for tech geeks only! fantastic series of articles on CRR & Aerodynamics

[Ron]

https://blog.silca.cc/tag/technical/page/1

if you are into aerodynamics and optimization of psi (comfort & speed) then you probably already know the names of Jan Heine & Josh Poertner. Im not a fan nor follower of the studies of Bicycle Rolling Resistance which misses the second component of CRR entirely. this data applies to road and gravel riding. happy reading.

 

[Tom K.]

Just tip toeing in, but seems interesting through Parts 1 and 2.

It's a funny comment on myself, I guess, that I'm an engineer for work, so I should find this fascinating.

But sometimes, for fun things like biking, I kinda just want somebody to tell me the conclusion, then go implement it!

 

[Ron]

there are 2 camps, the high psi group that thinks high pressure rolls faster and those who are correct in understanding hysteresis and vibration losses. . now lets complicate that by adding aero drag when a rim is less than 105% of the tire width (meaning the tire has to be narrower than the rim) at speeds as low as 15mph. oh, now correlate road surface into the mix. to make matters worse, unless you have a bike that will run at least 30mm of clearance, note I didn't say tire clearance you are are stuck at 25mm road tires which don't seat at 25; more like 27-28 which means your rim needs to be about 28-29mm external width to fall into the ratio. that's something bike and wheel manufacturers don't want to admit. (trek told me they have no studies on aerodynamic properties on the drag coefficient on tires that exceed the rim width, although they state they have tested 28's LOLOLOL) tire manufacturers are making matters worse by producing tires that inflate far above the stated width; Schwalbe being the biggest offender by far on their Pro Ones. their 25's inflate to nearly 29 on an 19mm+ rim.

Enves 4,5AR is where everyone else should be. I. would love to replace my Bonti xxx4's with a set and run a 28 up front.

 

[gwasson]

There was a podcast last year with Josh and the guys from Cyclingtips. I found it fascinating even if it did zero to change my riding.

https://cyclingtips.libsyn.com/tdf-stage-3-walking-the-pits-with-silcas-josh-poertner

 

[Ron]

ill have to listen. thanks.

 

[Ron]

I thought I would add this link to another independent study on wheel and tire CD. his work is pretty damning of manufacturer claims. time spent in different Yaw % by pro riders vs avg riders is the most significant finding as well as the wheel depth (you need about 45mm deep before savings kick in) interesting data and I have asked him to model results at 40 kph to get a much clearer picture of savings/cost since CD is a geometric progression and not linear. testing at 30 (18.5 mph) is fine but the jump to 50 kph (~30 mph) is not really useful (he admits this) and frankly, I'm coasting at 30 mph, not pedaling, so at 40 kph, 25mph, is a solid comparison point of where a solid rider can maintain on flats/rolling terrain. this way, you can see the true gains/losses as speed increases.

what is apparent is that bike stuff is so far more complicated than ski's!

https://www.hambini.com/blog/post/bicycle-wheel-aerodynamics-which-one-is-fastest/

 

[Fuller]

Coincidentally I just purchased latex tubes and valve extenders from Silca. They will be tucked under my new Continental GP 5000s. Marginal Gains FTW!

 

[Ron]

no tubeless????

 

[cantunamunch]

. now lets complicate that by adding aero drag when a rim is less than 105% of the tire width (meaning the tire has to be narrower than the rim) at speeds as low as 15mph. oh, now correlate road surface into the mix. to make matters worse, unless you have a bike that will run at least 30mm of clearance, note I didn't say tire clearance you are are stuck at 25mm road tires which don't seat at 25; more like 27-28 which means your rim needs to be about 28-29mm external width to fall into the ratio. that's something bike and wheel manufacturers don't want to admit.

Hunt have been reading all the same articles, and the proof is:

https://www.huntbikewheels.cc/colle...de-aero-road-wheelset-1549g-55deep-26wide-999

 

[Ron]

you didn't read the Hambini test results including Hunt and Flow wheels?

 

[cantunamunch]

you didn't read the Hambini test results including Hunt and Flow wheels?

Did you notice that the wheel I linked to is a new release specifically designed to meet the objections Hambini raised on the previous generation Hunt 50?

 

[Ron]

NO! is that in the text??? Thanks.

 

[cantunamunch]

NO! is that in the text??? Thanks.

I just noticed it isn't in that text, sorry.

I am trying to find the detailed discussion I was reading about changing the external width of those and therefore needing to introduce internal polymers in place of CF, to keep some semblance of lightness.

Either way, they should be available for re-testing sometime after the TdF

 

[Ron]

so... here's my issue with those rims, if you want o be aero as possible (and the gains are significant for any serious rider who averages at least 18mph on flats or rolling terrain) you can exclude real climbing sections, then you really need to have your rim at ~105% wider than your tire. plus, wider rims are more stable and change the tire profile. This allows lower pressures at lowered CRR's and improved grip/cornering. So that rim is still too narrow. I run Vittoria Corsa 28's on my Enve 45.5 Ar's which are 31mm wide external (25 internal) if your run 25's you need an external width of at least (at minimum) of 28mm.

 

[Ron]

btw- here's what Enve now recommends for PSI's based on internal rim width. its a starting point and for optimized speed, they told me to add 5psi or so, since road conditions really affect CRR, you need to play around but I will be testing 55-60 on my 28's. Studies by Josh and Jan are really starting to catch on.

scroll to the bottom for the chart

https://www.enve.com/en/products/ses-4-5-ar/

 

[cantunamunch]

I expected those objections from you when I saw the exterior dimensions

I'm pretty sure the new Hunt rims are targeted at "no-wider-than-25mm-and-we-still-want-market-leader-light" customers.

I still find it interesting that these geeky blogs do apparently affect engineering design, and the timing of the product release was extraordinarily interesting.

 

[Ron]

 

[Ron]

I'm pretty sure the new Hunt rims are targeted at "no-wider-than-25mm-and-we-still-want-market-leader-light" customers.

I guess Enve is no longer a leader. . You are seeing Zipp (Sram) Specialized (Roval ) and Bontrager move to wider, Bontragers XXX4 & 6 moved to 21 internals already. But the biggest barrier to the larger external width is that most road bikers frames still cant take a true 28 tire which seat up at 29-32. (yes, I'm talking to schwalble who need to revamp their pro one)

Aero overtakes weight and Crr very quickly which is why Aero bikes are always heavier than a climber like the Emonda. If I could buy a new road bike today, I would buy a Specialized Tarmac in a heartbeat. best combo out there for weight and Aerodynamics.

 

[Fuller]

Isn't it well documented now that the "Hambini Report" is a load of rubbish?

I have the xxx6 wheels on my TT bike and just put Continental 5000 with latex tubes on. There is a noticeable difference in feel and performance vs the stock Bontrager R3 set up.

 

[Ron]

Isn't it well documented now that the "Hambini Report" is a load of rubbish?

xxx6 wheels are awesome. I am selling my xxx4's BTW if anyone is interested. they are fantastic but I went with Enve 4.5ar's for proper rim/tire ratio for 28's and were 35% off! BTW- Hambini rated the XXX4's very highly

regarding Hambini's Aero testing, I haven't read one article to that effect. please post up. I'm always interested in getting the facts What part of his analysis is contested? the report covers a myriad of data from time spent in yaws to actual testing in his company's wind tunnel (aerospace BTW, not a home made garage version) I do know that Hambini stated that neither Flow or Hunt were able to argue his findings and he has not issued any retraction despite legal action from Flow. I've had a number of email conversations with Hambini and if you read his report, he freely admits that the number of variables for a real world rider are innumerous when it comes to Wind tunnel and Aero computational results. Many of the assumptions are also based on proven aero formulas used for the design of aircraft and the aerospace industry, so I'm certainly not at that level of intellect to argue these formula's. I can give you another major study that supports this but goes even further to say that most wind tunnel tests (and we are talking CDf) are faulted for many reasons. if a wind tunnel room is too small it affects the turbulence, also, rider speed will greatly change the time spent in certain yaw angles, the use of a pedaling rider vs fixed mannequin (either at vertical or horizontal cranks) or no rider will all wreak havoc on results. Also, simply testing one wheel not mounted will also change the results ( as does temp and humidity and altitude)

Roll resistance tests are mostly garbage and I'll wager the heavy, stiff cased 5000TL is not nearly as fast as the galvanized steel rollers show which reward stiff casings and punish pliable casings (which is opposite of how suspension works). And of course, tested results touted at 120 psi LOL.

here, happy reading. probably the most interesting and revealing study I have ever read


https://link.springer.com/article/10.1007/s12283-017-0234-1