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Discussion Starter #1
IM looking inot rims what size tire do u guys have with 20's and did u have to upgrade suspension..is the ride still good and does it rub thanx
 

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Black the Darkside
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Most are running 35 series tires. Tires will clear. If you lower it with springs clearance can be a problem. That's fixed by rolling the fender lips. That also calls for a wheel alignment. When you go from a 55 to a 35 series tires the sidewall lose a lot of flexibility and with that goes the qulity of the ride. You also lose HP do to the larger & heavier rotating tire mass. I went with 18" myself.
 

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Discussion Starter #7
i was gunna go with 19's but people are tellin me i have to get a 35 series tire anyway so i mine as well get 20's..i only wanted 19's cuz i though i could get a 40 series that wont rub.. and 18's r to small for my preference
 

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FreshWhiteWhip said:
i was gunna go with 19's but people are tellin me i have to get a 35 series tire anyway so i mine as well get 20's..i only wanted 19's cuz i though i could get a 40 series that wont rub.. and 18's r to small for my preference
I would go with the 40 series. You gonna lower it?
 

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Discussion Starter #11
so if i get a 40 series tire what size rims should i get so it does not rub..and no im not lowering it.and what size rim can a 255 go on
 

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CTS 3.6L 5sp Auto Silver Smoke with Neutral Interior
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FreshWhiteWhip said:
so if i get a 40 series tire what size rims should i get so it does not rub..and no im not lowering it.and what size rim can a 255 go on
:canttalk: I know I'll get burned by people (ie. RobertCTS), but I feel that 40 series should be used with 18's, the lower profile will make the 18's look more like well 18's and not 17's.

I have 245/35/20's and I have no issues with rubbing. In fact, I just loaded it up at Costco (full trunk and rear seat) sodas/water.. and had no issues with rubbing. The suspension is really strong and doesn't have the problems that other cars have regarding bottoming out (atimas, G35s..).

The 20's are really worth the money (granted you don't get robbed at a rim shop). Plus they will get you noticed and they set the car off.
 

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Definately go with 20's. I run 245/35/20's as I listed above, I have had a good 800lbs in the back seat and trunk of my car and it's never rubbed. The 20's fill the wheel well up nice and will give the car a more sporty feel and aggresive edge in corners. The ride is a little rougher than before, but i find that it was a little too soft for my likings in the first place. I'm pretty sure you cant put 255 rubber on this car without it rubbing, you would have to roll the fenders
 

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07 SRX V8 AWD Diamond White Sport Edition & 08 C6 LS3/418ci
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If you have any plan whatsoever in building this vehicle for spirited driving and/or limited track applications; DO NOT install 20" wheels as you will compromise the sport suspension geometry of the vehicle.

There have been many posts and threads on this topic and 20" wheels will fit and will look fine; however it is an engineering fact that you will absolutely compromise the integrity of the sports suspension system, rear thrust angle, front scrub radius, roll center and cause premature wear of your suspension hardware components.

It is an "unshakable fact". If you however are installing 20" wheels for aesthetic purposes; simply pick out what tickles your fancy!

If however, your application includes anything that may later incorporate a big brake kit, spirited driving and/or track applications;

here are the MAXIMUM WHEEL/RIM parameters:

Front: 19x8.5
Rear: 19x9.5

Front rubber size: 245x40x19
Rear rubber size: 285x35x19

The above application will not require you to roll your fender well lips assuming that you DO NOT install Eibach lowering springs; which I recommend you do not unless your looking for the low slammed look for appearance only.

I would suggest however that by plus sizing your rim and rubber, that you maintain your existing FE3 front and rear Sachs Nivomat shocks and not install the Cadillac rear luxury shock as you will compromise the dampening qualities of your rear sport suspension system.

A more cost effective and stronger approach is to install the Hotchkis front and rear adjustable anti-sway bar kit and the CTSV front and rear coil spring kit. We also stock the CTSV FE4 shock package that will provide you even stronger dampening qualities to match the rebound rate found on the CTSV coil springs.

There are plenty of single one piece light weight forged wheels available in the 19" diameter that are very cost competitive that we have access to.

If you would like to email us at: [email protected]*********************** we would be happy to at least point you in the right direction based on your application whether you purchase from us or on your own. Technical data is always free of charge!

best regards - Cadillac MotorSports, Limited.

Note: IF YOU PLAN ON INSTALLING A BIG BRAKE KIT AT A LATER TIME.....DO NOT ORDER WHEELS AT ALL AS THE REAR WHEEL/RIMS REQUIRE A DIFFERENT OFFSET THAN THE FRONT RIMS AND THE CTS GRAVEYARD IS FULL OF WRONG WHEEL/RIM SETS FROM THOSE THAT ORDERED THEIR WHEELS FIRST AND BIG BRAKES LATER!
 

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Smokin' 04 CTS said:
:canttalk: I know I'll get burned by people (ie. RobertCTS), but I feel that 40 series should be used with 18's, the lower profile will make the 18's look more like well 18's and not 17's.quote]

The idea is to keep your odometer, speedometer and DIC electronics correct. A 40 Series tire will give you errors on an 18" rim. You want 245x45x18" inorder to keep it the same as the OEM 225x55x17".:yup:

Pete has shared his thoughts on 20" rims before but unfortunately it usually falls on deaf ears. Also as I recall the most popular size rim used in the forum was 17" rims, not 20's.
 

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Robert is correct. In order to keep the factory sport suspension system intact as designed in Germany to the highest of standards and to keep your speedo calibation 100% correct with regard to RPM's; the proper engineered size wheel/rim and rubber given the factory roll center height would the the following:

wheel/rim size: 18x8.5"
rubber size: 245/45/18

I believe off the "top of my head" that the RPM conversion is 717 RPM's

When you "plus size" you must accomplish a number of things which include maintaing the same factory calibated RPM calibration of 717 RPM's. So therefore, when you increase the size of the wheel rim, there is a corresponding decrease in the size of the rubber to retain the same engineered wheel diameter and most importantly not compromising the given depth of the wheels offset and suspension geometry as this is where you do damage that is not visible to the human eye. This type of damage is premature wear to the trailing arm bushings, upsetting the balance of the vehcile roll center and rear tracking, possible pinching of the vehicle tires inside sidewall with the pinch bolts on the upper a-arms, negative camber and scrub radius issues as well as a host of a huge number of problems that will rear there ugly head later.

We have all traveled this road with different thoughts and theories and ideas. But the bottom line is that when you make a change in something that is engineered to perform a certain function as the FE3 sport suspension is......you need to understand that in all cases that there is either a positive or negative outcome.

If it is appearnace only that you desire.....put monster truck tires on it to your hearts content. It's what makes you happy that is important.

If it is "performance and longevity" and suspension geometry integrity that you want to preserve or improve upon; do not install 20 " rims, do not install Eibach lowering springs and do not remove your FE3 rear Nivomat shocks.

To do so in pursuit of "improving your sports suspension handling" is an absolute no-no and you have ruined your CTS sport suspension system.

If you want to maintain the integrity of your sport suspension system as designed and still increase the size of you wheel rims....it is possible, but there are limits. And those limits are posted above in my thread at 19".

Any other changes above and beyond those parameters has a negative effect on your sport suspension system without reservation whatsoever.
 

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I think there is a total of 2 or 3 guys here that autocross there car and non of them are running 20's. It's more for show.

Get whatever YOU want.
 
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