Vibration? at speed

[ucb]

I noted today a sensation which felt almost like the tyres had flatspotted when travelling at motorway speeds. It made the steering wheel vibrate gently left and right although the car tracked straight. Its almost like the brakes were grabbing on and off all the time. It happened this afternoon and the car had driven perfectly otherwise up until that point.
Now the car has been laid up for 4 months so I thought I was going to have to replace the tyres, but almost as quickly as it started it disappeared and the car then drove perfectly again.
I had a similar sensation the last time I drove the car before being laid up, but back then it had a battery which wouldn't hold any charge so it was replaced and the vibration went away. The car has been on a battery conditioner ever since and starts easily so I don't think battery charge was the problem again.

So, anyone know what it is? Wheel speed sensor? ABS module?

 

[ucb]

Just to add that it started after a period of hard acceleration joining a dual carriageway from a B road. I wondered whether the new battery was able to sustain the load required at high rpm's. I'll check it out tonight.

 

[spareone3]

. I wondered whether the new battery was able to sustain the load required at high rpm's. I'll check it out tonight.

You've lost me with that...

However,

Wheel(s) need balancing.

Underinflated tyres, sat long period making out of shape (as above).
Warped dics, sticking caliper (maybe).
Buckled wheel.

 

[ga41]

My first suggestion would be a wheel weight come unstuck unbalancing the wheel but you mention that the car felt fine on a later drive... Maybe a sticking calliper, although i've never experience this personally so don't know exactly how it would feel like.