Tire Size Question
02-11-2002, 11:58 AM
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Tire Size Question
Just got a 1994 933 c2. <img src="graemlins/jumper.gif" border="0" alt="[jumper]" /> Was never into tire details with my old standard cars. Just replaced them at the dealers. Now I have to change tires and read so much about sizes and difference between rear and front etc. Would appreciate if somebody could tell me what the numbers in the tire size mean and how to read them. BTW, my car has the following tires
Front 215/45/zr17
Rear 275/40/zr17
I understand that zr is high speed and 17 is the rim size. What is the 215 and the 45?
On the 993 forum, I was advised that the right combination is important to avoid ABS problems. My manual is in German and I cant read. I am trying to get an English one. In the meantime, can somebody tell me what is the right sizes I should fix for both front and rear. My tires need changing and I think I will change all 4. Is it okay to change only the front 2 for the time being?
Thanks for any assistance.
Front 215/45/zr17
Rear 275/40/zr17
I understand that zr is high speed and 17 is the rim size. What is the 215 and the 45?
On the 993 forum, I was advised that the right combination is important to avoid ABS problems. My manual is in German and I cant read. I am trying to get an English one. In the meantime, can somebody tell me what is the right sizes I should fix for both front and rear. My tires need changing and I think I will change all 4. Is it okay to change only the front 2 for the time being?
Thanks for any assistance.
02-12-2002, 08:56 AM
#2
Z
I have a 964 so I won't speculate on which sizes of tires are going to best or recommended for you. But some general data on what the numbers mean:
the first number is the width of the tire in millimetres. the second number is called the aspect ratio and shows the height of the tire wall as a percentage of the width. so in the case of a 215/45 tire, the height will be 215mm x 40% = 96.75mm
so from this, you can see that a 215/45 tire has a smaller circumference than a 275/40 tire even though the aspect of the wider tire is smaller.
to keep thing simple and to avoid exposing any lack of in depth knowledge I have, I would check out this website : <a href="http://www.tirerack.com/tires/tiretech/general/size.htm" target="_blank">Tirerack.com tire sizes</a>
You can get this site to give you the standard sizes for your model year so you can compare what you have now to what you should have. If you use the car for the road you should keep the circumference of the wheel/tyre combination as to close to stock as possible in order to have (a) no problems with ABS etc. and (b) the speedo working accurately. In your case with 275/40 on the rear you might have a slightly too big circumference compared to standard which I think is 255/40. The reason may be that a 275/35 tyre is very hard to find and that the previous owner defintely wanted the 275 width on the tyre for performance (looks...
)
Anyway, don't listen to my ramble - check the data on the web which should give you a good starting point.
I have a 964 so I won't speculate on which sizes of tires are going to best or recommended for you. But some general data on what the numbers mean:
the first number is the width of the tire in millimetres. the second number is called the aspect ratio and shows the height of the tire wall as a percentage of the width. so in the case of a 215/45 tire, the height will be 215mm x 40% = 96.75mm
so from this, you can see that a 215/45 tire has a smaller circumference than a 275/40 tire even though the aspect of the wider tire is smaller.
to keep thing simple and to avoid exposing any lack of in depth knowledge I have, I would check out this website : <a href="http://www.tirerack.com/tires/tiretech/general/size.htm" target="_blank">Tirerack.com tire sizes</a>
You can get this site to give you the standard sizes for your model year so you can compare what you have now to what you should have. If you use the car for the road you should keep the circumference of the wheel/tyre combination as to close to stock as possible in order to have (a) no problems with ABS etc. and (b) the speedo working accurately. In your case with 275/40 on the rear you might have a slightly too big circumference compared to standard which I think is 255/40. The reason may be that a 275/35 tyre is very hard to find and that the previous owner defintely wanted the 275 width on the tyre for performance (looks...
)Anyway, don't listen to my ramble - check the data on the web which should give you a good starting point.
02-13-2002, 07:12 AM
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Zumbera
Christa is right the rears you currently have are incorrect for your car and the rolling radius will be too large which could effect the gearing.
The correct sizes for a 993 on 17" rims should be 205/50 on the front and 255/40 on the rear.
They should also be N rated which means they have been homogolated for Porsche use
Christa is right the rears you currently have are incorrect for your car and the rolling radius will be too large which could effect the gearing.
The correct sizes for a 993 on 17" rims should be 205/50 on the front and 255/40 on the rear.
They should also be N rated which means they have been homogolated for Porsche use