fulcrum racing 5 tyre clearance

just bought a pair of these and it recommends using 25mm tyres. I don't have much tyre clearance on my current wheels with 23mm tyres . do the wider rims on the fulcrums mean there is a wider tyre and so reduces the depth of the tyre and therefore the clearance needed. don't want to splash out on new tyres if they wont fit.
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