My lbs shop only have this tires in 25mm, but i want to have 28mm. At my lbs they told me that this Conti tires are bigger than spect and they was not sure they wood fit my Roubaix 14' frame.
Is this true? Or are they only trying to sell me the tires they have?
My bike is spect for tires up til 28mm
They said 25mm is like 27-28mm and 28mm is like 30-31mm american Sizing they called it
Well, enybody have this tires in 28mm on a Roubaix?

Thanks

It depends on the rims. Wider rims will make a tire wider than spec.

Don't believe it. On 19 mm (external width) rims my 23's are just a shade under 23 mm. As oldnslow2 says, they will be wider on wider rims.

EDIT: I just corrected the mistake I had made saying internal width when I meant external.

For what it's worth I have 25c Conti4000sII mounted on Reynolds Assault wheels on my Tarmac and they fit. I agree that the tire is wider than 25mm. I'm pretty confident a Conti 28 wouldn't ft.

The 25mm measure between 27-28 on my Belgium rims. Even on my narrower rims they're still wider than 25mm...

I bet they're more likely to fit than not. I'm pretty sure a friend of mine has an older Specialized Roubaix and has been running 28mm GP4000 on wide Pacenti rims without issue. The newer versions of the frame are even more likely to accommodate 28mm due to the trend of going wider rims and wider tires.

My GP4000s 28c tires measure 31mm on my 17mm internal width rims.

Also check out this article. Continental Grand Prix 4000S II 23 25 28 mm Comparison

See the above correction.

My GP 4000s II 700 x 25s measure 27mm on HEDD Belgium + rims. So on some rims they do get sider than spec.

Yes, they are right. My Continental GP4000 SII of 23mm are exactly 25mm on a rim with 16mm inner and 21mm outer width.
So, I suspect that a 25mm Conti might be close to 28mm on the same rim.

I have a 25mm that is 24.5mm wide. Too lazy to take off to measure rim.

My 28s are coming out 28.4 on my fulcrum 5s

My GP 4000s II 700 x 25s measure 26.6mm on my Ultegra 6800 rims.

The 28mm GP4000S II will fit your Roubaix Disc no problem. I ran a 28mm on my SL4 Expert.

If they have one in stock, why don't they let you just mount it up and see? It all depends on rim width, but my 28mm Conti Grand Sport Race tires are almost exactly 28 on my 19mm outside width rims.

GP4000S measured width:

on a typical 14mm inside / 19mm outside width rim ( rim is from 2010.)
25c is 25.8 mm tire width

On HED Ardennes plus wide rims, 20.6mm inside / 25.5 mm outside width rim:
23c is 26.7 mm tire width, and this works great on this rim.
25c is 29.0 mm tire width (and 25c GP 4-Seasons is the same width.)

There is no such thing as a 23c, 25c or 28c tire. They are 23 mm, 25 mm and 28 mm tires, respectively. The "c" is part of the 700 designation, not the width.

Going along with others, my 4000S 25mm's measure at the high end of 27mm on the original HED Belgium rims, and 28mm's measure 31.7mm on Roval Axis 4.0 wheels (wide, but not overly so).

The 28's with latex tubes are amazing if you can get them to fit.

Thanks Dunbar. I will order 28mm!

My 25c GP4000s are 27-28mm on my Boyd Vitesse rims which are 23mm wide, 28mm deep.