Lighter bikes are faster up and downhill. Fact. They make your ride more easier, faster and more fun. A lighter 6" bike will be much more entertaining than a heavier one.

They're easier to manouvre on downhills, easier to pop in the air, you're less knackered from the uphill, it's easier to maintain speed on the downhill and so you enjoy yourself more.

I'd much rather a 27/28lb 5/6" machine to something as big as my current bike which is 30lb. So long's the geometry stays the same, I'd be faster. And no, lighter bikes are not knocked off line more easily until you get to super low weights sub 20lbs.

I'm convinced that losing 2/3lbs off a bike will have more affect than losing 6lbs off yourself, and is much easier. I'm 11 stone now and my riding doesn't really change whether I'm down to 10.5 or up to 11.5.

Grr.

All this 'have a crap' stuff.. you morons. Have a crap when you need a crap. A light bike is still quicker up hills. Ride what you want but don't tell me my taste is wrong just because you're an arsehole.

Lightweight stuff's great, until you encounter rocks. Then it tends to bend..

Never broken any of my lightweight bikes (21lbs) until last weekend when the freehub broke which was one of the most standard parts on the damn thing. And they take a damn hard pounding.

YOU may bend light stuff, but you may be an oaf.

pointless having a weenie bike (apart from for pose factor) if you're not going to race on it

What's pointless is not getting the bike you fancy because someone on a forum informs you that it is wrong.

As for the percentage weight thing – 28 mins up the Cwmcarn on my 21lb bike versus 32 mins on my 30lb bike. Insignificant? Not in a race. Which bike do I usually take? The 30lb one. What does that tell you? That light bikes are faster up hills – SHOCK! 🙄

when was the last time u didnt pick a bike up an check weight ?

people who care about how good their camera is spend the rest of their time licking windows and stalking celebrities

Let's not forget also that a light bike is much easier to accelerate sharply, decelerate, flick through corners, hoick up over obstacles and finesse over technical bits – all of which make a great big difference to your fatigue levels on technical climbs such as Cwmcarn, which could explain my times.

I must admit I've not noticed much difference when saving or adding 1-2lbs on the road bike.. but on the MTB the difference is stark.

And since when is recreational MTBing all about time to the top of the hill? It's about feel, and light feels good on climbs and singletrack.

Weight off the bike feels more noticable, because the bike weighs many times less than you. All that your legs power however is the bike+you.

I KNOW it weighs ABOUT…

Probably find its a lot more.

Probably not, as it was weighed on some scales which were calibrated (& owned by Trading Standards, who my brother in law works for)

Oh & a 'clem' is a stone. Old NorthEastern word for large stone or rock.

Let's not forget also that a light bike is much easier to accelerate sharply…

only if it escapes you – if you stay on the bike you have to accelerate at the same rate. The bike can move relative to you, but only within a limited envelope.

As for the percentage weight thing – 28 mins up the Cwmcarn on my 21lb bike versus 32 mins on my 30lb bike.

Well that's down to something other than bike weight – different tyres maybe? Unless of course you only weigh 3 stones and moving the weight is the only thing affecting your speed.

aracer – read the second post.

only if it escapes you – if you stay on the bike you have to accelerate at the same rate. The bike can move relative to you, but only within a limited envelope.

Yes, and it does that all the time on a technical climb.

Barnes – have you ever actually ridden a 21lb bike? Seriously?

And they take a damn hard pounding.

May I ask you where you live? Maybe I should ask my friend from hampshire you rode with me today to get a logging on here then and do some explaning…

I live in South Wales. Where it's pretty rocky. And I push my race bike harder than my other bikes due to being in a race.

Let's not forget also that a light bike is much easier to accelerate sharply, decelerate, flick through corners, hoick up over obstacles and finesse over technical bits

MWAHHHHHHHH yes you are absolutely right. Now do something go to Fort william. Take your bike with you. Take two set of tyre. One will be apure semi slick XC tyres. The other will be a pair of very heavy/sticky maxxis DH tyres. Now you ride the same course twice and you tell me if your above statement it right…

Uh, you're being stupid Juan. I'm f*cking obviously not saying a light XC bike is better for donwhill racing.

My race bike has 2.0 Racing Ralphs on it – hardly semi slicks.

Why don't you try riding the same bit of woodsy singletrack on a race machine with 2.0 RRs on it, then on a DH bike with 1kg DH tyres on it, see which feels nicer.

Stupid…

Well molgrips I am not atlking a bout a DH bike but same bike different tyres so you just can see you talk shite. Cornering braking, going through obstacle has more to do with grip than wieght… And I wouldn't want racing ralph for fire road they are as shite as they get.

http://www.analyticcycling.com/ForcesLessWeight_Page.html

Hmmm no mention of rotating mass of wheels & energy required to accelerate same….. technical not!

Juan – we are talking like for like here your, far as I am concerned I'd rather pay a wee bit more & have some similar tyres / rims at 100gms lighter if I can.

If you keep an eye on weight & avoiding becoming obsessive (although it can be a dangerous route to go down) you can easily shave 50g off each component which can amount to 1kg in a full build – okay so thats f all when compared with my 87kgs, but seems to make a difference in the weird & wonderful world that I occupy. 😉

Racing Ralphs get me through the technical sections of races pretty damn quickly. They work for me.

As for grip vs weight – it depends on the course. If it's very tight and technical (like say a Gorrick) then your overall speed will be slow, but there will be a lot of acceleration and deceleration. So grip is less important than low mass. And rolling resistance of sticky DH tyres is typically very high. Everyone interested in bikes knows this, apparently apart from you.

Do not tell me I am talking shite. I know a lot about bikes and I am very intelligent.

Something I learned in my early riding days 20 yrs ago, IT MAKES NO DIFFERENCE TO THE GRIN FACTOR.
Just ride the bloody thing.

Juan is wrong. I can't really put that much different really.

Well, I'm pretty sure I would break a 21lb race bike without changing my riding style and I'm no fatty or phat air freak.

But in answer to to OP – judging from the answers there seems to be plenty of weight weenie obsessed here. 🙂

Hmmm no mention of rotating mass of wheels & energy required to accelerate same….. technical not!

Oh dear….

Please show me the maths that demonstrates the difference between mass and rotating mass when the context is a bicycle….

Please show me the accelerations produced by the average STW rider….

Rotating mass in bicycle terms is just the same as mass; the old 'a pound off the wheels is worth two/three off the frame' might give some small advantage but you'd be better off getting more aero than losing weight.

I'm not saying light bikes aren't more fun, or more desirable, but the effect of bicycle weight when considered as a part of the total weight of bike+rider+Camelbak+water+all the other stuff people seem to need is way less important than people think.

Juan wrote, "MWAHHHHHHHH yes you are absolutely right. Now do something go to Fort william. Take your bike with you. Take two set of tyre. One will be apure semi slick XC tyres. The other will be a pair of very heavy/sticky maxxis DH tyres. Now you ride the same course twice and you tell me if your above statement it right… "

Do you think those tyres are better because they're heavy? Here's a better comparison- fit heavy XC tyres, something horrible like a Factory XC, then fit DH tyres that weigh less. WHich is better? Still the DH tyres. If you really believe that heavy is better, why is it that your only example has nothing at all to do with weight?

Please show me the maths that demonstrates the difference between mass and rotating mass when the context is a bicycle….

Well do a Physics A level and they'll tell you all about it 🙂

To accelerate a bike forwards, you need to give your wheels (and the rest of your bike) forward momentum, but you ALSO need to give the wheels angular momentum. The two are independent – you can have a wheel spinning and not moving forwards – and you can have it moving forwards (as in the back of a car) but not rotating.

Can I suggest something? Can all posters state the approximate weight of the lightest bike they have ridden? I'd like to see if anyone can say 'yeah I've ridden a 20lb XC machine and it felt no different to a 28lb AM machine'.

aracer – read the second post.

Yeah I saw that – so assuming you actually weigh 12st, 25% of the climb would have to be bits where the weight of the bike was the only factor in how fast you were going (due to "flickability") to explain the difference. If we get very slightly more realistic and assume that the "flickability" only has a 50% effect on your speed (with the other 50% being down to rolling resistance, air resistance, lifting your total weight up the hill etc. – ie all the normal things that affect your speed), then half the climb would have to consist of bits like that.

I still reckon it's the tyres – or maybe a less efficient pedalling suspension system – or just possibly psychological.

In compliance with your latest request I'll point out that I ride a 21.5lb full-sus (and have a <15lb road bike).

If it's very tight and technical (like say a Gorrick)

Now I am really laughty out loud.. Please if you think gorrick it technical get a grip…

Barnes – have you ever actually ridden a 21lb bike? Seriously?

of course not, as I've said before, I wouldn't take anything I felt as a measurement anyway. Certainly, if the bike accelerates differently to me for more than a very short period it will necessarily be somewhere else 🙁

Well do a Physics A level and they'll tell you all about it

Got one of those ta – got a fairly decent grade in it too. Also got an engineering degree. All that means is that I agree with crikey – the effect of acceleration on cycling (even technical MTB) is vastly exaggerated.

Crikey – way too long since I did my Physics & Maths A levels, but I can assure you that acceleration of a 800g weight weenie tyre & rim combo compared to the same of a 1300g all mountain/trail combo is significant – and then multiply that by all the start stops in a single mtb ride.

It's ok, honestly, there is a large section of the bike industry and a significant part of the advertising industry (in bike terms), plus a number of bicycle magazines who depend to a great extent upon people believing the 'reduce weight by X grammes and you'll be lots faster' thing.

It's not true, but that's ok..

As I said, it seems that bicycles don't obey the laws of physics anyway…

Light bikes are great, but they don't make you noticeably faster, unless of course:

There are two "non-technical" explanations for the effects of light weight. First is the placebo effect. Since the rider feels that they are on better (lighter) equipment, they push themselves harder and therefore go faster. It's not the equipment that increases speed so much as the rider's belief and resulting higher power output. The second non-technical explanation is the triumph of hope over experience—the rider is not much faster due to lightweight equipment but thinks they are faster. Sometimes this is due to lack of real data, as when a rider took two hours to do a climb on their old bike and on their new bike did it in 1:50. No accounting for how fit the rider was during these two climbs, how hot or windy it was, which way the wind was blowing, how the rider felt that day, etc.

Another explanation, of course, may be marketing benefits associated with selling weight reductions.

From wikipedia, and so taken with a pinch of salt, but still way more dependable than STW..

Crikey, if you understand the website you posted you must also know just how incomplete their model is. For one thing, it only gives rolling resistance up to "paved but rough surface" which would be more or less a very good fire road, beyond that you have to guess, and it doesn't qualify what sort of bike or tyre so the rolling resstances could be wildly off. It doesn't take into account variations in slope at all- when did you ever ride a completely constant slope? Or obstacles on the trail. But most importantly it doesn't give you the time lapsed, just the time saved which leaves the numbers meaningless unless you go digging.

Basically, if we could punch numbers into that and it'd tell us how long it takes us to ride the distance in total, that'd mean we could sanity check the numbers. I don;t need to give you numbers to show the weakness of the set you've provided. But, here are some anyway.

Take a nice sensible real world climb, let's say 10km of climb for 500 metres of gain- sounds like a fairly typical trail centre "one up one down" climb to me. Throw in my exact weight numbers.

The numbers that you get back say that if you save 3 kilos (the difference between my Kraken and my Soul, effectively) and it tells you you save 74 seconds, and that those 74 seconds equate to 340 metres. So simple maths, we have an average of 4.5 m/s, which would mean that you've done your 10km climb in 37 minutes, at an average of 10mph, no breaks. Don't know about you but I bloody don't!

In short, I think that both the conclusion you drew from the model is wrong, and the model itself is wrong 😉

From wikipedia, and so taken with a pinch of salt, but still way more dependable than STW.. 😆

Hmmm interesting, think I'll have to give my son a few calcs to do whilst he's revising for his mech eng degree & see what he can sus out from first principles.

Bet I'll still be pissed off that I put some 570g AM rims & fatter tyres on my prince albert though 😥

but I can assure you that acceleration of a 800g weight weenie tyre & rim combo compared to the same of a 1300g all mountain/trail combo is significant – and then multiply that by all the start stops in a single mtb ride.

but you're multiplying it by the wrong thing – yes, the angular component more or less doubles the effective inertia of the rotating components – but unless you take them off they have to accelerate at the same rate as the rest of the bike and the rider – which have about 50 times the inertia – so the the 1.3 – 0.8 = 0.5kg, even doubled up is still less than 2% of the all up figure.

…and energy used for acceleration in cycling (even technical MTB) is a tiny proportion of the total energy used.

Do you see what you've done? You've got me agreeing with sfb on a weight weenie thread. Have you no shame?!

The model isn't perfect, but it does go some way towards quantifying the silliness inherent in the 'help me save 2 kilos and therefore watch me ride off into the sunset at 100mph' argument.

It's also the best analysis of weight saving that I'm aware of, and, as above, if you can show me a better one, I'm ready and waiting.

SFB gets closer than anyone to the real decider; we all accept that power to weight ratio is the real defining equation when it comes to bicycle performance….

Changing bicycle weights by a realistic figure of 1, 2 or even 3 kgs doesn't impact that much on your power to weight ratio; the weight has to include everything from your socks to your multitool as well as you, your breakfast and your bike.

If lightweight was so great, why do mountain bikers ride about with half the bloody kitchen on their back?

If lightweight was so great, why do mountain bikers ride about with half the bloody kitchen on their back?

I don't – I also have light shoes, light helmet and light clothes (lycra rather than baggies).

Sorry – slight diversion there, I'll get back to arguing on your side again in a minute.

Ahem, 'most mountain bikers I see at trail centres'… 😀

Now I am really laughty out loud.. Please if you think gorrick it technical get a grip…

F*cking hell Juan if you were here I'd thump you. Maybe at the speeds you ride at Gorricks aren't technical, but at my lightening pace it's a white knuckle ride. Trails alone aren't what makes a technical ride, but of course if you knew more than c0ck all about biking you'd understand that. Otherwise, that Lewis Hamilton would have to be a right useless driver – all he ever drives is totally flat and smooth!

I'm a competent technical rider, and I've ridden all sorts of trails. So please stop insulting me for absolutely no reason. Your default positions seems to be that I am a complete idiot – whereas in fact, if you resepcted me as an experienced cyclist and took the time to talk through and understand what I am saying you might learn something, or at least see what I am trying to say. Riding a Gorrick course slowly is easy, riding it very fast is not.

As I said, it seems that bicycles don't obey the laws of physics anyway…

That or your model's incomplete…

From wikipedia, and so taken with a pinch of salt, but still way more dependable than STW..

Who do you think writes Wikipedia?

Barnes and others – your models seem only to take into account the amount of weight lifted over a height. This is clearly not the only factor in a technical off-road climb.

I did some calculations on here a while ago that showed that a given weight saving made far more difference to the acceleration, deceleration and handling of a bike than it did to the amount of energy required to lift it up the climb.

Here's something. You are using a simple model that takes into account the mass of rider and bike and the height of the climb. Of course, there is rolling resistance and air resistance to take into account, but those two things would be the same. But consider this – a flat piece of tight twisty singletrack ridden hard at say 15mph will raise your heart rate quite a bit. A flat piece of fire road at the same speed will hardly raise it at all. Try and ride the singletrack at 17mph and you will find it a hell of a lot more difficult than the speed increase woudl suggest. Why? Cos a lot of effort goes into controlling the bike and braking and accelerating.

I'm obsessing a little with weight, as being new to XC racing I took my stock trail steel HT, swapped a few components/tyres etc.. dropped 2-3lb out of the bike and I'm definitely noticably faster, I've timed myself on loops.

Can't see why people have a problem with trying to make their bike as light/perfect as possible for whatever budget they have to spend on thier hobby.

I have re spoke's first post of the page and, although he might be right to some extend he kind of forget something… I want to finish my bloody ride. I don't know how 27 lbs translate in real world figures (aka metrics), but it seems very light for me. To take the rim example, we (by we I mean me and my mates) have tried the DT rims (going from mavic 717 to dt whatever they are). After 2 month everyone is back to mavic. Dt were lighter but much more fragile. So all the weight figures you guys are quoting are good when you are doing "super gnar tech races like gorick" but when you ride to normal speed in the real stuff it's a whole different story. And yes I am sorry molgrips but putting gorrick and technical in the same sentence is talking shite.

Once again if light is better, light is stronger why oh why DH bikes are no XC light?

F*cking hell Juan if you were here I'd thump you. Maybe at the speeds you ride at Gorricks aren't technical, but at my lightening pace it's a white knuckle ride.

Ok I bet you the price of the plane fair to nice that
Gorrick ain't technical
And that I'll beat you up and down on a tech trail here.
Sound fair isn't it.

I had a ride with a friend of mine today. I use to ride at gorrick he uses to do very well (he won the sport category at busas in dorset) so not a "slow rider" by any account.

Now if you want I can ask him to pm you about today's ride.