wheel and tech info-maybe this applies to the Magnum also.

[carre']

there seems to be a debate over which size wheels and which size tires to use for 300C.

Here are the Specs on an OEM 300C wheel. These measurements were taken on July 6, 2005.

PCD: 5-114.3
Offest (O.E.): +24
Hub Diameter: 71.5mm
wheel size (O.E.): 18x7.5

OD (overall diameter) tire calculation:
heres the formula, width x 0.aspect ratio (divided by) 25.4 x 2 + wheel diameter.

Example for OE 300C: 225/60R18
so here it is, 225 x 0.60 (divided by) 25.4 x 2 + 18 = 28.629 inches

As for upgrading INTO a larger wheel,

From a performance stand point: 20x8.5 up front and 20x10 back rear, using a +20 offset for fronts and +25 offset for rear. Run a 245 wide tire up front and a fat 275 in the rear to have most contact patch, since this is a rear-wheel drive car. Why look like a front wheel drive car with 245 all around, might as well as bought a new Chevy Impala instead or a Acura/Honda.

For a SHOW stang point: 22x9.5 with a +15 mm offset, that way you don't have run spacers and still stay within the fender wall. Because of limitation whit tire sizes and availabilty, run a 255(Nitto) all the around or 265 (Pirelli) just in the front and a 285 out back. Niito one makes one size of 22" tires for the 300C.

These days it is very easy to find staggered(skinny fronts / wide rears) 20" wheels with out HAVING to go to multi piece wheels. A lot of companies make one pieces wheels in a 20" staggered fitment. 22" one piece staggered wheels are hard to find.

New tires sizes are not that easy make just to fit one car.

I hope this help some people out there with basic questions about wheels and tires
_________________
www.carrewheels.com

[bigdaddyoc]

I only find one problem with your suggestions. It would be a really bad idea to run 2 different size tires front and rear unless you can match OD exactly. Reason being, this car apparently has very sensitive monitoring equipment in regards to the BAS and ESP systems. The variances between front and rear tire sizes would definitely throw both of these systems off, which in certain situations could cause the car to react very oddly or even bad, such as loss of traction and extreme braking situations. I for one do not want to test this and find out the hard way. FROM what I was told if either of these systems is engaged and it takes its measurements but the OD of the tires is off between the two it could enable its controlled braking system to try and regain control and possibly put too much or too little input because of the misread measurements and cause worse loss of control then when you started. But thats just my 2 cents...I'm sure there will be those that try it and we'll just wait and see what they say.

[MySRT]

bigdaddyoc, you are right, I am sure if we do not watch out we could create lots of problems.
Here are a few sizes that match our stock tires.
245x55x18
275x50x18
295x45x18
335x40x18 - this sure would look good on the back
245x45x20
275x40x20
295x35x20 - a little off but still should work ok.

[E55 KEV]

When suggesting a staggered setup one would assume that the tires are upgraded correctely. BigDaddy, your post suggest that the person is using the wrong tire sizes and carre's post does not mention any wrong tire sizes or OE (heights).

If you have the same OD or height used on a staggered setup the ESP and other electronics will be fine. All of Mercedes AMG cars and many with Sport Packages come with staggered setups and ESP. The Magnum and 300C concept cars both had staggered setups. The 300C Concept had:

245/45/20 - OD = 28.7"
275/40/20 - OD = 28.7"

[Magnanimous]

Also agree that all four corners must be equal in OD. Otherwise computer senses that wheels are spinning at different speeds, ie. loss of traction, and and applies braking and/or cuts throttle. On the other hand, just driving around a corner will cause the wheels to spin at different velocities so there must be some fudge factor built INTO the traction control system to account for this.

My question relates to the size of the OEM tire. Is it 727mm, as the formula above would indicate or is it 711mm as stated on Tire Rack Site (continental does not have this size and tire on their web site, go figure) ? That's a 2% difference which will cause alot of speedometer error. Is it better to use the formula or the manufacturers specs? At 711mm the comparable 20" tire would be a 245/40-20 and this is the tire being offered at Tire rack and others. You could put this up front and say a 275/35-20 on the rear with less than a 1% difference between the front and rear and around 1% off OEM diameter at both ends. Can speedometers be recalibrated by the way?

[E55 KEV]

Hey carre', since you measured an OEM wheel why are the specs officially listed at 5x115 by Chrysler if it is really a 5x114.3. Those two are very close and only a .07mm difference. Did the wheels have any markings on the back?

[bigdaddyoc]

Too bad no one makes a 245/45/20 or I would be using it. The 245/40/40 was something like 6/10's of an inch shorter so I was trying to stay away FROM it by using the 275/40's all the way around. Trying to use the staggered setup will prove to be very difficult because there are so few available combinations that work. Someone needs to step up and make that 245/45/20 and it would change alot. As it is there are only 3 manufacturers that make a 275/40/20...so even then the choices are very limited.

[Magnanimous]

Hey Doc. Have you actually installed those 275's? It doesn't seem like there is a whole lot of clearance between the stock front tire and the upper control arm. What rim offsets did you use if I may ask? I will probably ORDER a package off the Internet and want to make sutre they will fit. Was curious about the front. If you stagger the fronts and rears by the way and have unidirectional tires, there goes any sort of tire rotation unless you want to have them dismounted and swapped side to side and we haven't seen how the Magnum is going to wear tires. Judging FROM the way mine pulls to the right, they won't last long.

[carre']

Hey carre', since you measured an OEM wheel why are the specs officially listed at 5x115 by Chrysler if it is really a 5x114.3. Those two are very close and only a .07mm difference. Did the wheels have any markings on the back?

Yes E55 KEV, I did measure it up against using a PCD tool. First I measured a 5-115 tool, it was kinda off, then we put a 5-114.3 tool, that was on exact. When it comes to wheels American Car Guys use the term 5X4.5" which if you calculate INTO metric terms it works out to 5 x 114.3 (4.5" = 114.3 mm). These days Car manufactures use the 115 as too refer 4.5", but like I said, 114.3 mm = 4.5 inches. The correct PCD is 114.3 for the 300C.

[cluv]

I put a set of KMC Stealth 20's on my Magnum, 245/40/20's in front, 275/50/20's in back. If you want to CHECK it out, I'm car #0063 in the Hemi LX Registry.[/img]

[MySRT]

That sure is a big difference in tire size. Have you have any problems with ABS or ESP codes? That more than 10% speedo error.

[E55 KEV]

I put a set of KMC Stealth 20's on my Magnum, 245/40/20's in front, 275/50/20's in back. If you want to CHECK it out, I'm car #0063 in the Hemi LX Registry.[/img]

The OEM tire of 225/60/18 is 28.6" and those sizes would measure:

245/40/20 - 27.7"
275/50/20 - 30.8"

Was that a 'typo' for that rear size?