Why are tubular wheels so narrow?
 

I’m looking at buying a used set of carbon wheels, and because of the price tubulars are seeming like an attractive option (and the weight is substantially less).

But I’m noticing that most of the carbon tubulars I’m seeing are like 19-21 mm wide. Why so narrow? And stop me if I’m wrong, but your aerodynamics are kinda wrecked if you go putting a 25mm tire on a 20mm wheel, right?

I'm stopping you.

So in your opinion, they are not wrecked by said scenario?

If you look at anything that is aero, you'll generally see a tear drop shape with the wider edge to the front. That wider edge is your tire, and the narrower trailing edge your rim.

Also, I have no idea how tubular wheels are spec'd. On a clincher rim, that would be a internal measure between the bead seat.

The tubular wheels I'm seeing spec an external width (because obviously there is no internal cavity).

Regarding aero, I agree with what you're saying on shape but the abrupt change where the tire steps down to the wheel I would think would disturb the air, although maybe not significantly enough to matter. Not trying to come off as argumentative, just trying to get some people's opinions.

Are wheel manufacturers still selling new tubular rims for non-track applications? I know as the market moved towards wider rims there was a simultaneous push towards tubeless setups, so I'd imagine tubular rim development effectively stopped and they're still selling the same designs they did before the wide rim trend hit. Just my uninformed speculation, though.

Go out and look at some tubular wheels with the tires already on them. Then find out the specs for both tire and rim. That might show you where you are right or wrong in your thinking.

Otherwise, I suppose the designers and engineers that have been doing this for years have some 'splaining to do, Lucy!

Correct.

They are not all narrow. I have Zipp 404 and Hed Singer 5 tubulars that match up to a 25mm tyre nicely.

A 25mm rim on a 25mm tubular tire would approach enclosing 1/2 of the tire depth and become specific to one tire size.

Even 'tho they say that aero is everything, it really isn't.

https://cimg5.ibsrv.net/gimg/bikefor...2670b224d.jpeg

You'll save more watts with a tighter jersey or bending your elbows more than with a 2mm wider rim.

25 mm is a wide tubular and 19-21 mm rim is a narrow rim. A 23 mm tubular probably has similar comfort to a 28 mm tubeless tire. In terms of aerodynamics, the cross sectional area is as important as the transition to the rim. Those who are riding tubulars are doing so for reasons other than aero anyway

A lot of things are marketed and sold as "aero", but if you're not nailing the NACA airfoil cross-section, it's not helping as much as you're being led to believe.

Marketing is all about making us feel insecure enough to buy their products. ;)

What's really bad is my rims change width every time a put a different jersey on.

Kind of offended noone tagged me in this. I still design and build molds for and sell tubular wheels.

No.

Not all tubulars are narrow. Its just that at one point in time we used to race on tubulars for road. That was at a time when we also used 20-23mm tires. People stopped buying tubulars for the road around the time that 23mm rims started coming in to fashion.

I have had 23mm tubular rims as well as 25mm tubular rims. So....seems like you're buying old used stock from road racing.

Aero - yeah it's not holding you back. The same guy that wins on a 25mm wide tubular is the same guy that's winning on a 20mm wide tubular The aero isn't hurting him unless its a pro world tour tt.

Very valid point.

Also, in my brief research for tubular tires, it seems like they're all in the $60-100+ dollar range per tire. Is that about right?

Back in the day, light was king. My first Zipp 303s were mid 1100 grams. 404s were mid 1200s. That was what was hyped. That was the primary reason I first got tubulars, because it was a full two lbs lighter than my clinchers.

Does that feel awesome on acceleration? I’m used to heavier aero rims and I’m definitely considering some super light tubs.

Yes. I raced before anybody talked of wheel weights but we all knew our rim weights (or at least the published weights). I raced rims that were 290 grams and lighter. Tires of 250 grams and lighter. Laced my rims with the equivalent of 1.8/1.5 spokes. The place that really paid was when the wheel you HAD to get on was passing you. A blessing every time you came out of a corner or the pack surged.

True but deep aero wheels diverged from NACA in order to accommodate wide yaw angles some years ago.

In terms of performance, tubulars are superior to clinchers (and tubeless) in every respect. And it is not the tires, but the rim profile. The superior tubular rim profile, that lacks the 'hooks' required to hold the clincher tire on, is lighter, stronger, more impact resistant, doesn't cause pinch flats, and a hell of a lot safer.

Tubular tires also have more useful air volume than a nominally equivalent clincher tire. The air volume between the braking tracks on clinchers serves no purpose, whereas with a tubular, almost all of the air volume serves to cushion the ride. So tubular tires are roughly equivalent to one clincher size larger.

Why don't you need wide tubular rims? Because the only purpose of the rim is to provide structural integrity to the wheel, and some surface area to glue the tire on. The rim width has little effect on the shape of the tire while riding in a straight line. So theoretically, with a tubular rim, if you had a strong enough bond, you could ride on a very thin rim. Of course, the wider the rim, the heavier, all other things being equal.

With clinchers, the shape of the tire is very much influenced by the rim width; you need fatter tires and rims to not only maintain the tire shape, but to prevent pinch flats. Again, you don't get pinch flats on tubulars. You can ride them at irresponsibly low pressure and have little risk of pinch flatting or even damaging the rims.

I have damaged a carbon tubular rim on a relatively small bump. That was with normal tyre pressure as well.
Many of the points you made have some truth to them but certainly not as much as you make out.

Time Trialist chiming in here, matching tire/rim width is fairly well known and the watt savings are significant and outweigh rolling resistance differences between comparable race tires. The Zipp study is like 10 years old and states that the rim width should be 100-105% of the tire width when mounted. Too lazy to dig it up but anyone into TT is aware of this and it's reflected in the front wheel setup.

So yes, having a bulging front tire is slow, possibly slower with a "fast" tire than a mid range tire that has the width matched.

One reason why you're not finding wide tubulars is that tubulars are starting to become an old, obsolete technology. Wider rims are a fairly modern trend.

Lastly, I'd like to state for the record that I don't really pay much attention to this on my daily riding road bike configurations, where I focus on comfort. On race wheels, whether it's road, track or TT, I do mind this sort of stuff.

EDIT: To be honest, I don't really pay attention to it on road racing wheels as well, just TT. When you spend that much time in the wind, it's really about your fitness, your position, and the sum of your marginal gains. As far as marginal gains go, things like tire/rim width and shoe covers offer a fairly high price to effect ratio

Curious what width front tire and rim on your TT bike. Mine is 23 tire on 24mm rim. Some say a 28 mm tire on 29-30 rim would be faster.

Run the narrowest tire at the highest pressure possible that is below the impedance break point and above where you pinch flat.