Tire Tread Aerodynamics
 

As I was riding this past weekend, observing my front wheel spinning below me, it occurred to me that nothing on my bike was moving faster through the air than the tread of the tire at that moment. I also realized that I hadn't read/seen anything discussing the effects of tire tread on aerodynamic drag. I would think the difference between a 25mm road tire and a 2.25" MTB tire would be somewhat significant because of both width and tread. Looking at just high-end road tires, how much difference would there be between slight variations of shallow patterns in what is considered a "slick" tread (Conti GP5000 vs. Pirelli P-Zero, for example)? Is it completely inconsequnetial, or are there a few watts difference?

To get you started: https://www.swissside.com/blogs/news/gravel-report

DT Swiss have just been granted a patent on tire surface pattern.
https://bikerumor.com/dt-swiss-swiss...d-tire-patent/

Excellent. Thanks for the info. Now, I'll try to wrap my dumb head around the data.

My P Zero Race TLR SL have a couple of gloves running in the direction of rotation. 15 watt advantage, at least.

This is the only article that comes to mind: What effect do tyres have on aerodynamics? | Cycling Weekly

Summary: JP Ballard from Swiss Side stated that Continental GP4000S II tire has sidewall and tread that improves transition of boundary layer from laminar to turbulent flow.

More recently (GP5000 vs. TT): Tire dependence for the aerodynamics of yawed bicycle wheels - ScienceDirect

At least. I’m going to put 2 on each wheel to double the advantage. Genius move.

fascinating. they state a 33% reduction in wind averaged drag for the tire with the seam, and state elsewhere that drag is 90% of the force to be overcome at 28mph, and the wheels are 10% of that. so, that little tiny seam of rubber results on a 3% reduction of TOTAL drag. almost unbelievable!

Aero depressions?

Yeah, we've all been there. It's ok to talk about it.

The bottom of the tire is going 0 so it pretty much cancels out. :)

Jan Heine stated in an article that fenders over the top of the tire confer an aero benefit but I’m not going to Google it right now.

And attaching a samsonsite size handlebar bag is also faster when times with a GPS device once. And steel turns a bike into a plane. Wool is faster. Notice the picture of the fender in Heine's photo, It is as long as an elephant's snout. I have never seen such a snout on a bike in the wild. He also claims really fat tires are faster and I suppose professionals some day will ride 48 mm tires.

Tire/rim interference can be measured and can easily be felt from wheelset to wheelset with variation of tire width thrown in.

Yes, a 1 inch wide tire has more area than a 2.25 inch tire. The fat tire is also taller. No rim is going to overcome that difference in the CdA department.

How concerned about aerodynamics are the people that don't ride paved roads? Or why would anyone that rides a paved road have much of any tread pattern on their tires?

That was a pretty puzzling result: he said that max speed was higher with the handlebar bag than without. It turns out that he'd recorded the ride on Strava so we downloaded his data file and looked at the speed. His max speed with the handlebar bag was a one-second anomaly where it jumped up by a couple of mph then in the next second it returned to normal. Without that one-second point, his max speed without the handlebar bag would have been higher. So his long blog post about the aero benefit of handlebar bags was based on that. We commented on his blog post explaining the one-second anomaly and he removed our comment but left the blog post up. (His GPS device was the iPhone he had in his pocket).

[Edited to add:] By "we" I meant, Tom Anhalt and I. I wasn't using the Royal We.

Just because it's a dirt road doesn't mean they're not roadies

Sounds like a GPS glitch, like the few times Strava thought I had exceeded 40 mph on a descent.

But only at a specific yaw angle, if I am reading the paper correctly; to analyze it more in depth would be too much like work.

That’s a very diplomatic way to put it.

Some are. Aero is a concern in gravel racing, especailly when it comes to some of the longer events. Watts saved matter when you're on the bike all day long.

I'm learning here that even the minimal tread pattern (if you can even call it that) on high-performance road tires makes some difference.

yeah, they lost me a bit - but i *think* what it said is up to a certain yaw angle, not one specific angle?

When some asked for data, he just closed off all comments and never provides raw data. But the results stand. Steel planes, suitcases are fast, fat tires are faster (settled) and snouty fenders are also fast. I am no diplomat and I no believe his results.

At least Flo and Swiss side will provide enough info that you can confidently say the 23mm GP4000 was the fastest tire on the Flo60 for some speeds. And the explanations make sense.

I reached 47 mph in my last gravel race, and I didn't get close to the podium. Do you think aerodynamics might matter to fast riders?

So when are they going to figure out what the airplane folk got a long time ago? Cover or hide those wheels. Forget faster tread. A full faring is faster. (For a brief time, planes with fixed landing gear and teardrop bubbles over the wheels were popular. Then it was deemed better to hide them entirely inside the wing or fuselage when not in use despite the added weight and complexity.

I won't buy a fully faired bike. Just bringing this up to point out that optimizing tire tread is going after the small stuff.

It is small stuff. The fact that is makes some difference is interesting to me.