I’ve purchased three sets of 28mm Conti 5000’s. Measured with Calipers, in order of use, they came in at:
30.5mm/31mm
29mm/28.3mm
27.8mm/27.3mm
Based on the Silca Tyre Pressure Calculator the exact same tyre, pending on batch has a 17psi delta. (31mm vs 27mm).
All same size rim? Tubes? Tubeless? I’m building up a new roadie and waiting on some 25mm GP5000 tubeless tyres to show up in the mail. Hoping they dont bulge out too far on my wheels for that supposed aero gain.
Manufacturing quality control for the win!
Identical. Same bike same wheels same tubes same tyres. Just different batches.
I’m starting to wonder if I should go to 30mm. Also makes me wonder what it’s like for those who don’t adjust their tyre pressure based on measured with.
What’s your inner rim? I’ve put Conti 5k on 21mm internal and it’s been (mostly) true to size. On 25mm internal I’d expect them to expand.
I thought it was 21mm not sure. They’re the DT swiss wheels that come stock with the 21’ canyon Endurace. I tried looking it up but couldn’t find it.
Either way all six tyres went on the Same rims
If they’re the tube type, they changed the size to more accurately reflect the rims people were using - the old ‘28’ which may have measured 28 on 13mm internal rims came out as closer to 32 so they sized them down a bit. They may explain some of it…
Now I’m wondering which is faster. I imagine the older set would have been more comfortable and grippier will see what this set is like v either way I’d feel better if they measured 28 and not 27.3.
I have the same bike. The stock wheels are 20mm internal width.
I mounted a set just yesterday and i received a new caliper for Christmas so I may as well add a data point even though I’m not to fussed about a mm or psi here or there.
24mm internal. Challenge latex tubes. 75psi. 29.08/29.28
I agree with 1-2 psi but 14 is pretty extreme.
For some. Ha. It’s not ideal, of course, but I’m from the days of pumping tires up to the max on the sidewall and then a few PSI for good measure. Even 17 won’t bother me much.
I wouldn’t know the difference if I hadn’t read this thread and decided to measure. 
I know others are far more particular than me.
As my wife would say, as she’s making fun of me;
What about the watts bro? What about the watts??? 
Got one a couple years ago. I use it all the time. Pretty useful for the bike tool kit but also entertaining.
Right up there with my Infrared Laser Thermometer in terms of actual need vs taking random unnecessary measurements 
28mm gp5k str on zipp 303s caliper out to 29.7 on the set I have! (Tubeless)
28mm regular gp5k on the dt Swiss arc wheels from my aeroad are like 28.1. (Tubes)
I was concerned the almost 30s wouldn’t fit the aeroad. Surprisingly, there’s plenty of room to spare!
Which year is your aeroad?
19
Holy crap! I’ve been running a pair of 28mm GP5000 clinchers purchased in Sept. 2000 and they measure about 30.5mm wide on Hed Belgium Plus rims which are 21mm internal.
I recently replaced one of the tires with another 28mm GP5000 clincher purchased in May 2021 and it measures 28.7mm. Manufacturing tolerance or change in construction? I’m aware there was a big change in labeled vs measured width from the GP4000S II as the 28mm size of that model measured over 32mm on these same rims.
All measurements taken with my super precise and highly accurate $10 Harbor Freight digital caliper.
These are non-round tires, so the tire will change shape with breakin and pressure.
They probably have different molds, but I’d wager the tire isn’t sitting on the rim right. Are these measurement after a ride? Are these all the same edition (TR, TT, plain)?
Maybe measure the casing width I mounted. Continental Grand Prix 5000 S TR 28 Rolling Resistance Review