Max rim section depth for crit/road racing??
 

Hi All,

Is there a max legal rim section depth for USCF crit and road racing? I couldn't seem to find this info on the USCF or UCI websites.

Any helpful info is greatly appreciated!

Thanks!

nope, you could run a disk if you wanted.

I know you can run a disc but I've always wondered about a front disc.

Track is going to be the only place alowed to run a front disc(maybe USA Tri, but I think it's outlawed there too).

If you show up with a disc front wheel to a crit, I am going to make sure I am at least a few bike lengths in front of you at all times.

If you show up with discs front and rear, I will put a frame bump in your spokes. I'll need a hole saw.

What USCF rule says this? I'm not familiar with any such regulation.

Disc wheels (front or rear) are not allowed for triathlons. However there is no maximum depth for the rims so you see some wheels with over 250mm deep rims (700c wheels are 622mm in diameter). They are basically disc wheels with the disc attached to the hub by really short spokes.

Disc's not allowed in tri's? Sorry, but you're wrong. They are perfectly legal for the rear. And the biggest non-disc at the moment is the Zipp 1080 at 108mm deep. Blackwell has claims of a 200mm deep wheel, but that would be the deepest out so far.

I would be wary of running any type of deep rim on the front in criteriums. Deep rim wheels catch a lot of air, which makes you squirrely, which is not what you want to be in a thick pack, especially going around corners.

The aero advantage of deep rims is minimal in a crit and completely cancelled out by so many other factors.

i would think that a lighter wheel that spins up easy is more inportant than aero, at least that's my feeling...the surges suck...most the time in your in a pack sooo..

Light and nimble only rules in the most technical of crits and the biggest of mountain races.
Otherwise, aero always takes precedence.
Lots of studies out there.

USCF was/is supposed to adopt UCI regs which state:


Has this not happened? I really haven't paid attention.

I've never seen any official ever checking anyone's bike, save for Junior roll-out.

No it has not. Only a few races under restricted conditions require UCI equipment. It's easy enough to check this stuff out before posting incorrect information.

Exactly. At all of the races I've been to, the Pro's are rolling on deep rims. Sure, their sponsors want them to display their products, but a pair of 404s flying by at 30+ is just as blurry as a pair of 202s.

And maybe I'm the only one who does this, but moving up the outside if/when the pack slows is often a very good idea, and I'd rather do that with some 50mm carbon wheels than my Ultegra/OP's. Not to mention the standard breakaway, which puts a premium on being aero.

Okay, I stand corrected. A few of the races I am doing this year are reported to be UCI rules, so I have them on the brain. I'll ammend my statement: Anyone who runs a front disc off the track is not the brightest bulb in the bin.

Sorry for my misinfo.

And while you're citing rules, go get Yoshi. He is obviously out to misinform the world too. :rolleyes:

I'm not a USAT official. I wouldn't want to comment on something I don't know anything about.

As a mainly crit rider, I think aero wheels help a lot in most crits. The ones with super slow hairpin turns (say, under 15 mph) are the exception. And this doesn't even apply to breakaway/chase efforts where aero definitely matters.

If you're in any sort of a normal crit, you'll be going pretty fast most of the time. It's unusual to slow down a lot for turns, and if you ride smart, you don't have to actually sprint out of turns too much - and that's no matter where you are in the field, not just the top 10 or whatever. You'll probably cruise at 22-32 mph (turns and straights included) and spike up to 40-42 mph (mainly flat course).

The aero wheels really help when the speed goes through the roof - a 5-10 mph surge for example, or you need to move up. If the field is already riding over the 30 mph range, you'll need to make a 35-40+ mph effort to move up. A box section wheel is hard pressed to go over 42 mph (just from experience, no backing data). However, it's not unusual to be able to move up at 44-46+ mph with aero wheels if you have a slight wind/draft or hill assist. Such a spike in speed is very difficult to make with box section wheels.

Aero wheels are especially helpful when the field is strung out or there's a crosswind (esp those wheels that do well in a crosswind). Once the field is strung out, the draft is not as significant as when the field is bunched up. You're going to have to work to keep your spot and an aero wheel will help you do that. I specifically bring my Specialized TriSpokes (HED3) for windy, flat airfield crits. I used to run a rear disk as well.

Finally, in a sprint, aero wheels could potentially increase your top speed by as much as 6 mph (personal experience). It seems that many riders have about the same wattage output in a sprint (i.e. 1500 watts peak seems sort of normal). Even if you jump at the optimal time, your 1500 watts only gets you a given amount of speed (frontal area, slope, wind, etc). If you can get even 2 mph by using more aero wheels, then you should.

I don't know for sure but I think the whole deep rim thing (and disks) have to do with limiting the speed the *spokes* hit the air. This is because the spokes are by far the fastest moving object on the bike. If you can reduce the spokes' drag, you'll reduce the bike's overall drag significantly since the rest of the bike is going at a much slower speed aerodynamically.

If your bike is going 30 mph, your tire is stationary on the ground (unless you're skidding). The top of your tire is going 60 mph. You can imagine your wheel sectioned so that the hub is 30 mph, 1/3 down is 20 mph, 2/3 down is 10 mph, all the way down is 0 mph. Then you go the other way - 1/3 up from the hub is 40 mph, 2/3 is 50 mph, top is 60 mph.

Based on a standard wheel (with tire) height, going 30 mph, the top of the spokes for the following shape rims hit the wind at the following speeds:
box (9mm) = 57.5 mph
slight aero (22mm height) = 56.25 mph
50 mm rim = 53.8 mph
66 mm rim = 52.4 mph
There's various other factors like rim surface area, the way air flows, etc, but nothing can dispute the fact that if you have a 700c wheel and you're going 30 mph, the spoke (or perhaps the spoke nipples) will be traveling at the speeds above based on rim depth and a 19 mm tall tire (I used 673 mm for overall wheel and tire height).

The spokes on the very deep section rim are hitting the air 5 mph slower compared to the box section rim. If you can go 30 mph on the box section rim (turn the wheels so the spokes hit the wind at 57.5 mph) and you switch to 66 mm deep rims, you'll be able to do about 33 mph for the same effort. Nothing except swapping wheels. Keep in mind this doesn't account for your body's drag - but it's a good way to compare spoke speeds to see what potential gains you might achieve by using different wheels.

On 50 mm rims, you'll be able to go 32 mph. Again, no additional effort. Same position, just gear up a bit for the higher speed.

On 22 mm rims, you'll go about 1/2 mph faster, about 30.5 mph.

I have a spreadsheet which does the calculations based on overall wheel height, bike speed, and rim heights you specify if anyone is interested.

The only time aero wheels don't work for you is if you have a very "jumpy" course - things like hairpins, wide straights dumping into a narrow and steep uphill, or a finish line less than the required 200 m from the last turn. Then accelerating to a very high speed in 1-2 less pedal strokes (from personal experience - 4 or 5 pedals strokes instead of 6 or 7) would be better than being able to accelerate to a higher top speed (which would take a total of perhaps 8-10 pedal strokes).

As for handling, aero wheels are definitely usable in crits with winds up to 30+ mph. You have to train on your front wheel so you get used to steering the wheel versus steering your hips - aero wheels get steered like a rudder. Once you do that you'll be comfy with aero wheels virtually all the time.

My helmet cam vids have me running either a DV46 (46 mm rim) or a Specialized TriSpoke in the front. You can see that my handling isn't affected by the wheels (and some of the races were quite windy).

For those that race in CT, NY, NJ, MA, and RI crits, this advice does not apply to you :)

cdr

I see what you did there. :D

:lol: no worries here at least, I have to get through my first crit at Bethel before I can dream of getting to the 3's!

Awesome advice as usual CDR.

I hate to nit-pick, but I'm gonna.

:)

I understand the point you're illustrating here, but your physics are off. Rather, you're not thinking about the situation from a physics point of view.

(It should be noted that what follows is a mathematician's interpretation of the physics of a rotating bicycle wheel. I only had to take Physics I & II, so my analysis is not nearly as in depth as something you'd see in, say, a fluid dynamics book.)

When dealing with a rotating object it's more helpful to think in terms of angular velocity. Every point on the wheel, regardless of distance from center, has the same angular velocity. If drag is represented by area x velocity (in the simplest of forms) then it becomes obvious how a deep dish rim would be advantageous. Note that I'm not even going to begin to touch on things like laminar flow as I am not knowledgeable enough to say anything on the subject, but there are other factors such as laminar flow that contribute to the equation.

Maybe there is a Mechanical or Aeronautical Engineer around that would care to give a more accurate description?

I'm only a Chemical Engineer, but since I have a few publications on the subject of fluid mechanics, maybe I can comment. carpediemracing's description is accurate enough for me in the context of a bike forum. (and fluid drag is caused by the relative motion of a fluid past a body, angular velocity is relevant only so far as can be used to describe linear velocity.)

I guess that is my issue. The linear velocity of a bike wheel at a point near where the tire contacts the road is certainly greater than zero. If it weren't there would be problems.

Maybe I'll ask my Aero Engineer uncle for a thorough description.....

This isn't horseshoes, "near" is not the same as "at" the point of contact.

Next time why not ask your uncle before wading in.