15 inch wheels with 13 inch brakes?

[shinoda]

I have 13 inch cobra brakes on the front of my 91 stang and I am wanting to run some 15 inch pro stars (skinnies) or something up front. What would your suggestion be to get something to fit. I could put some smaller rotors it but I really dont want to. I have heard of running spacers on the front but what would the drawbacks of that be? I also heard that you should not run the spacers on the street but I dont know why.

Any ideas?

 

[1970 slantroof]

The general rule of thumb is 11 1/4" rotors are the biggest you can run on 15" wheels and still have caliper clearance. I have 15" Minilite wheels for my 1970 and am running Granada rotors to allow clearance for the Cobra calipers. I will have to fire up the mill and create my own caliper brackets. Don't know about the spacers. Never have used them. You have to be careful not to change the "scrub radius". It will make is steer weird.
Howard

 

[YardSpecial]

AGAIN, Howard is the MAN !!!

 

[89MustangGX]

You can run a spacer on each side of the front to get them to fit, but you'd also want to run long studs as well.

 

[Matt90GT]

I have 13 inch cobra brakes on the front of my 91 stang and I am wanting to run some 15 inch pro stars (skinnies) or something up front. What would your suggestion be to get something to fit. I could put some smaller rotors it but I really dont want to. I have heard of running spacers on the front but what would the drawbacks of that be? I also heard that you should not run the spacers on the street but I dont know why.

Any ideas?

Its not the size of the rotor, but making the wheel clear the caliper. There are a few 16" wheels (read custom made 3 piece units) that clear, but you need 17s to clear.

Spacers exert more pressure and loads on everything. Thus not recommended.

If you are into drag racing, get the dual piston 99+ GT calipers and rotors. They fit under 15" wheels.

 

[1970 slantroof]

I'm not good enough with a computer yet to make a drawing and post it on this site so let me try to explain "scrub radius" with words.
Front ends on cars are designed so a line drawn vertically thru the upper and lower ball joints will intersect the ground very near the center of the tire tread contact patch. (side to side). This is called "zero scrub radius". It reduces the leverage the tire exerts on the steering when you hit a bump for example and generally makes the car safer and more pleasant to drive.
That is why front wheel drive cars have so much different offset on their wheels. The mechanics of the front wheel drive dictate that the line thru the upper and lower ball joints contacts the ground closer to the center of the car. In order to get the desired "zero scrub radius", the rims must offset the tire contact patch also nearer to the center of the car.
Using spacers on the front end screws up all this engineering and I personally would never do it. Many street rods suffer from this problem because of the mish-mash of parts some guys use.
I don't know if my explanation makes any sense or not. Not trying to tell anyone what to do or not to do, just trying to help you understand what effect these changes can make.
Howard

 

[shinoda]

good explanation

 

[shinoda]

how big of a spacer would i need to do this?

 

[Paul S.]

Bite the bullet and get the right wheel for the car.Bogart makes a wheel that fits properly.You need a 17 inch wheel to clear the calipers.