Final Build & Race

Well, the race has been and gone.

(Scroll down for final build pics, video and blurb!)

Unfortunately, I only managed one run, but it certainly could have been a lot worse… As I thought, the brakes didnt have a lot of power but that wasn’t a massive problem in and of itself. At the finish line i got out and had a look at the back and and the brake blocks were worn right down. No problem I thought – I have plenty spares, so just bolt a new set on and away we go. However, on the way back up the hill (being towed) something jammed on the rear right wheel and it stopped turning. As i was being towed I couldn’t stop, and the wheel and brake disc were worn right down leaving a massive flat spot on the wheel and disc. As I had no spare wheels and more importantly no extra brake discs, my day was done.

I was gutted, but in the end the car did prove a lot of people wrong, and a lot of my theories right, if only marginally…

  • The urethane wheels DID grip. I was taking it steady on my run, but I could feel that there was more in the tank.
  • The bearings in the wheels didn’t collapse, wear out or explode… People knew they would be spinning very fast due to the small wheel size, but they held up fine.
  • Sure, they weren’t super fast wheels, but i also think they perhaps weren’t as slow as some thought they might be! My time was 2min taking it fairly steady. Looking at other’s first runs, I was behind many, but certainly not the slowest on the day.

Ultimately though, one way or another, the braking force required at speed was just putting too much energy into discs and blocks that were too small to take the force and dissipate the heat. The discs were smoking at the end, and to be fair the amount of stopping power available didn’t inspire much confidence, with a very strong leg required to have much effect at all. Ultimately, when pushing, I also think that the amount of grip available (while not that bad) would not have been up to the levels of the tyres used by others. That’s an aside, but I think it’s worth admitting 🙂

Having said all that, regardless of relative success or otherwise at Harewood, the wheels were always going to be replaced anyway. I knew they would have a chance on the smooth track there, but many tracks are nowhere near as smooth – I’m already on with the search for better wheels and brakes, as you might imagine…

Other plus points were the chassis, seating position and steering – all worked really well and I’m super pleased with the results there. Of course, I will be able to keep most of the car as it is too so it’s not like I’m going to have to start from scratch. The journey continues I guess!

The event itself was fantastic and very well organised, and it was awesome to party the night before. I’ve never seen people have so much fun in an empty room with a few beers and a small karaoke machine with no songs on it… There were some great cars and it was incredibly interesting to look at all the different engineering solutions to what is essentially the same problem – going downhill fast… I met some truly great people too. Gravity racers are certainly a different bunch.

Finally, I’d like to apologise to anyone that cares for fucking off home early. After we’d chucked everything in the van my teammate and driver said he’d quite like to get off seeing as we were out as he had some stuff he could be doing at home. As I was mightily pissed off and feeling like a right dickhead I didn’t really argue, so away we slunk. Sorry guys.

Final Build

Now you know what happened, I’ll go through the final stages of the build. You can read the last part HERE to see how we got this far, or start at the beginning by reading from HERE. As I had to really ramp up the effort at this point to get the car finished, this is by far the longest of the blog articles so far…

Brake Discs

First up were the brake discs. These were to be essentially bolted to the inside face of the wheel to act as a durable braking surface. Mental, I know.

The brake discs were marked out and drilled to take the countersunk stainless bolts that would hold them to the wheel. Andy Ash kindly machined a small groove around the mid point as you can see, and this helped me get them perfectly in line. I printed some stickers at work with the holes marked out, applied them to the disc and then marked the points with a centrepunch before drilling.
Once the holes were drilled they needed to be countersunk. I did this with a larger drill bit and this was a tough stage. I went really steady so as not to go too deep – I wanted the bolt heads to be really flush to provide a smooth a braking surface as possible.
Once the discs were completed they were stuck to the wheel with double sided tape and then drilled through into the wheel. This was a make or break bit, and a full bottle of San Miguel was needed before I dare do it… Anyway, I managed….
Disc fully bolted in position. I went on to grind the tops even more smooth, and filled in the hex holes with superglue.

Front Steering

The front steering bits were almost done in the last blog, but I’d forgotten to weld on the steering arms… This meant I had to remove the bearings which to be quite honest I thought would be nigh on impossible as they took so much force to press in. However, Andy Ash said “just tap them out with a hammer” and whaddya know – out they came.

I drilled some holes in a bit of ply to give a secure base for the piece while I twatted it. Tap tap tap, turn and tap some more – eventually they came out. The whole process gave me some confidence in the strength of these bearings – I was ever more hopeful that they wouldn’t collapse when I went round a corner….

Next up the steering arms were made from 3mm steel bar. I drilled a hole in one end to take the rose joint, and shaped the other end so that I could weld it to the bearing carrier more neatly.

Using a flap disc and grinder to shape the end of the piece.
Close enough for rock ‘n’ roll!

No I had to calculate the Ackermann angle (it worked out at 16 degrees) and weld both steering arms on in some kind of accurate fashion. I made up a jig to hold the pieces in place, and fired up the TIG.

Holding the parts tight in position.
Measuring the angle with the digital angle finder.
All welded in place, nice and straight, too!
And…. the angles are both exactly the same! Noone more surprised than me…

Brake Mechanism

Now the discs were on the wheel, I could put the wheels on the back axle and think about the mechanism. This was essentially a bit more inch box with a bolt pivot and a brake block bolted to one end. Nylon washers kept it relatively smooth. Hey look, I took a video of the initial fit up:

With that almost sorted I needed to move onto the frame. I wouldn’t know exactly how to link up the brakes until the axle was mounted in the finished (ish) frame, so I left the brakes for now and moved on.

Finishing The Frame

Up to now, I had two large rectangles so I needed to join them together. I essentially welded in some uprights on all 4 corners.

Uprights measured, cut and ends angled. All in place to check the fit. I probably set it up on the ground and sat in it too, to check if I fit in it. I didn’t make engine noises, honest.
Welded and hauled outside for a look in the sunshine. Another tank of Argon down…

Next was the construction of the cross member that would form the “dashboard” – basically the past that would hold the business end of the steering wheel. I did this with a length of box section and some pie cut/bend shenanigans.

All measure up and the slices put in with the grinder and slitting disc. masking tape is brilliant for helping you to see what you;re doing.
Bent and welded up. I did use a jig and the angle finder to make sure it was the same at both sides. Standard.
The crossmember held in place to check for fit. Initially, it didn’t leave enough room for my legs to get past the steering wheel so I had to weld on a couple of short uprights to give more space. Ah well.
Welded in place, plus some additional sections to join the top and bottom chassis rectangles. At this point I tried a kart seat for fit. It did go in, but when I leant it back to give the position I wanted my knees were right up in the air. Save it for another day I think.


Next onto the steering column. The cross member at the top already had the bolt holes drilled for the pillow block bearing (20mm ID) so I could easily put this one in place.

Pillow block bearings in place, with steering column slotted in. 20mm tube doesn’t easily fit into a 20mm bearing as there was no clearance, so I spent ages shaving a bit off the tube with the flap dics. I love my grinder…
Bottom anchor section welded in. I needed to add a piece rather than using the front chassis member so that both bearings would be parallel. As you can see, the bottom piece is angled to suit.
next to make was the bell crank (I think that’s what it’s called?) This was made from 5mm bar, marked out and cut to shape with holes drilled to allow track rod fixing. The 20mm hole to allow slotting onto the steering column was quite tricky to drill.
Bell crank ready to fit. As you can see, the track rod ends go on quite nicely.
A quick note – at this point I managed to find some 90mm wheels, I couldn’t use them on the back as the discs had already been made to fit the 70mm wheels (and they wouldn’t have worked with the new wheels anyway) but they gave me a precious 10mm additional ground clearance at the front. They were softer too, so would help with grip on the likely unweighted front end.
The bellcrank welded onto the steering column.
Threaded inserts welded into the ends of the steering rods. of course, these were checked for length before doing this….
The steering system all bolted in place. All looking great so far – smooth action and good lock to lock range. Geared about 2:1 which is marginal, but the best I could manage really.

And hey look, a video!

The front end steering setup complete.

Back to the Brakes

Now I went back to the brakes and looked at how I could hook them up. The upright levers on each back wheel needed to be linked together with a cable, which would be anchored at one of the sides. When the cable was pulled, this would pull the tops of the uprights together, forcing the pads onto the discs. Most of this gap was made up with a piece of half inch bar, cut away at one end and with a flap folded over, welded and drilled to make a cable anchor.

One end of the brake bar. This will anchor the cable.
The other end of the brake bar, connected to the braking lever.

I didn’t get any more good pics at this point, but chose to move onto making the seat anyway. I knew the seat would need to be in place so the seating position was final. This would mean I could see where I had room to run the brake cable, and also where to position the brake pedal…. Which I had yet to make.


I stared blankly at the gap where a seat would be and realised that I had no idea how to make something that would a) fit, b) be comfortable, and c) wouldn’t look shit. I messed about with bits of plywood with the idea of sticking foam to it, but wasn’t really happy with anything I could come up with. Just not good enough. The next day I went to the tip and happened to see an old office chair and I thought “AHAAA”, dragged it out of the skip and bundled it in the back of the car. Once back in the workshop I took it to pieces and was left with a nice seat base and back, all ready with bolt mounting points. Lovely job.

The seat in rough position. I had to make up some small pieces and weld them to the chassis so I could bolt the seat in. You can see the ones for the base here.
Upright sections welded in to allow fixing of the seat back. All adds strength to the chassis, too, although i don’t really have any proper triangulation like I should have…
Seat back support bar welded in too. Look at my Argon bottle – it’s probably nearly empty (again)…

Finishing the Brakes

Now the car was nearing completion and it was a case of fabricating a brake pedal and plumbing everything in. I was desperately running out of time at this point so didn’t take as many photos as I should have, but there you go.

So the plan was to weld in another full chassis cross member to mount the brake pedal on. To this, I welded a small section from which to mount the pedal. Like the rear brakes, this was done with an 8mm bolt and nylon washers to keep it all smooth. I welded some 20mm tube to the top of the pedal. Looks a bit kart, doesn’t it?
A better shot of the pedal. You can see the cable attaching at the top. I used bike pinch bolts for this, with additional holes to allow the cable to run through the box section. This was because if I installed the pinch bolt the other way round, I wouldn’t be able to get a spanner on the bolt inside the top of the box section.
So there’s the cable on the frame. Now we need a cable anchor.
Cable plumbed through the seat and connected up at the back end. Ignore the black pipe coming off the Argon tank making my photo confusing. There’s only one cable…
Rear brakes connected up – a sexy closeup.
A quick trip to the shop for some beefier return springs…. Green cable ties to match the wheels as well. That’s how Benetton would have done it.
Cable anchor mounted on the chassis a few inches from the front pedal. One of my nicer TIG welds as well.

Bodywork and Graphics

At this point it was literally the day before I would need to set off for the race, so photos are slim on the ground as you can imagine. The body panels were made from 3mm aluminium composite (commonly called Dibond), and the “bonnet” section was made from 1mm PVC as it needed to bend to fit the contours of the steering column crossmember. The graphics are cut or printed vinyl, courtesy of my employer Ad Bell in Harrogate. And yes, it’s meant to be a replica of a late 80s, early 90s Benetton F1 car.

The sponsor logos ready to go on, along with a photo of the car to use as a rough placement guide.
Green vinyl being laid up and rough cut to size before application.
All done. it’s midnight at this point, and we’re setting off in the morning. Phew!




2 thoughts on “Final Build & Race

  1. Hi James,

    Great to meet you at the weekend.. even enjoyed your Karaoke !!!!

    You certainly did well especially considering it was your first time down a hill and Harewood is no easy course!

    As with all Gravity Racers you will have learnt a lot and will no doubt improve things ready for next years racing.

    In Canada mode now ! Lets hope we get some more World Records!

    All the best,

    Team Red Eye
    Bodrodz UK

    Liked by 1 person

  2. James, this is an excellent build blog, thank you for putting it together. I will reference it to new builders for ideas and guidance. I’m happy to hear that your design and wheels worked. Keep on innovating



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