I have Sport Techno staggered wheels on our Cayenne Turbo. I am currently running Nitto Invo 275/40/18s on the fronts and 305/35/18s on the rears. I am thinking of stepping up to a tire with a larger sidewall for comfort and appearance since the rears are already pretty worn after 8k miles.

I'm looking at BFG g-Force T/A KDWs in 265/50/20 and 295/45/20s which are approximately 30.4" in diameter.

1. Should I experience any problems with fitment?

2. Can I plug in my Durametric and adjust tire size so speedo isn't way off? (I have one and have just never used it)

 

I was thinking something stupid like XXX/XX/30 before reading your post. haha...

 

I thought the same thing for a minute... it scared me!

 

my summer tires are Vredestein 305/35/22 which is also 30.4" rolling diameter and they're fine. a very very slight rubbing when turned all the way when in low setting (mine has Techart lowering module) when the tire were new, but did not notice the rub marks getting any deeper.

speedometer is a little off, but not too bad. I got used to it.

 

FWIW, the Transsyberia Cayennes ran a 265/65/18, basically a 32" tire on stock parts.

 

Do it! I am shopping for a set of 18's to get the 265/65 set up.

 

After reading a lot of negative reviews on those BFGs, I decided to go with Yokohama Parada Spec-X which were cheaper and actually got really good reviews about ride quality and tire noise.

 

Never had Yokohama but tire noise was horrendous on my previous car. I was thinking of BFGs on Cayenne soon. That's a surprise.

 

I've never heard a bad word about the BFGs. They have been a loved tire of truck and Jeep owners for decades!!

 

Porsche told me that running those large Transsyberia setup tires would:

1. Negate my warranty, and

2. Require changing my rear end.

I think I'd contact tech support and get the right German rear end if I was going to do it.

 

That's crazy talk. Negative reviews where??? I've only heard good things directly from people, on reviews, and from my own use over about 200,000 miles now on a few different vehicles.

It's basically the best "install and don't think about again" tire out there. The speed rating is decently high, the durability is incredible, the traction in so many situations is wonderful. You just have to be sure to get the E range and the rated for snow versions. There are D and lower rated versions that otherwise look identical that are inferior.

 

Cole,

Are you sure? I thought I'd heard that the rear end had to be changed out to accomodate those larger tires?

I would be interested in those tires for durability.

Right now I am running General Grabber AT2's in 255/55/18 while touring and towing.

Porsche dealership in Anchorage told me that going with those huge tires required changing the rear end and voided the warranty.

 

Yes. I'm sure.


First off you can't just "change out the rear end" on a Cayenne. You would have to change the ring & pinion gears for both the front and rear differentials.

The stock Cayenne Turbo gets 3.70 gears. Factories often put different ratios in the same car for different markets. For example a Jeep Wrangler for a sea level market might get 3.07 gears and for Denver it will get 3:73 gear and if you want the off road package it will get 4:11 gears. All with the same axles and engine size

Take a look at this chart. First thing you need to know is that the engine rpm show should be at 65mph in your 1:1 gear. The Cayenne has a deep overdrive highway gear so it will drop the rpm even more.

The second thing you need to know is that these charts are to just give you an idea of what a tire size or gear change will do "in general" it does NOT account for power output of an engine. A gear change will have a much more dramatic effect on "performance" for a low power engine than a high one.

You can see that with the stock 3:70 gears and a stock 30" tall tire that the rpm is in the "best mileage and performance " range.

Switch to a 31.6" tall tire like the 265/65/18 and it drops more into the "fuel economy" rpm range and you may lose a touch of "performance".

This may be enough to notice on a V6 Cayenne and not at all on a Turbo. I run a 285/40/22 all summer long on my CTT as I'm sure many here do. It's 31" tall compared to the 265/65/18 BFG that is 31.6" tall.

If you really feel you need to get back the marginal performance loss and have a Turbo you could seek out front and rear differentials from a V8 or Touareg V10 that came with 4:11 gear ratios installed. Or a V6 that had 4:56.

Porsche like all manufacturers put in different ratios in different years to accomplish different goals. For the 2008 CTT they put 3.31s in it to take some of the initial "punch" out of it and help their fuel economy numbers. ( the same effect as putting on bigger tires on older Cayenne, check the numbers on the chart)






Source link for the 2004.
http://press.porsche.com/archive/pro...e_V6_Specs.pdf

Source link for 2008.
http://press.porsche.com/vehicles/08...enne_specs.pdf







...

 

My CTT has visited EVOMS and never has been the same.

Since their 540 package with an additonal part, an IPD plenum, I'd guestimate 577/587 for numbers. So, power isn't a problem on my old beast. Not at all. But I really want fuel range.

Towing with corn in my tank gives me maybe 11 MPG. With real gas I see 2.5 more MPG. Also, I do like to go off road. She's made for it.

Those 10 ply tires appear to make flat tires a thing of the past.

Cole, you really know your stuff. I am thinking about going with the BF Goodrich's. I imagine the ride might be softer but I'll bet there will be more road noise.

After almost 30,000 miles since August 2011, I have found that I enjoy towing at 43-44 MPH and get slightly improved MPG over towing at 54 MPH. that is on flat roads. Once I am in short hills, MPG drops to 8 MPG!

Going slowly with the load I have is less nerve wracking and I really see more of our beautiful country bu others get angry with me even when I am at 54 MPH for going so slowly.

My power and fuel efficiency with my mods and EVOMS tune added more than 25% to BOTH. Previously, I had to downshift into first gear to get my huge load (6,800 lbs at the wheels and 780 at the tongue) going. Now, I can leave her in drive and launch without even tapping the turbos.

I told EVOMS I wanted increased fuel efficiency and longevity. They said they could get me between 3-5 more MPG but no more. They also warned me it'd never drive the same; it'd be an entirely different drive.

Man, were they right!

I observed 13.8 MPG city before and over 18 MPG city afterwards unless I got into the turbos.

I have learned to check the winds before driving for safety and fuel efficiency. And I have learned to occassionally upshift to get more MPG.

I got more MPG on the highway with my 20" Diamaris than I get with my current tires. So, it is hard to compare apples to oranges.

All I can say, is when my car is running right, I really enjoy my ride.

 

PS I have been adjusting to get my tongue weight lower. My first trip to the scales showed 980 lbs at the tongue! Since that last weight of 780 I have removed a few things from the front of the trailer to get the weight down.

I believe the Toureg came out (and perhaps Porssche did too) with a 770 lbs tongue rating initially. The general rule of thumb is no less than 10% of your wheel weight on the tongue for safety.

Why the CTT has a 619 lbs tongue specification I don't know. But that really limits capacity to under 6200 lbs compared to the current rating of 7700 lbs.

I did not know that one adds the tongue weight to the wheel weight to get the gross towing weight when I bought this trailer. I thought I was well under weight with this trailer so that I could add water and still be under weight. The maufacturer's specificiations were 5500 wheel weight unloaded and 550 tongue weight but that was wishful thinking and before adding a pair of batteries, two propane tanks and and electric jack to the tongue. And all my junk.

When I add 58 gallons of freash water, I am maxing or exceeding the specs! Especially when I have full gray and black water tanks!!!

It really is a balancing act.