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I've only had one set of 22"s on any of the four 955's I've owned and I thought the ride comfort at highway speeds was unacceptable, went back to 21"s and it smoothed out.
I also needed upper and lower control arms at 90k miles. Coincidence?
Not related to the latest question, but I'm running 285/35R22 (seems like everyone's favorite size in this thread) on my 2004 S.
Drives fine, looks good, in my opinion.
However, the circumference is significantly (enough) different from stock that I don't think I'd be able to use the spare tire. Here are my calculations of the rolling radius of these 22's vs. the stock spare 18:
18/2 + 195*0.75/25.4 = 14.758"
22/2 + 285*0.35/25.4 = 14.927"
14.927 / 14.758 = 1.1% difference (22's are 1.1% bigger)
So this means the speedo will read 1.1% low, etc.
No suspension problems or repairs so far at 102k miles, with the 22's going on around 40k.
Does anyone know how far I could drive in an emergency on the spare before damaging something?
My planned solution right now is that I just won't plan to use the spare, but I do carry a tire plug kit and would try that if I can't easily get a flatbed ride. But I've still never actually got a flat tire in my car while I was in it, so I'm mostly worrying about other things than this.
Does anyone know how far I could drive in an emergency on the spare before damaging something?
Curious for an educated answer. I always thought as long as you don't lock the axles it wouldn't matter, but tire shops are sure adamant about ruining brand new tires shaving them down to match your old ones when you need a replacement.
Curious for an educated answer. I always thought as long as you don't lock the axles it wouldn't matter, but tire shops are sure adamant about ruining brand new tires shaving them down to match your old ones when you need a replacement...
And more specifically, my question is how "bad" is the 1.1% difference in rolling distance on one of the 4 tires? For temporary, perhaps speed-limited use, how far?
I believe the logic is that both the differential driving the small wheel and the transfer case have gears designed to accommodate different rates. And they are designed (like everything) to do this within a certain difference range. So at some point, the gears and bearings (chain?, belt?) are doing more work than they were designed for, overheat / overstress, and problems occur. The owner's manual for my X5 actually specifies this in terms of a difference in revolutions per mile (which of course is directly calculable based on the rolling distances).
I have not seen something for the 955. For example, looking for something like: "if the rolling diameters vary by more than 5 revolutions per mile, don't do it."
Then once we get the spec (if there is one), next question is to see who has exceeded it and had problems or not, either by trigger safe mode-type responses from the Cayenne, or by actually damaging parts.
If the answer is basically that the 1.1% smaller spare tire can't be used safely, then I'll just take it out now. And I'd much rather try to make a rational decision here and now, rather than trust myself to be smart on the side of the road some day.
What are the issues: 22” IMO suck on the highway. They will never balance as nice as a smaller wheel. So you will get vibrations at 80mph you won’t on a smaller wheel. You will feel every reflector/seam in the pavement. They suck for any off road, even simple curb climbing. The tires are wide so expect more hydroplaning at highway speed.
They look pretty cool. Mine came with 22” and my Ceyenne is a workhorse and I tow with it a lot but not interested in buying a smaller wheel although I would prefer. It all depends on what you will be doing....if you want it to look good then that’s your wheel.
And more specifically, my question is how "bad" is the 1.1% difference in rolling distance on one of the 4 tires? For temporary, perhaps speed-limited use, how far?
I believe the logic is that both the differential driving the small wheel and the transfer case have gears designed to accommodate different rates. And they are designed (like everything) to do this within a certain difference range. So at some point, the gears and bearings (chain?, belt?) are doing more work than they were designed for, overheat / overstress, and problems occur. The owner's manual for my X5 actually specifies this in terms of a difference in revolutions per mile (which of course is directly calculable based on the rolling distances).
I have not seen something for the 955. For example, looking for something like: "if the rolling diameters vary by more than 5 revolutions per mile, don't do it."
Then once we get the spec (if there is one), next question is to see who has exceeded it and had problems or not, either by trigger safe mode-type responses from the Cayenne, or by actually damaging parts.
If the answer is basically that the 1.1% smaller spare tire can't be used safely, then I'll just take it out now. And I'd much rather try to make a rational decision here and now, rather than trust myself to be smart on the side of the road some day.
I recently got a nail in my right rear tire and had to put the spare on about 2 miles from home.
As referred to above and calculated further above, I had pre-calculated that my 285/35R22 tires would be 1.1% bigger than the spare tire. Here's what I found:
No warnings or damage noticed from the ~15 miles of total driving with the spare tire on. Never exceeded 50 mph. But I still have doubts.
Before swapping on the new tire, I did a test in front of my house, counting / measuring revolutions over the few hundred feet straight line we've got there. 34 revolutions to be exact. I found that the 3 regular tires were all pretty much exact over that distance, but the spare tire, inflated to 45 psi, was actually 2.3% smaller than the others. So I guess the dimensions specified for the spare tire are not as exact as normal tires, which is understandable.
Knowing this, I'd be even more concerned about getting a flat and driving any real distance on the spare.
From what I found Cayenne 2003-2006, they show 109 and 108 for the smaller wheel sizes. But then for 20" wheels, they show 106Y as the tire spec load and speed ratings. They don't show any wheels bigger than 20", so I figure I'm OK with my 22's rated at 106W (I know, W is for up to 168 mph, Y is up to 186 mph, so I try not to spend a lot of time over 170). Also, they were on the car when I got it, so ...
The attachment here is a couple of pages I cut out of their spec for virtually all of their cars for the last 20 years.
I like the looks of the 22's, but since I have 20" SportTechno's with winter tires, I'm going to sell my 22's after the winter tires go on, then in summer, have the 20" SportTechno's refinished in satin black, along with my stock turbo exhaust tips ... I'll get 18 or 19" takeoff rims for next year's winter setup. As for the ride, they are fine, but living in Bend, OR, we have some bumpy, pothole roads around town, and I'd rather have more sidewall ...
06-03-2018, 08:16 PM
