New member to M45 site.

[outnmbrd]

I would like to thank everyone on this site for the excellent info.I was wondering if anyone was told by Tire Rack that 245/45/18's are to big for the stock 2003 m45 wheels.I ordered a set any way and they seem to be O.K.

[lfj2025]

I put 245/45 18 on mine. No problem.

[szh]

I would like to thank everyone on this site for the excellent info.I was wondering if anyone was told by Tire Rack that 245/45/18's are to big for the stock 2003 m45 wheels.I ordered a set any way and they seem to be O.K.

Welcome to NICO!

Whoever said that at Tire Rack is pretty much incorrect - surprising that they did this! The minimum wheel width for almost all the 245/45-18 tires that I know of is 7.5" (see my sticky thread at the top of this forum for more info on tires) and the OEM wheel width is 7.5".

So, it should work just fine!

Z

[cremecreme]

245-35-20's for me!!!! no rub...welcome to the forum

[szh]

I forgot to mention that I use 245/45-18 on my OEM wheels on my 2003 M45.

No problems whatsoever.

Z

[Bag302]

245/40-18's on the stockers here

[szh]

245/40-18's on the stockers here

Which tire do you have (model and speed rating and load index)?

The three 245/40-18's that I am aware of need a 8.0" minimum wheel width. The OEM 7.5" is below that width. Yes, it will work, but has a few things you need to be aware of.

First, it is technically unsafe, although the difference of 0.5" is small enough not to be classified as a "stretch" fit (which are usually really unsafe, IMHO).

Second, because the wheel width is less than the recommended minimum (let alone the wheel width used for tire section width and tread width specs), the tire actually lifts up a bit at the edges (changing the profile of the section) and reducing the effective tread width. Making the benefit of having the wider 245 width go down a bit.

With the OEM wheel, you would actually be better off using the 245/45-18 for performance and looks (since the 245/40 has slightly lower diameter and less "full in the fender" look).

Z

[Bag302]

Here is the link to the specs on the Fuzion ZRi http://www.tirerack.com/tires/...cQty=

The tires have 3k miles on them. I'm surprised that the distributer of this tire, Tires Plus would recommend thesefor this car. I'm also surprised that the Infiniti dealer didn't mention anything about them last week while getting the wheels balanced. Dealer did say they were tough because of the aggressive tread pattern.

All I know is that I'm forced to trust what they tell me.

Let me know what you think.

[szh]

The Infiniti dealer probably would not have looked at the tire closely enough to say much about it, or simply did not know enough. But, I wish he had done his job better!

If you look at the specs for the 245/40-18 Fuzion tire, a few issues jump out.

First is the minimum rim width: 8.0". This is not too far off the 7.5" of the actual OEM tire, so it is not a major stretch per se. While I do not recommend this slight stretch, it is not going to be a cause for major concern, other than the fact that the specifications shown will not be met - they are measured at a 8.5" wheel width. The actual tread width will be a bit lower as the tire lifts on the edges slightly - please don't compensate for this by lowering the tire pressure!!!

But, far more important is the load index - it is shown as 93 in the specs. This is low for a heavy car like the Infiniti M and is potentially unsafe.

While the value of 1433 lbs per tire, for a total of 5700 lbs, may seem to be sufficient (higher than the total weight 4000lb of the car), this is a static weight situation. In dynamic conditions, like actual front tire loading during braking, bumps on the road, etc., this load can be exceeded pretty easily.

This may not lead to actual tire failure, particularly when new, but the internal tire belts and support material are experiencing higher stress than they were designed for and may break sooner (internally, and hidden from view). Leading to poor tire aging - shows up as vibration and needing frequent balancing - and worsened handling, possibly tire failure, in less miles than what would make the tread wear out! Also, remember that the actual load index of the tire decreases with age, so what might work okay now, just gets worse with time.

BTW, with one notable exception, Michelin, the tire manufacturers generally do not build in any conservatism to that load index rating.

For the M, it is highly recommended that you get at least a 94 to 95, or higher rating, load index - and, if you do not get Michelin, the higher the better is preferred. For example, I use Goodyear Eagle F1 GS-D3 245/45-18 with a 100 load index. My tire spreadsheet lists only tires that meet the specs for the M.

The bottom line: in your shoes, I would contact the place you got the tires from and ask why they sold you a tire with lower than the minimum load index for the car - they should know better than to do that! Tell them that the car requires a 94 load minimum, and you can confirm this easily with Infiniti Corporate, and they should give you full credit for the tires for another brand/model with the correct load index.

In the meantime, I would strongly recommend that you run 42 to 44 psi minimum, measured when cold, to give you some margin - the index increases with increased tire pressure.

Z

[Bag302]

Thanks for the heads up. Can you point me to your tire spreadsheet?

[szh]

Thanks for the heads up. Can you point me to your tire spreadsheet?

Sure thing ... it is in the Basic Specs sticky at the top of the forum.

Z