Well…in the “**P2C Fork- Can a nonCervelo one work?” **thread, I linked to the following newsgroup exchange with Dr. Drela that occurred after the recent Velonews blurb on the jetstream forks:
The takeaway from all that was that the slots in the current Oval forks go through the legs in the opposite direction as what was assumed in Dr. Drela’s theoretical analysis. Combined with the actual wind tunnel test data here, it’s pretty easy to see that the time savings claims (for the current Oval forks) are pretty non-existent:
However, there’s a couple of interesting pics on cyclingnews.com this morning. First, is a new TT fork that appears to finally have the slots in the correct direction…but with the questionable placement of the brake behind the fork crown:
It also uses the slots on the rear stays (and has them in the proper direction as well). Unfortunately, as can be seen in the exchange above with Dr. Drela, the “gains” from this idea tend to be negated with a deep section wheel and completely go away with a full disc. The idea works best with spoked wheels. So…the slotted stays idea may be good for setups that don’t allow a rear disc (such as Kona) but any advantage goes away with a full disc.
Hmmm…I wonder if there’s a “break point” with this frame where a deep, spoked wheel (such as a 404, 808, or 1080) would end up actually faster than a full disc? Hmmm…
In any case, I’ll withhold judgement on the “1 minute savings over 1 hour” claim until they better explain what the baseline was for the comparison. They also still need to show that the predicted savings of the fork slots actually exist in reality.
First off, I’m totally taking credit for that seat stay idea. I thought about it (really!)…
2 things: I’m looking at the frontal area and L/D ratios of the Reynolds and the Oval, and I’m not sure I’d say the benefit is non-existent (though you’d probably need a lot more tunnel runs, since if there is a benefit, it’s pretty damn small).
Also, I thought that Cobb’s take on this (and maybe he can chime in if I’m wrong) is that the real ‘benefit’ was to be able to skirt the ratio regulations by using 2 blades? The fork in your link looks like a pretty good example of that at work.
Lastly, I’m still wondering about the ‘tri-spoke interaction’, since noticeably missing from the BTR report is “Oval with tri spoke”. I can’t be the only one wondering about that. Or maybe I am…
First off, I’m totally taking credit for that seat stay idea. I thought about it (really!)…
2 things: I’m looking at the frontal area and L/D ratios of the Reynolds and the Oval, and I’m not sure I’d say the benefit is non-existent (though you’d probably need a lot more tunnel runs, since if there is a benefit, it’s pretty damn small).
Well…it’s certainly not 55s over 40K, if anything, now is it?
Also, I thought that Cobb’s take on this (and maybe he can chime in if I’m wrong) is that the real ‘benefit’ was to be able to skirt the ratio regulations by using 2 blades? The fork in your link looks like a pretty good example of that at work.
Actually…I’m wondering if that Avanti fork is even UCI legal. It looks more like the depth of theBlackwell Time Bandit, which is not.
Lastly, I’m still wondering about the ‘tri-spoke interaction’, since noticeably missing from the BTR report is “Oval with tri spoke”. I can’t be the only one wondering about that. Or maybe I am…
The explanations from Dr. Drela lead me to think that the benefit of reducing the air velocity in the center of the fork is only useful with thin wire spokes. If you think about it, the spokes on a trispoke are like temporarily having a full disc in there for portions of the time, with nothing in between. As he said, the benefit goes away with a full disc in the middle…so, my speculation would be that there isn’t any reason to think that the trispoke would perform better…
Well, it’s hard to tell from that picture–but I’m guessing that the fork is actually pretty ‘wide’, when viewed from the front, and that’s how they’re making it UCI compliant. Given that Oval is really a road company, I have a hard time believing they’d put that effort into a fork if it weren’t UCI legal. I guess we won’t know until it’s out, though.
That front brake placement: hmmm… That’s not passing the eye-ball windtunnel test for me. I’d be curious to see some data on that.
BTW, did you see the full picture of that bike? There’s a suspiciously familiar looking fellow riding it!
Well, it’s hard to tell from that picture–but I’m guessing that the fork is actually pretty ‘wide’, when viewed from the front, and that’s how they’re making it UCI compliant. Given that Oval is really a road company, I have a hard time believing they’d put that effort into a fork if it weren’t UCI legal. I guess we won’t know until it’s out, though.
That front brake placement: hmmm… That’s not passing the eye-ball windtunnel test for me. I’d be curious to see some data on that.
BTW, did you see the full picture of that bike? There’s a suspiciously familiar looking fellow riding it!
Hehe…I didn’t look that close. But, now that you mention it, I think I’d recognize that skin tone and femur length just about anywhere…
Those fork legs would need to be awfully thick to be able to meet the UCI requirements at that depth. Besides, I don’t think this is necessarily Oval’s “baby”…if anything, I’m thinking Avanti is just licensing the idea from Oval (since their patent apparently covers any kind of slots in a fork).
Besides, I don’t think this is necessarily Oval’s “baby”…if anything, I’m thinking Avanti is just licensing the idea from Oval (since their patent apparently covers any kind of slots in a fork).
I’d say that’s fairly likely. Avanti are trying to dispel their image as a beginners brand that you upgrade away from here in NZ. The importer that owns the brand also distributes Specialized and frequently finds its own bikes being outsold by the better and more storied brand. This year they have revamped the range and are pushing this new chrono quite hard. The funny thing is that the 105 chrono (with no slotted fork or stays) costs slightly less than a DA equipped P2C and the Team Chrono shown on CN is the same as a P3C plus a set of Zipps.
Good bike for KW with a 75deg STA but not going to appeal to many triathletes. Also, while the stays may be slotted the seatstay yoke is a solid wall (no gap from brake bridge to seat tube) and the aspect ratios and width of the frame are poor. I’d guess that they asked Oval for a radical looking fork to try to get a selling point for the chrono as it sits alongside the Transition Carbon.
Would love to know what it’s supposed to be 2mins faster than. Ultimately I think it is going to prove to be a curiosity for trying the slotted stays but I don’t see a whole slew of races being won on it.
First, I have not seen in person and do not know, anything about the Avanti fork, I do suspect that they are leasing the rights to manufacture for that shape . The original thinking on the fork was how to make a fork as aero as the old Carbonaero fork, which became illegal under the UCI 5cm rule, while being as stiff as a good road fork. The twin blades solve the stiffness issues very well as most anyone who has ridden the fork can attest, this should easily carry over to the seat stays. At the time, I designed this fork specifically for Lance Armstrong to use in the Tour, but after the first year the sponsorship issues became to complicated. The aero performance goal was met in the original design in that it was equal or slightly better than the Carbonaero as used by Lance in '99, it has consistantly tested to be equal to other good aero forks and a little better than most. If you observe the fork in a smoke study in a controlled wind tunnel, you can easily see how the air is pulled away from the wheel spokes, measuring the wheel watts shows a drop and that is something I consider a good thing. In bicycles, things that apply to airplanes rarely work, we just don’t have enough horsepower, learning to manipulate airflow without increasing drag is a good way to spend your energy.
