Can't wait to see crr factored into the aero data.

That's coming...I've got a box full of S-works Turbos and both sizes of Turbo Cottons waiting for me to spend some "quality roller time" ;-)

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Thanks for testing the old H3/Specialized TriSpoke. While the new wheels are definitely better at higher yaw, it is cool to see that the H3 is still competitive in the 0-5 range. Can't wait to see what the in-frame numbers look like.

Unfortunately, due to time limitations, the H3 wasn't one of the wheel/tire combos tested in the bike :-(

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That's awesome Tom! Thanks to you and Specialized.

Also double thank you for reporting the data as CdA! In case anyone doesn't know, CdA is the drag coefficient in m^2. Good TTers are close to .20 and triathletes tend to be closer to .30. So the front wheel as measured here is ~7-10% of your total drag.

You can thank Chris and Cam (and Mark Cote too) for the reporting in CdA. That's the default output value they use.

Speaking of total CdA...you may find if interesting that when we did the "rider on" testing, my CdA was measured nearly smack dab in the middle of those 2 values...

...on my road bike, in the drops :-)

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Is that an S5, aero helmet, and skinsuit? Still really low.

Nope. That's with a trim fitting road kit, LG Course helmet, on the Venge ViAS with a single round bottle, Roval CLX64 wheels...

...and the CdA was only slightly higher on my custom steel Stinner (set up in "crit mode" with a Virtue bottle)

:-)

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There are some surprising results in there.

Most notably how good the Roval wheel is. I've liked the SW Turbo for a while; have been running it as a "crit" tire in 24mm mode. The Specialized outside rep showed data (that I haven't seen since online...maybe?) suggesting it was as fast, crr wise, as the GP4000s II. Aero properties notwithstanding, seems like a good tire choice.

Thanks for this! Very interesting

testing against a cc wheel, you..... really?? :)-

Well...this testing WAS just about aero, and you'll notice that there's a similar depth wheel with a metal, textured braking surface that basically ties it with the same tire.

Now, when judging overall performance, it's not just about the aero, right? ;-)

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depends on the event and weather conditions :)

need to read the specs on the roval, ie rim depth

can't test power to spin there?

edit: also I would be curious if the black jet performs any differently than a regular jet+ due to the braking surface treatment

I'm surprised to see such a large difference between the Hed 6+ with 24mm Turbo Cottons and the Hed 6+ with 22mm SWorks Turbos.

I guess I would have expected something more similar to what you saw with the Zipp 101 rims. I'm not too familiar with the tires, but from their website the tread pattern looks pretty similar. Are the Heds just really sensitive to tire width?

clincher only? or might you take a look at their tubulars

There are some surprising results in there.

The 24mm Turbo Cotton does poorly like all the other "open tubulars". Surprised that it was that bad, though.

One that seems odd to me is the Attack vs 23mm SS on the Flo 90. Really would have expected the Attack to win there. I guess at high yaw it does, but the SS is better at law yaw.

As I wrote in the text of the blog (you READ the text, right? ;-), THAT particular Turbo Cotton is my personal tire that had ~700 miles on it at the time of testing, so a big part of that is going to be due to wear and "growth".

The week after I had my tunnel visit, Cam Piper spent some time and did runs of each S-Works Turbo tire width and both Turbo Cotton widths on the Roval CLX64. In that case, the 24C Turbo Cotton plot was offset from the 22C S-Works Turbo by only ~.001m^2 between +/-5 degrees, or basically the same as the 24C S-Works Turbo. The 24C SWT does perform better at 10 and 15 deg than the 24C Turbo cotton though...but, is it enough to overcome the Crr difference?

That will be all gone over in a later blog post :-)

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Tubulars have VERY limited applications IMHO...and TT/Tri speed isn't one of them ;-)

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Yeah, I was surprised by that one as well...with the significantly lower Crr, and the "hit or miss" Crr performance of the Attacks...it's kind of hard to argue against the 23C SuperSonic as a front tire on that wheel.

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Tom,
How was the Attack mounted? IIRC wasn't is suppose to do better aero wise mounted backwards, or was that just a bad dream I had, hmmm!

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<We all know that light travels faster than sound. That's why certain people appear bright until you hear them speak>

Mounted as marked. I did recall the data showing "backwards" may be faster (Swiss Side testing?), but there wasn't time to try both ways so I ran it the way most would mount it.

edit: I found the apparent source of that "Attacks mounted backwards" meme (I think): http://www.swissside.com/...n-project-update-13/ ...although, I think it's probably a bit of a stretch to apply what they saw with the GP's to the Attacks. Yeah, the tread patterns are slightly similar...but...

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I read the text as well, although I didn't think that 700 miles would make such a big difference either. Do you have a picture of the tire? Is it super squared off?

How does Crr usually trend with use?

It's not "squared off" in any appreciable sense...it was used as a front. I suspect the big difference is from size/shape changes just from being mounted/inflated/flexed for that period of time. That tire measured between 0.3-0.5mm wider when mounted than a brand new tire.

Crr typically drops with use...again, partially due to size growth, but also due to the tread thinning from wear.

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did you mean 3-5mm, as 0.5mm is about 1/50 of an inch and on my 50 scale "ruler" that is not much

.3-.5mm is a decent amount when we are talking about tire casing stretch.

just something you wont note without calipers

...or, with a wind tunnel balance...apparently ;-)

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A little bummed about the H3. Been using that in all my tts this year.

I wouldn't be...to be fair, from 0-5 degrees of yaw it's within ~1W of drag as compared to the best wheel/tire combo in the test. And, as some have pointed out, this doesn't include "power to rotate", which has also been shown to perhaps be in the H3's favor.

For fast-ish TTs, experiencing yaw >5 deg is a fairly uncommon occurrence...

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Is there data available on power to rotate for various types of wheels? Disc vs 60-80mm profile vs spoke wheel ect? I have looked, but not found any.

you need to look harder. there is some pay for data on BTR but you can find other data floating around the web, you just need patience and to open a bunch of papers and read what they did in their studies. I have no links

Thanks, good to know data is out there. Any ballpark estimate on watt differences between Disc and 60/90ish wheel?

like anything, depends on yaw and speed. if concerned, just spend some time and inform yourself or do some field testing(it's built in then)

edit: also, tire width has impact on some I have seen, so.....

https://docs.google.com/...XRAL94hu0/edit#gid=0

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Blog | Twitter| Bike CdaCrr app

Dang, there is a lot more rotational drag on a spoked wheel than I thought there would be.

So are we better off deflating partially or completely if we aren't going to ride in the next couple days at least on race tires?

I doubt it would make much of a difference...besides, latex tubes "naturally" slowly deflate anyway ;-)

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Yeah, I should get around to that latex thing...

Make sure you read and absorb THIS first: http://austintriathlonstore.blogspot.com/.../01/latex-tubes.html

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It's been three days now, where is the next instalment?

Partially on my hard drive and partially in my head :-P

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Thanks for all the great insights you provide us so regularly!

I've tried to subscribe to your blog with no success. Probably user error. But maybe I am missing something. Can it be done?

Scott

There seems to be many points of view on aerodynamic torque/"watts to spin". Here are my notes when I looked at the literature a half dozen years ago:

http://www.biketechreview.com/...-torquewatts-to-spin

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Kraig Willett
http://www.biketechreview.com - check out our reduced report pricing
=================

I don't know...I've never tried to subscribe to my own blog :-) I'll poke around and see if I can figure anything out.

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It's been quite a while since I looked at how you were deriving watts-to-spin from the tunnel balance data...so, I forget, does that value include the tire-roller interface losses? (i.e. rolling resistance) If so, do you remove that from the calculations?

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The graphs with the wind on / no wind comparisons could be a bit misleading because it seems to assume that wind off drag represents rotational drag. This would also imply that the flows are linearly additive, which would only be approximately true in a special set of circumstances for (near infinitely) high-Re flow (see potential flow theory).

Because of the relative speed of a wheel to to the freestream, a rotational moment calculation would be heavily skewed towards flow at the top of the wheel (https://en.wikipedia.org/wiki/Cycloid) where flow is twice the freestream, whereas near the ground, the flow is traveling with the wheel surface (zero relative velocity). Since drag isn't linear, the physical effect is not the same as the average, and the true rotational cost is likely higher.

Hey man - first wanted to say thanks for your research !

I've been sitting on the edge of my seat waiting for you to post part 2!

Waiting to pull the trigger on either the ss or turbo cottons for IMFL as soon as you've finished running the numbers.

Any hints on which one is marginally faster?

Thank you sir

FYI, TomA posted part 2 yesterday

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<We all know that light travels faster than sound. That's why certain people appear bright until you hear them speak>

i'm more amazed that he got a CdA of ~0.27 on his road bike. My TT position right now may be ~0.23...

In the "real world" it's actually going to be a bit lower since that value includes the fixture drag :-)

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Technically, is this a frontdoor or backdoor brag?

Yes.

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Well earned brag at that.
Thanks for all of the data and sharing your thoughts.

what do you reckon your CdA would be if you buried yourself on the tops?

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Eric Reid AeroFit | Instagram Portfolio
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Dunno...but, based on my experience, it probably would be a bit harder to maintain a "fixed" position and get stable data. As tedious as I think field testing can be, being a "wind tunnel test dummy" is a bit of a drudge as well :-/

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And if a lot of ST folks took the time to do some testing they'd find that their triathlete CdA is higher than that...

A lot of triathletes have spent a lot of money to get aero but are still pushing way too much air with the most important component of all, the body...

Not just age-groupers, but pros too...For example, I witnessed a pro triathlete (one who recently finished fairly high up at Kona) register a CdA higher than that in a wind tunnel not long ago...

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Which pro was that if you can answer?

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I'd rather not say (since it wasn't MY wind tunnel session)...but some of you may be able to figure it out ;-)

edit: Plus it was a few years ago, and this pro is now on different equipment (maybe different position?) and may have a lower CdA now...but, the pro obviously has a huge "engine" since they were a top pro already at that time.

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Well there is no way it could be Brent or Tim, they are just too small IMO. I guess it could be Rappstar himself or Hoff but they both look pretty good despite be Jordan being like 6 4 with long legs. I guess I would me be most excited if it was Brent. That would give me some confidence that I need myself need to get to the tunnel.

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It wasn't Jordan...and I don't think I said it was necessarily a male ;-)

I'll narrow it down for you slightly...this athlete finished in the top 7 this year.

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Interesting results. The pictures of you on the 2 bikes look like you have more reach on the Stinner, which reduces the big wrinkle in the jersey and might narrow elbows. My eyeball wind tunnel makes me think that this favors the Stinner results.

I also can't wait to see your Crr results for the Specialized Turbo 22. Velo just published tests that put it slightly ahead of a GP4000. Maybe we will have a new best all-around tire.

You have a "keen eye" ;-)

The reach to the drops on the Venge was slightly shorter, but it wasn't my bike to go swapping stems on.

It was actually quite interesting how close it was otherwise...we basically just adjusted saddle height.

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It would be interesting to see how low your road cda would go with a lower head position. It looks quite high in the pics.... at least for what it could be....potentially..

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24 Hour World TT Champs-American record holder
Fat Bike Worlds - Race Director
Insta: chris.s.apex

That Stinner is a really pretty bike. It kinda reminds me of something Rob English would build. Simple yet elligent.

...or, with a skinsuit...or smoother shoes...or, a different helmet? Lots of things to still try out.

Actually, from what I've read, that LG Course helmet actually does fairly good job at that head angle...not so much at lower angles.

BTW, during the testing, I attempted to keep a consistent head position by staring at a particular level on the tunnel intake wind screen. So, that may or may not actually represent the "average" position I hold my head during typical riding.

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Thanks, that was our intent. Aaron was great to work with and this was a good project for him to try out some things he might otherwise not have ventured.



Is that a mash-up of elegant and intelligent? I like that :-)

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Here's how it looks in "normal riding-around mode" ;-)

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Out of curiosity, can I ask why the GP4000s II tire was not in the result set? Did you use it in the test?

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Chris Thornham
Co-Founder And Previous Owner Of FLO Cycling

Mostly because of time constraints and not personally having a "fresh" one on hand...plus, especially for the Flo 90, I was more interested in tires I would possibly run in a TT. Personally, it's not going to be a GP4000S...I'm not as "flat averse" as some folks are (especially for a front tire) and with lower yaw angles experienced, low Crr tends to win out...as can be seen here: http://bikeblather.blogspot.com/...sheriff-in-town.html

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Hey Tom,

Are you going to let us know what tire is faster when you combine aero with Crr? I keep checking your blog for updates ;)

Much appreciated.

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/kj

http://kjmcawesome.tumblr.com/

Ok thanks for the info. That data is interesting. We need to talk soon.

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Chris Thornham
Co-Founder And Previous Owner Of FLO Cycling

Tom, thanks for sharing this information.

If I'm interpreting things correctly, the SS23 may be the fastest / most aero combination. Just curious, do you think the aero gains of a SS20 are enough to offset what is given up in Crr to be a faster front wheel option?

It's coming...soon :-)

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Next year I'm contemplating the SS23 for my front and either the Conti Force or one of the Spec Turbos in 24c for the rear.

Can I have some details on the Stinner (pretty bike), so I have some idea what's being compared to the Venge?

All round tubes except for the headtube fairing, toptube and chainstays? It's hard to tell with the paintjob.

44mm headtube?

Downtube diameter (or width)?

Cervelo fork?

The only truly round tube is the seat tube :-)

Fork is first generation Cervelo S5 model

Tube specs is as follows:

HT: 44mm with Chris King Inset HS ("fairing" is actually only filler to cover internal cable routing tubes)

DT: Columbus Life Aero 42mm (run narrow end forward, simple CFD suggested that was faster, especially with bottle). DT is offset at BB to allow cables to exit and partially "fair" rear brake below BB.

TT: Columbus MAX bi oval (oriented with horizontal flat at HT, and vertical flat at ST, both to match tube widths better at HT and ST junctions)

Seat tube: True Temper HVERST1

Chainstays: Columbus life Oval

Seat Stays: True Temper Velo Seat Stays (teardrop shape designed by Yamaguchi)

BB: BSA threaded

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Hi Tom,

I'm comparing your Flo 90 results with Flo's recent aero data and having trouble translating the CdA in your aero data to the grams of drag reported in Flo's aero data. Is there a way to convert the metrics for comparison?

Scott

Assuming the Flo tests at A2 were run at 30mph tunnel speed, then you can use the rough ROT of "45g = .005m^2".

However, I believe the Flo tests have the fixture drag removed, while the test data from the Win Tunnel do not. Therefore, there will likely be a fixed offset between the 2 data sets at each yaw angle, although comparative deltas should be consistent across the 2 tests.

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