The first year I had my Bravo, I don't think the ABS kicked in once.

Now it seems to be on a daily basis - especially braking on rough roads.

The brakes work great so no issues there. The only real difference on the car is Michellin Energy tyres on the front rather than Goodyear Efficient Grip, but surely that wouldn't cause an issue?

At first I actually thought it was vibration from the engine when stopping sharply, but it only does it when braking, so guessing it must be the ABS. No warning lights come on the dash though.

Anything obvious to check for?

You don't get warning lights for ABS, and tyres can effect ABS greatly depending on how Much grip they do or don't have. Do you find the tyres worse than the old ones. ABS is to help the car stop without slipping, whilst also allowing some amount of steering in case of the need to avoid a collision. If your tyres aren't grippy enough to not slip under your braking conditions ABS will kick in thinking you have lost control.

Edit: In regard to me saying there are no warning lights, that's not strictly true. Whilst there is no light to say when ABS is kicking in there is a light that will illuminate on your dash if there is an error with the ABS system.

If the ABS kicks in every time you brake, but especially at slower speeds.. 0-15km/h that would show a problem with either a wheel speed sensor or more likely the magnetic ring that the sensor reads off.
A problem with the magnetic ring will not light up the ABS error light.

To troubleshoot you need to connect MES to the car's ABS Module/computer , go to the parameters tab, select all 4 of the wheel speed sensors; go the the graph tab, click on "Start" then drive the car at different slow speeds checking that all wheel speeds are close to equal.
In your case, i'm sure at least one of the speeds will show a much lower speed compared to the others. That is the corner you need to work on.

I think the magnetic ring only comes as part of the wheel bearing assembly.
If one of the corners is reading a speed of ZERO, 100% of the time then i would suspect the sensor... but if the sensor would be 100% bad or disconnected that would show an ABS error..so not your case. So: ABS magnetic ring.
Here is a test similar to what i mentioned:

Just for the info

The abs ring is on the driveshaft cv
And yes, there's an error if one of 4 sensors go bad.

To original poster:
Are you sure it's the abs feeling?
Check brake disks condition.

I believe tires are the same size front/back right?

Cheers guys. It's only when braking hard from high speeds and especially on rough roads. A slip road I use daily is basically like a rumble strip so I really try not to brake on it but it's a 70 straight into a left then right hairpin bend so not easy if someone sits right behind you.

The tyres are less grippy so that might be part of the issue. I'll be putting my 18s back on soon so see how it compares. Braking on a smooth road I don't have the problem.

Discs are aprox 18m old and pads roughly the same.

Quick update - rear shocks were replaced yesterday as one was starting to leak.

I'm thinking that was probably the cause and also explains the car feeling 'tail happy' on fast bumpy corners.