15x10 Rallye Wheel Question

[BobBejeski]

I have a 1971 Cuda340   that will be getting a 800hp 572 Hemi next year.     Being my goal is to keep the outside of this car looking as stock as I can (although inside will have some modern goodies)  I want to stay with the 15" Rallyes on the rear ,  however,  I still want to go with the largest tire I can in the rear.   I am thinking the Radial TA 295 50's would be great. I am doing the Lynx Coil System from RMS (already did the AlterKation in the front last month) so I shouldn't have to worry about the leaf spring clearance problem.     

   They make a 15x10 Rallye Wheel.  I think that tire should mount nicely.   

   My concern,   I don't want the wheel base to be any wider than stock.  I don't want them sticking out of the wheel wells or even close to it.  I want to keep it in stock looking.   The largest backspacing on these is 5.5"  .    I believe stock 15x7's was 4.5".  So I pick up a little there.  But 3" on each side, minus the backspacing seems like it gives me a total of 4" extra width on my wheelbase?    Is my thinking correct?   

   So does that mean I need to have a custom width rear/axles made to keep the stock wheel base so they stay in the wheel well correctly?

   Any opinions or anyway use the 15x10's
   And anyone have problems finding trim rings that don't leave an ugly gap?.

  Thanks,

   -Bob

[Mopar Mitch]

BobB -- your terminology is incorrect... "wheelbase" is the centerline front to rear wheels.   What your concern about is actually called the "track"width (center of tire width-to-center of tire width).

The factory rally rim of 15 (not 17)x7 has a 4" back space.   So, to keep the track width the SAME AS FACTORY, for every inch of extra rim width you simply add 1/2" to the back space.

Examples:  7" rim width, bs = 4"; 8" ... bs = 4.5"; 9" ... bs = 5"; 10" ... bs = 5.5".

With the 10" rim having 5.5" bs, there may be a bit of concern of the inside sidewall getting a bit too close to the leaf springs, but you're changing that setup, so, you're on you're on your own to find out if there will be any problems on interference.

Also, pending your ride height in the rear, the diameter of the tire, along with the additional spread of the tire on the 10" rim, may warrant you to flush the lips (just do it), as well as a few pounds with a mallet to the inside wheel well where the top of the tire may slightly rub the fender wheel-well (just above the folded lip).

With ~800 hp, you realistically should look at better gripping tires than the BFG T/As... those tires are built for mileage having a hard compound (TW ~400-450?).   Consider M/Ts or Hoosiers (yes, they make them for the street).  Also, a taller sidewall than a 50-series (say a 60-series, at least 275-60-15) will give you a better chance of gripping when you put the pedal-to-the-metal.   50-series and less (45-40-35-30) are better for cornering forces (having a WIDER square area of contact patch); 55-60-65-70 series are better for straight line acceleration (having a LONGER square area of contact patch).

[BobBejeski]

   Thanks for the response.   This is my first project,  and yes,  I am getting my terminology quite mixed up.  But that's how you learn...Thanks for the clarification. 

    I hear what you say on the tires,  and yes I am still contemplating that exact tire.   I want it to have the stock exterior look as much as possible, so that factors in.     

      I spoke to Wheel Vinitques,  and they can make a custom backspace on the 15x10's.  They can go all the way to 7.5"   I should have some good clearance with the Coil Spring setup.    I might be able to go maybe 6" or 6.5"   I am thinking that will help to get that center of the wheel a little closer to the outside so it looks a little closer to stock.  Then I might not have that gap with the trim rings which looks so ugly. 
     
    I was down at Carlisle and took some pictures (below) of cars that had the 15x10's but the centers were pretty DEEP DISH and the tires were out near the wheel well mouldings.   Stock,  I am almost 2" in from the edge of the wheel wells, and I want to try to keep that if possible. 

  Trying to avoid the look of these pictures.

  -Bob

[AARuFAST]

Larger tires make it impossible to remove them.
The axle has to hang to remove the tires..
Cannot raise the car with jack on pumpkin,
A car lift that hang the wheels is the way to go.

[340-FOUR- BARRELL]

Larger tires make it impossible to remove them.
The axle has to hang to remove the tires..
Cannot raise the car with jack on pumpkin,
A car lift that hang the wheels is the way to go.

So true. Been there. With most trucks removing oversize tires is not an issue when jacking the rear of a vehicle up at the pumpkin. It's not an issue with a 1955 Chevy Nomad. But with most cars it is a big tire issue getting them off the car if you are stuck on the side of the road with a flat. I have used a bumper jack with success.

[AARuFAST]

The indy challenger is Rob Scooby Dog. 
Look like 295 tires on rear....... send his a message.............

[HP2]

15x10 with the RMS Lynx system, easy. The first interference point to fitting 15x10 is the leaf springs. You've eliminated those. Are you keeping the stock e Body rear end housing? This matters because it impacts the backspace you need. The bolt in 15x10 solution is a 1" leaf spring relocate with a 68-70 B body housing and 5.5 backspace. However, a 5 or 5.5 backspace rim will have the trim ring gap on the front.

15x10 with 6 or 6.5 backspace with the stock E body housing would be a great way to keep track width centered like original and still keep the tire under the wheel lip opening. You should be able to get a 28x12x15 tire up in there without issue with this wheel. Maybe large rif you get int here and measure everything ver precisely and make sure the housing is centered in the car ( they aren't always). The added backspace should also keep the front side gap to a minimum.

I also agree with skipping BFG tires. They simply don't have any grip. You will probably want to look at a d.o.t. approved drag radial to have any semblance of grip at all.

My Challenger has the 1" relocate, 15x10 with 5" backspace, 67 B body housing and 26x12x15 tires. I have plenty of room all around and could probably to step up a size or two even further.

[BobBejeski]

Thanks HP,   great straight-forward answer.      For the housing,   Because its getting a Tim Banning 572 Hemi,   I don't want to stick with the stock housing.   Bill from RMS has said he has stripped those and after seeing the shotty factory welds, he didn't know how some of them held together.  He is recommending getting a 9" housing and getting Moser axles.   But as a mopar guy,   I don't know that I can sleep at night with a 9" (although Ford doesn't even make it anymore, its all aftermarket).

    I am considering a getting a Moser-Built 8 3/4 FABRICATED housing.   They look really cool and they can set it all up,  with axles and 4:10 gears , with disc brakes that will fit in those 15" rallyes.  So that's my current thinking.   

[crash340]

I have 15x10 5.5" bs with 295's, 70 B Body diff with 1" spring relocation kits, I have stock leaf springs in my 73 Cuda and no rolled fender lips, whilst its snug I don't have tire rub on springs or fenders, I also jack up the car under the diff centre and can take the wheels off without issue