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THIS DISCUSSION / SOURCE-DERIVED OVERVIEW
Discussion summary
YOUR RESEARCHC4 and C4S Tires Size, matching set
Leading reported evidence
Run on the oem
Suggestion or failed attempt
No successful repair reported for this finding.
0
Reported fixes
0
Unsuccessful attempts
1
Discussions
Read evidence and context
Explicit resolution reports before identified causes, performed actions and suggestions. Within each level, matching component labels precede direct query mentions and inherited thread context; successful versus unsuccessful discussion counts, owner confirmations and independent discussion support determine order. This is not a probability of success.
Discussions that contain suggestions
1
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Suggestion · Original poster
Btw, I was very careful on this matter with the Cayenne (06 CS Tit Ed.), as instead of running on the OEM set (on the OEM Techno's, 20 rims are 9" on front and 10" on rear) and came from new with all four on 275, I'm now on the second set staggered, i.e.: 275/40 on front and 315/35 on rear, and with those, the diff is pretty close to 0%.
Leading evidence: 'Run on the oem' (no explicit attributable resolution; this is a reported action or suggestion). Across 1 matching discussions, The most frequently discussed action is 'Run on the oem' (1 discussions). For that action, 0 discussions report a resolution and 0 report an unsuccessful attempt. No action has an explicit, attributable resolution report under the current rules. These are forum reports and suggestions, not a confirmed diagnosis.
Source reports, not a diagnosis or a success probability. Counts refer to discussions and can overlap.
Explicit resolution reports before identified causes, performed actions and suggestions. Within each level, matching component labels precede direct query mentions and inherited thread context; successful versus unsuccessful discussion counts, owner confirmations and independent discussion support determine order. This is not a probability of success.
Discussions that contain suggestions
1
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Suggestion · Original poster
Btw, I was very careful on this matter with the Cayenne (06 CS Tit Ed.), as instead of running on the OEM set (on the OEM Techno's, 20 rims are 9" on front and 10" on rear) and came from new with all four on 275, I'm now on the second set staggered, i.e.: 275/40 on front and 315/35 on rear, and with those, the diff is pretty close to 0%.
Explicit resolution reports before identified causes, performed actions and suggestions. Within each level, matching component labels precede direct query mentions and inherited thread context; successful versus unsuccessful discussion counts, owner confirmations and independent discussion support determine order. This is not a probability of success.
Discussions that contain suggestions
1
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Suggestion · Original poster
Btw, I was very careful on this matter with the Cayenne (06 CS Tit Ed.), as instead of running on the OEM set (on the OEM Techno's, 20 rims are 9" on front and 10" on rear) and came from new with all four on 275, I'm now on the second set staggered, i.e.: 275/40 on front and 315/35 on rear, and with those, the diff is pretty close to 0%.
Explicit resolution reports before identified causes, performed actions and suggestions. Within each level, matching component labels precede direct query mentions and inherited thread context; successful versus unsuccessful discussion counts, owner confirmations and independent discussion support determine order. This is not a probability of success.
Discussions that contain suggestions
1
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Suggestion
[The XRC option, Sport Techno wheel, uses ET 63 in the rear with a 17mm spacer]
These are separate views of the same evidence. Frequency alone does not establish a fix, and these counts must not be added together.
Run on the oem
No successful repair reported for this finding.
0
Reported fixes
0
Unsuccessful attempts
1
Discussions
Read evidence and context
Discussions that contain suggestions
1
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Suggestion · Original poster
Btw, I was very careful on this matter with the Cayenne (06 CS Tit Ed.), as instead of running on the OEM set (on the OEM Techno's, 20 rims are 9" on front and 10" on rear) and came from new with all four on 275, I'm now on the second set staggered, i.e.: 275/40 on front and 315/35 on rear, and with those, the diff is pretty close to 0%.
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Suggestion · Original poster
Btw, I was very careful on this matter with the Cayenne (06 CS Tit Ed.), as instead of running on the OEM set (on the OEM Techno's, 20 rims are 9" on front and 10" on rear) and came from new with all four on 275, I'm now on the second set staggered, i.e.: 275/40 on front and 315/35 on rear, and with those, the diff is pretty close to 0%.
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Suggestion · Original poster
Btw, I was very careful on this matter with the Cayenne (06 CS Tit Ed.), as instead of running on the OEM set (on the OEM Techno's, 20 rims are 9" on front and 10" on rear) and came from new with all four on 275, I'm now on the second set staggered, i.e.: 275/40 on front and 315/35 on rear, and with those, the diff is pretty close to 0%.
Counts describe captured discussions, not unique people or a diagnosis. Author identities are not reliably stored. Exact duplicate evidence is counted once across matching discussions; one discussion counts at most once per action/state. Multiple repairs reported together remain a combination. Suggestions and failed attempts do not establish a fix. Matches cover whole discussions and can include related faults, model variants and incomplete threads.
10 eligible posts · 0 unverified posts · 1 discussions match the subject in their title or opening post.
Rennlist: 1 discussions
0 evidence records excluded for query context · 0 excluded by outcome qualification · 0 adjusted by outcome qualification.
0 acknowledgements have no verified action link; they do not establish a repair result.
Generation: 20261026T081417Z · outcome-qualification-6. Deterministic extraction; no AI model inference. How we use sources
I would be interested to know what is the factory specs about the Tires Sets for C4/C4S.
I had a dealer installation on a C4, i.e.: on 18" rims and they are:
Front : 225 x 40
Rear : 285 x 30
It took some time to realize, but I'm thinking now that this may be very wrong, as :
225 x .4 = 90 while 285 x .30 = 85.50
..or about 5% in the circumference size !
This should be quite bad for the center differential !!
Do anybody know what is the factory specs for the circumference difference in % ?
the tire sizes are the correct OEM sizes for a narrow body C4 on 18x10 rear wheels.
the difference in circumference is 1.4%
your math is wrong.
you need to account for the wheel diameter as well.
this may help you.
http://www.miata.net/garage/tirecalc.html
C4S is wide body. For the C4S:
Stock front is 18x8 ET 50 5x130 with 225/40 ZR 18 N3 tire.
Stock rear is 18x11 ET 45 5x130 with 295/30 ZR 18 N3 tire.
[The XRC option, Sport Techno wheel, uses ET 63 in the rear with a 17mm spacer]
I believe the rolling diameters for my car stock were 25.2" front and 25" rear. That's a bit less than 1% difference. The Advan AD08's in the same sizes both claim 25.0" so in theory they're the same rolling diameter.
You can find lots of threads about it, with no definite answer. The more difference, the shorter lifetime the viscous center diff will have (with lots of caveats). Most people say to stay within 4%, which is a pretty big difference. My personal preference based on nothing but reading threads and gut feel is to stay within 2%.
Thank you very much for the very good answers.
And, thanks for the (right) point on my wrong math.
So, I'm on about 1.4% difference, and these are the OEM sizes.
I'm happy to now know that.
Fyi, I tried (I still have a set of turbo twist hollow somewhere in the garage !) the 11", ET45, but, it is true that they stick out on the narrow body. This is why, I went to the "funny" "turbo twist non hollow" 10, ET65, that I do not think they are OEM at all, but, at least, they do fit the the rear nicely.
(In the front, I noted that for both narrow and wide body, rims are the same, i.e.: 8", ET50.)
(Originally, I was on 17" rims and never asked myself that question, as I kept putting the same tires on, but got a 2nd set, i.e.: "turbo twist" and very recently had this doubt !)
Btw, I was very careful on this matter with the Cayenne (06 CS Tit Ed.), as instead of running on the OEM set (on the OEM Techno's, 20 rims are 9" on front and 10" on rear) and came from new with all four on 275, I'm now on the second set staggered, i.e.: 275/40 on front and 315/35 on rear, and with those, the diff is pretty close to 0%.
(For info, when towing, i.e.: 6'000 pounds, the 315 on the rear imo, do improve the lateral stability.)
PS: Funny to know that on the Lambo Diablo VT, the front wheels are smaller but the center differential is still happy as a gears ratio in the front do the adapting job !
Hello Dennis,
I heard this already (we are a bit out of topic, but..).
I think it is a question of manuf. years, and in 06, they started to have Techno's in 9 and 10.
I bought a 5th wheel, (not an OEM, a cheapo knock-off), that is a 9" and mounted the best of old 275/40 on it. Some time, I take it with us as spare (but not often, ..as it take a lot of space in the back !)
