tire size for wheels

[Hoss]

I've tried to find the answer to this question before I asked this so please bear with me on this question that seems so simple I don't know why I don't already know the answer to this.

Anyways, here goes. What size tires will fit on 7 and 8 inch rims? width wise obviously. For my Z i want something like 245/45 on either 16s or 17s whichever will fit, but I'm just curious as to which rim width I would need for 245 wheels.

Thanks alot,

[Curtis240Z]

245s would need 8" wheels. I hope you have your plan laid out because that size would need coil-overs or flares.

[Hoss]

to be honest, i don't have an exact "plan" but i was planning on using eibach springs and tokico HP shocks. i have not found any coilover sets for the 280z. would 8" wheels work with that set up if i get flares? or would it rub on the suspension somehow?

could you also point me in a direction to find some coilovers for the 280z?

[John Coffey]

Coil overs for a 280Z are the same as for a 240Z except the threaded tube needs to have a larger ID. I sell the parts and complete strut assemblies.

The best fit on an 8" rim from a performance perspective is a 225 width tire. A 245 width tire works better on a 8.5" wide wheel with 9" being the best. Here's a shot of 245/40-17s on 8.5" wide wheels:

[Arne]

The best fit on an 8" rim from a performance perspective is a 225 width tire. A 245 width tire works better on a 8.5" wide wheel with 9" being the best.

I agree with John. If you are limited to 7.5-8.0" width, stick with 225s. I have 225/45-17s on 8.0" (on the BMW, not the Z) and the fit is near perfect. You'd definitely want 8.5 or more for best results with 245s.

[Hoss]

so im guessing that i am in fact limited to 7.5-8" wheels since im not using coilovers?

[Walter Moore]

so im guessing that i am in fact limited to 7.5-8" wheels since im not using coilovers?

You are limited by the back spacing of the wheel. On a 240Z anything more than about 5 inches will cause the tire to rub on the spring, or the strut housing at the bottom of the spring.

I am not sure about the 260/280, but I suspect they are similar.

The "back spacing" is the distance from the square-up (mounting) surface to the inner flange (car side) of the wheel. This is different from offset, which is the distance from the square-up to the center-line.

For a 245/45 on an 8 inch wheel you have a section width of 243mm, which means you need an offset of 5mm or less. (That is just a rough guess, don't take it as undisputed truth.) The springs will rub on the tire, not the wheel, so you need to use the tire section width, more so than just the wheel width when trying to calculate if a tire/wheel combination will fit on the car. Tires will have a slightly different section width depending upon the wheel to which they are mounted.

BTW, I don't know about racing applications, but I have a 2002 edition of the Tire and Rim Association standards book, and they list the "Measuring Rim Width" (nominal wheel width) for a 245/45 tire (in both 16 and 17) as 8 inches. The approved rim contours are 7 1/2J 8J, 8 1/2J, and 9J (J means passenger car bead profile.)

The nominal wheel width for a 225/45 is listed as 7 1/2 inches.

That means nothing from a racing perspective, but for street use an 8 inch wheel would be considered the typical width for a 245/45 tire.

[Hoss]

Wow, thanks that was very informative. So now I understand that I need to know the tire width and wheel offset to find out if it will rub. Is that for when the wheel is turned or straight? Is there a way of figuring out if rubbing will occur at the maximum turning angle?

I was at one point thinking about going with smaller front wheels/tires than the rear but I'd prefer to use 245/45/16 or 17s on all 4 corners.

[Zedyone_kenobi]

My question is what is the use for the car? Are you planning on racing it. I see your soon to have a stroked 3.2 in your signature. If the car is just going to be on the street, then why the need for 245's. That is a huge amount of rubber on the road. Going too wide on a car can sometimes lead to ill handling effects in steering feel. I guess it depends on what you are looking for. I find that sticking with a tire that will fit perfectly and then buying the stickiest tire possible often leads to better results. As light as Z's are, the tires are not worked as hard and I think you can get away with 225's quite nicely. I have 205's on mine, and they look 'the business' in my personal opinion.

[Hoss]

It's not gonna be a racecar, just something for me to have a ton of fun out on the streets during the summer. Maybe take it to the drags and the track a couple times a year, but mainly just street use.

Maybe if i go 245/45/17 in the rear and go 205/45 in the front? Or something like that

[Hoss]

I just don't want too little rubber that I end up burning out the tires alot faster than normal.

Maybe someone could post what size tires theyr using and how much hp they have? I'm looking to make around 300-330hp after my stroker.

[John Coffey]

I find that sticking with a tire that will fit perfectly and then buying the stickiest tire possible often leads to better results.

Exactly! Tire compound is more important then tire width.