BUILDING A CYCLEKART
BUILDING A CYCLEKART
BUILD SERIES no. 1: Rear wheels and hubs
One of the core principals of Cyclekarts is that there is no master set of plans. No one way to do things. Every car is different - figured out, usually seat-of-the-pants, by its builder. While there are some consistent key components and general guidelines, variety, individuality and resourceful inventiveness are treasured.
I do not presume to violate this core principal but I don’t think showing examples of what we have done and offering some explanation, some part numbers and sources is going too far.
We will start with rear wheels and hubs. We will do the drive systems soon but there are three types and they effect how the wheels are done: live axle (two wheel drive), free wheel (one wheel drive) and differential (two wheels driven but with power apportioned in reaction to load). These drive systems lead us to two hub types: keyed and free spinning.
An important point to remember on free wheels is that they generally are not moving at a dramatically different speed from the engaged wheel and, therefore, not much different than the axle they are spinning on. They do not require sophisticated bearings just smooth surfaces and some grease.
We are starting with the wheels because the wheels are the most difficult parts to track down. Go straight to E-bay. You won’t have great success searching by size, 17 x 140 for example, but if you search by motorcycle model you will find loads of options in a wide range of prices and in an equally wide range of conditions. You are on your own to sort that out! Finding a perfect wheel at a good price is a quest for the holy grail.
For rear wheels (and we have also used them for fronts) Honda CT90 wheels have been far and away our favorites. They are pretty easy to find at decent prices, they are robust and straight forward to convert. We’ve also used front wheels as rears (again CT90’s) and even CB125 wheels. Bloody Mary tried newer model, aluminum rimmed (Yamaha) wheels but they didn’t survive a single race weekend. Most of the wheels below are steel rimmed, 17 x 140 wheels from the 70’s. 140 wheels are well suited to 2.50 and 2.75 tires. 120 wheels are well suited to 2.25 and 2.50 tires.
The blog photo is a CT90 wheel being modified for Bloody Mary. The bearing bosses are cut off both sides of the hub and AZ 2561 (or AZ 2562) “mini-hubs” are used on the inside and the outside. This scheme works well where the hubs need to be free spinning or keyed. Bloody Mary generally runs with one wheel drive but has the option of also running with a live axle for poor traction conditions. The hubs are connected by 5/16 grade 8 bolts (through holes drilled in the hub casting). The Azusa “mini-hubs” sandwich 1/8” thick steel disks against the wheel hub casting. On the inside this rides against the steel drum brake liner (Shown in the blog photo) and on the outside in a similar manner against the webs where the rubber “coaster” goes on a CT90. The disks in this case are laser cut. The advantages of this scheme are: minihubs are inexpensive and light, having them inside and outside gives great leverage for the wheel on the axle. Short lengths of 1” x 1/8” wall steel tube (DOM) are slipped over the 3/4” threads on the axle to locate the outboard minihub. Appropriate thrust washers are used on the free spinning wheel and the inboard side of the hub is backed up with a shaft collar on the axle. 36” axle. All the axles we have used are 1” diameter.
A more robust (and heavier) solution has been utilized with the same CT90 wheels on the Peugeot. In this case, a laser cut 1/4” thick clover was welded to an AZ 8237 weldment to create a hub. On this car, the axle nut tightens down directly on the clover hub and the wheel is then attached to to the hub. The axle nut had its corners blunted to allow this to work. This car has a live axle so both wheels are keyed. 34” axle.
The Miller uses the Peugeot scheme on the rear wheels with subtle improvements. The clover fits inside the drum brake seat and the wheel nut is out board against a spacer. 36” axle. Initially the Miller also used CT90 rears as front wheels.
The Fiat uses a similar scheme but instead of creating the hub with a weldment, an AZ 2282 hub has been used. The useless 1/2” studs that come on this hub have been removed and the hub re-drilled for 5/16 bolts. In this case the AZ hub has also been carefully ground down to fit directly against the drum brake liner without an intermediate disk. The wheel hub bearing boss was ground down to the height of the coaster webs on the other side so, on this car, the wheel nut is behind a blank outer plate. 36” axle, although, this axle was bent in rough driving and is soon to be replaced with a 34” axle narrowing the rear track a little.
Panhard scheme is similar to the Peugeot where an AZ 8237 weldment has been welded to a laser cut disk to make the hub. The Panhard however has an optional free wheel and so the wheel nut is outboard with large thrust washers between it and the wheel assembly. On the inside of the hub, between the hub and the axle bearing is a needle roller thrust bearing - fancy! 38” axle.
The GN uses CT90 fronts as rear wheels. It previously sported a different scheme but those wheels are now on the Bloody Mary (described above). The CT90 fronts are married with Azusa 2282 hubs. These are the same hubs used on the Fiat but in this case the 1/2” studs have not been removed, rather they have been ground flat on their outer faces so that they slip snugly inside the drum brake liner on the wheel hub. This adds extra strength to the assembly. There is no outer disk in this scheme. 5/16 bolts are run from the face of the wheel hub to the axle hub (new holes added). The GN is a live axle (well, it would have to be wouldn’t it!) so both sides are keyed. As on Bloody Mary, 1” x 1/8” wall steel tube is slipped over the 3/4” axle threads with a further appropriately walled tube slipped over that to net out to the bearing seat size.. 34” axle (with lots of threads showing = narrow track)
The Austro-Daimler uses macho Honda CB125 rear wheels. Initially these were installed with the large bosses facing out (as you usually see when these wheels are used on cyclekarts). Combined with this car’s differential axle, this made for a very, very wide rear track!CB125 wheels are 17x160. In the second installation the axle hubs were mounted on the opposite side of the wheel hubs with the axle hub going inside the wheel. The AZ 2282 hub was used, and as on the Fiat, the 1/2 studs were removed. The hub is in the usual relationship to the axle but the wheel is reversed. The 5/16 mounting bolts are going the opposite direction the 1/2 studs would have gone. This scheme required drilling the hub casting out with a hole saw and hand-filing to fit the reversed hub as well as grinding the AZ 2282 hub down to fit the drum brake seat. Differential axle is 38” long.
The work was worth it to make an attractive installation out of the beefy CB125 wheels. These are very easy wheels to find if you don’t mind 3” tires. Watch out though, some CB 125’s had 18” rear wheels.
Azusa parts (cited as AZ XXXX) are readily available from many different web stores. Prices are cheap. Delivery is generally fast. More sophisticated parts could be used but then things start to get too serious and too expensive! The Azusa pdf catalog is available at:
http://www.azusaeng.com/catalog/dwnld/azdwnld.html. Download a copy, we will be referencing it over and over as we move through other parts of the cars.
Wheels are laying in motorcycle junkyards across America. If you have a local used part source like BentBike in Lynnwood and Kent you can pick through the bodies yourself and try to talk them down to a sensible price. At least there is no packing and shipping charge on local wheels. Quality of used wheels varies radically. They are usually bent to some degree - which you can usually improve a bit with some patient “love”. The wheels are also usually rusted to some degree - none of our cars have chrome rims, they have all been painted to hide their secrets. Absolute perfection really doesn’t matter, especially on grass and dirt. Wobbly wheels are more troublesome on pavement. Seriously bent wheels though are no fun to drive.
Monday, January 17, 2011