As I research a set of new wheels, the wider wheels (~23mm) and wider tires(25mm) are very popular for training. Discussion generally centers around the quoted sizing, but what about the "as installed" sizing? I've come across some info citing that the installed width of tires on a wider rim exceeds the quoted size. For example, some 25mm tires installed on 23mm rims will measure out close to 28mm.

How do I calculate this prior to purchase? Is there a standard forumla?

Contact tech support or buy & measure. Is there a reason you are concerned with the exact size?

Measured width is only marginally related to quoted width anyway. I can't run 25c GP4Ks on Belgiums on my S1. I haven't measured, but I'm told the 23cs (which I do run) get to almost 27mm mounted on these rims anyway. Trial and error, unfortunately.

Just for the sake of building a data base, I just measured my nominal 23 mm GP4Ks on Kinlin XR200 rims (20.5 mm outside to outside width as measured) and found the installed width to be 23.5 mm.

Considering a build with Pacenti SL23 rims, which measure 24mm. Combined with 25mm (likely GP4Ks), I just want to make sure I understand the final width as installed to ensure they'll fit my bike. I run 25mm Gatorskins on Mavic Aksiums now and prefer them over 23mm tires.

I'd try my luck with tech support. If they'll respond, they should have that info, I would think...

To have enough clearance I'd want the frame rated for 28c tires. Be aware, though, that 23c GP4Ks on SL23 rims will feel tons better than 25c Gatorskins on Aksiums. I speak from experience.

Hi,

The installed width of a tyre does depend on the rim width.

Your miles off talking about 23mm rims and 25mm tyres.
Its the inner rim width that matters regarding tyres.
23mm rims take 40mm to 50mm tyres typically.

15mm rims take 23mm to 32mm tyres.
28mm is a nice size for a training tyre .

rgds, sreten.

I think my rims are ~ 15mm. They are ~ 20mm outside
width. Fitted with a 30mm rear and a 32mm front.

My input to the database using Farsports carbon 38mm rims (20.5mm outside, 13.5mm inside):
Veloflex Corsa 23s measured 22.5mm wide;
Veloflex Corsa 25s measured 24mm wide.

Rgr sreten. The Pacenti is 18mm internal width - for discussions sake anyway. Will contact Pacenti.

In my experience, going from a 19mm to 23mm rim tires that measured 23mm measured 25. Tires that measured 25 measured 28. You can interpolate or extrapolate from those two points if you like.

Hi,

That is pretty wide for a 25mm tyre so I wouldn't be surprised
if the tyre measured a little more than its nominal width.

18mm will take nominally 25mm to 42mm tyres as a cautious range.

rgds, sreten.