marting wrote:
I'm on the cusp of making the transition to tubeless . I was about to install GP5000TL 25mm on my HED Jet 6+ Front / Jet 9+ Front & Rear, Jet+ Disc rear wheels when I was reminded of Josh Poertner's "Rule of 105" (
https://blog.silca.cc/...ure-and-aerodynamics).
In summary, this says that "the rim must be
at least 105% the width of the tire". Rim width here means the widest part of the whole rim, not the width of the brake track.
My Jet6+ rims measure 27.5mm at the widest point. Dividing by 105% tells me that my tires should therefore be no wider than 26.2mm.
I believe that GP5000TL 25mm tires measure more like 26.5mm on these rims (possibly even wider because of the thicker casing than the tubed version). That's close, but it still violates the rule, and therefore probably isn't a good choice, especially as they grow with age.
I'm currently running GP4000SII 23mm, which come out at ~25mm on these rims - that's 109%, so comfortably on the right side of the rule.
So, a couple of questions:
- Why doesn't Continental make a 23mm GP5000 TL? This would seem to be a perfect aero solution for these (and similar) rims. The 25mm looks like it may be too wide for good aerodynamic behaviour in gusty/high yaw conditions, and the 28mm will definitely not be a good answer (for these rims).
- If GP5000 TL 25mm isn't the right answer for me, what is? The GP4000Sii had (for me) the perfect combination of aero/rolling resistance/puncture resistance. Andy Tetmeyer @ HED: what have you found to be the fastest in your testing?
This setup was addressed earlier in the thread - you can CTRL-F and search for GP5000 to find. Someone reported that they installed the GP5000 on Jet Plus and it measured 26.11. Note, however that they didn't specify if it was the tubeless version, and most tires stretch out over time and grow in width. When I've used tubed 25mm Conti GP
4000's on those rims, they've always inflated to 28 - 28.5mm.
"Why doesn't Continental make a 23mm GP5000 TL?" My guess is that they saw how their sales were trending, and the market in general is trending, and made a business decision. Most decisions like this that don't make sense in the wind tunnel or engineering department are due to the accounting department. While aero is king in here, you'd be surprised at how little much of the market or manufacturers are concerned with it. Our recent home page article addressed a related issue of
hooked vs hookless rims - leaving the hooks on pushes the tire width in a bit (to aid in aerodynamics), but the rim molds are more expensive and complex. Hookless rims can have other benefits, but it doesn't help with the Rule of 105.
If you want Andy @ Hed to get a notification of your questions, you'll need to reply to one of his posts - otherwise he may not find it (I'm not sure how closely he is watching/scanning this thread day-to-day).