Do You Really Need Round Wheels?
You need to clean and inspect your wheels before you go to the track. Every time. You normally have the wheels off to bleed the brakes so clean the wheels and look for problems. Check the stud holes for wear, and pay particular attention to the lug nut seat area. Spend some time looking for cracks. Remember your wheels may very well be older than you are.
All wheels flex in a corner. Every time you take a corner at the limit you’re flexing your wheels. Spins, running over the curbs and trips through the run off areas add their own unique extra stresses. Remember the grip of a race tire causes a lot more wheel fatigue than street driving.
Refinishing Magnesium Wheels The main enemy of magnesium is moisture. Carefully bead blast the bead area with very clean glass beads and don’t use too much pressure. Harvey Weideman weidmanwheel@sbcglobal.net) cleans the wheels with solvent and then bakes them at 2000 F for a couple of hours to make sure all of the moisture is out of the metal. After the wheels cool to about 750 F he coats them with zink chromate. Harvey never lets the wheels get too cool and tries to do the painting when the humidity is low.
He also keeps the wheels in the warming oven at 750-800 F for an hour to flash. Then he applies a good 2-part primer. Again he’s careful about not letting the wheels get too cool and watching for moisture as the primer cures. Harvey then applies a sealer, followed by a color and then a clear coat. Only after the clear is dry does he let the wheels go to room temp.
Paint vs. Powder Coating There are a lot of reasons to like paint and not too many reasons to like powder coating. The first problem is the heat that’s generated when baking the powder coating. You want something in the range of 3000 to 4000. Higher temperatures tend to magnify the problem. Magnesium is especially problematic because of what’s known as outgassing, which is the release of a gas that was trapped in the magnesium. Powder coating shouldn’t be applied to the rear contact area or the area that contacts the lug nuts. You powder coater has to carefully mask these areas off. Also, if the powder coating is too thick it’ll hide any cracks that develop in your wheels. The metal beneath the powder coating may crack and this crack won’t be visible. Whether you powdercoat your wheels or just paint them you always want to use the thinnest possible coat.
Wire Wheels Wire wheels are actually a system. There’s the axle hub, the wheel hub, the spokes, the rim and finally the knock-off nut. Wire wheels require periodic maintenance and checking the hubs and wheels should become a standard procedure.
The weight of your car is actually suspended on the few spokes that are uppermost in each wheel and they’re constantly moving into and out of this weight-bearing position when the car is moving. Add side loads from cornering and you can understand the stresses that cause the spokes to stretch and move around.
Spokes usually break at the nipple or at the hub. This break is often hard to see if it’s behind the hub or within the nipple. To locate a bad spoke, take a small block of wood or a very small hammer and lightly tap each spoke. If it makes a “tinging” sound, it’s tight. If not, it is loose. Hold off your temptation to tighten the loose spokes until you’ve finished your inspection. The spokes stretch and the spoke holes will also wear. This change in tension causes the rim to run out-of-round. Run a pencil around the spokes and note whether any the spokes make a sound that’s markedly lower in pitch than the others. Tighten these 'flat' ones with a spoke wrench and you’ll maintain the wheel in a round condition.
Next, check the wheel for trueness. Raise the car and secure it on jackstands. Find a suitable tool rest (a jackstand works well) and hold a screwdriver or other pointed object right next to the edge of the rim while slowly turning the wheel. If the wheel isn’t true, the gap between the tool and rim will change as the wheel is spun.
If the wheel moves side to side you have lateral run out. If the rim moves up and down you have radial run out. If the wheel stays pretty true (1/16 of an inch or less) it’s probably going to be okay with a tune up. If there’s a big wobble your wheel is going to need a lot of work or even replacement.
If the splines on either the wheel or axle hub are worn, the solution is replacement of both the wheel and the hub. If you put a new wheel on a worn hub, or vice versa, the new component will quickly wear out.
It makes no difference if you have aluminum, steel, magnesium or wire wheels the basic rule it always the same. Check them carefully before you go on the track. It’s never fun to have to throw a wheel away. It’s better to throw a wheel away though than throwing a whole car away because never noticed the crack in the wheel.
