25c Tyres - tight clearance

[Ajax Bay]

I have ordered some Continental GatorSkin wire bead tyres in 23c which I am aware come up slightly larger as per the GP 4000s.

Hope it turns out well.
https://www.bicyclerollingresistance.com/road-bike-reviews/continental-gatorskin-2015
As a 'Big Fella' risk mitigation of sufficient pressure will be important.

 

[bigfella]

I'll second those comments on the frame, very nice. I would stick with 23c myself although it does help having a bendy seat tube occasionally
View attachment 567488

Indeed it does, but you cannot beat steel! ;-)

Hope it turns out well.
https://www.bicyclerollingresistance.com/road-bike-reviews/continental-gatorskin-2015
As a 'Big Fella' risk mitigation of sufficient pressure will be important.

Thanks for that document, very helpful to have handy.

 

[bigfella]

Oh and the tyres are here, the verdict is in....

 

[bigfella]

23c Continental GatorSkins are fitted, here is the rear wheel clearance, as you can see, very tight indeed! Took several photos, to show the gap varies slightly.

I also took the vernier calipers to several points around the tyre to measure the width at 120psi, as suggested, over 23mm and nearer 25mm. The ID of the rims is 17mm, so more or less as per the required tyre specification for the Fulcrum Racing 5s.

 

[SkipdiverJohn]

I read about this; there is a theory that a tyre forms a balloon shaped cross section so using a wider rim in some cases could increase the tyre height.

It doesn't work like that. If you grip a deflated balloon in one hand then get someone to pump air into it, the bit held inside your hand doesn't expand much because you are physically preventing it. The bit sticking out at the sides does the expanding -
If you measure a tyre bead to bead with a tape measure, you get X inches or mm or whatever you want to measure in. The small amount in the well of the rim is constrained by the wall of the rim. The open side of the carcass can only expand out to the internal rim width. The carcass itself doesn't stretch much because of the ply construction. Once the open side of the tyre cannot expand any further because of the rim, the resulting shape of the tyre depends on the structure's ability to resist the air pressure. The cross section of the tyre will not necessarily be round, in fact it will almost always not be truly round.

 

[Adam4868]

My carbon bike only just takes some 25 tyres.Even at that it's tight.

 

[Ajax Bay]

23c Continental GatorSkins are fitted, here is the rear wheel clearance, as you can see, very tight indeed! Took several photos, to show the gap varies slightly.

Well done.