Solid front axle again

[Cat Daddy]

Good morning everyone,

So I’m debating on making myself a Locost. The Donor is a Datsun b210, and if I go through with it all I want the weight to be extremely low. And I want the car to be extremely simple. Hopefully 1000lbs. The engine in these cars, an A12 is extremely light, the transmission and rear axle as well. Very lightweight with a 145mm ring gear.

I have a lot of upgrades for the engine and car already. I want the front to be based on a solid axle so that I can run a very simple steering and suspension setup. Ultimate performance is not the goal. Simple to setup and simple to handle is the goal.

With the anemic power plant and light weight I plan to modify a “book” chassis and reduce weight in a few areas. And add a few extra things to make it slightly more comfortable and quiet (floor reinforcement)
I have 10” wheels for the car that just barely clear the brakes and I would like to use them as well.

So the question is,
What locating and suspension method would be very lightweight and simple. My mind keeps going to the tried and true transverse leaf. It would be situated in front of the crank pulley in between the engine and the radiator.
Are there any decent lever shocks available?
I’m hoping for about 6” of wheel travel.
I’m also hoping for a high front roll center to keep the front level when cornering and soft over expansion joints etc.

Thoughts?

[Warren Nethercote]

Six inches of wheel travel and light weight are probably conflicting requirements with a transverse leaf spring. Coil-overs would give you a better shot at it but they would need to be REALLY long. Six inches of wheel travel may be extraordinarily big for a road going vehicle in any event. Ordinary IFS might be simpler and even lighter in the end, with care. But that is speculation on my part.

[ngpmike]

The transverse leaf goes against the lightweight theme also. Better would be Coilovers. There's a reason that lever action shocks are rare these day. For even less weight, look at torsion bars. For inspiration, check out sprint cars and midget racers. That's one place that "lightweight and simple" are the rule rather than the exception. It sounds like an interesting project, keep us posted!!!

[Cat Daddy]

I was thinking 6” didn’t seem like much!? Haha! I’ve seen locosts often run 4” which is hard to imagine! I read that F1 teams were complaining about having only 5” or something once.

I figured if it only weighs 1200~ with me in it... I’d run a pretty soft mono leaf up front (stock rear from the Datsun maybe? Weighs probably 20-25lbs)

It definitely doesn’t need to have great geometry. I just want all 4 wheels squared up and for it not to have bad roll steer. Letting tire compound do the work!

[davew]

Cat daddy
I think you missed a decimal point, on the 5" . The F-1 was .5" if lucky.
The B-210 should be a really good donor for a Locost.
Before you jump off the deep end spend some time reading different suspension design books.
In the long run you will save time, $$$, and have a much more enjoyable car.
Any of these will be worth the effort.
Race and Rally Source by Allen Staniforth is excellent
Race Car chassis by Forbes Aird
Chassis Engineering by Herb Adams
New Directions in Suspension Design by Colin Campbell; more advance but actually compares all the different types of systems.
These are probably the best out of the 15 or so design books that I have.
What is your location? The crew here can be very helpful, and possibly close by.
Davew

[Driven5]

Let's make sure we're all talking the same thing here too. Six inches of wheel travel can be interpreted two ways. A combined 6 inches of bump and droop, or just 6 of just bump. The former would be entirely reasonable for one of these cars, the latter not so much.

[Cat Daddy]

Yes I have read lots of chassis books over the years and tuned in many cars for the track, etc. that’s all fine and dandy, but not what I’m looking for if I start welding this thing up at all.

6” would be total travel from full droop to full jounce. Seems very achievable, 4 or 5 would be fine.

I guess I was wrong on the F1 reference. I saw an ad now for an F2 that said “a plush 4” of wheel travel” ha!

Why I am interested in a Locost solid front axle:

Steering box mounted to the frame: no bushings, no leaks.
Crossover track rod: no bump steer, no geometry at all to consider in this configuration.
Drag link: set toe and go. No welding, no bending, no geometry.
No camber adjustment: no adjustment, bend it in at -1.5 and let it be.

So this leaves the locating and springing. Still thinking about that part. Light and simple. Performance a distant 4th.

[Lonnie-S]

It sounds like you know your way around cars, so I hope this suggestion won't be insulting, but have you considered doing an "Austin 7 Special" kind of car? There's no reason why a Locost chassis can't be adapted to the look, but the 7 Specials were even simpler mechanically, and many had solid front axles. And, there's no reason why you couldn't do a build log here either. You might just start something.

If you do a Google Images search using the "Austin 7 Special" phrase as an argument, you'll see many examples.

Cheers,

[davew]

That's a great call , with a "7 Special" and a period correct 50's style body with the solid front axle set in front of the body.
You would not see one of those ever day! That would be a fun project.
I love watching the old English vintage race cars, like at Goodwood or hill climbs. But you would have to inject oil into the engine, to get enough white smoke with a modern engine
Davew

[seattletom]

So this leaves the locating and springing. Still thinking about that part. Light and simple. Performance a distant 4th.

This brings fuzzy images to mind of quarter-elliptical springs locating the axle out front...

But Indy-style torsion bars would be cool, too.

[ngpmike]

But Indy-style torsion bars would be cool, too.

They're still quite common with Midget racers & Sprint cars which should make them easy to source!

[Driven5]

Using a conventional transverse leaf as a locating device is probably fine for puttering around and hard parking, but that's about all I'd use it for. Correctly configured, an axle only need 4 links to fully and properly constrain its motion. This would lead me to consider either a 3-link+panhard or triangulated 4-link. For the latter, I would be inclined towards the 'Satchell Link" configuration, which would have longitudinal/parallel uppers and lowers triangulated at 35-45 degrees with the inboard end connected to the chassis and outboard end connected to the axle.

Now that's not actually to say I'm against the leaf spring idea either. If outboard coils would not provide the right 'look', the mechanism to run them inboard might not save much weight over a mono leaf either. I'd be doing the center mounting more like a Corvette though. One of the main considerations would be figuring out how to achieve the desired spring rate.

And of course that still leaves open the issue of dampers. If outboard coils spoil the look too much, would outboard shocks be likewise? And if the dampers are run inboard, why not just wrap them in coils at that point?

Or you could go for more of a modern/vintage fusion...

[Sean in CT]

Love supermodifieds. This one uses double A arms with only one coil over on the front. interesting story. IIRC it was very fast but did not turn to the right so well, so it was considered unsafe then outlawed

On a serious note, the midget parts are lightweight and durable plus use torsion bars for that "clean" look
Check out the sprint/midget section of speedway motors to see some examples

https://www.speedwaymotors.com/Speedway ... ,8740.html

[Driven5]

A couple more thoughts:

I agree that a torsion bar setup out of a spring car catalog would be a bit more off-the-shelf while also certainly making for a neat and fairly unique look, although they're also probably not the cheapest nor lightest option either... And like the transverse leaf, you'd still have to figure out a good looking (and decent functioning) damper solution.

To use standard terminology, I believe the drag link steers while the tie rod sets toe. A crossover drag link is a good solution for reducing roll steer in 4x4's that have a relatively short distance from the steering box to the axle, especially for crawlers that don't as often hit 2 wheel bumps. However, while a crossover drag link can be pretty good in articulation, it will still have a bit of 2-wheel-bump steer. The layout of these cars puts the driver further back in the car and could potentially allow for a 'full length' drag link that could be positioned to follow an arc that minimizes both roll and bump steer. And to fully minimize roll steer, that involves correctly positioning and orienting the locating links. It all just depends on where you draw the line for 'good enough' though.

[Driven5]

Ok, so thinking about this some more, packaging a steering solution that minimizes bump/roll steer for a triangulated 4-link on the front is a bit of a packaging nightmare. However, it seems to me that you should be able to minimize bump/roll steer with correctly setting up equal length Panhard and crossover drag links mounted to follow the same fundamental arcs. Being front engine doesn't lend itself the best to a center mounted 3-link, but the overconstrained binding of a 4-link+Panhard can also be minimized by dialing in the correct amount of convergence between the links on each side if you don't mind the spindles being cantilevered out a bit more than ideal to allow for the steering lock.