The unique Lotus steel wheels on Elans, Plus 2s, Europas and some Sevens consist of a standard "J" rim (5.5" wide on Plus 2s, 4.5" wide on others, all 13" diameter) riveted to either a "bolt-on" or "spin-on" type stamped center manufactured by Rubery Owen & Co. The knock-on wheel was conceived by Chapman for quick removal without the extra weight and cost of incorporating the Rudge splined hub used in wire-spoke wheels for many years. Chapman even prevailed on the manufacturer to make the wheels from lighter-gage steel than they thought safe. In fact these wheels do crack from fatigue after many miles of hard driving on high-grip rubber, but they perform well and are durable when used with original-spec tires. Thorough inspection of the wheels is a critical part of periodic maintenance.

Wheel maintenance consists of washing them with the rest of the car, checking tightness of the nuts, and balancing them every few years (the manual recommends a 3000 mile interval). Knock-on spinner threads should be kept clean and dry (never greased). The tapered nuts on four-stud wheels should be torqued to 25 ft/lbs; the octagonal "federal" center nut torqued to about 200 ft/lbs or a good pull on the long-handled wrench; the three-eared nuts should be whacked solidly with a 5 lb lead or copper hammer until they stop tight. A rawhide or rubber hammer cannot deliver the impact necessary while a lead hammer will do the job without marring the chrome plating.

Balancing is best done by a shop that can strobe balance wheels on the car so that all revolving components (brake rotors, hubs etc.) are taken into account. The car is jacked up and the wheels spun to about 100 mph and in many cases the car shakes violently from imbalance. Weights are added and positioned as required until vibrations are eliminated. The result can be a dramatically smoother ride, reduced wear on steering and suspension components, and a small gain in horsepower. Each wheel then needs to be marked for its position on the car and on the hub so that they can be returned to their balanced positions if removed.

Wheels that have been abused often are so bent or loose on the studs that balancing is not enough to restore performance. Wheels that are rusting, bent, scraped or dented, or cause the center nut to work loose, must be repaired or replaced. The best way to proceed in these cases is to jack each corner and spin the wheel by hand to observe any obvious radial or lateral runout. Then take all the wheels off the car (include the spare) for close inspection. Clean both sides with soap and water and/or degreaser if necessary and look for:

- Curb damage such as a bent rim and deep scrapes

- Rust, often in the joint between rim and center

- Cracks starting from a drive peg hole, from the inner point of a Lotus-logo shaped ventilation hole, or from the center opening on knock-on wheels

- Ovalling of drive peg holes from loose nut(s) allowing the wheel to wander on the hub (it should locate on the drive pins with no perceptible play) which also causes:

- Enlargement of the center opening on knock-on wheels (look for steel curled back to the inside.)

If the wheel has cracks or has very advanced corrosion it will need to be replaced. Drive pin hole and vent cutout cracks are the sign of a seriously fatigued wheel where welding will likely only be a temporary fix. Badly damaged rims can be replaced, retaining a good center, but a complete replacement is the best solution when possible. Good used wheels are often available, and new reproduction knock-on wheels are now available through Lotus parts suppliers.

The other problems can be repaired easily. Dents in the rim can be straightened at a good wheel shop. The rims are trued laterally and radially, and the rim edge can be filed down if scraped. Paint and minor rust can be blasted away with abrasives in a blast cabinet. When completely bare a final inspection is made for cracks and serious corrosion. If all is well the wheel is ready for paint.

Originally the wheels were painted silver ("dull aluminum") on the Elan and Europa, or black on some Elan Sprints and Plus 2s (some Plus 2s had chromed rims). The backs and inside rim of all silver wheels were semi-gloss black. A professional auto painter can do the best job of applying durable coatings with a deep shine, but money can be saved and originality of appearance preserved by painting the bare degreased steel with a good rattle-can primer and several coats of silver or black. Rustoleum Hard Hat #2115 Aluminum very closely matches the original silver. Be sure to get paint into the joint between center and rim to prevent rust, and to paint the outside edge of the rim next to the tire sidewall. Ideally the paint should cure for a few weeks before remounting tires or installation in the car.


STEEL WHEELS RETURN

New production 4.5 x 13 knock-on and 5.5 x 13 knock-on wheels are now available. They are made with slightly heavier-gage steel (new 4.5 x 13 weight 15 lb vs 12 lb original) by a different manufacturer, and powder-coated silver or black. Price is about US$200 each. These have 'safety rims' which, unlike the originals, do not require inner tubes for blow-out security.


Further reading:
Robinshaw, Paul and Ross, Christopher; Authentic Lotus Elan & Plus 2, Motor Racing Publications, Croydon 1995 Haskell, Hugh; Colin Chapman Lotus Engineering, Osprey, London 1993

By Randall Fehr
Seattle, USA
Revised September 2003