Rule of 105

Triathlon Forum
1

So many wheels currently emphasize internal rim width but fail to mention external width. I have yet to see a study that shows that the rule of 105 no longer applies. Many of the new wheels with a hookless rim have an internal width of 25mm which then requires a tire with a minimum nominal width of 28mm. A Conti 5000 S TL tire mounted on a 25mm internal width rim is going to measure 30mm or more. The external width must therefore be a minimum of 32mm to stay within 105% of mounted tire width. I understand combined rolling resistance/aero but why would I ever buy a wheel that would violate the rule of 105%?

Example: the Enve SES 4.5 AR has an internal hookless bead of 25mm and external width of 31mm. The wheel requires a 28mm tire. Why would I ever buy this wheel if I wanted optimal aero? What am I missing? I understand a wider rim gets heavier but I would always choose marginally heavier to stay within the rule of 105.

Am I wrong?

2

Following this thread, hoping that Josh P. will chime in or one of the other aero gurus.

3

i can’t answer for josh; he’s eminently capable of doing his own writing. but i will state this following from memory. josh worked at zipp/sram starting from roughly 2000 and until he bought silca, which was 2013 or 2014 as i recall. during the very early years of his zipp he and others began to understand that having a rim wider than the tire created a trailing edge as the wind exited the wheel.

the obvious best solution this is a toroidal rim shape. the problem: HED owned the patent. the solution: somehow get yourself a share of that patent, which is exactly what zipp did at the time josh was zipp’s technical director. the work done in those early years post-2000 that validated the “rule of 105” was done largely by HED, and zipp, and bontrager. what do they all have in common? they were makers of aero wheels with toroidal rim shapes.

but to your problem of a hookless system where a tire is 2mm or 3mm larger than the internal bead width of the rim: who here is riding a tire in any non-tubular system where the tire is not at least 2mm larger than the internal bead on the rim? for the last generation it’s been a 23mm tire on a 17mm internal bead width; or a 25mm tire on a 19mm bead width. the differential between tire size and internal bead width is almost certainly greater on the wheel you’re riding - whatever it is - than this 3mm differential that offends you.

4

I think you have misinterpreted my question. I am not concerned with the size of the internal bead vs nominal tire size, I am referring to the mounted/inflated tire width approaching or exceeding the external width of the rim. i.e. the inflated tire width is 99% of the external rim width.

i can’t answer for josh; he’s eminently capable of doing his own writing. but i will state this following from memory. josh worked at zipp/sram starting from roughly 2000 and until he bought silca, which was 2013 or 2014 as i recall. during the very early years of his zipp he and others began to understand that having a rim wider than the tire created a trailing edge as the wind exited the wheel.

the obvious best solution this is a toroidal rim shape. the problem: HED owned the patent. the solution: somehow get yourself a share of that patent, which is exactly what zipp did at the time josh was zipp’s technical director. the work done in those early years post-2000 that validated the “rule of 105” was done largely by HED, and zipp, and bontrager. what do they all have in common? they were makers of aero wheels with toroidal rim shapes.

but to your problem of a hookless system where a tire is 2mm or 3mm larger than the internal bead width of the rim: who here is riding a tire in any non-tubular system where the tire is not at least 2mm larger than the internal bead on the rim? for the last generation it’s been a 23mm tire on a 17mm internal bead width; or a 25mm tire on a 19mm bead width. the differential between tire size and internal bead width is almost certainly greater on the wheel you’re riding - whatever it is - than this 3mm differential that offends you.

5

I think you have misinterpreted my question. I am not concerned with the size of the internal bead vs nominal tire size, I am referring to the mounted/inflated tire width approaching or exceeding the external width of the rim. i.e. the inflated tire width is 99% of the external rim width.

i can’t answer for josh; he’s eminently capable of doing his own writing. but i will state this following from memory. josh worked at zipp/sram starting from roughly 2000 and until he bought silca, which was 2013 or 2014 as i recall. during the very early years of his zipp he and others began to understand that having a rim wider than the tire created a trailing edge as the wind exited the wheel.

the obvious best solution this is a toroidal rim shape. the problem: HED owned the patent. the solution: somehow get yourself a share of that patent, which is exactly what zipp did at the time josh was zipp’s technical director. the work done in those early years post-2000 that validated the “rule of 105” was done largely by HED, and zipp, and bontrager. what do they all have in common? they were makers of aero wheels with toroidal rim shapes.

but to your problem of a hookless system where a tire is 2mm or 3mm larger than the internal bead width of the rim: who here is riding a tire in any non-tubular system where the tire is not at least 2mm larger than the internal bead on the rim? for the last generation it’s been a 23mm tire on a 17mm internal bead width; or a 25mm tire on a 19mm bead width. the differential between tire size and internal bead width is almost certainly greater on the wheel you’re riding - whatever it is - than this 3mm differential that offends you.

i must not understand you. i have a 28mm tire on a 25mm zipp 353 nsw, with a hookless bead. that tire measures slightly less than the rim width at the rim wall. about 1mm less. so, i guess my wheel/tire system conforms to the rule of 103.

if you’re strongly adhered to the cult of 105 you’ll want to make your rim 2mm wider than this, and the easiest method, historically, is to deploy a toroidal architecture. this isn’t a hooked or hookless issue. it’s a rim shape issue, and you face the same calculus if you’re using a hooked bead system.

6

Am I wrong?

Assuming the the Rule of 105 still applies and your only concern was aerodynamics above all else, you might be right. But if your only concern was aerodynamics not sure why you’d buy a 4.5AR anyway. The 4.5 is kind of an all-purpose wheel. Not a TT wheel.

If I was doing a pure 40K TT, I might dig up some 2010’s era wheel I could fit a 23mm or 25mm tire to. For almost all other racing or riding, I much prefer this more recent generation of wheels.

7

I think you have misinterpreted my question. I am not concerned with the size of the internal bead vs nominal tire size, I am referring to the mounted/inflated tire width approaching or exceeding the external width of the rim. i.e. the inflated tire width is 99% of the external rim width.

i can’t answer for josh; he’s eminently capable of doing his own writing. but i will state this following from memory. josh worked at zipp/sram starting from roughly 2000 and until he bought silca, which was 2013 or 2014 as i recall. during the very early years of his zipp he and others began to understand that having a rim wider than the tire created a trailing edge as the wind exited the wheel.

the obvious best solution this is a toroidal rim shape. the problem: HED owned the patent. the solution: somehow get yourself a share of that patent, which is exactly what zipp did at the time josh was zipp’s technical director. the work done in those early years post-2000 that validated the “rule of 105” was done largely by HED, and zipp, and bontrager. what do they all have in common? they were makers of aero wheels with toroidal rim shapes.

but to your problem of a hookless system where a tire is 2mm or 3mm larger than the internal bead width of the rim: who here is riding a tire in any non-tubular system where the tire is not at least 2mm larger than the internal bead on the rim? for the last generation it’s been a 23mm tire on a 17mm internal bead width; or a 25mm tire on a 19mm bead width. the differential between tire size and internal bead width is almost certainly greater on the wheel you’re riding - whatever it is - than this 3mm differential that offends you.

i must not understand you. i have a 28mm tire on a 25mm zipp 353 nsw, with a hookless bead. that tire measures slightly less than the rim width at the rim wall. about 1mm less. so, i guess my wheel/tire system conforms to the rule of 103.

if you’re strongly adhered to the cult of 105 you’ll want to make your rim 2mm wider than this, and the easiest method, historically, is to deploy a toroidal architecture. this isn’t a hooked or hookless issue. it’s a rim shape issue, and you face the same calculus if you’re using a hooked bead system.

So I’m assuming your setup of a 28mm tire w/ a zipp 353 measures 31 mm tire width (mounted) and 32 mm external rim width. Which ends up at ~103% like you said. I think what the OP is asking is why doesn’t the rule of 105% apply here? If it does, you would better off running a 25 mm tire on that wheel for optimum aerodynamics. Let’s ignore the fact that a 353 isn’t a wheel that should be used when you are aiming for peak aero.

If we want to look at a real example where peak aero matters, let’s look at a zipp 858 with a 23 mm vs 25mm tire or an enve 7.8 with a 25 mm tire vs a 28 mm tire. In both of those examples, the larger tire violates the rule of 105% but the industry marketing is pushing everyone towards these larger tires.

8

I think you have misinterpreted my question. I am not concerned with the size of the internal bead vs nominal tire size, I am referring to the mounted/inflated tire width approaching or exceeding the external width of the rim. i.e. the inflated tire width is 99% of the external rim width.

i can’t answer for josh; he’s eminently capable of doing his own writing. but i will state this following from memory. josh worked at zipp/sram starting from roughly 2000 and until he bought silca, which was 2013 or 2014 as i recall. during the very early years of his zipp he and others began to understand that having a rim wider than the tire created a trailing edge as the wind exited the wheel.

the obvious best solution this is a toroidal rim shape. the problem: HED owned the patent. the solution: somehow get yourself a share of that patent, which is exactly what zipp did at the time josh was zipp’s technical director. the work done in those early years post-2000 that validated the “rule of 105” was done largely by HED, and zipp, and bontrager. what do they all have in common? they were makers of aero wheels with toroidal rim shapes.

but to your problem of a hookless system where a tire is 2mm or 3mm larger than the internal bead width of the rim: who here is riding a tire in any non-tubular system where the tire is not at least 2mm larger than the internal bead on the rim? for the last generation it’s been a 23mm tire on a 17mm internal bead width; or a 25mm tire on a 19mm bead width. the differential between tire size and internal bead width is almost certainly greater on the wheel you’re riding - whatever it is - than this 3mm differential that offends you.

i must not understand you. i have a 28mm tire on a 25mm zipp 353 nsw, with a hookless bead. that tire measures slightly less than the rim width at the rim wall. about 1mm less. so, i guess my wheel/tire system conforms to the rule of 103.

if you’re strongly adhered to the cult of 105 you’ll want to make your rim 2mm wider than this, and the easiest method, historically, is to deploy a toroidal architecture. this isn’t a hooked or hookless issue. it’s a rim shape issue, and you face the same calculus if you’re using a hooked bead system.

So I’m assuming your setup of a 28mm tire w/ a zipp 353 measures 31 mm tire width (mounted) and 32 mm external rim width. Which ends up at ~103% like you said. I think what the OP is asking is why doesn’t the rule of 105% apply here? If it does, you would better off running a 25 mm tire on that wheel for optimum aerodynamics. Let’s ignore the fact that a 353 isn’t a wheel that should be used when you are aiming for peak aero.

If we want to look at a real example where peak aero matters, let’s look at a zipp 858 with a 23 mm vs 25mm tire or an enve 7.8 with a 25 mm tire vs a 28 mm tire. In both of those examples, the larger tire violates the rule of 105% but the industry marketing is pushing everyone towards these larger tires.

this is a road wheel and as such it has a lot of jobs. the sawtooth design of the 353 NSW is designed for provide for aero performance, however… i don’t know about you, but the better the aero performance the more (in my experience) the wheel is vulnerable to sidewind feedback. this is just a no-go on a road bike (for me). what i want in a road wheel is decent aero performance; the capacity to ride a wider tire; very little sidewind feedback from the wheel; and the other stuff (flat resistance, hardiness, vibration absorption, etc.).

zipp loves its105 adherents and had you all in mind when it made its hookless bead road wheels. the 303 S, 454 NSW, 404 Firecrest can accept a 25mm tire and, voila, you get your 105. but this particular wheel i’m riding, the 353 NSW, is not made with this in mind.

9

I think you have misinterpreted my question. I am not concerned with the size of the internal bead vs nominal tire size, I am referring to the mounted/inflated tire width approaching or exceeding the external width of the rim. i.e. the inflated tire width is 99% of the external rim width.

i can’t answer for josh; he’s eminently capable of doing his own writing. but i will state this following from memory. josh worked at zipp/sram starting from roughly 2000 and until he bought silca, which was 2013 or 2014 as i recall. during the very early years of his zipp he and others began to understand that having a rim wider than the tire created a trailing edge as the wind exited the wheel.

the obvious best solution this is a toroidal rim shape. the problem: HED owned the patent. the solution: somehow get yourself a share of that patent, which is exactly what zipp did at the time josh was zipp’s technical director. the work done in those early years post-2000 that validated the “rule of 105” was done largely by HED, and zipp, and bontrager. what do they all have in common? they were makers of aero wheels with toroidal rim shapes.

but to your problem of a hookless system where a tire is 2mm or 3mm larger than the internal bead width of the rim: who here is riding a tire in any non-tubular system where the tire is not at least 2mm larger than the internal bead on the rim? for the last generation it’s been a 23mm tire on a 17mm internal bead width; or a 25mm tire on a 19mm bead width. the differential between tire size and internal bead width is almost certainly greater on the wheel you’re riding - whatever it is - than this 3mm differential that offends you.

i must not understand you. i have a 28mm tire on a 25mm zipp 353 nsw, with a hookless bead. that tire measures slightly less than the rim width at the rim wall. about 1mm less. so, i guess my wheel/tire system conforms to the rule of 103.

if you’re strongly adhered to the cult of 105 you’ll want to make your rim 2mm wider than this, and the easiest method, historically, is to deploy a toroidal architecture. this isn’t a hooked or hookless issue. it’s a rim shape issue, and you face the same calculus if you’re using a hooked bead system.

So I’m assuming your setup of a 28mm tire w/ a zipp 353 measures 31 mm tire width (mounted) and 32 mm external rim width. Which ends up at ~103% like you said. I think what the OP is asking is why doesn’t the rule of 105% apply here? If it does, you would better off running a 25 mm tire on that wheel for optimum aerodynamics. ** Let’s ignore the fact that a 353 isn’t a wheel that should be used when you are aiming for peak aero. **

If we want to look at a real example where peak aero matters, let’s look at a zipp 858 with a 23 mm vs 25mm tire or an enve 7.8 with a 25 mm tire vs a 28 mm tire. In both of those examples, the larger tire violates the rule of 105% but the industry marketing is pushing everyone towards these larger tires.

this is a road wheel and as such it has a lot of jobs. the sawtooth design of the 353 NSW is designed for provide for aero performance, however… i don’t know about you, but the better the aero performance the more (in my experience) the wheel is vulnerable to sidewind feedback. this is just a no-go on a road bike (for me). what i want in a road wheel is decent aero performance; the capacity to ride a wider tire; very little sidewind feedback from the wheel; and the other stuff (flat resistance, hardiness, vibration absorption, etc.).

zipp loves its105 adherents and had you all in mind when it made its hookless bead road wheels. the 303 S, 454 NSW, 404 Firecrest can accept a 25mm tire and, voila, you get your 105. but this particular wheel i’m riding, the 353 NSW, is not made with this in mind.

I know it’s a road wheel. That’s why I said to ignore this fact in this scenario. You used it in your example to reply to the OP when he clearly is looking for a peak aero solution… why you did… I’m not sure.

10

SES 7.8 is consistently one of the fastest wheels and great in crosswinds compared to even 60mm wheels, including HED Jet Black 6. Of course there is correlation because deeper wheels are generally faster and present a greater area to the wind, but the shape can have a surprising impact compared to even 2-3cm of wheel depth.

Not sure what this has to do with 105 though. 105 applies to wheels of all depths and wheel lines often come in all depths with the same internal/external widths.

To answer the OPs question, companies are ignoring 105 now because aero is yesterday. Hookless wheels, light frames, and big tires are the flavors of the day. You see mention of grip and comfort in all the marketing materials for these new setups. The reason you don’t hear about aero is simply because they aren’t as aero.

Hookless makes 105 harder to achieve for obvious reasons but luckily we aren’t forced out of hooked wheels yet.

11

I think you have misinterpreted my question. I am not concerned with the size of the internal bead vs nominal tire size, I am referring to the mounted/inflated tire width approaching or exceeding the external width of the rim. i.e. the inflated tire width is 99% of the external rim width.

i can’t answer for josh; he’s eminently capable of doing his own writing. but i will state this following from memory. josh worked at zipp/sram starting from roughly 2000 and until he bought silca, which was 2013 or 2014 as i recall. during the very early years of his zipp he and others began to understand that having a rim wider than the tire created a trailing edge as the wind exited the wheel.

the obvious best solution this is a toroidal rim shape. the problem: HED owned the patent. the solution: somehow get yourself a share of that patent, which is exactly what zipp did at the time josh was zipp’s technical director. the work done in those early years post-2000 that validated the “rule of 105” was done largely by HED, and zipp, and bontrager. what do they all have in common? they were makers of aero wheels with toroidal rim shapes.

but to your problem of a hookless system where a tire is 2mm or 3mm larger than the internal bead width of the rim: who here is riding a tire in any non-tubular system where the tire is not at least 2mm larger than the internal bead on the rim? for the last generation it’s been a 23mm tire on a 17mm internal bead width; or a 25mm tire on a 19mm bead width. the differential between tire size and internal bead width is almost certainly greater on the wheel you’re riding - whatever it is - than this 3mm differential that offends you.

i must not understand you. i have a 28mm tire on a 25mm zipp 353 nsw, with a hookless bead. that tire measures slightly less than the rim width at the rim wall. about 1mm less. so, i guess my wheel/tire system conforms to the rule of 103.

if you’re strongly adhered to the cult of 105 you’ll want to make your rim 2mm wider than this, and the easiest method, historically, is to deploy a toroidal architecture. this isn’t a hooked or hookless issue. it’s a rim shape issue, and you face the same calculus if you’re using a hooked bead system.

So I’m assuming your setup of a 28mm tire w/ a zipp 353 measures 31 mm tire width (mounted) and 32 mm external rim width. Which ends up at ~103% like you said. I think what the OP is asking is why doesn’t the rule of 105% apply here? If it does, you would better off running a 25 mm tire on that wheel for optimum aerodynamics. ** Let’s ignore the fact that a 353 isn’t a wheel that should be used when you are aiming for peak aero. **

If we want to look at a real example where peak aero matters, let’s look at a zipp 858 with a 23 mm vs 25mm tire or an enve 7.8 with a 25 mm tire vs a 28 mm tire. In both of those examples, the larger tire violates the rule of 105% but the industry marketing is pushing everyone towards these larger tires.

this is a road wheel and as such it has a lot of jobs. the sawtooth design of the 353 NSW is designed for provide for aero performance, however… i don’t know about you, but the better the aero performance the more (in my experience) the wheel is vulnerable to sidewind feedback. this is just a no-go on a road bike (for me). what i want in a road wheel is decent aero performance; the capacity to ride a wider tire; very little sidewind feedback from the wheel; and the other stuff (flat resistance, hardiness, vibration absorption, etc.).

zipp loves its105 adherents and had you all in mind when it made its hookless bead road wheels. the 303 S, 454 NSW, 404 Firecrest can accept a 25mm tire and, voila, you get your 105. but this particular wheel i’m riding, the 353 NSW, is not made with this in mind.

I know it’s a road wheel. That’s why I said to ignore this fact in this scenario. You used it in your example to reply to the OP when he clearly is looking for a peak aero solution… why you did… I’m not sure.

sorry. i guess we agree? kind of?

there are no name-brand hookless beaded rims so far released that i know of that are tt/tri specific. everything so far is for road/gravel. but the general tenor of the 105 argument this week is that it’s another reason not to buy a wheel with a hookless bead. here’s from a parallel thread ongoing now: “for me at least, i’ll stick with the known and rule of 105 until someone presents evidence otherwise. hookless doesn’t seem to be quite mature enough yet anyway.”

there’s a really good, really defensible, reason for someone to avoid a wheel with a hookless bead: because that person don’t want one. imho best to just leave it there, rather than to invent excuses. my favorite road wheels in general are not made with wheel/tire aero as the design driver, and that’s regardless of the bead style. when someone harshes on a road wheel because it fails to meet this standard, this is when it moves from the rule to the cult of 105.

12

I think you have misinterpreted my question. I am not concerned with the size of the internal bead vs nominal tire size, I am referring to the mounted/inflated tire width approaching or exceeding the external width of the rim. i.e. the inflated tire width is 99% of the external rim width.

i can’t answer for josh; he’s eminently capable of doing his own writing. but i will state this following from memory. josh worked at zipp/sram starting from roughly 2000 and until he bought silca, which was 2013 or 2014 as i recall. during the very early years of his zipp he and others began to understand that having a rim wider than the tire created a trailing edge as the wind exited the wheel.

the obvious best solution this is a toroidal rim shape. the problem: HED owned the patent. the solution: somehow get yourself a share of that patent, which is exactly what zipp did at the time josh was zipp’s technical director. the work done in those early years post-2000 that validated the “rule of 105” was done largely by HED, and zipp, and bontrager. what do they all have in common? they were makers of aero wheels with toroidal rim shapes.

but to your problem of a hookless system where a tire is 2mm or 3mm larger than the internal bead width of the rim: who here is riding a tire in any non-tubular system where the tire is not at least 2mm larger than the internal bead on the rim? for the last generation it’s been a 23mm tire on a 17mm internal bead width; or a 25mm tire on a 19mm bead width. the differential between tire size and internal bead width is almost certainly greater on the wheel you’re riding - whatever it is - than this 3mm differential that offends you.

i must not understand you. i have a 28mm tire on a 25mm zipp 353 nsw, with a hookless bead. that tire measures slightly less than the rim width at the rim wall. about 1mm less. so, i guess my wheel/tire system conforms to the rule of 103.

if you’re strongly adhered to the cult of 105 you’ll want to make your rim 2mm wider than this, and the easiest method, historically, is to deploy a toroidal architecture. this isn’t a hooked or hookless issue. it’s a rim shape issue, and you face the same calculus if you’re using a hooked bead system.

So I’m assuming your setup of a 28mm tire w/ a zipp 353 measures 31 mm tire width (mounted) and 32 mm external rim width. Which ends up at ~103% like you said. I think what the OP is asking is why doesn’t the rule of 105% apply here? If it does, you would better off running a 25 mm tire on that wheel for optimum aerodynamics. ** Let’s ignore the fact that a 353 isn’t a wheel that should be used when you are aiming for peak aero. **

If we want to look at a real example where peak aero matters, let’s look at a zipp 858 with a 23 mm vs 25mm tire or an enve 7.8 with a 25 mm tire vs a 28 mm tire. In both of those examples, the larger tire violates the rule of 105% but the industry marketing is pushing everyone towards these larger tires.

this is a road wheel and as such it has a lot of jobs. the sawtooth design of the 353 NSW is designed for provide for aero performance, however… i don’t know about you, but the better the aero performance the more (in my experience) the wheel is vulnerable to sidewind feedback. this is just a no-go on a road bike (for me). what i want in a road wheel is decent aero performance; the capacity to ride a wider tire; very little sidewind feedback from the wheel; and the other stuff (flat resistance, hardiness, vibration absorption, etc.).

zipp loves its105 adherents and had you all in mind when it made its hookless bead road wheels. the 303 S, 454 NSW, 404 Firecrest can accept a 25mm tire and, voila, you get your 105. but this particular wheel i’m riding, the 353 NSW, is not made with this in mind.

I know it’s a road wheel. That’s why I said to ignore this fact in this scenario. You used it in your example to reply to the OP when he clearly is looking for a peak aero solution… why you did… I’m not sure.

sorry. i guess we agree? kind of?

there are no name-brand hookless beaded rims so far released that i know of that are tt/tri specific. everything so far is for road/gravel. but the general tenor of the 105 argument this week is that it’s another reason not to buy a wheel with a hookless bead. here’s from a parallel thread ongoing now: “for me at least, i’ll stick with the known and rule of 105 until someone presents evidence otherwise. hookless doesn’t seem to be quite mature enough yet anyway.”

there’s a really good, really defensible, reason for someone to avoid a wheel with a hookless bead: because that person don’t want one. imho best to just leave it there, rather than to invent excuses. my favorite road wheels in general are not made with wheel/tire aero as the design driver, and that’s regardless of the bead style. when someone harshes on a road wheel because it fails to meet this standard, this is when it moves from the rule to the cult of 105.

This is how I see it: With the move to hookless, wider rims, and lower pressures on road/gravel wheels, there’s a lot of confusion if you are a triathlete who’s primarily aero driven. The bike/triathlete industry (mfg’s, media - slowtwitch included, etc) keep talking about this shift and how it’s better than what we’ve had in the past. This may be the case for roadies but most if not all are failing to mention that tri/tt isn’t there yet or there is minimal if not no benefit to be gained. The triathlete reads all these articles about hookless, wider tires/wheels and wonders why would he/she want wider wheels/tires when this goes against common knowledge amongst aero minded folks. Hence they end up being confused that they aren’t the target audience of this new product or article.

Why do you think a tt/tri specific wheel hasn’t gone hookless yet? Is it because there isn’t much to be gained for peak aero? I see no point in taking an enve 7.8 or a zipp 858 and making it hookless AND wider. Going wider seems to defeat the purpose of those wheels. Even making those wheels hookless where you can’t run more than ~75 psi doesn’t seem to make sense unless you are riding on some really really really rough roads… which is very much the exception in most TT’s/tri’s.

Hope that all makes sense?

13

SES 7.8 is consistently one of the fastest wheels and great in crosswinds compared to even 60mm wheels, including HED Jet Black 6. Of course there is correlation because deeper wheels are generally faster and present a greater area to the wind, but the shape can have a surprising impact compared to even 2-3cm of wheel depth.

Not sure what this has to do with 105 though. 105 applies to wheels of all depths and wheel lines often come in all depths with the same internal/external widths.

To answer the OPs question, companies are ignoring 105 now because aero is yesterday. Hookless wheels, light frames, and big tires are the flavors of the day. You see mention of grip and comfort in all the marketing materials for these new setups. The reason you don’t hear about aero is simply because they aren’t as aero.

Hookless makes 105 harder to achieve for obvious reasons but luckily we aren’t forced out of hooked wheels yet.

I agree. I see where I have been labeled a cultist because I referenced the rule of 105 lol. In any case I agree the Enve 7.8 is awesome! I have the disc version and it is my race wheel for Crits and RR even if hilly. I have other Enve sets and other carbon wheel sets for several bikes. I have no aversion to new tech and I embrace it. Have a hookless set too. I had referenced the Enve 4.5 because it got great reviews and I considered but at the time Cont 5000 TL 28 was hooked only. I liked that tire and so I purchased the Cannondale Knot 64 hooked with 21 internal and 32 external for the sole purpose of having a mixed wheel set for Road/dirt and comfortable training. I am not bothered much by cross winds even here in windy Boulder and love my 7.8s on windy days. As you mention they are very stable and in my opinion much better behaved than the Knot 64 in a cross wind although maybe the 28 has something to do with that. In any case the speed difference between my 7.8 with 25mm 5000 TL vs Knot 64 w/28mm is not even a contest when the hammer is down.

14

I think you have misinterpreted my question. I am not concerned with the size of the internal bead vs nominal tire size, I am referring to the mounted/inflated tire width approaching or exceeding the external width of the rim. i.e. the inflated tire width is 99% of the external rim width.

i can’t answer for josh; he’s eminently capable of doing his own writing. but i will state this following from memory. josh worked at zipp/sram starting from roughly 2000 and until he bought silca, which was 2013 or 2014 as i recall. during the very early years of his zipp he and others began to understand that having a rim wider than the tire created a trailing edge as the wind exited the wheel.

the obvious best solution this is a toroidal rim shape. the problem: HED owned the patent. the solution: somehow get yourself a share of that patent, which is exactly what zipp did at the time josh was zipp’s technical director. the work done in those early years post-2000 that validated the “rule of 105” was done largely by HED, and zipp, and bontrager. what do they all have in common? they were makers of aero wheels with toroidal rim shapes.

but to your problem of a hookless system where a tire is 2mm or 3mm larger than the internal bead width of the rim: who here is riding a tire in any non-tubular system where the tire is not at least 2mm larger than the internal bead on the rim? for the last generation it’s been a 23mm tire on a 17mm internal bead width; or a 25mm tire on a 19mm bead width. the differential between tire size and internal bead width is almost certainly greater on the wheel you’re riding - whatever it is - than this 3mm differential that offends you.

i must not understand you. i have a 28mm tire on a 25mm zipp 353 nsw, with a hookless bead. that tire measures slightly less than the rim width at the rim wall. about 1mm less. so, i guess my wheel/tire system conforms to the rule of 103.

if you’re strongly adhered to the cult of 105 you’ll want to make your rim 2mm wider than this, and the easiest method, historically, is to deploy a toroidal architecture. this isn’t a hooked or hookless issue. it’s a rim shape issue, and you face the same calculus if you’re using a hooked bead system.

So I’m assuming your setup of a 28mm tire w/ a zipp 353 measures 31 mm tire width (mounted) and 32 mm external rim width. Which ends up at ~103% like you said. I think what the OP is asking is why doesn’t the rule of 105% apply here? If it does, you would better off running a 25 mm tire on that wheel for optimum aerodynamics. ** Let’s ignore the fact that a 353 isn’t a wheel that should be used when you are aiming for peak aero. **

If we want to look at a real example where peak aero matters, let’s look at a zipp 858 with a 23 mm vs 25mm tire or an enve 7.8 with a 25 mm tire vs a 28 mm tire. In both of those examples, the larger tire violates the rule of 105% but the industry marketing is pushing everyone towards these larger tires.

this is a road wheel and as such it has a lot of jobs. the sawtooth design of the 353 NSW is designed for provide for aero performance, however… i don’t know about you, but the better the aero performance the more (in my experience) the wheel is vulnerable to sidewind feedback. this is just a no-go on a road bike (for me). what i want in a road wheel is decent aero performance; the capacity to ride a wider tire; very little sidewind feedback from the wheel; and the other stuff (flat resistance, hardiness, vibration absorption, etc.).

zipp loves its105 adherents and had you all in mind when it made its hookless bead road wheels. the 303 S, 454 NSW, 404 Firecrest can accept a 25mm tire and, voila, you get your 105. but this particular wheel i’m riding, the 353 NSW, is not made with this in mind.

I know it’s a road wheel. That’s why I said to ignore this fact in this scenario. You used it in your example to reply to the OP when he clearly is looking for a peak aero solution… why you did… I’m not sure.

sorry. i guess we agree? kind of?

there are no name-brand hookless beaded rims so far released that i know of that are tt/tri specific. everything so far is for road/gravel. but the general tenor of the 105 argument this week is that it’s another reason not to buy a wheel with a hookless bead. here’s from a parallel thread ongoing now: “for me at least, i’ll stick with the known and rule of 105 until someone presents evidence otherwise. hookless doesn’t seem to be quite mature enough yet anyway.”

there’s a really good, really defensible, reason for someone to avoid a wheel with a hookless bead: because that person don’t want one. imho best to just leave it there, rather than to invent excuses. my favorite road wheels in general are not made with wheel/tire aero as the design driver, and that’s regardless of the bead style. when someone harshes on a road wheel because it fails to meet this standard, this is when it moves from the rule to the cult of 105.

This is how I see it: With the move to hookless, wider rims, and lower pressures on road/gravel wheels, there’s a lot of confusion if you are a triathlete who’s primarily aero driven. The bike/triathlete industry (mfg’s, media - slowtwitch included, etc) keep talking about this shift and how it’s better than what we’ve had in the past. This may be the case for roadies but most if not all are failing to mention that tri/tt isn’t there yet or there is minimal if not no benefit to be gained. The triathlete reads all these articles about hookless, wider tires/wheels and wonders why would he/she want wider wheels/tires when this goes against common knowledge amongst aero minded folks. Hence they end up being confused that they aren’t the target audience of this new product or article.

Why do you think a tt/tri specific wheel hasn’t gone hookless yet? Is it because there isn’t much to be gained for peak aero? I see no point in taking an enve 7.8 or a zipp 858 and making it hookless AND wider. Going wider seems to defeat the purpose of those wheels. Even making those wheels hookless where you can’t run more than ~75 psi doesn’t seem to make sense unless you are riding on some really really really rough roads… which is very much the exception in most TT’s/tri’s.

Hope that all makes sense?

on the aero wheel thing: i would be quite surprised if there are not, prior to kona this year:

  1. multiple wheel manufacturers producing tri-oriented wheels with hookless beads;
  2. additional very desirable hookless-compatible low-crr tires.

now, as to the rest of your post, i think i’ve been pretty clear about the use case of the wheels i’ve been writing about. i have never shown a hookless-bead wheel on a tri bike i don’t think. never photographed that, published that, or exhorted people to ride that wheel that way. the only exception to the above is for wheels that could be dual use, such as a 65mm CADEX or a zipp 404 firecrest or 454 nsw. but notably both CADEX and zipp have chosen to push only their bead-hook wheels to the tri market so far.

nevertheless, you’re right on the frequency of articles on this tech, and let me be clear and transparent why this is. aero wheels are coming using this tech. we have a lot of folks in triathlon who think anything less than 100psi is a flat tire. when these wheels show up in our sport, our audience needs to be equipped for how these wheels are used.

so, my strategy has been to write often about this tech; and to provide help on the reader forum; and via our global db of hookless wheel and tire compatibility. further, this db that i maintain is going to get an upgrade: every place where you see an OK, that OK will be replaced with a pressure recommendation. a number, in psi. those numbers will be for a set of circumstances: tri (as the use case); a given road surface, rider weight, and so on. there will be a front page article announcing this, and a prompt here on the forum, once those pressure recommendations take the place of the OK.

all this is going to happen by, say, june 1 or thereabouts, because you’re going to start to see the wheels and tires made with this tech begin to flow for use in triathlons. i want everyone to be versed in this tech by that time.

finally, i think you’re right to ask this question: is the max pressure of 72.5psi too low for the use of this tech in tri? i think this is a valid question for heavier riders who will want to ride a 25mm tire on a hookless wheel. this we can discuss, if and when these wheels come to market.

the conversation that has not been had, yet, is what vibration means to speed in a mechanical system (a bicycle); and what vibration means to performance in a person. the concept is obvious when the vibration is obvious, and the trends in suspension in both MTB and increasingly in gravel are evident. we haven’t had that discussion yet in road and tri in any meaningful way, and when we do i think this will inform the discussion set-ups for tri bikes.

15

Ah, the rule of 105. I hope Josh comments on this.

105% is just an easy to remember ratio that fit the nominal popular external rim/tires combinaisons of the day it was first postulated. In truth, from a physics standpoint what matters is that the tangent angle between the tire and the rim be close to 15 degrees.

16

I posted about this in this thread: https://forum.slowtwitch.com/…_P7708688/#p7708688

But never got a real answer other than something along the lines of “wide tires are awesome”, at least the last time I looked.

17

I have never used hookless wheels, but I was looking more at the photo of the wheel/tire that you posted in the ‘73 psi’ thread. Even if that wheel does not follow the rule of 105 (not sure if it does or does not), but, from appearances at least, it sure looks like that the transition between the rim and tire IS impressively smooth.

You seem to be one of the more experienced people on here regarding hookless. Do you find, all other things being equal, that hookless set ups have (typically) much smoother rim to tire transitions than identical or nearly identical hooked rim set ups?

18

I have never used hookless wheels, but I was looking more at the photo of the wheel/tire that you posted in the ‘73 psi’ thread. Even if that wheel does not follow the rule of 105 (not sure if it does or does not), but, from appearances at least, it sure looks like that the transition between the rim and tire IS impressively smooth.

You seem to be one of the more experienced people on here regarding hookless. Do you find, all other things being equal, that hookless set ups have (typically) much smoother rim to tire transitions than identical or nearly identical hooked rim set ups?

this is enve’s narrative.

this is from their defense of hookless page.

Enve-hookless-journal-2-5.jpg

19

Thanks.

Not sure if you are the right expert to ask, but, given that B-747s use hookless rims at over 200psi, is there ANY way to get slightly narrower hookless rims/tires to work safely for bicycle applications in the 73psi to 110psi range?

20

Thanks.

Not sure if you are the right expert to ask, but, given that B-747s use hookless rims at over 200psi, is there ANY way to get slightly narrower hookless rims/tires to work safely for bicycle applications in the 73psi to 110psi range?

i’m not an expert! just an informed reporter, and an enthusiast with quite a bit of experience on hookless systems (bicycles, and i’ve flown on a 747).

you may be able to make a safe system that runs over 73psi in a bicycle but, practically, no and for this reason: the ETRTO is the governing agency that’s driving this. they state a max psi of, actually, 72.5 (500 kilopascals, aka 5 bar). they also prescribe exactly how the wheel systems are to be made. bicycle wheel companies now make their hookless systems to match this spec, because this is their get out of jail free card. if anything ever happens to a wheel or tire, they can say, “look, i did my job, i made the wheel to spec.”

tire systems will engineer their tires to work with this spec. again, “look, you’re honor, the tire is made to perform on a wheel to the ETRTO spec.”

so, nobody is going to make a higher pressure wheel or tire unless the wheel makers can convince the ETRTO that a system exists that can be safely inflated to a pressure above 5 bar. that said…

these are high air volume systems. you don’t care about PSI. you care about spring rate. let’s say you and the bike altogether weigh 200lb, and it’s a tri bike, which roughly equal weight on the front and rear tire. that means each tire has 100 pounds pressing down on it. if that tire compresses, say, one-tenth of an inch with you aboard, there’s a calculation for that. maybe easier in metric: 40kg per mm? something like that? that’s the spring rate of your tire at appropriate pressure.

i think what you want is a particular spring rate. it’s kind of like the rockwell number in a non-elastic material. these are all measures of how much a system indents or deflects when force is applied. you want your tire to be appropriately hard, but not too hard. right? if your high air volume tire system achieves that same tire deflection at a lower pressure, why do you want the high pressure?