23/25/28 wheels...and clearance.

[livpoksoc]

currently running bontrager 700x23 on my trek madone & been reading about the differences. If i want to switch to 25/28s, how much additional clearance would I need to look for in the calipers and the frame?

 

[Ajax Bay]

Decide what the limiting factor is (ie chainstay, seatstay, fork, bridges, fork crown) and measure what you have now and what the actual dimensions of the tyres you have on now (not the 23 on the side). This will give you the parameters for a replacement tyre. The problem you then have is that real tyre dimension data is sparce - if people can point towards any useful resource, I'd be grateful. 'Rollingresistance ' records some 25-622 measurements, but width only.

In theory (forgive tgtse) you need 1mm extra each side and 2 on top for 23 > 25 and a further 1.5mm and 3 on top for 25 > 28.

Some 25s come up small, some large and same for 28s. Fwiw my Continental GP4S 28-622 measured width iirc is/was 25.9mm at 100psi on a 15mm inside rim. The Marathon Plus 28 I put on (mid end-to-end, replacing a Giant PR2L (or something)) was 29mm plus and more importantly for my mudguards, much (ie 6mm) 'higher' so was fouling the bridge, when I sat on the bike - NB spun OK without a load (off topic: when you sit on a bike the distance between the hub centre and the top surface of the tyre increases). The rear mudguard had to go.

As far as clearance to get through the calipers/blocks is concerned, again your own measurements will guide you. I have 'normal' 105 calipers and my 26s (28-622) slip through them without adverse effect, though I deliberately do not have the blocks on a tight tolerance to the rim (and accept that I'll need a little early movement in the brake levers before braking effect).

 

[livpoksoc]

Decide what the limiting factor is (ie chainstay, seatstay, fork, bridges, fork crown) and measure what you have now and what the actual dimensions of the tyres you have on now (not the 23 on the side). This will give you the parameters for a replacement tyre. The problem you then have is that real tyre dimension data is sparce - if people can point towards any useful resource, I'd be grateful. 'Rollingresistance ' records some 25-622 measurements, but width only.

In theory (forgive tgtse) you need 1mm extra each side and 2 on top for 23 > 25 and a further 1.5mm and 3 on top for 25 > 28.

Some 25s come up small, some large and same for 28s. Fwiw my Continental GP4S 28-622 measured width iirc is/was 25.9mm at 100psi on a 15mm inside rim. The Marathon Plus 28 I put on (mid end-to-end, replacing a Giant PR2L (or something)) was 29mm plus and more importantly for my mudguards, much (ie 6mm) 'higher' so was fouling the bridge, when I sat on the bike - NB spun OK without a load (off topic: when you sit on a bike the distance between the hub centre and the top surface of the tyre increases). The rear mudguard had to go.

As far as clearance to get through the calipers/blocks is concerned, again your own measurements will guide you. I have 'normal' 105 calipers and my 26s (28-622) slip through them without adverse effect, though I deliberately do not have the blocks on a tight tolerance to the rim (and accept that I'll need a little early movement in the brake levers before braking effect).

Thanks...it seems trial and error may be best. I am running a 622x14 Bontrager rim and any resources I can find never mention a 14mm wide rim. I would call the dealer where I bought the bike but they have folded now.