bicycle weight and commuting times

[welshwheels]

I have often wondered if the weight of the bike does make me faster on my commute I bought a road bike in the summer and it definitely  made me faster over the hybrid i was using  6 or 7 minutes each way on a 11 mile quite hilly commute ! i found this Bicycle weight and commuting time: randomised trial -- Groves 341 -- bmj.com . I changed from hybrid to road bike the gentleman in the link upgraded to a carbon road bike  and found over a 27 mile commute was no quicker . Anyone else on the forum got similar experience ?

[MSeries]

The trouble with commuting is the stops. All bikes are the same when stopped. It's so easy to lose much time due to circumstances beyond your control and hard to make it back up by exploiting the bikes lightness.  Are you sure it was the lightness of the bike that made you faster or was it the improved position of a road bike that enables you to ride it more effectively ? Wieght your road bike so it's the same weight as your hybrid then repeat the trial. To answer your question from my experience,  I have no idea, I never timed my commute when I did it regularly and my bikes all weight about the same anyway.

[hellymedic]

Note Anecdata from BMJ...

[iakobski]

The trouble with commuting is the stops. All bikes are the same when stopped.

If you're just talking about weight, all bikes are the same when doing a constant speed on the flat. A lighter bike & rider will accelerate faster for the same power, so the more stops, the more likely the light bike will be quicker. Same with hills - the OP mentions hilly - the light bike will climb quicker for the same power.

Are you sure it was the lightness of the bike that made you faster or was it the improved position of a road bike that enables you to ride it more effectively ? Weight your road bike so it's the same weight as your hybrid then repeat the trial. To answer your question from my experience,  I have no idea, I never timed my commute when I did it regularly and my bikes all weigh about the same anyway.

Yes, as the BMJ paper says, a lighter bike is only a tiny percentage of the bike + rider so a time saving of 10-15% is unlikely to weight alone. Aerodynamics is a big difference out on the open road, even riding on the tops, and perhaps a bit from the tyres. When I changed from a light, skinny-tyre hybrid to a drop-bar bike my commute times went down by a similar amount, the weight of the bikes was about the same.

[MSeries]

So the time saved by the improved acceleration has to be greater than the time lost by being stationary.

so the more stops, the more likely the light bike will be quicker

It is not as simple as that though is it. It depends on how long the stops are. With no stops and same contants crusing speed, the lighter bike will be quicker since it can be got to that crusing speed in a shorter time. Add a stop, same duration for both rides and it'll still be quicker due to the less time needed to get to the cruising speed. But commutes are not like that, stops are uncontrollable, the weight of the bike has no influence on how long the stops are. But yeah, the theories say that lighter bikes are faster for the same rider under the same conditions (which rarely happens on a commute)

What about accelerations down hill ?

[TimO]

A lighter bike is likely to be faster, for the reasons stated, but I don't think the difference is going to be much.

The difference for me on a fifty minute or so commute, between a lightly loaded bike, with the wind behind me on a Monday morning vs a heavy load, with wind and rain against me, in the cold, at the end of a hard week, with poor traffic conditions is possibly ten minutes, ie about 20% variation from the easiest to the worst.  Most of that is down to the conditions, and not the bike.

The difference between a fast bike and slow bike is probably something like ½mph for my average speed (my average, average commuting speed is about 14.5mph).

I haven't tried my commute on the fast red bike (or indeed done anything on it, because of the recent weather!), but it may turn out to be able to get me into work in half an hour, although I doubt it, since doing better than evens through London traffic is pretty damned unlikely.

[hellymedic]

This is a hilly commute. The rider is likely to apply his brakes and ride cautiously if the bike feels skittish; this may be more likely with a lighter bike...

[mrcharly-YHT]

^+1

It's been very interesting for me, going back to the mercian from the ribble. The ribble is essentially a road bike, with road bike handling. The mercian is a touring/mtb.

The mercian is lighter, by far. However, at speed the steering gets lighter and lighter; I get a bit cautious about pushing it. The Ribble feels rock solid at speed, but is not good at slow speeds; indeed, it gets 'shimmy' when riding at 10mph.

In decent conditions and visibility, I'm much much faster on the ribble; cruising speeds of 19-20mph, vs 16-17 on the mercian.  But in bad weather, lousy visibility, I'd rather ride the bike that has predictable handling through potholes, over chunks of snow, and that's the mercian.

So I think it is horses for courses. Yup, it's all about the bike, Lance.

[MSeries]

Shimmy for me has always been caused by bad tracking or uneven luggage distribution, not low weight. Bike design & it's loading defines it's handling. Low centre of gravity usually means bikes are more stable at all speeds and this is particularly apparant at high speeds when things happen quicker. There is a lot more to it that just weight.

[tonycollinet]

Saving in bike weight is a tiny proportion of weight of bike + rider. According to a fag packet calculation I've just done based on my weight, and cruising speed, over one Km I would save about 0.1s if my bike weight was reduced by 4Kg. So for my 14km commute, and assuming on average, a stop every 1km, then I'll save about 1.4 seconds due to bike weight alone. For someone 25kg lighter than my rather lardy 85, then the saving only goes up to around 2 seconds. (Calculation assumes flat ride)

So any significant difference must come from other factors:

Tyres = lower road drag
Rider position = greater efficiency
Rider position = lower wind resistance
Nice new clean bike = lower bearing resistances, and drive train drag

Probably the biggest effect is:

Shiny new bling bike = try harder.

[Ham]

The trouble with commuting is the stops. All bikes are the same when stopped.

Sorry to disagree but it's much easier to see and be seen with go faster bling when you're stopped 

I think apart from the actual weight, there is the responsiveness factor, which is all to do with the stickiness of the tyres (weight, tread), gearing, drivetrain, plus the feeling on a lighter bike that you get more back from pushing the pedals, which is encouraging.

[simonp]

My fastest commute times have been done on my Pompino.  I conclude that riding a bike that makes you want to ride like a bandit is the biggest factor.

I reckon I could beat the time on my carbon bike, but not by a great deal.  17 minutes for a cross-town 8.5km commute is already pretty quick.

I gain most from not having a pannier and having a saddle bag instead, reducing wind resistance.  25mm tyres are a much better bet than the heavy 32mm tyres on my Galaxy.

[matthew]

My fastest times to work have been on my fixie, home is on the geared. I conclude that given the weight of luggage I haul to the office the weight of the bike is negligable.

As both frames are drop barred tourers the handelling is simmilar and the tyres the same, it is the ballance between the climbing / decending that counts.

On the way into work I climb the 'scarp' slope of the hill (bump) and decend the dip slope so not being able to change down forces me to muscle my way up and I don't spin out on the way down. Therefore the fixie is faster.

On the way home the dip slope would not have me changing down and I spin out on the scarp slope at 25-30mph where the geared bike goes on to 35mph.

[hellymedic]

My fastest commute times have been done on my Pompino.  I conclude that riding a bike that makes you want to ride like a bandit is the biggest factor.

I reckon I could beat the time on my carbon bike, but not by a great deal.  17 minutes for a cross-town 8.5km commute is already pretty quick.

I gain most from not having a pannier and having a saddle bag instead, reducing wind resistance.  25mm tyres are a much better bet than the heavy 32mm tyres on my Galaxy.

Yebbut Cambridge is a bit different from the Peak District, innit?
Lumpy commutes are a different ball game...

[Biggsy]

I don't doubt that bike weight makes only a small time difference on a typical commute, but this research isn't much use because not enough variables were eliminated.

"My new bike seemed wonderful, if somewhat uncomfortable".

Even if the discomfort itself didn't affect his efforts (unlikely), the fact that one bike is more comfortable than another shows that there is more difference between the bikes than weight.  Yet this is supposed to be specifically about bike weight.

Groves would have been better to have used the same bike all the time, but with lead weights in the frame tubes for half the time.

I'm afraid it takes more than the author being a doctor and the write-up done in a formal style to convince me.

[mattc]

Groves would have been better to have used the same bike all the time, but with lead weights in the frame tubes for half the time.

Good point - it would have made a much less "interesting" article, but far more useful!

[pdm]

I'm afraid it takes more than the author being a doctor and the write-up done in a formal style to convince me.

You should also be aware that the Christmas edition of the BMJ is traditionally reserved for off the wall, amusing and otherwise "fringe" articles, mainly meant as entertainment; although many do try to make a serious point as well.

[arvid]

If you're just talking about weight, all bikes are the same when doing a constant speed on the flat.

No. Increased weight is increased rolling resistance. </somebody'swrongontheinternetIhavetocorrecthim>

[Biggsy]

No. Increased weight is increased rolling resistance. </somebody'swrongontheinternetIhavetocorrecthim>

Even when tyre air pressure is suitably increased? </somebody'smaybenotrememberingsomethingIhavetomentionit>

[mattc]

Friction = weight x mu [coeff of friction]

I don't _think_ you can beat this, if you compare two bikes both at optimum tyre pressure.
[but I'm being cautious, as tyre friction is a funny business!]

Whatever the details, I'm fairly sure heavier bikes/riders/luggage go slower even on pan-flat roads. I've seen it on the internet! But the difference is very small, much less than the difference when climbing.

Track riders (on longer events like the hour) wouldn't bother so much on cutting weight otherwise.

[Biggsy]

Friction of tyre against ground is only a small part of rolling resistance.  Flex within the tyre is the major part.  How that is affected by weight, when the tyre is at optimum pressure, is too complicated for me to even start thinking about.

[arvid]

In a velodrome it's worse because in the corner you get a G extra or so, maybe even more. And an extra G is a doubling of the rolling resistance.
This is a reason that velomobiles don't have a real big benefit in a velodrome, since they're around 20kg at least, most 30-40kg.

Extra weight also has an effect on bearings. I agree that weight is usually negligible on an upright at constant speed on the flat. But that doesn't mean it has no effect.

[itsbruce]

My two bikes are fairly different animals (if both steel): a fixed gear track frame with drops and a Charge Mixer (flat bar road bike with alfine hub).  My commute to work is the same on either; variables like traffic lights and weather are hugely more significant.  It would require more consistent conditions than a London commute to give one an advantage over the other.

[hellymedic]

This is from the Christmas BMJ, which is not very serious.

Each commuting journey is subject to many variables.

Biggsy's right of course about an 'uncomfortable' bike. Lead weights would not change the rotating weight though.

If the collected body of commuting yacf members had the motivation, time and energy, we could repeat this experiment and gather more statitically significant data.

I suspect a very slight increase in speed would result from using a lighter bike, but the difference may be unimpressive.

[tonycollinet]

Very Very unimpressive