Author Topic: How important is weight?  (Read 3660 times)

How important is weight?
« on: November 18, 2011, 03:04:54 pm »
Replying to another thread got me thinking about weight, along these lines. Most of us come from the world of DF bikes. These are very similar to each other - differences are measured in a few mm's or degrees. and one of the few variables is weight. So whatever category of DF bike you ride (e.g. Racing / Touring / Audax) weight is one of the things you can vary. However on a 'bent there is not such a degree of uniformity. And they (with a handful of exceptions) weigh more than a DF. Variables exist in wheel size, wheelbase, seat height, seat to b/b height and riding position (reclined or upright (closed)). Does weight lose some of its importance amongst all these? What do you think?

I don't race. I'm a tourist and enjoy faster one day rides. My diary entries (I know, I'm a sad git!) of ride times and conditions on my 'control' circuit do not seem to demonstrate that the lightest bike is the fastest. This year my fully tour kitted ICE B2 has produced the best times with my Giro 26ATT (a much lighter machine) close behind. I suspect that the B2 closed position and slightly lower, relative to the seat, bottom bracket enable me to produce power more efficiently. It could be other factors. First time out on a borrowed Nazca Fuego Allround produced a similar time to the average of the other two. I would be interested to know what you have found.

Cheers

John

Re: How important is weight?
« Reply #1 on: November 18, 2011, 03:54:20 pm »
Weight is just one of the physics factors. A heavier bike will be slower uphill and faster downhill. Getting the weight into motion takes more effort on a heavier bike, and there is a slight increase in rolling resistance. If your route is flat, with very few stops, a slightly more aerodynamic position is more important than weight.
The more stops and the more hills you encounter, the more important weight becomes. And the faster you go, the more important aerodynamics become, because wind resistance is exponential.

On Cyclevision this year I did the 50m dragrace on my 10kg Brompton, hoping I'd do better than two years ago on my 17kg Furai. My times differed close to nothing. I could not put myself off against the seat on the Brompton. Apparently that makes up enough to accelerate not any faster than a 7kg heavier bike with way larger wheels.
Forgive me Father, for I have sinned. It has been too many days since I have ridden through the night with a brevet card in my pocket...

Kim

  • Timelord
Re: How important is weight?
« Reply #2 on: November 18, 2011, 04:50:43 pm »
IMHO (and my opinion isn't really worth much, as all my bikes are some flavour of 'heavy') you have to consider the whole system.  That means the weight of the bike as a fraction of the weight of the bike plus rider plus luggage.  In my experience, a few kilos here or there are easily lost in the noise unless you're literally doing nothing but climbing all day.  Other factors such as ergonomics, aerodynamics, weather conditions and rider physiology and psychology make far more of a difference.

With a touring load, I'm measurably faster on the HPV Panzerfiets[1] than I am on my (slightly lighter) Dawes, mainly I think because of the much greater comfort meaning fewer short breaks - four panniers destroy most of the aerodynamic advantage of the recumbent.  Without a load, I'm still faster on the Panzerfiets as the improved aerodynamics make more of a difference than the increase in weight, an effect that obviously increases with flatness of terrain and headwind.  In reality, the wind direction and whether my digestive system is cooperating that day make far more of a difference.

You never get back on the descent what you lose on the climb, but on rolling terrain high-speed recumbent descending enables you to carry enough momentum into the next climb that you can roller-coaster a lot of the way up, to the point where it's entirely possible to keep up with (and on a good day, smugly shoot past) lightweight uprights.



[1] Shouldn't it be Panzerrad?
Careful, Kim. Your sarcasm's showing...

Re: How important is weight?
« Reply #3 on: November 18, 2011, 05:09:49 pm »
With the trailer on the back of my trike it works out roughly as an extra 10 Kg of shopping in it slows me down by around 1 mph.
This is in rolling terrain, ~1,000' climbing in 20 miles.

On a bent it more about how long you can stay above 15-20 mph when the aero advantage of the lower position kicks in vs sub-10 mph hill climbing where the greater power/weight ratio of an upwrong wins.

Re: How important is weight?
« Reply #4 on: November 18, 2011, 09:59:19 pm »
Yeah, I agree that weight is just another factor to take into account. All other things being equal it matters. But.. rarely are all other things equal.
The point about maintaining speed is spot on. On tour my mates leave me on the steep climbs but on a rolling road with shallow climbs the B2 is faster for as long as I don't drop below about 20kph. I suppose what I think is that we have to forget applying DF standards - they don't apply in the same way. Panzer thingy monsters should't be fast but sometimes they are!

Valiant

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Re: How important is weight?
« Reply #5 on: November 22, 2011, 03:13:27 am »
It matters a huge ammount when the lift is broken and I have to carry it up 7 flights of stairs. Thankfully mine only weighs about 12kg.
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Re: How important is weight?
« Reply #6 on: November 22, 2011, 09:51:07 am »
I wouldn't worry much about weight up to 15kg or so, after that it would need to be offset by aero capability - the latter which is well worth having.

I once checked the speedo on a certain hill out of Redditch on my commute on 3 different configurations - Speed Ross alone (13kg) went up at 8.5mph, while faired SR (15kg) and part-faired ToxyZR (17kg) went up at 8.5mph.  This made me realise that a faired SR  is actually more aero than the Toxy as this is my fastest setup overall!
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Tigerrr

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Re: How important is weight?
« Reply #7 on: November 22, 2011, 12:10:51 pm »
I have a heavy HPV speedmachine  and a Fujin SL.  Both lowish and roughly similar air profile I think. The Speedmachine is a pig going uphill and empties my tank. The SL almost keeps up with uprights uphill, and leaves something in the tank. On the flat there is not much in it to start with but after a few minutes at full chat on the HPV I have to ease up or my head explodes whereas on the SL I can keep going longer, and faster.
On a long ride with mixed terrain the difference is huge - on a short or flat ride much less so. The HPV is thus great for the commute and the SL is great for 200's or ripping round Richmond Park.
I think it depends if you want to go fast/far. If you do then go light is what I reckon.
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Re: How important is weight?
« Reply #8 on: November 22, 2011, 02:57:13 pm »
I'd say much the same for the speedmachine - mebbe not so much the head exploding ;) (edit - my knees would probably give up first !) - but on a fast commute (~ 9 miles) I certainly know about it. But the added comfort of suspension with surrey roads makes up for it.
I must admit I've not really got my legs around a decent hill-climb speed other than sitting and twiddling at something that my knees don't whinge at, compared to years of riding a DF..


I agree with the rolling road thing - there's one route I do (Egham>Woking>Guildford) that does quite a bit of that, on the mtb (hard tyres)  I lose momentum on the ups, on the SPM I seem to keep a fair bit of momentum, and maintain a more consistent cruising speed despite it's weight.

Re: How important is weight?
« Reply #9 on: November 23, 2011, 08:06:36 am »
Surely the easiest way to compare the effect of weight "all other things being equal" is to lose/gain a few pounds and then to ride the same bike. I suspect lighter will be faster...
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Re: How important is weight?
« Reply #10 on: November 23, 2011, 10:11:23 am »
I agree generally lighter will be faster. But, I'm wondering whether the large number of variables mean that other factors carry as much weight (sorry!) as ...errr..  weight? For example I find that too much recline affects my ability to climb. A closed riding position really helps on the steep stuff.

Interesting that others have found 15kg to be the point at which lard really begins to tell. I'd agree with that.

I take Wobbly's suggestion as my new year resolution - lose two kilos! Target weight 81 Kilos!

recumbentim

  • Only 6 SR,s No hyper yet
Re: How important is weight?
« Reply #11 on: November 23, 2011, 06:30:07 pm »
If I lose 10 kgs and get a lighter bike I my be able to answer the Questions. I think the former will have more effect than the latter.

Re: How important is weight?
« Reply #12 on: November 24, 2011, 10:06:20 am »
Quote
I think it depends if you want to go fast/far. If you do then go light is what I reckon.
Not sure I'd agree with that, though it's extremely hard to get any sort of objective proof of anything like this.  Also are we talking about perfect conditions (which never exist) - a less aero bike will be hammered more by headwinds relatively.  For steep audax routes then yes the weight is the most important but for general A to B distance riding, where I would typically average 17-18mph over rolling terrain, I'd go for aero I think.
The Kettwiesel Ripper turns his hand to upwrongs...

Re: How important is weight?
« Reply #13 on: November 24, 2011, 08:08:26 pm »
After 5 or 6 years exclusively on recumbents(PDQ and then a SMGT) I bought a quality tourer(R Randonneur) I had been doing rides of 50 or 60 miles on the recumbents nearly always in hilly terrain with biggish mountain passes(N Wales not the Alps!).I reckoned myself pretty fit. But after 60 miles on SMGT with say 500 -700metres of acsent/descent I used to feel pretty well excercised and would only have considered doing a 100 miles plus in the same terrain as something to do out of necessity or something to prove. I think it would have left me knackered. I am nearly 60.
After a week or so with the Randonneur I ventured out on a longer spin and missed a train back home so cycled back again. Total miles just 100. I was really quite suprised how much energy I still had left. I put the difference of ability to go the extra miles down to less weight. Recumbent is still my favourite bike but I reckon for covering distance and ignoring a slightly complaining backside wieght is a factor.

Tigerrr

  • That England that was wont to conquer others Hath made a shameful conquest of itself.
  • Not really a Tiger.
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Re: How important is weight?
« Reply #14 on: November 25, 2011, 01:38:49 pm »
After 5 or 6 years exclusively on recumbents(PDQ and then a SMGT) I bought a quality tourer(R Randonneur) I had been doing rides of 50 or 60 miles on the recumbents nearly always in hilly terrain with biggish mountain passes(N Wales not the Alps!).I reckoned myself pretty fit. But after 60 miles on SMGT with say 500 -700metres of acsent/descent I used to feel pretty well excercised and would only have considered doing a 100 miles plus in the same terrain as something to do out of necessity or something to prove. I think it would have left me knackered. I am nearly 60.
After a week or so with the Randonneur I ventured out on a longer spin and missed a train back home so cycled back again. Total miles just 100. I was really quite suprised how much energy I still had left. I put the difference of ability to go the extra miles down to less weight. Recumbent is still my favourite bike but I reckon for covering distance and ignoring a slightly complaining backside wieght is a factor.
you are broadening the topic to include those weird upright or DF things which seem to be so popular lately.
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Re: How important is weight?
« Reply #15 on: November 25, 2011, 10:22:12 pm »
Sorry, wasn't thinking  :-X

HTFB

  • The Monkey and the Plywood Violin (RIP)
Re: How important is weight?
« Reply #16 on: November 25, 2011, 10:32:42 pm »
wind resistance is exponential.
Cubic, at worst.

Re: How important is weight?
« Reply #17 on: November 26, 2011, 08:39:44 am »
wind resistance is exponential.
Cubic, at worst.
Wind resistance goes up at square of the speed.
Power needed to go at that speed goes up at the cube.

Re: How important is weight?
« Reply #18 on: November 26, 2011, 08:55:15 am »
It matters a huge ammount when the lift is broken and I have to carry it up 7 flights of stairs. Thankfully mine only weighs about 12kg.

That made me LOL, but is surprisingly relevant.  Ultimately whilst you may be able to tolerate some degree of extra weight, because it improves aerodynamic and/or comfort, if it makes the machine impractically heavy, then it's promblematic.

This is of course as true with a fully loaded upwrong tourer, not that I've ever had to dismantle the luggage off of a bike to carry it up and down a set of stairs at a station, oh no. ;D
Actually, it is rocket science.
 

Re: How important is weight?
« Reply #19 on: November 26, 2011, 11:22:33 am »
It matters a huge ammount when the lift is broken and I have to carry it up 7 flights of stairs. Thankfully mine only weighs about 12kg.


This is of course as true with a fully loaded upwrong tourer, not that I've ever had to dismantle the luggage off of a bike to carry it up and down a set of stairs at a station, oh no. ;D

Ah. But have you noticed that when you are travelling with aforesaid 12kg machine every lift and escalator works. When you are travelling with a 30 kg loaded upwrong or 'bent none of them do? :-X

Re: How important is weight?
« Reply #20 on: November 26, 2011, 01:39:45 pm »
It matters a huge ammount when the lift is broken and I have to carry it up 7 flights of stairs. Thankfully mine only weighs about 12kg.
This is of course as true with a fully loaded upwrong tourer, not that I've ever had to dismantle the luggage off of a bike to carry it up and down a set of stairs at a station, oh no. ;D
Ah. But have you noticed that when you are travelling with aforesaid 12kg machine every lift and escalator works. When you are travelling with a 30 kg loaded upwrong or 'bent none of them do? :-X

Well, there is a sort of Heisenberg uncertainty principle, as applied to lifts working, as in the probability of a lift working, or existing, is inversely proportional to the weight and manoeuvrability of a load.  It also works for pushchairs, prams, cats in carriers, heavy luggage etc, but I'm getting OT ...
Actually, it is rocket science.
 

Kim

  • Timelord
Re: How important is weight?
« Reply #21 on: November 26, 2011, 04:09:53 pm »
In my experience, which is admittedly from the perspective of someone mostly[1] able-bodied with regard to heavy lifting, manhandling recumbents is much more about shape and getting good leverage around the centre of mass than the actual weight.  Even if it weighed 10kg, it would still be a long rigid thing.  And if it weighed 10kg it would probably be made of carbon fibre and have exposed delicate bits that don't like getting bashed.

If there's significant luggage, that has to come off for serious lifting, because it unbalances everything.

Though, to be honest, I don't think recumbent bikes are that much worse than small-framed (so you can't carry them on your shoulder because the space is full of bottle cages) upwrongs, other than when going round tight corners.  Trikes, OTOH, are a whole other badger.



[1] I will go to some length to avoid carrying bikes (or anything else awkward or heavy) down stairs, because of the high risk of knee injury.
Careful, Kim. Your sarcasm's showing...

Wothill

  • over the hills and far away
Re: How important is weight?
« Reply #22 on: November 28, 2011, 10:22:03 pm »
wind resistance is exponential.
Cubic, at worst.
Wind resistance goes up at square of the speed.
Power needed to go at that speed goes up at the cube.

Hang on. I agree with the first: wind resistance is proportional to the square of the speed, but the second surely contradicts that. How could you measure wind resistance other than in units of power? Or did I miss a step in the logic?

Anyway, the upshot is that wind resistance is more important (compared to weight if accelerating or going uphill, or rolling resistance) if you go fast. This may be behind the varying experiences of the effect of weight reported here: some people go faster than others (or have hillier rides) and therefore the importance of wind resistance vs weight actually varies according to how fast you ride as well as the proportion of time spent slogging uphill.

Re: How important is weight?
« Reply #23 on: November 29, 2011, 03:05:18 am »

Wind resistance goes up at square of the speed.
Power needed to go at that speed goes up at the cube.

Hang on. I agree with the first: wind resistance is proportional to the square of the speed, but the second surely contradicts that. How could you measure wind resistance other than in units of power? Or did I miss a step in the logic?


Wind resistance is a force - you can measure it in lbs or Kg, but purists would use Newtons.
To get the power required to maintain that force you need to bring time and distance into it, as there's clearly no way that you can sustain the speed that you just calculated the wind resistance for if the force you can generate is at a lower speed (the force you can generate at the driven wheel is a product of engine torque (rider strength) x gear ratio).  Sheldon Brown's "gain ratio" is useful for working that out, since it can directly translate leg strength to tractive effort.
You have to multiply by the speed again to get the power figure from the torque, thus increasing from the square to the cube.

Tigerrr

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Re: How important is weight?
« Reply #24 on: November 29, 2011, 10:37:37 am »
So - weight not an issue if you have legs like the hulk and generally ride around at awesome speeds, or not very far, or not on hills. In this case the aero effect is king.  Or weight not an issue if you ride around very slow or mostly downhill.
However if you ride around quite fast and quite far, and go uphill - you may find that weight and aero advantage is helpful.
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