08 997 C4s wheels 8/57 11/67 ?
08-27-2019, 09:03 AM
#1
08 997 C4s wheels 8/57 11/67 ?
I had my car in to the shop and the tech suggested that my car possibly had the wrong offset. My car has 19 carrara classics that are 8/57 and 11/67 with spacers. I assumed the spacers were because the car is lowered with eibachs. Looking into the fitment chart here:
https://www.alloywheelsdirect.net/in..._chart/porsche
it looks like I should have 51 in the rear:
19x8 57 235/35R 19 19x11 51 305/30R 19 Porsche
The best I can tell is that I have NB S wheels on my car with spacers:
19x8 57 235/35 R19 19x11 67 305/30 R19
https://www.alloywheelsdirect.net/in..._chart/porsche
it looks like I should have 51 in the rear:
19x8 57 235/35R 19 19x11 51 305/30R 19 Porsche
The best I can tell is that I have NB S wheels on my car with spacers:
19x8 57 235/35 R19 19x11 67 305/30 R19
08-27-2019, 11:55 AM
#2
You have a set of narrow body wheels on your car. However, your spacers are probably putting you on the correct offset. I don't think that would create any negative impact on the suspension if you are properly compensated. However, the rear will have less dish than the 4S version.
08-27-2019, 12:01 PM
#3
Rennlist Member
You have normal narrow body offsets with ET67 on a rear. There is nothing that you should do. Many for aesthetic reasons just put 15mm spacer to bring wheels out. ET51 is smallest you could do typically without looking at lower springs. Fronts are the same.
08-28-2019, 10:16 AM
#4
RL Community Team
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A 305 rear tire is a little wide for an 11" rear wheel. 305s run better on 11.5" or 12" wide wheels and instead of the tread profile rounding at the contact patch because it's being pulled in on the sides, it gets flattened, which I proves the contact patch and footprint. 295s are the proper width tire for the 11" rim, but I'm sure many people run the 305 not thinking about or understanding what I wrote first, because wider must be better, right?
Also, 53 is a normal OEM front offset, but that's on a 8.5" wide wheel, and I personally think 50 is the ideal front offset and what I had my custom Forgelines made to. 57 sets the outer lip of the wheel further in and that 1/2" narrower width means it's another 6mm or so further in (half of that 1/2" difference - the other hald of it makes the inner lip 6mm further out) so you're a good 1/2" to 3/4" inset with the outer lip on those wheels and probably why there's a spacer installed - is it a 12mm?
When you wear out these tires, if you don't love the look of the current wheels, I'd consider upgrading to something that sits right without the spacers and handles the wider tires better.
Also, 53 is a normal OEM front offset, but that's on a 8.5" wide wheel, and I personally think 50 is the ideal front offset and what I had my custom Forgelines made to. 57 sets the outer lip of the wheel further in and that 1/2" narrower width means it's another 6mm or so further in (half of that 1/2" difference - the other hald of it makes the inner lip 6mm further out) so you're a good 1/2" to 3/4" inset with the outer lip on those wheels and probably why there's a spacer installed - is it a 12mm?
When you wear out these tires, if you don't love the look of the current wheels, I'd consider upgrading to something that sits right without the spacers and handles the wider tires better.
08-28-2019, 01:30 PM
#6
RL Community Team
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That means I could probably go to a 315 or maybe even 325 on my 12" rears, and then move to a 245 in the front to achieve the same grip balance. I run 315s on my 12" wide Cayenne wheels and that works fine.
08-28-2019, 03:02 PM
#7
Yes, my factory wheels are 19X11 with a 51 backspace and my tires (for the remainder of the summer) are the Bridgestone RE050A with the rim guard in 305/30R19. They have a bit more square edge coming up from the rim than the 295s I think. Carrera S 2 I think is my wheel.
Anyways, on the Carrera 4 models, you've got to consider the tire diameter offset to keep the front diff happy. At the same time as many have noted, one brand's 305 may be the same width as another brand's 295, which if the aspect ratio is true means that there are variances in the F/R offset. Porsche obviously have designed for this since everyone goes through 2 sets of rears for every 1 set of front and we don't have reports of front diffs blowing up constantly. Porsche specs a 295 winter tire size in both the 19 and 18" wheels. But I wouldn't want to push things too far. Going to a 325 on a 4S without going up a size on the fronts is probably asking for trouble, same with going down to a 285. I run a 265 winter rear, but it is a Porsche specific size and has a different aspect ratio. I don't think a 315 would fit well on the 11" rim and would probably be over-driving the front diff.
Anyways, on the Carrera 4 models, you've got to consider the tire diameter offset to keep the front diff happy. At the same time as many have noted, one brand's 305 may be the same width as another brand's 295, which if the aspect ratio is true means that there are variances in the F/R offset. Porsche obviously have designed for this since everyone goes through 2 sets of rears for every 1 set of front and we don't have reports of front diffs blowing up constantly. Porsche specs a 295 winter tire size in both the 19 and 18" wheels. But I wouldn't want to push things too far. Going to a 325 on a 4S without going up a size on the fronts is probably asking for trouble, same with going down to a 285. I run a 265 winter rear, but it is a Porsche specific size and has a different aspect ratio. I don't think a 315 would fit well on the 11" rim and would probably be over-driving the front diff.
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08-28-2019, 03:33 PM
#8
RL Community Team
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Yes, my factory wheels are 19X11 with a 51 backspace and my tires (for the remainder of the summer) are the Bridgestone RE050A with the rim guard in 305/30R19. They have a bit more square edge coming up from the rim than the 295s I think. Carrera S 2 I think is my wheel.
Anyways, on the Carrera 4 models, you've got to consider the tire diameter offset to keep the front diff happy. At the same time as many have noted, one brand's 305 may be the same width as another brand's 295, which if the aspect ratio is true means that there are variances in the F/R offset. Porsche obviously have designed for this since everyone goes through 2 sets of rears for every 1 set of front and we don't have reports of front diffs blowing up constantly. Porsche specs a 295 winter tire size in both the 19 and 18" wheels. But I wouldn't want to push things too far. Going to a 325 on a 4S without going up a size on the fronts is probably asking for trouble, same with going down to a 285. I run a 265 winter rear, but it is a Porsche specific size and has a different aspect ratio. I don't think a 315 would fit well on the 11" rim and would probably be over-driving the front diff.
Anyways, on the Carrera 4 models, you've got to consider the tire diameter offset to keep the front diff happy. At the same time as many have noted, one brand's 305 may be the same width as another brand's 295, which if the aspect ratio is true means that there are variances in the F/R offset. Porsche obviously have designed for this since everyone goes through 2 sets of rears for every 1 set of front and we don't have reports of front diffs blowing up constantly. Porsche specs a 295 winter tire size in both the 19 and 18" wheels. But I wouldn't want to push things too far. Going to a 325 on a 4S without going up a size on the fronts is probably asking for trouble, same with going down to a 285. I run a 265 winter rear, but it is a Porsche specific size and has a different aspect ratio. I don't think a 315 would fit well on the 11" rim and would probably be over-driving the front diff.
I was just mentioning what I might do on my car which is a 2S so the F/R relationship isn't as critical as long as its within the windows of the PSM and ABS systems.
08-29-2019, 08:48 PM
#9
My 2006 C4S came stock with Carrera Sports Wheels
Front
-8.5 x 19 et 55 front with 235/35/19 tire. I added 5mm Porsche spacer to get an et 50 mm
Rear
-11.5 x 19 et 67 rear, but with Porsche 17mm lightweight spacer to correct it to a 50mm offset. Came this way stock from factory. 305/30/19 tire. Seems like on some early C4's Porsche used narrow body wheels with 17mm spacers. Maybe due to inventory on hand or that some deeper C4 wheels with proper offset had not been manufactured yet.
I will agree with 305 rear tire on 19x11. Although Porsche shipped most wide body cars with a 305 rear tire, regardless if 19x11 or 19x11.5. I tend to agree with the "look and function" of a tire that is slightly stretched or has rounded corner from sidewall to flat tread vs a more squared of edge/corner. It's a personal taste issue. I also do not like tires that look too stretch with the metal of rim out further than the bead lip.
Just be aware that on the AWD C4 cars that Porsche wanted that relationship between a 235 front and 305 rear to work with the front to rear ratio of the transaxle/differential. With that said I do not think any damage would happen if you were off my 10mm 305 vs 295 tire in the rear on a AWD.
I will say this... as far as looks are concerned. If your C4S is on stock springs then going with a smaller tire, 295, will make that "wheel/fender gap" look even bigger and your suspension look taller. Keep us posted!
Front
-8.5 x 19 et 55 front with 235/35/19 tire. I added 5mm Porsche spacer to get an et 50 mm
Rear
-11.5 x 19 et 67 rear, but with Porsche 17mm lightweight spacer to correct it to a 50mm offset. Came this way stock from factory. 305/30/19 tire. Seems like on some early C4's Porsche used narrow body wheels with 17mm spacers. Maybe due to inventory on hand or that some deeper C4 wheels with proper offset had not been manufactured yet.
I will agree with 305 rear tire on 19x11. Although Porsche shipped most wide body cars with a 305 rear tire, regardless if 19x11 or 19x11.5. I tend to agree with the "look and function" of a tire that is slightly stretched or has rounded corner from sidewall to flat tread vs a more squared of edge/corner. It's a personal taste issue. I also do not like tires that look too stretch with the metal of rim out further than the bead lip.
Just be aware that on the AWD C4 cars that Porsche wanted that relationship between a 235 front and 305 rear to work with the front to rear ratio of the transaxle/differential. With that said I do not think any damage would happen if you were off my 10mm 305 vs 295 tire in the rear on a AWD.
I will say this... as far as looks are concerned. If your C4S is on stock springs then going with a smaller tire, 295, will make that "wheel/fender gap" look even bigger and your suspension look taller. Keep us posted!