Tyre Profile Question

[Jiyujin]

Hey all,

Looking to buy some new tyres and was wondering if 50 or 60 series would fit okay, primarily the P7 225/60R18. I've read here that most owners are using 30 to 40 series.
Any help is appreciated!

[RX25SE]

Use this to play with sizing but maintain near as possible to the original diameter.

http://www.1010tires.com/Tools/Tire-Size-Calculator

[zch91]

What are the stock wheels that the car was fitted with? 17x7 +55 with 215/45/17 ?

As long as it complies with the +15/-26mm overall rolling diameter of the above then there should be no issues.

[BillyCorgi]

There may be lots of information on this forum regarding tyre sizes applicable to a Liberty.
So, here something may be repeated?

For starting it is noticed that you are in Gold Coast Queensland and your vehicle is an MY08 2.5i Liberty Wagon.
It is understood that Queensland is covered under Vehicle Standards bulletin 14 for non-standard tyres.
This states "4.2.4 Overall Nominal Diameter
The overall diameter of any tyre fitted to a passenger car or passenger car derivative must not
be more than 15mm larger or 26mm smaller than that of any tyre designated by the vehicle
manufacturer for that model"

The largest wheel tyre combination for a 2.5i Liberty is 215/45 R17
The largest wheel tyre combination for a Spec B Liberty is 215/45 R18

To fit tyres based on the Spec B size of 215/45 R18 you may need to also fit the Tyre Placard from a Spec B to your vehicle.

Anyway, doing the math the largest tyre combinations based upon the 18inch wheels would be
215/45 R18 at 650.7mm diameter (standard)
205/50 R18 at 11.5mm larger diameter
185/55 R18 at 10.0mm larger diameter
165/60 R18 at 4.5mm larger diameter
Your proposal of 225/60 R18 are 76.5mm larger in diameter?
If you wish to go to 60 series tyres then you would need to convert to 16 inch rims and consider
215/60 R16 at 13.7mm larger diameter.

You may like to do a Google search on "Vehicle Standard Bulletin 14"

[Adrian2627]

As well as being illegal it would mess up your gearing and make the car a slug, mess with fuel economy, and possibly even your ABS/VDC as all the calibrations will be out. As Billy said if you want to run a 60 series tyre, which will reduce the cornering performance but increase comfort, you will have to go down in rim size.

[Jiyujin]

What are the stock wheels that the car was fitted with? 17x7 +55 with 215/45/17 ?

As long as it complies with the +15/-26mm overall rolling diameter of the above then there should be no issues.

Hey all,

Thank you for the information and advice.
Yes, 17x7 +55 with 215/45/17 are currently on the vehicle but I would like to put 18x7 +55 rims on in the near future and am searching for appropriate tyres that are not too low in profile.
Would like to keep them legal and not affect fuel economy or gearing...
Thanks!

[Jiyujin]

Thanks BillyCorgi!
Yes, there is a lot of information here so I was at a loss at what is within the legal boundaries of the State.
I have only been back in the country for 6 months or so and am still trying to get my head around things. I'm looking to change my current rims and tyres from 17s to 18s as the tyres are on their way out.
Based on the information you have written here, 215/45 R18 would be suitable and within the law.
Cheers!

There may be lots of information on this forum regarding tyre sizes applicable to a Liberty.
So, here something may be repeated?

For starting it is noticed that you are in Gold Coast Queensland and your vehicle is an MY08 2.5i Liberty Wagon.
It is understood that Queensland is covered under Vehicle Standards bulletin 14 for non-standard tyres.
This states "4.2.4 Overall Nominal Diameter
The overall diameter of any tyre fitted to a passenger car or passenger car derivative must not
be more than 15mm larger or 26mm smaller than that of any tyre designated by the vehicle
manufacturer for that model"

The largest wheel tyre combination for a 2.5i Liberty is 215/45 R17
The largest wheel tyre combination for a Spec B Liberty is 215/45 R18

To fit tyres based on the Spec B size of 215/45 R18 you may need to also fit the Tyre Placard from a Spec B to your vehicle.

Anyway, doing the math the largest tyre combinations based upon the 18inch wheels would be
215/45 R18 at 650.7mm diameter (standard)
205/50 R18 at 11.5mm larger diameter
185/55 R18 at 10.0mm larger diameter
165/60 R18 at 4.5mm larger diameter
Your proposal of 225/60 R18 are 76.5mm larger in diameter?
If you wish to go to 60 series tyres then you would need to convert to 16 inch rims and consider
215/60 R16 at 13.7mm larger diameter.

You may like to do a Google search on "Vehicle Standard Bulletin 14"

[30rbullet]

I have wondered this as according to my gps my speedo is under.
If I am doing 100km/h I am actually doing 95km/h.

[BillyCorgi]

If you are intending to upgrade from 215/45 R17 and upgrade to 18 inch wheels, then you may also consider 225/40 R18.
These will be slightly smaller than the 215/45 R18 however are potentially a lower cost alternative.
My Spec-B wagon was running 225/40 R18s when I bought it.

[Shaheenis]

235/40/R18 <5mm variance from standard RD on stock GTB suspension also common Ford tyre so attractivley priced (too low and you may risk scrubbing).

viewtopic.php?f=19&t=21448&start=60#p349480

viewtopic.php?f=19&t=21448&start=60#p349537

[Tonic]

Please correct me if i am wrong my learned friends,

I went to the potenza 225/40/18 because they were a good deal at the time. Bit noisier on the road bit rougher ride.

I Like a bit wider tread and therefore higher cornering speeds.....ahh speed....

But that is a bit deceptive because 225 @ 40 is a 90mm wall and the stock 215 @ 45 is 97mm wall. Consequently the rolling diameter is now lower by 14mm by calculation and the speedo is showing 10% over actual whereas before it was about 3%.

I don't mind because i'm sure it has saved me from a few speeding ticket disasters........

I guess to get a bit slippery i'd go back to the 215/45/18 combo with a cheap tyre.

[Manaz]

TL;DR - you can't increase wheel size AND tyre profile without sacrificing either tyre width or seriously screwing your car up (and breaking the law in the process).

As a general rule, you want to stay as close to the stock rolling diameter as possible. Profile is the height of the sidewall expressed as a percentage of the width. So:

A 215/45R18 tyre has a 96.75mm sidewall (this is the stock size tyre on an 18" wheel).
A 215/45R17 tyre has a 96.75mm sidewall (yes, exactly the same as the previous one, because profile doesn't take rim size into account).
A 225/40R18 tyre has a 90mm sidewall.
A 235/40R18 tyre has a 94mmmm (very close to stock!).
A 225/60R18 tyre would have a 135mm sidewall - that's 38.25mm (nearly 40%!) difference to the stock 18" tyre size. That's substantial, and would likely cause problems. To stay reasonably close to the rolling diameter you require, you'd have to go down to a 165 or maybe 175 width tyre - and that'd just be silly (and you'd still end up with a short, stiff sidewall anyway!).

For a given tyre width, if you go up a wheel size, you generally need to go down a profile (45 to 40 for example) to maintain rolling diameter. If you want to maintain sidewall height or even increase it, you simply can't go up a wheel size.

I'm actually looking at moving from the stock 18" wheels on my MY09 GT Spec.B to 17x7.5" rims with 235/45R17 tyres. The reason for this is that I want to increase ride comfort very slightly, whilst at the same time lowering wheel weight and running a wider tyre. This takes me from a 96.75mm sidewall to a 105.75mm sidewall (an increase of 9mm, or roughly a centimeter - but then I'm also dropping an inch of wheel size as well, meaning I end up with a rolling diameter difference of around 5mm difference - or a variance of around 0.85%, well within specs and laws.