boybike

My 05 Cayanne (Spriings no Air Suspension) came with 18" wheels and I have just changed over the the Pirelli Scorpion Ice & Snows (Connecticut Winters!). Being a Newbie to performance cars, please help me with the following question:

I am thinking of getting a set of 20" wheels for spring / summer driving and please ignore the fact that I KNOW they will look much cooler than my current wheels, my questions are:

1). What will they do for the ride quality (Wife complains that my car is much stiffer than the Lexus RX300 (DUHH), will the ride over our famous pot holes have her complaining more than usual?

2) What are the pluses in handling vs. the 18"?

3). On those rainy summer days, will I lose any breaking distance / slip and slide easier?


Thanks

Bruce
I know

ltc

Bruce,
Welcome to Cayenne ownership. Take 2 aspirin, keep your fingers crossed and hope for the best.

A search will yield much more additional info, but here is my 2 cents:
1. Ride will not be noticeably stiffer, as a 20" will have slightly stiffer sidewalls, but this is not as great as the spring rate.
2. A 20" wheel/tire will have a stiffer sidewall and larger contact patch.
3. Tread pattern/tire choice aside, you will not suffer more sliding...see #2 above.

I have 18" Cayenne wheels for winter and 20" Cayenne design wheels for spring/summer. FWIW, I have PASM and don't really notice a difference between 18" and 20" with the suspension set to normal/normal.

Please keep in mind that you will be replacing 20" tires fairly frequently; I got 20K from mine and it's time for new ones in the spring. However, having 2 sets of tires will help in this regard. You can search for more info on this as well.

TimC.

I have the 20" Cayenne Design rims with the Michelin Diamaris...I just changed over to my winter set: 18" Cayenne Turbo rims and I am running the "235/60HR-18 Dunlop Grandtrek WT M2 N0 (Porsche OE) XL" tires
I have not seen one snowflake yet, but here are my .02 cents on ride:

I do have the air suspension and always ride in Comfort mode since the vehicle automatically reacts for harder driving. The first thing I noticed with the winter tires was a spongy feeling going over bumps when I drove out of the tire dealer. I don't have springs, but I was expecting a HUGE difference between the two sizes, but there really wasn't.
In terms of rain performance I would rather have the 20" Michelins, the width is much more which means more rubber on the road for summer, but the tread is also really designed well for rain performance. I tried to push the Cayenne speed past my "comfort zone" during this huge downpour we had a few weeks back just so I knew where the limit was. I was on a pin-straight highway in the middle lane with no cars around and I was slowly turning the wheel back and forth looking for any slippage or hydro-planning and to my amazement this thing was driving like it was on rails !! I will keep the details of the speed I was traveling to myself since there are a few members who find the need to yell at people to remind them what the speed limit is and how dangerous this is, and the fact that you cant slow down any faster...etc...but lets just say it was north of the 65mph limit and I personally wanted to establish where the limit was and to my amazement it was even past my personal "insane zone" The weight of the vehicle really helps in this department. This really proved to me that this thing is much more capable than you think.

Good luck with your decision!!

FYI here are some details from Michelin on the Diamaris:

"The 4x4 Diamaris is Michelin's Street/Sport Truck Summer tire that provides their highest level of wet and dry traction for luxury sport utility vehicles. Used as Original Equipment on the BMW X5 4.6is, Porsche Cayenne S and Cayenne Turbo, the 4x4 Diamaris is also available in the large rim diameter sizes appropriate for other light trucks.

On the outside, the 4x4 Diamaris molds a wet weather tread compound into an asymmetric tread design that features large outer shoulder blocks that contribute to steering response and cornering confidence. A continuous center rib enhances steering precision and high-speed stability while two wide circumferential and multiple lateral grooves channel water to reduce the possibility of hydroplaning. Internally, two high-tensile steel belts are reinforced by Michelin's BAZ technology (spiral wrapped nylon Banded At Zero degrees to tire rotation) to enhance stability at high speeds while improving tire uniformity and reducing weight to assure an even ride quality.
"

ajauch

I think most of the folks on the list who use the Cay in the snow are using the dual rims strategy. I'm on winter (Pirelli Scorpion Ice & Snow) tires on the 18" Cayenne "S" rims (got them on ebay) right now. Love the Scorpions so far. Even in the dry, performance is quite good. Snow traction is excellent.

Over the course of several 4x4's, I'm pretty much in the dedicated winter tire camp. Expecially with the CT where you can really explore the additional grip a dedicated summer tire can give you. This also eliminates the "all season" tradeoffs you get into when you only have one set. So, that pretty much means two sets of rims and allows you to go for the 18's in winter (mandatory) and go for larger in Summer if you feel like it.

As far as rim sizes go, I'm not a huge fan of the 20" rims. Key issue for me is unsprung weight. If you're not careful, you can wind up adding a hundred pounds or more of unsprung weight to your car. This weight also has interia and will resist being rotated. This means reduced 0-60 performance.

If you go with a tire of similar WIDTH and only do a "plus 2" upgrade (increasing rim size but not width) then you're not really increasing the contact patch of the tire. The shorter sidewalls give you sharper turn-in but don't really produce significantly better performance on the street. IMHO, this is primarily a cosmetic upgrade. Car & Driver did a very interesting study where they took a vehicle (I think it was a 350Z) and did objective performance runs with 17-18-19 in wheels. The 17 inchers did the best. The C&D guys basically felt that the lower weight of the 17's made the difference and overcame any advantage of the larger wheels. Of course, if you spend the big bux and get wheels that are larger but don't weigh more than stock, that's a different story.

(Caveat: I'm not an automotive engineer. This is based on stuff I've read in car mags and what I've felt in the seat of my pants driving my CT with various wheels and tires)

In the rain, the SIZE of your contact patch compared to the weight of the vehicle is the most telling indicator of when you will hydroplane. Remember, it's WHEN not IF. For a given depth of water, you will eventually reach a speed that the tire cannot evacuate. Anyway, skinny tires are actually better in standing water than wide ones. This is the theory behind those gooyear aquatreds with a deep vee down the middle, efecctively turning the tire into two skinny tires side by side. At any rate, most modern tires are able to handle small amounts of standing water at freeway speeds. One nice byproduct of the extreme weight of the Cay is that it's able to maintain a contact patch longer than a lighter vehicle. My CT with summer (Conti SportContact 255/55R18) tires is very stable in heavy rain on various road surfaces. It seems less liable to hydroplane than pretty much any vehicle I've ever had. My Boxster was pretty much the worst. Huge tires and relatively low weight means bad news in standing water.

Alex

BobbyB

I too and in the dedicated winter tire camp - But even here you have choices between a performance winter tire and the regular winter tires. Most of the difference is in the turning response. As far as ride, winter tires have come a very long way and the comfort level has vastly improved over the years.
I find very little difference in the ride quality between 16" & 17", 18" & 19" or 19" & 20" tires of the same brand. But when you go from 17" to 19" or from 18' to 20" there is a difference. I don't find it to be a jaw shattering difference but you know the difference. If your wife complains about the ride if it's not like the RX300, wait for a windy day and remind her that the car is not rocking from side to side. But the ride on 20" wheels will be no where close to the ride of an RX300. Oh but the fun!!!!