A disc is always faster.

Put in a latex tube.

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Once, I was fast. But I got over it.

Depends on course. But I'd opt for disc with latex tube in 95% of scenarios

Eyeballing this and making a few assumptions:

Difference b/t disc and 90mm rear wheel will be a very small CdA penalty favoring the disc.

BUT: the marginally wider rear wheel and tire on the Jet will have a better Crr than the disc, maybe enough (?) to minimize the CdA penalty of spokes compared to the disc with a shitty inner tube.

What may tip the balance in favor of the spoked wheel are:
- tubeless is more resilient regarding punctures
- wider tire at a lower pressure maybe more comfortable
- wider tire at a lower pressure has (for this case marginally) less rolling resistance compared w/ narrower, high pressure tire

If the athlete really wants the disc: replace the butyl tube with latex or TPU, either or which has better Crr and flat resistance, and swap in the latest GP5k clincher (Amazon can deliver next-day, right?)

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no sponsors | no races | nothing to see here

the disc is going to give you a 2-4w reduction in drag just from spoke drag.

At zero to a really low yaw number that will vary a bit rider to rider the wheels will be mostly the same. There isn't much difference between a 32spoke box and disc at 0 yaw. At 1 yaw the difference increases and increases as you go out.

At higher yaw angles the disc can become exponentially faster than the jet 9. The higher the yaw angle the faster the disc will be.

If you look at the forecast and it's a really low wind day the wheels will be close, slightly favoring the disc just because lower spoke drag. If it's going to be windy/windier then there will be times that the disc wheel will be providing outsized gains to the jet9.

Let's say that the wind is blowing from some direction at 6-10mph gusting to 15mph. There will be time periods where the disc wheel could be as much as 20w faster, there will be times where it's only 8w faster.

Don't forget to add in that the jet9 will stall eventually at some wind angle while the disc will turn to negative drag and it provides a bit more stability.

Hope that helps.

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Brian Stover USAT LII
Accelerate3 Coaching
Insta

Bingo!

Heck, can you move the 25 mm tire to the disc? Maybe the wheel won't accommodate, but that is free (excepting time), you'll need to get the butyl tube out anyway and there is no waiting for an Amazon delivery!

Discs go whomp-whomp-whomp, so the choice is clear.

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Very interesting! I'm on the lighter side and have stayed away from discs as I apparently wrongly assumed it would be less stable in the wind (and also because of the costs). Thanks for the insights as usual!

Thanks everyone - I know the BEST choice but it's a little bit of a compromise game in this singular situation.

I understand this math - it's a really complex game of "oh shit my bike broke" and "hey - I'll bring mine to IW and you can use it" and - wait - what tire and tube do you have on that disc? What I really ought to do is get my HED jet disc set up but too much going on with other projects.

I mostly wondered if the skinny older tire plus butyl tube v the tubeless faster tire would outweigh the Jet 9.

We are going to run the Zipp disc with latex it looks like. Promise either way it's going to be a fast bike split ;)

Brent

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DFRU - Detta Family Racing Unit...the kids like it and we all get out and after it...gotta keep the fam involved!