SPA Design Formula Mirrors

TL;DR "High impact nylon", they sure can take a beating

You already know them as they are the de-facto standard upgrade for the Caterham.

From factory, KLY mirrors are fitted to the sidescreens (in EU that is), or modified and attached to the windscreen stanchions for IVA compliance in the UK. Those are just alright, not the best looking, but they do the job and keep their setting once tightened enough.

A common gripe people have with those is the blurry vision they provide because of vibrations. My experience was no different. So I let the hype get the best of me and got a pair of "SPA" mirrors like everyone else.

My provider of choice for that kind of motorsport-y stuff is Demon Tweeks. A pair of convex mirrors in black nylon did cost me 106 €. You can also get them in white, and the cheapest option have a flat mirror. There is also a very unreasonably-priced carbon fiber version (300€+ a piece), that I have seen in person on a car, and they age very poorly. They really looked sad and tired after a few years.

Getting deep into the history and specifications in search of dimensions of the base plates, I read that SPA Technique is an American company, and the naming of the mirrors product line is not consistent as it's both called SPA Design, and SPA Technique. Anyway, since 2024 Spa Design has been taken over by Lifeline, we know them for their fire suppression systems and steering wheel quick release fitted at the factory by Caterham.

Anyway, mirror dimensions (113x52mm), hole diameter (6mm) and spacing (38mm) were provided on the Demon Tweeks product page.

The most common way of attaching them to a Caterham (for people in forums and Facebook groups), is the "Eccles" mounting kit. It basically replaces the lower hinge of the side screens with a 3D printed (or now CNC'd aluminium) bracket to which the mirror base is attached. It does not seem very convenient, and would probably scratch the plastic window's surface. As "Eccles" has since discontinued production, he kindly provided the file for everyone to print themselves. You will find a lot more, including the 3D models on this Caterham Diaries blog post.

Instead, I decided to design an interface plate that would replicate the "KLY" mirrors base and have the "SPA" attach to that.

As I hadn't got my car back yet at the time, I asked House of Speed to lend me a mirror, and we went on and get a brand new one from their inventory. Not overthinking it, I just scanned the base on a flatbed scanner, with poor results. The next scan was more successful as I placed the mirror base on quad paper in which I traced (and cut) the shape with a scalpel. That scan was transformed to a vector format using the first random online tool I could find, and finally imported in Tinkercad. That's an education tool for kids more than a proper CAD package but I don't care, I've been using it for over 8 years and I like it.

With that scanned shape available as reference, I was able to recreate a clean shape using combinations of basic rectangles and circles. As the original cast aluminium base is hollow, I hollowed my design as well, just by 1mm, leaving just 1mm of contact surface on the perimeter.

A first prototype was printed but was 1mm too short. That one didn't even have any mounting for the new mirrors.

Second one used the "Eccles" file as a reference for the shape of the SPA mirror base, that I also recreated. I chose to use the rather long fasteners provided with he new mirrors and made the small base protrude quite a bit from the long KLY shape. That prototype was printed for each side, and used for 2 weeks. The shape I copied from the Eccles was rather wide and didn't match the SPA base close enough for me. On the driver side, the mirror did interfere with the windshield wiper when the door was fully open. It was all good on the passenger side.

A third prototype was a bit thinner overall (7mm), also allowing the original screws to sit 1mm inside rather than having the head flush, and had the SPA base mounted without any protrusion. This was allowed by sourcing M5 screws with 6mm threads and using 6mm heat set inserts. It did improve the position of the driver mirror resting on the wiper arm.

Finally, a fourth model was whipped up, now centering the small base on the long plate rather than sticking to the 20mm offset from the front I chose initially. As I was confident the mirror wouldn't mess with the wiper anymore, I did print a pair of those during the night, and installed them first thing in the morning before going to that morning's "Static Rally", my first of the year with the Caterham. This time I set the rusty original screws and oxidated nylstop nuts aside (to be stored with the KLY) and used the stainless steel fasteners provided with the new mirrors to attach my adapter plates to the sidescreens. 

It's only now that I realize that I could have saved the hassle of removing the supports from the print had I printed v3 and v4 face down on the print bed, with no supports at all.

⚖️ What about weight ? We're talking 125g for a SPA Design Formula mirror on its base, compared with 355g for an OEM KLY mirror. Once again removing 500g from the car, or 65% from the mirrors.

🫨 What about vibrations ? I'm the first surprised that it changes anything at all. But it does. From why I can guess, combining an aerodynamic shape with minimal weight makes a huge difference. Maybe the convex mirrors help a bit too. That's objectively really good now.

💥 What's my deal with "high impact nylon, they can take a beating" ? When I first fitted them in a hurry on a Sunday morning before a blat with 6 other Sevens, I didn't tighten the ball joint screw enough, and the driver side ended hanging down. Which in itself is alright. But by the end of the day, the back and forth motion of the mirror shell on its arm untightened the screw that keep the mirror attached. It fell on the road just as we were reaching our village, at 60 km/h, bouncing on the center line like a rubber bouncing ball (🎬see video below). Never undefeated, I drove back and we found the mirror intact on the ground, with only minor scratches on the shell. Driving by, I also spotted the screw !  So I drove back once again, and got the screw back as well. I didn't push my luck for the washer. I just thought that if I was in charge of their manufacturing, that washer would be identical to the ones they provide in the kit to attach the base - and it was. I polished the visible scratches on the top of the shell (and managed to get them out with minimal effort), and got the mirror back in position.

In the end, I adjusted the mirrors to my liking, removed them from the car and tightened the ball joint for good. After what I removed the mirrors from their arms and got a rubber o-ring on the end of each arm, as well as below the top washers. The screws also got a drop of Loctite thread locker for good measure.

⁉️ What's my deal with using emojis as bullet points like I'm ChatGPT ? Come on, they're fine.

EDIT : all fixings were since replaced by black ones, also made of stainless steel