Front Differential Chewed due to incorrect wheel/tire se up
#212
Your front drive is useless with a 305/30/19 and 235/35/19 combo since your rears are bigger than the fronts. The viscous coupler of the AWD system requires that the rear wheels turn slightly faster than the fronts otherwise you can not transfer positive torque to the front. Very simple....
The reason I ask is because when I leave the line hard and also power shift 1st to 2nd but not spinning the tires,my front chirp looking to dig in...And my rear tires are are a bigger diameter by .4''..
Thanks for your info..
#213
HI..Interesting....If I may ask,where did you get or learn that??
The reason I ask is because when I leave the line hard and also power shift 1st to 2nd but not spinning the tires,my front chirp looking to dig in...And my rear tires are are a bigger diameter by .4''..
Thanks for your info..
The reason I ask is because when I leave the line hard and also power shift 1st to 2nd but not spinning the tires,my front chirp looking to dig in...And my rear tires are are a bigger diameter by .4''..
Thanks for your info..
To look at this from the point of the viscous coupler, when the front wheels are smaller then the rears (as in a 235/35/19 and 305/30/19 combo) they will obviously spin faster then the rears. When the fronts spin faster then the rears then they drive their respective vanes within the viscous coupler faster than the vanes connected the the cardan shaft / rear drive. In essence, the front wheels are transferring torque to the rear through the viscous coupler. This happens until the rears start rotating faster due to slippage for example. An easy analogy would be this: You have a pipe with a motor on the front of the pipe turning a propeller midway in the pipe facing another propeller connected to a motor at the back of the pipe. If the front motor spins the propeller faster then it will push whatever "medium" is inside past the slower turning propeller in the rear. The front wheel drive portion of our AWD system is incredibly basic when you really grasp the simplicity of it's operation. Hope this helps....
The only limitation that Porsche puts on the AWD system viscous coupler is the 5mph difference between the rotation of the front and rear wheels which works out to 21 revs per mile difference of the front to rear axle at 180mph. This limitation most likely has to do with the overheating of the temperature sensitive silicone fluid due to rotational differences of the input/output vanes in the viscous coupler.
Here is a good read that explains the AWD system on our cars on page 257-259:
http://books.google.com/books?id=Raa...eather&f=false
Last edited by pwdrhound; 06-19-2012 at 04:16 PM.
#216
Spec Sidewall Radius Diameter Circum Revs/Mile Difference
225/40-18 3.5in 12.5in 25.1in 78.8in 804 0.0%
235/40-18 3.7in 12.7in 25.4in 79.8in 794 1.3%
295/30-18 3.5in 12.5in 25.0in 78.4in 808 0.0%
315/30-18 3.7in 12.7in 25.4in 79.9in 793 1.9%
on either an 8.5 or 9 front wheel and 12 rear.
225/40-18 3.5in 12.5in 25.1in 78.8in 804 0.0%
235/40-18 3.7in 12.7in 25.4in 79.8in 794 1.3%
295/30-18 3.5in 12.5in 25.0in 78.4in 808 0.0%
315/30-18 3.7in 12.7in 25.4in 79.9in 793 1.9%
on either an 8.5 or 9 front wheel and 12 rear.
#217
Spec Sidewall Radius Diameter Circum Revs/Mile Difference
225/40-18 3.5in 12.5in 25.1in 78.8in 804 0.0%
235/40-18 3.7in 12.7in 25.4in 79.8in 794 1.3%
295/30-18 3.5in 12.5in 25.0in 78.4in 808 0.0%
315/30-18 3.7in 12.7in 25.4in 79.9in 793 1.9%
on either an 8.5 or 9 front wheel and 12 rear.
225/40-18 3.5in 12.5in 25.1in 78.8in 804 0.0%
235/40-18 3.7in 12.7in 25.4in 79.8in 794 1.3%
295/30-18 3.5in 12.5in 25.0in 78.4in 808 0.0%
315/30-18 3.7in 12.7in 25.4in 79.9in 793 1.9%
on either an 8.5 or 9 front wheel and 12 rear.
#218
Here is a tid bit of info..If the tire spec for diameter is given on a certain rim size..
It will be a smaller diameter on a wider rim and a bigger diameter on a narrower rim..
I HAVE measured this many times on my tire installs..A .5 " width can make a .25" diameter difference..
Just sharing my findings
It will be a smaller diameter on a wider rim and a bigger diameter on a narrower rim..
I HAVE measured this many times on my tire installs..A .5 " width can make a .25" diameter difference..
Just sharing my findings
Last edited by johnspeed; 09-14-2012 at 02:42 PM.
#219
Here is a tid bit o info..If the tire spec for diameter is given on a certain rim size..
It will be a smaller diameter on a wider rim and a bigger diameter on a narrower rim..
I HAVE measured this many times on my tire installs..A .5 " width can make a .25" diameter difference..
Just sharing my findings
It will be a smaller diameter on a wider rim and a bigger diameter on a narrower rim..
I HAVE measured this many times on my tire installs..A .5 " width can make a .25" diameter difference..
Just sharing my findings
#220
Every tire is different. A Nitto NT01 in a 315/30/18 fits perfectly square on a 12" rim while a Michelin will be stretched a bit. NT01s run wide, a 315 is more like a 325..... A 235/40/18 NT01 will also fit perfectly square on a 9" rim while a PS2 will be stretched..
#221
i have only found about 6 tire sets that fit the 315/235 combo and they are basically split between the 100 treadwear and the 220 treadwear. michelin, pirelli,kumho,falken,nitto,toyo. any others? for me im leaning towards the pirelli
#222
i do realize that but my point was oem is a pirelli p zero which calls for a 11.5" rim and yet porsche runs it on a 12" rim against the recommendations of the tire manufacturer.
i have only found about 6 tire sets that fit the 315/235 combo and they are basically split between the 100 treadwear and the 220 treadwear. michelin, pirelli,kumho,falken,nitto,toyo. any others? for me im leaning towards the pirelli
i have only found about 6 tire sets that fit the 315/235 combo and they are basically split between the 100 treadwear and the 220 treadwear. michelin, pirelli,kumho,falken,nitto,toyo. any others? for me im leaning towards the pirelli
me, i would go with any of these: michi's/pirelli's/b'stones/yokos ( i'm leaning toward yoko advans when i need new front AND rears myself ).
up to now, i've stayed with the ps2's simply because i think those are the best made of the sample group. but i have NO data to back that up, AND they ain't cheap, obviously.. just my experience with the 315/30 size. as for the choices you've got, i wouldn't worry about any of those on a 12" wheel. too many of us have run them for too long without issues.
in my uneducated opinion, those are THE sizes ( the 9x12x18 combo ) for this car.
#223
So to beat this dead horse again... I'm keeping my 305/30/19 rear tires. what's the best match for the front? I established my 235/35/19s were a NO GO the hard way. Is a 235/40/19 a good match? or was it 225/40/19?
#225
Isn't this what the problem was??? Out of the sizes mentioned, depending on manufacturer and rim size, the 235/40/19 will likely be the best match. Based on pure size, it is slightly taller, which is desirable and has been mentioned before, and well within the safe range. Out of all the sizes mentioned, 235/35/19 is the worst match. My 2 cents having done a lot of the same research myself and currently running 19" rims.