Time Trial / Time Trialling / TT

Like everything else, it's hard to find any comparative test results. Sticking a thumb in the air based on what is out there, it looks like a Super 9 CC could be worth up to 5W @ 40km/h against an uncovered 808FC at the (high) yaw angle where the disc is generating maximum lift.

Super 9 is probably the only disc worth upgrading to, not going to be much difference between all the others + you'll benefit from the wide rim. You run massive tyres for 24hrs right? You might be fucking up your 808fc aeros with a >23c tyre.

That's similar to what I've read but I've found nothing much, certainly nothing conclusive about 808FC with covers fitted. My gut (shutup) is to err on the side of durability and reliability and go for the normal wheel with covers. Also, Spesh tested my frame with 808FC and/or Zipp disc rather than FFWD disc and 808FC is cheaper than Zipp disc because power meter. Then there's ENVE.. ;)

buys toaster instead

808FC on G3 is about £1300 + whatever RalTech wheel covers cost = a more serviceable wheel but heavier and I have no idea about the aeros?

If you're going with RalTech, you might as well build a good strong cheap rim and let the covers handle the air, there's not much point having a £700 rim under cover unless you're going to be uncovering it for IM 'no discs' races. My first choice rim to go undercover would be a Mavic XM819, but you'll probably want something with a brake track :-)

Yeah, my tyres are ~27mm so they're definitely an aero disadvantage but fitting the 808FC rear would shave some weight over the old 808, give me wide rim for the fat tyres I run and perhaps be more aero. Also, using Raltech covers would be lighter than my Aerojackets and the G3 would be lighter than my current SL. Braking would be shitter that's about the only disadvantage.

That's my plan. I have a mavic kysrium (super stiff but terrible aero's) that is fully covered with a raltech. Aluminium braking surface, reasonably light, cheap and easily repairable. Somethung wider would be good, but this will do for now.

Which strong, fast, light and wide rim instead of the 808FC?

Any of the usual suspects:
H+Son Archetype
Kinlin XC279
Velocity A23
Mavic A719

One would imagine that the 808fc's aerodynamics are designed around not having a disc fairing attached, so the advice to just get a cheap wide rim and raltec is good. Even an expensive aluminium rim (Hed) and the fancy lightweight Raltec covers is going to be cheaper than any Zipp offering, and you get to using a Powertap.

Speaking of discs is anyone after a flat disc? I have a renn 575 which is now surplus to requirements. Campag free hub so 11spd compatible. Clincher. Super loud as its a honeycomb structure.

I do already have a G3 on Archetype. It did cross my mind to use it. Needs to be fixed first. Stupid Powertap. :)

Already have G3 on Archetype. Needs servicing first. Shitty PT.
Guess I should contact raltech.

Archetype with RALTechs would be a good combo, that's what I was briefly considering running last year before I made it rain and bought other stuff instead. A covered 808 is pretty good aerodynamically, Wheelbuilder tested it:

http://www.wheelbuilder.com/aerodisc-data.html

Yeah, I have that combo now. How come the 808 still test faster than boring rim? I want faster not slower than what I have now.

The 'boring rim' was a DT RR585, a very narrow (19.5mm) clincher. The 808 was an unspecified tubular. Not really a like for like test. They don't say which tyres they used, but if they were not exactly the same profile and tread on each wheel, all bets are off as Flo found 80g of drag between different tyres:

Interesting that the Vittoria did so badly. Veloflex Records apparently test really badly on a Hed 3, perhaps the glue on tread affects airflow over the wheel?

On the other hand, some testers show the Vittoria winning it all back in rolling resistance, and the Flo30 tests might not translate to other wheels.

Would be interesting to mess with the edge of the tread band on some cold process tyres, you might be able to dick about with boundary layer control by having a wavy edge.

Does Crr increase in the same way as wind resistance as speed increases?

No its proportional rather than proportional to the square like aero is iirc.

Does Crr increase in the same way as wind resistance as speed increases?

C_rr is a coefficient, like C_dA. The power needed to overcome rolling resistance is the product of C_rr, load and speed.

Because of the different relationship, the optimal tyre, after balancing C_rr and C_dA, could be different at different speeds, e.g. a fast rolling but poor aero tyre could be better at low speed, but a slow rolling but aerodynamically slick one could win out at high speed.

Obviously, what we really want is one tyre to rule them all; the ride and handling of the Open Corsa Evo, the strength, durability and aero performance of the GP4000S and the low C_rr of the Veloflex Record, preferably all wrapped up in an an ultra light weight proper UST tubeless package. With a cherry on top.

It's funny that one - the tubular VF Records I think are more aero than the clinchers as I have a trispoke with a tubular Record on it which is an absolute wheel killer. I may be able to test that vs. a clincher Record as I've got a mates clincher trispoke in the shed too and a clincher Record somewhere in a box. Less of a lip from tread to casing on the tubulars from memory, that might be all it is.

When I used to run a clincher trispoke I'd swap between a Record and the old Bontrager 19mm aero wing (no difference between). The Bonty ended up being the main choice for racing as it was totally bombproof.

Yeah, matching tyre to rim is uber important. Unfortunately, hippy matches tyre to rim more in terms of... BIGGER! do it! yeah! so I'm basically fucked.

Silicon the tyres to the rim and all bets are off...

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