Deaf to Heft

Interesting article by Barney about the relative lack of importance of weight in a mountain bike. He mentions a recent test of three bikes where one was a couple of pound heavier than all the others but it “rode light” and everybody loved it. I assume that was the Orange Segment in the recent Nu-Skool 29er test. But either way, it raises a few interesting points.

Can a bike really ride lighter than its weight?

Is there really some arbitrary weight beyond which a bike starts to feel heavy? Thirty pounds is often mentioned, but even if there were some critical weight it seems unlikely that it would just turn out to be an integer multiple of ten in imperial units.

I think it can ride lighter that its weight, sure. Loads of variables like the article said.

Plus when do you want it to “ride light”? On the way up? On a steep or gradual climb? A straight line descent? A techy descent?

I am a lightweight. In my experience of borrowed and rented bikes, anything over 14kg starts to feel a bit heavy. More to do with the amount of power I can generate than the bike’s weight I reckon. Most recent example was a DH bike I rented for an uplift day. As long as there was zero pedalling I was ok. I’d rather have had less travel and a lighter bike because sometimes you need to pedal up to speed to hit the right lines.

it is a bit weird

I have a road bike (moderately posh frame with chinese weelz). It’s pretty light.
Although I don’t ride that much, I also have a “winter road bike” (cx frame that I’ll never again ride off-road). It’s still pretty light but has a bit heavier wheels, plus mudguards

I’ve been on the cx bike since the wet weather started but Saturday I went out on the road bike as it was dry again. Christ it felt fast in comparison ! Not top speed, which you might understand (lower, wheels are a bit aero) but accelerating. I’ve never bought into that shit before but it was apparent to me (course, may have been the effect of the sunshine but I don’t think so

MTB-wise, I have a rigid ss and a geary full-sus and they’re too different to make a sensible comparison but I am now a bit of a believer in light wheels, at least for “feel” if not actual speed. Occasionally I have a quick go on other bikes and there is sometimes a funny heavy-front feeling that I definitely don’t like but can’t explain (I don’t think it’s actually a heavy front end though it could be weight distribution – I like forks that are “too long for the frame” and maybe that’s why)

I have a bit of a feeling that sus bikes feel slow if the suspension is highly damped and that this new marketing term “rides high in the stroke” is more likely somehow quicker to reset and so feels fast – I reckon that’s why everyone likes new pikes, Bos forks etc though I admit I’ve never had a go on either)

Having ridden lots of bikes and lots of weights and lots of styles 2 12kg bikes ride differently, 2 identical bikes (ie mid to top end) with a 1.5kg difference ride differently. Simple maths/physics says it’s harder to move an object that is 1kg heavier. It takes more effort to move that object.

I think the thing to remember is that, even for pretty extreme Mountain biking, the average gradient we cycle up is actually pretty shallow.

Take an “average” ride, lets say 30km linear distance with 1500M of climbing, which you aim to complete in 2hrs (15kph average speed)

Lets take two scenarios, for Case 1, you’re on your XC carbon HT, and for case 2, on your chunky DH bike:

Case 1: Total mass 90kg (10kg bike + 80kg rider & kit)
Case 2: Total mass 95kg (15kg bike + 80Kg rider & kit)

So the work done and average powers work out as follows, over this average gradient of just 2.25deg:

Case 1: 1324 Joules at 184 Watts
Case 2: 1397 Joules at 194 Watts

In reality, if you wanted to output the same amount of power riding the DH bike as the HT, your average speed has to fall to just 14.21Kph, and you ride takes 6min 40sec longer to complete.

So, if you’re doing an XC race, well, finishing nearly 7min later is going to hurt your chances of winning, but if you’re out for just a ride with your mates, it’s less important!

It’s also probably worth looking at the instantaneous pedal torque and what maximum gradient we can climb as a result

With 26″ wheels (old skool) and a bang-on-trend 1by 32/42 ratio, for an 80kg rider, peak crank torque on 175mm long cranks is 137Nm. So, for a 10Kg bike, that means you can theoretically climb a 39.84deg slope before stalling, with your 15kg bike, that’s down to 37.36 deg.

In all cases, it’s pretty obvious that the minor mass difference you bike makes is almost certainly, outside of actual racing, swamped by other factors.

Thanks maxtorque, that’s the kind of analytical response I love 😀

Of course, it’s even “worse” than this in practice as your DH bike may be more efficient over rough ground than your XC HT. I’ve noticed that, if the ground is sufficiently bumpy then my Five will be faster even on the flat than my Solaris. The Solaris still tends to win overall, which is why XC racers don’t ride trail bikes, but the differences can be surprisingly small. In fact, now that the surfaces have got really slippy, the Five tends to be faster everywhere, simply because (for reasons I don’t fully understand) I tend to stay off the brakes a bit longer.

Can a bike really ride lighter than its weight?

This is physics so the answer is no.

Maybe the bike that is “riding lighter” is “riding optimally”.

Thanks for the feedback, folks 🙂

Mattjg:

This is physics so the answer is no.

Actually, the point I was making is that it’s psychology, so the answer is quite definitely yes. ‘Ride’ in this context is referring to the subjective interpretation of ride quality, rather than absolute physical characteristics of same…

Its not just about the calculations of how much energy you need to move a heavier object, its in the (admittedly wooly sounding) feel of the bike when moving it around, bunnyhopping, jumping etc. Look at BMX’s, the last 5 years have seen a massive drive to lighten those and they’re not doing it so they can ride 2% faster up a hill.
The overall weight of a bike does not tell all, you need to look at how that weight is distributed e.g. Pedals – the weight of these probably has nil effect on handling (ask yourself this – have you ever weighed your shoes / socks?) wheras a heavy wheel or fork can have a big effect.

Actually, the point I was making is that it’s psychology, so the answer is quite definitely yes. ‘Ride’ in this context is referring to the subjective interpretation of ride quality, rather than absolute physical characteristics of same…

Yeah but your perception is back to front. What’s actually happening is the bike that’s perceived to “ride light” is actually riding optimally, and the bikes that are, relatively, perceived to “ride normally” are actually “riding heavy”, or not optimally.

Sooner or later there’s an overlap between physics and psychology. Physics wins because, as we all know, all science is either physics or it’s stamp collecting.

Yeah but your perception is back to front.

Nope. There’s way more going on than basic perception, and it’s all based on expectations, beliefs etc etc. top down rather then bottom up processing.

as we all know, all science is physics or it’s stamp collecting

Do we really? Good luck trying to explain psychology in terms of physics… 🙂

Good article. Too much talked about weight when perhaps strength or stiffness are more important.

Barney all science is applied physics.

What?

Yeah but your perception is back to front. What’s actually happening is the bike that’s perceived to “ride light” is actually riding optimally, and the bikes that are, relatively, perceived to “ride normally” are actually “riding heavy”, or not optimally.

I’m not sure if you’re serious. To all intents and purposes they’re exactly the same, just a different way of thinking/saying it.

Sooner or later there’s an overlap between physics and psychology. Physics wins because, as we all know, all science is either physics or it’s stamp collecting.

…! 😯

Mattjg. Are you, by chance, a physicist?

But all physics is applied maths, if you take that logic. And something like – say – systems neuroscience is *quite* hard to simply describe purely in terms of physics, reductio ad absurdum or not.

Be that as it may, my central point stands: perception of how a bike rides is in part based on expectation.

No I’m not a physicist.

And something like – say – systems neuroscience is *quite* hard to simply describe purely in terms of physics, reductio ad absurdum or not.

Lots of things are hard, that doesn’t mean they’re wrong.

Be that as it may, my central point stands: perception of how a bike rides is in part based on expectation.

Fair dos.

Sunny day here, let’s go ride bikes.

@njee am not serious in the sense of thinking it’s important

http://xkcd.com/435/

My HT feels lighter than my FS, even though it is steel and I’ve weighed it, it is monstrous.

….but it still rides ‘lighter’

I think the stiffness and lack of linkage gives that impression, everything feels direct and responsive which I think confuses things.

balls == mathematician

Going back to one of the original posts, I think on the road, weight does make a difference. I know that on my heavy steel cx bike with road tyres I’m around 1 – 1.5 mph slower on average speed than on my “nice” road bike with the same tyres. The cx bike weighs around 2kg more, the position isn’t that different.

On the road there aren’t many variables so weight can have a bigger influence but off road you are throwing in suspension efficiency during pedalling and how well the bike rolls over terrain plus the roughness of the actual terrain which different bikes roll over with different levels of efficiency. In this scenario weight becomes far less important in my opinion.

There was a sort of scientific test in WMB a couple of years ago where they climbed a rough track at a constant wattage on three bikes, hard tail, mid travel FS and #enduro big travel FS. All virtually the same weight. Conventional wisdom says the hard tail climbs faster but it was actually slower than the mid travel trail bike because this bike had a better balance of traction, stiffness and ability to roll over the rough bits.

I’m sure there was also a university study of someone’s commute that showed that the weather had a much bigger influence on speed than anything else!

2kg more? So assuming a system weight of 80kg with your light bike, that’s 2.5% more mass. The only way that makes your average speed 1mph slower is if you spend all your time climbing at 40mph.

If like a more ordinary mortals you average 20mph riding on undulating route, I’d expect that 2.5% increase in mass to make at most 1%, or 0.2mph difference. Clearly there’s some other reason for that difference in speed – the difference the extra mass makes is lost in the noise.

Regardless of rider weight, my experience is a light bike (or perhaps to a degree a bike that “rides light”) is more fun to ride.

I had a proper light bike once – SS rigid with scandium frame and carbon forks – it was like riding a cloud.

Well it’s not scientific, I’m just telling you what my experience is from looking at strava and my bike computer. It’s entirely possible that stiffness is a factor – the cx bike is steel and the road bike is aluminium. It’s also relevant that I live on the edge of exmoor which has a lot of shortish but steep climbs. Any ride will average about 100 feet of climbing for every mile ridden. My Sunday ride last week was 42 miles and 4800 feet which is a very different profile from my mates in Southampton Sunday jaunt of 50 miles and 1450 feet. “Average” riders here will average around 16mph, there aren’t many except the semi pro club racers than average 20 plus.

For the record, I’m light and a fairly good climber – top 25% at least on strava segments. Maybe weight makes more difference if the route has more climbing or maybe it’s just down to overall efficiency of the bike, who knows. I will add that there is a noticeable difference in climbing speeds between the heavy and light wheelset I have for my nice bike…..

Not more than 2.5% difference, which is 0.4mph given your average speed. That’s if all of your ride is climbing – TBH my 1% figure was already based on quite a hilly route, if half your ride is spent climbing steeply enough that you’re only working against gravity then you might see 0.2mph difference for your average speed.

If your heavy wheels are 0.5kg heavier, then you can presumably notice a difference of <0.1mph.

The more you climb the more it matters, certainly. Every gram that’s lifted costs energy.

To my mind the original point is about handling rather than speed.

You can’t have a thread about bike “riding light” without mentioning the rather important fundamental difference between Mass and Inertia. Very much not the same thing at all……. 😉

Well computers and stopwatches are pretty accurate. Whatever, I’m only telling you observed facts I doubt I’m. The only one with this experience – obviously there are other factors. Weight will add to fatigue which will affect power output over time. Your sums don’t take that into account.

Scientists of the time said the earth was flat but it didn’t make it true did it?

Aracer’s points on weight vs performance are right in that 2kg won’t make the 1-1.5mph av speed difference, I think there are differences in bikes that can affect what we put in and get out though. Often it gets put down to weight alone when it’s more about feedback from inputs and how that affects how our perceptions of effort or motivation to work. It’s tricky to quantify but some bikes have something about them that means I ride them well, eg feedback that ends up in a higher or lower speed most of the time. It may be the way they accelerate under the first push on the pedal or the way they feel balanced over linked turns or the ride position encouraging a bit more effort, or not, etc. Usually an effective combination of factors, not one thing alone. Basically if you can work with the bike effectively a kilo or 2 makes no real difference. If the bike’s working against you somehow, even if it’s light it may not be that fast over a longer ride.
Ergonomics is a lot harder to get to grips with than weight so it gets less attention. So many variables and it comes down to whether you can tune into them or not, I try to, not easy though. I don’t weigh my bikes, have no more than an estimate for any of them and no real interest in it – as long as there’s no pointless/dead weight on there and they do the job, all’s well (so there’s still a psychological need for them to feel a ‘reasonable’ weight?). Yet for a longer race I’d swap out a few parts to save a kilo or two if possible, for what the watts or calories saved are worth.

Its seems to me that bike weight has remained surprisingly constant

It sems that for every reduction in weight we have added something that makes the bikes heavier. keeping the typical trail bike around 30lbs

In rough order we have

Suspension forks
Rear suspension
Disc brakes
dropper posts

Oh and ever more gears

So I think I started on my heaviest bike which was rigid and over 30 lbs (18 gears)
Then I had a couple of 28ish lb rigids
The second became a 29lb hard tail
Now I have a 30lbish FS with disc brakes

Never ever really done anything to save weight. But I’m grateful to everyone who did because without progress I wanted have added all those features for no extra weight

Ceeper I love data like your. One day try riding the light bike with a weight added to take it upto the cx bike weight. Oh and do you ride the CX bike in worse weather/winter, that might effect the data

Other factors, which are what are making the difference in your average speed. Position on the bike. The clothes you wear. How cold and windy it is. It’s not the weight.

Weight will add to fatigue which will affect power output over time. Your sums don’t take that into account.

Only if you’re pushing harder to maintain the same speed, but you’ve already told us you’re going slower. If your effort levels are the same (if not then all bets are off) it makes no difference at all.

Scientists of the time said the earth was flat but it didn’t make it true did it?

Gosh, not sure where to start with this one. Are you suggesting that basic physics concerning how much energy it takes to lift a given mass is likely to be wrong, or somebody will discover that actually different laws apply to bicycles?

Out of interest, which time are we talking about when scientists thought the earth was flat?

I think bike weight is the biggest and most over-obsessed distraction in cycling. It clearly matters when you’re fighting for podium places and marginal differences are critical but for the vast majority of cyclists, on and off road, it’s just a way to help you spend more money to enjoy a placebo effect.

In terms of handling, I have noticed a big difference in making a bike feel lighter (in a good way) by:

Shortening the effective stem length and widening the handlebar
Swapping a front tyre to a much lighter one with a rounder profile
Reducing (speeding up) rebound damping

Width and weight of tyres.

High volume Enduro gnarr tyres make my bikes feel more heft is required and not so skippy than when they have smaller volume and skinnier tyres. Feeling the affect of rotational mass.

But without the numbers… 😉

Lots of people thought the earth was flat but I doubt any of them were what we’d call a scientist.

Love STW – no opportunity for a meaningless spat ever ignored!