Go Back  Bike Forums > Bike Forums > Road Cycling
Reload this Page >

Bike Wheel Phsyics - some WOW info

Road Cycling “It is by riding a bicycle that you learn the contours of a country best, since you have to sweat up the hills and coast down them. Thus you remember them as they actually are, while in a motor car only a high hill impresses you, and you have no such accurate remembrance of country you have driven through as you gain by riding a bicycle.” -- Ernest Hemingway

Bike Wheel Phsyics - some WOW info

Old 08-02-11, 10:12 AM
  #1  
cyclezen
OM boy
Thread Starter
 
cyclezen's Avatar
 
Join Date: Jul 2005
Location: Goleta CA
Posts: 3,122

Bikes: a bunch

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 44 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
Bike Wheel Phsyics - some WOW info

some interweb searching discovered this...
did a search to see if this had been presented here before... nadda

bike wheel physics - the down and dirty, 'bling'-proof numbers

A big 'good going BRO' to John Swanson for tacklin this undefined 'performance' profile of the modern Bike Wheel.
John - you a BF member? if so, kudos to you!

the intro - http://www.bikephysics.com/intro.htm

the study paper - http://www.bikephysics.com/paper.htm

The numbers - http://www.bikephysics.com/rails/wheel/list

man, this blows away a whole lotta 'Bling' factor when it comes down to what you're getting for your money...

would be good to see numbers for all the 'Fab' wheels currently feted...

sortta timely excerpt re the recent threads on tires/tubes:
"...I have one other public service announcement. I just showed that the moment of inertia of a front wheel is about 0.04 kgm2. Now let's consider a tire of average radius 0.335 meters. From Weight Weenies the average weight of a Michelin Megamium 2 is 265 grams. The average weight of a Veloflex Corsa is 160 grams. The difference between stock tubes (107 grams) and light ones (60 grams) is about 50 grams.
So... the difference between “heavy” tires and tubes and “light” tires and tubes is about 150 grams. This works out to a difference in moment of inertia of 0.017 kgm2. Compare that to the wheel we just analyzed. Could you imagine the sales coup if someone could claim their wheels had 40% less MoI than their competitors?! Riders would line up to give testimonials about how much faster they accelerate and how much energy they save in a long race. That doesn't happen for tires though. Makes you think, doesn't it?
This just goes to show that nice tires and tubes are a great and inexpensive way to get a significant performance boost. The benefits are even greater if you decide to switch to tubulars since you'll save another 50-100 grams. Also, higher quality tires generally have a better ride quality and lower rolling resistance. There really is no downside and no reason to ride crappy tires."
cyclezen is offline  
Old 08-02-11, 10:15 AM
  #2  
Runner 1
Cookies!
 
Runner 1's Avatar
 
Join Date: Apr 2011
Posts: 629

Bikes: Red Huffy, CAAD10 Rival

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
Cool find. The effect of tires on moment of inertia has been known for awhile, but for some reason everyone's concerned about saving 3 grams in the hub.
Runner 1 is offline  
Old 08-02-11, 10:28 AM
  #3  
Psimet2001 
I eat carbide.
 
Psimet2001's Avatar
 
Join Date: Jan 2006
Location: Elgin, IL
Posts: 20,593

Bikes: Lots. Van Dessel and Squid Dealer

Mentioned: 20 Post(s)
Tagged: 0 Thread(s)
Quoted: 600 Post(s)
Liked 23 Times in 18 Posts
Originally Posted by Runner 1 View Post
Cool find. The effect of tires on moment of inertia has been known for awhile, but for some reason everyone's concerned about saving 3 grams in the hub.
The bane of my existence.
__________________
PSIMET Wheels, PSIMET Racing, PSIMET Neutral Race Support, and 11 Jackson Coffee
Podcast - YouTube Channel
Video about PSIMET Wheels

Psimet2001 is offline  
Old 08-02-11, 10:28 AM
  #4  
asgelle
Senior Member
 
Join Date: Apr 2006
Location: Albuquerque, NM
Posts: 3,683
Mentioned: 9 Post(s)
Tagged: 0 Thread(s)
Quoted: 381 Post(s)
Liked 15 Times in 8 Posts
He should have begun his reasearch with a review of prior work. He would have found Kraig Willett did something similar only not considering the wheel in isolation, but using the equation of motion for the total bike rider system. http://biketechreview.com/reviews/wh...el-performance

Take away message. Wheel inertia is a trivial component to the power demands of the entire system. (50% change in wheel inertia changes power required by 0.02%.)
asgelle is offline  
Old 08-02-11, 10:30 AM
  #5  
FactVord
Senior Member
 
Join Date: Jun 2011
Location: Queens, NY
Posts: 744

Bikes: 2011 Scott S30, 2012 Tarmac SL3

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
Thanks for sharing! The paper was very informative.
FactVord is offline  
Old 08-02-11, 10:41 AM
  #6  
Homebrew01
Super Moderator
 
Homebrew01's Avatar
 
Join Date: Jul 2004
Location: Ffld Cnty Connecticut
Posts: 21,046

Bikes: Old Steelies I made, Old Cannondales

Mentioned: 10 Post(s)
Tagged: 0 Thread(s)
Quoted: 799 Post(s)
Likes: 0
Liked 30 Times in 22 Posts
Too bad it's so old with so few wheels tested and no real aerodynamic testing .....
__________________
Bikes: Old steel race bikes, old Cannondale race bikes, less old Cannondale race bike, crappy old mtn bike.

FYI: http://www.bikeforums.net/forum-sugg...ad-please.html
Homebrew01 is offline  
Old 08-02-11, 10:46 AM
  #7  
cyclezen
OM boy
Thread Starter
 
cyclezen's Avatar
 
Join Date: Jul 2005
Location: Goleta CA
Posts: 3,122

Bikes: a bunch

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 44 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
Originally Posted by asgelle View Post
He should have begun his reasearch with a review of prior work. He would have found Kraig Willett did something similar only not considering the wheel in isolation, but using the equation of motion for the total bike rider system. http://biketechreview.com/reviews/wh...el-performance

Take away message. Wheel inertia is a trivial component to the power demands of the entire system. (50% change in wheel inertia changes power required by 0.02%.)
well ok, I will look at it closer
but already the problem is putting the human variable in the system
yes, it all comes down to human performance, but measuring any 'component' in a system means removing as many variables as possible, the human variable being and having the most variability...
2nd - he discounts 'acceleration' and inertia completely'
in a race, acceleration and decel happen constantly - he discounts wheel inertia as 'placebo',
using the same wheels, anyone having to ride the rivet for a few laps would easily discern the difference between a 300g/110g tire/tube and a 200g/70g tire/tube and a hi-perf tubular...
under a relatively constant velocity aero is certainly king; but when having to brake down to 22 mph and then accel back up to 30, 4x times in a mile, for over 1 hr, I think other factors might also come to play...
cyclezen is offline  
Old 08-02-11, 10:55 AM
  #8  
ahsposo 
Thoroughbred Member
 
ahsposo's Avatar
 
Join Date: Jan 2010
Location: Santa Anita
Posts: 7,087

Bikes: A Home Built All Rounder, Bianchi 928, Specialized Langster, Dahon Folder

Mentioned: 23 Post(s)
Tagged: 0 Thread(s)
Quoted: 3032 Post(s)
Liked 97 Times in 67 Posts
Yeah, this was very interesting.

The author not only is pretty good (as far as my feeble understanding allows) at analysis he's pretty funny, too.

What he can't codify (if that's the right word) is how some wheels seem to be "lively" and some aren't. When I was growing up almost all of my wheels were 32 spoked 2X box section tubular rimmed. Maybe it was a subtle difference in spokes and their tension but some wheelsets just seemed to have a little more life in them.
ahsposo is offline  
Old 08-02-11, 10:57 AM
  #9  
asgelle
Senior Member
 
Join Date: Apr 2006
Location: Albuquerque, NM
Posts: 3,683
Mentioned: 9 Post(s)
Tagged: 0 Thread(s)
Quoted: 381 Post(s)
Liked 15 Times in 8 Posts
Originally Posted by cyclezen View Post
2nd - he discounts 'acceleration' and inertia completely'
in a race, acceleration and decel happen constantly - he discounts wheel inertia as 'placebo',
using the same wheels, anyone having to ride the rivet for a few laps would easily discern the difference between a 300gm/110gm tire/tube and a 200gm/70gm tire/tube and a hi-perf tubular...
I think you mis-state his conclusion. He doesn't begin by assuming acceleration and inertia can be discounted. He looked at the results of the analysis (verified by race data) and based on the results says those factors are insignificant. It's a conclusion not an assumption. As to discerning the difference in equipment, a rider might be able to tell there's a difference between two sets of equipment, but that doesn't mean she can correlate the perceived difference to a change in performance. I can certainly tell the difference between my clinchers and tubulars, but when I considered it closely, what I was noticing was the difference in the sound they made. There's no reason to believe on or the other is faster based on the sound they make.

Accelerating from 22 mph to 30 might sound like a lot, but looking at the data from the P,1,2, crit accelerations are only 0.02-0.03 g. Compare the power required to perform such accelerations to riding at 28-30 mph and you'll see that inertial effects truly are trivial.

But really this is old news. Plenty of other people have confirmed these conclusions through analysis and experiment.
asgelle is offline  
Old 08-02-11, 11:32 AM
  #10  
cyclezen
OM boy
Thread Starter
 
cyclezen's Avatar
 
Join Date: Jul 2005
Location: Goleta CA
Posts: 3,122

Bikes: a bunch

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 44 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
Originally Posted by asgelle View Post
I think you mis-state his conclusion. ... As to discerning the difference in equipment, a rider might be able to tell there's a difference between two sets of equipment, but that doesn't mean she can correlate the perceived difference to a change in performance.

Accelerating from 22 mph to 30 might sound like a lot, but looking at the data from the P,1,2, crit accelerations are only 0.02-0.03 g. Compare the power required to perform such accelerations to riding at 28-30 mph and you'll see that inertial effects truly are trivial.

But really this is old news. Plenty of other people have confirmed these conclusions through analysis and experiment.
I will read it more closely, as I said. However my initial reaction is still 'human' is the 'fly' in the system.
Higher level crits usually run at 28 to 32 and sometimes but rarely fall to 25, and what brings the avg down ARE the corners and the decel/accel.
so the power requirements are usually as extreme as a steady 28, since one is rarely below that, the added burst of power needed for the constant accels, put the overall effort way higher than a steady 28-30.
maybe old news, but I haven't read 'plenty' of other people' yet.
Thanks for this study, I will read it throughly and any ref he gives...
Aero is king... and was even for when we did TTs on our road bikes
But what works in a crit or a shorter circuit race with lots of rollers might not be that easy to asnwer.
Codifying the difference between less aero wheels - Ksyrium elite, Neuvation MX and a WH540 is also a worthy thing.
cyclezen is offline  
Old 08-02-11, 12:22 PM
  #11  
nhluhr
John Wayne Toilet Paper
 
nhluhr's Avatar
 
Join Date: Feb 2006
Location: Roanoke
Posts: 1,951

Bikes: BH carbon, Ritchey steel, Kona aluminum

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
The author is quite enamored with himself for somebody who extrapolated aerodynamic data from a coast-down test and neglected countless real-world variables.
nhluhr is offline  
Related Topics
Thread
Thread Starter
Forum
Replies
Last Post
Bill
Road Cycling
9
06-16-18 05:10 AM
OwenMeany
General Cycling Discussion
4
12-09-15 12:25 PM
JasonC
Road Cycling
19
03-09-09 11:39 PM
thebeatcatcher
Bicycle Mechanics
3
04-21-08 05:47 AM
sillygirl
Road Cycling
11
04-19-05 06:28 PM

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

Copyright © 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.