Skateboard Wheels on a Gravity Racer?

Well, this is the first post on the blog and it’s funny that its content represents a real turnaround in the design of my first gravity racer. Unfortunately, budget is low, and if my first car is ever going to turn a wheel in anger I really need to start thinking about the cheapest possible solution. As with F1, necessity is the mother of invention, and having practically zero budget has meant some serious thinking.

With my first design, the LGR001, a lot of the cost was going to come from the expensive Sturmey Archer drum brake hubs (about £70 each), and that’s before each has been laced onto rims with pukka slick tyres. With thought, it has become clear that that kind of build just isn’t going to happen for the foreseeable, especially as I haven’t had much luck rustling up a sponsor/driver. So, cheap is king, and I’ll be driving it myself. As the design for this car (the LGR002) progresses I’ll add the spec to its own page HERE.

Anyway, the expensive wheels were part of the main problem, so a cheaper solution that still has the possibility to go fast needed to be found. In short – skateboard wheels – or more specifically, longboard wheels – a larger variant.

Longboard skateboard wheels on a gravity racer
Longboard wheels are typically in the 70mm diameter x 50mm wide range, and take 22mm x 7mm bearings, with an 8mm axle hole.

Here’s my current thinking:

Positives:

  • Street luge riders have reached 100mph+ speeds using these wheels, so the speed is there.
  • Longboard wheels and bearings can be had from £15 a set, brand new – extremely cheap compared to other solutions.
  • Simple 8mm axle and nut arrangement to hold them on.
  • These wheels are small, so have minimal aerodynamic effect, allowing for a car with small frontal area and totally enclosed bodywork.
  • Wheels can be swapped easily, allowing adjustment of chassis balance by having different hardness/size wheels front and rear.

Negatives:

  • No easy way to have brakes other than a scrub arrangement on the wheel or road surface.
  • Potentially quite a hard ride, although softer wheels will help on rougher terrain.
  • The contact patch of the wheel is short (maybe 3mm front to back) and then the full width of the wheel. This means that any aspect of the steering geometry that isn’t “flat” (all four wheels flat on the same plane) will mean a drastic loss of grip on one wheel. At the same time, a flat/square steering geo could mean a skittish steering action.

With the steering issue in mind, I opened a thread on my favourite F1 technical forum (read it here) about building in some geo-based self centering on the steering action. I also got to work in TinkerCAD, drawing up the steering parts, with a mind to getting a friend to make the stub axle bit that holds the steering bearings.

Pic1

As you can see from the drawing, the frame will be just 25mm mild steel box section, and I needed a way to easily fix the steering components onto it with minimal fabrication, as I only have a grinder, hand drill and welder. The odd shaped part that you can see in the drawing will hold the axle (an 8mm bolt) and also the two kingpin bearings. This will be connected the the chassis with two sections of steel bar (maybe 20mm x 3mm) and a couple of bolts. A mate with a milling machine is looking at making the fancy bit for me, so I’ll know more when he comes back to me. More to come!

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4 thoughts on “Skateboard Wheels on a Gravity Racer?

  1. Hi James just been having a read through the blog.
    Have a look a documentary called the signal hill speed run of you haven’t seen it all ready it’s available on red bull tv and has some great videos off skate cars and the problems they had stopping them.
    The problem skateboard wheels is the a soft wheel although good for traction they can flair up at speed on luges and with weight of a car this maybe more promenant ( source doctor danger)
    Noticed you work in Harrogate … I have a crappy pillar drill at my work in Pannal your more than welcome to Bob in and use it

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    1. Hiya Will – thanks for the comment!

      I watched this last night and it was quite humbling to be honest. Here’s me talking this and that, and there are the boys and girls who did it and have the scars to prove it. Still, the fact that they never really worked out how to add brakes to skate wheels, and that they still used lean-steering was heartening as there are defo areas that can be improved on their initial designs.

      Awesome film though – thanks for the heads up! 🙂

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      1. Have you considered building a simple street luge to get a feel for the skateboard wheels. I’ve been toying with idea for a while they look fairly straightforward to build from wood and may help as a test bed for wheel and axle/steering setups.

        I’ve been looking at small wheel options to replace the kart wheels I run and think mountainboard wheels have great potential they are cheap made from nylon and have holes that could be used to mount a custom disc carrier

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  2. Since the beginning I’ve always wanted something with a steering wheel that drives essentially like a “racing car” as that’s what I would be doing if i had the money 🙂 Although, after watching the film and having a think, I reckon I’m ruling out any sort of super streamlined shape for my first build. I know this will limit my speed, but I’m looking to learn as i go, and as Andy Ash has said – the speeds that fast Donnie and the rest are doing is bloody scary!! So I reckon a more upright driving position with a kart style seat is the way forwards for my first build. Already got the wheels and steering wheel coming this week, and a design for the brakes in mind – new blog to come!

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