strayduck

Last year I switched from 23mm tires on box rims to some 25mm Continental 5000s on some 2019 Zipp 303 rims and enjoyed the added comfort but ended up with a few pinch flats that I didn't love. So I thought, why not keep going and throw some 28mm on? So I bought some and they measure almost identically to the 25s using my Park Tools DC-1!

25mm tire: 27.7mm wide
28mm tire: 28.01mm wide

As for the height, it was kind of hard to measure the inflated height of the tire alone so I used the clamp to measure from the inside of the rim to the top of the tire:

25mm tire: 70.74mm
28mm tire: 69.72mm

Has anyone else experienced this?

If I'm aiming for optimum tire pressure using https://axs.sram.com/guides/tire/pressure it looks like I'm using the same calculation for both, which just doesn't seem right.

biker128pedal

The Conti tires seem like they are sized for narrower rims. I upgraded to Bontrager carbon wheels and drove me crazy.
Tire Pressure Width Rim (mm)
Conti 5000 23mm 100 psi 27.64 mm 19
Conti 4000 23mm 115 psi 26.9 mm 19
Conti 4000 25mm 105 psi 27.99 mm 19
Conti 5000 25 mm 115 psi 25.63 mm 14
Conti 5000 23 mm 14
Conti 5000 23 mm 112 psi 25.64 mm 19

Iride01 

The ISO/ETRTO sizing isn't about external width of the tire. It doesn't take into account the thickness of the material on the tire casing.

The tire casing is the actual structural part of the tire that the ISO size is measuring for width. It's also not required that they hold to the level of tolerance you appear to desire.

Koyote

Nothing abnormal about this. Actual width is dependent on numerous factors, including manufacturing tolerances.

I run WTB Resolutes on one of my bikes, and they have a stated width of 42mm. On my rims, which are actually on the narrow side (19.5mm ID) for such tires, they come out to about 44.25mm wide.

Wildwood 

Pinch flats? Better air-up, especially on carbon rims.

There are variables to consider even on the same rim - tire pressure, age/mileage of the tire, accuracy of the measurement.

But to answer the question succinctly = Yes, I have measured tires ~2mm off from the manufacturer's stated width.
The only time it was a concerning issue was when I was trying to fit too fat a tire under a brake, or when it might rub a chainstay.
Why won't this tire fit?!? I really need this tire to fit !! I want this this fit - now. Stupid tire! Stupid manufacturer!

Vittoria Rally used to be a bad offender, years ago (better now, I think). Lumpy tires would measure 23mm in one spot, spin the tire get 24+mm in a different spot. But they were cheap, with a nice damping cotton casing.

surak

I don't have a caliper but secondhand I've read that the tires will get a bigger over time. You are presumably comparing used 25mm to brand-new 28mm.

jadocs

Dang your 28 mm tire is narrower than my 25 mm.

My Master Olympic has Reynolds AR58 (19mm ID) and the 25mm Schwalbes measure 27.9 mm wide on the rim.

WhyFi

Are you sure that the 25s are GP5k and not GP4kII?

In general, the latest generation of tires are narrower, and running truer to nominal size when mounted to rims with internal widths in the 19mm range. The net result is that you'll see a lot of current gen tires at about the same measured size as a previous gen tire that was one nominal size smaller.

mstateglfr 

Its basically the same width, so at this point just add more pressure to not pinch flat.

strayduck

Lots to respond to here. Sounds like a variation of a couple of millimeters from tire to tire is not out of the ordinary. Wildwood I had the same problem on my old Merlin, except that it was a width problem rather than a height problem; the chainstays were set up with so little clearance that a "23mm" pair of Conti 4-seasons rubbed a nice polish into their inner surface on their first ride! After noticing the problem I measured the tires and they were 25mm. Now that I write that out I guess this isn't the first time I have run into this kind of problem!

Answers to questions above:

Yes, they are definitely Grand Prix 5000s and not 4000s IIs

Yes, I am comparing new 28mm 5000s measurements to 1-year-old 25mm 5000s

I could add more pressure but was already running the 25mm tires at 80psi front / 85psi rear. According to SRAM this is already 5psi above their recommendation for my weight. They didn't feel particularly squishy. The rims can handle greater pressure so I could add a little more and see how things go.

I had kind of expected that I'd get a little more volume with the 28's but the fact that the height measures the same as the 25's means that this isn't the case. equal height and width would be the same volume which means the same pressure requirements.

Hiro11

Totally normal: the dimensions printed on the sidewall are only directional as true measured width can vary widely based on the specific manufacturer and on the specific rim you're using. I just went down to my bike room and used some calipers on a couple of bikes:

Wheel 1: Rim: Enve SES 4.5AR Tire: Panaracer Gravelking slick, nominally 32mm and mounted tubeless at 41psi. Measured width: 34.45mm
Wheel 2: Rim: Giant SLR-1 Tire Continental GP5000TL, nominally 28mm and mounted tubeless at 76 psi. Measured width: 27.97mm

The Giant rim has hooked bead seats with an ETRTO nominal width of 17mm, which is pretty average for what people commonly use. As a result, the measured width is damned close to the nominal width.
The Enve rim has hookless bead seats and an ETRTO nominal width of 25mm, which is fairly massive compared to most road rims. Also, the hookless configuration allows the tire to bulge out even wider. The result is the measured width of the tire is a lot wider than the nominal width even at pretty low pressures.

This is just two examples, on most of my bikes including road bikes, gravel bikes, mountain bikes and a fatbike the measured width varies a bit from the nominal width.

skidder

Also consider the width of the rim. You've got two different ones there, I'll bet they are not the same width where the tire mounts, so that can cause some variation on ho the tire sits on it. Biggest issues are trying to use tires that are small or too large for your rims - both can cause problems. If it looks like the tires are seating properly on the rims (it appears both are in your photos) I wouldn't worry about them if the ride is comfortable.

And yes, I've seen variations where one manufacturer's 28mm tire is as big as another manufacturer's 25mm tire (both worked fine). Me, I use 28s or 32s on my bicycles (35s on my tourer), mainly for the comfort vs a 23mm tire.

79pmooney

Are those the same width rims? (What matters is the inside width of the flanges. Measure that; like the tires, don't rely on the published numbers.)

Flip Flop Rider

slap some 32's on there

Flip Flop Rider

believe this, the getting bigger over time for sure

aclinjury

is Zipp still making dimples as if they have a real effect?

Sy Reene

Nice data, but pretty irrelevant. If I'm reading OP correctly, he has 2 of the same model tires, in 2 different sizes, from the same manufacturer, measured on the same rim. So, I'd say no, this isn't normal (or at least it shouldn't be)

I think it's the same rim, he just thought he'd try a wider tire.

mstateglfr 

wat

This is the same rim and same model tire, just a different size. That should eliminate any of the variation you associate to different tire brands and rim profiles.
As a consumer, I expect a 28mm tire to be about 3mm wider than a 25mm tire that is the exact same brand and model when mounted on the same rim.

That's a bare minimum expectation, really.

Hiro11

I feel like the guy in Office Space being reminded of TPS report cover sheets. Got the memo, guys.

WhyFi

Did you see the part where the tires are from the same manufacturer, difference sizes of the same model, and on the same rim?

Branko D

​​​​It’s probably an effect of the rim width being well beyond etrto standards as they are for pairing a rim with a 25mm tire, making the 25mm really very wide on them.
​​​​
​​​You can't blame it on the tire manufacturer that the sizing doesn't work as intended in this case.
​​​​​​

jay4usc

i think it’s the width of your rims. Check out the link below, it compares different size GP5ks and it includes its width measurement

https://www.bicyclerollingresistance...000-comparison

md11mx

This is why I always review the customer comments before I purchase products. It has saved me from numerous headaches.

Wildwood 

This is one reason to have numerous bikes - to put racing tires on race type bikes, and city tires on bikes with city tire clearances and mountain bikes with mushy tire clearances.

Variety is my spice.




Clear your handlebars and your mind will follow....

mstateglfr 

Hey OP- this kinda sorta happened to me last night.

I have some 28mm GravelKing slicks that measure out to 29.11mm on H+son Archetype rims at 75psi.
I just put some 32mm GravelKing Slicks on other Archetype rims and they measure 30.18mm at 75psi.

The 28 are black wall and the 32 are tan wall, but its the exact same tire model.
Maybe the 32s will expand a bit. Whats funny is that they replace some Conti GP4k 28mm that measured to 31.44mm on the Archetype rims. So I currently have a 32mm tire on there that is 1.3mm narrower than the old 28mm tires that were on there.


Oh well.