rubiksoval

If you're going to be wrong, I guess it's helpful to be polite.

But the fact that you think weight and aerodynamics are the only two things that tire/tube choice affects demonstrates a pretty significant lack of understanding about the topic. So not sure why you're trying to argue about it.

Sy Reene

I came across the below chart on trainingpeaks, which I think is speaking to your point ( https://www.trainingpeaks.com/blog/u...ng-resistance/ )? If you compare a tire setup (eg. Gatorskins) with a ~.006 CRR to a tubular like Corsa Speed (.003 crr), the 160lb rider on Gatorskins needs about 20 watts additional output to equalize to the Corsa rider? And this is more than gained at 20mph using aero wheels vs. box rims or somesuch?

KraneXL

But I don't think that. However, the two are closely related but not inseparable. And as I alluded, each can have significance, but to what extent depends on the instant and the environment. Just as torque and horsepower are related. But which is more important?

rubiksoval

Sure. You don't think that because you apparently don't know it. And you don't know what you don't know.

Your example is a non sequitor. CRR affects the rider at all times. It's always significant. And even in a solo cross wind in which wheel aerodynamics are at the most useful, it's still more significant.

rubiksoval

It doesn't matter the speed. That's why CRR is so important. If affects you always.

The differences in tires are bigger than the differences in wheels. You're not going to gain that back with wheel aerodynamics.

Gatorskins on aero wheels are slower than fast tires on nonaero wheels. Obviously, if you wanted maximum speed, you'd go for a setup that has the best blend of rolling resistance, aero, and puncture resistance.

RChung

This thread? This is why we can't have nice things.

You lose your bet. Not just I, but lots of others have measured differences between wheels not just in the lab but from data collected from real rides on real roads.

This is almost always right, unless you're already using good tires and tubes, or are using extremely crappy wheels.

Aero wheels certainly help, but they have poor bang for the buck. Good tubes and tires have pretty damn good bang for the buck.

You may know the rule of thumb that at TT speeds on a flat course, an improvement in CdA of .01 is roughly equivalent to an improvement in Crr of .001, and will save you roughly 1 sec/km. Two things: first, that's at TT speeds on a flat course, and many of us don't ride like that on an everyday basis. Second, compared to the aluminum semi-shallow 32-spoke wheels that come standard on most road bikes, a nicer set of after-market wheels (but not the most aero) might reduce your CdA by something like .01 - .015. (As an aside, 2 spokes is worth approximately 15 mm in rim depth, ballpark; and the aero benefit of a rear wheel is roughly half the aero benefit of the front wheel).

Here's another useful rule: Crr scales exactly like slope, so a difference in Crr of .001 is exactly like a difference in slope of .001. That's always and everywhere, whether you're going fast or slow; uphill, downhill, or on the flat. If you are using Conti Gatorskins with a butyl tube, you're costing yourself maybe .003 in Crr vs. a pretty good tire like a Conti 4000S with a latex tube (I'm comparing with the 4000S because it's a pretty common tire). That's a difference in "slope" of .003 everywhere, so on a 64 km (=40 mile) ride, that's like climbing an extra 200 meter hill.

So, if you have a power meter and use Golden Cheetah, there's a simple way to evaluate how much benefit you'd get for *your* riding style at *your* speed on *your* typical terrain. Pick one of your typical rides, then go into Aerolab. For now, we don't care about the "fit." Just note the difference at the end of your ride between the Virtual Elevation and your actual elevation. Either increase or decrease your Crr by .003. Notice how the difference between VE and the actual elevation changes. You'll see that it agrees with .003 * total distance. Now put the Crr back where it was originally. Either increase or decrease your CdA by an amount so that the difference between VE and actual elevation is equivalent to .003 * total distance. That's how much CdA would have to change in order to match a change in Crr of .003 for you, on your ride, on your terrain.

If you're not using Gatorskins, you might not want to use .003 as the improvement in Crr. Try it with an improvement in Crr of .001.

I ride in the Bay Area, where the terrain is hilly. For me, I'd need a decrease in CdA of about .02 for every improvement in Crr of .001. I'd need to spend a couple thousand dollars on wheels to match the improvement of going from butyl to latex tubes. For me, latex tubes cost about $10 per tube more than butyl, so that's a couple thousand bucks vs. 20 bucks. Latex tubes are great bang for the buck.

burnthesheep

If we’re talking TT, bets are off. I’m not very strong and can TT over 25mph. Close to 30 doing power intervals. A few 3min or so KOMs at 32ish.

At that speed, a rear disc at certain yaw can save loads over a turd rear wheel. And a front 808 or trispoke boatloads over a box.

Lets be real, people may train on Gators and butyls but who honestly races on them? I wouldn’t even go for an unofficial PR TT ride on crap tires/tubes. What a waste of a heaving effort.

I can’t wait for good weather to try out the HED 3 and disc. With fast tubs. Awwwwww yeahhhhhh. Hnnnngggg.

rubiksoval

Oh, lots. Lots and lots. There's a local cat 1 that's both a coach and a mechanic(!) that frequently shows up to race Zipp 404s with gatorskin tubulars. I asked him once why he had such a fast wheel with such a slow tire and his response was punctures (in a crit, no less). There are always stories (though probably less than before) of pro triathletes and amateur triathletes and all racing gatorskins because they're so afraid of punctures.

And I'd assert that the vast majority of people racing clinchers are using butyl tubes. In my area, at least, I know they are. I tell my teammates every year about latex and crr. So far only one seems to have listened. Oh well. The move to tubeless (if it ever really gains traction) will render that moot, but for the last few years I've taken advantage.

burnthesheep

The time lost in an IM using Gators is probably more than the time to change a tube out. Lol!

Assuming Gators and butyls vs latex and good tire gotta be more than 5 minutes over a full IM.

Easily. In a TT I did latex and Conti TT was about a whole 1/2mph faster than GP4000s and butyls.

KraneXL

Why not use helium instead of air? How much time could I shave off then?

rubiksoval

Again, it's not weight. It's rolling resistance. That's what's important. That's the point of latex tubes.

Seattle Forrest

That, and also because the power saved at 6 mph just isn't important to many of Zipp's customers.

Seattle Forrest

You know how a lot of tires come folded up in a box, and you unfold them when you open it up, and it isn't a struggle to unfold them, but it's not zero effort either? Something like that happens when you ride. Always, as long as the wheels are turning. If you hold a wheel in your hand, the outside of the tire is a circle, but get on the bike and it's not a circle anymore because the contact patch is flat. As the wheel rolls forward, the part of the tire in contact with the road changes. Which means you're constantly flattening part of the tire. Remember about how unfolding them takes a little bit of effort? Same basic thing when the tire rolls. Some tires are tough like leather, others are supple like silk. Completely separate from weight, harder tires are harder to move because they resist flattening into a contact patch more. That effect is called rolling resistance.

ColonelSanders

A very nice explanation.

HTupolev

And a few of them literally are silk.

asgelle

Not exactly. Rolling resistance comes from the difference in energy it takes to deform the tire at the front from the energy recovered when the tire returns to its original shape at the rear (plus a geometric factor). A tire can take a lot of energy to deform, but if more of that is returned, it can have lower rolling resistance than one which takes less to deform, but doesn't return that energy.

Zaskar

Rolling resistance is a constant.
Aero is exponential.

At lower speeds, rolling resistance matters more than aero.
As speed increases, the power to overcome the air/wind increases exponentially... and becomes the bigger factor... the biggest factor... bigger than rolling resistance

Plus, 35-45mm aero carbon wheels look cool. That's also a constant. ;-)

asgelle

Once again, it is not. Drag force is quadratic in velocity, a polynomial function. Isn't it just as easy to get is right as get it wrong?

Zaskar

Wait, you just said it was "cubic, a polynomial function" then "quadratic in velocity." Are cubic and quadratic the same in this case?

Next you're going to say 45mm carbon wheels aren't cool. And everyone knows that's been proven. I think it MIT... no, Stanford.

asgelle

Power is cubic, force is quadratic. Both are polynomials.

Seattle Forrest

I know. But I'm trying to make the concept accessible, and the springing back part seemed like complicating they picture unnecessarily. But yeah, it's a inseparable part of what's going on.