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Street-legal electric 4-wheeler build

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MalibuMan Cas Tuyn
Weert, Limburg, Netherlands   NLD
One step forward, the brakes.

As I heavily rely on bicycle components to keep my CK light, and already have bicycle rims and hubs, it is only natural I go with bicycle brakes. Because my wheels will be single-side mounted, rim brakes are not possible, so I need to chose between drum brakes and disc brakes. On my velomobile I have drum brakes and after many kilometers they start to fade and they are not the quickest stoppers. So disc brakes it is.

A typical mountain bike with rider is about 120 kg, and has 2 wheels to brake. On average 60 kg/brake (I know the front brake will work harder).

My CK will have a weight of about 200 kg, me included, but that is spread over 4 wheels. On average 50 kg/brake. So I think 4 bicycle brakes will suffice.

On the BikeMotion exhibition in Utrecht, The Netherlands I met the people from Magura, who make brakes for bikes and motorbikes. They have a special brake set for three-wheeled transport bikes, called the Big Twin. It is one hydraulic handbrake with two 160 mm brake disks, designed for heavy loads. I will get 2 sets of those.

Some fabrication will need to be done to have 1 foot-pedal operate these 2 handbrake handles, I plan to mount them in parallel, with a bar across both handles, and connect the foot-pedal not in the middle, but 1/3 away from the front brake handle. This offset favors the pressure on the front brakes, so I get 2/3 of the stopping power on the front brakes and 1/3 of the stopping power going to the rear brakes.




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MalibuMan Cas Tuyn
Weert, Limburg, Netherlands   NLD
Just ordered 4 brake discs, size 180 mm. The ones on the photo above are 179 gram each, but Magura also makes the HC model (148 gram) and SL2 model (118 gram). I ordered the SL2's.

That adds 472 gram (for all 4 discs) to my CK.


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Smoky Silver Member Don Schmok
Salmon Arm, BC, Canada   CAN
Real light cheese graters you got there!



1929 Riley Bitsa

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classical-gas Scot Laughlin
Bellingham, WA, USA   USA
In most of the US, a powered vehicle with more than three wheels is a car, and must be registered, which requires inspection, and meeting a long list of regulations and equipment requirements. Under four wheels ( and over a certain top speed and power output) is a motorcycle, and requirements are much less... which is why so many power assisted velocars are three wheeled.

Three wheels brings a host of design problems, mostly related to tip over if not cornered very conservatively. Center of gravity has to be very low relative to track width (which is effectively half the track of the paired wheels) and all three wheels should evenly share the vehicle weight, so 2/3rd of the weight should be over the pair, 1/3rd over the single. None of this is easy to accomplish in a light vehicle that needs to be visible(over the window sill of a light truck) to motor vehicle drivers.

Lead acid batteries in an electric vehicle is stupid, given the power density of modern LiFePo, and other chemistries. Almost any Lithium battery pack will halve the weight and double the range of lead acid, and last years longer under the demands of an electric vehicle. Budgeting and designing for modern batteries will do more for the performance of the finished vehicle than anything else you can do.

MalibuMan Cas Tuyn
Weert, Limburg, Netherlands   NLD
In Europe, there is a category L7 which allows 3 or 4 wheels for a light electric vehicle. Since I am experiencing all the disadvantages you mention in my 3-wheeled velomobile, I am building a 4-wheeler. Transport costs to the USA will be so high it will never visit Tieton, however there is European Festival of Slowth in France every year that I want to visit once it is finished.

To minimize regulations I will build this first CK according to moped rules, and have chosen 48 Volt as the difficult and expensive EMC certifications are only needed for 72 Volt and higher.

I will most certainly choose LiFePo4 batteries, but still have to decide between bulky battery blocks and expensive Tesla-style batteries with built-in BMS, which are created from many tiny round battery cells.

Greenspeed Ian Sims
Knoxfield, Victoria, Australia   AUS
Hi Cas,
I've seen a lot of disc brake on cycle karts, and if the aim is to look authentic, they scream "fake" to me. I used to offer disc brakes on my recumbent trikes, but when Sturmey Archer started offering the 90 mm XL-SD drum brakes, I tested them and found them better than some disc brakes. So specified them on my Magnum trikes, and have had no complaints, as once they are bedded in they will lock up the wheels.

My other worry would be using 700c or 29" inch (50-622) wheels on a 4 wheeler. While they might be fine on a two wheeler where to machine banks into the corners, I think they are recipe for disaster on a three or 4 wheeler, due to the cornering loads.

Many years ago, when I was doing Electrathon racing, I choose 20" wheels, and a guy suggested I try his machine which had 26" wheels. After a few laps of the velodrome, which is banked, I turned out through the side gate at low speed, and the left hand wheel collapsed!

He said "Is this what you do your competitor's machines?"

Here is a pic one of my Magnum trikes . Note the 20" wheels and drum brakes. Plus a pic of the Electrathon machine. Weighed 78 kg with Ohio 2 hp motor and two car batteries. Won the last race we entered by 3 laps.


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MalibuMan Cas Tuyn
Weert, Limburg, Netherlands   NLD
Hi Ian,

For authenticity I hope it will look traditional from a mile away ;-) and then surprise you with some modern touches as you get closer. If you see the complaints about the solid rear axle and driver back problems you will forgive me for putting in a rear suspension.

The wheels I have already bought are designed for trike transport bikes, so should be able to handle considerable side-load. I am aware of the issue.

Your picture with the negative camber wheels like 1980's BMW 3-series rear wheels reminds me that on my velomobile the 2 front wheels are also placed in a negative camber. In a corner the outside wheel gets the most force, while the inside wheel gets less force, so maybe I should put a negative camber in my wheels too.

In many designs I see that the bottom A-arms are longer than the top A-arms, which introduces negative camber under load. To get the line through the turning points to hit the tire contact patch, my uprights will make a bend at the top towards the body, so the top A-arm is already shorter on the wheel side, maybe I can make it shorter on the body side too.

I plan to make the upright from thick-walled Aluminium pipe 40 mm, cut at 45 degrees, rotated and then rewelded to create a 90 degrees bend. If you look at the picture, you can see:

  • the size of the brake disk determines the distance from the spindle center to the brake caliper
  • the size of a hole to put a wrench through to fasten the bottom joint
  • the height of the wheel determines the place of the contact patch relative to the bottom joint, and a line through both gives me the location of the top joint

BTW, that Rocket is a beauty.


(sorry for the sideways picture, the original is vertical, so it must be a 'feature' of the forum)

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Greenspeed Ian Sims
Knoxfield, Victoria, Australia   AUS
Hi Cas,
Thanks for the reply. I'm pleased to see you are aware of the problem with the larger diameter wheels. Negative camber will certainly help, although I guess only to the amount to the proportion it is towards 45 degrees, at the limit of adhesion.

Tests done by a Velomobile builder and myself found there was no increase in rolling resistance up to 10 degrees of negative camber. Thus the Magnum uses 5 degrees of negative camber to reduce the width of the trike, to compensate for tire distortion on cornering, and to reduce rolling resistance on the turns.

The steering geometry is also designed to increase the camber on the outer wheel as the steering is turned, and to reduce the camber on the inner wheel.

The unequal length wishbones are designed to compensate for camber change with roll, to keep the outside wheel vertical, so they would not necessarily increase the negative camber unless you use shorter virtual swing arm lengths, which might give too much jacking effect, unless the virtual pivot is low.

The virtual pivot is where the lines drawn through the wishbone pivots meet in front view. Most car virtual swing arm lengths are about 1.5 times the track width.

Please be aware that unlike steel, aluminium welding is not as strong as the parent material, which I have discovered to my cost :-( Thus while I am now making my trike frames from 7005 aluminium, I am still making the kingpins from steel, and have reduced the number of welds in the 7005 frames.

I will be interested to see how you progress with this project.

Thanks for the compliment on the Rocket. Had a lot of fun with that machine. Here is a pic of my son, Paul, racing it.

Ian Sims.


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MalibuMan Cas Tuyn
Weert, Limburg, Netherlands   NLD
My chassis and wishbones will be steel, and I will braze them so the material does not suffer weakness at the joints.
Motor and reduction transmission mounts will be Aluminium extruded rails, so I can tension the chains by sliding them in the rails. No welding there, all screwed to the chassis.
The uprights and spindle I chose Aluminium as they are unsprung weight.
And body panels will be Aluminium too, again for weight and ease of bending.
Inside floor, inside wall, chair, dashboard, and maybe the battery box will be multiplex connected by screws to tabs I weld on the chassis, so they add rigidity.

Maybe I will have to build the battery box from steel due to the fire hazard and/or safety regulations.

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