From Paul Geithner's Triumph Spitfire

Links, References & Technical Information

Upgrading Triumph Spitfire Wheel Studs

Something to seriously consider, especially when using alloy rims, is to upgrade from the stock 3/8 inch, 24 threads per inch wheel studs to ones that are thicker and longer. Being as thin as the stock studs are, they are susceptible to over-torquing, and being as old as many are, they likely have been overtorqued by someone in the past. Fitting wider wheels with wider, stickier tires and making other suspension improvements allows the car to generate more cornering force, which puts more stress on the studs. Furthermore, alloy rims have thicker center sections than steel ones, and so the lug nuts may engage fewer threads, making a somewhat marginal situation even worse. Upgrading to thicker 7/16 inch or 12mm studs that are longer than the stock ones is good insurance.

Because there are so many studs to choose from and it’s difficult to get stud dimensions or search for studs according to their dimensions, choosing suitable substitute studs is a real chore. One very good option that I learned about a few years ago from some fellows on an automotive forum based in the U.K. is to use Land Rover Freelander studs (part number CLP9037L). These studs are 12mm thick, 1.5mm per thread (i.e., M12x1.5) and they have the right knurled diameter (0.510-0.520 inches, or about 13.0 to 13.2 mm) so they will fit snugly and just right into Spitfire and GT6 hubs. Freelander studs are 2 inches long, 1.3 inches of which is threaded, versus the stock Spitfire and GT6 studs that are 1.5 inches long, 7/8 inch of which is threaded (1/8 inch on the end is an unthreaded “easy start” shoulder). The comparison photo below clearly illustrates the dramatic difference..  

One particularly good thing about these Freelander studs is that they have the same beveled/chamfered head shape and 5/8 inch head diameter as the Spitfire and GT6 studs. They are a perfect fit and will not cause any interference problems with the rear brake slave cylinders. However, in early 2010 a friend of mine bought some Freelander studs that came with the more common square-edged head shape found on many other studs:

My friend contacted Land Rover to inquire about the different head shape, and he was told they’ve changed suppliers (and apparently the specs for head shape too). If you receive a batch of these square-edged studs, then it’s possible to machine a chamfer to the underside of the head, even if you don’t have a lathe. One method is to carefully but firmly chuck each stud into a drill press (being careful not to damage the threads) and spin it while you carefully grind away a beveled edge with a grinder, Dremel tool or file:

It’s a good idea to machine this chamfer into the heads of the studs so as to avoid possible interference that can occur between the stud heads on the backside of the rear hubs and the rear slave brake cylinders as the wheels turn.

These Freelander studs should work fine with any alloy wheels on a Spitfire or GT6. However, if you find the studs to be too long for your application, like if you’re using closed-end lug nuts and they bottom-out on the ends of the studs before they seat on the wheel (possible with thin center section steel wheels but very unlikely with alloy wheels), there are some simple options. These include drilling-out the blind hole in each closed-end lug nut a little bit more, using open-ended lug nuts or just shortening the threaded ends of the studs a little bit before installing them. Also, because the shoulder of the Freelander studs is a bit longer than the stock studs, there will be about 1/16 inch of it exposed through the front hubs and rear drums (see photos below). If using steel wheels or alloy wheels with mag lug nuts, check to see that the nuts seat all the way. There shouldn't be a problem, but if there is, then drill-out the first 2mm of thread in the nuts. With alloy wheels that use cone-seat (i.e., acorn) nuts, there are no issues.

Changing studs is simply a matter of removing the hubs, pressing or carefully hammering out the old studs, and pressing in the new studs. These studs are too long to fit them without removing the hubs, and besides, installation is much better with the hubs off the car. At the front, unbolt the brake calipers and move them out of the way, remove the center dust caps and the wheel bearing retaining nuts and remove the hub and brake disc subassemblies. Then, separate the hubs from the brake discs and carefully press or hammer out the old studs, press or carefully hammer in the new ones, and reassemble everything. At the rear, remove the brake drums and pull the hubs with a “Churchill” hub puller to make it easy and to protect the hubs from damage. Borrow one or consider purchasing one yourself (Canley Classics and Rimmer Brothers sell them). Once you’ve removed the hubs, you can press out or carefully hammer out the old studs and carefully press or hammer in the new ones--being careful not warp the hubs--and reinstall the hubs on the car. A shop manual is good to have if you are unfamiliar with all of this to help you out with instructions and torque specs. Note that pressing the new studs into place before reinstalling the hubs on the car is preferable to pulling each stud home by torquing down hard on a nut and a stack of washers. You don’t want to risk overstressing or otherwise damaging your new studs, even though they are pretty strong and a lot stronger than the thinner stock studs. Pressing studs out and in is easy enough using a vise and some deep sockets.

With the new size studs, you'll need new, matching thread lug nuts too, and these are commonly available from wheel suppliers, auto parts retailers or specialty vendors like Lug Nut King. A good torque range for nuts on M12x1.5 studs is 66-86 ft-lbs (i.e., 89-117 N-m). 

Enjoy your new studs on the road with confidence!

Paul Geithner