I've gone from DT 5.1d's to Stans 355's, but still using the Nobby Nic 2.25" tyres, front and rear.

I've noticed the tyres seem to have a rounder profile and are wider, is this normal or am I just being daft?

It's only when you get to the extremes of tyre/rim combo's (ie. a 2.5" tyre on a Mavic 717, or a 1.5" slick on a Mavic 729) that you really need to worry.

2.25" Nobby Nic is going to be fine on pretty much any MTB rim you can buy I'd suggest. It will have a rounder profile on some, and a squarer on others…

They certainly appear to have a much rounder and therefor wider profile on my Stans.

might need to drop to a 2.1 on the back 😯

they will be wider as their volume is the same but the width at teh bottom is smaller – the extra is taken up by the sides 'billowing' out a bit more.

I run 2.25 NN on Mavic 717's and you do have to keep the pressure up a bit to stop them rolling on the rim.

Had 2.25 Racing Ralphs on 5.1's, then tried them on 4.2's, more skitish in corners.

They'll be fine – I have a 2.35 HR on one of mine & run a pair of 2.25 NNs on Mavic 719s

The tyre fitting the rim is not the issue – maybe I should've explained that – it's the fact that my bike isn't overly generous on rear tyre clearance.

So 2.1" Rocket Ron it is then