BUILDING A CYCLEKART
BUILDING A CYCLEKART
BUILD SERIES no. 6: Steering
For the most part, steering systems on our cars are dirt-simple. All but one car has direct, go-kart type steering. Steering shafts (columns) are 5/8” Ø steel rod. Most of the shaft components are in the AZ 1868 kits. Shaft lengths used vary and most shafts have been extended by welding an additional length of 5/8 rod onto the non-splined end. The GN has two shafts welded end to end in order to get splines on both ends. The GN is the odd ball (again). Its first iteration made an attempt at wire&bobbin (cable) steering. This was a bad idea taken from the inspiration car. The wire&bobbin was replaced by a small sand-rail type rack&pinion unit. This unit is very quick by normal car standards but feels sluggish next to the direct go-kart steering on the other cars. Shaft mountings range from pillow block bearings to bronze bushings to simple slip holes. The Miller has a junk yard VW Jetta u-joint welded into its shaft to allow the Pitman arms to swing through a more beneficial plane. To hold the shaft end steady a 5/8 heim joint was used.
The arrangement of tie rods, their locations relative to the springs and the directions of spindle arms vary greatly from car to car as you can see in the images. Tie rod choices have varied from tubular AZ 1849, to economy solid AZ 1843 to deluxe solid AZ 1842. A couple cars incorporate moderate ackerman. Some have carefully considered geometries others do not. In the end most of the subtleties are entirely lost in the mayhem of driving!
Steering geometries are less critical with stiff (limited motion) front axles, Fiat and Miller as examples. Geometries are more important (and can be quite vexing) when extreme travel is possible as it is on the Peugeot and GN.
One subtlety that does make a very apparent difference on all cars is toe angle. Choices have ranged from strong toe-in to slight toe-in to neutral. One car runs well with a touch of toe-out. Toe in is when the front wheels point inward, toward each other to the front. Toe out is the opposite. Generally speaking, modest toe-in helps keep the wheels from wandering. This effect is most noticeable when driving quickly on a smooth surface. The trade-offs for toe-in are scrub (the tires scuffing as they run slightly crossways to the line of travel) which slows the car down, wears out the tires and can be less predictable on turn-in to a corner. A little toe-out gives great turn-in on corners but is challenging to drive quickly in a straight line. Current general consensus is very slight toe-in.
The other factor that has the greatest effect on steering is the back axle. The live axle cars understeer severely on firm footing. The effect is greatly diminished on dirt or grass at speed. Slow speed maneuverability is sorely compromised by a live rear axle but as soon as you can break the inside rear wheel free either by spinning it or lifting it, maneuverability returns.
Steering wheels include off the shelf, AZ 1801/1805 go-kart wheels (Panhard, Fiat and Miller) and scratch made aluminum and mahogany wheels (Austro-Daimler and the Panhard in concours trim). Bloody Mary has an AZ 2293 butterfly kart wheel. The Peugeot uses the dressed up core of a kart wheel. The GN uses a 1960’s Italian, after market, leather wheel.
Photo montages in order are: GN, Miller, Bloody Mary, Austro-Daimler, Peugeot, Fiat and Panhard.
Sunday, January 30, 2011