Midgetec

One of the decent accomplishments of the last month was getting the big wheels mounted to the little car - at least the front ones that is...

The 13x4 stock wheels weren't going to suit this little beast, so my son John and I started looking. After figuring out what we might need in terms of offsets to use the existing front hubs, we settled on the line of wheels that fit the BMW E39 chassis (late 90's to early 2000's 5-series).

There is a big selection of nice looking wheels in the sizes we were interested in, and we found a set on eBay for a decent price. Now, the challenge is making these 16x7.5 monsters fit on the Midget - the pitch circle diameter went from 4" to 120 mm, and the number of lugs went from 4 to 5. And we were going to need about 5/8" worth of spacer for each front wheel. After trying to make it way too complicated, John and I did some brainstorming and came up with a pretty good solution.

It started with a way to hold the hub for drilling it:

Next up was locating the lugs on the hub. The BMW wheels are hub-centric, meaning they center themselves on a protruding ring on the hub, and then the bolts hold them in place once tightened. Since our hub didn't have the 74.2mm ring, we wanted that hub-centric ring and we needed a spacer as well. Turns out the BMW spacers have the rings, so we bought a pair of 15mm spacers (H&R - very nice quality). And to locate them on the hub, we just laid them on top with a dial indicator, and moved them around until there was no runout when we rotated the hub:

In the above photo you can see the 1/4" pins standing on the spacer to locate them. Once the spacer was accurately centered and clamped in place, we drilled a couple of 1/4" holes to pin it in place. It had to be removable because the brake rotor attaches to the hub with 4 bolts beneath the spacer, so the pins were an easy way to positively locate it and still have it be easily removable. Of course torqueing the lug nuts really holds everything together, so the pins just keep it centered when initially installing the wheel.

So now that the spacer is pinned on, we needed to drill the holes for the lugs. We bought some 12 x 1.25 lugs that had a knurl diameter of .505", and to provide an interference fit (a fancy word for "install with big hammer"), we conveniently had to drill a 0.500" hole. But we wanted to locate the hole exactly, even with the hub-centric ring. And the best way to do that is with a transfer punch. The spacer had 15mm holes, and so McMaster-Carr (www.mcmaster.com) had the transfer punch in the mail to me the very next day:

Placing the punch in the spacer hole and whacking it with a hammer (the big one) gave us a perfectly located center punch mark right where we needed it.

And that allowed us to start drilling. We chose to do two passes, first with a 7/32" then up to the 1/2" bit. I know we should have done at least one more, but this worked OK.

Here is the first pass:

Note the stainless steel hose clamp around the base of the hub. That allowed us to lock it down prior to drilling, then loosen, relocate for the next punch mark, and tighten down again... And once the drill press is set up, rotating the hub should put every punch mark right under the bit - and it did!

The photo above shows the four inner holes for mounting the rotor, and the four former lug holes, and the 5 pilot holes for the new lugs, and also the two holes for the spacer locating pins.

As Colin Chapman would say, we were "adding lightness", although not intentionally. Of course you could argue that we were also "adding weakness", but I don't really think this is the weak link. The spindles will be, however, but like many car problems, that one can be fixed later with a credit card...

Where were we... Next, we made the second pass on the lug holes, and then used the big hammer again to install the lugs. Finally, we slipped on the spacer and pushed the locating pins in, and here's what it looked like:

By the way, we did have to do a bit of grinding on the back of the hub to give a level surface for the lug head to rest:

And now, with a test installation on the car:

And with the wheel fitted:

Ahhh, 205-40 16's on the Midgetec. How sweet it is.

Well, until we tackle the body work for the fender flares that is...