by my riding style - tootling along and holding something back for later. It's also possible that my bum/wrists may hurt a bit more, depending on geometry. However, if for some bizarre reason I found that someone had entered me into a time trial, and I was actually pushing to go fast, then it's quite possible that I'd finish a bit quicker on the lighter bike. But not much quicker. And both times would be embarassingly slow.

 

[Rohloff_Brompton_Rider]

We all know aero makes a difference on descents and the flat, for example a velomobile can weigh 34kg's and goes like stink - until it hits a hill that is.

 

[KneesUp]

Every single gram matters to some degree, as the laws of physics will confirm.

Exactly - you cannae change the laws of physics - every amount of mass requires energy to move.

It all rather depends on what you mean when asking if it matters though. My bike weighs about 13.5kg (inc lights, batteries, full guards and lock) but as a consequence it is sturdy, so I don't mind hopping it off kerbs (Sheffield likes a shared use path that ends at a crossing, and if there is no traffic it's quicker just to ride off), rattling it down cobbled hills or thudding through the many and various collections of potholes, patches and speed humps that constitute back roads around here. It is totally unfazed by such things, and because it has fat tyres it remains relatively comfortable. As a comparison, the worst road surface I commute on is downhill. The one time I did it on 25c tyres I had to brake the whole way down as it was so rough it was shaking my glasses off and I couldn't see. I buzz down the same road (in the same glasses) on my current bike at c.30mph with no problems.se

So of course weight matters, but 'heavy' doesn't necessarily - 'bad' Heavy sometimes means 'not fragile' which is a good thing. As others have pointed out as well, it's the total weight of bike, accessories and rider that matter. Me and my 13.5kg bike weigh only just over 90kg together, which isn't so much compared to some bike and rider combinations.

 

[Rohloff_Brompton_Rider]

I like this thread, it makes sense of my noticeable difference between my Brompton and my fixie.

(108kg (me) + 15kg (Brompton) - (108kg + 9kg (fixie)) = 6kg

6kg ~= 4.88% + 8% (2 x IGH friction losses, dyno hub and M+ tyres)

Therefore ~ 13% energy loss going uphill (where aero is moot due to my climbing speed being less than 12mph).

It feels about that as well.