Analysis Paralysis on C4S tire sizing
#1
Intermediate
Thread Starter
Analysis Paralysis on C4S tire sizing
I could use some help here.
I am having 19x8.5" and 19x11" Forgestar wheels built for my 04 C4S. So, obviously, I'm moving to 19" tires.
From the reading I have done, I have to take into consideration of the tire speed in relation to front and back because of the viscous coupling for the AWD system.
Factory tire size:
F: 225/40-18
R: 295/30-18
Roughly looking at revolutions per mile charts and tire diameter charts, the front tires rotate approximately 4.007% faster than the rears
19" tires
F: 235/35-19 (for 8.5" width wheel)
R: 305/30-19
This would equate to the front tires rotating more per mile by a 2.95% difference.
Would this drop in difference cause a problem with the drivetrain?
I am having 19x8.5" and 19x11" Forgestar wheels built for my 04 C4S. So, obviously, I'm moving to 19" tires.
From the reading I have done, I have to take into consideration of the tire speed in relation to front and back because of the viscous coupling for the AWD system.
Factory tire size:
F: 225/40-18
R: 295/30-18
Roughly looking at revolutions per mile charts and tire diameter charts, the front tires rotate approximately 4.007% faster than the rears
19" tires
F: 235/35-19 (for 8.5" width wheel)
R: 305/30-19
This would equate to the front tires rotating more per mile by a 2.95% difference.
Would this drop in difference cause a problem with the drivetrain?
#7
Captain Obvious
Super User
Super User
This shroud have been determined BEFORE commissioning the rims. My suggestion is to stay as close to the OE ratio as you can.
As a side note, all the racing watercooled 911s that I've seen had 18" rims. None went bigger than that. Something to think about when looking for performance enhancements in the future.
As a side note, all the racing watercooled 911s that I've seen had 18" rims. None went bigger than that. Something to think about when looking for performance enhancements in the future.
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#8
255 would be the max I think. It could also affect driving characteristics.
Much depends on which particular tire you will choose as each of them has a different shoulder profile.
For example ... I had a 295/35/18 Bridgestone S02A on a 10J rim which was way to big. The tire lost its squareness at the shoulder. Which influenced cornering stability. However when I put on the Yokohama AD08r295/35/18 it looked much more tight and square then the Bridgestones. Most probably due to its extra stiff and stronger carcass.
So each tire type will cope differently with the extra width. Me personally, I would not go wider then 245. Moreover the balance between width in the front and rear is also important. So it depends also on that. But of course each person has its preferences and if it is for cruising around then it is less important.
Much depends on which particular tire you will choose as each of them has a different shoulder profile.
For example ... I had a 295/35/18 Bridgestone S02A on a 10J rim which was way to big. The tire lost its squareness at the shoulder. Which influenced cornering stability. However when I put on the Yokohama AD08r295/35/18 it looked much more tight and square then the Bridgestones. Most probably due to its extra stiff and stronger carcass.
So each tire type will cope differently with the extra width. Me personally, I would not go wider then 245. Moreover the balance between width in the front and rear is also important. So it depends also on that. But of course each person has its preferences and if it is for cruising around then it is less important.
#11
#12
Intermediate
Thread Starter
This shroud have been determined BEFORE commissioning the rims. My suggestion is to stay as close to the OE ratio as you can.
As a side note, all the racing watercooled 911s that I've seen had 18" rims. None went bigger than that. Something to think about when looking for performance enhancements in the future.
As a side note, all the racing watercooled 911s that I've seen had 18" rims. None went bigger than that. Something to think about when looking for performance enhancements in the future.
This only came to the surface when I was looking through the forums and ran across the tire dimension conversation and the differential. I was not aware of the rotational speed difference between the front and back. I assumed the overall tire circumference was the same front to back.
#13
Intermediate
Thread Starter
#15
Captain Obvious
Super User
Super User
I am staying as close to the ratio as possible. Also, my car will never see the track. I'm not really into that side of things. My C4S is a nice weather driver and "cars and coffee" regular. It probably sees less than 3000 miles a year. So I don't consider the wheels a "performance enhancement".
This only came to the surface when I was looking through the forums and ran across the tire dimension conversation and the differential. I was not aware of the rotational speed difference between the front and back. I assumed the overall tire circumference was the same front to back.
This only came to the surface when I was looking through the forums and ran across the tire dimension conversation and the differential. I was not aware of the rotational speed difference between the front and back. I assumed the overall tire circumference was the same front to back.