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Goodness, Continental Grand Prix 4000s II 28mm tires run large

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Goodness, Continental Grand Prix 4000s II 28mm tires run large

Old 11-04-18, 01:04 PM
  #1  
daoswald
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Goodness, Continental Grand Prix 4000s II 28mm tires run large

I have Fulcrum Racing Quattro LG wheels with an internal width of 17mm.
I have Conti GP 4000s II tires in a 28mm size mounted on my Synapse.

While the tires do work great, I think I would be generous to say there's 2mm clearance on either side of the rear wheel at the chainstays. More like 1.5mm on the left side, and 2.5mm on the right -- I guess that's just how the bike and wheels are built. Luckily the wheels and frame are laterally stiff enough that there is no rubbing at the chainstay.

Anyway, yesterday I put a caliper to the tires and realized that they come in at a whopping 34-35mm width at their widest point. No wonder I'm cutting it so close. Various reviews I've seen for this tire suggest it might run 2mm-3mm wider than advertised, but in my case it's more like six to seven millimeters. I love how these tires ride and feel, but this is just a word of warning, they run big. If your frame is less spacious you may encounter difficulty with these tires. I suspect that a 15mm internal rim would pull them in narrower, but at least with a 17mm rim they run 6-7mm wider than advertised. When you think about it, it's a feat of engineering that they could be as light as they are given their size and longevity.

My rear tire is about halfway through its tread life. I'm tempted to move back down to 25mm in back when it comes time to replace. The front is practically new, and has better clearance, so I'll end up slightly mismatched if I do that, though.
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Old 11-04-18, 01:13 PM
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My Conti Ultrasport 25mm measure exactly 28mm.
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Old 11-04-18, 01:13 PM
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On my rims, they are 35mm. I look at that as an asset. I am significantly faster on them than my 28 mm (true to size) Clement 120tpi Straddas. If they fit, stick with them, and enjoy the ride.
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Old 11-04-18, 01:39 PM
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Originally Posted by daoswald View Post
I have Fulcrum Racing Quattro LG wheels with an internal width of 17mm.
I have Conti GP 4000s II tires in a 28mm size mounted on my Synapse.

... I put a caliper to the tires and realized that they come in at a whopping 34-35mm width at their widest point.
Originally Posted by wgscott View Post
On my rims, they are 35mm. I look at that as an asset. I am significantly faster on them than my 28 mm (true to size) Clement 120tpi Straddas. If they fit, stick with them, and enjoy the ride.
I also consider this good news!

I've wanted to try a set of "real" 700x32 road tires on one of my hybrids for a while. I wound up getting a set of Conti GrandSport Race 700x32, which measure 34.05mm & 33.87mm on a set of Rhyno Lite rims using a digital caliper. The Rhyno Lites measure 27mm outer and 22mm inner, so they're fairly wide rims.

Last edited by Doctor Morbius; 11-04-18 at 01:43 PM.
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Old 11-04-18, 01:40 PM
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On Mavic e2, a 28 = 25, but why sweat 3mm?

but I note this is a forum of the obsessives on the minutiae..
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Old 11-04-18, 01:42 PM
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Originally Posted by Lazyass View Post
My Conti Ultrasport 25mm measure exactly 28mm.
Hmmm, I have a pair of UltraSport 700x25 folding mounted to Mavic Open Pro rims and they measure 25.22mm & 24.99mm.
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Old 11-04-18, 02:33 PM
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Originally Posted by Doctor Morbius View Post
Hmmm, I have a pair of UltraSport 700x25 folding mounted to Mavic Open Pro rims and they measure 25.22mm & 24.99mm.
My internal rim width (HED's) is 21mm and yours are 15mm.
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Old 11-04-18, 02:42 PM
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The caliper looks crooked but it's not. I see it's actually closer to 29mm.



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Old 11-04-18, 03:18 PM
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On my 2018 Trek Domane the Conti 4000's run 30mm.
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Old 11-04-18, 04:08 PM
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This is part of the reason I donít use continental anymore. Thereís seems to be no real consistency with sizing. I know tires will measure different with different rim widths, but there should still be better consistency than this. A number of years ago, continental tires usually ran small. I had two sets of Grand Prix 4000 s IIís in 25mm and they both measured at barely 23mm. I had several sets of 28mm gatorskins and a set of Grand Prix 4 seasonís in 28mm and they all measured closer to 25mm and that was on h+son rims no less.

A 28mm measuring at 35 is a bit ridiculous. I could see a 32 maybe coming in closer to 35, but not a 28. I prefer panaracer nowadays because their tires are more consistent, both in performance and sizing. My 32mm gravelkings measure 32.5 in the front at about 70psi and just over 33 in the rear at 90psi.
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Old 11-04-18, 04:43 PM
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Michelin runs just as big, at least the ones I've had.
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Old 11-04-18, 05:02 PM
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Doesn't this practice of Conti, just help them get to where they can claim really good rolling resistance for any given nominal-size tire? I agree with Seamuis.. there's no advantage of trying to always guess how the manufacturer is going to fudge it's numbers. If Conti wants to sell a 33mm GP4Ks, then do this and label them as such. There's no magic benefit to being sold a tire wider than its nominal size.

Also, a 17c rim is not 'wide' in consideration of mounting a "28mm" tire and can't be considered the explanation for the size screwiness. Actually if tire size methodology is based ETRTO standards, a 17c rim falls in the middle of what ETRTO recommends for a 28mm tire (the 3 ETRTO sizes being 15C, 17C and 19C)
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Old 11-04-18, 05:36 PM
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Schwalbe pro one 28 on Enve 4.5AR = 32 @ 60psi
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Old 11-04-18, 10:03 PM
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My GP4000 II 28's are 32mm wide on a 22mm internal 26mm external rim
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Old 11-04-18, 10:10 PM
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On the same rims (HED Belgium Plus), my 38 mm Compass tires are .... 38 mm.
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Old 11-05-18, 06:10 AM
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Iíve been convinced for several years that continentals sizing is screwy on purpose. I know a lot of different manufacturers can have tires that donít measure perfectly, but I donít know of any brand thatís Ďconsistentlyí as off as continental, as to not be on purpose. I wouldnít tell anyone not to buy them, because of course as far as performance goes, they are always top notch. But like the OPs situation, it could be pretty frustrating to buy a 28mm tire and end up with one so much bigger that it doesnít properly fit and may even risk damage to your frame or worse. Iíd say thatís unacceptable from such a large company. My LBS is pretty performance oriented and sells a lot of continental tires. One of the mechanics there has told me that heís had countless complaints about continental tires being either larger or considerably smaller than labeled, when I brought it up in conversation. On a racing bike with specific clearences, thatís a problem. Imagine buying a 28mm tire and you canít fit them into a dura ace 9100 rim brake, because itís several sizes too large. There are too many other choices of performance tire out there now, to risk dealing with that nonsense. Bit of shame really, because Iíve always liked continental.

Last edited by seamuis; 11-05-18 at 06:13 AM.
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Old 11-05-18, 08:14 AM
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This is on HED's website

*Note: Our wide rims increase clincher tire volume, causing actual inflated sizes to be larger-than-advertised on the tire. Inflated sizes will be 1-2mm wider on our 23mm C2 rims, and 2-4mm wider on 25mm Plus rims.
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Old 11-05-18, 09:33 AM
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Originally Posted by Lazyass View Post
This is on HED's website

*Note: Our wide rims increase clincher tire volume, causing actual inflated sizes to be larger-than-advertised on the tire. Inflated sizes will be 1-2mm wider on our 23mm C2 rims, and 2-4mm wider on 25mm Plus rims.
this is always an important point to keep in mind, and I donít want anyone to think Iím just hating on Continental but as far as my frustration goes, I experienced consistent undersizing, even on wider rims. And in the OPs case, roughly 7mms larger goes well beyond what I think is acceptable from the listed size. A size that large can only be had, if the tire is physically larger than what it should be. And itís not just an issue of frustration, or possible safety, but also an issue of economics. Depending on where you purchase your tires, you may not be able to return tires that have been removed from packaging and mounted. For me though, I just simply stopped buying continental. I understand the OPs frustration though.
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Old 11-05-18, 09:47 AM
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I'd be curious to know how the rolling resistance figures stack up when comparing actual widths across brands.
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Old 11-05-18, 09:49 AM
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Originally Posted by Lazyass View Post
This is on HED's website

*Note: Our wide rims increase clincher tire volume, causing actual inflated sizes to be larger-than-advertised on the tire. Inflated sizes will be 1-2mm wider on our 23mm C2 rims, and 2-4mm wider on 25mm Plus rims.
Irrelevant to my observation. I'm using wheels with a 17c internal, which is within the sweet spot for 25 and 28mm tires. Yet my 28mm Conti GP4000sII tires measure in at 35mm. They fit, but just barely. I'm quite surprised that there are no rub marks on my frame given the fact that I can barely see light between the tire and the frame. Really, the tire is too big for the frame, but I've been running it for 1800 miles without problems. Nevertheless, I'll probably move down to the next lower size, or switch brands when I finish the wear on my "28mm" Conti.
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Old 11-05-18, 11:25 AM
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Originally Posted by daoswald View Post
Irrelevant to my observation. I'm using wheels with a 17c internal, which is within the sweet spot for 25 and 28mm tires. Yet my 28mm Conti GP4000sII tires measure in at 35mm. They fit, but just barely. I'm quite surprised that there are no rub marks on my frame given the fact that I can barely see light between the tire and the frame. Really, the tire is too big for the frame, but I've been running it for 1800 miles without problems. Nevertheless, I'll probably move down to the next lower size, or switch brands when I finish the wear on my "28mm" Conti.
my h+sons are 17.6 internal width and and every conti tire I had was several mmís too small. But you are right, thereís no way a 17mm IW could produce a 35mm mounted size. Iím very surprised though, to hear that youíve been riding it like this, mainly because Iím surprised the tires clear your brakes. What brakes are you running, and how much clearance do you have? Iím very curious.

Last edited by seamuis; 11-05-18 at 01:00 PM.
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Old 11-05-18, 12:57 PM
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My 25mm Contis measure 28mm inflated on my Hed Belgium C2 rims (23mm external).
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Old 11-05-18, 03:10 PM
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After putting it off for years, I finally went out and bought a proper digital caliper. My Conti's 25mm are 28.43mm.
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Old 11-06-18, 12:13 AM
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Originally Posted by seamuis View Post


my h+sons are 17.6 internal width and and every conti tire I had was several mmís too small. But you are right, thereís no way a 17mm IW could produce a 35mm mounted size. Iím very surprised though, to hear that youíve been riding it like this, mainly because Iím surprised the tires clear your brakes. What brakes are you running, and how much clearance do you have? Iím very curious.
Cannondale C2 caliper brakes. I think they're approximately the level of Shimano 105, which is the groupset from which most of my drive train is composed. No clearance problem at all at the brakes. And the front fork is fine, too. It's only the chainstays that are alarmingly close to the tire.
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