What size tyres for 18" 350z rims? - Skyline Owners Club

patty · 22nd October 2008, 12:22 PM

I have some factory spec 350z 18" rays on my r33 gtr and was after a little tyre advice.

Currently the rears have 245/45/18 and 225/45/18 on the front, would the same tyre sizes be ok or what do you guys suggest?

Here's a link to the wheels 350z wheel specs Track 18" v.1, 3rd on the list.

Cheers!

**Big Mark** · 22nd October 2008, 01:51 PM

As it's a GTR you REALLY should have the same size tyres/wheels both front and rear.
If they're not the same, or at least very, very close in overall diameter then you could eventually screw up the transfer case and it can also play havoc with the ATTESSA.

The ideal size to keep the diameter the same as the original 17's would be 245/40-18. With the 245/45-18's you're running about 4% over, which means your speedo will read lower than your actual speed by 4%.

One way or another, you should get the fronts and rears matching ASAP.

**Squeak** · 22nd October 2008, 02:05 PM

What Mark said ^^^ sound advice

patty · 22nd October 2008, 06:43 PM

Cheers for the info Big Mark much appreciated, i shall take that advice onboard when i buy some new tyres.

Is it equally important for both front and rears to be the same overall width? or is it acceptable to have narrower wheel/tyre combo on the fronts such as in my case?

You're also bang on about my speedo being out ;-)

**Big Mark** · 22nd October 2008, 08:39 PM

Short answer is basically yes, it's important to have the same size all round, ie same width, same section and same rim size.

Reasonings broken down into a bit more detail below:-

For the sake of the transfer case it's more important to have the same rolling radius.
eg. the standard tyres on an R33GTR are 245/45-17's which have and overall diameter of 652.3mm.
Your current setup has 659.7mm (225/45-18) on the front 677.7mm (245/45-18) on the back......this means your fronts are spinning almost 3% quicker than the backs which isn't good for the transfer case.

For the ATTESSA system, it's more a case of levels of grip. ATTESSA basically detects slip and apportions power appropriately to maximise the traction that the car has between front and rear axles.
If you've got narrower tyres at the front, the amount of mechanical grip is, in most cases, going to be lower and this can confuse the ATTESSA system. So in order for ATTESSA to work properly, the same level of mechanical grip should be available front and rear, ie matching tyre sizes

patty · 23rd October 2008, 01:25 AM

Thanks again Mark for taking the time to explain in detail, i have been enlightened!

22nd October 2008, 12:22 PM	#1
patty Skyline Enthusiast Registered User Join Date: Oct 2008 Drives: R33 GT-R Posts: 13	What size tyres for 18" 350z rims? I have some factory spec 350z 18" rays on my r33 gtr and was after a little tyre advice. Currently the rears have 245/45/18 and 225/45/18 on the front, would the same tyre sizes be ok or what do you guys suggest? Here's a link to the wheels 350z wheel specs Track 18" v.1, 3rd on the list. Cheers!

22nd October 2008, 01:51 PM	#2
Big Mark Apathetic Moderator Membership No. 068 Join Date: Dec 2005 Location: Canada / South Hants County: Outside UK Drives: This and that Posts: 2,061	As it's a GTR you REALLY should have the same size tyres/wheels both front and rear. If they're not the same, or at least very, very close in overall diameter then you could eventually screw up the transfer case and it can also play havoc with the ATTESSA. The ideal size to keep the diameter the same as the original 17's would be 245/40-18. With the 245/45-18's you're running about 4% over, which means your speedo will read lower than your actual speed by 4%. One way or another, you should get the fronts and rears matching ASAP.
	__________________ I used to be someone around here! Now I'm quite happy being no-one somewhere else. Normal services will resume....sometime in 2010

22nd October 2008, 02:05 PM	#3
Squeak Has stopped squeaking Administrator Membership No. 395 Join Date: Jan 2006 Location: South East County: Essex Drives: A slow red thing Posts: 8,746	What Mark said ^^^ sound advice
	__________________ Skyline Owners Club - UK based owners club for all marques of the Nissan Skyline Video Channel - Videos of past events & meets, Trackdays, Santapod & Driveout's Want to buy a banner ad or trade on the forum? Find out the details here.

22nd October 2008, 08:39 PM	#5
Big Mark Apathetic Moderator Membership No. 068 Join Date: Dec 2005 Location: Canada / South Hants County: Outside UK Drives: This and that Posts: 2,061	Short answer is basically yes, it's important to have the same size all round, ie same width, same section and same rim size. Reasonings broken down into a bit more detail below:- For the sake of the transfer case it's more important to have the same rolling radius. eg. the standard tyres on an R33GTR are 245/45-17's which have and overall diameter of 652.3mm. Your current setup has 659.7mm (225/45-18) on the front 677.7mm (245/45-18) on the back......this means your fronts are spinning almost 3% quicker than the backs which isn't good for the transfer case. For the ATTESSA system, it's more a case of levels of grip. ATTESSA basically detects slip and apportions power appropriately to maximise the traction that the car has between front and rear axles. If you've got narrower tyres at the front, the amount of mechanical grip is, in most cases, going to be lower and this can confuse the ATTESSA system. So in order for ATTESSA to work properly, the same level of mechanical grip should be available front and rear, ie matching tyre sizes
	__________________ I used to be someone around here! Now I'm quite happy being no-one somewhere else. Normal services will resume....sometime in 2010

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22nd October 2008, 06:43 PM	#4
patty Skyline Enthusiast Registered User Join Date: Oct 2008 Drives: R33 GT-R Posts: 13	Cheers for the info Big Mark much appreciated, i shall take that advice onboard when i buy some new tyres. Is it equally important for both front and rears to be the same overall width? or is it acceptable to have narrower wheel/tyre combo on the fronts such as in my case? You're also bang on about my speedo being out ;-)

23rd October 2008, 01:25 AM	#6
patty Skyline Enthusiast Registered User Join Date: Oct 2008 Drives: R33 GT-R Posts: 13	Thanks again Mark for taking the time to explain in detail, i have been enlightened!

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