Choosing the wheels

- Early January -

My current favorite choices at this stage are Compomotive CX-Rs and the new Caterham 8 spokes. Neither are a very cheap option. Other than that, I'm open to suggestion. I think I'd like 13" wheels, as that's what Hoopy Poopy says are best. I like the fact that they are likely to be lighter than a larger wheel, cheaper, and they tyres will be cheaper too - the 205/45R16s on the 21 were very expensive for the better tyres.

- February 10 -

IanG has managed to find himself a set of crack tested, sound, Barnby magnesium wheels for 300GBP. Jammy so and so. He looked unconvinced at my decision to use 13's, but without actually explaining why. Thinking about this later, I figure it's because I'm planning to run this race chassis as a road car, so I need all the ground clearance I can get. Perhaps 14's or even 15's would be a better choice.

2nd visit to STM

- Mar 16 -

The Audi calipers are physically larger than the Sierra ones, which may mean that they won't fit under 13" rims very well. As STM have a selection of wheels lying around, Ian said that if when they're investigating fiting the calipers they'll try various wheels on as well, to see what will fit.

Wheels sourced

- June 5 -

This morning, at 6.30, some Barnby magnesium wheels, as used in the Caterham R400 race series last year, fell off a Team Parker Racing truck in Cambridge service station. Luckily I happened to be there to pick them up.

Boy are they light! 3.7kg for the front (13x6.5) and 3.9kg for the rear (13x8.5). Whilst this type of wheel was somewhat notorious during the race series for falling apart, this set have been crack tested, so should be fine. Team Parker have plenty more (the regulation wheel is different this year) so grab 'em whilst you can.

Later in the day, I did a quick search for tyres that might fit the rears. There aren't that many if you're not able to run racing slicks... So, my best bet for continued happiness is to contact Barnby Engineering and get them to supply me a new set of 6.5" rims - the centres and rims just bolt together, so it should be easy to change them over.

Tarting about with the Mags

- June 18 -

I'd managed to borrow a friend's car today, so I took the wheel shod with slick to Kingsway Tyres. They got the slick off for me free of charge, and said they'd be happy to put on the new tyres when I got them, for a fiver each.

I rang George Polley Motorsport, and got some prices for Yokohama A539s and A021Rs. The 539's are a bit harder wearing, and were great in the wet on the 21, and adequately grippy for road use in the dry. The 21's are softer, not quite as good in the wet, but more grippy in the dry. In the end, I decided I'd go with whatever was cheapest. Before I called, I'd settled on 185mm width tyres (as wider ones are more prone to aquaplane), and I wanted as deep a profile as possible, to get the ride height of the car up, and the revs down for motorway cruising. The choice, then was 185/60R13 in both tyres, and 185/70R13 in the 21s.

In the weird world that is tyre pricing (which I think is controlled by the same model as air travel prices, fluid dynamics and female reasoning) the better, bigger tyres, the 70 profile 21s, came out the cheapest at 35GBP a corner

So, having got the tyres I wanted at maximum bargination, I took the Barnby Mag centres off to Morley Brothers in Milton to get them powder coated. Kevin quoted me 12GBP each for blasting and a gloss black coating. He's aware that they're magnesium, and is going to get the blaster people to do it gently. Somehow.

Then I rang Mike Barnby to ask if my hew rims had been dispatched. True to his reputation as being slightly tardy in actually delivering goods they haven't, but he assured me they would go off on Monday...

Then I cleaned up all the rims I have got, including the 8.5"s that I'm selling on.

Finally, to round off a pretty successful day, I looked in Google for a supplier of aero stiff nuts for when I put the wheels back together, and found Allscrews, a company in Slough that seem to stock just about any useful fastener you can shake a stick at. No indication of prices on the somewhat cheesy website, but they're definitely getting a call.

Centres back from Morley Bros

- July 6 -

I picked up the mag wheel centres from Morley Bros today. They've come up lovely (and I guess so they should - his quote went up to total £80 ). The one that was originally already powder-coated had to be stripped by hand apparently, as magnesium reacts with the stripping agent that they'd normally use to remove in-situ powder coating. This process involved pouring a tiny bit of stripper on, and scrubbing it off as soon as broke through the powder. For the entire wheel. Ye-owch. There's a guy someone near Bury St Edmunds (where the stripping was done) who no doubt would like to meet me in a dark alley somewhere for a bit of a word in my shell-like

Rebuilding the wheels

- July 12 -

There's been quite a bit of work getting the wheels back together. First problem was that they didn't fit over the hubs anymore, because there was powder coat on the inside edge of the central hole and on the stud holes. Mr Dreme dealt with the first problem very nicely, and a small round file the latter. Next problem was one that I've heard people whine about, but never really thought anything of until it happened to me: magnesium is a very soft metal, and as you put the wheels on and off the studs, little shards of magnesium get scraped into the stud threads, and act to block the wheel nuts going on. Completely. So, a lesson learned there - I'll remember to carry a little brush around with me if I ever get this car on the road. Oh, and a deep 19mm socket, because the standard 19mm wheel wrench is too fat to fit in the holes that the wheel nuts sit in.

Then a somewhat more fundamental problem. With the nuts done up all the way, there is a gap a little over 6mm between the back face of the wheel and the hub. After considering all sorts of options (different studs, nuts, cutting down all the existing studs and nuts, big fat washers under the nuts etc etc), I've decided that the best thing to do is get a couple of 7mm spacers made up.

Unfortunately nowhere stocks spacers of 7mm depth; 6mm and 8mm are easy to come by though

Fortunately, Jonathan Rarity, aka JB7, a friend from Tour7 has just set up a business Artistic Engineering doing (amongst other things) CNC routing. So he's making me some

Satisfied that the centers all sit on the hubs OK, the next thing to do was to bolt them back into the rims. The two older sets of rims were all ready to go, so 32 capheads, washers and nylocs later, they were done. The new rims were supplied in two halves, inner and outer, and they needed to be siliconed together to make them air-tight. I bought some clear drying silicone in a convenient pressurised container, and put a bead all round the outer edge of each mating surface, so that when they squeeze together, the sealant will tend to squeeze into the rim rather that out and over the centres. This should ensure air-tightness.

Another 32 capheads, washers and nylocs later, the job was done.

Spacers arrive

- July 21 -

The spacers have arrived from JB7, and they fit a treat - just very slightly on the loose side of an interference fit, needing a light tap with a mallet to bed them down. And the wheels fit too. The only problem is that on the off-side, the spacer forces the one of the wheel stubs out to be slightly non parallel. All the spacers do it, so it must be a slight tolerance problem with the hub. What I'll need to do is modify one of the spacers slightly to be a looser fit.

- August 15 -

As I was faffing about in the garage anyway, I spent a bit of time releaving the holes in JB7's offside wheel spacer. The hub has a slight intolerance that means when the spacer slides over the studs it slightly forces them out, which in turn means the wheels won't fit over them anymore. All the spacers gave the same problem, so I picked one of them and made the stud holes a bit bigger with a file.


This page last updated on: Sunday, Jul 16 2006