Will the $100 big brake kit work with 13" wheels?

The short answer is maybe, but not likely. I'm sure it depends on the 13" wheels.

The center line to the high point of the caliper is 5 7/8" you would need 1/4" clearance. So you'd need an inner diameter of 12-1/4" at the inside of the wheel. The wheel profile is also not flat, it tapers from larger on the inside of the car to smaller towards the spokes. The tightest clearance on my 14" wheels with 30mm offset is by the spokes. That outside part of the caliper also has a smaller distance from center line (5-5/8") than towards the inside of the calipers where the cooling/reinforcing fins and fittings are.  I have over 1/2" at the outside point of the caliper ( by the spokes), but with the balancing weights, there is less than 1/2".  So theoretically it is possible that the big brake kit will work with 13" wheels but it would be really tight.  Caveat Emptor.

If you wanted to test it you could buy 1 rotor and 1 caliper, slide the caliper over the rotor, and bolt up your wheel with out it being mounted on the hub...allow for 1/16" between the rotor and the carrier.  If it doesn't fit, return the parts for a refund.  You may even be able to take a loose wheel to a local auto parts store and have them pull the parts and see if they provide the clearance for your particular wheels and offset.

Suspension and the $100 Big Brake Kit for the MK1 Fiesta - Redux

I mounted the the suspension back on the Fiesta with the new big brake kit.  I also had some new springs and a replacement right front Boge strut already built up.  Eventually, the Koni sport struts will go on.

New suspension

Here are some final notes about the brake swap:

1.) you will need new caliper bolts. They are m12 - Fine(x1.5) x 30mm long mounting bolts. I bought bolts from BMW and they were a touch too long and would hit the Rotor. Make sure they are Hardened. I got these from True Value Hardware for $2.50 each.

2.) Have your Machinist mill off .175" of material from the caliper brackets to center the hub on the rotor.

3.) You will have to drill out your existing Hub holes to accept the larger M12 mounting bolt.  

If you want to be able to swap back to your stock calipers, you will need to drill and tap the stock carriers to to accept the M12 caliper bolts.  I have two sets of carriers, so I will do this with one set incase I ever need or want to go mount up the stock wheels.

Caliper with milled surface (-.175)

Big Brakes

New springs and replacement strut