Tire question?? 84 944 what size should I use?
 

I know that the factory calls for a 215/60/15, What other sizes will work? I have cookie cutter wheels

205, 215, or 225
by
50, 55, 60, or 65
by
15

How much will this change my speedometer?

Here, use this:

http://www.miata.net/garage/tirecalc.html

CJ was giving you suggestions of what will not change your speedo.

Use the above and keep the same front diameter overall.

Thanks andrewgoh, that link is very cool

With 16" wheels is it the same? also, can you go 245 in the rear? Not that I would want to just curious?

You can get the closest match to overall diameter if you put a 235 on the 16 inch wheel. But 235 is kinda rare.

245 is very common and the match is fairly close too, maybe 1/4 inch bigger radius or 1/4 inch smaller. That's what I'm going to do next year, even though I hear it will increase understeer.

I swopped from a 215 / 60 / 15 to a narrower 195 / 65 / 15 (about the same outer diameter) with a remarkable diffrence, a softer ride, lighter steering (no power steering fitted on my 83 model), and a general more pleasant drive ... I must say that the high speed handling is not what it was, more body roll, but then I avoid now higher speeds.
My manual states that apart from the 215's wheels, it was also specified to use 185 / 70 / 15 when it came out in 82 / 83.

i think that 245 would be a bit too much rubber for a NA944. I mean, every pound of unsprung weight is worth ten pounds sprung... and it's not like I feel like I need wider tires when i drive my car anyhow

if you are wanting to change some handling aspect an easy key to remember is...

-traction (to an extent) comes from your weight per square inch in contact with the ground, so if you reduce the first number*width* you will reduce the foot*tire in contact with gound* and in turn increase your traction between (very noticable if youve ever drove a car with wide tires in the snow)

-control and response is going to come from the second number, the smaller the sidewall this stiffer it will be (in most occasions) giving you more resposive handling and more of a "feel" for the road if you will,

--if you are more of a highway, and very casual driver or maybe if you have a car you would like to leave the line with much more force for stoplight racing or of that effect a larger tire might work better for you

--if you are a driver that likes more agressive driver with lots of hard turning and would just like a feel for the road a tire with less sidewall might be better for you

overall just find what you like ive always had to drive the car to get a feeling for how i would like it to perform, i hope i made sense (its been a long day) and happy driving

operationcougar :
as far as traction,
Your theory is correct, but your physics are wrong. When you go to a different size tire, you are not changing the pressure per square inch and here's why: The tire has to put the same pressure to the ground and therefore needs to apply the same contact patch size tot he ground. The tire, if it's narrower, just has a more elongated, yet narrower contact patch. If the tire is wider, the contact patch is shorter and wider. The only thing that will affect that is the weight of the car and the pressure in the tires.

On my 944, I like the stability in corners, so I use a 225/50 15 on my cookie cutters. I wouldn't go wider than this on a 7" rim width. The difference in the tire is about 1 inch. The difference is not even noticeable as far as the speedometer goes - it reads a little low, but then again I hardly ever use it anyway.

yeah, i was off a little bit, it was kinda late i dont know *excuses*

im a fan of the wider on the back, i can force a slide a lot easier and thats where the driving is fun, plus with the wider tires you get a lot less hop on the rear end-nice and smooth--

It is the middle number 245 / ?? / 16 that determines the overall diameter...aspect ratio.....has to be factored into the width (245).

245 = Tire width in cms

?? = aspect ratio (how tall compaired to width)

16 = wheel size

Obviously, the larger the wheel size the lower the aspect ratio needs to be so the overall diameter of the setup does not change.

Yes you need to pick a middle number (aspect ratio) too, which you divide by 100 then multiply times the 245, then times 2, and then add 16 inches I think. I couldn't remember what the best middle number is which works for the 245 x 16 on a 944 so I didn't mention it. Use the Tire diameter calculators from various websites, makes it easy.

The main reason I want 245s in the back is I figure I can pick up more chicks that way. Can't be worse than how many I've picked up using the car so far with only the 215s.

Good luck, with the tires and the chicks.

Look at the tirerack's specs and you can get an idea of the overall diameters compared to sizes.

215/60 = 25.5 diameter
225/50 = 25" diameter
245/45 = 24.6" diameter (but won't fit a cookie cutter well if at all)

check out tire specs - here's an example of sizes compared to diameters ( I just used this b/c it's what I run):
http://www.tirerack.com/tires/Spec.jsp?make=Yokohama&model=AVS+ES100&vehicleSear ch=false&fromCompare1=yes&partnum=25VR5ES100

I have 205/55/16s on the front and 225/50/16s on the rear. I definitely like the look and feel of the wider tires in the back.