so getting new 305/30/20 fitted tomorrow, will I get tires warning indications on the dash for pressures as there new, if so how do i reset when there inflated to correct pressures or will everything reset after driving

 

There is no resetting needed on this system. The sensors just need to be properly synced to the car by the tire installer.

 

Just drive. The warnings will go away and the pressures will start reading after a couple days, assuming you have the right frequency transponders.

 

Funny to see this today, as yesterday I got a warning about low pressure on my nearside rear tyre. I took my XE into the local dealer, (who are excellent BTW) to ask this very question. They took the car in, checked the pressures, inflated to correct pressures, and washed the car, all at no charge ! The warning came up as I started the car, and disappeared as I drove off.

 

It amazes me that people don't check tyre pressures frequently. I check mine every trip (I'm paranoid!) - it only take a few presses on the steering wheel..

 

I check our pressures periodically.

A needed to add a couple PSI last fall when the weather cooled, but all winter , spring, and summer, pressures were good.

So FINALLY, the ambient temps cooled again, and sure enough, all corners were down about 3 PSI.

 

so tires fitted , started car and no pressure warning, all good

 

Not sure about your couple of days point, my experience has been somewhere between immediately and a couple of hundred yards

Agreed and another few button presses and I check engine oil level

 

That's more problematic for me as the car is so sensitive to level - there are only a few places I go that are really level, and my oil is spot on there, but the slightest incline and I get the overfilled message. I park uphill on my sloping drive so it always shows underfilled there.

 

Powerhouse what car did u put the 305's on? I have a 2010 xfr and want to put 305's on 10.5 rims but worried they wont clear
Thanks

 

I have 305/30 r20s on 10.5" rims with no issues.

 

They *should* fit an XF with no problems although it is possible they will stick too far into the wheel well and foul on the suspension.
Stock XFR rears are 285/30ZR20 on 9.5" rims, so 10.5" rims will move the outer edges of the wheels .5" in each direction and 305 tyres will move the outer edges of the tyres 10 mm in each direction. There is plenty of room in the wheel well / arches for the outward movement, you can go 20 mm (about 7/8") out from stock and clear easily, I'm just not sure about the inner clearance but it should be OK.
Of course all bets could be off if your new/different wheels have a much smaller offset than the stock wheels.
Stock XFR offset is a whopping ET +66, that is they are pushed way in, and other stock XF rear wheels are ET +49, so if your new wheels are for example ET+25 (not uncommon) the outside of the tyre will stick out 41 mm more than the XFR rears, and going to 305's will increase that by another 10 mm for a total of 51 mm. That is near as dammit to two inches, way too much!
Bottom line - the most important measurement is the wheel offset.