Why don't you do a test? Find a 140lb person, make them ride your heavier bike, time it. Then give them 10lb of stuff to put in their back pack, put them on the lighter bike, see what happens.

Hi kilgoretrout,
You don't end up lower on the other side of the bump, because the bike is moving down into the bump, not you, same as the suspension on your bike.

snowslave, sounds a good idea. I guess you'd need one of those power tap cranks to measure the amount of power the person is using too, and some other clever stuff to make the test suitably accurate.

Pfft – you've not even taken the colour of the bike into your calculations. Everyone knows that a rad colour will be quicker.

It shouldn't really matter what weight the bike is, the lighter rider will usually have a better power to weight ration and will therefore get up the hills easier. There are always exceptions to the rule, but you will never normally see a heavy guy in the polka dot jersey.

@Ian:- Basically you bastardized the wrong bit of pop physics terminology stolen from MBUK…

@mavisto:- While the lighter individual has a higher personal power to weight ratio on their own, couple them with a 10Lb heavier bike and the entire Rider + Bike package has a lower relative power to weight ratio, which is of course the one that matters in the given scenario…

cookeaa

If the lighter rider was carry a rucksack with the 10lbs in it I might agree with you, but the rider isn't actually 10lbs heavier, only the bike is. So the actual weight of the bike they are moving is only a proportion of the 10lbs because the road is taking the real loading.

The great thing about Mountain Biking is that there's too many variables for this comparison to ever mean anything 😀
cheers

Why are you assuming that a lighter rider has a higher power to weight ratio?

you will never normally see a heavy guy in the polka dot jersey.

Or in fact riding the TdF.

I have a 22lb hardtail and a 28lb full susser, the lighter bike overall is quicker on a run. Although down hill the full susser is quicker. This means I find the lighter bike makes up more ground on the uphills than it loses going down. When I put weight on I just get slower.

The great thing about Mountain Biking is that there's too many variables for this comparison to ever mean anything

YUP, couldn't agree more!

I used to weigh 10 stone, I now weigh closer to 12 stone. I was a skinny runt as a teenager, now I'm in my late 20's I filled out a little, and most of that 2 stone gain is muscle. So I'm actually quicker on my bike most of the time than I used to be when I was younger (fitness notwithstanding!) as although I'm heavier than I was, my power/weight ratio is probably slightly better.

Put me on a 35lb bike next to a guy 10lb heavier than me on a 25lb bike, and I can tell you who's going to be quicker… Unless he's seriously unfit, the slightly heavier (in the grand scheme of things) guy on the significantly lighter bike is going to be quicker. Why? Well I'd suggest it would be mostly due to rotational weight. A heavier bike has heavier wheels and tyres 9 times out of 10 than a lighter one, and this is the key I think. Force required to accelerate rotational weight increases as a square of the weight, so if your wheels were twice the weight, they'd require 4 times as much effort to accelerate… Or so the theory goes…

But there are still WAY too many variables as mentioned before…

here is some intersting numbers,, a bit off topic

rider 92.8 kg 6ft plus rider

kona kula primo hardtail front 37.2 kg rear 70kg
Blur full sus front 43 kg rear 65kg

both bikes large size

not sure the numbers will add up totaly as the measurments were only done on a pair of bathroom scales and an average of a few goes

So… going back to my previous post, given two roughly similarly fit riders, does anyone genuinely believe that the 40lb bike will climb as fast as the 20lb one without a massive disparity in riders.

Fwiw, my 30.5lb Pace RC405 with Pikes and big rotors, wheels, tyres, was fast enough to get top ten in the weekend warrior class at one of the Lee Quarry races. I did kind of wonder how much difference my 23lb race bike would have made, I think it might have been worth a couple of places, then again, there wasn't a huge amount of climbing per lap.

@Ian, I'm still not seeing what you're claiming. You seem to want to say that when you ride over a bump you're lifting all the weight of the bike but only some of the weight of the rider and that therefore if bike+rider weight is the same then the combination with the lighter bike will be better.

Assume the road is level,you climb over the bump,you retain contact with it and then return to the same level again with you at the same position on the bike as you were before the bump, you must have had to lift the whole weight of the rider+bike up and over the bump. Where am I going wrong here?

@snowslave, like the idea of the test, doubt I have the resources to create anything approaching a rigorous scientific version of it, but would be interested to see the results.

@BadlywiredDog, isn't that what we're debating? I've not yet seen a good reason to think that assuming both riders have equal strength but the one on the 40lb bike ways 20lb less than the one on the 20lb bike, that there will be a difference (assuming also that the bikes have similar specs bar). I take it the one potential place where there is a good reason for thinking the weight of the bike is important is the force required to turn heavier wheels, but I guess if we also keep the wheels the same then I'm not seeing why the 40lb bike should be slower if it's got a lighter rider.

but I guess if we also keep the wheels the same then I'm not seeing why the 40lb bike should be slower if it's got a lighter rider.

I think the thing is that it REALLY depends where the weight is (both on the bike and on the person), and what it's doing…

If a bike has a heavy frame, but is otherwise fairly light, it's only like carrying a couple of pounds of extra fat on your body. It's not really worth worrying about. But wheel weight, especially rims and tyres, will be fairly detrimental to performance.

On the other hand, if your body weight increases due to muscle gain, this is going to actually have an improvement on your performance on the bike (most likely), whereas obviously a few pounds gained in fat won't help. But a couple of pounds on your belly will be FAR less detrimental than a couple of pounds added to your wheels.

I'm quite tempted to blame thatcher at this point

@snowslave, I fail to see how building bikes out of coal would help matters.

I disagree with the view that losing body weight is the same effect as losing bike weight – cheaper on the wallet maybe!

Yes, both have more inertia and need more energy to get them moving. But your body mass is distributed around your body and moving that around is quite efficient. When riding, bike mass is attached your extremities: feet, hands and bum a bit, and moving it means putting your energy through the bars and pedals/sprocket/chain/sprocket/freehub/wheels/tyres which is more lossy.

Here's a half-@rsed analogy considering the "extremity" aspect: Imagine holding/moving a basketball at arms length for half an hour (ouch). Now do it with a medicine ball (bet you can't). Yet the difference in mass between these balls is just a few pounds compared to your 160lb body mass. Will losing 5lb of body fat make it easier to handle the medicine ball?

Another view. Can an uber fit, but petite rider pedal and throw a 40lb bike around as easily big, powerful rider? I have found that my limit for an enjoyable ride is sub 30lb. I can ride heavier bikes, but it's a struggle to move it around and pedal productively because I'm not powerful enough.

Finally, if reducing the weight of your bike by 1kg only has the same effect of leaving a 1L water bottle at home, why do competitive riders spend disproportionate sums on light bikes?

Comments?

Didn't MBR do a thing a while back where they timed a bike over a set course, weighed it down, lightened it up, weighted the rider etc. I can't remember what the conclusions were, sorry.

It's like bikes operate under a whole different set of physics than everything else!

People keep on mentioning rotating weight and claiming it is so important. I think you'll find that the rotating weight thing and its popular saying 'pound of the wheels is worth three off the frame' doesn't actually stand up to much serious scrutiny.

Rotating weight becomes more important during acceleration, but the actual acceleration that your average middle-aged IT manager is capable of exerting tends to be somewhat less than significant.

Anyway, as you were….

I thought the reason rotating weight was so important in mountain biking was because over rough ground you had to keep on accelerating the wheels, as bumps try to stop them?

I thought the reason rotating weight was so important in mountain biking was because over rough ground you had to keep on accelerating the wheels, as bumps try to stop them?

Various roady sites, http://www.roadbikereview.com in particular have this discussion about once a week. The upshot is that weight on the wheels is far, far less significant than everyone assumes, largely because the accelerations are so small, and heavier wheels tend to have a flywheel type effect; ie they don't slow down as much, so don't need as much acceleration….

I'm surprised that no one has mentioned how a 40lb bike would tire much quicker uphill than someone on a 20lb bike, regardless of how heavy they were to begin with. Quite a ridiculous post.

YOu haven't read his post.

Imagine you ride up a hill on the 40lb bike.
Now you switch to the 20lb bike, but carry a 20lb rucsac.

What's the difference?

People seem to have got lost in the whole idea that the lower weight person can handle the bike less well etc etc.. but if you look at it like it was originally intended..
The only answer is that the lighter person will be better. With rigid forks added then we can rule out all the faff people have come up with. SO all that matters now is distance and weight. Now for the total this will be identical. However, assuming the rider has the extra weight spread across their body, moving their legs the same distance will mean more work done. This means that with work done being equal, as stated in the original post, the heavier rider will be able to pedal less well regardless of bike weight. Meaning the light rider will win.

BadlyWiredDog – Member
Didn't MBR do a thing a while back where they timed a bike over a set course, weighed it down, lightened it up, weighted the rider etc. I can't remember what the conclusions were, sorry.

The conclusion would of course be that a 140mm full-sus bike is ideal for all riding in the UK regardless of weight or rider (or terrain for that matter), and that you are a numpty if you ride anything else, or wear lycra, ride road bikes etc, with a sub-text of "BUY SPECIALIZED, BUY SPECIALIZED".

Got lost? The original posting said the riders were of equal fitness, ergo the heavier bike will tire the lighter rider quicker uphills, and more likely the heavier bike will take more strength to pilot down too.

I recently changed bikes, losing 6lb.

I then lost 28lb off me.

The difference it made in each instance was probably about the same to be honest (ergo it seems bike weight is the winner), but you have to factor in that I have a much lighter wheelset and the body weight loss also equalled extra fitness.

However, losing 6lb off a bike can cost a lot of ££££££'s and losing weight has saved me money, as I'm eating less.

From a personal perspective I wouldn't want to lose more than another 7lb from me, so I'd get to a point where the only option would be the bike, although I'm not sure I'd want to go much lighter than 28lb for a 6" FS.

@TheArtist, thanks for that, very interesting.

"accelerations are so small"

On the road bike, yes the accelerations are minimal because your effort is maintaining constant speed.
Totally different off-road – constant variations is speed due to bumps, changes in gradient and braking = lots of acceleration.
So I assert that the light wheels have a significant reduction in required effort/power in off-road situations

BTW. In the MBR "experiment", they just stuck a heavy backpack on a skinny rider; adding to rider weight but not rider power. If you are 6' 2" and fit, much of your extra weight is muscle and you have proportionately more power. Ergo, you can handle a heavier bike.

Waffle, waffle, waffle…

Surely back in the real world, it works like this. The same rider will generally be quicker on a lighter bike than a heavier one if other variables – rolling resistance etc – are equal. So what you want is the lightest possible bike that's fit for your intended purpose – might be 35lb for downhiller or 18lb for a pure XC race bike.

Of course you're better off being light and strong as well, but the whole thing about rider weight is only relevant in the sense that big, fat blokes use it as a rationalisation to buy a lighter, expensive bike on the 'I need all the help I can get ticket'.

If you are 6' 2" and fit, much of your extra weight is muscle and you have proportionately more power. Ergo, you can handle a heavier bike.

Handle maybe, but you'll still have to work proportionately harder on climbs to lift that extra bulk against gravity won't you, so the extra power may not be 'enough' 😉

Another excuse made by big people – 'It's all muscle'…

No shit sherlock

But OP said to assume both riders could output the same power. Bike & rider combined weight is the same for both too.

Doesn't this thread only exist because some poor people can't afford to make their bikes lighter and so have to think of ways around it?

Doesn't this thread only exist because some poor people can't afford to make their bikes lighter and so have to think of ways around it?

LOL
Or
Doesn't this thread only exist because some fat people can't be bothered to loose weight and so have to think of ways around it 🙂

😆

OK, slightly different scenario, but I have looked at my log for commuting betwen 2006 and 2009. Rider fitness and weight have varied a bit, as has bike components, expecially tyres – BUT, over that period of time I have had access to either 2 or three bikes for riding to work, and the relative mileages and average times for the same journey cast some light on the heavy bike vs light bike question…

Bike 1 – 2715 miles, average time 1:07:51, best 0:53:31

Bike 2 – 454 miles, average time 1:12:22, best 0:55:53

Bike 3 – 1058 miles, average time 1:12:14, best 0:55:32

I am really surprised by the results too!

Bike 1 is a circa 24lb race geometry hardtail. Very quick uphill on the commute, but a bitch to handle on the downhills. It's no coincidence that this bike has by far the highest mileage on this journey – it's light, quick and the bike of choice.

Bike 2 is also a no surprise – a circa 32lb Giant Reign. Fun on the DH section of my commute, but a tractor everywhere else. When I rode this to work I was absolutely shattered by the time I got home.

Bike 3 is a real surprise – a Pace RC305 built up to about 25.5lb. It feels slower uphill that the other HT, but is quicker DH – all down to the geometry rather than the rather modest weight difference. BUT, the average time on this bike is almost the same as that for the Giant, which always left me knackered (the Pace doesn't).

I guess that the Giant must have been significantly quicker downhill to account for the similar times. FWIW, I sold the Reign, because it wasn't getting enough use. For all day rides it was just too heavy and impaired my endurance too much

rkk01, you log your commuting times and bikes that you've used. 😯

That IS dedication.

Anyway, you've proved that a lighter bike is quicker than a heavier bike on that particular journey. Well done.