SRT8 Wheel Stuff (long, multiple posts)

[hemiwagn]

My Magnum SRT8 was built Aug 22/05 and delivered August 31/05. It came with the 3 season Goodyear F-1 245/45/20’s front and 255/55/20’s rear. I intend to put aftermarket wheels on the car for the summer, using the Goodyear F-1s for now. When the F-1s wear out, I would like to go to a slightly wider rear tire probably on a 10” wide rim. The stock rims, nice as they are, will be used in the winter with winter only tires. The winter tires will likely be 255/55/20’s on all 4 corners.

I undertook to get as much dimensional and other info about the stock SRT wheels as possible so I can be sure that the aftermarket ones will clear the big brakes our cars have.

DISCLAIMERS:
1/ I have a Mag SRT8, but much of what is covered here should also apply to the 300C SRT8 too.
2/ Yes this thread might be better in the wheels and tires section, but since it is applicable to only the SRT8 I posted it here.

I had a number of questions that hopefully my 5+ hrs in the garage will help answer.

Question 1: What is the offset of the SRT8 wheel?
I had no accurate way to measure this since I could not precisely determine the centerline of the wheel with the tire mounted. But lucky for us, Chrysler may have actually stamped it on the inside of the rim: See pic of inside of rim. Can we infer from this that the offset is -25.5 millimeters?


Question 2: What do the factory rim/tire combinations weigh?
-- See pics of tire/wheel on scale—this is the 255/45 tire and it looks like it weighs about 61 lbs.
The 245/45 tire/wheel, (no pic taken) weighed a bit less at 59 lbs.

Question 3: How much clearance is there at the front for a tire bigger than the stock 245/45/20?
There appear to be two tight areas: area A/ at the top of the tire where a bolt connects the upper “A” arm to a “C” shaped vertical arm; and area B/ between the inner edge of the rim and the outer edge of the aforementioned “C” arm.

Area A: See thumbnail pic – with the 245/45 tire there is about ½” of clearance. With the 255/55 tire (sorry no pic) there is about 3/8” of clearance.

Area B: --see next post

[hemiwagn]

Area B: I took two pictures of the inner side of front wheel. One with the 245 tire and one with the 255 tire mounted on the front. Somehow I forgot to actually take a measurement – but as you can see from the attached pics, there is more than enough room for the larger tire. I would estimate there is ¾” to 7/8” of space. (While it is close, the arm moves with the wheel so tight clearances are okay.)

Bottom line—255’s will fit fine on the front – but we knew this as there are numerous posts in other threads by those who have changed to this tire size. Still, I wanted to satisfy myself and better understand the clearance issues.

Question 4: How much clearance is needed for the SRT’s big Brembo brakes?
The first step in answering this was to try to measure how far the outside edge of the caliper is from the wheel mounting surface. It appears to be about 38 millimeters. See attached 2 pics, one is a close-up and the other is a perspective shot so you can see how I took this measurement. Basically I placed a level flush with the outside edge of the caliper and measured from the hub mounting surface to the edge of the level.

...more in next post...

[hemiwagn]

The second step was to determine the distance from the centre of the hub to where the caliper protrudes the most. This appears to be approximately 120 millimeters. (See attached pic).

Third step was to attempt a measurement of the caliper clearance on the actual rim. At 120mm from the centre of the wheel, the spoke of the rim is approximately 47mm to the outside of the mounting surface. The maximum clearance (at the end of the spoke closer to the rim’s edge) is approx 72mm (not really relevant but put mentioned for reference.) The procedure involved placing a level flush on the hub surface and measuring from the bottom edge of the level to the inside edge of the spoke. There are 3 pics of this procedure: one showing the 47mm measurement, one showing the 72mm measurement, and one perspective shot showing the overall procedure. (The black splatter on the inside of the rim is from the chassis undercoat I had done – and I have not yet cleaned that off the rim).

So then, from the above we can deduce that the clearance between the SRT caliper and rim should be about 47mm – 38mm = 9mm (about 3/8”).

[hemiwagn]

The fourth and final step was a reality check to see if the 9mm clearance is reasonably accurate or not.
See attached pic of a flat carpenter’s pencil taped to the caliper. The flat side is 7mm and it fit in with a little play on each side. So the 9mm clearance “seems” about right.

Question 5: Is there room at the back for a tire larger than 255/45/20?
The limiting area is on the inside leading edge of the back wheel. See attached 2 pics. I did not take precise measurements because with the car raised the wheel was ‘dropped’ more than normal (unless I get airborne which is not permitted by my Senior Officer (it is actually her car). But informally I would estimate about 1” of clearance. The plastic rivet holding the inner wheel well liner may be the limiting factor. But I feel pretty confident I could put 285/40’s back there some day. Note the yellow paint daub inspection mark on the fuel fill hose that goes into the tank. There are dozens of these in different colors all around the car (mostly under the hood and underneath the car). In 25 years, restorers will have great debates about color and location of these. Somebody should shoot a bunch of pictures to document them for the ages.

The 6th and final question: Since I was doing most of this stuff late at night in the garage, was I alone?
Apparently not. See final two pics of the little observer who was hanging around just outside the garage.
<end post>

[Gorgle]

Hemiwgn,

I'm sure I'm not the only one on this forum who's been waiting for someone to provide difinitive info on the SRT8 wheels. From all of us, thank you.

Now, to apply this info: If we want some "cheap" wheels for winter tires, what's out there that will fit over our Brembo's?

[need4speed]

Thx .. good information

As for winter wheels, if you don't want to run your factory 20's, go to tire rack, search on winter wheel/tire combos, choosing your car, it will give you 3-5 18" & 19" wheel options ..... along with tires ....

I bought a set of the Borbet ones, which are the widest at 8.5" so they will also double as my drag wheel ..... I had them powercoated black ...... they have not been on the car yet .....as, my recent trip to the dragstrip was cancelled ... due to a modification not coming in like it was supposed to .....

[goddardzilla]

Couple of comments

Re question 1 what is the offset?

Your MagSRT8 wheel probably has the same offset as the 300cSRT8 in which case see the thread HERE

Unless things have changed recently, all other things being equal, narrow tires are better for winter snow/ice grip. It concentrates the weight at a smaller contact area, increasing pressure and the ability to better bite into snow.

Zilla

[hemiwagn]

Thanks all for your positive comments.
need4speed: let me know if your wheels fit you SRT. I agree (along with zilla) that narrower is better for snow.
Zilla thanks for the link to the thread -- somehow I had not seen it before.
A question -- how do you embed the hyperlink in the text of your message?

[Gorgle]

Originally Posted by need4speed

As for winter wheels, if you don't want to run your factory 20's, go to tire rack, search on winter wheel/tire combos, choosing your car, it will give you 3-5 18" & 19" wheel options ..... along with tires ....

Need4speed,

Thanks for the reference. I'd been to TireRack before, but hadn't explored the "Winter" links before.

Now I'm worried. This was supposed to be hard. Is it really that easy? I'd feel a lot better if you had yours installed already. (There's always this nagging doubt in the back of my mind that somebody at TireRack prepared this list of wheels on a Monday morning with a hangover.)

[goddardzilla]

Originally Posted by hemiwagn

Zilla thanks for the link to the thread -- somehow I had not seen it before.
A question -- how do you embed the hyperlink in the text of your message?

I've PM'd you