What size tires?

[peterpit]

Just picked up a set of 14"x 6" aluminum rims for my 76 280z and looking for suggestions for what size tire to use. car will be used as a weekend driver. Thanks!!

[2ManyZs]

Tough question. No good answer either.

First, a lot of the tire manufacturers are steering away from 14 inch tires so the choices are becoming more limited.

Second, you need to decide which brand tire you want and which aspect ratio you would like to have. 50, 55, 60 ,65, 70 series??

You would almost need to find a tire size chart to decide which will fit your wheels and your need. With a 6 inch wide wheel you will probably want to stay with a tread width of 7 inches or slightly less. So, you probably will be looking at a tire size of 185 -205, but the deciding factor is which aspect ratio you decide on. A 185/50 and a 205/60 are going to be pretty close to the same width. Just remember the lower the aspect ratio the wider the tire will be, so a 195/70 will be narrower than a 195/50. So while I can't give a decisive answer I hope this helps.

Also each tire manufacturer gives a recommended wheel width for their specific sizes so you would almost need to get with a tire dealer to find out exactly what sizes will fit and then choose a tire brand.

[zedhead260]

A 195/70 will NOT be narrower than a 195/50.

195 is the tread width in millimetres or section width. The sidewall or aspect ratio represents the percentage of the width.

The main thing to consider with tyres is that the diameter of the wheel / tyre combination remains the same (or there abouts) as stock. Otherwise it will affect the cars overall gearing, but more importantly your speedo reading will become inacurate.

To find the diameter you need to do the following calculation, but first you need to convert the section width from millimetres to inches (divide by 25.4), and then divide the aspect ratio by 100 to give you a decimal.

Then calculate 2 x (section width x aspect ratio) + wheel rim diameter.

Hope this helps.

[AxtellZ]

My 260 i bought in August has new Firestone F-570 195/70/14's on the same size rim. Looks stock, and seem to be a really decent tire, FWIW. Haven't been on the track, but hold nicley for "spirited" driving so far. HTH,

[ZwolleY]

I will also be putting new tires on a 14x6 wheels. What size tire came stock on a '72? What is the stock wheel size? My car now has 175x14 tires. I know these are small, considering the trend to mount large tires, but are they o.k. for normal driving (I guess they must be)? The Fall 1996 issue of ZCar Magazine has a discussion of aftermarket wheels. The thinking in this article may be outdated though.

[Royce]

zedhead260,

2manyZs is right a 195/70 will have a narrower tread than a 195/50. 195 is not the tread width but is the widest point of the tire bulge when mounted on a particular rim size. If you look at a tire site they will tell you tread width, tire size, rim size used for measurement, overall diameter, etc.

peterpit,

I had 14x6 wheels on my Z and ran several combinations. I would say the 205/60 looked like the best fit on the wheel but if you are looking for better tire performance a 195/60 would probably fit better. I wouldn't go with 50 series on that rim unless you car is lowered because you will have a big gap between the tire and the wheel well.

aapiss,

If I remember correctly the stock wheel size in '72 was 5" and the tires where 175R14, I believe this was before they used aspect ratios on tire designation but I think it works out to be close to 75 series.

Hope it makes sense and helps!

[carguyinok]

keep in mind as you change tire size it will throw off your speedometer.

[ZwolleY]

To what extent does it change the speedometer? Is there a % change as tire size changes?

[Royce]

The speedometer gets a reading at the transmission, so changing the relationship of the transmission output rotations/wheel rotations causes the guage to read inaccurately. So any change to diff ratio or tire size may result in the speedometer to be incorrect. Yes the change will be by percentage but small tire size changes will not make much of a difference. If you go to http://www.geocities.com/z_design_studio/ and input your Z trans type, diff ratio and tire size you can use the resulting interactive graph to determine what your speed should be at a given RPM. Then compare to your actual results, of course this assumes your tachometer is correct!

Have fun!