Changing from low profile tyres - Nsar
I am getting fed up with always having soft tyres.

I am now having to top up my tyres weekly and every now and then I'll drive off and find that a tyre is down to single figures and then after re-inlfating it stays Ok for ages ie not a slow puncture.

Don't know if it's a feature of low profile tyres but can I simply put normal profile tyres on without affecting the car's set up?



Changing from low profile tyres - Westpig
I've done some research into doing the same for my wife's car....and if what i've been told is correct it's not as straightforward as it could be. Trouble is my knowledge base isn't brilliant either.

I'm told that low profile tyres on a car with alloys designed to 'fill the hole' i.e. look right in the wheel arches...would mean that you couldn't swap from the low profile to a higher profile tyre without putting smaller wheels on as well

e.g. our car has 17" wheels with low profiles. If i want a higher profile tyre on it (for better ride comfort) i'd need the 16" wheels that the manufacturer could have put on there in the first place.

Changing from low profile tyres - nick
I doubt it's anything to do with the profile of the tyre. Get your friendly local indy tyre place to test the wheels in a water bath to trace the leak. Perhaps the alloys have corroded a little where the tyre bead sits and need cleaning up.
Changing from low profile tyres - Nsar
It seems to affect all four randomly though. I suppose all four could be affected.

Changing from low profile tyres - adverse camber
I think Nick has it spot on.

But yes, to put higher profiles on you'll need smaller wheels - In some cases not possible because of the size of the brake discs/caliper position.

I guess it should also be said - notify your insurer of this modification :)

Changing from low profile tyres - Battles
Sounds like a fitting problem causing the air loss, not a 'feature' of low profile tyres.

I swapped the low profile tyres from my Lexus IS to a slightly taller profile (45 section to 55 section) and didn't change the wheels. The wheels were alligned (or whatever the technical term is for the laser arrangement) afterwards and I've noticed nothing untoward.

I swapped them after reading that other owners had done the same and it had the desired effect (smoother around Edinburgh's awful roads).
The car does look a bit funny with them on when parked next to a similar car.

The Lexus dealer advised that the wheel size wouldn't need to change as the car is offered with 18" wheels, mine are 17", and that the 18" wheels still leave enough space to install snow chains if required. He did, kindly, offer to sell me a set of 16" wheels (about one millon pounds plus VAT plus fitting) on the off chance that I wasn't happy with his advice.
Changing from low profile tyres - adverse camber
Battles,

Did you have your speedo/odometer ecu recalibrated or are you now showing incorrect speed and distance. Did you tell your insurance co?
Changing from low profile tyres - Battles
AC,
Didn't get any calibration done other than to visually check the speedo indicated speed before and after against my Garmin sat nav and the Road Angel that's fitted, though I did do a bit of maths before parting with any cash.
If I can find the notes, or do it again, I'll post it.

I had concerns about the effect on ABS and the traction control but the TC is certainly more useful now than before, though I accept that it could be down to having much better tyres.

Better tyre availability was one of the reasons for switching. Well better tyres at lower cost.
I was using the German ADAC reviews and finding that some highly regarded tyres were either not available in the size I needed or were prohibitively expensive. Upsizing gave me a number of new options.

The insurance company (More Than) asked if I was modifying to improve the performance (can't remember the exact wording) but I was looking for a less harsh ride so that's what I said.

Edited by Battles on 07/08/2009 at 21:36

Changing from low profile tyres - Battles
Some maths:
The 55 section tyres increase the diameter by 22mm.
Why are tyres in a mix of metric and imperial?

They're now 21.6" tall versus 20.8" with the 45 section tyres.

21.6xPi gives a 67.82" circumference which is 4% larger than before. That would make the speedo 4% less accurate than before, so it'll show the car travelling slower than it actually was, but the speedo previously showed the car travelling faster than it was (66mph on Garmin at indicated 70mph).
66 + 4%= 68.4. Does that mean that it'll now show 68.4 mph?

Does any of that add up correctly?
I'm starving and haven't eaten since lunch.

I will eat and then go and drive at 70mph and report back.