natzoo

Recently I have been pondering the choice of rims and tires for the track. On the road, the recent trend has been gravitating towards 25c tires and 28mm wide rims. The zipp firecrest "toroidal "shape is an example of this. The arguments are summarized by one of the designers at Reynolds here and zipp here

The conventional roadie wisdom:
1) less rolling resistance w/wider tires
2) more crosswind stability with fatter rims

Obviously for indoor tracks, I think a 160psi tire and lack of crosswinds kinda nullify those two points. However, for less than perfect outdoor tracks, I am wondering if roadie conventional wisdom applies.

Do (outdoor) track riders benefit from wider tires (21c vs 23c) and toroidal rims?

Regarding rim depth, according to the zipp PDF and FlO wheels, it appears that at low yaw angles (<5deg), 30mm-60mm wheels all have about the same drag. The exception seems to be the full disc.



Indoor tracks should have almost zero yaw angle since there are no crosswinds. Does this mean that the rim depth does not matter as much? It seems to be validated by the mavic IO has which has a "shallow" ~60mm rim depth, as opposed to something more extreme like a 90mm depth.

And finally more general, how much aero testing is done on track bikes and equipment? The road market is much larger compared to track with many more sponsors, consumers, and media attention. So it makes sense for large companies to invest in aero testing for the road. Sure the top track riders have their riding positions tested with varying existing equipment, but how much of the effort is spent designing new equipment?

Take for example, the ubiquitous Mavic IO and Comete have been around for more than 10 years. I wouldn't really consider Mavic at the forefront of aero technology. Wouldn't modern materials and technology contribute to a better (or at least different) design?

gtrob

A company like Trek is going sell millions of Speed Concepts, so you can find plenty of white papers on their bikes. Track equipment seems to be produced by companies without the capital for the same type of aero testing most of the time, so probably lacks the comparative data we are looking for.


regarding front wheel, I think it makes sense to assume 0 yaw indoors. Its kind of why I stopped looking for a front disc, as the data I found it didn't beat my 808 front until some decent yaw. FWIW I think I read somewhere the discontinued the 1080 because it wasn't beating the 808, so bigger rim isn't always fastest.


All that said, 100gr off the front wheel in drag, works out to be just under 1 whole second in a 4k pursuit. Wheel Performance, Criterium Corner So you have to put things in perspective when looking at charts like these. 20gr difference is probably within testing and manufacturing tolerance, so can probably be ignored entirely. So when you get into rim shapes and profiles, its looks like it matters on a chart because we visually see its 'better', but when you use the data to figure out actual times, it really is insignificant.

natzoo

That s a good point. I think it seems that the wider fatter trend in road cycling is more for crosswind stability and cornering grip.

What is interesting is what the reynolds engineer writes:


He seems to suggest that really narrow tires and rims are more aero. It would be interesting to see how "significant advancements" could be applied to specific narrow rim designs.

But I guess in the bigger picture, a full disc will always be the most aero, and an 808 deep rim is already pretty darn close. It really seems like the new advancements in modern rims are mostly for crosswind and high yaw performance.

So what does this mean for outdoor tracks? haha

Dalai

Alex is one of the few people I've found posting data. He tested a front disc (Zipp 950 conversion) against both 808 and 42mm Shamal. Indoors he found the Shamal as fast as the 808 and did find the disc fractionally faster.

Aero schmaero - Main Topic Area - Timetrialling Forum - Page 2

natzoo

Awesome. It seems like the real world velodrome data seems to affirm the:

50mm ~= 80mm
disc slightly faster than 80mm

I'm thinking of building a budget carbon wheelset. I might consider running 60mm deep rims to save some weight and some $$$

carleton

Don't forget to add practical experience into your decision.

Deeper isn't always better, especially on the front. On windy days, 80mm can be a handful for most riders including me at well over 200lbs. 40-50mm on the front is a great safe bet for weekly and special occasion race wheels.

Here's what I'd suggest:

A:
Front: 50mm
Extra Front: 80mm (for non-windy days if you have the cash)
Rear: Disc

B:
Front: 50mm
Extra Front: 80mm (for non-windy days if you have the cash)
Rear: 80mm

I like this combo. It comes out looking sorta like this:


C:
Front: 50mm
Rear: 50mm

D:
Front: 80mm (use your training wheel on the front on windy days)
Rear: Disc

E:
Front: 80mm (use your training wheel on the front on windy days)
Rear: 80mm

carleton

Sorry, I'm late to this thread.

Aero testing exists for the track. From what I've seen is that once you get a set of race wheels with 40, 80, or 5 spoke front and a decent rear (disc or 80mm) then you have about 95% of any gains you are going to get from your wheels and tires. Tires that are sticky and inflated properly all work about the same.

Source: Me. I've owned 'em all: Zipp 404 front/rear, Zipp 808 front/rear, Zipp disc, Mavic Ellipse, Mavie IO/Comet, etc... They all feel different, but none were head and shoulders above the others that I could tell as far as aero is concerned. Of course, I'm a rolling refrigerator...so there's that.

carleton

The Shamal is/was a great wheel!



I believe that the Gipiemme Tecno 416 is a replica of that rim that may be still in production:




At 16 spokes, this is a great option for non-sprinters who don't lay down lots of torque during standing start work.

Don't forget the Mavic Ellipse. This is a GREAT wheel that is fast. I matched my sea-level F200m PB using these wheels. Similar profile to the Shamals but with 20 bladed spokes instead of 16. I think the blades make a big difference:

Dalai

Actually Gipiemme was the rim supplier for the Shamals.

carleton

Ha! Really? That explains a lot.

If I were a lighter rider, I'd make a set of wheels from the Gipiemme rims.

Also, the Campy Pista tubular wheels are similar but 20 bladed spokes like the clincher Ellipse:

Baby Puke

Plenty of big riders used the Shamal as a front wheel back in the day. It was the go-to wheel for sprinters for a while. Here's Chiappa riding one vs. Gane in 2000.

carleton

Another similar wheel is the older Campy Vento:



Get a front and use a track skewer or re-lace a set of rims to track hubs.