Thursday, February 17, 2011

Equipment - Light Wheels vs Aero Wheels

One of my big shocks in 2010 was my experience with heavier aero versus lighter non-aero wheels. Conventional wisdom, pushed hard by aero wheel companies, dictates that aero normally trumps non-aero, even with a relatively significant weight penalty.

Technically speaking aero wheels should offer advantages at all speeds, not just higher ones. This should make up for the low overall weight gain of the "aero" part of the aero wheels. When you consider a whole bike and rider (I'll use myself as an example) weighs in at a good 180 pounds or so, adding or subtracting a pound won't make a huge difference, even on a climb.

However, if you can reduce the amount of energy required to ride a given speed by a small percent, you get that benefit all the time. It's like interest on a savings account - for small balances it's a small benefit but it's measurable.

The question becomes, "Is it worth it?"

So for my savings account, if I make 0.5% interest, I may see a tangible amount of interest, a verifiable one. But if it's $5 a year interest on $1000 balance, or 42 cents a month, is it actually significant?

It may not be if the bank requires me to drive, say, 50 miles or so extra miles a year, which would mean I'd spend that $5 on gas alone.

Likewise, aero wheels, although they offer a tangible benefit, may be like my 0.5% savings account interest. Is it worth it?

Well, now I'm conflicted.

I used to believe in the blanket statement of deep rims all the time. But now... I realized something wasn't right last spring when I started riding on the tall profile, aerodynamic, and relatively heavy Jet6/Jet9 clincher set. I had a harder time making accelerations to match others, and found that although I could cruise once up to speed, my legs got a bit zapped when I did the actual accelerations.

TsunamiTwo with Jets.

After some experimenting with the Jets and the not-as-aero Bastognes, I found an interesting compromise.

TsunamiTwo with the rear Jet9 and a Bastogne front.
The front helped with stability but I got severely shelled on this day.

For "easier" training rides (17-19 mph solo, 20-21 mph group), I find my non-aero clinchers work well, better than the aero ones. I spend so little time at significant speeds (25 mph or higher) that the 1-2 lbs weight penalty to get aero benefits becomes significant.

I tried to compromise by using just the rear aero wheel, but it's still much less responsive on hills and when accelerating (responding to surges). The rear does help on sustained efforts though, especially if I'm already up to speed. This ends up my choice if I'm doing some riding in areas with cross/tailwinds and I think I'll see some sustained speeds (i.e. group ride).

Even for races I'll use the Bastognes because the accelerate much easier. I use a lot of my reserves accelerating hard to counter attacks and just get out of a corner. I used my aero wheels for a few weeks in early 2010 races at the Rent but got totally shelled because the third or fourth super hard acceleration just killed me.

(When I used aero tubulars which are lighter and more aero than my clinchers, I did fine.)

So until you go really fast in a group (25-27 mph avg speed) heavy aero wheels seem to be a disadvantage. A steady state 25 mph to me screams aero wheel. Jumpy races which average 25-27+ mph scream aero tubulars.

The issue here is weight. I'm not contesting the aero bit; it's the weight I don't like. HED builds the Jets as "faired" wheels - there's a whole structure there without the aero fairing, and then they add the aero fairing. I heard something a long time ago about race cars - everything needs to do at least two things. If a part only has one function, you're losing efficiency.

On the Jets the fairing acts only as a fairing. A separate rim acts as a structural member of the wheel. In contrast, HED's Stinger tubular wheels use the fairing as a structure as well as a fairing. This wheelset ends up really light. It's the whole "rim or fairing" thing.

This means there's light at the end of the tunnel- carbon rimmed clinchers which use the fairing as structural members. This includes wheels like the new Zipp 404 carbon clincher or the various Reynolds carbon clinchers.

(And, I hope, some wide rimmed HED carbon clinchers...)

Such rims normally weigh little. They spin up very quickly, allowing you to accelerate with low perceived effort. If you don't use them all the time they'll feel really, really fast when you do use them.

Where to draw the line?

The Jets I have (Jet6/Jet9) weigh about 1970g per pair. They feel like Mack trucks, or, based on my recent travel experiences, like a jet (you see how I did that?). They accelerate slowly but keep accelerating, eventually topping out at pretty high speeds. The front wheel catches more wind than a non-aero wheel, making the set up less than desirable for top speed truck drafting runs (anything over 45 mph).

The Bastognes, which I'd choose for most races over the Jets, weigh about 1550g per pair. That's about 430 grams less than the Jets, or just a touch under a pound difference. That's a lot for just rims. They feel pretty fast when I jump on them and they feel nimble when I'm tossing the bike around. They feel a bit limited in top speed. I should point out that they feel extremely stable in gusty drafting conditions, like following trucks at over 50 mph, but that has to do with the profile, not their weight.

My Stinger6s weigh somewhere south of 1400g per pair, and they feel fast. The tubular tires weigh less than clinchers so the weight savings increases that much more, maybe another 100g per wheel. I haven't drafted a truck on them because I use them almost exclusively for racing, but they're fine for 35 mph chases and leadouts as well as 40 mph sprints.

Therefore...

I think any wheelset under 1600g feels relatively light. Anything over 1800g feels heavy. 2000g, it feels weighted, not just heavy. I think 1800g is about the right limit for aero wheels as far as not compromising the jump.

I really like the Stingers and I'm happy with how they ride and accelerate. Of course I'd want a Stinger9 rear and a Stinger4 front, for more aero and more stability respectively. I'd like to have matching carbon clinchers (they don't exist at this time), weighing in at, I hope, somewhere around 1600g, less if possible.

Combined with the aluminum rimmed Bastognes I'd be happy if that completed my wheel inventory.

8 comments:

StevenCX said...

Build up some generic carbon clinchers with Asian rims; 50mm deep wheelset comes in around 1540 grams. I'd like to see carbon clinchers from HED too; I bet they have something in the works.

Justin said...

I had a set of HED Jet6 wheels - not the Stingers, but the ones with the fairing. I sold them and got some 303's because of the weight savings. In other words, I traded in aero for lighter. (My HED had a PowerTap, so total savings was 800 grams). I love the easier spin-up of the 303's, and they feel better climbing too.

Anonymous said...

Have you tried the Jet 6 by itself? Most of the aero benefit comes from the front wheel, since thats where the undisturbed, non-turbulent air is. The Jet 6 front it also lighter, so you could probably get in under your self imposed 1600g's simply by replacing the back.

Of course, if you'd just like to get rid of the wheels, I'd be happy to oblige. Let me know where I can pick them up.

-K

Aki said...

The generic rims would be good if they came in the wide rim width - a Stinger is so wide (25mm at the brake?) that it's hard to move from them to normal wheels. For me I have to unclamp the cable to get the brake to open far enough - I guess on DA or SRAM you have to file the brake caliper a bit or use slightly worn pads. The width really helps aero as based on both HED and VeloNews's testing. Even the "wide" C2 alum rims are significantly narrower than the tubulars - my barrel adjuster is almost all the way out for the clinchers, then I bottom them out for the tubulars.

I haven't tried just the Jet6, not sure if it's because I tend to seek stability first. I used to ride with a Trispoke/HED3 up front and a non-aero rear, so I understand the concept. I guess I like the way the Jet9 looks on a bike. heh. Seriously I've used the non-aero front to gain stability in crazy descents, and a tall rear wheel helps with that too. Around here it's less an issue so maybe I'll try it.

Anonymous said...

Hey sprinter, I've been following your blog for quite a while now, and I'm really impressed with your writing. Its not just an average "I went to this race, I trained today blog". I feel like I've gotten to know you personally from all the posts I've ready.

Anyways, I'm just surprised that your blog isn't more popular and more people follow it, keep up the good work

Aki said...

Thanks for the nice comment. I kinda laughed at "why don't more people follow the blog?" bit. Although I'm not necessarily aiming at becoming a huge blog, I used to check to see if more people were reading the blog recently.

I stopped checking after a while, but recently poked in there again. Although readership doesn't seem to be up a lot, the blog is ranked a lot higher in the technocrati site than it used to be ranked - so either a lot (like millions?) of marginal blogs are gone or the algorithms used to calculate ranking have changed.

I have to admit my inspiration ebbs sometimes and it's pretty obvious when it does; life isn't always "on", or there's stuff no one needs to read about like "and then I did the dishes".

So thanks for reading and spread the word :)

Travis Miller said...

Have you ever tried racing on a really light set of wheels? Like a pair of 202s, 303s, or something similar? (1,100-1,200gm)

The difference between 1,100gm and 1,600gm feels huge. It makes those accelerations much easier.

If you spend most of your time in the pack, the aerodynamic benefits of deep wheels are much different than being on your own.

Aki said...

Although it's unclear to me exactly how much a 202/303 rim weighs, I've raced similar weight rims as the Zipp 280/380 (which seem to be earlier versions of the 202/303), with rim weights in the 280g range. I also raced Zipp 340s for a while.

Although the rims spun up better I found myself lacking both top end in a sprint (i.e. somewhat solo) as well as top speed in a pack (for moving up, a key factor if a rider has to sit in like I do). I eventually moved to using a TriSpoke front with either a Zipp 440 rear or a disk wheel (built with a 290-300g rim).

With dual TriSpokes I could move up on slight downhills at incredible speeds - I clocked 45-48 mph in a rolling crit course one year while in the field, moving up at will on the fast sections of the course.

Having said that, it'd be interesting to try even "aero" 1100g wheels, like Lightweights or MadFibre or whoever.