All I got is “smooth is faster” and my fastest times out here are on wide tires. So take it for what it’s worth.
I don’t want to argue that 32 on the rovals isn’t faster. I’m just saying the way they got to their conclusion is just broscience.
How would you isolate the RR of the wider tyre or the aerodrag from the whole system doing it outdoors with so many uncontrolled variables. It’s entertaining but not scientific.
I run 44mm Slicks on rough pavement, light gravel so I agree smooth is fast, especially for longer days. Optimizing tyre to wheelwidth on deep wheels to gain 1W is great if you have already optimized everything else.
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Of course, they are youtube entertainers first and foremost and not scientists. But they are not separating aero drag from rolling resistance. Had they done many more laps, used the chung method, or even some kind of aero sensor system they might have come up with better data. I don’t think the 3-20 second differences they came up with don’t really mean anything other than they were all essentially the same.
Could it be the case where wider tires are faster than skinnier tires and they’ll be even faster when run on wider (and deeper) rims that meet the rule of 105? The Nextie, 3T, and Light Bicycle rims are the only ones I can think of that are wide enough.
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Optimizing my position in the peloton, in the wind, likely buys me more than a watt here or there on my wheels. I’m not usually time trialing or attempting to set the hour record on the track.
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Yes. Rolling resistance, grip, impedance, comfort, etc play a role. In many cases these can dominate the aero gains from staying within rule of 105.
However, If you choose a tire based on your preference on the above an then pick a wheel within the rule of 105, that combination will very likely be faster than if you choose a wheel out of the 105 rule for the same tire.
However, most of the time we don’t have that many alternatives and it’s more pragmatic to change tires rather than wheels.
We’re starting to see more road/gravel wheels with external width above 32mm. I’m excited to see how they’d perform with wider tires.
Hello.
First off, please excuse that I am speaking in generalities. I am appreciative that you are taking stabs at filling in the blanks with specifics.
My theory as to why there is zero data available on the searchable internet today, is that there is often a 3 to 5 year lag time between the bleeding edge of the industry latest discoveries, to those facts landing into Early Majority. Think about how Josh has stated that once Silca discovered wider is faster, that every pro was lying to each other about their tire widths and PSIs. And even going as far as to mislabeling their tire widths.
The second theory is that even if you had this data, it simply takes time to get people to understand the results, let alone understanding the pros and cons in the design of the test protocol and why these were chosen in lieu of alternatives. There are many ways to muddy the water, as demonstrated by the FLO article you linked.
So while the absence of data is definitely true, putting all my eggs into that basket wouldn’t be my first choice. But maybe you have reliable leads, or you’ve done your own testing.
Several years ago, I have taken wheelsets into tunnels and varied tire widths. Even in my limited sampleset I am finding that 105% isn’t holding true at all. The tunnel operators weren’t surprised.
I believe your takeaway of “don’t create a big lightbulb” is correct. But I also think there’s an opposite side of the same coin which is that one does not have to obsess over getting 105% exactly.
So that’s the holistic takeaway I was hoping people would come to:
- Don’t lightbulb
- But also don’t stress if it’s not a perfect 105.00000000%
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I think we are in 100% agreement as I posted similar. The 105% rule was for pros/elites and really just a general guideline from over a decade ago.
I think we could generalize that as the tire gets wider than the rim, you lose some watts though maybe you gain in rolling resistance. A millimeter or two or three won’t make any difference to 99.9% of amateurs and recreational cyclists.
I’ve never come near a wind tunnel, but I’ve listed to several episodes of Marginal Gains so I’m obviously a major expert 
.
The catchphrase there is “it depends,” and they make the point again and again that there are subtleties to aerodynamics that make some setups out perform others in ways even Josh (with 1000s of tunnel hours) would never predict. Just posted elsewhere, but e.g. they found RaceKing 2.2s to be more aero than many 40mm tires (for some reason, they don’t know why.) Josh also related a story of someone back in the day hand-modifying a road tire with some shoulder tread that make it exceedingly aero on various rims; try as they might they couldn’t make a production tire that was as good.
All to say that, at best, we’re going to get some very broad “rules of thumb” and I think 105 is still a solid one. But there will certainly be 105-complianted setups that are slower than lightbulbed setups, because of voodoo.
Have there been tests that showed a light bulb setup (significant difference between rim and tire widths) to be faster than a 105% setup or even 100%?
All these tests we are are discussing in this topic haven’t showed a light bulb versus anything close to 105%.
Flo showed the narrow tire to be faster in the wind tunnel. NorCal cycling’s tested tires were all smaller than the 35mm wide Roval rapide front rim they used. Their 32mm tire tested at 31mm and their 34 at 32mm.
I’m sorry, there was no voodoo. Dylan found that the Race King (52mm) was on par with a 45mm tire but he was already breaking the 105 rule by a large amount and his differences were in the 1-2 watt range. That could easily be explained by tire blocks at the edge of the tire, or the shape of the Race King compared to the other tire. Dylan’s elbow out slightly. And, can they even measure 1-2 watts that precisely?
In his test the 35mm tire was the fastest in the wind tunnel. No doubt. He intentionally chose a slower setup because it was only a few watts and he’s riding on chunky gravel for 200 miles.
People keep trying to support this 105 rule dead thing with anecdotes when all the wind tunnel tests and even the anecdotes show that if you want the fastest aero setup, the tire should at least be slightly smaller than the rim.
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You might need to be a member to hear it, but Ronan asked Xavier about his opinion on the “Rule of 105” at about the 40 minute mark. His says that the rule was only really relevant in rims shapes that are no longer being used. His comment is that the best tire size is depending on the particular wheel itself and the shape of the rim and not just on how wide the rim is at the brake track
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Great, but the guest gave a BS non-answer. He says to ask the manufacturer what the faster tire is for your rim.
105 was just a guideline. What still stands is that any lightbulb shaped tire/rim combo (tire wider than rim), is going to be slower. It’s not even going to be airfoil shaped. So optimal is doing to be somewhere between 100% and up.
I think it is becoming increasingly clear that the 105 Rule is not the sacrosanct “rule” that people once believed it was.
As noted, rim shapes have changed, but just as importantly, tires have changed. The Rule of 105 was done with clinchers / tubes many, many years ago. We were running both narrower rims and tires.
The one thing about aerodynamics is that it is always changing with designs…which requires more testing.
When you listen to Josh Portner talk about it, it was just a guideline. It was never a hard and fast rule.
Sure, I can see that maybe the original rims were torroidal Zipps and 105% represented the best airfoil for that kind of rim.
Still, there is zero data that shows a 32mm tire is going to be the fastest tire on a 28 or 30mm wide rim. You can’t go wider than the rim.
Whatever is “fastest” may be more up in the air and only known by wind tunnel testings. From the specs I’ve seen, the vast majority of race wheels still specify 28mm as the designated tire. If one wants to be aero optimized around tires measuring 30-32-34mm, they are going to need to search out wider rims.
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Sure…which is why I said “people” and not “Josh Poertner”.
What Xav is saying is that trying to hit 105% dead on is not this magical number the way so many people out there claim it is. I’ve seen countless posts on messages boards across the web over the years of people trying really hard to come to as close to 105% as possible. But as he (and Ballard and a number of other people who do a ton of testing around this stuff) the fastest tire width is going to be dependent on the shape and width of the time. Maybe it’s 101, maybe it’s 105, maybe its 107.
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That’s not what he said on the podcast. Why do you guys invent stuff to defend someone who appeared on a podcast?
Who cares if a million punters on forums over the years have repeated Portner’s guideline. Personally, I’ve never ever seen anyone trying to hit 105% bang on.
Not sure why you keep so defensive about this whole “rule 105%” thing? It’s weird
What I see is a guy that sells wheels and aero testing services say that you can only know the answer by consulting experts that have tested your wheels in a wind tunnel.
Interestingly, I’m looking at the wheels he’s selling with a 26.7mm brake track. They recommend a 23-25mm tire. The 23mm Corsa Speed was their fastest tested tire. That measures 25mm actual and thus:
1.068%.
The second fastest tire is the Corsa Speed 25mm (actual 27mm). It only loses .1 watt to the 23mm tire.
99%
Third fastest is the 27mm Gp5000 TL (actual 27mm). -5.7w
Thus as an estimate, the 105% rule is still holds up a decent guideline. There doesn’t seem to be a penalty for going with a smaller tire. There is clearly a penalty for going fatter and fatter and exceeding the width of the rim.
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I have no vested interest in the 105% rule.
Why did you feel the need to make something up to defend the point of view of the podcast guest in order to counter my argument?