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I'm in the scribbling stages of my 50s Grand Prix roadster wannabe build. After looking at the Watson roadsters that made such an impact at Indy I got to wondering about the feasibility of running a Watson style solid axle up front. It made for a simple and relatively clean suspension arrangements.



I was already wanting to use sprint car style torsion bars on all four corners. I thought it looked cleaner than having a set of coilovers bouncing in the breeze.

The car is intended for driving and enjoying, not racing or autocrossing.

A solid axle looks to be a bit easier to setup than an independent and the steering components form a sprint car would transition over nicely.

There is a mild weight penalty. My target weight for this single seater is under 2000 lbs despite the use of a 625 lb Mercedes V12 engine.

Thoughts?

For a street driven fun car, there's no reason for it not to work. Thousands of street rods do it all the time. The parts to build a Watson "homage" would be readily available. I say "Go For It"!

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Mike - Read my story at http://twinlakesseven.blogspot.com/

Think of the build as an Indy roadster without the offset driver and suspension. I want everything centered up.

I also think that if done properly the solid axle would remove some of the "kit car" look.

I don't think the axle is a problem, but you probably will have to scale up the roadster a lot to fit an engine like that in it.

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Marcus Barrow - Car9 an open design community supported sports car for home builders!
SketchUp collection for LocostUSA: "Dream it, Build it, Drive it!"
Car9 Roadster information - models, drawings, resources etc.

I used to own a Mallock that had a solid front axle cut in half and then pivoted at each end. The two halves overlapped and there was a single trailing arm on each side. Ray Mallock said that they handled as well as the later independent front end cars.

Ford pickups had the same "twin I beam" setup. I think it is safe to say that the Mallocks handled better than the pickups.

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Chuck.

“Any suspension will work if you don’t let it.” - Colin Chapman

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I've even seen a few street rods built with a "Twin I-Beam" set-up. I believe one of them was built by Roy Brizio, or maybe Andy.

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Mike - Read my story at http://twinlakesseven.blogspot.com/

It'll work fine but result in a rough ride due to the high unsprung-to-sprung weight ratio.

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Midlana book: Build this mid-engine Locost!, http://midlana.com/stuff/book/
Kimini book: Designing mid-engine cars using FWD drivetrains
Both available from https://www.lulu.com/

Indeed.

I've brought the engine home and need to make a low stand for it. Once that is done I'll have to snuggle up to the engine and work on the driving position and chassis layout.

The center driving position is what really throws things off.

This is the car I really want to build but the project will be scrapped if I am forced to use a 4, 5, or 6 cylinder. Those exhaust notes are not right for the car and I refuse to do that.




This one had a V12 at a bit of an angle to clear the driver.

I recant the above if you use a 600-lb engine!

_________________
Midlana book: Build this mid-engine Locost!, http://midlana.com/stuff/book/
Kimini book: Designing mid-engine cars using FWD drivetrains
Both available from https://www.lulu.com/

Here's an outline to compare a couple of Ford engines. The point is the size of the modern DOHC powerplants. I tried to find a picture like this that showed a 289/302, the little one in this picture is a 351 which is a good size bigger block, deck height 9.5" vs. 8.2".

The W196 had an inline engine, I'm sure you know...

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Marcus Barrow - Car9 an open design community supported sports car for home builders!
SketchUp collection for LocostUSA: "Dream it, Build it, Drive it!"
Car9 Roadster information - models, drawings, resources etc.

Yes, I'm a bit of an enthusiast when it comes to the W196. I've collected tons of info on the cars and have toured the museum in Stuttgart.

The W196 has a pretty low but relatively wide cowl. It's not as sharply curved as many others.

The W154 has a slightly higher cowl but it has more of an arch that is relatively unnecessary. It holds a DOHC V12.



This is the engine I'm using.



I will be playing with some Ducati throttle bodies to determine if it will have 12 ITBs in the valley or laid over the valve covers. That will determine cowl height.

I seriously considered going to a beam axle on my car, but it turned out to be substantially cheaper to go with a normal independent front end.

Most of the "drawbacks" of a beam axle assume a worst-case scenario; a heavy axle hung from long floppy leaf springs with no lateral location and no means of preventing spring windup on braking. The single-transverse-leaf with radius rods usual for street rods is a big step up from that.

I've driven many thousands of miles in large trucks with a "worst case" beam axle, and other than "here, it drives like a truck" they drove like anything else.

One *big* advantage of a front beam axle is you don't have to wank about with force-based or geometric roll centers, roll center migration in bump, roll, or single wheel bump... if you use a Watts link you can point to the pivot bolt and say "Where roll center? There roll center!"

You *do* have to be careful laying out the steering geometry. Generally you'd use a steering box and drag link. It's not rocket surgery; street rodders do it all the time.

If the bits are in your price range and the shape fits your available space, go for it!

I've got torsion bars in mind so there wouldn't be any wonky buggy springs moving the axle about.

A little detour took my by my sister's house a couple nights ago. Her husband races sprint cars and builds Midgets and dwarf cars. We spent a good amount of time going over his sprint car's suspension. His preferred form of racing requires turns in both directions so he's pretty well versed in handling issues.

Being able to source stuff from the sprint car guys makes it tempting.

Very understandable!!!

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Mike - Read my story at http://twinlakesseven.blogspot.com/