If you want to stay with 15", the M/T SR radials may be the best d.o.t. approved tire for your application. They are speed rated to H, have a modern tread design, and a fairly stiff sidewall. Since they offer these in wheel diameters from 15-20", I'd say they are a more modern tire than a BFG.

The Viper caliper kit will fit inside 15" wheels if you use the stock 11.75 rotors. Stepping up to 13" rotors will require the 17" wheels, however.

The guy telling you stories about 15 vs 17 inch tire deflection is doing just that; telling you stories. It is unfounded. Negative camber gain is the result of the physical dimensions and layout of the suspension parts and pick up points. It has nothing to do with tire sidewall. Sidewall height is a part of the total suspension make up, but will not change camber gain all by itself. This is one of the advantages of using the FJM spindles. Their taller height creates additioanl camber gain through their cycle because they shorten the effective length of the upper control arm.

BTW, if you want a really trick, cost conscious track only tire, check out the Towel City link above. Their racing slicks have a couple of degrees of camber built into them. For more grins, put your rear axle housing into a press and bend the tubes 1-1.5 degrees to create negtive camber in a solid axle rear suspension as well. That really messes with the IRS guys when you can lay down as much lateral grip as they can.

The thing about 15" tires being better for traction is somewhat true for drag racing applications where the large sidewall can absorb the launch shock and create grip instead of spinning. Not the greatest thing for lateral loading, however.

An intersting note is that to generate around 1 g of force on a drag strip launch, you would need a somewhat dedicated drag race suspension in a somewhat serious effort bracket racer that would not be much fun on the street. To generate that same 1 g of force laterally, you only need the right combination of components that will make your street car more fun to drive. Kind of makes me wonder why more guys aren't thinking handling instead of drat times.

For the leaf spring rate, it is all about the final wheel rate. Looking at their web site, the XV front t-bars and s-bars look to be around 1.125, smaller than the 1.22 your planning on using. Similarly, they use a pretty sizeable rear sway bar, looks about 1" in diameter. Another thing to note is the XV rear bar is much more straight than a stock mopar rear bar. So even though it is not a lot larger than a stock bar,.75 vs 1.0, the lack of bends create a more rigid bar that is going to more effectively control motion than the pretzel shaped stocker. So you are putting more wheel rate into the rear with the sway bar, so you can go lighter on the spring rate.

TonyC - thanks for the great explanation, as always! So a stock mopar front suspension doesn't create more camber when it compresses? (because of a 15" tire compressing because of soft sidewall) I wonder because this guy drives the http://www.olympia-charger.com/ and I supposed he knows a lot!?

Yeah, I know on the wheel rate.. still surprised that the swaybar on the rear can make up for soft leafsprings. I hope my car isn't to stiff, although I am used to stiff european cars and our roads are mostly in perfect condition...

I was planing to keep the 11.75" with my FMJ calipers or then go with the 13" Viper setup... but this would mean 17" wheels... I just loved the way my last musclecar drove when I switched to 17", what a difference! Same with Gionni's 71 stock 340 RR with his 18/20", he drove the 1/8" faster than most of the cars with much bigger engines because he just had much better grip with this modern tire compound than the others with this crappy Radial T/A's...
But thanks for the tips, will look into those tires!

In stock form, mopar suspensions do create additional negative camber under compression and positive camber under extension, so he is right in that regard. Compared to some popular chevy and ford designs that create positive camber under compression and negative in extension, us mopar guys have had it pretty good from the start.

The whole point of negative camber gain is to keep the tread of the tire in contact with the ground as the car body rolls over. The more the body rolls, the more negative camber gain you want to have. So long as the tread face is in contact with the road, whether it is a 15" or 17" rim doesn't matter. The additional sidewall of a 15 may allow this transition to be smoother than a comparable 17 because the sidewall is a part of the suspension system and can absorb bumps better than a 17" sidewall, which can be an advantage. However, I don't think that I would say a mopar suspension will work better with a 15" than it would with a 17" simply based on rim diameter.

A 15" tire being faster than a 17" tire in his case is entirely possible because he is using competition tires with very rigid sidewalls. Stiffer than or equal to a 17", well, possibly, but I've never compared themside by side. I know 15" oval track racing slicks have a VERY rigid sidewall to them. Yes, a 15 slick is going to much faster than a 17" street tire. In competition tires, the selection of 15" tires is equal to and possibly better than in 17". Since there are very few companies that make both 15" and 17" tires in identical street treads, it would be tough to do a one for one comparison. However, if run side by side and optmized for each tire, a 17" tire may actually be able to use a softer wheel rate than a 15" tire because of the sidewall differences. Can't say I've ever tried it though.

Also consider that increasing the rim size adds to unsprung weight, so it is possible to have a 17" combo that weighs considerably more than 15" combo, but that all depends on rim and tire selection. I have seen some guys post weights of 17" wheels that were several pounds heavier than a factory rallye wheel, which is pretty heavy to begin with. With the Nascar spec, steel racing wheels he has on that Charger, he probably only has 18-20 pounds worth of wheel, which is incredibly light for a steel wheel.

This is great stuff, has there been any updates on what you guys have done to your cars and or the differences you felt with different springs and tires?
CAN'T WAIT.
I am planing on 15" Minilites with I hope some sticky rubber.

I'am not sure where to post this but I thought this was a good place,it was very interesting for us guys that are into corners and stopping.
Its a link to a cobra site that I found while looking for tires.
I hope it happens.
http://www.ffcobra.com/forums/showthread.php?t=175512

It had been mentioned by XVmotorsports that they were going to try and offer parts of their upper level stage kits (like the K frame,upper and lower arms,etc..)so that they could be more price competitive and it would be more affordable for the average car crafter. I was hoping that they would have done this by now.

I have purchased other upgrades from them and have not been disappointed.

Yes I really like the period look with the fat tires and Minilites.
Any ideas on back spacing for the Challenger with 275/60,15s? 15x8 with 4"B/S sound good?
I had a set of 17" torque thrust with regrets. On the highways with all the truck ruts
I was being pushed from one side of the lane to the other. I also noticed that when in a hard corner I could hear the 15s getting loose, but with the 17s I would all of a sudden loose it completely. Maybe just me and maybe just those tires.
I figure if they could run 15s back in the day and have a blast I am sure i can.
I was looking at M/T street tires in 26x10 and 28x12,15.
Unless that Toyo story on the Cobra site comes true.
I thought Tim was getting out of the sales.
When I was at the spring fling at Willow Springs I couldn't get a clear answer from him about his wheels and or his oil pan that I wanted.
Oh Well.
It's not over yet.
Thanks.

While I am here at the key board, what do you think about 1.16" torsion bars or .96" bars?
I have just found a set of new 1.16 bars for my Challenger after reassembling my front end.
Thinking I'll go with the .096 bars until I feel I have to go bigger.
340 5spd, torque boxes, tubular upper control arms,
boxed lower control arms, 12" disc swap,1.15" front sway bar, Mopar H/D rear springs which seem at first to be softer then the stock 318 springs I took out.
High tech testing, me standing on them with a measuring tape.

Thanks autoX, the 26x10 tire is very close to a 245/60 and the 28x60 is closest to a 275/60.
Are you saying to run a 275/50 up front?
sounds a bit big, but wow that would be something.
Here is a good story I found in HotRod a little while back, Thats the look and the performance I am talking about. http://www.hotrod.com/techarticles/scca_trans_am_racing_1966_1972/photo_09.html

Sorry again about your web page.
Thanks again for the input.

Well, lets see. A 235 is about 9 1/4", a 255 is 9 7/8" and a 275 is close to 10 3/4" wide. Lotta tire. So to step from a 235 to a 275 will require enough space for an extra 1" of tire on each side of your existing 235 combo. If you've got the inch, a 275 will fit.

The most backspace you can put under there with a 15" rim is 4.75. Beyond that you run into control arm interference. With a 17" rim, you could easily run 5 or 5.5 inches.

I am thinking that the M/T radials in the 26x10/15 and 28x12/15 would be a good setup in the Challenger.

I'd say a 26x10x15 is a bit smaller than a 275. But, that is just looking at the hard numbers on a ruler. Actual application with tire design, compounds and rims can alter this some. Double check your section widths to make sure. If you have 235s on there now, verify its section width agains the 10" M/T claim to see how much larger you actually are going to be at, because I'm thinking those M/Ts are bigger than a 245.

Also, I'd say that the 28" rear tire is going to be a bit tall. The original TA racing slicks were a ten inch tread on an 8 inch wheel. Modern comparison would be like a 285/50 on an 8" rim, so an M/T 26x12x15 may be closer in appearance to a vintage T/A look than the 28" tire.

I have toyo RA1's 255-50-16 which is a 26" tall competition type tire on a 16x8 wheel. They work, i mean they stick really well as the car actually "rotates" thru the turns with ease now. I see talk of 15 & 17 but no 16 inch tires....btw the "prepared" mustangs use 245-50-16 and those cars are vewy vewy fast...

A 17 inch wheel/tire combo to give a 26 inch diam tire would do little to improve my handling and the ride would be stiffer than it already is. Taller tires do not add much to the handling.

I have a great set of 16" wheels but was having a real hard time finding 16" rubber.
I really thought that the 255's were no longer made.
I try again.
Thanks for the tip.

The trans/am look is 27" tires rear.
Here's a pic

I think this thread is going off topic, but it's great info.
Maybe we should have a section just for corner carving, suspension mods and tires.