Different tyre speed setting on car

Strider590

Tyre pressure is ALL about the vehicle it's on, it's about the weight of the car and the balance of weight front/rear.

Heavy cars with narrow tyres would need much higher pressures than a small car with wide tyres.

A front engined car, would need more pressure in the front tyres, a rear engined car would need more on the rear.

My Vectra (1600kg) needs about 34psi, my kitcar (600kg) needs around 18psi.

Speed ratings are all about the stiffness of the tyres sidewall, having different ratings on the same axle is an MOT failure.
If you want a soft ride, you go for the lowest rating allowed on your car (check your cars maximum speed), if you want cornering performance and a stiffer ride, then you go for a higher speed rating.

Iceweasel

My worries on this are not that T rated tyres my be adequate or not - it's the mix.

T on one axle and V on the other is going to give unbalanced handling that the vehicle designer never took into account.

This is not just one rating category different - it's 2 different.

But as the OP has not come back to tell us what car this is, we are all speculating as to the seriousness of this.

As far as an MOT is concerned - you can have any mix you like - even stupid inappropriate ones as load and speed-rating are not part of a Class 4 test.

Inappropriate tyres for the use of the vehicle is covered under Road Traffic Law if I remember correctly.

Just because something is not failed under MOT inspection (or not being inspected in this case) does not make it safe or legal.

Ultrasonic

Iceweasel wrote: »

T on one axle and V on the other is going to give unbalanced handling that the vehicle designer never took into account.

Out of interest, how do tyres of different speed categories differ in a way that will affect handling? Will this be any different to tyres of different makes/models/tread depths fitted front and rear?

Iceweasel

Ultrasonic wrote: »

Out of interest, how do tyres of different speed categories differ in a way that will affect handling? Will this be any different to tyres of different makes/models/tread depths fitted front and rear?

My understanding of it is that different speed ratings have different construction, especially in the flexibility of the side-walls.

That's certainly the difference between 2 speed ratings of the same spec tyre from the same manufacturer.

I know of no ordinary vehicle where the maker specifies different speed ratings front and rear with a 2 step difference.

Different load rating front and rear would be technically correct for many vehicles, but that would complicate things regards a spare and swapping tyres around to even wear.

For the best handling characteristics you generally need the same tread pattern and spec all round.

Having said that there are of course exceptions - staggered fitments is one and twin-rears on vans is another.

In ultra-high performance situation (think top-of-the-range Porsche for example) you can have wildly different specced wheel and tyres front and rear.

But the manufacturer designed/decided that - not some naive previous owner trying to safe money at the possible expense of safety.