I working on & planning to build another racer for 2024 

I learned a lot from building & testing Polaris

...but, I would like to try-n-upgrade many things like:

Roll over protection 

...so, the driver is more enveloped

Wheels

...properly designed for the "loads" that will be inflicted upon them

...a wider "foot print", for better traction

...stronger, no plastic

...bolt-on, for quick change ability

Brakes

...stronger, Hydraulic system & properly sized rotors 

Axles

...upgrade to 5/8" spindles, in the front

...& a 5/8" grade 8 bolt in the rear

Steering

...properly size the pitman arms, to the wheel diameter

Maybe something about like this:

Specify parameters & work with in them

So, with the measurements
...& the diagram posted above, I started measuring, marking & cutting pieces

I started at the top, making the roll cage
...(2) pieces 1/2" Schedule 40 water pipe (actually 5/8"ID x 7/8"OD with ~1/8" wall) ~60" long
...marked at 3" intervals
...& then, bump bent 

* When making "stuff" where (2) matching pieces are required, I usually try to make both pieces, at the same time (it's easier to make matching pieces)

Here is a top view drawing of the top & mid layers, of the chassis 

...& a side view drawing, of the bottom rails

The top layer is the (2) curved top bars of the roll cage 
...the mid layer is mainly the upper side impact bars
...& the lower layer is the base rails 

* Notice, the highlighted 20" x 20" c**kpit area

...& 16" x 16" leg tunnel area

So, some measuring, marking & bump bending on a couple pieces of pipe (~78")

...& we have a couple of mid level "side impact protection" bars

...then, cut (3) ~14" crossmember bars

Then, after some squaring & aligning...everything, I tac welded

...the curved top bars

...to the cross bars

...& also, to the mid level bars

** Notice, I used the "work bench top" (old door)

...to screw down alignment boards

...& to "pin" the pieces "in place"

I also, used a ratchet strap to add "upper pressure" for holding the roll cage together, for welding 

Another view

I propped the rear of the "canopy" up at ~20"
...& the front at ~14"

Then, worked on dry fitting the base rails

Then, added some "props" to mimic some of the "braces"

...to see if/how all of the measurements & everything was working out here "in the real world"

I also, started thinking about how the front should look

...& bounced several options around

But, we gotta keep the weight "in mind"

...because when adding pieces, it can "add up" pretty quickly 

* Notice, I started curving the base rails upwards a bit (in the front)

...& the "hood" bars downwards a bit

They say "If you can't take Mohamed to the mountain
...bring the mountain to Mohamed"

So, I brought the bender, to the chassis
...& did some more bending

I bent the upper rails, downwards a bit more
...& the lower rails, upwards

So then, I could just use (1) crossmember

Now, it's time to double & even, triple check...everything

...by "eye" (eyecrometer)

...& using instruments (tools)

Mainly checking for overall squareness

...& that everything is "about" where it should be (structurally)

A view from the rear 

Then, start double checking that components "fit" about where they should

...like the seat

...& the battery box area

After most everything checked out "within specified parameters", I went ahead & made up & installed, a front seat mount (which also doubles as a mid-chassis, cross member)

Started working on & installing the "truss bars" 

* Notice the "truss bars" that "run" next to the seat, needed to be curved a little bit (to "clear" the seat)

I also, made up & installed a curved cross member, in the rear, that will also help support the driver's weight, while entering & exiting the car 

To help double check component locations & fitment, I added a few more "props" 

This pic mainly shows the pedal(s) location

...which is (~36") from the bottom/rear of the seat 

This pic shows a CAD "mock up" battery box, in relationship to the pedal(s) location

...to double check that there is adequate clearance, to actuate the pedals

I also, mocked up a potential spindle location with a "prop" steering shaft & tie rod

...to double check "swing" clearance, for these components too

Here is a pic with a wheel "propped" in place

...just to double check 

This pic shows an old circular saw blade, used as a "prop" steering wheel (to help mock up it's location)

...to double check the distance, from the seat back to the "steering wheel" (~24")

This pic shows the steering shaft height, in relationship to the seat (~12")

This pic shows the mounting bracket height (from the floorboard up) which checked out at (~15")

I found a (3) wheel hydraulic disc brake system, for Hammer Head go karts (~$75.00)

It has heavier duty (more properly sized) components (thicker rotors & bigger calipers)
...& also, provides braking for all (3) wheels (for better control)

It comes with the Master Cylinder

...(3) Rotors 

...& (3) Calipers (already plumbed & the system bled)

* A couple of extra bonuses are

...the rear caliper has a parking brake feature incorporated

...& the Master Cylinder has an automotive style brake light switch, already built in 

FYI: this video shows, this type of brake system, being mounted on a kart

* A couple of important factors to pay close attention to are:

1.) Check out the cast front wheel hubs, that are "normally" used with this brake system

2.) Notice where the master cylinder is mounted
...& how that mount is fabbed & installed

3.) Also, take notice of the size of the front rotors, compared to the size of the tires, they will be controlling
...& the size of the rear rotor, compared to the size of the rear tires, that it has to control 

Well, I'm not going to use those China-cheap hubs, for a couple of reasons

1.) Those hubs are for use with metric bolt pattern (6") rims (tallest tires available ~15")

...& I would like to use (8") rims (with taller ~16"+ tires)

2.) This brake system is for a race car

...& will be controlling larger/taller tires

So, I'm thinking about using (3) of the larger 8" rotors (like used on the rear) in the front & rear (which should increase the stopping power)

...but, the smaller 5" rotors, have a 6-bolt pattern

...& the larger 8" rotors, have an 8 bolt pattern

Further explanation:

For comparison, here is an 8" rim/~16" wheel

...with an 8" rotor (sitting on it)

...& then, a 5" rotor (sitting on top)

This comparison makes it easy to see that

...the ~16" wheel would have a bit more than a ~3:1 leverage advantage, over the 5" rotor

...whereas the ~16" wheel would only have ~2:1 advantage over the 8" rotor

So, using 8" rotors (being more proportionately sized to control a ~16" wheel)

...plus, a Hydraulic system

...& (3) wheel braking

...& should provide this racer with better/superior stopping power 

The wheels that I'm going to try, on this racer, are normally used on golf carts.

They are 8" steel rims that are 3.75" wide & have 4.80 x 4.00 x 8 Diamond Pattern Turf Tread tires

They are brand new "take offs" (meaning that the golf cart buyer wanted fancy wheels/tires installed)

I found a set of (4) of them on eBay for ~$75.00 & that's
...~$18.75 per wheel
...or ~$9.38 per rim
...& ~$9.38 per tire

* These are probably not the best tires for racing
...but, we have endless options available for 8" rims (when we get to that point)
...& for ~$9.00 ea. they are perfect for initial testing

FYI: these steel wheels weigh ~8lbs. (ea.) w/tires
...as opposed to ~3lbs. (ea.) w/wheels, that the plastic bicycle wheels on Polaris weigh

So, this "upgrade" comes with a ~15lb. "weight penalty"
...but also, has a (4th) wheel
...so we have a spare tire, that's all ready to go

For comparison, here is (1) of the (~16") golf cart wheels next to (1) of Polaris's (~20") wheels

* Notice the golf cart wheel is only a few inches shorter, than the bicycle wheel

...but, has almost double the width 

Plus = better traction

Minus = higher rolling resistance

You wrote

"* Notice the golf cart wheel is only a few inches shorter, than the bicycle wheel

...but, has almost double the width 

Plus = better traction

Minus = higher rolling resistance

I do not think this is correct. Oddly, wider tires seem to have less rolling resistance. It has been discussed before in the tires section and there is some good test data comparing wider and skinner bicycle tires on the Internet. Here is what I posted:

The wider tire having lower rolling resistance is counter intuitive but it makes sense to me. Most rolling resistance comes from the tire deforming to create the contact patch-going from a round tire to a flat spot on the road. The more the rubber has to move, the greater the energy loss. This is why a larger diameter tire should have less rolling resistance than a smaller diameter tire. The greater arc of the larger diameter tire is closer to the flat line of the road and changes less.

The wider vs. thinner tire is due to the shape of the contact patch and geometry. The skinny tire contact patch is long and thin while the wider tire contact patch is short and fat. If everything else is equal, than the rubber in the center of the arc of the skinny tire has to move further than the rubber in the middle of the wider tire.

The key, of course, is 'if everything else is equal'. Different tire construction such as thicker rubber or inability to run higher pressures are going to weigh in too. We get our lowest rolling resistance just before the tire wears through. This makes sense since the rubber is very thin and it takes less energy to deform it. Not ideal for finishing the race though.

I'm going to need a couple of dual flange hubs, to mount the wheels & brake rotors, on to the spindles

It's basically, just a piece of 1 1/2" OD steel tube

...that rides on a couple of #99502 bearings

...& has a couple of bolting flanges welded on (like this)

But, for this application we need custom bolting flanges, on each side

...an (8) bolt flange on (1) side to mount the rotor

...& a (4) bolt flange on the other side, for the (4) lug wheels

For fitment & measurement purposes, I made up a mock hub, out of wood & steel

Installed a couple of bearings, for mounting on a spindle

Then, drilled holes

...mounted a rotor

...& also, bolts for mounting the wheel

*The thickness of the wooden flanges isn't important

...the measurement from outer flange face to outer flange face, is the measurement that we need 

Here is a look, at the back side of the "mock" hub, mounted on the spindle

Now, we can use the "mock" hub, on a spindle w/Rotor, to start working on a Caliper bracket

Back to the CAD (Cardboard Aided Design) 

Added a Caliper, to the CAD bracket, to check fitment & clearance

Then, double checked fitment & clearance, from multiple angles

...& with a wheel

It looks like a bent "tab" (kinda like this) could used to bolt the Caliper bracket, to the arm on the spindle

This would securely attach the caliper bracket to the spindle

...& also, "act" as a "stop"

...so, the bracket can't "travel" around the spindle (especially when braking)

Next up, Caliper bracket CAD (template) to steel (~10g) 

Making (2) at once, helps to make them match 

To cut out the (2) 1/2 circles, I first installed a notch, right in the middle

I put the (2) caliper brackets, end to end

...aligned the (2) "notches"

...clamped them down to a 1/4" steel, backer plate

...& then, used the (2) "notches" as a "guide" to drill a 1/8" pilot hole (in between the (2) caliper brackets & thru the backer plate too)

Then, drilled the 1/8" pilot hole, out to 1/4" (for use as a hole saw guide)

Then, used a 1 3/4" hole saw to, cut the (2) 1/2 hole(s)

Used a 5/8" drill bit to install the spindle hole

Now we have a couple of "rough" Caliper bracket(s)

...that "fit" on a 5/8" Spindle 

Hey Babbydeers,

I have the lower section of roll bar supports installed

...but, winter has put progress on hold, for a bit

This is my work bench

...& our current temp is ~15* 

...but yes, when I get back at it, the roll bar support bars will come just about to the top (see drawing) 

Here is a rear view, of a whole front wheel unit

Caliper mounted on the bracket

...bracket mounted on the spindle

...with the hub, rotor & wheel

Side view, double checking clearance

It looks like each unit requires ~8" (from the outer edge of the wheel to spindle bracket)

Custom dual flange front wheel hub drawing

The huge frontal area was driving folks nuts!

...just the windshield area was ~15"w x ~32"t

Thinkin' about it a bit more

...just a helmet & a couple of roll bars should dramatically reduce the aerial drag

So, she's goin' topless 

Something like this should be rule compliant

...but, I don't totally "love" it 

DIY A-frames

DIY bushings

DIY CO shock & spindle mounting brackets

DIY front suspension

Still not totally loving the roll bars

Re-calculating...re-calculating...

So, let's try something different

Maybe something like this

Another view

This version passed this helmet clearance test pretty well 

...but, it didn't seem to pass this clearance test

Here is a video with some info on an F1 Halo 

How The Halo Works | F1 TV Tech Talk | Crypto.com - YouTube

Version 2

Raised the windshield "line" ~1"

...& added a taller rear roll "hoop" 

A couple of buddies brought to my attention

1.) The fact that the way the front Halo support, was attached to the center of the dash bar, that there was a potential for the dash bar to buckle.

Which could cause the steering wheel & column to collapse
...potentially injuring &/or pinning the driver in the ****pit, "if" the vehicle ever rolled over or flipped. Not good 

2.) A center windshield support could/would be irritating to try-n-look around &/or thru for an hour

Plan B: Let's try some A-Pillars

Another angle/view

Notice how this concept would transfer the "load" or force (in a roll over) down to the upper side frame rails

...& also/then, down to the lower frame rails (lower supports to be added)

&

How the dash bar & steering are now totally separate from the "load path" 

The kool blue seat is from BMI karts (~$80.00)

Polyethene (not fiberglass) racing seats are a durable seat made of almost indestructible plastic perfect for racing go karts.

Racing Polyethene (Plastic) Sprint Seat | 660220 | BMI Karts And Parts

I made the rear seat mounting bars out of some 1/2" steel tube

I used a hydraulic press & a DIY forming die

After pressing, the end of the tube looks like this

After pressing (side view)

Made another, added some 1/4" holes & then, did some rounding & shaping 

mm

Here is a drawing of the rear swing arm that I have in mind

The axle/spindle will be "open ended", to facilitate easy tire changes, without having to "mess with" the sprocket/chain & brake system 

The axle/spindle will simply be a 5/8" x 7" bolt

...mounted thru/with a dual wall design 

...& the inner wall will double as the rear caliper bracket

Kinda like this (upper illustration shows the front spindle & the lower show the rear dual wall concept

Swing arm parts

After welding

The other side

Here is the other half of the rear swing arm

A "spacer" helps to space them apart & keep them parallel

...then, made sure everything was good-n-square (before welding)

Also, added a bushing holder

...made up a DIY bushing (a piece of 1/2" ID. reinforced rubber hose with a 1/2" OD. steel insert, for use with a 3/8" bolt) 

...& a mounting bracket 

To facilitate rear wheel "track" adjustment (if necessary)

I made the swing arm mounting bracket adjustable

This way shims/washers can be inserted in between the (2) brackets

...in the appropriate place

...which will affect/adjust the angle of the rear wheel 

Lets get back to the roll bar or hoop 

...& according to the rule book

4 ROLL BAR
1. The roll bar must protect the driver's head/helmet in the event of a roll-over. It must be tall and wide enough to do this considering the full range of possible movement.
2. The roll bar structure must be triangulated with at least three legs or panel equivalent. Triangulated bracing can be either forward or rearward. With three legs bracing must extend from the top of the roll bar and securely attach to the vehicle structure, with four legs, each of the braces must extend to within 4" of the top. Any roll bar that is constructed from more than one continuous piece must be reinforced and braced triangularly from all junctions/joints in addition to the top.
3. The roll bar structure must appear to be sturdy enough to withstand the vehicle being dropped, upside down, from an altitude of one foot, with the driver inside without failure.
4. The drivers helmet must be below a straight line drawn from the top of the roll bar to the top of the highest
structural point when the driver is securely belted in driving position.
P A G E 6. E L E C T R A T H O N A M E R I C A

Before

After extending the rear

...& adding a "leg" or brace

 T

Another view

I also, added a 4" x 8" gusset

...across the 5-way junction for additional strength

...& to "lock' everything together 

It looks to me like it will meet:

3. The roll bar structure must appear to be sturdy enough to withstand the vehicle being dropped, upside down, from an altitude of one foot, with the driver inside without failure.

What do you'all think? 

Hey Archer,
Thanks!

I installed a coil-over shock, in between the chassis & swing arm

Another view

A buddy of mine, used my drawing to make some custom wheel hubs (for use with Chinesium brakes/rotors & standard golf cart wheels) 

My "mock up" rear hub is on the left

Looks pretty professional

The rotors weren't "true"

...so, he "trued" them up a bit

...& included a "proximity pin" to ensure "if" taken apart it can only be re-installed (1) way 

Here is the hub mounted on the swing arm

Caliper mounted

Clearance seems to be OK

On this racer, I'm going to try a Boma BM-1024GD

It's 60VDC

...2,000W (brushless) motor (max RPM rating of ~5,600)

* The motor has a 10 tooth (drive) sprocket

...& the wheel has a 48 tooth (driven) sprocket

...which gives a 4.8:1 gear ratio

&

The 16" wheels that we are using, have a circumference of ~51"

So, let's say the motor has a "loaded" speed of ~5,000 RPM's

...& we are running a Gear Ratio of 4.8:1

...& the tires are ~51" in circumference 

Let's "do the math" 

Ballpark Equation
MS/GR=ASxTC=IM/FT=FMxHR=FHxMM= MPH

Motor Speed/Gear Ratio=Axle Speed x Tire Circumference = Inches per Minute traveled/Foot (12) = Feet per Minute traveled x Hour (60) = Feet per Hour traveled x MPH Multiplier (.000189) = Miles Per Hour

5,000(RPM's) / 4.8(GR) = 1,041.67 (axle speed)
1,041.67 x 51 = 53,125.17 (inches per min traveled)
53,125.17 / 12 = 4,427.10 (feet per min traveled)
4,427.10 x 60 = 265,626 (feet per hour traveled)
265,626 x .000189 = 50.20 MPH 

Keep in mind that the Ballpark Equation doesn't factor in things like: rolling resistance, Aerodynamics, overall weight etc.
...it just gives us an idea of what "may be" possible with a specific set up (motor RPM's, gear ratio, wheel size etc.)

I used a straight edge to align the motor & wheel sprockets

...marked where the motor needs to go

...then, installed (4) 5/16" x 1" slots in the motor mount

I used (4) 5/16" x 1" Carriage bolts to mount the motor 

* Notice how the "square" under the heads "fit in" the slots

...so, the motor can be tightened down with just (1) wrench

I used the straight edge again to double check sprocket /chain alignment

...Another view (straight "down the line") 

* Notice (after alignment) I used a couple of pairs of Vise-grips, to "lock the motor mounting plate "in place" for welding

A view with the chain installed

Master cylinder & bracket 

Brake master cylinder linkage

Master cylinder mounted to the bracket

...bracket mounted to the chassis

...& the linkage connected too

Another view 

I've seen F1 race cars that have switches & stuff on the steering wheels

...so, I was thinking maybe something like this 

Let's start off making the steering wheel itself

...using a 1/8" x 6 1/2" x 13" piece of Aluminum (from old sign)

Drilled some big 'ol holes

Added a couple of bends

Cut out the middle section(s) for hand grips

Did some trimming

...& even a bit of polishing (left side)

* Notice the "fancy" steering wheel mount?

To make the on steering wheel "instrument holder" for the gauges & switches, I harvested some ridged plastic from the back of an old TV

Cut out a piece & started marking for the cut-outs

Kinda like this

After adding some "hand grips"

...& polishing it up a bit 

* The upper section houses the power meter & the control switches (On/Off, Forward/Reverse & 3-Speed selector)

...& the bottom area is for the speed-o-meter (cell phone w/speed-o-meter app)

Here is the steering wheel, installed 

Another view

* Notice, to ease entry & exit, I included a "flip up" feature