When you tension the spokes, you're essentially pulling the spoke bed down from the brake track. A "V" shape is very well equipped to handle that since that is the shape that the loads would naturally take from the brake track to the spoke bed. A "U" shape requires more support to maintain the "U" shape. Tie a rope between two fixed points, where the rope has plenty of slack to hang down. Unloaded, the rope might naturally be happy to hang in a "U" shape. Clip a small weight to the rope and it will instantly assume a "V" shape. A "V" shape is naturally aligned with the spoke loads, where a "U" shape isn't. You need to add material, and therefore weight, to support the "U."

I would be very skeptical of "U" shaped rims that are much lighter than what you see from the majors. Our target for a 52mm rim is 480g. We might get a little under that, but not much. I've run the weight vs aero drag iterations through the analyticicycling.com calculator six ways from Sunday and the amount of aero gain our Rail rim has shown handily beats the minor weight penalty over lighter, more "V" shaped rims, in everything short of a TT up Alpe d'Huez. In that case you'd be using a whole different type of wheel anyhow.

Dave, not sure if this is all that relevant to the discussion but here goes anyway:

You talk above about designing your wheels for 23mm tires, which, I think makes sense given the trends as of late. However, did you give any consideration to inner rim width as it relates to tires and aerodynamics. Some tire companies build a "leading edge" into their tires like Zipp, Bontrager and Continental. However, wide inner rim width seems to have the inverse effect naturally, it makes the tire broader and rounder, less of the quality leading edge.

This is probably something that is nearly impossible to test in isolation but I keep thinking about wheels/tires as a system, and though wider rims improve one part of the aerodynamic system, it seems by broadening the tire you are having an inverse effect on the tire's aerodynamics. Obviously the rim gains make up for the tire losses, and then some, but i wonder if one were to keep a 15-16mm inner rim width(paired with a 25ishmm outer diameter), the system might be more aerodynamic, though probably a little heavier. You also throw out the improved ride quality of wider rims.

What he mentioned was that they started with the inner width and built around that. So as long as the entire shape is built for that width and a "23" tire then the aerodynamic advantage is retained. It's not like they took a traditional inner width and did all the aerodynamics and then later decided to increase it.

NGMN -

We actually started from the baseline of wanting an 18mm inside width. Our mantra for this wasn't necessarily to make the most aerodynamically slippery rim in the world. We wanted to make it ride well, be shallow enough to use pretty much whenever, not so deep that it got really heavy, etc.

We've ridden a whole whole lot of tires on A23s (which are very slightly less than 18mm wide on the inside) and though we like some better than others, there's no tire that we didn't prefer on a wider inside width rim than on a narrower one. We like it so much that we started the whole process from that premise. Think "Moto GP" tire as opposed to "Model T" tire.

You are correct that the wider inside width makes tires set up wider, but I'm not sure what you mean by rounder. They generally set up less tall (height from outer edge of brake track to outside of tire circumference) on wider rims. Across 23mm tires, I found a very reliable conversion rate that a tire will set up 1mm wider for every 2mm of increase in inner width. This was on 3 different width rims with a bunch of different tires. The height conversion was less linear, but it was directionally stable - tires had a lower profile on wider rims.

Wheels and tires are absolutely a system, but we don't necessarily think of them as a stable system. Judging by closeout offers that I see, the wheel/tire systems that have launched have had trouble gaining traction (bad puns are free today). People are by and large going to use the tires that they want to use. A 23mm ProRace 4 SC has a different shape and width than a 23mm Vittoria EVO CX. We tried to make the wheel as "tire agnostic" as we could, within that 23mm general range. We didn't have the chance to test different tires in our last tunnel trip, but we will next time. I wouldn't take it as a postulate that any particular tire shape is universally "better" across all wheels. What works great in one might not in another. We gave it our best shot to try and make a rim that would pair well with any tire. I don't necessarily think that there are any rims out there that scream to me as being bad except when paired with a specific tire, but I don't know maybe there is one?

Aerodynamics is a huge part of the equation, right? But so are handling and road feel. We have one hill around here that's got two really fun switchbacks, and I time myself down it all the time. The fastest I get down that stretch is on A23s, which is just data that's telling me what I already knew - I'm calmer going faster on wider rims than I am going less fast on skinny rims. I know that it would take some meaningful amount of aero benefit (like, a lot) to overcome a half bike length I might be giving up three turns per lap in a crit if I wasn't cornering as well as I could be.

We tried to keep the whole picture in mind, with aerodynamics being a huge part of the picture but not the whole thing.

Thanks

Well said. I really appreciate the openness and well thought out nature of your rim development.

As I said, I know that ride quality is a part of the wider rim trend. Zipp is obviously an "aero" focused company, and has stayed with a narrower inner rim width compared to most(16.25mm), in part to support narrowed tires(they still allow 21mm on their wheels) but I've wondered if its also a part of tire aerodynamics.

By the way, Bontrager has said that their rims are designed for their aero tires, but again, it seems more a reflection of the tire itself as opposed to any magical wheel/tire combination.

I think the 303 was designed on the premiss of using a wider tire and it does have a tire bed of 17.25. Now it would have been very interesting for November to have tested their design against the shallower and lighter 303 versus the 404, but that might not have worked in their favor so much.

The only reason we chose the 404 is because it's such a universal benchmark for a wheel that does well in a lot of areas. The wind tunnel can only tell you about wind drag, and our rim tested much closer to a 404 than any comparison we've ever seen of a 404 to a 303. From our perspective, being able to say "we're awfully close to the aerodynamics of a 404" is a far more valuable statement than "we're aerodynamically better than a 303" would have been. We may test against a 303 in the next round, but there's a lot of data on the magnitude of the distance between a 303 and a 404, so there may be better references for us to be able to make. Wind tunnel time is still expensive.

Our target weight is within 5g of the claimed weight of a set of 303s.

We're NOT making any claims to being a better wheel than anyone else has got, especially not Zipp. We used a 404 as our measuring stick because it's pretty much the Alpha Dog wheel out there.

I figured you did it to say you were close to the deeper 404. However, I am not so sure that a 303 with a 23 or 25 wouldn't be just as close to or better than a 404 that is paired with the wrong tire. Zipp's data does show that the 404 is faster with a 21 and tires have a significant impact on the aerodynamics of a wheel as you have also noted. That is why it is wise that you guys designed your wheels from the outset with a 23 in mind. So, you are right it is much better to say your wheel is almost as fast as the deeper 404 run with the wrong tire than saying it slower than a shallower and lighter 303 run with the right tire.

However, this is all conjecture on my part and I doubt we'll ever know if a 303 with a 23 is faster than a 404 with a 23 since it wouldn't behoove Zipp to release that data. But since you are at a much better price point it may not hurt you so much to concede (if you test the 303) that you are almost as good as Zipp even if their shallower, lighter wheel is faster in the tunnel. That is a test I would love to see you win, though.

Dave, the more I read about your process and intention behind the Rail the more excited I get about seeing them in production! Really appreciate you taking the time to converse

Dave - I would *love* to hear an update when you rims are available for sale individually.
Please do keep us updated here, it would be very much appreciated by many Weight Weenies!

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KyleFoo (WW member) contact at FarSports got back to me last night. Here's the Q&A ::

About 700c 50mm*25mm rims, details as bellow:

1. What is the spoke hole count and can it be customized? 20/24H.
2. Internal or external nipples? both are ok.
3. Rider weight limit? 110kg.
4. Is UD carbon matte finish available? ok.
5. What is the cost per rim? 176US$/pc.
6. Can these be made without the basalt brake surface? (I am building a bike with disc brakes and so the brake track is irrelevant, and I don't like the look of the 3k finish of the basalt brake track). Ok, UD.
7. Can you send me pictures of this wheel highlighting the following : Send you section drawing, pls check it.





I have since asked about actual photos of the wheels, but maybe those will have to wait. However, $176 per rim isn't that bad. It's encouraging to say the least.

Can anyone compare that profile to a current wheel? It doesn't look like a Firecrest to me, but I admit I'm not the most familiar with rim profiles.

Hey Tharmor,
I posted this link earlier in the thread:
http://www.flickr.com/photos/glorycycles/6100156377/

It gives you an idea of where the shape stacks up. To me, it looks pretty similar to the Pre-FC 303, which was really wide but not super blunt. Now, it should be noted, looking like is not the same thing as being it but at $176 a rim, might be worth a shot.

I have to agree with you on that it looks a lot like the Zipps before Firecrest. I'm still waiting for HongFu to give more info about these ::





It would appear to be tubular only, which would be a bit of a disappointment for me personally.

That seems like you would be testing the limits of some brake calipers with those rims. The calipers might not get into their maximum leverage range.

Received these today from FarSports.
25mm outside; 18mm inside, 50mm depth, 20/28H
Weight: F493g; R500g

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