Tyre Size - Advice

Richard Baker · January 23, 2004

I am thinking of buying a set of the 18" Lexus styling wheels and new tyres.

I have an IS Sport (lowered by 15mm) i also have the Lexus lowered springs fitted - another 15mm.

I would like to 'fill' the arches and i wonder what the best tyre size would be? Could i maintain the 45 or could i go up a size or two?

I will also need an arch liner for the drivers side fron t wheel, but why just the drivers side?

Any advice would be appreciated.

BESTY · January 23, 2004

i would stick to 45 walls wid 18 inch wheels,thats what i want soon,hey you say you have an extra lowering kit 15 mm ,where is that from. :)

ColinBarber · January 23, 2004

If you change the diameter of the rim+tyre then your speedo and odometer will be out.

Chris.S · January 23, 2004

The recommended size used by Lexus on the styling kit are 225/40 ZR 18

45's with 18's would cause your speedo to show the incorrect speed

RX-Men-8 · January 23, 2004

If you change the diameter of the rim+tyre then your speedo and odometer will be out.

45's with 18's would cause your speedo to show the incorrect speed

Yes, it'll read about 3 to 4 percent less than with the 225/40R18s. Speedo's are known to overread 5 percent easily (my IS200 does), so you'll really have to watch the needle. I agree it'll fill the arches better, though.

Cheers,

RX-Men-8

Maz · January 24, 2004

I have 18 x 8 alloys with 225/40/18 tyres all round, offset is 45...

as show in this picture,

18x8 alloys with 225/40/18 tyres all round

Richard Baker · January 24, 2004

Many thanks for the info - i will go for the 225/40 ZR 18 tyre size.

Besty - Lexus lowering kit factory part number - PZ439-C1721-00.

Supplied and fitted by Lexus technicians at a cost of £360.00 including Gold Discount.

Apparantly, they are re-badges Eibach springs?

Anyway, this might be the expensive way of doing it, as i would'nt have a clue myself. Also peace of mind that a Lexus technician has fitted them.

I have noticed a real difference, the ride is a lot firmer but you notice every small pot-hole, the cornering has vastly improved. Also, the front has settled and dropped by just over 20mm and the rear by at least 15mm.

Does anyone know why an Arch Liner is required to the front L.H ?

jonthebarber · January 24, 2004

Try this site for tyres - very impressed :winky:

http://www.blackcircles.com/

BESTY · January 24, 2004

Many thanks for the info - i will go for the 225/40 ZR 18 tyre size.
Besty - Lexus lowering kit factory part number - PZ439-C1721-00.

Supplied and fitted by Lexus technicians at a cost of £360.00 including Gold Discount.

Apparantly, they are re-badges Eibach springs?

Anyway, this might be the expensive way of doing it, as i would'nt have a clue myself. Also peace of mind that a Lexus technician has fitted them.

I have noticed a real difference, the ride is a lot firmer but you notice every small pot-hole, the cornering has vastly improved. Also, the front has settled and dropped by just over 20mm and the rear by at least 15mm.

Does anyone know why an Arch Liner is required to the front L.H ?

thanks pal :winky:

Richard Baker · January 25, 2004

Thanks for the info regarding speedo and odometer readings.

Does any know or has anybody ever measured the overall diameter of an 18" rim with a 40mm tyre.

The reason i ask is that i measured my standard 17" rim with a 45mm tyre and the overall diameter is just under 600mm.

As i am trying to fill the arches i assume that an 18" rim and 40mm tyre would have a larger overall diameter, but by how much?

ColinBarber · January 25, 2004

Please note that the /40 or /45 rating does not mean 40 or 45mm. It means the ratio of the width of the tyre compared to the height. This is why when you have wider tyres you need a lower ratio to maintain the correct height.

This link may help with the wheel diameters:

http://www.toyo.co.uk/index.php?fuseaction...c4a784cdc7c94d0