Hot Rods The Underslung Chassis, Dead Forever ?

I'm very slowly building an underslung special, minimum diameter wheel I can use is 21" because of the factory axle drop. A straight I beam or tube axle is almost necessary if you don't want the frame below wheel diameter. The scrub line is definitively the most difficult on such a build.

 

I'm dealing with a guy in his early 90s, still out in the shop every day, over the phone the only way you can tell he's that old are his euphemisms and occasional slang. Past that he's still as sharp at his chosen directions taken more than 70 years ago and is still the head judge in a Marque specific club. Met a guy in October who is 94. Has a stunning and important car collection, still sharp, candid, and bought a new 2023 Vette. Fuck age, it's a number. Older means you've seen and done more (or sure as hell should).

Now that we got that cleared up I never much cared for the concept. I give quarter to the American Underslung from the teens because it represents a daring and brave departure, or in today's vernacular they're just kool as fuck. As fillibustered above scrub line and actual use have to be considered but sometimes what works just, well, works. 20" Kelsey Hayes wire wheels would look funky...

 

You belong here,just expect to find some negative feedback from the peanut gallery

 

Blah , blah , blah , blah , negative , negative , blah , blah ....

 

@Art Gertz Your initial post give a quick sketch of an idea and asks for opinions.
You got 'em!
Your later posts covered even more ground, all of it more "What If's". With any project, you need to be able to walk before you run. I didn't go back through your old posts, but judging from the other comments, they didn't see any previous builds of even regular skills, let alone advanced stuff.

As said, underslung has been done a few times, but it's very rare, due to the issues mentioned.
A V16 project can be done, but it's a huge undertaking. I'd suggest youtube channels Greg Quirin and Alan Milliard for engine stuff in this area.
A T bucket is the light, open, anything goes basis, and it or a Speedster are most likely to be a decent basis for the offbeat thoughts. This part of your premise is the most reasonable.
Aluminum frames have been discussed here many times. The main consensus on them seems to be while it's lighter, it requires greater fab skill, superior design skill and can fatigue without as much warning. I'd suggest looking at trailers with all aluminum construction to gauge what the typical over the road chassis looks like.
Finally, torsion bars are great but why use 2 different springs? A lever shock makes more sense.

There are solid reasons why traditional hot rods are built using the systems they do. We all have "What If" thoughts, but if you are really wanting to build this, have a firm understanding of what is common, why it's the standard choice, apply the same parameters to your new design and figure out what it's going to take in research, money, fabrication, and inevitable rework to make it do the same or better. If it is just to get an argument going, ask why sinks are positioned under faucets!

 

My Dad is 89 and out in his shop every day restoring tractors. If it's a International or Farmall he can quote any spec from 1939-1964. He would laugh in he face of anyone saying he is too old or doesn't have enough time to be doing what he enjoys.

 

Let's talk about a t frame with standard 2x3 tubing (aluminum here, proper thickness size). A limited suspension movement of 2 inches up, 2 inches down (very small, but this is a light, minimal rod). Half the diameter of the axle.
3 inches of frame, 2 inches of compression, say an inch of axle radius. That's 6 inches below axle centerline IF the spring is not taking any of that space. Spring can be mounted inboard or outboard of frame or on top of axle. It would probably be a good idea to have a bump stop, too.
This gives a minimum of a 12 inch wheel to prevent scrub. Good so far, frame limits droop, spring can limit rise. What will the corner weight be to calculate spring rate? 1200-1800 total? 300-400 each sound good? Will it need additional locating links? How will steering be incorporated?

At this point, what is going to be part of the frame design to counter twist? Those kickups you are avoiding help counter this, although only a small bit. Using the engine as a stressed member helps, but adds NVH and adds new concerns, especially with the different material choice.
You can worry about shock design and mounting later, but it would be a good idea to research what is available to work with that weight and travel.

Let us know what ideas you have for these concerns.

 

This is the very reason I suggested buying a Hot Rod and then personalizing it.
There is nothing wrong with dismantling it and changing a few things to make it HIS car

What Art hasn't mentioned here is his fabricating experience [or lack of] and starting out at 75 trying to build a "complicated car disguised as a T bucket" would probably never see the light of day.

We all know of people who are elderly and playing with tools and equipment until they die. They probably have been doing this since their teens , and not just starting out now.


Personally a hotrod with twin alloy V8's and a rear transaxle, plus underslung stressed member frame, rising rate suspension with composite components is way off topic here and is more like an immature schoolboy dream.
He might as well stack supercharger casings on top of each other while he's on a roll.[to impress the kids]

The OP sounds like a 13 year old boy daydreaming about cars
I'm done with the mentality of this thread

I'm going through the same process now with a friend [who is now 72] trying to help him build a Bucket.
The real challenge is he doesn't want to spend $$$ [he makes Ebenezer Scrooge look like Santa Claus] and he goes off on a tangent and takes on other projects and never finishes them.

 

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Don't let age prevent you from starting a project. It doesn't matter in the end if it gets finished or not. Whatever the outcome, it is far better than sitting around waiting for the reaper to call your number.

I do agree that your build is not really HAMB appropriate, but don't let that stop you. Maybe, for a start, this should be moved to the off topic section...???

 

Here ya go...

 

Good catch, @2OLD2FAST !
T based (26-27, not 25), underslung. Even looks like it's got room for a V16!
Depending on OP's desires for rolling stock and springs, this would be valuable to get if for no other reason than to take a lot of measurements and swap over parts to their AL frame.

 

If you are not using parallel leaf springs, the frame does not need to be "under" the axles at all. It could end just short of them. 1/4 elliptics or torsion bars would let you set the frame height wherever you want.
But I'm not sure how the aluminum frame will work with any of this. Seems like the biggest hurdle

 

Even without FIA oversight, It's the safer way to build a chassis. On the flipside, how many over-slung cars out there, with oil pans, transmissions and other components, would fail this criteria ?

 

True, plan is a solid axle in front. Rear mounting point of 1/4 elliptic is mounted for safe ride height with respect to axle drop. Aluminum can be adequate as a frame material. It takes a sound design to make it work. A simple torsional deflection test, will prove this. Could even measure front/rear deflection. I will measure before rigid mounted drive train and roll bar assembly.
Thanks for all the positive inputs, Art.

 

I remember some of that build, not the alum frame though and I remember some kind of top. I remember for some reason he had the king pins/axle upside down, never could figure out why. Maybe to clear underslung chassis.

 

I seem to remember a company years ago at the GNRS who was manufacturing I believe '32 chassis out of aluminum, didn't they stop because of cracking issues?

 

Boyd built a couple cars with alum frames [Alumatub] but I don't think he had them [frames] for sale. Maybe same place that had alum axles and rad rods.

 

I remember a famous race car incident where the car had a simple flat tire and the bottom of the car scraped on the asphalt so badly that the driver didn’t survive. I think it was at Indy. I like the look of underslung but I also like having my balls intact.

 

The first WSP officer who saw you with that car in Washington would give you a scrubline ticket and I wouldn't be surprised if they had it towed. To me it is strictly a pro fairground car to unload in the back lot at Goodguys and cruise around the grounds and then take back to the trailer at the end of the day.

I thought about running my late 20's early 30's Chevy framed boat tail roadster as an underslung but it would mean coming up with a straight tube axle and some stiff and pretty flat front springs. I finally figured out that even with the 18 inch Chevy wires I wouldn't have the scrub room to be legal and I have already had too many scrub line tickets with my 48 just as you see it in my avatar.

 

Building a car all depends on your personal skills, depth of wallet and desire to build it. Then facilities and equipment come in to play.

Then comes in to play the thing about how you plan to use it. If it is a driver on the street and road you have to make sure that the lowest part of the chassis will not touch the ground if you pull all four valve cores out and let all the air out of the tires. I don't think there is one state where that is not the law.
Otherwise if it is lower it is what I call "Pro fair ground" and is trailered to all events that it is taken to and driven from the trailer that is parked out back with the other trailers and only driven from the trailer to the place it is parked and maybe every two or three hours fired up for a lap around the fair grounds to get the attention of anyone who didn't stop and look at it and then taken back and parked.

It sounds 99.9% off topic for this board but it is your call on how you build it.

 

I suspect that packaging considerations militated against the underslung front axle fairly early. The impracticalities are e.g. the radiator having to sit either behind or ahead of the axle, fender inner valances having to have holes for the axle to go through, headlight posts becoming convoluted, etc. etc. In other words, there is a moving axle between the frame and everything that needs to be attached to the frame in that region. By contrast an underslung rear axle is comparatively easy to do. That is why overslung front axle + underslung rear axle was close to the norm for cars of more sporting persuasion for many years. Morgans were that way (except with their traditional sliding-pillar ifs) right up to the new aluminium-composite cars.

That V16: don't abandon a dream if it's something keeping you alive. There's enough in my life preventing me from actually building anything, but I don't know how I'd live without all that's constantly going on in my head. One thing I've found, though: the further out of reach my dreams get, the more fanciful they become. Whenever it looks like there is an actual practical chance, they come down to earth quite rapidly — but that doesn't mean they suddenly become something else. The pie-in-the-sky stuff does inform the semi-realistic stuff. I learn a lot that way.

 

On the scrub like stuff, realistically, if you can maintain control with just any single tire blowing out, you are good. I mean the only time I could imagine all 4 tires failing simultaneously is if you drive over one of those spike strips. So that buys about another inch or so of low. Aaaaand you can use really tall skinny tires....
Also depends on where Art drives. Here in Atlanta, I think you could run around I285 in a Formula 1 car and not raise suspicion.

 

Thank you SIR.

Ben

 

It wasn't Boyd, It was a small booth with 2 frames around 2005, at least one was polished and bare. I believe they talked about them in Street Rodder.

 

I was going to suggest someone ask Ayrton Senna about the importance of scrub line, but you beat me to it.

 

Yea I believe that incident prompted a whole new set of design standards.

 

Which is strange, racing stuff has been blowing past that hard fast rule for a while.Maybe F1 got the message, but the drive for suction is strong.
1986

1990

2011

2020

 

Un

 

Underlung works well for me. And it's matched with a lowered rear cross member. It's about stance. Even for a pre-WW1 car and this is how they did it.