aero bottle weenieness
At the WI Tri Rally, Rich noted that on his P3, he uses an aero bottle in the front, rather than the now-in-vogue torpedo mount, and an Arundel bottle on the down tube.
This season, I've been riding with a torpedo mount, and I really do like it because it avoids the usual spillage issues associated with the PD aero bottle. However, Rich convinced me (along with reviewing my own thoughts) that for a race, the PD is what I will use (with a bent/hidden straw) because of the ease of drinking and that I'll drink more. I have caught myself drinking less with the torpedo mount. Probably not good if race day is hot.
I tried to find some data out there beyond the intuitive idea that the Arundel (and its cousins, e.g., XLab, Botrager, Specialized, etc) really are more aero. There may be some, and it's probably true, but I didn't find good data. However, I did find the following post on Slowtwitch by Cobb himself (2008):
I finished a week of testing riders two weeks ago and we had run some of these test. Here are some numbers to look at. These are the average drag in Grams for a sweep of "0" - "20" degrees.
[1] - 5'9" male @175lbs - Trek TTX w/ Trek aero bottle on seat tube. 3072gr.
[2] - Trek TTX w/ No bottles 3059gr. ** 20 gr. is nothing that will show up in the real world.
[3] Cervelo P3 No rider - Round Rocket Science bottle on Down tube - 1024gr.
[4] P3 No rider - Trek aero bottle on down tube - 1079gr.
[5] P3 No rider - No frame bottles - rear Hygro tail - 1198gr. Not having a rider probably was not a fair test for the rear setup.
New Blog - www.johncobbresearch.com
50 g of drag reduction is nothing to sneeze at, especially if it's as cheap as a $10-12 bottle (and cheaper than the choice it replaces!). It's too bad he doesn't compare it to a garden variety round water bottle in this post.
If you're unfamiliar with the Rocket Science bottle, it's basically a plain old round water bottle, but has (for lack of better terms) dimples. I assume Trek/Bontrager are being used interchangeably here.
If you look at the Rocket Science web site, they tout a claim based on Cobb to save something like 1/3 lb of drag at 30 mph. vs a normal bottle (ca. 100 g). (Cut that by about a factor of two to get to 20 mph) They have another article/press-release here.
These data appear consistent with one another, in that the order could be: regular bottle > aero bottle > dimpled bottle... but it seems so odd that the texture on a bottle would make such a big difference (and why aren't whole bike surfaces dimpled if it does?)
Anybody out there have any further insight/data/whatever?
Comments
I figure the least frontal area I present to the wind the better and in general airfoil shapes are best. By no means is this perfect and I'm sure someone can prove me wrong, but without access to a wind tunnel to test MY position on MY bike with MY components I just don't trust wind tunnel data. I have no idea whether or not the profile aero drink or horizontal bottle is is actually less drag on my bike, but logically the horizontal bottle seems better to me. Plus I like not getting splashed and not having to refill it. I tested it multiple times racing this year, and I started in my aero bars the entire time while throwing out the old bottle, grabing a new one and drinking from it. It really just comes down to personal perference as the difference is probably just noise in real world conditions.
Just my thoughts, please continue to look into this and share as I like to read along and learn.
I agree with Matt that tunnel data done by others on other set ups must be taken with a grain of salt. A friend of mine who has worked extensively in tunnels [not on bike stuff] tells me that a lot of the data is "black magic" and that there are lots of ways to manipulate the data. Further, sometimes the testing is counter intuitive. I suggest going with what is comfortable within reason. If you do not think that you will remember to drink unless you have a straw in your face I think that is what you need. It will not matter that your bike split was 12 seconds faster if you forgot to drink anything for 6 hours.
I prefer the way the torpedo mount works in general (and the whole column of stuff that is in a series of wind shadows), but I think I'm going with the PD for the race because of the whole "drink enough" thing being that much easier with the PD. But for most of my rides, the spill/neatness thing wins out. :-) Also, I know you're right about the "my bike (etc)" quotes. If you really want to be confused, look into what people/companies/etc claim with regard to rear hydration systems! It really illustrates that point.
And again, Chris restates why I'm planning on using the PD for a potentially hot race.
After reading a bunch on this subject, I've decided that you can drive yourself to drink (pun somewhat intended) trying to figure out what is best - and you will find a lot of contradictory information.
Thanks for the link.
The tests all showed that for round tube bikes [which none of us have BTW] seat tube was better.
I would not put much if any stock in any of the JackMott stuff. He has no knowledge, has done no testing and can't even ride fast or run for that matter. He is excellent at parroting advice he reads in other places and responding quickly though. The problem is that unless you know the source of the parroted advice you can't make any judgment as to its validity. Rappstar is worth paying attention to as are the MIT guys.
Yeah, I hear you and generally agree on JM - it was Rappstar x2'ing what he said in that thread that cemented it for me.
"The tests all showed that for round tube bikes [which none of us have BTW] seat tube was better."
I don't have the reference, but I remember reading an article saying that although aero bottles mounted like the PD will improve a road bike's aerodynamics in some cases, it doesn't have as much effect on a tri bike that has aero tubes.
In addition, I have a question and a comment.
My comment is about the PD. I know people hate the splashing, as do I. However, I have started to put a piece of saran wrap over the opening and lock it down with the cap. It is only good till the first refill, but..NO splashing. I usually just stick a finger through to let me refill.
Question is-what is the hidden straw thing?
There's a well-publicized study on water bottle placement (http://www.slowtwitch.com/mainheadings/techctr/waterbottles.html) that is getting a little long in the tooth now, in that it was done with bikes with round tubes. (I don't recall if they were road bikes or tri-geometry bikes with round tubes.) I don't recall ever seeing similar study with modern style head tubes on a tri bike, but most people seem to think it's still a "do no harm" shape and one of the least bad options, regardless of whether it actually "helps" any more or not. there may be real data somewhere, but as above, it probably depends on rider position, and so on, to a degree anyway.
The Saran Wrap thing is one of many variations. You could almost certainly cut a small slice in the Saran Wrap and still have next-to-zero splashing (assuming it's not overfilled) and be able to fill on the fly without the awkward poking/stretching/tearing step. Haven't tried this myself.
Subsequent to Cobb's original article, someone (Can't recall if it was Cobb or the MIT guys) did another similar test. I remember reading the original text of it, and they discovered kind of by accident that the exposed straw coming out of the top causes a measurable amount of drag. In fact, they estimated that a straw at full height causes as much drag as the difference between a race wheel and a normal wheel. (Hence, you'll sometimes here people talk about the $800 straw....)
The work-around for the straw is to cut the hard plastic part down just a bit, so that no more than an inch (maybe less) protrudes from the drink bottle, and then replace the soft part with REALLY soft tubing with the same ID. Then you can kind of fold the tube over and shove it under the loop of the black cap or some other strap you like. Then you just flick it out to drink and put it back when you're done. This adds a LITTLE hassle to drinking, but it's not bad. I am a chemist, so I have gobs of tubing in my lab, but you can probably go to a decent aquarium shop with the hard part of the straw in hand to get what you need.