Q's about lessons learned with iBike & Footon Servetto

[tosterbe]

John-

Perhaps this has been asked/discussed elsewhere, please forgive a potential duplicate thread.

Any chance we can get some data from the Giro to play with?

How does the team manage things like wheel changes. For example lets say a rider normally is using 46mm wheels and for a hilly stage, moves to a 32mm. I would presume they switch profiles but what happens when a third wheelset is introduced, lets say a 66mm. What does the team do in this case?

Thanks,

Todd

[rruff]

The aero and weight differences between these would be too small to worry about.

[benlane]

rruff - are you sure?Kind of negates the point of changing the wheels to suit the terrain if there is no discernable difference?

[rruff]

rruff - are you sure?Kind of negates the point of changing the wheels to suit the terrain if there is no discernable difference?

It's discernible with careful testing, but the iBike uses an approximation of CdA (they don't vary it with body position or wind direction) and weight (it will vary a few pounds during a ride depending on hydration and what you are carrying). The difference in wheels will be quite small compared to these factors.

[tosterbe]

John,

Can you weigh in here and shed some light on the subject.

Back to rruffs point, for those who have DFPM and an iBike, what differences are there in the plot of power when you have an iBike profile which was setup with deep (lets stick with 66mm for arguments sake) wheels and you are using 20mm wheels. What do the plot of the power curves look like? What does the plot look like in the opposite situation (20mm ibike profile, but using 66mm deep wheels)?

From a perceived effort perspective, I do notice a difference between my Reynolds strikes and a pair of Neuvation m28s in terms of maintaining speed over time. I would think that if I can 'feel' a difference, iBike would be sensitive enough to measure this difference. I guess the real question comes back to is there any real statistical difference in the power measurement/computation given the ever changing weight and wind combined with the CdA estimate.


Todd

[rruff]

I made the chart below a few years ago based on aero tests done by Tour magazine. It gives you an indication of what you might expect when changing wheels. On average a set of 66mm deep rims would reduce CdA by ~.015 compared to your 27mm rims. This would be roughly a 4-5% reduction in total aero drag. You can apply this change to some of your ride files to see how much difference this makes. On a ride that is flat and you are going pretty fast, this would be a 3-4% difference in power... if you are climbing a lot, it will be a very small effect.

The combined errors on the iBike are greater than 4% most of the time... even if you have a perfect calibration. By all means you would like to get the CdA dialed better than +-5% if possible, but I'm fairly certain that the team is not worrying about it. What do they do about body position and clothing, which can account for a bigger change? Think about the variations in weight depending on how much water and food is being carried and how dehydrated the rider is... this could vary by 5-10 lbs easily during a ride, but there is no way to easily account for it.

AeroWheelsTour_Aero_02_05_06_07.jpg (36.49 KiB) Viewed 8557 times

[lorduintah]

Ron -

The CdA may not change much, but angular momentum does play a factor in all of this, too. The deeper rims will have more momentum - one of the reasons to use them on the flats and to go to a small profile on hills for climbing.

Tom

[rruff]

High momentum is actually a small benefit on climbs (assuming that mass is fixed). It (very slightly) evens out the speed fluctuations, reducing air resistance. Pros are restricted to 15lb which is a pretty easy target with reasonable equipment. So the deep rims are really better on a climb... unless you plan on doing lots of surges... which is rarely a smart thing to do anyway.

[crazymadcyclist]

Whilst i can't specifically add iBike measurements/data, I did however find the following web site some time ago that is rather interesting wrt this topic (from an academic perspective) , ie what is the theoratically calculated difference when using deep profile vs std profile rims.;

http://www.analyticcycling.com/WheelsClimb_Page.html

The site provides a mathematical model for a rider under differing situations eg gradients using differing rim profiles. It then calculates the distance/time advantage (disadvange) associated with the rims contribution. Great to play with but you need to get data on the wheels' inertia and coef of drag, which in some case you can get or derive , for example for the Dura Ace c50 that i use i got (borrowed) a copy of the report from the second set of links below which helps to estimate input factors to the theoretic model. You can also try the intertia test (pendulum) as laid out in analyticcycling.com website

http://www.rouesartisanales.com/article-15505311.html
http://www.rouesartisanales.com/article-15988284.html

I think that at the end of the day it is all theoretical and other factors can also influnce performance such as just simply having a good/bad day I also suspect the impact of rim profile is relatively small compared to changing riding position, helment(gear), shoe covers etc.

CracyMadCyclist

[rruff]

You'll note that if all the other variables are the same and you start with a speed that is the same as what you average, then the wheel inertia has no effect.

There is a calculator here that you might like to play with: http://www.whitemountainwheels.com/SpeedPower.html