Different Tyre Size For Front And Back Wheels

jasear · January 6, 2010

Hi,

My car (Lexus RX300 2001) just went through an MOT. The front tyres needed replacement. The size of the front tyres were 225 60 17. For some reason these seem to be extremely rare tyres and I could not find them anywhere. The MOT station had some 225 55 17 and they suggested that I use these as it wont make much of a difference so I got them.

However I recently noticed that when I am driving on the motorway and go around 80 mph the car starts shuddering a bit. I can feel this on the steering as well as in the car. It use to shudder a bit before I got the tyres replaced but not as bad as this and I just thought at the time that maybe the wheels require balancing.

I am not an expert on this subject so would be grateful for your input. I am not sure if this is because of the tyre size change or something else? Could this be because I have 225 55 17 in the front and 225 60 17 at the back? Or is this something else?

jasear · January 6, 2010

Someone please help!

ihpj · January 6, 2010

Have you had the wheels re-balanced then? Your post is unclear I'm afraid.

As for wheel size, I cannot comment for sure as I know squat about MKI RX, but as the only difference appears to be the aspect ratio - the tyres fitted should be OK. Maybe you have a bent rim or something causing the vibration?

Unity · January 6, 2010

Since the RX is a four wheel drive vehicle I'd imagine that the internal components of the drive mechanism are set up for all the wheels travelling at the same number of rpm. Changing the profile of the tyre changes the rpm of that wheel so I guess at speed the strain between what the drive mechanism is doing vs what the wheels are turning at becomes noticeable.

My last car was an A4 quattro and I definitely remember being told that if the rear vs the front wheels differ in size (even by the front tyres being new and the rear worn) you can get weird noises, driveshaft wear and poor handling.

Hope that helps,

Unity

jasear · January 10, 2010

So if I change the back tyres to be the same as the front i.e. 225 55 17 then it should be fine`?

I am just concerned whether now they have to be the exact same brand?

Unity · January 12, 2010

I'd have thought it would improve things as that is how the car is designed to work. However, before spending more money on tyres you'd probably be best phoning a couple of dealerships to see if they agree. It would be a pain to spend more cash and not fix the problem.

Cheers,

U

Dmg · January 24, 2010

I'd have thought it would improve things as that is how the car is designed to work. However, before spending more money on tyres you'd probably be best phoning a couple of dealerships to see if they agree. It would be a pain to spend more cash and not fix the problem.
Cheers,

U

I agree as I have had Audi quartos and range rovers and you must have the same size tires front and back . .I would recommend the same make and tread front and back to get the best handling balance out of the car.

Having 55 and 60 ratio tires on the same car is bad news and will wind up the diff