BlackTurboS

Hi Guys,

I'm sorry for asking a dumb question. I know this is a dumb question but I did tons of online reading and I can't wrap my head around it...

I currently have 21" wheels on my CTTS with 295/35R21 tires. Great for summer.

I want to go to a 20" wheel for winter with a winter/all season tire. But, in going to the 20" wheel I want the overall diameter of the tire to be the same. Meaning, decrease the wheel size by 1" but increase the amount of rubber by 1" to have the same overall tire size. I don't want a smaller tire in my wheel well, I don't like that look.

Can anyone help me figure that out? I have my wheels which are 20x10 (same width as my factory black Porsche 21"s). Just need to figure out the the tire with more rubber!

Thanks and sorry again for asking a dumb question. I tried but can't wrap my head around the tire sizes and millions of choices.

mtnrat

Try here:

http://tire-size-conversion.com/tire-size-calculator/

BlackTurboS

You are the man! Thank you. For some reason I couldn't find that in my searching. Thanks again.

Robotpedlr

The stock size for 20" wheels is 275/45/20 which should equal the diameter of your stock 21". I have 21" summer and use the Bridgestone Blizzacks on my 20" winter set up. And am very happy with it.

BlackTurboS

Thanks Robot for the feedback, I am debating between the Blizzak's, Pirelli Scorpions, or just doing an all-season on the 20's and selling my 21's.. The only problem with that is I love the OEM 21" black porsche wheels and it would pain me to get rid of them... but makes economical sense.

Brit6

I wouldn't run all-seasons in the winter, especially in Philly.

BlackTurboS

Thanks Brit, I appreciate the feedback. All my previous SUVs had all seasons on them and had no issues - but I understand the Porsche is a different animal. In that case, I'll plan to go with 20s with winter tires (we had a rough winter the past few years). I'd like to go to 19's but my brakes don't allow it. Thanks again for the feedback, sincerely appreciated!

BlackTurboS

Sorry one last question Robot. What is the width on that wheel? Would that be a 20x10" to fit the 275/45/20?

thanks

mtnrat

You should be able to go with 19's. Read this thread. I am running 19's for winter on my 2006 CTTS
https://rennlist.com/forums/porsche-...-s-brakes.html

Andy E.

If you have the red calipers on your CTTS, both 18's and 19's will fit. One of our PCA members here in Montreal ran 18's with winter tires on his wife's 2008 GTS without any issues.

See the attached PAG recommendations for winter tires.

mtnrat

I have Red calipers on my CTTS and 18" absolutely will not fit. Tried em. 380 mm discs will not allow 18's. 18's did fit my 05 CTT with Red calipers. I don't think the colour of the calipers is indicative of what wheel will fit. The GTS does not have the big brakes of the CTTS.

Sniffer

The way I read that attachment 19" is the smallest size a 2009 Turbo S can run - see note "3" beside the 18" variant

"3) Not for Cayenne Turbo with engine power kit “E81”, Cayenne Turbo S or Cayenne Turbo
as of model year 2009."

bweSteve

Agree with mtnrat & Sniffer...

OP BlackTurboS never posted exactly what YEAR his CTTS is,... so it may be tough to completely & accurately tell him exactly whether 18's or 19's would fit.

I know that 18's will NOT fit over my 958 (2012) CTT red Brembo's - 290mm front calipers / 380mm front rotors.

WINTER:
But I also know that my 19" Porsche OEM Sport Design rims DO INDEED work (fit over calipers).
I decided to go with 265/50-R19 Michelin Lattitude Tour All-Seasons (hoping they are Ok for Baltimore winters)

For SUMMER: I currently run the OEM 21" 295/35-R21 Michelin Lattitude Sport on the OEM 21" Turbo rims.

I have room in my garage for wall-mount tire racks that allows me to hang my extra set on the wall of my garage (along with several other sets of race slicks for my '68 & '69 Camaros).

But I have NOT yet run a full Baltimore winter on these All-Season Michelin Latitude Tours. So I will report out on this AFTER I get to drive in a nice snow storm,... and the sand of Hatteras Outer banks, NC in the Spring.

=Steve

Sniffer

Its a 2009, he "introduced" us all to it when he purchased

See here - clicky

BlackTurboS

Sorry guys - you are right I should have mentioned the MY. It is a 2009 as sniffer mentioned. I don't expect you to look back at my previous posts but thanks Sniffer for pointing that out.

I don't have any intention of going to an 18" tire so its a non issue. I'm looking at going with a 20x10 with the 274/40/R20 as recommended on the diagram posted above (Thank you for posting that). I'm going with the Niche Sport Circuit 20x10 for winter with the Pirelli Scorpion snow and ice 275/40/R20.

I'll provide some feedback on the road noise/handling/etc. after I load them on the vehicle in November.

As for the current setup. I have the OEM 21" black wheels with 295/35/R21 Contis. They handle very well, quiet on the road (pavement dependent obviously), and I couldn't have been happier - even though they were quite expensive ($1800 I think). I highly recommend the Continentals in place of the Pirelli P Zero that last about 10k miles from what I read. I've put 3k miles on the Conti's and show no signs of treadwear. Keeping in mind I am somewhat of a gentle driver. I take it easy on her until I replace the boost diverter valves and brakes (in November as well).

More to come on my upgrades....
PBBrakes 8 pot kit as recommended by Lupo.sk (November)
Niche Sport Circuit 20x10s with Pirelli Scorpions (November)
Forge Boost Diverter Valves (November)

This past weekend I did the front/rear/transfer case fluids as mentioned by the guys on this forum, it was a piece of cake. I also drained the tranny fluid and replaced it with OEM Porsche tranny fluid, checked the temp to 40C as mentioned and that was also super easy. [EDIT] I also changed the filter, o-rings, and plugs. I used the Suncoast Triptronic Transmission Maintenance Kit. I looked at buying the parts elsewhere but by the time I added it all up it was close to the same price. And I didn't want to skimp on cheaper fluid at the risk of impacting my transmission. I wanted to put OEM fluid in, OEM filter, etc. Suncoast is my personal favorite and the kit was super easy to do on the Cayenne. I didn't even jack it up, just set the ride height to the highest setting and had enough room to do all the work. I highly recommend doing this. My 09 CTTS has 70k miles and it now shifts as smooth as butter compared to prior to the change. Just be prepared to catch the fluid that runs out as you are filling it.

NOTICEABLE decrease in shifting smoothness, drive noise, and overall smoother feel to the vehicle.

With the oil change, diffs, and tranny - I just swapped over 20 quarts of fluid in the Cayenne. She is a thirsty girl huh?