It’s only 2:1 if the mass is absolutely and 100% placed completely at the tyre OD as my maths earlier showed, and due to the square term in the inertia calc, it drops off drastically as the mass is placed further towards the wheel centre. Ie at 90% of the wheel/tyre OD, it’s 1.8:1.

However, in all cases, it’s small beer compared to accelerating the riders mass!

Are you able to back that up with, you know, some, like, science, or something?

Yes, although I think maxtorque has done it to death.

KE (linear) = 1/2 m v^2

KE (rotational) = 1/2 I w^2

where I = moment of inertia and w = angular velocity.

Speed of wheel at tyre is v = w * r (r is wheel radius here)

Moment of inertia = m * r^2 (r is distance of mass from axle)

Assuming we’re adding mass right where the rubber touches the road, r is the same in both cases and cancels to give:

KE (rotational) = 1/2 m v^2

So for mass on the edge of the wheel the rotational energy is the same as the linear energy, so a ratio of 2:1 compared to something with no rotational energy. This intuitively makes sense: a mass on the rim of the bike is moving at the same speed as the bike as a whole, it’s just going round in circles.

At any other point it’s scales with the square of the ratio i.e. (r(mass)/r(wheel))^2, so weight at the axle itself has zero rotational energy.

Massive difference? See the calc I did a bit earlier. 200g less on the rims/tyres makes 0.5% difference, 400g less 1% (I’m assuming a factor of 2, which is good enough for this discussion). So over 8 laps that’s like doing one extra hairpin in terms of fatigue even on your rather unusual CX course with 12 hairpins. I very much doubt you could notice the difference.

It is as a means of determining whether they “certainly made the bike accelerate quicker”.

Sure training based on feel is a valid thing to do, as is drinking when you feel thirsty, but those involve physiology where feel is important. Trying to determine a 1% or less difference is a totally different matter – here physiology is a problem, because it’s quite easy to have 1% difference on any given day without being at all aware of it. The fundamental issue though is that’s a limit to how small differences humans can detect – IIRC it requires ~3% to 5% difference in something like this for a normal human to be able to tell the difference.

It’s possible you’re feeling something other than the difference in acceleration, but most likely your “feel” is just placebo effect.

I need to get me set of them placebo wheels!

What tyres for placebo wheels?

Seriously though, why upgrade the stock wheels on a bike then if it’s all in the mind? A new set of decals should in theory be enough.

Because placebo effect provides a real advantage!

There clearly is a very small real advantage in lighter wheels, though mainly it’s the same advantage as having a lighter frame, but if you’re going to upgrade your wheels because you want to get a real speed advantage get aero ones.

A new set of decals should in theory be enough.

You’re misunderstanding the placebo effect – new decals will only provide an advantage if you think new decals will make you faster. Of course it’s more difficult to get a placebo effect benefit for professional cynics like me

Seriously though, why upgrade the stock wheels on a bike then?

numerous reasons spring to mind but they could be…

– more aerodynamic
– more reliable/serviceable
– a pretty colour
– wider rims
– stonger
– stiffer
– and yes lighter*

It could be any number of the above or combinations of the above that you’re searching for, just because weight at the rims makes very little difference overall to your speed doesn’t mean there aren’t other valid reasons to look at the performance of your wheels.

The point is don’t get suckered into the whole ‘saving weight at the rims is the most important thing’ line of BS that often gets trotted out.

*it might make very very little difference, and certainly not in the rotational sense, but weight lost off the bike is still weight lost off the bike when it comes to hauling it up hill, it’s no less valid to want to lose weight from wheels as well as other places.

I feel the need to point out that I’m not suggesting lighter rims makes no difference at all, it might even be enough difference to be worth upgrading. Simply that it’s impossible to notice the difference they make to how fast you accelerate.

I have light wheels on the roadie myself, though that’s mainly down to the hubs, rims are semi-aero and no lighter than an Open Pro. It seems that I go faster with them than more ordinary wheels, but that’s based on the stopwatch over a long ride and I’d put it down to them being more aero (if there is a real effect, it might be placebo) – I certainly can’t feel the difference when riding.

t is as a means of determining whether they “certainly made the bike accelerate quicker”.

Sorry, unless you can prove that…..it’s just your opinion vs mine & I’ll take mine – since I was the one there..

I gave my proof up there – do you reckon you can feel a <1% difference in acceleration when nobody else can? It’s been scientifically proven that such small changes are impossible to feel, even in situations where you are comparing them far more directly than you were – nothing to do with my opinion, this isn’t something we’re voting on. Sure you were the one there, you were feeling a placebo effect.

I reckon I can feel the difference between a wheel set that weighs 1.9kg & one that weighs 1.5kg without a shadow of a doubt. Which is 400g lighter which is roughly 20-25% lighter so a bit more than your “1%”.

Yeah, I can feel that.

(You’d have to be an insensitive clod not to be able to quite frankly…)

I’d also like to point out that humans can be pretty sensitive. So whilst the numbers are small, light wheels certainly feel nippy.

I also suspect that handling on twisty singletrack is much improved by lighter wheels, but cba to do the maths. The gyroscopic effect of the wheels tends to resist turning the bars and also pivoting the bike.

I’m sure you could by picking them up. You might even be able to tell the difference in terms of the bikes handling (I’ve already suggested that, molgrips). I’m sure you couldn’t feel the difference they made to your acceleration which is what you are claiming. There’s plenty of scientific research on placebo effect.

Which is 400g lighter which is roughly 20-25% lighter so a bit more than your “1%”.

Which makes 1% difference to your acceleration – have you missed that point?

It’s been scientifically proven that such small changes are impossible to feel

Doubt that. Maybe if you are sitting in a car or passively on a bike but when you are pushing hard on the pedals you can feel how they respond. Your whole body is involved in the movement.

1% difference? Really? It doesn’t really matter whether you’re passive or active, you’re still trying to detect that 1% change.

1% difference in what? Overall forward acceleration? Or the rate of change of reaction against your foot..?

The former I’m sure I couldn’t tell. But the latter I reckon I could.

Put it another way – I have a 26″ bike with 1300g wheelset and 450g tyres; I also have a 29″ bike with 1800g wheelset and 750g tyres. There is a HUGE difference in the way it feels to accelerate on the bikes. I’ve not timed overall sprinting speed but they feel very different.

An experiment for you if you like. Get 2 identical bottles, one empty, one full. Get 2 mates – one puts either the empty or full bottle on your bike, then hands it to the other mate and walks away before the second mate holds it for you while you get on (I’m making it double blind here – you need to have no contact with anybody who knows the details of the experiment). Then you get on and accelerate up to speed in a straight line whilst sitting in the saddle (standing up you’d likely be able to tell the difference in mass from how the bike moves). Mate catches you when you stop so you can’t feel the bike independently. Repeat several times and note which one accelerates faster.

Fiver says if you follow that you can’t accurately determine which the full bottle is.

They’re fundamentally the same thing in terms of perception, you’re still sensing your foot accelerating 1% faster, the force will be the same.

Probably other differences between your 26 and 29 in terms of the way they feel, especially if you’re standing up, though it could just be placebo. Placebo effect is why any experiment based on feel where the experiment subject is aware of a difference is pretty worthless. Which is why even if you times them (which would eliminate the other differences in feel) you’d not necessarily get valid results (though any real difference in acceleration due to the heavier wheels would almost certainly be less than the experimental error anyway).

I’m sure you couldn’t feel the difference they made to your acceleration which is what you are claiming

Actually, I don’t think that’s what I did say…..(CBA to check TBH)

What I can say, unequivocally, is that on lighter wheels I go uphill faster ergo worth buying.

You can agree with that or not, but hauling nearly 1/2 kg less in whatever form up a hill you are going to notice – particuly in the wheels..

Fiver says if you follow that you can’t accurately determine which the full bottle is.

I won’t take your money..

They’re fundamentally the same thing in terms of perception

Says who? You studied physical perception have you? Or are you just making hypothesis based on experience?

I know I could tell the difference between heavy and light wheels. You won’t convince me to doubt my own experience. So it’s not worth derailing an otherwise interesting physics thread with this kind of thing 🙂

If you are ever in Cardiff I will let you ride my bikes and you will see it’s nowhere near placebo effect!

Because it would take so much effort to read where I quoted you a few posts ago? 🙄 The full quote:

Speaking from experience swapping to lighter wheels on my road bike certainly made the bike accelerate quicker.

What I can say, unequivocally, is that on lighter wheels I go uphill faster

So now you’re feeling a 0.5% difference?

…but it gets better:

hauling nearly 1/2 kg less in whatever form up a hill you are going to notice – particuly in the wheels..

So you’re particularly going to notice the difference in something which makes 0% more difference to your climbing speed than losing the weight somewhere else?

I won’t take your money..

No, you won’t

You won’t convince me to doubt my own experience.

I’m not expecting you to doubt your own experience – I’m sure it was a real experience and you felt a real effect, I’m simply suggesting that the reason for the difference you felt isn’t what you think it is.

The trouble is I won’t – I’m sure I’d feel a difference, but that won’t prove why – and if you think it’s possible to, then you probably don’t understand placebo effect. Yes it is an ultimately pointless thing to debate if you don’t understand or refuse to accept the power of placebo on human perception – if you’ve not done a proper double blind trial then no scientific journal would accept your findings. I outlined the steps you’d need to take to eliminate placebo a few posts earlier – if you haven’t done that then it’s impossible to rule out.

Are you really trying to say that reducing a bikes weight by 1/2 kg will make no noticeable difference?…

If so, that, is just cobblers..

As for checking on what I said?

Yeah it’s late & I CBA – what of it?

I’m saying that you won’t be able to “feel” a 1% difference in acceleration, which is the difference losing 400g on the wheels will make (if it’s all in the tyres/rims). I’ve said several times that there are other things you can feel, and even pointed them out in my experimental protocol.

Agree, I don’t think you can feel the difference and the difference in an hour long ride is also pretty insignificant.

In fact since moving back to a track bike a few months back I first rode it with heavy wheels with very heavy tyres (a Marathon+ !) Since swapping out the wheels and tyres and reducing by 800 grams I still haven’t beaten my time over a 13 mile loop that was ridden with the heavy wheels.

What you can feel is how it turns, changes direction, how the front wheel lifts over things etc,. plus it all makes up part of the overall weight of the bike so is weights saved towards that which when added up may be a bigger difference.

This bit about ‘feel’. Placebo effect is based on belief only, changes in bike kit can increase performance in a way that’s more about a small actual change giving a minor feel feedback that’s then acted on by the rider, magnified. For others it may be no more than placebo but I believe we can be pretty sensitive to feel, also agree that we don’t actually perceive eg 1% difference in acceleration.
Some riders will feel a change between 2 wheelsets where the rim + tyre combo is marginally lighter, say 150g on a light road bike. You won’t feel the difference in performance. But we can be very well tuned or sensitive to how a bike feels, handling response and muscle memory etc, and the feel in wheel response when handling the bike during acceleration may be noticed, slightly, at first, assuming tyre pressure and road conditions etc stay the same. That feel is usually linked to ‘must be faster!’ thoughts about the new kit and there’s a something like a feedback loop that makes you willing to put a bit more effort in, so the new kit may be faster in that way.
Since climbing involves a lot of those small accelerations or moving the bike around the feel might be attributed to better climbing performance overall. The actual difference due to the wheel weight drop would be really hard to measure with everything else going on. It’s tiny. But feedback is a big part of how we respond to variations in bikes, imo.

Where has the 400g figure came from, when I switched wheels from stock to stans iron cross on my basic cx bike I lost 2kg! That’s a massive difference. Another point is the chances are an upgraded wheelset will have faster engagement which makes a difference.

in relation to another sport I read about the biology that demonstrates humans are incredibly good at sensing acceleration, much less good at sensing speed.

When I said massive difference I mean in term of feel, strava times, and places in a fun local race over summer on subsequent weeks. Obviously that brings into account others performance, but if we are talking about racing it’s the most important metric

Where has the 400g figure came from, when I switched wheels from stock to stans iron cross on my basic cx bike I lost 2kg!

400g is a typical weight save and a good number to use. Saving 2kg by changing wheels is very much an exception. Taking a typical middle of the road wheel-set weighs around 1700g then to save 2kg your wheels would have to have weighted 3.7kg. I don’t actually know how you could make a set of wheels that heavy?

What you can feel is how it turns, changes direction, how the front wheel lifts over things etc

Which is what I’ve been saying all along, and also +1 to what jameso wrote – I got lazy and attributed it to placebo when as I made clear with my testing protocol, people can feel a difference, just not with the performance (it is still like placebo because they’re feeling something which isn’t real).

@kerley, I also changed tyres, but basic shimano hubs, unbranded spokes and rims, cheap stock wire bead tyres, to iron cross wheelset with light Clement folding tyres saved me 2kg according to my scales.

Which is what I’ve been saying all along

Also got to bear in mind things like the lateral stiffness of the wheel, the sounds it makes (seriously), tyre pressure (i’d not be surprised if just getting some top end tyres and optimsing pressure for low CRR makes more difference to acceleration AND feel than loosing a kilo on wheels).

That still seems a huge difference. The sort of wheels you’re describing should only be ~2.3kg, so only 800g more than the Iron Cross, which means the original tyres would have had to be ~1kg each which is unrealistic – I’ve got some cheap wire beaded CX tyres here (in fact that’s what I still have on my crosser!) and they’re nowhere near that weight. Are you sure you weren’t weighing the old set with a cassette and disc and the new ones without?

Though in any case, if we assume a fair amount of the difference is at the hub, then that’s maybe 3% difference to your acceleration – if you’re seeing more improvement than that to your Strava times then it’s not the weight. Probably those Clement tyres which will decrease the amount of energy you’re using all the time, not just for the small amount of time you’re accelerating, will change the feel etc. If you want to attribute a change to losing weight then you have to keep everything else the same!

Aracer – do you remember the conversation about autism spectrum disorders? And that we often struggle to notice how we come across in conversations? This is one of those times – said with friendliness and no aggression!

You said this:

and if you think it’s possible to, then you probably don’t understand placebo effect

Now you’re right, I’ve never done an experiment like this, but I’ll bet you haven’t either. So you’re hypothesisng, and from that you’re concluding that I’m unintelligent to the extent that I don’t understand the placebo effect. So you’re basically implying you’re so much cleverer than me that you must be right. Hopefully not deliberately, but that’s how it reads.

Anyway.

I think you are arguing a different point. I agree that in your test outlined above you probably won’t notice the difference in 0.5kg total mass when you ride the bike. You probably won’t notice 1% difference in forward acceleration.

However I think you WILL notice the feel of the bike and how it responds, because humans are very sensitive to touch, and to reaction against our limbs. Jameso puts it better than me.

I hired a 27lb road bike a few summers ago, after having been riding my own 20lb one. I noticed no difference *except* when accelerating briskly out of junctions etc. Having done so much road riding, my brain was tuned in to the gear I was in and the way the pedal would respond to my pressure and how many pedal strokes I’d need at what cadence. On this bike, I’d stand on a pedal and it would take longer for that pedal to start responding to my pressure. Small cues like this give the *impression* of the bike being slower. It would be slightly slower too. But I’m not noticing the difference in forward acceleration, I’m noticing the cumulative effect of various physical cues. But I still notice.

By way of helping the thread – a polite response would be something like

“Well I can see you’ve thought about it but I just don’t share your conclusions”

rather than

“That’s rubbish, you don’t know what you’re talking about”

🙂

Except you are lumping in standing up, moving the bike around and (probably) a different set of gear ratios, different bars, stem, position, tyres and so on.

So identifying *just* the wheel weight in regards to its effect on acceleration is all but impossible.

aracer – Member
…The sort of wheels you’re describing should only be ~2.3kg…

the wheels that came on my cdf weigh 2.4Kg.

shimano 475 hubs, something-or-other rims, plain-guage spokes, etc. no discs, no QR’s, no tubes, no tyres, nothing left to remove.

2.4KG!!!!!

as a consequence, they’re more or less indestructible. And as i made the mistake of servicing them once, they will never die. Yes they’re heavy, but it’s only something I can feel in a village-sign sprint – and only then when i’m looking for excuses…

(i.e. i can’t really feel it at all)

That road bike was just one example – I have replaced wheels on the same bike, I have replaced tyres on the same bike, and I do notice.

So identifying *just* the wheel weight in regards to its effect on acceleration is all but impossible.

a) that’s just conjecture

b) I’m not saying you notice its effect on overall forward acceleration. I’m saying you notice its effect on the FEEL of the bike. As I said I have no idea if I’m overall faster with the lighter wheels or not.

Well that certainly wasn’t my intention at all – maybe it’s my ASD meaning I hadn’t realised it did, maybe you’re reading into it things which aren’t there. So my apologies. Because I know that you’re intelligent, probably just as intelligent as me, when I write replies to you they’re written with that in mind – maybe I should explicitly write that when I reply 🙂

I have done experiments a bit like that, and scientific testing like this is something I know a fair bit about – probably more than most on here – though that says nothing about intelligence, simply that it’s something I’ve done and researched. There’s nothing wrong with not fully understanding effects like this – all sorts of things I don’t understand (and if you’re aware of that you’re way ahead of a lot of the population).

I think you are arguing a different point. I agree that in your test outlined above you probably won’t notice the difference in 0.5kg total mass when you ride the bike. You probably won’t notice 1% difference in forward acceleration.
However I think you WILL notice the feel of the bike and how it responds, because humans are very sensitive to touch, and to reaction against our limbs. Jameso puts it better than me.

Good, you agree with me. I really was hoping you would, because I credit you with that much intelligence. As far as I can work out jameso is explicitly agreeing with me. I have tried to point out several times that I accept you can feel the difference, which is why the test protocol is designed the way it is to try and eliminate that.

Though I came in on this because there was a claim that lighter wheels “certainly made the bike accelerate quicker” and that isn’t something you can tell by feel. We can stop now if we’re all agreed on that!

a) no, maths and physics.

b) you don’t notice the weight of the wheels in regards to their acceleration, you notice the shiny newness of the wheels, the stiffness, the pick up, the sound, the correctly inflated (and higher quality?) tyres, the lower inertial effects of moving the lighter bike from side to side. And so on.

2.3kg wasn’t that bad a guess then!

a) no, maths and physics.

You’re saying that you can prove with maths that I won’t notice lighter wheels?

b) you don’t notice the weight of the wheels in regards to their acceleration, you notice the shiny newness of the wheels, the stiffness, the pick up,

Pick up – is that not the same as acceleration?

Can you define ‘pick up’ for me? Cos I’m struggling to come up with one that doesn’t mean you actually agree with what I’m saying. I think you do anyway – you just aren’t reading my posts properly.

Let me clarify my point:

– Light wheels probably won’t make you actually go much faster
– If they do make you accelerate more, you won’t notice the forward acceleration
– You will however think they feel quicker. And it’s not your imagination, they have real effects that produce that impression

So you will notice the effects of lighter wheels, as you say, you just won’t notice the speed in itself.