Weight vs Speed

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Re: Weight vs Speed

Postby foo on patrol » Sat Jul 21, 2012 5:30 pm

Train harder and you will go faster and worry about light bikes later! :wink:

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by BNA » Sat Jul 21, 2012 7:27 pm

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Re: Weight vs Speed

Postby RonK » Sat Jul 21, 2012 7:27 pm

Alex Simmons/RST wrote:
clackers wrote:A UK doctor a couple of years ago kept meticulous records of alternating a long fast commute each day between a carbon and a steel bike, and published the results in Lancet, IIRC. Nothing between them.

And it was a pretty ordinary piece of science writing too. I sure hope the same Doc doesn't do medical research.

But it was published on the Internet, so it must be true. Well, at least if it supports your point of view.

Actually I read that report, and couldn't understand how you could draw valid conclusions about riding a short distance on a course that includes traffic controls. Turns out it was written for the Xmas edition of his college newsletter. The Xmas edition is apparently well-known for its spoof reports.
I challenged Australian Cyclist magazine for publishing it as fact a couple of years ago.
Cycle touring blog and tour journals: whispering wheels...
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Re: Weight vs Speed

Postby clackers » Sat Jul 21, 2012 9:53 pm

RonK wrote:. Turns out it was written for the Xmas edition of his college newsletter.


Turns out you're wrong, Ron.

http://www.bmj.com/content/341/bmj.c6801.full

;-)
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Re: Weight vs Speed

Postby Cadel » Sun Jul 22, 2012 6:35 pm

Alex Simmons/RST wrote:
PawPaw wrote:Add 3kg in the form of 2x 1 litre water bottles to your bidons, and strap another to your top tube.
Then see if you can sustain the same average speed over 20 minutes, for roughly the same heart rate.

There is so much slop in HR response that any speed difference would be less than the noise associated with such a variable.

PawPaw wrote:What would even be more accurate is to use a power meter before and after, and hold the watts at the same level for both intervals, and see what difference you get in average speed.

In order for it to be accurate, you will need to know, precisely, the environmental conditions in order to do such an analysis.

Even a minor change in wind undetectable to a human would be enough to mask such results.



Thank you all again.
Due to my ignorance, it never crossed my mind that weight has a far bigger impact on climbs than on flat roads, but it does make perfect sense!

Now, the next question (and last for a while) that I have is :D What impact does the air resistance have to a commuter (Kona dew city) vs a road bike (like giant defy) on a flat surface assuming the same conditions?

Would my avg speed increase on a giant defy because my sitting position is more 'aerodynamic'? Would the increase be noticeable or not really...?

I know, the easiest thing to do would be to hire the defy for a day and try it myself, but I imagine that someone on the forum has both a commuter and road bike and is able to share their experience...

And the second part of the question :P, which may sound silly but then again I hope someone has the patience to answer :) Would a racer like giant TCR be noticeable faster than an entry bike (defy) considering the more aggressive position? A rough estimate please...

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Re: Weight vs Speed

Postby jimsheedy » Sun Jul 22, 2012 6:57 pm

Cadel wrote:
Would I notice a speed increase by applying the same force, considering the total weight 87kg dropped by 3.5% to 84kg?
Assume the bike geometry, tires profile etc remain the same.

...


Not when your going downhill
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Re: Weight vs Speed

Postby Cadel » Sun Jul 22, 2012 8:07 pm

jimsheedy wrote:
Cadel wrote:
Would I notice a speed increase by applying the same force, considering the total weight 87kg dropped by 3.5% to 84kg?
Assume the bike geometry, tires profile etc remain the same.

...


Not when your going downhill


Have you tried stand up comedy?
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Re: Weight vs Speed

Postby jimsheedy » Sun Jul 22, 2012 8:12 pm

Cadel wrote:
jimsheedy wrote:
Cadel wrote:
Would I notice a speed increase by applying the same force, considering the total weight 87kg dropped by 3.5% to 84kg?
Assume the bike geometry, tires profile etc remain the same.

...


Not when your going downhill


Have you tried stand up comedy?



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Re: Weight vs Speed

Postby Cadel » Sun Jul 22, 2012 9:21 pm

jimsheedy wrote:
I'm here all week. Try the Veal


Isn't the waitress worth tipping??!!
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Re: Weight vs Speed

Postby clackers » Mon Jul 23, 2012 10:50 am

Cadel wrote:
Now, the next question (and last for a while) that I have is :D What impact does the air resistance have to a commuter (Kona dew city) vs a road bike (like giant defy) on a flat surface assuming the same conditions?


I think Alex's graph showed air resistance becomes the major impediment at high speed.

At 30 kmh your chest is unfortunately acting as a sail.

Have a look at those time triallers who are trying to fold their body up into a downhill skier's stance to avoid this.

Or the road descenders who get off the seat altogether and hold themselves over the frame with their rear effectively under the saddle!
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Re: Weight vs Speed

Postby PawPaw » Tue Jul 24, 2012 12:27 pm

I've been using aerobars for the last few weeks, for the first time.
Have always been aware that 70-80% of my effort is against wind resistance, and am surprised more are not.
The bars make a ~3kph diff in the 30s - I can comfortably sit on 35kph on the drops for half an hour, but on the aerobars it jumps to 37-38 for a similar HR and RPE.
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Re: Weight vs Speed

Postby Cadel » Tue Jul 24, 2012 2:12 pm

PawPaw wrote:The bars make a ~3kph diff in the 30s -.


Thaks PawPaw, that is exactly what I read in a cycling b ook that I picked up from the library today.

For all the enthusiasts interested to learn more, your local library will probably have a few good books written by professional riders.

For the clowns who suggested that I should train harder and not worry about weight :), I'm not worried..., just curious.
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Re: Weight vs Speed

Postby Mrfenejeans » Tue Jul 24, 2012 2:49 pm

I wouldn't say that the "Train Harder" advocates are Clowns.


Here's an Example to show you what difference Training harder can have:

I weigh 92kgs and can average 34.5km/h over 50km's, this has taken me 18months to get to where i am now and currently ride 10hours a week and go to the gym.


Weight alone doesn't contribute to over all speed, its the combination of the both weight and strength. Heck if i weighed 75kg's id be Flying.
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Re: Weight vs Speed

Postby Cadel » Tue Jul 24, 2012 3:54 pm

Mrfenejeans wrote:I wouldn't say that the "Train Harder" advocates are Clowns.


You are absolutely right mate!

I've only called them clowns because they state the obvious but didn't contribute anything else:)

If you don't mind me asking, what was your average speed after 3 months into it and how did you progress throughout the 18 months?
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Re: Weight vs Speed

Postby __PG__ » Tue Jul 24, 2012 4:10 pm

Alex Simmons/RST wrote:
clackers wrote:A UK doctor a couple of years ago kept meticulous records of alternating a long fast commute each day between a carbon and a steel bike, and published the results in Lancet, IIRC. Nothing between them.

And it was a pretty ordinary piece of science writing too. I sure hope the same Doc doesn't do medical research.


It was published in either the Christmas (or April fool's?) edition that has a tradition of including a 'light hearted' medical research article. It wasn't designed to be a rigorous scientific study, rather a good chuckle.
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Re: Weight vs Speed

Postby __PG__ » Tue Jul 24, 2012 4:12 pm

My current bike is about 10.5 kgs. I've test ridden a few bikes recently that weigh between 6.8 - 8.0 kgs.

The difference between the newer bikes and my old steel beast are night and day, especially when accelerating. Some of that can be attributed to better power transfer due to a stiffer frame, but a lot of it will be due to weight.
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Re: Weight vs Speed

Postby Snoopy007 » Sat Sep 08, 2012 12:07 pm

I'm pretty new to road cycling, but when you think about it, yes weight does make a difference, even on the flat road, because your body has to push that extra amount of weight (3kg) in this case. I know that your bike does some of the work and da da da, but the fact still remains that yes it will make a difference even if it is very slight. On the down hill it wont really make much difference, but as some have said, it's on the climbs that you will feel the pain if your bikes too heavy.

I can't give you a calculation method unfortunately. But from prior experience (even though it is very little i have realised that really weight shouldn't be relied on too much, in this case dropping 3kg i think would be a good idea, but things like paying 90$ to buy a bottle cage that is 12 grams lighter then your current one is just a waste of money. Personally in your case i would try to get near that 9.5-9kg (or if it costs too much buy a new bike!) but in most cases it wont really make a difference.

I have a Merida Race Lite 904, with my pedals and everything onboard (speedo etc) it weighs around 9.2kg. I bought being a bit uncertain as there were other bikes that had a similar price but they weighed a few hundred grams less. The reason i went with this one was i found that it had full 105 rather then a few FSA components (nothing wrong with that though).

The best piece of advice i can give you if you would really want to gain speed is get better rims and tires, buy a good pump for 30$ and make sure they're pumped to the correct pressure before each ride and this will give you the best chance for being quicker. Also if it doesn't destroy your comfort, you could try lower your saddle a bit more and get into a more aerodynamic position.

Final verdict: Shed that 3kg also get a good set of tyres and rims. Even if you shed 1-2kg it would hep but the main thing is just to get kilometres into your legs =)
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Re: Weight vs Speed

Postby scotto » Sat Sep 08, 2012 10:18 pm

Acceleration and weight are inversely proportional. Gravity wants to keep you on the ground, so when that ground isn't flat weight is good or bad.

Just listen to foo and train harder. The bike is the least important part of the equation. Unless you're in the bicycle trade!
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Re: Weight vs Speed

Postby azeng97 » Sat Sep 08, 2012 10:31 pm

Well force = mass * acceleration so if you decrease mass, there will be a higher acceleration with the same amount of force. If you arent pedalling ie. no force is applied, its the same deal - the more the mass, the lower the acceleration (in this case negative acceleration ie. deceleration). So basically mass and acceleration are inversely proportionate...with basic calculation being F=ma..
So with a 12kg bike: F(constant)=12a
therefore a = F/12
With a 9kg bike: F(constant)=9a
therefore a = F/9
so the 9kg bike will have a 12/9 increase in acceleration, but obviously other factors have to be considered such as friction etc but yeah you have the idea...
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Re: Weight vs Speed

Postby clackers » Sat Sep 08, 2012 11:36 pm

azeng97 wrote:..
So with a 12kg bike: F(constant)=12a
therefore a = F/12
With a 9kg bike: F(constant)=9a
therefore a = F/9
so the 9kg bike will have a 12/9 increase in acceleration.


Ummm, you have a rider on this thing, right?

If they weigh 70kg, remember the increase in acceleration is only 82/79, not 4/3 as you calculated.

That's 1% instead of 33%.

And this is only for the seconds taken to accelerate, not its maximum speed, which is typically limited by power generated vs air resistance, not weight.

This is how big blokes like Cancellara can win time trials against whippets.

But climbs .... :smile:

And to complicate things, a 500g saving in your wheels lets you accelerate quicker than a 500g lighter frame!
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Re: Weight vs Speed

Postby azeng97 » Sun Sep 09, 2012 9:33 am

clackers wrote:
azeng97 wrote:..
So with a 12kg bike: F(constant)=12a
therefore a = F/12
With a 9kg bike: F(constant)=9a
therefore a = F/9
so the 9kg bike will have a 12/9 increase in acceleration.


Ummm, you have a rider on this thing, right?

If they weigh 70kg, remember the increase in acceleration is only 82/79, not 4/3 as you calculated.

That's 1% instead of 33%.

And this is only for the seconds taken to accelerate, not its maximum speed, which is typically limited by power generated vs air resistance, not weight.

This is how big blokes like Cancellara can win time trials against whippets.

But climbs .... :smile:

And to complicate things, a 500g saving in your wheels lets you accelerate quicker than a 500g lighter frame!


Oh yeah oops forgot about the rider lol...you're right haha
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