Two Things: The Rule of 105 is No Longer Real, and 1 more...

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maxim809
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Posts: 884
Joined: Sat Feb 25, 2017 6:28 am

by maxim809

Hi everyone,

the tl;dr's are IN BOLD

1. We are rebranding the Racing forum to Watt Weenies. This is now a place to discuss all aspects of performance gains, without judgement. We may consider shadow-copying topics from other boards here to get inertia going.

2. In that spirit, I also want to use this board to keep up to date on latest learnings. This could be sharing brand new topics (novel cycling kit textures; new learnings about nutrition). It could also mean sunsetting old rules that may have once been true in the past, but no longer apply based on new learnings.

So with that, according to Escape Collective performance process podcast, it's looking like the age old adage of Rule of 105 no longer applies with wider rims and tires. Because their full podcast is behind a subscription, I want us to respect EC and be careful not to transcribe, and instead encourage those to maybe consider supporting EC to get the details.

But the tl;dr is those of us running road bikes with modern wide tires and modern rims, should move away from the Rule of 105, and consciously make an effort to stop perpetuating this to our friends, families, and dog.

https://escapecollective.com/podcast-ae ... p-ballard/


by Weenie


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warthog101
Posts: 945
Joined: Wed Sep 25, 2013 10:05 am

by warthog101

kervelo wrote:
Mon Apr 22, 2024 7:06 am
From 2022:

https://blog.flocycling.com/aero-wheels ... ou-slower/
Read that. Can't hear the other link as I'm not paying.
The tyre widths were very close to the rim width and they did say not to discard the 105 rule.
The tyre still needs to be pretty close to the rim width if it is to be wider it seemed to indicate.

CampagYOLO
Posts: 767
Joined: Thu May 06, 2021 3:58 pm

by CampagYOLO

warthog101 wrote:
Mon Apr 22, 2024 9:25 am
kervelo wrote:
Mon Apr 22, 2024 7:06 am
From 2022:

https://blog.flocycling.com/aero-wheels ... ou-slower/
Read that. Can't hear the other link as I'm not paying.
The tyre widths were very close to the rim width and they did say not to discard the 105 rule.
The tyre still needs to be pretty close to the rim width if it is to be wider it seemed to indicate.
That seems to be the consensus now that the tyre should be about the same width as the widest part of the rim. Significantly wider tyres than the rim will still lead to aerodynamic losses.

CarlosFerreiro
Posts: 428
Joined: Thu Jan 08, 2009 1:41 pm
Location: Shetland, Scotland

by CarlosFerreiro

Giving up a rule of thumb is fine, now we need each manufacturer to step up with windtunnel data on a full range of WAM tyre widths? :lol:

maxim809
Administrator
Posts: 884
Joined: Sat Feb 25, 2017 6:28 am

by maxim809

Thanks for the link from FLO. It's an interesting perspective.

2022 FLO's testing is only on their own set of wheels with two sizes of GP's. Small test matrix.
2024 Swiss Side's claims testing on a variety of wheels with a broad set of sizes and tire models. Larger test matrix.

Swiss Side claims they have not seen Rule of 105 hold across their matrix. In a follow-up they stated there isn't even a rule of thumb they could even provide when it comes to aero gains, because it is so system dependent. FLO's testing is looking at combined aero and rolling resistance, and concluding CdA+Crr can be better even when breaking 105. Swiss Side is claiming they have not observed correlation between 105 and aero gains in their sweeps.

I took that as either:
1. Rule of 105 either having suffered from Cause and Effect fallacy due to limited sample size
2. It could have been true in the past with flat V-shaped rims tubulars, but no longer applies with today's setups.
3. Fundamental differences in the testing protocols between 2002 and 2024

I like my chances with Swiss Side. The podcasts have a free section by the way. There's interesting stuff related to aero.

by Weenie


Visit starbike.com Online Retailer for HighEnd cycling components
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warthog101
Posts: 945
Joined: Wed Sep 25, 2013 10:05 am

by warthog101

CampagYOLO wrote:
Mon Apr 22, 2024 9:56 am
warthog101 wrote:
Mon Apr 22, 2024 9:25 am
kervelo wrote:
Mon Apr 22, 2024 7:06 am
From 2022:

https://blog.flocycling.com/aero-wheels ... ou-slower/
Read that. Can't hear the other link as I'm not paying.
The tyre widths were very close to the rim width and they did say not to discard the 105 rule.
The tyre still needs to be pretty close to the rim width if it is to be wider it seemed to indicate.
That seems to be the consensus now that the tyre should be about the same width as the widest part of the rim. Significantly wider tyres than the rim will still lead to aerodynamic losses.

That is my take too.
The podcast stopped before talking about the 105 rule for me.

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