Installing ADR Type 29 rims on a Xebra Sedan

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Here's your ordinary Zap Xebra 12" wheel If you visit Hardkor Engineering you can find longer studs to make mounting a thicker 13" wheel safer, by having more threads to engage the lugnuts.


The stud on the left is the Zap stock stud. The one on the right is an ATV stud, slightly longer, same threads, but a larger head. The one in the middle has been "adapted."


I ground away at the top of the head to make it fit in the backing plate, using the TLAR method* and chucked the stud in an electric drill, holding a grinder gently against it while spinning the drill. This reduced the diameter of the enlarged shoulder, slightly reducing its effectiveness, perhaps.


Not too exciting, just the rear wheel assembly with the rear wheel removed. The parking brake is to the left and the hydraulic brake is to the right. Simple and effective.


In this shot, the cotter pin and axle nut and washer have been removed. I started to remove the brake disk bolts, but realized that it was a lot easier to loosen the nut if the partking brake was set.


The four bolts holding the brake disk to the wheel plate have been removed. The parking brake is holding everything together, along with the hydraulic brakes.

Clearly visible in this photo are the two parking brake bolts. They are threaded only near the head and once released, pull out as very long pins. These pins serve to allow the brake pads to float when the brake lever is released. It's a little tricky to get the bottom one out, as the frame interferes slightly, but if it's removed last, it works.


There's not much stress on the cable in this position, probably less than when it's engaged and it's not knocked around during the rest of the project, so I left it to hang.


This is a curious sort of thing to find. This is the left rear brake assembly, marked with a big "R" on the housing. The right rear brake assembly is marked with a big "L" in the same location! It's not a good idea to hang the brake assembly from the hose, so have a piece of wire handy and support the assembly from the coil spring once removed.


The bolt to remove the hydraulic brake assembly is barely visible in this photo, positioned just to the right of the axle and below the bolt that holds the caliper together. It has to come out and it's better if you don't get the wrong one.


Here's an out of focus photo of the lower bolt holding the hydraulic assembly in place. They loosen easily and return easily when re-assembling.


A nice clean wheel with the brakes removed. You can see the hydraulic assembly hanging from the coil by a wire (a strong wire) and the brake disk is resting on the axle at this point.


In this photo, a pair of bolts have been pushed through the holes previously occupied by the brake disk bolts. On the back side, a pair of nuts are threaded on the bolts. As the nut is tightened, it pushes against the disk, which pushes against the frame. I was concerned about distortion, but did not see any during the process.


The side view shows the bolt pushing against the brake disk. Be sure to rotate the brake disk so the holes to not line up with the bolts. The ends of the bolts get flattened slightly and require a wrench to remove them, so use bolts you can consider disposable. Obviously the bolts should be long enough to push the bearing free (about 3").

After a few turns on each bolt, the bearing begins to slide out pretty easily. The bearing is not particularly wide, but is well packed with the wonderful blue Zap grease. Use caution to avoid getting dirt or debris into the bearing and grease.


A different view of the released bearing and backing plate. You can also see the slight discoloration on the brake disk caused by the bolt pressing against it during the removal process.


The narrow wheel bearing is almost completely visible here. A good reference is the nut used as the removal tool. Once the plate is off, pushing out the old studs and putting in the new ones was a simple matter. One can use a bench vise, a bench press, or in my case, a hammer and small anvil. To replace the bearing and plate, I slid the assembly over the axle joint and put the washer and axle nut in place. Using a leverage bar to keep it from rotating, I tightened the axle nut until I felt it "bottom out" and inserted the cotter pin.


Here's the final result. Obviously there's no rubbing while on the jack stands, but even after it was lowered and taken for a spin, we had no problem. With two people in the car and one really bad bump while cornering, I think I might have heard a little rubbing. Our Xebra will probably never have more than two people, so rubbing is not likely to be a problem.

This project was made necessary by the limited length of the stock Xebra studs and the much thicker wheel of the ADR Type 29. It is about 10 mm thick at the studs, while the stock Xebra wheel is about 2 to 3 mm thick. Using stock studs provided only 4 thread engagement, something with which I was not comfortable. The upgrade has resulted in eight and five-sixths turns engagement, a one-hundred percent improvement. If there is a puncture, it will be necessary to place temporary washers behind the stock spare wheel to get enough grip from the stock wheel nuts, although I may just grind off the end and make them pass-through nuts, since they are hidden by the ADR wheel covers.


If you didn't know this was not factory stock, you might not even notice. The new wheels look great and the ride seems to be somewhat improved. Our first test run resulted in an honest 38 mph in a slight headwind. On the way back from the supermarket, we managed a very tiny downhill, reached over 40 mph and when it leveled off, we were still going 39.6 mph. The Drain Brain readings were much higher, as expected, but less than double my usual feather-footed levels. This week, my wife will make her commutes and return with real figures to compare.

Post-installation Update

The wheels have been in use on a daily basis for the last five days, with five trips, three of which are indicative of our regular use patterns. The general feeling is that starting power requirements are increased, which makes sense because the larger wheels are an effective gearing increase. Top speed is up to 40 mph as noted above, on level ground. I'm a light-foot on the go-pedal, so I've seen normal current draws at normal speeds, but also find that the new tires and wheels make for a more pleasant ride.

Day #
Trip Dist
Max Amps
Before Wheel Change
After Wheel Change

The smaller trips can be disregarded as too short for statistical value. The trips of 12.2 miles are my wife's regular word-day travels and the trips of longer distance are those of my "get-to-drive-the-Xebra" type. I'm easier on the go-pedal than my wife is, so the watt-hours per mile figure are consistently less.

I discovered a slight complication to the TLAR method (That Looks About Right) in that the head of the stud being ground off can still protrude into the space occupied by the brake disk. On one wheel, I had one stud head thin enough and three of them not thin enough, so they contacted the face of the brake disk, near the hub, not the braking surface. The one stud that was the right thickness (thinness) created a small warp in the assembly and perhaps a bit of "no-brake" drag as well.

I don't believe it's dangerous, but it made periodic dragging noises and a pulsing deceleration (not a pulsing brake pedal though) which irritated me no end. Yesterday, I pushed out the studs and used a more precise TLAR method and replaced the studs. My wife reports that she no longer hears the noise and doesn't feel the goofy braking problem, so I must have gotten it correct.

I'm going to order a few replacement studs though, and have a machinist match the factory stud. I ground down the serrated portion a little bit too much and the stud didn't grip the hole properly, which made it a little bit challenging to remove the wheel lug nut. Once I got it out and properly contoured, I applied the very-handy-industrial-strength-adhesive known as J.B. Weld and put it all together again. I'll feel better when I have the replacements in hand and installed though.

My warning would be to use great caution and more precision than I did when cutting material from the new studs. I don't think there's any real danger, just a lot of inconvenience.