Aug 20

August 20, 2005

Rolling resistance test for new wheels, rear caliper brake, photos of the mold and a video

The last time I did a Crr test, I did it with the Rocket lean steer trike. My numbers were horrible (Crr .009) and seemed to agree with the Crr tests John Tetz was doing with his new trike. Theory states that the Crr of a trike should be no lower that the Crr of a two wheeled vehicle, but the truth is that trikes have appreciably higher rolling resistance.

I ran two sets of tests, the first with the M5 which was running a 120 psi 700 racing clincher on the rear and the small 20 x 1 1/8 100 psi M5 tire on the front. The Crr averaged out to .0054 which is about what I would expect for that wheel combination. The road is not very smooth with two large cracks running through it.

The second set of tests were with the new Carbon sandwich frame lowracer. The rear wheel is a 180 psi tubular with a disc on one side only and housed in the wheel dome (as pictured above). The front wheel is a 650 120 psi clincher. Both tires are racing slicks. The Crr averaged out to .0037

So how do these numbers relate to speed? Let's run power simulation for both vehicles assuming they have about the same drag coefficient with a power input of 150 watts:

Bike: CdA Watts Speed
M5 2.8 150 31.2 kph
Carbon Lowracer 2.8 150 32.3 kph
M5 with average fairing .6 150 47.5 kph
Carbon Lowracer with average fairing .6 150 50.7 kph
M5 with Varna faring .215 150 60.7 kph
Carbon Lowracer with Varna fairing .215 150 66.8 kph

You can see that a small difference in Crr translates to a fairly substantial difference in resulting speed - the reason I wanted to go with an unusually large 650 front wheel.

The excel spread sheet I used to calculate the data is Crr Estimate V2.0 by John Snyder. Here is the Crr data:


I installed the rear caliper brake and I am pleased to say it works very well. I cut a notch out of the rear of the frame and bolted on a brake hanger.

I had to add some carbon to reinforce the area that takes all of the braking load

I also bonded the right hand rear wheel dome to the frame to make getting at the rear wheel much easier. I am now going to bond some smaller aluminum bolts to the frame on the other side to better secure the other wheel dome.


I got some photos of the fairing mold. They went and sanded it down without considering the glue lines! There is a slight wavy finish caused by the differing density of the glue. They have sprayed a thick coat of epoxy based primer into it and I am going to hand sand it smooth. I'm not very happy about sanding down a female cavity, but I will give it a try.


Here is a short vid of the carbon lowracer in action


Still to do:

1. Add a rear caliper brake
2. Trace the real perimeter outline using an actual fairing half shell (when I get one!), and cut out the perimeter
3. Edge laminate the perimeter
4. Thicken the frame to avoid using the spacers on the brackets
5. Bond in the bottom brackets
6. All of the above mentioned lightening mods
7. Bond on the right hand rear wheel dome.
8. Bond fasteners to frame for the left hand wheel dome


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