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Crr of water inflated tires
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TOPIC: Crr of water inflated tires

Crr of water inflated tires 5 years, 6 months ago #26943

  • howardjd
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Two years ago after reading about Sosenka's hour record setting 3.2 kilo rear wheel I decided to do some field testing with my powertap on the effects of wheel inertia on cycling performance. I compared air inflated tires to water inflated tires and got suprising results for the water. About 20sec faster over a 9mile time trial on a gently rolling course at 300watts. I posted this info on a Tri forum and got a lot of slack with everybody just thinking I was a crazy lunatic for even performing such test. I was even told the Crr of a water inflated tire is higher than for air, with no studies in the least to back up the claim. The real unfortunate part is my hardrive crashed and I lost all my data and I have been struggling for a year and nine months now to get over Oseitis pubis so I can continue testing. I am really curious if there is any info out there on the effect on Crr for water inflation. Once I am healthy I plan on trying vegatable oil for inflation.

Re: Crr of water inflated tires 5 years, 6 months ago #26946

  • kraig
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Sorry to hear about your computer and health woes.

Your anecdote sounds interesting, howard.

When you find the time, please document what you did so that others can attempt to replicate your results. Post your final report here if you feel comfortable with that.

I look forward to reading what you produce.
-kraig

Re: Crr of water inflated tires 5 years, 6 months ago #26948

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Yeah I was pretty shocked with the results. I tried to get some triathletes on Slowtwitch.com to try out the test but no one was willing to take the time to do so. Most of them seemed like they already new how the results would turn anyway and werent very open minded about it. Funny part about the data is I even had backed it up on a thumb drive and when I went to open the files everything was blank like it did'nt save properly or something. I do hope to recruit some volunteers to perform some tests as I hope to use this subject for my senior seminar. Also the test isn't really valid if there isn't more than one rider whom does it, and I'm interested to see how different rider types take to riding a heavier wheel inertia.

The conclusion I have come to so far is that there is no on ideal set of wheel inertias but rather for every rider, course, and conditions there is a set of ideal wheel inertias for opitmal peformance.

I'm attaching a non analytical paper about my ideas behind wheel inertia and cycling performance and how riding heavier than whats considered normal wheels can be benefical in a lot of cases. In particular long course triathlon and time trial in the following cases flat courses, courses with long shallow grades, roll coaster courses with series of short step hills less than about 20 feet in magnitude, and windy days.

Re: Crr of water inflated tires 5 years, 6 months ago #26949

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Hmm I tried attaching the file but it did not seem to work. I can email it if you like.
Also as soon as I'm healthy again I'm going to perform a much more controlled study on several courses types and will certainly share the info. That may be past the new year though.

Re: Crr of water inflated tires 5 years, 6 months ago #26952

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putting water in tires sounds to me to be very entertaining! i know folks have done that to test blow off of the bead interface of clinchers. riding that kind of deal sounds like fun to me. I'm very interested in reading what you come up with.

here are the allowable file extensions for attaching things:
zip,txt,doc,gz,tgz
Attachments:
-kraig

Re: Crr of water inflated tires 5 years, 6 months ago #26956

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Here's my paper "Riding Heavy and Why", still a little rough and a little speculative, but covers all the main ideas I learned when riding heavier than normal wheels and studying the physics behind the effects of wheel inertia.
Attachments:

Re: Crr of water inflated tires 5 years, 6 months ago #26958

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thanks for attaching that Jason. At over 9000 words, I didn't read all of it, but did skim through many chunks of it.

I think constructing a testable hypothesis and presenting data that speaks to this hypothesis would be a good next step for you.

Filling tires full of water still sounds entertaining to me!
-kraig

Re: Crr of water inflated tires 5 years, 6 months ago #26961

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My plan was to test air vrs water on several course types of 4-5miles in length at around say 200-250watts to allow for more test runs. Then to run shorter tests on a flat course at a high sutained wattage like 400-450. Then run some uphill only trials, and down hill only trials. Then I would do filming of riding on rollers with air and water to try and prove the hypothesis that higher wheel inertia decreases movements perpendicular to the direction of travel. Ideally I would like to recruit other riders of different builds but that may be tough. Hopefully my professors will approve this topic for my Senior Seminar and by 2013 I can get going on it.
I could also do trials of just coasting down one hill an then marking how far I get up the next hill and coasting down a hill on to a flat to see how far I make it.
Last Edit: 5 years, 6 months ago by howardjd.

Re: Crr of water inflated tires 5 years, 5 months ago #26962

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howardjd wrote:
... on rollers with air and water to try and prove the hypothesis that higher wheel inertia decreases movements perpendicular to the direction of travel.


Great! Here is the start of a testable hypothesis. Have you done some math that predicts perpendicular motion to the direction of travel as a function of wheel inertia? If so, what were the results of this math figgerin'?
-kraig

Re: Crr of water inflated tires 5 years, 5 months ago #26977

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This is something I got to work on. In principle if you have two rotating wheels of the same geometry with different angular momentums and you apply a the same force/time the one with more angular momentum will deflect less. I want to set up a model for this but I'm not exactly sure how, I know it has to be a three dimensional model becuase your not changing the angular momentum by changing the angular speed but rather by changing the plane of rotation. It seems the mathematics is somewhat complicated to predict what will happen if you apply a force perpendicular to rotating bodies axis, you also have to factor in the contact point of the road. I'll most likely seek the assistance of my professor. I also wanted to try and make a scale model to measure displacements of rotating bodies, but I'm not really sure what I could use to apply a consistent and measurable force. By the way do you know possibly a good value for the Coefficent of static friction for a typical bicycle tire? I need this to calculate what the break point is for somebody to start sliding horizontally on the road.

Re: Crr of water inflated tires 5 years, 5 months ago #26978

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howardjd wrote:
I know it has to be a three dimensional model


Sounds a bit complicated? I'd suggest starting your modeling more simply and building complexity after you gain confidence in the model/methodology/your "skillz".

Furthermore, if the hypothesis is that, as a function of decreasing wheel moment of inertia, a greater distance has been traveled due to larger/more frequent lateral deviations, or that: as a function of decreasing wheel inertia, more power is required to achieve a reported average speed over a fixed distance...then, i think you can start ballparking the magnitudes at play with a simplified analysis. If the outcome of that analysis suggests a significant effect on cycling performance, then that seems like a really interesting exercise!
-kraig

Re: Crr of water inflated tires 5 years, 5 months ago #26986

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I'm confused, if this were true then I should find old chromed steel wheels with heavy tires and fill them with water. Please, I'm not trying to give you flak, but if the science of cycling has evolved the way it has by testing, then one would think that at some point they would have figured out that heavier tires would have showed better results, this hasn't been the case and it's why lighter and lighter tires and wheels have come out...with aerodynamics playing the lead role today.

Now if water for some reason due to it being fluid and in motion is causing some sort of unknown effect then maybe... How much water pressure do you use? Same as air?

So obviously I'm confused with your results.

Re: Crr of water inflated tires 5 years, 5 months ago #26987

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Well for one thing I did'nt have enough well controlled trials to make any conclusions. At most I figured out there at least is not any significant loss and that higher inertia does markedly effect the riding qualities of the bike. Aside from numbers and data I found by perception the bike to be easier to ride straight and to apply power to the pedals because of the larger amount of angular momentum.
As far as studies go I have never actually seen an in depth qualitative study of the effect of wheel intertia on cycling performance, its kind of crazy actually. And I don't mean one that is done by a hand full of grams either. To be through you would have to test a wide range of interias with a wheels of the same geometry with same tire. The equipment would have to be highly specialized to do this. My research was fairly limited because the only means I had of keeping wheel geometry, tires and tubes constant and dramatically change the wheel inertia was using water, which adds in the variable of whether the Crr changed. Ideally you would want to test a range of some standard wheel, 1.5X inertia, 2x inertia, 3x inertia, 4xinertia, and mabye 8x and 16x for kicks. I mean a really good spread to get some extremum points for the data. Done on a range of course types, wind conditions, and rider types. Wheels have already got about as light as then can get so testing heavier is the way to go.
Most of the analysis of wheel inertia on cycling performance has been done only be using a two dimensional model of F=MA leaving out the extra dimensions of real world cycling; lateral motions on the road, slip angles, and rotating about the contact points and the concept of angular momentum. Also most cycling mathmatical models only take into account the energy required to over come drag and leave out discussion the stored energy of the bike rider system. Just imagine riding with Zero stored energy and you'll understand how important the stored energy of your system is, altough most of it comes from your body.
Also the benifit of riding heavy are very much oriented towards course, conditions and rider type. Big strong rider, flat and windy course, ride heavy. Criterium, ride light. Peleton riding do to the need of lateral movements, light. Time trial, heavier. I do realize heavy and light are very vauge but I'm only have a couple months of research under my belt of riding wheels of varying inertias and don't know of anyone else personally who's conucted any research so its really hard to pin point anything. To me any modern racing equipment is in the same range of inertia, go double or triple and your getting into the heavy range. I have one wheel sitting in my garage that weighs 12 pounds which I've dubbed the air hammer, just wish I was healthy enough to ride it.
Hopefully I answered some of your questions.
I'm a one man team so I've been hoping some others out there might at least try running some trials of air vrs water. Because you certainly would need many different rider types, terrain types, and wind conditions to get a good analysis.
As far as the water having some unkown effect like say on rolling resistance, that is the question I was hoping to have answered. I originally posted this information on Slowtwitch and someone told me water would have a Higher Crr than air but I have never seen a study to back this up. As far as pressure the air was run at 100 psi and the water was run at 90psi because thats as high as I could get it with the pump. The air was first otherwise I would have run both at 90 psi. If I ever recover from this injury and am able to ride again I plan on testing vegatable oil.
Also I know the common saying aero trumps weight, but imagine if you were on the moon at 1/6th the gravity and no atmoshpere or mabye mars what type of wheels would you ride then? what type of wheels would Goliath ride, how about a 6 year old girl? or the predator? or for an all down hill course no curves? all down hill course curvy? all up hill 2% grade? all up hill 10% grade?
Howards therom, For every rider course and conditions there will be an Ideal moment of inertia and geometry of construction for each wheel that will allow the rider to perform at an optimal level.
One last thing, I actually saw a NASCAR study that showed wheels of higher interia having a slightly better fuel economy but the drivers preferred lighter becuase they had better acceleration and allowed for quicker lateral movements.
Last Edit: 5 years, 5 months ago by howardjd.

Re: Crr of water inflated tires 5 years, 5 months ago #26988

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howardjd wrote:
... I plan on testing vegatable oil.


I think it would be more entertaining to test chocolate pudding the next time around. That way we could gain some insight on whether or not "the proof of the pudding is in the testing".
-kraig

Re: Crr of water inflated tires 5 years, 5 months ago #26989

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That may be hard to get through a pump.

Re: Crr of water inflated tires 5 years, 5 months ago #26990

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howardjd wrote:
That may be hard to get through a pump.


I think you can pull it off. I look forward to the pudding taste-test results!
-kraig

Re: Crr of water inflated tires 5 years, 5 months ago #26991

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But seriously though the idea is that the fluid in the tire may effect rolling resistance, it would be interesting to see if there was any difference between oil and water inflation. Someone did mention to me that because the Prandtl number for oil is so high compared to air and water that there may be a significant impact on the rolling resitance. I was also told water inflation should have a much larger rolling resitance because its an incompressible fluid. All the better if it is higher, just means riding heavy is even better than I thought.

leftover pudding would make a good snack once testing was complete.

Re: Crr of water inflated tires 5 years, 5 months ago #26992

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howardjd wrote:
... it would be interesting to see if there was any difference between oil and water inflation.


Personally, I think chocolate pudding vs air is a more entertaining comparison.
-kraig

Re: Crr of water inflated tires 5 years, 5 months ago #26993

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You split the bill with me to buy all the pudding I'll be sure to give it a go, that is if I can ever get over this injury and if it will go through the pump. You have to submerge the pump in a barrel to pump with a fluid so it could take around 30 gallons of pudding to do. I guess you could make it a little runny to help it through the pump.

Re: Crr of water inflated tires 5 years, 5 months ago #26994

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howardjd wrote:
I guess you could make it a little runny to help it through the pump.


That's the spirit! Can't wait to see your testing protocol/results that stand up to the rigor of the internets/academia...it'd be really cool to see chocolate pudding cited in the "literature". You'll also be famous on the internet!
-kraig

Simple way to model energy storage in cycling 5 years, 4 months ago #27004

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Well I've come up with a simple way to show how you can actually gain energy from adding mass to your wheels, or in other words capture energy you added to your bike rider system as gravitational potential at the top of a hill
here's a hypothetical example

rolling course 3 percent grade, hills of 10m in elevation, 666m trough to trough, 25mph avg, 30mph or 13.3 m/s terminal velocity on the decents. 30watts average rolling resitance, 200kilo bike rider system Examining the effect of adding 1kilo addtional weight to the rims of a set of typcial racing wheels.

Rotational kinetic= 1/2 I W^2 Translational Kintetic = 1/2 M V^2

I= m r^2 W at terminal = 38 rad/sec

total energy of additional mass at terminal = 353.87j
energy to lift 2kilos 10m= 200j
energy lost from increase in RR = 18j over the 666m
gained energy 135j
which if this was a 40k course with identical hills would yield about 2watts.

This is just a hypothetical situation and would be better done using a course profile and power tap data to retrieve the actuall average speed and terminal velocity and use the Crr of your tires to calculate the actual rolling resistance. Anyway this is just a simple example to show it is possible to see a net gain from riding heavier wheels. The idea is that on a roller coaster course where you don't stay at terminal velocity very long adding mass to your wheels can help you capture energy stored in your body and frame at the top of the hill there as helping you up the next hill or carrying you faster on a flat.

Re: Crr of water inflated tires 5 years, 4 months ago #27005

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I’d suggest checking your work using the free tools at analyticcycling.com

Deriving the equation of motion of a cyclist, and then solving it (which is not what you’ve done below) is fairly straightforward.
-kraig

Last Edit: 5 years, 4 months ago by kraig. Reason: can
The following user(s) said Thank You: JollyRogers

Re: Crr of water inflated tires 5 years, 3 months ago #27010

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Maybe this will help. I've found this guy to be a fun and educational read from time to time...

www.training4cyclists.com/how-much-time-...-cost-on-alpe-dhuez/
Richard Wharton
www.onlinebikecoach.com

Re: Crr of water inflated tires 5 years, 3 months ago #27011

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Yeah I've seen this before but it really doesnt help me because the trials did not involve turning around and coming back down the mountain. I'm personally most interested in looped return to start zero net change in elevation courses, as are most triathlons. Still interesting though, Jackmott on slowtwitch claimed the slower times for the water inflation were due to increase in Crr. So this is actually kind of the origins of my question here what is the effect of water inflation on Crr. Jackmott from slowtwitch claims it increased it altought Ive never seen any study claiming such. A all uphill course showing water inflation slower doesnt really seem to me be any evidence for an increase in Crr. As far as all the riding I did with water on looped courses I could find no loss in time, but an increase in rideability for the application of long course triathlon type solo time trialing, steady and straight.

Re: Crr of water inflated tires 5 years, 3 months ago #27012

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howardjd wrote:
Yeah I've seen this before but it really doesnt help me because the trials did not involve turning around and coming back down the mountain.


FWIW, in competition, I'd never freely choose to go up _and_ down alp d'huez with water inflated tires...however, for fun, I'd go up _and_ down alp d'huez with chocolate pudding inflated tires...y'know, to see if the proof of the pudding is in the testing!
-kraig

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