Monocoque wheels

I've mentioned Bob Britton before, the builder of the Rennmax cars in Sydney...

Britto is a thinker and an innovator, even though he spent an awful lot of time building replicas of Brabham's and Lotus' chassis over the years.

One of his pet hates was always cast alloy wheels. "Anyone can get a pattern made and machine a casting!" he'd tell me from time to time. But for the most part, castings were something he saw as an overweight and difficult part of a car. He'd rather fabricate things.

So, about 1970, he came out with a wheel that he felt had some nice advantages over the castings that everyone else was using. A monocoque wheel, a wheel made up of several spun pieces of aluminium riveted together.



As can (almost) be seen, it was all based on a small cast alloy boss, with an outer section that formed the outer bead of the wheel. Other sections made up the balance of the wheel, with a triangulated formation being derived from these sections that gave it lateral strength.







It was a fairly clever way of doing the job, even if it meant some extremes in tooling for the various spinnings that were required for different wheel widths (they came in 10", 12", 14" and 16" if I'm not mistaken). But they were fragile in the event of a crash... hence there aren't that many around any more.

Later, when building the BN6s (1973 or so) he put his thinking cap on again and came up with another way to do it, but his monocoque wheels always grabbed me... they looked neat and they did the job well.

Edited by Ray Bell, 13 January 2017 - 14:20.

It seems to me Fred Puhn was manufacturing and selling spun aluminum modiular wheels under the "Chassis Engineering" name as early as February, 1967. In March that year he won a feature race at Playas de Tijuana on a set. He suppled many to first-rank racing teams before releasing the concept to a major aftermarket wheelmaker.

One of the selling points was modular repair: a bent "pieplate" could be replaced if the rest of the wheel was serviceable.

Another: changing wheelwidth was as simple as bolting in a different stuffing to the pieplate sandwich.

Fred's name has come up in a Maserati thread or two, and I'd be surprised to learn he doesn't look in here from time to time.

They would have been spun rims on a cast centre though, right?

This is something totally different...

Tony Simmons put out 'composite' wheels in 1966 or so here, the earliest going on his Hustler SC1 when he returned to racing after crashing the U2. But it wasn't a new thing even then... I believe that the concept had been around for a while in Speedway circles.

I am reminded of the "Melmag" wheels of the early seventies. These were formed from spun inner and outer halves, bonded to a honeycomb centre, with a strap in the middle covering the honeycomb, and joining the two spinnings together. They were very light. The trouble was that they had a reputation for returning to component form with explosive force while the tyre was being overinflated to get the bead to pop out.

Yes, the Melmags were very popular for a short time. I recall Frank Matich used them, so they must have been the lightest wheels available in F5000 size circa 1972.

Not all GP teams used them, though...

The American wheelmakers Centerline were making alloy wheels since the late 60's in the fashion you describe Ray - it I understand it correctly - that is, the rim riveted to a machined (non-cast) centre. I had a set on a Torana SS hatchback I owned in the 80's.

I think we do have a misunderstanding... look at the picture...



The only casting is the bit that the fixing bolts go through... just a circle right in the centre, a 'hub' where the wheel studs stick through. The rest is spun aluminium, three or four pieces, all riveted (with epoxy sealant where necessary) together.

In the photo, all you can see that's a casting is the little bit that's visible through the centre hole in the outer spinning.

They are monocoque in the sense that the strength of the wheels is drawn from the formation of the spinnings and the triangulation of the spinnings as they are riveted together.

If I understand you correctly, Nick, the wheels you describe have a polished solid disc that is fixed to spinnings that make up the rim... and the rim alone, the beads and well base.

Britto's wheels had spinnings that go right to the centre of the hub, and nothing thicker than 3mm beyond that cast 'hub' that you can just see in behind the outer spinning.

Edited by Ray Bell, 13 January 2017 - 14:14.

Yeah Ray, I misunderstood the concept - although to be honest, I'm not sure I've got it yet. But then, I have troubles with the workings of a can opener.

I must be failing in my description...

A drawing might help... I'll get details and scan something for you.

Originally posted by Ray Bell
I've mentioned Bob Britton before, the builder of the Rennmax cars in Sydney...

Britto is a thinker and an innovator, even though he spent an awful lot of time building replicas of Brabham's and Lotus' chassis over the years.

One of his pet hates was always cast alloy wheels. "Anyone can get a pattern made and machine a casting!" he'd tell me from time to time. But for the most part, castings were something he saw as an overweight and difficult part of a car. He'd rather fabricate things.

So, about 1970, he came out with a wheel that he felt had some nice advantages over the castings that everyone else was using. A monocoque wheel, a wheel made up of several spun pieces of aluminium riveted together.



As can (almost) be seen, it was all based on a small cast alloy boss, with an outer section that formed the outer bead of the wheel. Other sections made up the balance of the wheel, with a triangulated formation being derived from these sections that gave it lateral strength.

It was a fairly clever way of doing the job, even if it meant some extremes in tooling for the various spinnings that were required for different wheel widths (they came in 10", 12", 14" and 16" if I'm not mistaken). But they were fragile in the event of a crash... hence there aren't that many around any more.

Later, when building the BN6s (1973 or so) he put his thinking cap on again and came up with another way to do it, but his monocoque wheels always grabbed me... they looked neat and they did the job well.

I don't think that was a new idea by that time. While the manufacturer's name escapes me, and I can't locate my 1949 Bell Auto Parts Catalog (Bell Auto Parts was an early speed shop in the late 1940's, catering to the hot rod/dirt track/dry lakes and Bonneville scene) shows a modular wheel similar in concept but not in shapes to that wheel, made from aluminum. These were built for the then very popular midget race cars of the day (those cool little V8-60, Elto, and 91cid Offy oval trackers), but were surpassed by the Halibrand cast magnesium wheels for the very reason you mention (about the rarity of Britton's wheels today)--the turned aluminum wheels just didn't hold up in wheel-banging racing action nearly as well.

Also, isn't "monocoque" somewhat a redundant term for a wheel? Monocoque, as I understand it, is generally meant to describe an aircraft or motor vehicle structure wherein the "skin" of the airplane or an automobile body is actually a stressed member of the construction, as opposed to being merely panels hung on to cover an existing structure, with those surface panels having no further structural purpose? I think the correct terminology here is "modular".

Art Anderson

I will post a diagram soon... but in the meantime, please stop confusing these wheels with anything you might call modular.

They are nothing like them.

Hmm - towards the end of its career in Jack Brabham's ownership his midget speedcar '28' was fitted with cast-alloy centred wheels designed by Ron Tauranac and cast by a great and enthusiastic friend of Jack's, Arthur Gray, at Belshaw's Foundry in the Sydney area. The cast-alloy wheel centres carried bolt-on steel rims. The idea was that rims quite commonly sustained damage while racing on the cinder tracks, and now Jack and his pals could speedily detach a damaged rim and replace it with a fresh one. That way he wouldn't miss a race (aka "earning opportunity").

DCN

Not actualy 'monocoque' wheels but Tony Kitchener of F5000 fame made some Glassfibre wheels for his F5000 cars. They survived on one car through to the mid 80's, winning the French Hillclimb Championship during that period. He exhibited them at an early 70's Racing Car Show in London but couldn't find any buyers! Now why doesn't that surprise me?

Regarding "Frank S"es comments on Fred Puhn's "Chassis Engineering" (CE) wheels.

IIRC they are/were a two-piece wheel, bolted together, not a 3-pce modular. They were spun-aluminum like two kitchen pots, the bases bolted together. Very simple and very light. They had to be taken apart to change tyres (no drop centre) but this allowed a damaged half to be replaced or off-sets and widths altered easily.
I think they were marketed using "Monocoque Wheels" as a brand name.

There are some pix at this site:
http://members.aol.c...vbms/parts.html


The early (1970) Centerlines were also two spun halves like the CE wheels, but were riveted together.
They had a drop centre to allow tyre changes.

The earliest riveted together wheels I can recall were used on Jack Nethercutt's 1965 Mirage Group 7 racer.
They were made of multiple sections, something like Britton's wheels.

Any pictures of Nethercutt's wheels?

I'm despairing here that nobody seems to understand that these wheels aren't like BBS and Simmons and CE and Circle Track and Mawer and Costa and so many others that have been made using spun rim sections over the years.

Britto spun the lot... the wheel comprised the following components:

A 5" diameter cast aluminium centre boss, machined and drilled for fixing and to attach the spinnings.

Three spun sections in spun 3.2mm aluminium... one making up the outer section of the wheel, including the bead, one making up the inner section of the wheel including the bead (with different depths to these spinnings for varying offsets and widths), and one forming the triangulation between the inner and outer sections, being a cone in shape.

A fourth spun section was 16g aluminium which rivetted into the outer section as shown in the photo, with the inner joint using the same rivets as the triangulating cone. This formed the well base.

Must get that diagram done!

Re: Nethercutt Mirage http://www.tamsoldra...kesPhotos1.html
As Frank said, it was a thing of beauty and it has survived- in pieces. A former employee of mine (and of Nethercutt's) claims to have enough of it to rebuild plus various patterns and tooling. He told me he personally built 5 or 10 sets of the "monocoque" wheels.
Anton

Originally posted by antonvrs
Re: Nethercutt Mirage http://www.tamsoldra...kesPhotos1.html
As Frank said, it was a thing of beauty and it has survived- in pieces. A former employee of mine (and of Nethercutt's) claims to have enough of it to rebuild plus various patterns and tooling. He told me he personally built 5 or 10 sets of the "monocoque" wheels.
Anton

Not that I disagree, but that would be Tam, of Tam's Old Racecar Site, who praised the Mirage's looks.

I really would like to see it in the flesh, moducoque wheels and all.

Thanks for the correction, Frank. We've got to keep things straight!
I'll have to look this guy up and find out if he still has all of the pieces, parts, hunks and chunks.
Best regards,
Anton

Looks to me like Nethercutt's wheels were indeed like Britto's... and they're described as monocoque too.

Now how can I draw these things?

Originally posted by Ray Bell
I will post a diagram soon... but in the meantime, please stop confusing these wheels with anything you might call modular.

They are nothing like them.

Ray,

I guess I look at any sort of assembly such as Britton's wheels, wherein they are riveted together, with the intended option of being "de-riveted" for repair or replacement of parts as "modular" in concept.

Even this construction concept wasn't all that unique to Britton. American Racing Wheels in the US, arguably not competion wheels, but rather for the street also used a riveted construction, with the center-section being of cast aluminum, then riveted to a rolled steel rim (chromed for appearance), giving the hot rod crowd the look of a mag wheel with the durability of a steel rim, in addition to a corrosion-resistant center.

Not knocking the Britton wheel, just that it likely was better suited to smaller, lighter cars. If this type of wheel construction had been truly the be-all, end-all of racing wheel design, there wouldn't be anyone producing cast wheels for racing today, it would seem.

Art Anderson

Art... they weren't intended to be dismantled at all...

And their shortcoming was the labour-intensive nature of their manufacture. Britto often finished up putting more of his own time into his bits and pieces... that was his failing, I guess.

Again, I stress this... these wheels were nothing like what's popularly known as 'modular' wheels.

The earliest advert for Chassis Engineering wheels I find is in November, 1966.
There may have been some prior to that, but not in my meager collection of literature.
Gridlines, November 1966

The best wheel picture I could find is a drawing in an advert in the July, 1967 Gridlines

A larger view of the drawing:

Nothing like the Rennmax construction... this design seems to use a solid disc in the middle to stiffen the rim sections. Probably good thinking, and perhaps with some lightening (cutouts, large diameter drilling) of the stiffener it would be very light indeed.

A simple wheel to make, I'd say, but there's one problem with spinnings from which it would certainly have suffered...

When the bead section is made very deep, as is done to give caliper clearance, and also for rim inset width, the metal becomes very thin at the bead. This was one of the issue Britto also sought to address with his.

I'll get hold of some coloured pens today and do a diagram...

The original monocoque wheel was produced starting in 1965 by Chassis Engineering Company, originally of National City, CA and later Santee, CA. It was designed by Fred Puhn, a racing car designer (the Quasar, a SCCA D Sports racer) and author (How to Make Your Car Handle, 1981, and The Brake Handbook ,1985). Fred's partner at Chassis Engineering was Carter Penley Jr., a fiberglass and carbon fiber specialist, who later went on to form Penley Sports, one of the originators of carbon fiber golf club shafts.

The racing wheel portion of Chassis Engineering was acquired by David Boone in 1976 and renamed Monocoque Wheel Company. Although the original monocoque wheel had been designed for sports racers and formula cars, road racers had actually become a relatively small part of the company's market — drag racers early on discovered the light and strong wheels and became Monocoque Wheel's biggest customer base.

The production process for the wheel was pretty interesting:

1) Each half of the wheel was formed from 3/16" sheet T-6061 aluminum spun at relatively low speed on a huge lathe using rollers over a male mandrel consisting of multiple sections which could be added or taken away to produce wheel halves of different depths. A giant torch was used to soften and anneal the aluminum during the spinning process. This process took a lot of skill to avoid thinning the material in the outer bead areas, but properly done, the overall thickness of the aluminum could be maintained within a few thousands. It also took a lot of fortitude: working a 30" diameter spinning hunk of metal in front of a 2 foot flame in the 105F summers of Santee, CA was not for the faint of heart.

2) After spinning, the rim edge was rough trimmed and heat treated to a T6 level.

3) The raw wheel halves where anodized, or occasionally, powder coated.

4) The heat-treated and anodized wheel halves where machined on a precision lathe to true up all of the mating faces. This was a critical part of the process overlooked by some of the cheaper imitations.

5) An aluminum billet spacer was individually machined to match the dimensions of the two halves. Optionally, 1" or 1-1/2" lightening holes where drilled in the half faces between the center hub and the rim bolts.

6) The wheel was bolted together using aircraft grade hardware and the rim bead edges where trimmed true to the center mounting pad area.

7) The center joint crevice was sealed with silicone and an o-ring.

Here's what the classic Monocoque Wheel Company wheel looked like in cross section:



David expanded the business throughout the 70's, 80's and 90's, improving quality and introducing innovations like a 3-piece modular wheel with spun outer rims and a cast or billet center and an extremely light 17" spindle mount front drag racing wheel (under 6 lbs each versus over 7 lbs for competitors products).

Over the last few years Monocoque Wheel Company found it harder and harder to compete against larger firms like Centerline who could afford to make little or nothing on their racing product — essentially operating it as loss-leader marketing for their much bigger street market. David was a racer at heart and never really wanted to produce wheels for the street. David closed Monocoque Wheel Company in 2002.

Good information, Richard... they look like nice practical wheels...

Thanks for going to the trouble.

Originally posted by Frank S
The earliest advert for Chassis Engineering wheels I find is in November, 1966.
There may have been some prior to that, but not in my meager collection of literature.
Gridlines, November 1966

The best wheel picture I could find is a drawing in an advert in the July, 1967 Gridlines

A larger view of the drawing:

Frank,

Interesting exploded drawing! Again, looks just like the 12" rims that were being made for Midgets in the immediate postwar years. Essentially, this is a "split-rim" design, designed to allow tire-changing without the use of tire irons or a tire-mounting machine, such as one might see in a tire store today.

Even the split-rim midget wheels weren't at all new. Split rim wheels of this same layout were widely used on heavy-duty trucks in the US before they were systematically outlawed by the various states over safety issues (not sure just what those issues were, but they are almost non-existent today, even on antique trucks. This is not the same as the "clincher ring" wheel used on trucks for decades, wherein one side of the rim is actually a split ring, designed to seat into a shallow channel in the rim itself upon inflation of the tire, but rather a rim in two halves, bolted together.

But, there is more: Perhaps the first 50% of the entire WW-II production run of the Willys/Ford MB Jeep were produced with a rim design virtually identical to this, as were almost all the Dodge WC-series 3/4 ton military trucks during that conflict. These made it possible for a quick tire replacement in the field, without the need for specialized tire-changing tools (very convenient if you had to replace a 6 or 8-ply tire under combat conditions). These rims, too, were phased out of Jeep production sometime in 1944, and were eliminated from all postwar Dodge 4X4 production. They are seen frequently, however, on restored military vehicles to this day. Even today, almost all large agriculture equipment wheels use this basic concept, again for ease of changing large, stiff tire casings.

Art Anderson

indeed the main concerns with modern race wheels are weight and strength....but there was a time when the strength of a wheel depended on the type and seasoning of the wood or the number and pattern of wire spokes....early experiments in alternative wheel construction abounded [indeed well before tire technology caught up!]...while doing a bit of research on the harry miller concept of a cast alloy wheel and the bugatti reduction to practice of the same concept[!] i came across countless varities of the "monocoque" concept made between the teens and the early thirties...they tended to include a cast center[to accept bearings] a rim[more on that later] and a pair[or more] of conical discs attached to form a triangulation and thus a strong [perhaps not light,but not prone to rot,shrink or have wire spokes loosen or break...]

the reason i brought this up was not that modular,disc,or monocoque wheels are not just an old idea but the vast array of forms that were tried. with the switch from high pressure "clincher" tires to steel beaded "straight side" tires, endless forms of beaded,split,lock ring,reversible,drop-center versions were offered..in combination with the many forms of multi component "disc" wheels,a lot of design bases were covered...admittedly the addition of spun alloy was a more modern technological addition,but it seems to me another good example of what i came across all too often in thirty + years as a designer...if you think it's new and unique,you'll find it was done in 1888 or 1914 or 1976 or all of the above!

I can hear Britto saying, if he read your post, "He's right you know, there's nothing new under the sun!"

But at least he did thing of ways around problems... I look forward to showing him the Nethercutt pic next week. He might have seen it before, he might have read about the car in Autosport at the time... or he may not have.

It should be interesting...