desending
itboffin
Posts: 20,072
I'm curious does losing weight have a direct impact on your ability to descend at speed?
I'm not talking about the bonus speed you get from carrying more than your average sir twiggo build, I'm talking about say you lose 5-10lbs but are a fairly fearless rapid desender how much of an impact should weight loss have?
On one of my hilly commutes I can normally tuck in and hit 35+ mph this morning I was only just touching 20 ish 25 with some assistance, WTF! That can't be right?
I'm not talking about the bonus speed you get from carrying more than your average sir twiggo build, I'm talking about say you lose 5-10lbs but are a fairly fearless rapid desender how much of an impact should weight loss have?
On one of my hilly commutes I can normally tuck in and hit 35+ mph this morning I was only just touching 20 ish 25 with some assistance, WTF! That can't be right?
Rule #5 // Harden The Feck Up.
Rule #9 // If you are out riding in bad weather, it means you are a badass. Period.
Rule #12 // The correct number of bikes to own is n+1.
Rule #42 // A bike race shall never be preceded with a swim and/or followed by a run.
Rule #9 // If you are out riding in bad weather, it means you are a badass. Period.
Rule #12 // The correct number of bikes to own is n+1.
Rule #42 // A bike race shall never be preceded with a swim and/or followed by a run.
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I thought this was going to be about retracting something that had already been sent.
Regarding descending, I don't think losing a bit of weight will make that much difference.0 -
notsoblue wrote:Just how much weight did you lose?!
12.5lbsRule #5 // Harden The Feck Up.
Rule #9 // If you are out riding in bad weather, it means you are a badass. Period.
Rule #12 // The correct number of bikes to own is n+1.
Rule #42 // A bike race shall never be preceded with a swim and/or followed by a run.0 -
Does sound odd - maybe a glitch with the speed reading if not a headwind? I've lost a similar amount of weight and I can't say I've noticed any difference in descending speed.FCN 3 / 40
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Get back to school, an object with more mass does not fall faster under gravity. Unless you have significantly reduced your frontal area and therefore the air resistance it doesn't make one bit of difference.0
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No it shouldn't make that much difference.What do you mean you think 64cm is a big frame?0
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Drfabulous0 wrote:Get back to school, an object with more mass does not fall faster under gravity. Unless you have significantly reduced your frontal area and therefore the air resistance it doesn't make one bit of difference.
You get back to school, and perhaps do some physics whilst you're there.
Take a full can of Coke and an Empty one, start them rolling down a ramp and see which reaches the bottom first. You'll find that the full one wins every time.0 -
i go down hill faster than my mate who is built like a bent paper clip.
im an ex rugby player so im of a "slightly" heavier build (17 stone)
surely if i was to weigh the same as my paperclip mate i wouldnt out accelerate him goin down?Keeping it classy since '830 -
I used to think this...Drfabulous0 wrote:Get back to school, an object with more mass does not fall faster under gravity. Unless you have significantly reduced your frontal area and therefore the air resistance it doesn't make one bit of difference.
But now I think this...You get back to school, and perhaps do some physics whilst you're there.
Take a full can of Coke and an Empty one, start them rolling down a ramp and see which reaches the bottom first. You'll find that the full one wins every time.
But I can't for the life of me remember why. Something to do with relationship between velocity and force on objects in a viscous fluid or resistive force being a fixed component of total frictional force.0 -
UndercoverElephant wrote:Drfabulous0 wrote:Get back to school, an object with more mass does not fall faster under gravity. Unless you have significantly reduced your frontal area and therefore the air resistance it doesn't make one bit of difference.
You get back to school, and perhaps do some physics whilst you're there.
Take a full can of Coke and an Empty one, start them rolling down a ramp and see which reaches the bottom first. You'll find that the full one wins every time.
My physics may be a little rusty, but I'm sure this is to do with friction and acceleration, if the ramp is long enough they will reach the same velocity, although the full one will accelerate faster. I am willing to be corrected so in the interests of science I am off to buy two cans of Special Brew.0 -
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Drfabulous0 wrote:Get back to school, an object with more mass does not fall faster under gravity. Unless you have significantly reduced your frontal area and therefore the air resistance it doesn't make one bit of difference.
And that, gentlemen, is where the phrase 'a little knowledge is a dangerous thing' comes from.
(Drfabolous0: It's the other way around. from a standstill, they both accelerate at the same rate, but the full can will accelerate for longer)0 -
Well fair enough then, I'm still gonna get the beer, just to be sure like.0
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Drfabulous0 wrote:Well fair enough then, I'm still gonna get the beer, just to be sure like.
You should, in the interests of science, naturally. In fact, you should repeat the experiment with lots of different cans to be sure.0 -
You're right, I wonder if bitter rolls faster than lager, and how the beer is affected by the rolling process. Now I have something constructive to do with my afternoon.0
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airbag wrote:From a standstill, they both accelerate at the same rate, but the full can will accelerate for longer)
^ This.
They will initially accelerate at the same rate until resistive force becomes significant compared to forwards force, at which point the acceleration of both will begin to decay, faster for the lighter body than the heavier since resistive force for both will be the same (as proportional to viscosity, velocity and surface area) but forwards force will be larger for the more massive body.
The lighter body will reach terminal velocity earlier.
EDIT: I should have added: but that velocity will be lower than for the heavier body.0 -
Yes but when losing weight the CdA will change as well, less area for sure but does the Cd go up or down? But yes a heavier body has more force to overcome drag, but the drag will be greater (but proportionately more?)
I don't think 12.5lbs off someone of circa 13stone would make more than 1 or 2 mph difference (in the coke can analogy the weight change is probably 99%!), a small head or tailwind would have more effect.Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.0 -
More importantly the title of the thread is incorrect, it should read "Descending".What do you mean you think 64cm is a big frame?0
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cyclingprop wrote:More importantly the title of the thread is incorrect, it should read "Descending".
In which case, all the physics is wrong. I was assuming he was cutting down on mailing parcels.0 -
UndercoverElephant wrote:cyclingprop wrote:More importantly the title of the thread is incorrect, it should read "Descending".
In which case, all the physics is wrong. I was assuming he was cutting down on mailing parcels.
Well that makes physics seem like childsplay, the price of the parcels is calculated by weight unless one or more dimensions are above a threshold in which case a weight will be estimated volumetrically. Furthermore discounts for commercial accounts are based on the amount of units sent so in certain circumstances it can be cost effective to send hundreds of empty boxes through the post to oneself. It seems akin to the maths used to calculate gas bills.
I made a start on the beer can experiment but now I have only empties, off to get more.0 -
Did ewe too knot reed the forth post?UndercoverElephant wrote:cyclingprop wrote:More importantly the title of the thread is incorrect, it should read "Descending".
In which case, all the physics is wrong. I was assuming he was cutting down on mailing parcels.0 -
If anyone truely thinks weight doesn't effect descending then please meet me a the of big hill and we will do a free wheel est descent....
Had I the same argument on my ride to Jog when anothrr cyclist argued thay it was about the bike frame geometry and handling, he argues to colagno frame was faster thab mine down hil. He lost both freewheel test and pedalling like a maniav test (although i was spun out about 40mph at which point pedling didn't matter).
The best way ive had it explained to that potential energy at top of the hill is greater the greater the height of the hill and the greater the mass. Forces acting against accelerations are to donwith rolling resistance which if tyres correctly inflated ahould be about equal, and wind restistance which all depends on how small you can make the front end, here the difference between the light and heavy rider is smaller thab the diference between potential enrgy. Hence heavy riders are faster downhill......--
Chris
Genesis Equilibrium - FCN 3/4/50 -
doublepost0
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^^ Sketchley has it right.
When I go snowboarding with my mate, let's call him Big Jim, he likes to claim that his ability to out-accelerate me (straight downhill from a standing start, no turning) is due to skill.
I reckon his considerably greater potential energy might just be a factor...Misguided Idealist0 -
JZed wrote:Sketchley wrote:. Hence heavy riders are faster downhill......
I would argue the same until you meet JonGinge on a descent.
This.
Weight plays its part, but technique and confidence are far more important. Especially as most long descents involve lots and lots of corners. So yeah, Sketch might win on a dead straight descent, but on anything with corners my money would be on Jon every single time.
I fricking hate descending.- 2023 Vielo V+1
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- 2020 Canyon Ultimate CF SLX
- Strava
- On the Strand
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I would think JG would be able to brake later into corners than most people, especially downhill.0
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Agreed a smaller rider can offset the difference by descending better, it also helps to be a loony.... Me I'm a fairly confident downhill, a lot of that is due to bike which loves going fast downhill....
Also agree re braking, as it will take more force to slow me down for a bend then Jon, so he might have shorter stopping / slowing distances which means he's going faster for longer into the corner, but this might be countered by me being able accelerate faster on the other side of the bend for all reasons above.... The point is we are not comparing apples with apples here, if Jon timed himself down a hill then went back to the top strapped 7kgs to his back and did it again he should be faster.....
I also wonder if mass affects speed you can take a corner.....--
Chris
Genesis Equilibrium - FCN 3/4/50 -
