I just bought a set of 28mm Conti GP5000s to put on my Wheelworks Maker wheelset which has an internal width that measures 19.5mm. I expected them to measure about 30mm, but they are only measuring 27mm, which is the same width my 25mm Schwalbe Ones measured when fitted. This makes no sense. Anyone else had this issue? Could they be 25s mistakenly labelled as 28s?
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When continental went from 4000s to 5000s they went from designing around a 15-17 mm rim to a 20-21 mm rim as wheels have got wider. Schwalbe may still be assuming a narrow rim. (I have 25 mm pro ones which measure 28 mm on 19 mm internal rims)
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I wish they’d all keep to a standard! I’ve found some info on the Continental website. It seems to suggest that they use different width “measuring rims” and for different tyre sizes, but it’s unclear. 
They say their measurung rim for 28s is a 19 mm internal width. So, they should measure 28mm on my 19mm wide rim, but they don’t.
I think you need to have an inner rim width of about 25mm for those tires to plump up to 30mm. I have GP500 STRs in 28mm on Enve SES 4.5s (25mm internal width) and they measure right at 30mm.
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In all the info on their website, Conti only provide two examples explaining tyre width in relation to rim width. They explain that they use a “measuring rim” that seems to vary in width depending on the size of the tyre.
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Yes, I’ve read all the ETRTO stuff. This is only concerned with recommended tyre width/rim width combinations with regard to safe usage. They say nothing about how tyre widths vary with rim width.
I’ve had GP5000s vary by a millimeter or so between batches. Mounting 32’s on 25mm IW rims have measured 33mm and 34mm for tyres purchased months apart.
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I found a drop in width going from GP 4000 to 5000 on same rim ( int width 22 November RCG) . Searched on forums and it seemed that was the prevailing experience.
The 4000 measured 30-32 and the 5000 measures 28. I have just gone tubeless 30 so will measure up to see what they are.
I have the maker Disc V1 2015 with a panaracer SS 28 at the moment but will likely go back to Conti so will be interesting to see what the 5000 sits at on a 19.5 internal rim . Wheelworks said that rim was at the time designed to take 23-40 . I have used as road and gravel ( widest 38/35 limited by bike clearance ). Running tubed currently . Tempted to run tubeless.
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I also have the V1 ENVE SES 3.4 with a 25 on them .. I’m going to do some measuring! Just for interest., SES were also wide for their time ( 19mm internal on the 30 mm deep , 16mm on the 40mm partner )
28 sat just tad too wide for a circa 2010 carbon road bike
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Yes, it seems they changed their “measuring rim” size when the 5000 came in. I was going to get the 30s, which will probably measure about 29 on my wheels (I’m interested to know how they fit yours), but apparently that size of the regular GP5000 has a slightly different construction to enable safe ebike usage. They’ve sacrificed slightly higher rolling resistance for slightly better wet weather grip. Not sure how different that would feel in real world use. I can’t go to 32s because my brakes probably wouldn’t fit over them.
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Does it clear your frame and brakes? Yes? Then relax, stop measuring things and go for a ride.
Every tire and manu measures out slightly different then whats stated on the casing. As long as it fits the rim and frame, just go out and ride.
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Not helpful. I’ve just spent a fair bit of money on wheels and tyres to get wider (within the confines of rim brakes) and to improve comfort and ride quality. The $180 I spent on new supposedly wider tyres is completely wasted if I use them as those tyres turned out to be no wider than the ones I already have. Thankfully the shop let me return them. So, now I’m just trying to figure out how to achieve the size that I want. I have other wheels tyres to ride in the meantime. I don’t know about you, but I don’t have money to burn, and I like to get what I want when I spend it.
There is a section on design rim widths for given nominal tyre widths in ISO 5775-1. A 25 and a 28 share a 19 mm design rim. Normally I’d say we can only expect a tyre to match its nominal width IF it is mounted to a rim matching its design rim… but your experience is that both nominal sizes don’t line up even though your rim is very close to the design rim for both.
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what age/generation are the Schwalbes?
Agreed that it would be nice for Continental to publish more of a range of “expected tire width when inflated on X internal width rim” but, well, they seem to show no interest beyond what you’ve found.
Ronan’s post is quite helpful here, in general.
FWIW: I have 28mm Conti 5000 tires mounted on some older stock Campagnolo Zonda wheels with a 17mm internal width, and they measure at 26.6mm wide. The older Vittoria Rubino Pro 28mm tires I have (designed before the wider internal rim width times) measure at 28.2mm on the same Zonda wheels. So… yeah.
The 30mm 5000 is what I have on my Moots, which has modern, wider wheels. They measure at 30.4mm.
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They’re the Schwalbe One V-Guard 25. They came on a second hand set of wheels I bought. I’d say they’re probably from around 2019.
How long have the new tyres been pumped up and sitting? That’s not to stay you still don’t have a discrepancy, but I’m curious if it will make any difference on your rims
Do you find the ride quality of the 30s feels much different to the 28s? How wide are the rims you have the 30s on? Apparently the 30s have a slightly different construction to enable safe ebike usage and have sacrificed some ride quality for slightly better wet weather grip.
The 30s are a lot more plush than the 28s. I run them on a rim that’s 22mm internal, 28mm external, using TPU tubes. Yes, the construction is e-bike friendly but honestly I don’t notice any difference in ride quality. That said, they track very well on wet pavement: descending the rain-soaked mountain roads on this year’s Etape du Tour Femmes was very assured.
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