I thought I'd address some of your points to add some clarity. burnthesheep wrote:
I read a bit of this. I could have sworn I posted in here before, but must have been a similar thread somewhere else. I searched.
At the end of the day you've still got two parties both with possible selfish motives.
Some takeaways from this from an average joe with an engineering background.......
On the comments about tire fit, pressure. 0.1psi difference in shape, etc......
-Yes, you can find noticeable and measurable differences in molds. I used to try to work for a major corporation that makes consumer products. The fit of some molded components greatly affected reliability of filling/assembly of the parts in the plant. We would try to optimize our use of specific lots/runs of parts to improve reliability. Also work with the molder to make the parts closer in similarity. FWIW, this was fit between the little plastic cap in your deodorant stick and the body of the container. If it doesn't fit right, it leaks/falls apart on the assembly line making a damn mess.
However, this claim that they could call and confirm it as the "best mold" would imply that the tire mfg already had aero data to backup the claim as one mold being "better" for either CRR or aero. How would a tire mfg know that for aero for pairing to a specific wheel, based on mold? I am skeptical of that.
We did not call Conti to confirm. We called an engineer who used to work at a competing wheel company and he came to the same conclusion. One mold in particular was more aero than others. This seems to be universally true for those who test. Our molder didn't know whatsoever about our situation (which worked better) until I measured about 1000 parts by hand from each of the 4 different molds we used. Then, I could confirm which ran best by running the data from lots of samples, and figure out which mold ran best on the production line.
You simply can't run one, two, or even three tires from 3 to 4 molds and use that to say "mold x is always best". You'd have to do it with a LOT of samples. Sample size IMHO is too small to make that claim.
I agree that sample size is important here. To come to a more thorough conclusion more tests would need to be run. That said, one mold does seem quite a bit better than others. After you've done that you could notify your molder of parts about your situation. Conti isn't going to know in advance which mold produces the best aero shaped tire for YOUR specific wheel. They may know which one has the best aero profile in a generic sense, which according to you guys is crap if you adjust the air pressure by 0.1 psi anyway.
I think you are taking the 0.1psi number out of context. We noticed aero differences with 5+ psi changes. The 0.1psi references the accuracy of our pressure gauge. More on that level of accuracy below. If I called the molder and off the cuff said "I'm testing some of your parts here, which mold is best?" They're probably going to tell you which one has the most consistent parts that don't have defects or rejects (shorts, overshots, etc). Not which one functions best as a "part interaction".
-Next, yes, a pressure change in a tire probably would matter for aero. I can concede that idea. You could easily confirm the difference by using a handy dandy 3D scan tool to capture the profile of the tire/wheel interface for whatever range of pressures you want. Then PROVE there's a difference by showing it. I did a google search on F1/Nascar and tire pressures and it didn't at a fast glance have as much to do with aero as with handling and management of heat during a race (warm them up quicker to optimal, keep them there somehow, etc..) Nascar being closed wheel racing wouldn't matter anyway. So I found that whole exchange about tire pressure a bit odd since this is an aero discussion.
We did a study showing the affects pressure has on aerodynamics. We studied this in the A2 wind tunnel. The reason tire pressure was part of this discussion is because inaccurately setting your tire pressure could impact your results. -$2000 for a sensor may sound cool, but that's run of the mill industrial instrumentation. Doesn't touch optical density meters or retractable pH probes on cost. But sure sounds fancy. I'd invest in that 3D scan tool.
We have a $2000 pressure sensor because we are the ones conducting the tests. If our test pressures are not accurate then our results are rather useless. We chose to purchase a highly accurate sensor because we've shown that pressure effects aerodynamics. This whole situation seems unfortunate.
Cooler heads will often prevail in the realm of public opinion, except in our current US politics it seems.
As a consumer/enthusiast, one thing of all this that often doesn't get answered is the "why". We keep getting the what in terms of lots of "watts" thrown around. But not the why.
When we're talking .1psi tire pressures that even pretty anal amateur time trialists who might reach speeds close to 30mph.....probably won't be able to replicate that. Not to mention how the tire warms/cools or loses/gains pressure during the event.
We are not suggesting that every athlete needs to purchase a $2000 pressure sensor accurate to 0.1psi. However, we are trying to help people understand that pressure is important and that there are better solutions for measuring tire pressure than your standard floor pump. Let me explain. Our studies have shown that a 5psi pressure difference can have a noticeable affect on aerodynamics. A standard floor pump is accurate to +/- 8psi. If you use a floor pump to measure pressure you could be 5 psi off in the wrong direction. Instead of a $2000 sensor, there are other more accurate and affordable gauges that can easily be carried in a bag and used to set pressure on race day. I understand that these are marginal gains, but people love marginal gains. All when you've got 50% of buyers tossing the wrong tire size on there all together and using grossly 10psi too much or too little. Not even 1psi, but probably 10.
I think the best thing that could happen is the wheel suppliers agreeing on a once a year "shootout" at the same tunnel, same protocol. Not different days, different tunnels, different operators, slightly different protocols. Maybe even hand the wheels off to someone like "Car and Driver".
Chris Thornham
Co-Founder And Previous Owner Of FLO Cycling