wheel offset
08-07-2015, 08:31 PM
#1
Pro
Thread Starter
wheel offset
I'm interested in some new wheels, and in doing some research discover that the manhole style have different offsets for different yrs. I have read
1983 - 86 fronts, 65mm rears, 65mm
1987 - 91 fronts, 65mm rears, 52.3mm
my question is I own an 86.5 so what do I have? If I pull them will I see it embossed on the back? Curious because I just bought new tires and may have got the wrong size. Thanks for any help.
1983 - 86 fronts, 65mm rears, 65mm
1987 - 91 fronts, 65mm rears, 52.3mm
my question is I own an 86.5 so what do I have? If I pull them will I see it embossed on the back? Curious because I just bought new tires and may have got the wrong size. Thanks for any help.
08-07-2015, 08:42 PM
#2
Nordschleife Master
The giveaway is the width of the rears. On S4's (87-91) the rear manhole cover is ET52.3 and 16x8.
The 16x7's are all ET65, front and rear.
The S4 rears fit the earlier cars just fine - although they'll push the car to understeer a bit more.
And yes, you'll see it embossed on the back of the wheel face, along with Porsche part numbers etc.
The 16x7's are all ET65, front and rear.
The S4 rears fit the earlier cars just fine - although they'll push the car to understeer a bit more.
And yes, you'll see it embossed on the back of the wheel face, along with Porsche part numbers etc.
08-07-2015, 08:51 PM
#3
Pro
Thread Starter
Thank you Hilton. I'm going out to check right now. I needed new fronts, and dealer put same size and make as rears, but also moved rears up front and new to the back. If they're diff. offset I'll be all mixed up.
08-08-2015, 05:06 AM
#4
Rennlist Member
The S4 wheel set was a logical development for the 928 so that it could accommodate a 245x45 section at the rear. A simple fact of life is that this particular section size is getting more and more difficult to obtain as time passes with 18 inch rims being the de-facto stock size these days- even 17 inch tyres are getting more difficult to obtain.
The problem 928 owners face is that wheel sets generally speaking are not designed for the 928 steering geometry and thus other Porsche wheel sets do not fit correctly up front. Wheels with too little offset are the norm, particularly so up front where as Hilton says they are designed to have a ET65 and thus give a neutral scrub radius of about 13mm in the process.
Folks can and do run with ET50 wheels up front and cosmetically they look very good because they fill out the wheel arch nicely but once you start working the car against the clock on a track then you see the difference not to mention other characteristics such as tramlining. Many folks drive their cars "socially responsibly" so do not notice these debits but the thing is why have a high performance machine if the performance part is compromised?
There are off take wheel sets that get close to 928 offset specs [Panamera?] but still fall short of the mark. If you can get a set of S4 wheels and find the correct tyres that would also be good.
If you are on 7x16 inch rims then logically they should be fitted with 225x50 rubber all round but with a 86.5 model that is giving around 300 bhp I suspect the rear will struggle for grip especially so if you have no LSD fitted.
On a separate note I do not personally subscribe to rotating the tyres on these cars just because [in this instance] you can. I rather suspect such action will compound any lack of grip issues but to be clear I have no specific experience of this. I also like to have fresh rubber all round but that is me.
Rgds
Fred
The problem 928 owners face is that wheel sets generally speaking are not designed for the 928 steering geometry and thus other Porsche wheel sets do not fit correctly up front. Wheels with too little offset are the norm, particularly so up front where as Hilton says they are designed to have a ET65 and thus give a neutral scrub radius of about 13mm in the process.
Folks can and do run with ET50 wheels up front and cosmetically they look very good because they fill out the wheel arch nicely but once you start working the car against the clock on a track then you see the difference not to mention other characteristics such as tramlining. Many folks drive their cars "socially responsibly" so do not notice these debits but the thing is why have a high performance machine if the performance part is compromised?
There are off take wheel sets that get close to 928 offset specs [Panamera?] but still fall short of the mark. If you can get a set of S4 wheels and find the correct tyres that would also be good.
If you are on 7x16 inch rims then logically they should be fitted with 225x50 rubber all round but with a 86.5 model that is giving around 300 bhp I suspect the rear will struggle for grip especially so if you have no LSD fitted.
On a separate note I do not personally subscribe to rotating the tyres on these cars just because [in this instance] you can. I rather suspect such action will compound any lack of grip issues but to be clear I have no specific experience of this. I also like to have fresh rubber all round but that is me.
Rgds
Fred
08-08-2015, 12:17 PM
#5
Nordschleife Master
If you have an 86, and the wheels are original, you have 16 x 7 all the way around.
The S4 16 x 8 rears are visibly different from the 7 fronts. It's not really obvious, but you can see it if you look closely.
The 7 are slightly convex (dished outwards) and the 8 are slightly concave (dished in).
My car had, for some strange reason, a single 16 x 8 on the front, and 3 16 x 7 the rest of the way around. I didn't notice it, but the 'eagle eyes' on here spotted it immediately.
Here is my intro thread with pics of the wheels (cue the "One of These Things Is Not Like The Others" song from Sesame Street):
https://rennlist.com/forums/928-foru...o-screwed.html
The S4 16 x 8 rears are visibly different from the 7 fronts. It's not really obvious, but you can see it if you look closely.
The 7 are slightly convex (dished outwards) and the 8 are slightly concave (dished in).
My car had, for some strange reason, a single 16 x 8 on the front, and 3 16 x 7 the rest of the way around. I didn't notice it, but the 'eagle eyes' on here spotted it immediately.
Here is my intro thread with pics of the wheels (cue the "One of These Things Is Not Like The Others" song from Sesame Street):
https://rennlist.com/forums/928-foru...o-screwed.html
08-08-2015, 06:26 PM
#6
Pro
Thread Starter
thanks W.J. I was looking at a pic. on pelican of a blk. 928 and was wondering what was with the wheels. I looked at yours and did notice it right away. so mine are all 7". What wheels did you go with and can you direct me to a pic. thanks for the help guys.