new tyres-fuel economy

New tyres will improve economy if they are the same and account is made of the reduced diameter of old ones if worn and of course using same pressures.

But if you change to a lumpier / wider / type will get worse.

As your implying Sfletch , maybe your wheel alignment has been mucked up but it would have to be bad and soon visible.

Get a long piece of string and run it round car across all 4 wheels at once and look to see that both front and rear of your front tyres are just touching string at same time to indicate wheels are pointing approx straight.

Are the replacement tyres the same size as the old ones?

Hi sfletch,
"...it is not my vehicle"
Did you check the NO Plate to make sure it was your Hilux?
Just kidding ;)
Are the tyre size the same as you had before?
"now turbo is screaming" So it's reving higher? means smaller Dia tyre.
"towing a caravan up hill " sounds like a bigger Dia tyre
"thinking of getting wheel alignment re-done............"
I agree with Robin."to be bad and soon visible"
But this shouldn't effect revs or it's towing ability.
Hmmm, you've got a few dramas, hope you find the culprit.
Post back when you do find it please.
Cheers.

Sounds like the new tyres need more pressure.

If the wheel alignment was causing that much difference, it would have to be so far out you could see it. You would not have to measure it.

I agree with those who have asked about tyre size. The standard size tyre on your car was most likely a 205 x 16, The diameter will be around 735 mm. All other factory option tyres will be so close to that diameter that it dosen't matter. If your new ones are much larger then the car will start to perform as you described. The larger the diameter the worse it will get.

I got a set of new Geolanders and found them to be good. None of the problems you described

if the turbo is audibly "screaming",Id suggest there is something else wrong. Unless the tyre bloke accidentally did an alignment on the turbine "wheel" there is nothing he could do to make the turbo "scream".

as i said...as simple as it sounds.....tyres are exact same diameter as previous tyres that they replaced....225/75/16 AT.......if anything these are less agressive than B F G which i had before....all i have done is walk in change tyres to exactly the same size as previous ones , get a wheel alignment and walk out......its like walking thru a door between good and bad....flicking a switch....... and it is that much noticable ... i dont understand it....i am at a loss to know why ?????? spoke to tyre place today they will check it next week . i dont think a couple of psi will make this much difference .

Did the string line thing....one side as straight as i could get it .... the other side pointing inward about 5mm .... dont know if that would be enough to make a big difference but guess if driving in a straight line both tyres could be pointing inward even if ever so slightly ??????