Vendetta or Silvio?

[Charles.Plager]

 Hi trplay,
 You can use roll

Hi trplay,

You can use roll down tests to evaluate different bike, rider, positions with pretty good precision. And it's a lot cheaper than $500/hour.

 

[trplay]

I hear this all the time.

I hear this all the time. Show me the data. Seems its always suspect because of one variable or another.

 

[John Tolhurst]

You can do this effectively

You can do this effectively if you have two persons the size and weight, then you run the bikes together and beside each other. That removes the effect of different wind patterns from one run to another. You make changes on one bike only until it is beating the other, then make changes on the other. Incrementally you can improve both.

 

[Charles.Plager]

 If you know total mass of

If you know total mass of bike/rider and the elevation profile of a coast where you save precision time, distance information (GPS), you can solve for CdA and Crr. The more trials you do, the more accurate.

 

[trplay]

Show me the data.  I remember

Show me the data. I remember when Steamer was really hot on this. Never have seen any real world results. I have a roll down hill and play the game often but no matter how hard I try to keep everything the same rarely do I get consistent results. But I could punch out a bunch of numbers and make a claim. I have no doubt a wind tunnel would give me a helmets aero data accuracy more precise than I would get by rolling down a hill over and over. With that said I think I'll do some roll downs with and without a helmet tomorrow. Now if you were a manufacturer which data, a companies roll down test or an A2 wind tunnel spread sheet would look better on an advertisement?

 

[Charles.Plager]

Steamer is still really hot

Steamer is still really hot on this. You can see some real world results in this thread.

I'm hoping to write my own software to do this as well. Stay tuned.

 

[trplay]

I remember following that

I remember following that that thread and call me the cynic if you may but I don't remember seeing data that applies to my bike or equipment. I applaud their efforts and know RChung knows what he is doing. Call me the cynic but there is no way I can duplicate his expertise rolling bikes down a hill and developing anything consistent enough to be accurate. Certainly no where near the confidence to apply the results into road result predictions. I believe the term is garbage in garbage out. This is an interesting program that is kind of fun to play with but I have yet to match the results. (I use tri bike, relax drops since the formula doesn't list recumbents.)

 

[Charles.Plager]

I disagree with the validity

I disagree with the validity of the results. Unless you are worrying about seconds on hour courses, repeated runs (with not too much wind) will tell you exactly what you want to know and how much of an effect it will be. And you can argue that doing the tests in the real world will make it more relevant than the lab tests.

What roll down tests don't tell you are about drive train efficiency. This shouldn't matter too much for Cruzbikes unless you're worrying about IGH versus derailleurs...

As I mentioned before, I'm hoping to get some software up and running myself to help answer these questions.

 

[trplay]

I use .035 for my mechanical

I use .035 for my mechanical loss. Garbage in garbage out? I don't know.

 

[Charles.Plager]

 Here is another with

Here is another with measured values. 3.5% is not completely unreasonable...