New tire rolling resistance test - 23mm, 25mm, 28mm & 32mm GP5000 tires

[sfo1]

so how does one calculate their optimal tire size for their rim ID/OD?

Suppose you use a 25mm GP5000 tubeless with a rim that has 19mm ID and a 28.4mm OD? Would that create a 'u shape' or an 'o shape?'

Would a rim with 17id - 25od be better since its narrower and the od is 25mm?

I guess the q becomes for a 25mm GP5000 tubeless, what is the optimal rim ID/OD for fast & versatile?

Originally Posted by joshatsilca

We have data on this in our Tires and Aero Blog post: https://blog.silca.cc/part-5-tire-pr...d-aerodynamics

You are correct, that next to having the proper size tire for your rims, replacing them as soon as they begin to show wear makes a very big difference!!

[joshatsilca]

Originally Posted by sfo1

so how does one calculate their optimal tire size for their rim ID/OD?

Suppose you use a 25mm GP5000 tubeless with a rim that has 19mm ID and a 28.4mm OD? Would that create a 'u shape' or an 'o shape?'

Would a rim with 17id - 25od be better since its narrower and the od is 25mm?

I guess the q becomes for a 25mm GP5000 tubeless, what is the optimal rim ID/OD for fast & versatile?

Excellent question!! There is a core problem in the industry now that there aren't really standards for those sidewall sizes of tires... so traditionally the size was outer casing width when installed on a 13 or 15c rim.. there was even a movement a while back to use a special tool and naming system to fix this and sadly it died out! Leaving us with different manufacturers doing all sorts of different things.

We have a graph of measured sizes on our site so you can see an example of the trends, but with each new tire size and each new rim inner width it just gets worse. Technically, there is a thing called the ETRTO which is now part of ISO that controls this but it was safety based and people have completely abandoned it.. by ETRTO, the widest rim you could use for 23mm tires is 17c and things like that.

Here is our data set with various size GP4000 on various rim sizes:
https://blog.silca.cc/tire-size-pres...-we-got-to-now

For aerodynamics the key is for the rim to be at least 105% the measured tire with.. this rule is pretty old, I coined it in 2000 when rim shapes were much simpler, but still holds true in nearly every example I can think of..

As for U vs O shaped tires, the wider the bead seat the more U shaped the tire can be, however, the greater the risk of tire blowoff as the bead width grows, so ETRTO says that anything wider than 17C is a risk, some manufacturers say 19.5mm is the limit and others don't say anything, but I've personally seen 23mm tires come off of 21mm bead width rims on more than 1 occasion so it's helpful to understand the risks and limits.

[sfo1]

So (for aero) on a 25mm tire the wheel OD should be at least 26.25?

On the ID (again assuming 25mm), a 19mm should be a max “safe” width?

Not a lawyer nor looking for any certainty (but I did just finish a fine Manhattan), but I am in the middle of a build and have not finalized wheels. I ride 25mm GP5000 tubeless and was narrowing my search.

Any swag at min/max ID/OD for these tires on a disc road machine?

[El Chaba]

Originally Posted by Mark McM

My observations have led to a different conclusion. Decades ago, most people rode wider tires than often seen today - 1" (25mm) tires were uncommonly narrow, and most people rode tires between 1 1/8" (28mm) and 1 3/8" (35mm) wide (these were the days before Kevlar bead tires and hooked rims). Pressures were typically in the 70 - 90 psi range.

Then, starting in the early '80s, people started believing that narrow, high pressure tires must be faster, and tires and rims capable of handling high pressures started being made. During the time that frame tubes started growing in size/diameter, typical tire widths started shrinking and tire pressures increasing - 23mm tires became common, and many were even riding 20mm tires, at pressures up to 120 psi or more.

The move toward wider tires today isn't to mitigate the extra stiffness of modern frames (even the old frames from yesteryear had too much vertical stiffness to provide much shock absorption) - its to mitigate the ridiculously high pressures that people been using during the last few decades.

This was the trend. Tubulars can't be removed from the equation, though. until the late 70's there was no performance tire alternative to tubulars. At that time, racing tires had narrowed slightly, but the top racing tires from Wolber, Clement, d'Allesandro, etc. were in the 23-25 mm range. There was a desire to make the clinchers *look* like the tubulars and to approach their performance as much as possible. A big problem was getting the tire to stay on the rim at the pressures that would be required for a narrow tire. Michelin was the major player and worked (primarily) with rim makers Mavic, Super Champion, Rigida, etc to develop hook beaded rims. Michelin heavily marketed their "Elan" model which looked incredibly narrow at the time. When the "aero" craze hit in the early 80's it was game over for wider tires.

[dddd]

It seems to me that the narrow tires and rims of the 70's and 80's made more sense in the context of that era's aluminum rim technology, when having a wider rim and/or tire came with a pronounced weight and/or aero penalty.

When the Open Pro rim finally arrived in the 90's, with it's wider 15mm inside width, an equillibrium of tire and rim sizes seemed to sensibly land at 23mm tire size on these wider (yet still lightweight and strong) rims.

For riders whose speed averages below the CAT1 level, 25mm tires on the i15mm rims was and is still a great setup and fits nearly all frames ever made.
The 25mm tire size allows some manipulation of tire pressure without undue risk of pinch-flatting in most cases.

It is only with the latest rim technologies (both metal and composite) that wider tires make sense in the realm of racing performance on paved roads, with budget concerns limiting choices in a lot of cases. So it's become a very complex combination of needs evaluation combined with smart shopping and keeping abreast of the various performance parameters of what is on the market (all at any point in time).

[hobbanero]

Josh's posts on suspension losses are really interesting, and point towards a lower pressure for overall speed. This test uses a diamond plate roller, rather than a smooth one, to try and capture some of the suspension benefit.

[HTupolev]

Originally Posted by dddd

It seems to me that the narrow tires and rims of the 70's and 80's made more sense in the context of that era's aluminum rim technology, when having a wider rim and/or tire came with a pronounced weight and/or aero penalty.

When the Open Pro rim finally arrived in the 90's, with it's wider 15mm inside width, an equillibrium of tire and rim sizes seemed to sensibly land at 23mm tire size on these wider (yet still lightweight and strong) rims.

The 70s weren't an era of super-narrow rims and tires. Most high-performance road bikes came stock with tubulars in the ~25mm range, while the more entry-level clincher-equipped bikes tended to have 28s or 32s. Hooked-bead 700c and 27" clincher road rims from the late 70s and early 80s usually had inner widths in the ballpark of 17mm.
This didn't carry a serious weight penalty, as quality single-walls rims could actually be reasonably light; the original 17mm-internal rims on my 70s touring bike are only a few tens of grams heavier than an Open Pro, and they're hardly a weight-weenie part.
And while aerodynamic drag will tend to be higher for a wider tire, that's not necessarily true of wider rims. It's often quite the opposite, which is why modern aero rims are often as wide or wider than their intended tires. Also, rim aero wasn't something that anyone was paying attention to in the 1970s.

Tire widths took a very sharp nosedive in the mid-to-late 1980s.

[dddd]

Originally Posted by HTupolev

The 70s weren't an era of super-narrow rims and tires. Most high-performance road bikes came stock with tubulars in the ~25mm range, while the more entry-level clincher-equipped bikes tended to have 28s or 32s. Hooked-bead 700c and 27" clincher road rims from the late 70s and early 80s usually had inner widths in the ballpark of 17mm.
This didn't carry a serious weight penalty, as quality single-walls rims could actually be reasonably light; the original 17mm-internal rims on my 70s touring bike are only a few tens of grams heavier than an Open Pro, and they're hardly a weight-weenie part.
And while aerodynamic drag will tend to be higher for a wider tire, that's not necessarily true of wider rims. It's often quite the opposite, which is why modern aero rims are often as wide or wider than their intended tires. Also, rim aero wasn't something that anyone was paying attention to in the 1970s.

Tire widths took a very sharp nosedive in the mid-to-late 1980s.

Peugeot and some others were fitting 20mm 700c clinchers to bikes in the late 1970's, though racers still mostly used tubulars for all but perhaps training miles.

I didn't really notice when clinchers started to be used for racing (I was into motorcycle racing then mountain bikes during those years), but as the narrow clincher tires got better and rims like the O4CD became available, they became more viable for a lot of sporting use if not high-level racing.
Using a pair of Mod58 Singlewall clincher rims as opposed to the typically i13mm narrow clincher rims had enough of a weight penalty to be noticed, and the aerodynamics would have suffered as well. By the mid-80's those rims had a minimum of 36 spokes in nearly all cases (versus 32h for the narrow double-walled rims). I actually used Mod58 touring rims for training rides with a variety of tires from 20mm to 25mm (printed size on those was 25 or 28mm respectively).
I was light enough not to notice any flex with the Mod58's, but the wheels felt quite heavy versus any O4CD wheelset.

Prior to the Open Pro rim with it's 15mm inside width, the 13mm inside width was a wide as anyone seemingly knew how to make for sporting use at modest weight and with good durability! So these i13mm rims made perfect sense for the 23mm tires that were becoming the standard heading into the 90's (riders finally having decided that 23mm tires were better overall than 20mm tires).
It did seem to be the case in the early 90's that a slightly wider pair of tires added far less weight than a slightly wider pair of rims, that is until the wider Open Pro rim appeared (replacing the i13mm Reflex rim).

So to me, it all made sense in evolutionary terms, other than perhaps the ten years it seemed to take for riders to start using 25mm tires on those ubiquitous Open Pro rims! But as for the 20mm tires, their only net virtue was that they kinda looked like tubular racing tires and so had marketing value.

Editing here to note that tires labeled as 25mm or 28mm in the late 1970's and into the eighties were actually several millimeters narrower than that.
In that era of seemingly weird sizing "standards", tires labeled as 700x25c often also carried embossed lettering showing "20-622".
Similarly, even in the early 90's, a tire labeled as 700x32 might have embossed lettering showing 26-622, and which measured about 26mm wide on an i15mm rim.
So the later "20mm" tires were sized the same as many earlier "25mm" tires, and which I find typically measure about 21mm on period narrow rims.
And those older "28mm" tires typically measured barely 24mm on narrow rims. A lot of Specialized tires come to mind from that era, because they were so popular, but others followed suit. It wasn't until the 23mm size arrived that printed tire width was, suddenly, in the ballpark.

[froze]

Originally Posted by m_sasso

Now they need to combine wind resistance in these tests to get a partial picture of real world performance!

EXACTLY!!! some years ago I saw a wind tunnel test done, I think it was the reason Conti came out with the Attack line of tires, where a 23mm tire was used on the front and a 25 on the rear, and the test discovered that the combination was a tiny bit faster...HOWEVER, that stupid test didn't take load conditions into consideration. Seems like everyone wants to test for one or the other but not both at the same time! I still use a 23mm tire on the front and a 25 on the rear because of that test I read, I just don't use Conti tires, also not saying I'm right, I do it because both tires wear out at about the same time and I don't have to bother with rotating my tires! But I think if they're going to do tests like this they need to add on the effects of wind.

[dddd]

Originally Posted by froze

EXACTLY!!! some years ago I saw a wind tunnel test done, I think it was the reason Conti came out with the Attack line of tires, where a 23mm tire was used on the front and a 25 on the rear, and the test discovered that the combination was a tiny bit faster...HOWEVER, that stupid test didn't take load conditions into consideration. Seems like everyone wants to test for one or the other but not both at the same time! I still use a 23mm tire on the front and a 25 on the rear because of that test I read, I just don't use Conti tires, also not saying I'm right, I do it because both tires wear out at about the same time and I don't have to bother with rotating my tires! But I think if they're going to do tests like this they need to add on the effects of wind.

Good points, I remember those mis-matched Conti's being 22mm and 24mm front and rear.

But it is incredibly difficult to accumulate "combined effects" data over the varying conditions of roads and wind conditions.
Different riders have different drafting habits, and regional riding conditions are hugely variable in terms of pavement conditions, speed variations and wind conditions, not to mention that, for testing, a single rim and tire have to be chosen for each test!
If we were to be very sophisticated about all this, then likely the results would point to completely different front and rear rims and tires being used on the same bike at the same time, just to be optimized for some specific set of riding conditions and for a specific rider.

I can imagine a future bike computer or app that evaluates the rider's riding conditions over time (including speed, grade, wind vectors and vibrations), accumulates the data, then refers to a database of tire and wheel parameters to suggest an optimal pairing of wheels, tires and pressures.
And while we're at it, the same computer might be logging data on all of the rider's blood chemistry and vital signs parameters over the course of the ride, to be evaluated by yet another computer algorithm which makes suggestions in real time.

[19wisconsin64]

These tires were supposed to be my secret speed weapon this season, but thanks to the original poster I'll just have to train harder like everyone else. No really..... I was really counting on those watts.

Fixed gear, 25 mm, tubeless GP 5000 installed on wider clincher carbon aero rims. It will be interesting to see how these will compare to my old and fast carbon fiber tubular Easton TKO wheelset at the track that ran with 25 mm Continental Competition tires.

The new rims i purchased have an inner width of approx. 20-21 mm. The velodrome the wheels will mostly be ridden on is located in Queens, New York City - the much loved but much in need of re-surfacing Kissena Velodrome. The track is so bumpy that at high speeds regular high pressure tires bounce and skittle along the track in some places. Hopefully this new setup will be easier to push along at higher speeds. My road bikes now have wider rims, the HED Belgium plus, and with a 25-28 mm tire boy do these wider tires make a difference in speed!

[sfo1]

Seems wide road now starts at ~20mm inner.

Originally Posted by 19wisconsin64

Fixed gear, 25 mm, tubeless GP 5000 installed on wider clincher carbon aero rims.

[robertbb]

Originally Posted by joshatsilca

robertbb, thanks for the comment and thanks for giving me a great opportunity to plug some SILCA pumps with super accurate gauges!! In all seriousness though it was the last 10+ years of doing this that inspired us to make super accurate gauge pumps, and if you read our Road to Roubaix Blog story you'll see that we considered this secret so secret that I travelled around Europe with a $1000 gauge for a few years in a pelican handgun case and we only used it out of site of other teams and the media.. Now we make a handful of pumps with specially tuned digital sensors to achieve 0.5psi accuracy at these types of pressures which are used by more teams than those we 'officially' work with.

As for latex, look at the modern latex, we sell tubes made by Vittoria which have a new formula with graphene in them and leak so much slower than the old ones. When we plotted Cancellara's roubaix run in 2010, we measured his tires to have nearly 1psi per hour loss.. so we tuned pressures so they would be perfect a few hours into the race when he was on the worst cobbles.. The new generation of latex tubes might lose 4-5psi per 24 hours, and will save you 2-5 watts per tire which is a bigger savings than a full ceramic bearing upgrade for about 1/50th the price!!

The very first floor pump I ever bought when I first started cycling about 15 years ago is a Silca Pista floor pump from a shop that was closing down here in Melbourne. Paid AU$90... I still use it today... quality stuff! Not sure I can justify a new pump.

But I am curious to give those latex tubes a go. Which ones are they exactly? And how do they go with carbon rims... (Campagnolo Bora)?

[jpritchet74]

Originally Posted by robertbb

But I am curious to give those latex tubes a go. Which ones are they exactly? And how do they go with carbon rims... (Campagnolo Bora)?

If you do long twisty descents that require heavy braking then don't do it. The rims can heat up and cause the tubes to POP. Otherwise do it. I use latex with my carbon clinchers and don't worry about it at all because I never ride where I would have a long twisty descent that would require heavy braking, so my rims don't get hot.

[froze]

Originally Posted by robertbb

The very first floor pump I ever bought when I first started cycling about 15 years ago is a Silca Pista floor pump from a shop that was closing down here in Melbourne. Paid AU$90... I still use it today... quality stuff! Not sure I can justify a new pump.

But I am curious to give those latex tubes a go. Which ones are they exactly? And how do they go with carbon rims... (Campagnolo Bora)?

I have a 40 some odd year old Silca that needs to be rebuilt completely but the cost to rebuild (kit was $68 if I remember correctly) it exceeded just buying another pump, so i opted to get a Birzman Maha Apogee IV floor pump instead that I got on sale for $30.

I can't find those new Vittoria latex tubes, all the ones I see for sale in the US appear to be the old latex tubes that will leak air out fast, no mention of a new formula to prevent that anywhere on the boxes or description, so not sure if the new latex tubes Vittoria simply didn't mention the fact on the boxes or if the new ones just haven't made it to market yet.