Can I fit 20mm tubs onto 25mm rims?

1297193504

I've got 26mm corsas on my 25mm Yoeleo carbon rims, but 26 is a bit wide for my fork. So I'd like to change to someting narrower. I was about to go with 25mm corsa speeds but they are out of stock now, and since I've got a climbing bike, I'd like it to be lighter. So I came across this tufo tub but it's 20mm wide, would I have promblems if I mount them on wider rims?

sungod

the radius of the rim bed will be too large, a fair bit of the base tape will have poor/no adhesion, at best it's likely to squirm around, at worst it could roll off on a corner

it'll vary with the rim bed, but i've found even a 23mm on a 25mm wide rim too narrow, constant scritching noises as the edges of the base tape tore away from the glue as the wheel rolled

btw wiggle has 25mm corsa speeds in tan wall...
https://www.wiggle.co.uk/vittoria-corsa-speed-g20-road-tyre-tubular

brosondav82

Trust me, this is a bad idea. Always match tire and rim chamber sizes. If the tire chamber is larger, then it will "move out" inside the wheel, especially when braking. A slightly smaller width is possible (if you pull it on the rim), since the camera will still, due to its elasticity, take up all the space under the tire. But this option will be less reliable than the "native" size. A heavily stretched chamber will burst faster. So the choice is yours.