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Tire sizing madness

Old 08-19-19, 03:55 PM
  #1  
Banzai
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Tire sizing madness

I know it's been hashed out before, but it still drives me bonkers.

The accepted wisdom anymore seems to be that 25mm is the "sweet spot" for performance, the place where rolling resistance gains haven't been lost to weight and aero drag. However...

Most of the tires I see tested at the 25mm size actually plump up to 27-28mm, ESPECIALLY on the new wider rim standards that are in vogue. (My Michelin Pro4 Endurance tires plump up to just shy of 29mm on Pacenti Forza rims.) So does that mean that 28mm MEASURED is truly the sweet spot? Particularly since most are now being ridden/tested on internal 18-ish, external 23-24mm rims? Or if measured 25mm is the sweet spot, at a particular rim width in numerous tires wouldn't that make labelled 23mm actually the best performer?

And while tire measurements have long been problematic, it seems even more so now with the wide rim trend. If wide rims are the rule, and if all 25s balloon to 27-28, then do current measurement standards have any meaning? (I believe current standards are on a "classic", narrower, internal width of closer to 15mm).

These are the thoughts that occasionally spin through my head while out for a solo afternoon ride.
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Old 08-19-19, 10:35 PM
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I didnt realize 25mm is the accepted wisdom for ideal width.
But I dont really buy into wind resistance for 3mm of tire width being what's keeping me back from riding faster.


What runs thru the mind on long solo rides certainly can be seemingly random.
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Old 08-19-19, 10:37 PM
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Unless you're on aero wheels, it doesn't make a difference.
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Old 08-19-19, 10:44 PM
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I would be surprised if what you referring to wasn’t taken into account. Seems to me, to test the aerodynamics of the tire, they mounted it on a wheel. It would make sense that used several different kinds of wheels.
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Old 08-20-19, 06:35 AM
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Given the number of variables involved, road conditions, rim width and type, weight of the rider, type of riding, etc, defining a so-called "sweet spot" is simply impossible. I arrived at mine through trial and error. And I'm very content with my choice, 700 x 25 tires. Yes, they plump up a little, but not too bad. Also, I'm 175 pounds so I tend to run higher pressures than the waifs who race.

FWIW, I never considered aerodynamics when choosing a tire. I'm not fast enough for that to be a concern.
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Old 08-20-19, 07:07 AM
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Tire choice is not a huge investment. buy one size, ride it and if you want to try a different size, spend the $100 for them. That's less than a half way decent jersey.
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Old 08-20-19, 09:00 AM
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Originally Posted by GlennR View Post
Tire choice is not a huge investment. buy one size, ride it and if you want to try a different size, spend the $100 for them. That's less than a half way decent jersey.
Or its twice the cost of a perfectly fine jersey.

So its apparently...
crap jersey for $30 --> perfectly fine jersey for $50 --> halfway decent jersey for $100 --> decent jersey for $200 --> nice jersey for $250 or more

I look forward to the day I can own a decent jersey.
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Old 08-20-19, 09:03 AM
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Originally Posted by mstateglfr View Post
Or its twice the cost of a perfectly fine jersey.

So its apparently...
crap jersey for $30 --> perfectly fine jersey for $50 --> halfway decent jersey for $100 --> decent jersey for $200 --> nice jersey for $250 or more

I look forward to the day I can own a decent jersey.
Or 10x the cost of a tee shirt.

But thanks for not staying on topic.
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Old 08-20-19, 09:20 AM
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Originally Posted by GlennR View Post
Or 10x the cost of a tee shirt.

But thanks for not staying on topic.
re straying off topic- Im not the one comparing tires to jerseys, but regardless- its what I do best. I thought about converting tire cost to socks, but then I decided not to since I wasnt sure if I should use 'decent' or only 'halfway decent' socks in the conversion.

I did find it funny that you think a decent jersey costs $200, but $100 is more than enough to get tires. I would figure someone that views $200 as the threshold for decent jerseys would spend more on tires. But it appears you found the value point on tires, so you are halfway there!
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Old 08-20-19, 09:25 AM
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Originally Posted by mstateglfr View Post
I did find it funny that you think a decent jersey costs $200, but $100 is more than enough to get tires. I would figure someone that views $200 as the threshold for decent jerseys would spend more on tires. But it appears you found the value point on tires, so you are halfway there!
You didn't read his post correctly.
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Old 08-20-19, 09:30 AM
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I’m not having any issues with choosing a tire, or something like that.

I was just pedaling along, thinking about how the numbers are more meaningless than ever. And hence, how meaningless the articles that say 25mm is the current “ideal”

It’s post-modern cycling: what does 25mm even mean?
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Old 08-20-19, 10:12 AM
  #12  
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Originally Posted by Banzai View Post
I’m not having any issues with choosing a tire, or something like that.

I was just pedaling along, thinking about how the numbers are more meaningless than ever. And hence, how meaningless the articles that say 25mm is the current “ideal”

It’s post-modern cycling: what does 25mm even mean?
Along these lines, Panaracer recently changed the label on the Gravelking SK tires to more accurately reflect real world sizing. The tire used to be labled 700x40c but they changed the lable to 700x43c because 43 mm was closer to the actual size in most cases.

https://www.panaracer.com/news/detail.php?id=13

Some cried foul, as if they were trying to fool buyers into thinking the tires were wider. Others praised their honesty. Either way, the tire could be anywhere from 41 mm to 46 mm depending on pressure and rim width. How does a manufacturer accurately size a tire given such a wide variety of applications in the field?

Perhaps sizing nowadays is a guideline rather than a statement of fact. Maybe manufacturers should label tires with a nominal measurement and uncertainty such as 700x25c +/- 3 mm. I don't know.


-Tim-

Last edited by TimothyH; 08-20-19 at 10:15 AM.
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Old 08-20-19, 10:36 AM
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Originally Posted by mstateglfr View Post
re straying off topic- Im not the one comparing tires to jerseys, but regardless- its what I do best. I thought about converting tire cost to socks, but then I decided not to since I wasnt sure if I should use 'decent' or only 'halfway decent' socks in the conversion.

I did find it funny that you think a decent jersey costs $200, but $100 is more than enough to get tires. I would figure someone that views $200 as the threshold for decent jerseys would spend more on tires. But it appears you found the value point on tires, so you are halfway there!
Actually my analogy was inflated, most jerseys are in the $80-$100 range with my most expensive being $130 since it was a custom design.

My point was tires are not a major decision, my set of GP4000IIS were $85 for the pair including shipping.

Now that this is cleared up you can go back under the bridge and wait for the next topic to derail.
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Old 08-20-19, 10:40 AM
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My road bike has ENVE SES 3.4 Disc wheels on it. ENVE always said those wheels are optimized for 25mm wide tires. I put 25mm Conti 4000SII's on them and they measured 29mm wide. Fast forward to 2019 and the 25mm Conti 5000 TL which is reputed to be narrower than the 4000. Because of this, I contacted ENVE customer service and asked if the wheels were optimized for the OLD 25mm tires or the NEW (narrower) 25mm tires. Their answer was yes.

I mounted the 5000TL's up on the ENVE's and they measure 27.5mm wide. Slightly narrower than the max outside rim width -- just as ENVE designed them.

So . . . at least for ENVE, they are telling you the wheels are designed for the stated number on side of the tire while knowing (and designing for) the actual width of the tire. Perfect.
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Old 08-20-19, 10:49 AM
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Originally Posted by GlennR View Post
Actually my analogy was inflated, most jerseys are in the $80-$100 range with my most expensive being $130 since it was a custom design.

My point was tires are not a major decision, my set of GP4000IIS were $85 for the pair including shipping.

Now that this is cleared up you can go back under the bridge and wait for the next topic to derail.
This thread is about tire sizes- there is nothing new to say that isnt already been said hundreds of times each month. It takes work to derail a thread like this and Im exhausted. Unfortunately, it stormed last night. HUGE storm. The creek rose quickly and washed me out of my home. I cant go back under the bridge and rest until waters recede.
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Old 08-21-19, 01:19 AM
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Originally Posted by Banzai View Post
I’m not having any issues with choosing a tire, or something like that.

I was just pedaling along, thinking about how the numbers are more meaningless than ever. And hence, how meaningless the articles that say 25mm is the current “ideal”

It’s post-modern cycling: what does 25mm even mean?
If you’re looking for a shred of intellect or inquiry in bike media, you will always be left sorely disappointed. Except maaaybe CyclingTips but I don’t want to sell them too hard.

For tubulars, which pros use, 25mm tires are actually 25mm tires. The bike media made a big deal about pros going from 23mm tubulars to 25mm tubulars but amateurs have gone from actual 23mm tires to 30-32mm measured. My 25mm tire measures around 30mm. Everyone’s sweet spot is different. Mine is on the wider side because I like grip and my bike is uncomfortable and my roads are crap. Someone who is very heavy and tends to pinch tires or break rims may need a bigger tire for the same preferences. Someone riding on flat, glass roads may want a narrower tire. It’s personal, for now. Conditions are too variable and the human body too fickle for science to draw a firm conclusion yet. Maybe one day someone will make something that measures tire compression over the course of your ride and can make a recommendation (I know about the TireWiz, but that only recommends pressure, not size?).

Until very recently, most aero wheels were very narrow. 15-17mm internal widths, and maybe 23-25mm wide. And yet they would say that these rims are optimized for 25mm tires that measure 27mm across. And we all know (now at least) that a bulbous tire is terrible for aero. There was also an incongruence between mfg recommendations and what the ETRTO allowed - 25mm tires weren’t allowed on anything more than 17mm rims - which made it impossible to achieve the 105% ratio. They’ve allegedly updated the list of approved rims widths but they’re dragging their feet for releasing it.

Don’t look to the bike media for any sort of guidance. Don’t even look to bike companies for technical expertise. Someone posted about their experience with ENVE, which pretty much sums up what you can expect from the tier of engineers that end up in the bike industry. There are no standards. There is no integrity. There is no rigor or precision. Find your own truths from your own experiences, or your friends or maybe (gasp) forums.

Last edited by smashndash; 08-21-19 at 01:56 AM.
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Old 08-22-19, 08:57 PM
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Originally Posted by Banzai View Post
Most of the tires I see tested at the 25mm size actually plump up to 27-28mm, ESPECIALLY on the new wider rim standards that are in vogue. (My Michelin Pro4 Endurance tires plump up to just shy of 29mm on Pacenti Forza rims.) So does that mean that 28mm MEASURED is truly the sweet spot?
My 28mm GP5000TL's measure 28.8mm with maybe 0.2mm variation around depending on pattern etc. Same F/R, at 65/75 psi respectively. My rims measure 23.5mm, but that's on the outside (didn't check while mounting the tires, and those SOBs aren't coming off again anytime soon!). All measured using calipers, the tires carefully so as not to compress the rubber. They don't seem particularly plump or balloonish to me... Only slightly wider than the rims.
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Old 08-23-19, 10:31 AM
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All you need to know if your tires are optomized for the rim is does the tire overlap the rim. If that little 3mm wider overlaps the wheel you will trip the wind and lose value of those deep wheels. Weight of the rider and road surface will factor into the width of the wheels and tires.
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Old 08-23-19, 11:10 AM
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Originally Posted by Banzai View Post
I know it's been hashed out before, but it still drives me bonkers.

The accepted wisdom anymore seems to be that 25mm is the "sweet spot" for performance, the place where rolling resistance gains haven't been lost to weight and aero drag. However...

Most of the tires I see tested at the 25mm size actually plump up to 27-28mm, ESPECIALLY on the new wider rim standards that are in vogue. (My Michelin Pro4 Endurance tires plump up to just shy of 29mm on Pacenti Forza rims.) So does that mean that 28mm MEASURED is truly the sweet spot? Particularly since most are now being ridden/tested on internal 18-ish, external 23-24mm rims? Or if measured 25mm is the sweet spot, at a particular rim width in numerous tires wouldn't that make labelled 23mm actually the best performer?

And while tire measurements have long been problematic, it seems even more so now with the wide rim trend. If wide rims are the rule, and if all 25s balloon to 27-28, then do current measurement standards have any meaning? (I believe current standards are on a "classic", narrower, internal width of closer to 15mm).

These are the thoughts that occasionally spin through my head while out for a solo afternoon ride.
I am interested in using these same tires on my stock Trek Emonda SL 5. Is there enough clearance to run them?
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Old 08-28-19, 03:36 PM
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"Measurebation"
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Old 08-31-19, 11:26 AM
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Quantitative reasoning
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Old 08-31-19, 02:10 PM
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If you're obsessed with aero, the mounted width of the tire should be the same as the external width of the deep section wheel.

If you're obsessed with comfort, the tire should be the widest one that will fit on the bike.

Everything else is a compromise in one direction or the other.
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Old 08-31-19, 07:08 PM
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I had been riding 25's until I got my Forza rims.
Now I am back on 23's which "plump out" to about the same size as the 25's I was previously using.
25's are still better on my older model Open Pro's.
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Old 08-31-19, 08:56 PM
  #24  
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Oh yeah - I saw some news about the new Schwalbe Pro One souplesse tubeless tires, and the OPs question was directly addressed: with these new tires, Schwalbe's nominal sizes accurately reflect width when mounted on 19mm internal width rims.
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