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cplager 09-04-14 05:54 PM
Originally Posted by dynaryder (Post 17100740)
Wrong. I noticed a world of difference swapping tires on my bikes. In one case I went from 1.95" Crossroads to 2" Marathon Supremes,in another I went from 45mm Borough XC's to 42mm Contact Lites;both were much more pleasant to ride in stop-and-go traffic,and were easier to climb up steep hills.
That's rolling resistance, not wheel weight.

dynaryder 09-04-14 06:03 PM
Originally Posted by cplager (Post 17100755)
That's rolling resistance, not wheel weight.
No,in both cases the tire size and tread pattern didn't change significantly,just the weight of the tires.

cplager 09-04-14 06:31 PM
Originally Posted by dynaryder (Post 17100789)
No,in both cases the tire size and tread pattern didn't change significantly,just the weight of the tires.
Neither tread nor tire size have necessarily large effects on rolling resistance. If you can the difference, it was rolling resistance. The weight difference between tires is miniscule compared to the weight of the rider and the bike.

meanwhile 09-05-14 04:54 AM
Originally Posted by dynaryder (Post 17100789)
No,in both cases the tire size and tread pattern didn't change significantly,just the weight of the tires.
Ok: you know less than nothing about rolling resistance. (The mystery is why you think otherwise.) Carcass flexibility is the main determinant. The Supreme is about the lowest RR touring tyre (the Grandbois and Almotion are probably faster, but little else) because it uses a race grade carcass and compound; the Crossroads are poor.

Oh - and I doubt you understand width: wider = LOWER RR; you probably think the opposite.

meanwhile 09-05-14 04:56 AM
Useful links on rolling resistance:

MTB Tire analysis - rolling resistance and snakebite resistance





Bicycle Quarterly rolling resistance tests: Spring 2013 - Weight Weenies



Technical Q&A with Lennard Zinn - Rolling resistance redux - VeloNews.com





Fast Tires 2013 - Part 2 - Slowtwitch.com



JV's Cycling Blog: The latest tire rolling resistance data is out!!



wide is fast for road

Tech FAQ: Seriously, wider tires have lower rolling resistance than their narrower brethren - VeloNews.com


lower psi can be faster

Technical Q&A with Lennard Zinn - Rolling resistance redux - VeloNews.com


Tyres can make 25% difference on road, drum testing wrong:

Bicycle Quarterly: Performance of Tires | Off The Beaten Path

Rolling Resistance and Tire Pressure | Velochimp





Charts

Tyre Rolling Resistance Data

Mountain Bike Tyre Rolling Resitance

Tire test results from german "bike" magazine

meanwhile 09-05-14 05:09 AM
Originally Posted by dynaryder (Post 17100740)
Wrong. I noticed a world of difference swapping tires on my bikes.
Yes. There was a difference but you didn't understand the cause.


Huh? First,you just proved yourself wrong. You actually had to put effort into spinning that wheel up,while hitting the brake required almost none.Second,what does this have to do with riding the bike?
I'm sorry: I thought that experiment was idiot proof. But you seem to believe that the energy stored in two identical wheels spinning at the same RPM can be enormously different: I honestly thought this was too absurd to need addressing. Energy stored in the wheel is 0.5 x mass x radius x the square of spin rate; the energy stored in the wheel is the same whether the bike is rolling down an alpine mountain with Lance The Liar onboard or upside down with a 12 year flicking the pedals around.

Which, to be honest, should have been explained in high school physics when you were about 12.

Second,what does this have to do with riding the bike? In that example,there's only the momentum of the wheel spinning,when riding the bike you have the weight of the bike+rider,plus gravity if going down hill to deal with.
What it does it that it shows that contribution of THE WHEEL MASS to the above is minuscule. Which is what we were discussing. The process you are struggling with is called "coherent logical argument"...

VegasTriker 09-05-14 01:49 PM
You can ignore the laws of physics but you can't repeal them.

Drew Eckhardt 09-05-14 05:12 PM
Originally Posted by gpo1956 (Post 17084132)
Would an average rider riding 50-75 miles a week in semi hilly terrain see a noticeable difference going from a 34 lb bike to say an 18-20 lb bike?
Sure. A 160 pound rider would be nearly 8% faster up the steepest hills on a 20 pound bike than a 34 pound one. On hills where he could only manage 10 MPH before he could go 10.8 MPH, and he'd be nearly 4.5 minutes faster to the summit of a hill that used to take an hour to climb.

meanwhile 09-05-14 05:36 PM
Originally Posted by Drew Eckhardt (Post 17103963)
Sure. A 160 pound rider would be nearly 8% faster up the steepest hills on a 20 pound bike than a 34 pound one. On hills where he could only manage 10 MPH before he could go 10.8 MPH, and he'd be nearly 4.5 minutes faster to the summit of a hill that used to take an hour to climb.
That's unless the heavier bike "planed" better. Which has happened under pretty convincing testing..

Weight of a Steel BikeGeorgena Terry

In this issue, Jan tested a titanium bike against a steel randonneur bike. It was a real world test: two guys racing each other up the same hill, one on the ti bike, one on the steel. They swapped out the bikes several times. Both were evenly matched in terms of strength, endurance and weight.
The weight of a steel bike is always of interest. This steel bike was 9.6 lbs heavier than the ti bike, but it climbed as well. It sounds implausible, but as Jan explained, when the weight of the riders was taken into account, the steel bike plus rider was only 5% heavier than the ti bike plus rider, but the steel bike “planed”, helping the rider generate the extra power needed to overcome the weight difference.
Fans of Jan’s bike testing will know there is an advantage to a bike that “planes”. This is a bike that is in synch with the rider and flexes in a way that “gives back” some of the rider’s energy to the drivetrain.
..Heine is a NASA Fellow and knows his testing. Indeed, he is **German.**

..What planing is about is the energy from the pedal stroke that torsions the frame. Some frames are especially efficient at returning it; some are especially bad. Confusingly, the ideal frame for one rider may be different to another because of the interactions between pedaling style, bodyweight, etc, and this behaviour.

dynaryder 09-05-14 06:04 PM
Originally Posted by meanwhile (Post 17101798)
Energy stored in the wheel is 0.5 x mass x radius x the square of spin rate; the energy stored in the wheel
The wheel has a tire on it(you do ride with tires on your wheels,right?). The weight of the tire contributes to the mass of the wheel in the real world,because you can't ride a bike without them. Discussing the wheel by itself is pointless.

Originally Posted by meanwhile (Post 17101798)
Which, to be honest, should have been explained in high school physics when you were about 12.
Ah,that's my problem. I was 15 when I started high school(10th grade for SAHS). If you were in high school at age 12,you must've been a genius. I bow to your knowledge,and will leave the thread.

meanwhile 09-06-14 04:06 AM
Originally Posted by dynaryder (Post 17104110)
The wheel has a tire on it(you do ride with tires on your wheels,right?).
Yes: IT HAS A TYRE ON IT WHETHER THE BIKE IS THE RIGHT OR WRONG WAY UP. This is included in mass in both situations...

Ah,that's my problem. I was 15 when I started high school(10th grade for SAHS). If you were in high school at age 12,you must've been a genius.
No, just British.

meanwhile 09-06-14 07:25 AM
There's an excellent wikipedia article - I already sent the link to Mr Fantasy Physcis - on bicycle performance here:

Bicycle performance - Wikipedia, the free encyclopedia

cplager 09-06-14 07:28 AM
Originally Posted by Drew Eckhardt (Post 17103963)
Sure. A 160 pound rider would be nearly 8% faster up the steepest hills on a 20 pound bike than a 34 pound one. On hills where he could only manage 10 MPH before he could go 10.8 MPH, and he'd be nearly 4.5 minutes faster to the summit of a hill that used to take an hour to climb.
Almost, yes, if he's going slowly enough. But not at 10 mph is where the difference will become less as the aerodynamic drag becomes important.

It's not that weight is irrelevant. It's that it is exactly as important as it is, and most people overestimate it.

Bike calculator web pages are great for answering these questions.

meanwhile 09-06-14 07:37 AM
Originally Posted by cplager (Post 17105208)
Almost, yes, if he's going slowly enough. But not at 10 mph is where the difference will become less as the aerodynamic drag becomes important.
No, you're wrong now. The guy specified a steep hill where the cyclist could only make 10mph and at this speed aero is NOT important. Power needed for work against gravity and RR is LINEAR with speed, but aero is SQUARED. Which means that aero dominates at speed but drops away to be trivial at lower speeds.

http://www.schwalbetires.com/images/e_img_1162_1.gif

You shouldn't take the particular values in that graph as gospel - just that AR is a curve and that RR and gravity are linear.

It's important to understand this, because when you do then you understand that what is optimal for TDF racing speed is not necessarily relevant to Audax or commute speed. A TDF team uses narrower tyres with higher RR for their low aero drag, but at the speed of an Audax or commute then a wider tyre with higher AR but lower RR will be faster.

cplager 09-06-14 07:42 AM
Originally Posted by meanwhile (Post 17105226)
No, you're wrong now. The guy specified a steep hill where the cyclist could only make 10mph and at this speed aero is NOT important. Power needed for work against gravity and RR is LINEAR with speed, but aero is SQUARED. Which means that aero dominates at speed but drops away to be trivial at lower speeds.

http://www.schwalbetires.com/images/e_img_1162_1.gif

You shouldn't take the particular values in that graph as gospel - just that AR is a curve and that RR and gravity are linear.

It's important to understand this, because when you do then you understand that what is optimal for TDF racing speed is not necessarily relevant to Audax or commute speed. A TDF team uses narrower tyres with higher RR for their low aero drag, but at the speed of an Audax or commute then a wider tyre with higher AR but lower RR will be faster.
No, what I wrote was correct. At slow speed, aerodynamic drag is not important, but it starts to become important at 10 mph. But nice try.

meanwhile 09-06-14 07:44 AM
There's a terrific article on rolling resistance and aero here:

Tire Rolling Resistance | Roues Artisanales

In general terms, the total drag of a cyclist will consist of 80% tire rolling resistance and 20% wind resistance at 10 km/h or 6 mph. At 40 km/h or 25 mph the numbers will reverse, with total drag consisting of 80% wind resistance and 20% tire rolling resistance.
As a general rule, most riders who try to get higher performance at commute speeds put exactly the wrong tyres on their bikes, almost everyone worries about weight too much, and some people believe quite insane things about wheels. (These beliefs have been stoked by years of marketing and pressure on cycling magazines to write absurd things, the aim being of course to extract money from people.)

meanwhile 09-06-14 07:56 AM
Originally Posted by cplager (Post 17105236)
No, what I wrote was correct. At slow speed, aerodynamic drag is not important, but it starts to become important at 10 mph. But nice try.
This is stupid.

Because

1. When aero starts to become important wont be the same, even on the flat, for different types of bike and different tyres

2. It becomes important later going uphill because the other forces - gravity! - are greater. And the guy specified a STEEP hill

You mentioned online calculators, but you obviously don't use them! Here's a reasonable example for a rider on a steep hill at the speed you gave:
[TABLE]
[TR]
[TD="align: left"]Frontal Area[/TD]
[TD="align: right"] 0.50[/TD]
[TD]m[SUP]2[/SUP][/TD]
[/TR]
[TR]
[TD="align: left"]Coefficient Wind Drag[/TD]
[TD="align: right"] 0.50[/TD]
[TD]dimensionless[/TD]
[/TR]
[TR]
[TD="align: left"]Air Density[/TD]
[TD="align: right"] 1.226[/TD]
[TD]kg/m[SUP]3[/SUP][/TD]
[/TR]
[TR]
[TD="align: left"]Weight[/TD]
[TD="align: right"] 75.0[/TD]
[TD]kg[/TD]
[/TR]
[TR]
[TD="align: left"]Coefficient of Rolling[/TD]
[TD="align: right"] 0.008[/TD]
[TD]dimensionless[/TD]
[/TR]
[TR]
[TD="align: left"]Grade[/TD]
[TD="align: right"] 0.050[/TD]
[TD]decimal[/TD]
[/TR]
[TR]
[TD="align: left"]Wind Resistance[/TD]
[TD="align: right"] 2.5[/TD]
[TD]kg m/s[SUP]2[/SUP][/TD]
[/TR]
[TR]
[TD="align: left"]Rolling Resistance[/TD]
[TD="align: right"] 5.9[/TD]
[TD]kg m/s[SUP]2[/SUP][/TD]
[/TR]
[TR]
[TD="align: left"]Slope Force[/TD]
[TD="align: right"] 36.8[/TD]
[TD]kg m/s[SUP]2[/SUP][/TD]
[/TR]
[TR]
[TD="align: left"]Cadence[/TD]
[TD="align: right"] 100.[/TD]
[TD]rev/min[/TD]
[/TR]
[TR]
[TD="align: left"]Crank Length[/TD]
[TD="align: right"] 170.[/TD]
[TD]mm[/TD]
[/TR]
[TR]
[TD="align: left"]Pedal Speed[/TD]
[TD="align: right"] 1.78[/TD]
[TD]m/s[/TD]
[/TR]
[TR]
[TD="align: left"]Average Pedal Force[/TD]
[TD="align: right"] 101.4[/TD]
[TD]kg m/s[SUP]2[/SUP][/TD]
[/TR]
[TR]
[TD="align: left"]Effective Pedaling Range[/TD]
[TD="align: right"] 70.[/TD]
[TD]degree[/TD]
[/TR]
[TR]
[TD="align: left"]Effective Pedal Force[/TD]
[TD="align: right"] 260.6[/TD]
[TD]kg m/s[SUP]2[/SUP][/TD]
[/TR]
[TR]
[TD="align: left"]Speed[/TD]
[TD="align: right"] 4.00[/TD]
[TD]m/s[/TD]
[/TR]
[TR]
[TD="align: left"]Power[/TD]
[TD="align: right"] 180.4[/TD]
[TD]watts[/TD]
[/TR]
[/TABLE]


So at the speed you specifed, work against weight will be FIFTEEN TIMES work against air resistance! And this is with only a 5% gradient.

...Bike performance calculators: knowing about them doesn't make you any smarter if you're not smart enough to freaking USE THEM!

cplager 09-06-14 11:51 AM
Originally Posted by meanwhile (Post 17105270)
This is stupid.

Because

1. When aero starts to become important wont be the same, even on the flat, for different types of bike and different tyres

2. It becomes important later going uphill because the other forces - gravity! - are greater. And the guy specified a STEEP hill

You mentioned online calculators, but you obviously don't use them! Here's a reasonable example for a rider on a steep hill at the speed you gave:
[TABLE]
[TR]
[TD="align: left"]Frontal Area[/TD]
[TD="align: right"] 0.50[/TD]
[TD]m[SUP]2[/SUP][/TD]
[/TR]
[TR]
[TD="align: left"]Coefficient Wind Drag[/TD]
[TD="align: right"] 0.50[/TD]
[TD]dimensionless[/TD]
[/TR]
[TR]
[TD="align: left"]Air Density[/TD]
[TD="align: right"] 1.226[/TD]
[TD]kg/m[SUP]3[/SUP][/TD]
[/TR]
[TR]
[TD="align: left"]Weight[/TD]
[TD="align: right"] 75.0[/TD]
[TD]kg[/TD]
[/TR]
[TR]
[TD="align: left"]Coefficient of Rolling[/TD]
[TD="align: right"] 0.008[/TD]
[TD]dimensionless[/TD]
[/TR]
[TR]
[TD="align: left"]Grade[/TD]
[TD="align: right"] 0.050[/TD]
[TD]decimal[/TD]
[/TR]
[TR]
[TD="align: left"]Wind Resistance[/TD]
[TD="align: right"] 2.5[/TD]
[TD]kg m/s[SUP]2[/SUP][/TD]
[/TR]
[TR]
[TD="align: left"]Rolling Resistance[/TD]
[TD="align: right"] 5.9[/TD]
[TD]kg m/s[SUP]2[/SUP][/TD]
[/TR]
[TR]
[TD="align: left"]Slope Force[/TD]
[TD="align: right"] 36.8[/TD]
[TD]kg m/s[SUP]2[/SUP][/TD]
[/TR]
[TR]
[TD="align: left"]Cadence[/TD]
[TD="align: right"] 100.[/TD]
[TD]rev/min[/TD]
[/TR]
[TR]
[TD="align: left"]Crank Length[/TD]
[TD="align: right"] 170.[/TD]
[TD]mm[/TD]
[/TR]
[TR]
[TD="align: left"]Pedal Speed[/TD]
[TD="align: right"] 1.78[/TD]
[TD]m/s[/TD]
[/TR]
[TR]
[TD="align: left"]Average Pedal Force[/TD]
[TD="align: right"] 101.4[/TD]
[TD]kg m/s[SUP]2[/SUP][/TD]
[/TR]
[TR]
[TD="align: left"]Effective Pedaling Range[/TD]
[TD="align: right"] 70.[/TD]
[TD]degree[/TD]
[/TR]
[TR]
[TD="align: left"]Effective Pedal Force[/TD]
[TD="align: right"] 260.6[/TD]
[TD]kg m/s[SUP]2[/SUP][/TD]
[/TR]
[TR]
[TD="align: left"]Speed[/TD]
[TD="align: right"] 4.00[/TD]
[TD]m/s[/TD]
[/TR]
[TR]
[TD="align: left"]Power[/TD]
[TD="align: right"] 180.4[/TD]
[TD]watts[/TD]
[/TR]
[/TABLE]


So at the speed you specifed, work against weight will be FIFTEEN TIMES work against air resistance! And this is with only a 5% gradient.

...Bike performance calculators: knowing about them doesn't make you any smarter if you're not smart enough to freaking USE THEM!
4 m/s is 9 mph, not the 11 mph of the faster bike.

When climbing hills, your average rider is going to be, in general, less aero than usual.

But, yes, it all depends.
And even with the example here, the effect with the given rider weight is 7.7% at most, and this only for climbing very step hills.


There are other effects that will make a bigger difference sooner for most types of riding (changing the tires could on most 34lbs bikes will make a bigger effect that will be noticed everywhere, not just on hills).

meanwhile 09-06-14 12:48 PM
4 m/s is 9 mph, not the 11 mph of the faster bike.
Ooh - that will cut gravity from being FIFTEEN times more than aero to only TWELVE TIMES! You wi- No, seriously: this is stupid. And the example I gave was not using only a 5% hill. Which no one would even notice in San Francisco, and is a lot less than the variation you find in "flat" English roads.

But, yes, it all depends.
No, it doesn't. Some things remain ludicrous beyond comprehension. One of them is saying that a cyclist climbing a steep road at 10mph will have do a major part of his work against air resistance. This. Is. Always. Silly. It isn't even true of a pathetic 5% gradient. Really steep starts at, oh, 10%. And plugging in even 6m/s there we get

[TABLE]
[TR]
[TD="align: left"]Wind Resistance[/TD]
[TD="align: right"] 5.5[/TD]
[TD]kg m/s[SUP]2[/SUP][/TD]
[/TR]
[TR]
[TD="align: left"]Rolling Resistance[/TD]
[TD="align: right"] 5.9[/TD]
[TD]kg m/s[SUP]2[/SUP][/TD]
[/TR]
[TR]
[TD="align: left"]Slope Force[/TD]
[TD="align: right"] 73.5[/TD]
[TD]kg m/s[SUP]2[/SUP][/TD]
[/TR]
[/TABLE]

..So wind resistance won't even noticeable.

(Forces on Rider)

Going over to SF, I once delivered a package on a street with something like a .27 gradient. (Cars can only park at right angles to the road and my bikes front wheel went light!) Imagining that I could climb it at 10mph ( which would take about 1500Watts, and I have to admit is a little beyond my sustained personal best) then

[TABLE]
[TR]
[TD="align: left"]Wind Resistance[/TD]
[TD="align: right"] 5.5[/TD]
[TD]kg m/s[SUP]2[/SUP][/TD]
[/TR]
[TR]
[TD="align: left"]Rolling Resistance[/TD]
[TD="align: right"] 5.9[/TD]
[TD]kg m/s[SUP]2[/SUP][/TD]
[/TR]
[TR]
[TD="align: left"]Slope Force[/TD]
[TD="align: right"] 198.6[/TD]
[TD]kg m/s[SUP]2[/SUP][/TD]
[/TR]
[/TABLE]

JameB 09-06-14 01:22 PM
Originally Posted by gpo1956 (Post 17084132)
Would an average rider riding 50-75 miles a week in semi hilly terrain see a noticeable difference going from a 34 lb bike to say an 18-20 lb bike?
Assuming you're actually an average rider, you will see a difference. You will be able to accelerate faster and sustain higher speeds for a longer period of time because of the lowered mass. I'd say you will see anywhere between 10% to 15% increase in average speed if you tried only as hard as you did with your 34lb bike.

But of course, your muscles will make the maximum difference. You could ride a bike that weighs 10lb but if you just don't have the power to pedal, you're not going to see any difference...

Dave Horne 09-06-14 03:03 PM
Now I know why I prefer to bike alone.

gpo1956 09-06-14 04:46 PM
Originally Posted by Dave Horne (Post 17106243)
Now I know why I prefer to bike alone.
Good one.

dynaryder 09-07-14 05:47 PM
Originally Posted by meanwhile (Post 17105204)
There's an excellent wikipedia article - I already sent the link to Mr Fantasy Physcis - on bicycle performance here:
Since you insisted on dragging me back in via PM,this pretty much sums it up:
Originally Posted by cyccommute (Post 17107617)
By all means go look at the links but before you do, look at this article on bicycle drag. It clearly shows how little importance rolling resistance of the tires has on the over all drag on a bicycle. The whole discussion above has been about how to reduce a tiny fraction of drag. The whole discussion is mostly a tempest in a teapot and, in reality, has only an marginal effect for the commuting cyclist. Reducing rolling resistance is important at a professional level where tenths of a second make a difference but for the bicycle commuter, rolling resistance makes little difference.

Weight, on the other hand, can make a huge difference for a bicycle commuter. We are constantly slowing, stopping, starting and accelerating. Adding more weight to the wheels of the bicycle means that we have to put more energy into riding to get back up to speed and then, once at speed, we have to keep putting more energy into the system to keep it at speed due to air resistance which is a power curve vs a linear curve for rolling resistance. Going to heavier, wider tires may give a cushy ride but you have to pay a penalty for it.
Also love how you're arguing with links over my personal observations from actually riding in the real world.

And now I'm done. I will not come back to this thread,and keep your PM's to yourself.

korbjonathan 09-13-14 07:37 PM
yes


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