goodspeed928

Im thinking of putting 225/45/16 on the back
of 86, Will they fit? <img src="confused.gif" border="0">

Curt

What tire size do you have on there now?? I dont see why they wouldnt fit.

It seems to me that a lot of people dont understand what the numbers mean when they talk tires. A 225/45 16 is not that large of a tire. If im not mistaken the 225 is the tire width in milimeters aprox. 8.8" wide, the 45 means that the sidewall height is 45% of the width, so on a 225 the sidewall height would be 101.25 milimeters approx. 4" tall and of course the 16 is the rim size.

Now my question is, can you add up all the numbers and does that equal your total tire height? or does it very slightly. For the tire above it would be 4" + 16" + 4" = 24". Is that right??

Susan K Thomas

Here's a really good description of tire sizing information:

<a href="http://www.tirerack.com/tires/tiretech/general/size.htm" target="_blank">Tire Rack tire size information</a>

So, a 225/45-16 will have a smaller rolling diameter and shorter sidewall than a 225/50-16 (recommended size on 16 x 7 wheel)

Back to work...
<img src="graemlins/yltype.gif" border="0" alt="[typing]" />

Susan Thomas
DEVEK
<a href="http://www.devek.net" target="_blank">DEVEK Home Page</a>

goodspeed928

Sorry, I ment 255/50/16

Susan K Thomas

On a 16 x 7" rim, you cannot mount a 255/50-16!!! The tire is way too wide for the rim. <img src="graemlins/nono.gif" border="0" alt="[nono]" />

A wheel to tire ratio of .88 to 1.0 is desirable for predictable wheel/tire performance and sidewall behavior.

Susan Thomas
DEVEK
<a href="http://www.devek.net" target="_blank">DEVEK Home Page</a>

bcdavis

On my 83, 245/50/16 rubbed.
A 245/45/16 was the ticket.
Just slightly lower profile.
You might squeeze a 255/50/16 in there, but you would need to roll the fender lip. I agree with Susan, that if you have stock wheels, that will be a bit too big, and will look like a big donut. I doubt handling will improve. Although drag racers do it all the time. But I doubt it will help on a regular racetrack. Play with tire pressures if you want better times at the track... Or get some used slicks...

BrianG

So... a 7" rim X 25.4 = 177.8 mm metric rim width.

A 1.0 ratio suggests a 180mm tread width while a .88 ratio suggests a 200mm tread width

This sounds a bit skinny <img src="graemlins/oops.gif" border="0" alt="[oops]" />

Curt

I agree with Brian. I think the ratio of .88 to 1.0 is a bit conservative. If thats the case the recomended tire for a 7" rim would be aprox. 200mm I have 225/50 on my 7" rims and they look okay. I do think a 205 is kind of small.

BrianG

With 7" rim X 25.4 = 177.8 mm metric rim width:
a 1.0 ratio suggests a 180mm tread width while
a 0.88 ratio suggests a 200mm tread width (205)
a 0.8 ratio suggests a 222.5 tread width (225)
a 0.75 ratio suggests a 237 tread width (245)

given the stock 16" tire being 225-50 the sidewall is (I hope trig functions haven't changed in 30 years) <img src="graemlins/c.gif" border="0" alt="[ouch]" /> ....... 268mm

so, a 245 tread width with a (yikes, more trig
<img src="graemlins/crying.gif" border="0" alt="[crying]" /> ) 45 degree aspect ratio should get pretty close to the same total tire height.

The question is..... "if Porsche recommended a 0.80 tread width to rim width ratio, how bad an idea is a change of 0.05 or abour 4%. <img src="graemlins/icon501.gif" border="0" alt="[icon501]" />

BrianG

Oops....... make the 6.25%

Porsche928Driver

Keeping this simple:
245/45 will work on the factory 16"x7" rims. That's as wide as you can go!

Many people use 225/50 on the front and 245/45 on the rear.

goodspeed928

245/45/60 would be cool but
lower right? My driveway is the limit, NO more
room.

BrianG

Nope. <img src="graemlins/c.gif" border="0" alt="[ouch]" /> The sidewall height of the 245-45-16 is the same as the 225-50-16. <img src="graemlins/jumper.gif" border="0" alt="[jumper]" /> The middle number is the cord angle across the tread, but for all practical purposes you can use it as a percentage of tread width to give you sidewall height. The angle is out of 90 and the percent is out of 100, so it's close. <img src="graemlins/burnout.gif" border="0" alt="[burnout]" /> see my last post on this thread.

John Struthers

Well...
Do you have to adjust the shocks for proper ride height then or is it still in the ballpark?
If you are only changing the rears, then adjust for correct ride height, rear only, does this affect the handling adversely due to the change (?) in front to rear weight transfer or does the ride height adjustment automatically correct for balance? <img src="graemlins/icon107.gif" border="0" alt="[icon107]" />

BrianG

If the sidewall height is the same then the axle center height will not change. This means that there is no ride height change. Going from the 225-50-16 to the 245-45-16 creats essentially no difference except for tread width. The question is: "Will a 245-45 behave on a 7" wide rim?"