suspension thoughts for short wheelbase lightweight bucket

[rodjr]

So my build is underway, lakes modified inspired 23 bodied car. I have lasered and formed my own channel frame from crs sheet at work. I have a speedway medium arch rear spring that will sit in a model t rear crossmember with toyota 7.5 axle behind. Front is forged 26" monoleaf that will sit under the front crossmember with 4" drop axle mounted in front of the spring and crossmember. Wheelbase will be right at 90", steering will be sprint car style. guesstimated weight of 1400-1500 lbs soaking wet with a mostly aluminum buick turbo v6, th350 and me in the drivers seat.
My questions for the suspension guru's here are;
springs, will they need to be spread? does not seem i would need to preload much?
shocks that will work best?
radius rods? 4 bar? length?
Basically i am wondering what setups will work best with a short light car? I have given this alot of thought but i would love to get some opinions from some experienced sources.

 

[Zandoz]

I can't help with your suspension questions, since from the sound of it you are farther than I. But I am wondering about your choice of body. My build will be with a GM 60° V6, 700R4, and an 8" stretch body. With that combination it's been quite a squeeze to bring the wheelbase in at 92.

For what ever it's worth, my uneducated front suspension choices are a conglomeration of Speedway 4-bar parts, a pair of Speedway garage sale generic adjustable shocks, a 31" mono leaf, and a 48" Super Bell 5" drop tube axle. The bars are 21.5" center to center, and I plan on starting out the shocks on their softest setting. My rear suspension will be a monster of my own doing...not much that will apply to anything else.

 

[rodjr]

My body is the std rpm body. my wheelbase would have been much shorter but i am choosing to mount the rearend behind the spring. my body will not cover the kick up and i left a little extra room between the firewall and engine as there is a bit going on with the turbo. My main rails are 75.5" along the top.

 

[Zandoz]

It looks like mine will be 82" from the leading edge of the round front crossmember, along the top of the main rail, to the start of the 45° kickup. Taking off 8" for the stretched body would put my wheelbase at 84" and my top rail at 74". <shrug>

 

[meangreen]

OK, the questions you ask can be answered with several options. First of all you need to decide on the wheelbase and ride height. I recommend that you take the body and wheels outside and mock them up in position, moving things around until you like the look from 10, 15, and 20 feet away. Proportion and stance are the two most important factors in the overall appearance of the vehicle. If you are simply trying to build the car as short as possible you may be disappointed with its looks when you are finished; it may appear stubby and out of proportion to its height. More importantly, you may be unhappy with the ride quality; the shorter the wheel base, the harder it is to find the proper spring/shock/link combination to avoid a "choppy" ride. Also, the body location between the wheels is important. If the front is too short in relation to the rear it will look out of proportion. When you find the look you like, take some measurements.

The suspension is 50% matter of preference and 50% practicality. Rule of thumb - parallel 4-bar is the freest moving, least-binding type available. If you are using a tube front axle I recommend using parallel 4-bar (because the tube axle is rigid and won't twist). If you are using an I-beam axle you can use either 4-bar or hairpin radius rods (because a beam axle is flexible). On the rear, again, the parallel 4-bar is the least binding. If you use hairpin or ladder bars on the rear they should be rubber mounted at the axle housing so they can flex without damaging the housing. A rule of thumb for hairpin radius rods - the longer the radius rods, the better the ride.

Yes, your springs should be spread slightly when installed. You don't need a lot of preload, just enough to help keep the suspension centered on the chassis when cornering. If you have no preload you will need a panhard bar to keep the axles centered.
I am not fond of monoleaf springs because they are not "tune-able". If you use a multileaf spring you have the option of adding or deleting leaves to fine-tune the ride (spring rate).

As a matter of reference, the roadster in my avatar has a 97 inch wheelbase, beam front axle, hairpin radius rods on both ends, and it weighs 1630 pounds. It rides good, steers like a go-kart, and corners like it's on rails.

 

[Golly]

Why such a short wheelbase? stretch it out a bit, it'll ride much better for a start, and be easier to build and work on.

 

[EX JUNK]

OK, the questions you ask can be answered with several options. First of all you need to decide on the wheelbase and ride height. I recommend that you take the body and wheels outside and mock them up in position, moving things around until you like the look from 10, 15, and 20 feet away. Proportion and stance are the two most important factors in the overall appearance of the vehicle. If you are simply trying to build the car as short as possible you may be disappointed with its looks when you are finished; it may appear stubby and out of proportion to its height. More importantly, you may be unhappy with the ride quality; the shorter the wheel base, the harder it is to find the proper spring/shock/link combination to avoid a "choppy" ride. Also, the body location between the wheels is important. If the front is too short in relation to the rear it will look out of proportion. When you find the look you like, take some measurements.

The suspension is 50% matter of preference and 50% practicality. Rule of thumb - parallel 4-bar is the freest moving, least-binding type available. If you are using a tube front axle I recommend using parallel 4-bar (because the tube axle is rigid and won't twist). If you are using an I-beam axle you can use either 4-bar or hairpin radius rods (because a beam axle is flexible). On the rear, again, the parallel 4-bar is the least binding. If you use hairpin or ladder bars on the rear they should be rubber mounted at the axle housing so they can flex without damaging the housing. A rule of thumb for hairpin radius rods - the longer the radius rods, the better the ride.

Yes, your springs should be spread slightly when installed. You don't need a lot of preload, just enough to help keep the suspension centered on the chassis when cornering. If you have no preload you will need a panhard bar to keep the axles centered.
I am not fond of monoleaf springs because they are not "tune-able". If you use a multileaf spring you have the option of adding or deleting leaves to fine-tune the ride (spring rate).

As a matter of reference, the roadster in my avatar has a 97 inch wheelbase, beam front axle, hairpin radius rods on both ends, and it weighs 1630 pounds. It rides good, steers like a go-kart, and corners like it's on rails.

Meangreen, you've given an excellent overview of planning a build along with explaining the reasons for choosing certain parts. I only hope that more builders will read this and take it to heart and follow your excellent advice.

Jim

 

[rodjr]

The object is not to be as short a wheelbase as possible, in fact it is about 8" longer than it has to be. With the shorter and taller turbo v6 I had to pay particular attention to proportion. Actually the car will look low and long for what it is. Any longer and it will look deliberately over stretched. I do have a rpm tube axle, but I would like to use longer narrow v shaped radius rods skinned outside with sheetmetal, front and rear, as this would look very lakester. Not sure I can talk myself into 4 bar as I do not like the look. this will not be a daily driver by any means, summer short trips is it. Is there a way to mitigate the problems with tube axles and radius rods? for example how do you rubber mount them to rear end (or front) as suggested here?

 

[meangreen]

Jim - Thanks for the compliment. Like you, I have done all this more than once...

Rodjr - OK, rather than rewrite the whole process and re-post a bunch of pics here, take a look at my detailed build thread over on Club Hotrod. I was a member over there before I discovered this site several years ago and had already started the thread, so finished it there. Anyway, here is the link:
http://www.clubhotrod.com/hot-rod-talk/30400-another-build-thread-yep-my-track-style-t.html
You'll need to join to see the pics (it's free). The first part is all about the front suspension and making the radius rods, spring mounts, etc. The part about rubber-mounting the rear radius rods is on pages 7 - 9. I don't like to mount the front end in rubber as it can cause caster change during braking and possibly front end shake or chatter at speed if/when the rubber starts to break down. What I first posted above is what I have learned and proven to myself many times over the years. Still, there are a lot of hotrods on the road that have tube front axles with hairpin style radius rods. I don't like to do that, but you can get away with it on lightweight cars. As for sheet-plating the outside of them for appearance; it's a cool look but the plates add stiffness to the radius rods. Since something somewhere HAS to flex when cornering and the plate eliminates the flexibility from the radius rod, you stand the chance of fatiguing and breaking the brackets off the front axle or breaking the Heim joints where they attach to the frame. Either could be very scary or possibly deadly! My advice is either don't put the plates on the front radius rods OR switch your tube axle for an I-beam. If you go ahead with the tube axle and the sheet-plating of the radius rods, keep a close eye on everything. Look constantly for stress cracks with a magnifying glass and use safety washers on the Heim joints.

 

[rodjr]

Thank you! Could sway bar bushings (rubber or poly) be used for this type of mount also?
So what i am thinking is, chromoly 4130 axle brackets with stainless radius rods (Strength and flexability), with a very thin 24 ga ss skin (minimize stiffening) stretched to maximum length possible. I would do heims (with safety washers) everywhere except rear housing mounts, which would be rubber bushing type.
Not sure i want to buy a new axle, but i will count my money and consider it. I am headed up to demming this evening to watch the mini sprints run, and have a look at some of the suspension tricks they use. Our programer at work is building a 3/4 scale 32 sedan with a gsxr engine From scratch (currently forming his own body) and told me to go up and have a look at these guy's and what they do.

 

[choppedtop]

I have a 3/4 scale 32 roadster. Had a 60hp flathead with 5 speed. Took it out Tuesday, and replacing with 4 cylinder 153 chevy, and powerglide. My wife wants to start taking it to some of the car shows.

 

[meangreen]

Rodjr - The hard neoprene, teflon, or nylon bushings that are commonly used in 4-bar setups are too dense (hard). Rubber is better because it is "crushable" which allows the movement necessary to relive the stress on the rear end brackets. If you looked at my build thread, I use 3/4" I.D. tubing for the outer shell and make the bushings out of 1/2" heavy duty heater hose. It fits snugly into the 3/4" shell and a 1/2" bolt goes through it (with a little persuasion) and it's fiber-reinforced. The bushings last about 8 to 10 years of normal driving before needing replacement.

Have you considered making covers for the front radius rods that are bolted on instead of welded? That would allow for the necessary flex and could still look good. You could even form them from aluminum or stainless steel and polish them to a mirror finish.

Not sure what they are doing in mini-sprints because they don't run anywhere around here, but a lot of full-size sprint cars use parallel bars on the right front and a single bar on the left. There is no binding that way, but not sure if it's good for the street, especially in a hard-braking situation on asphalt...

 

[rodjr]

Yes, i considered bolting covers on, or perhaps dzus fasteners. I am going to do some shopping today and see if i can talk myself into trying to sell the tube axle and buy an i beam, not sure yet. I have to ask, and i mean no disrespect in doing so, why do so many vendors sell front kits with tubes and radius rods if this is an issue?

 

[rodjr]

I am going to stick with the tube axle and as much flex as i can build in. Meangreen, do you use anything besides the rear axle bracket to capture the bushings? Seems to me the radius rods would rub the inside of the bracket or be pinched in if bolts were too tight. I guess what i am saying is, what stops metal to metal between radius rod end and axle bracket?

 

[Zandoz]

Why such a short wheelbase? stretch it out a bit, it'll ride much better for a start, and be easier to build and work on.

On mine that was a typo...should have been 92", not 82".

The reasons for going with a short WB...That's what I need to keep the overall length under 10', so that I can use a shed for winter storage. The first T hot rod to capture my attention..the original pre Big Daddy version of Tweedy Pie. I spent a lot of years having fun driving short wheelbase MGs, and I'm hoping to recreate some of that fun in a T body.

 

[meangreen]

Rodjr - Vendors sell what they can make the most profit on and they leave it to the end user to figure out whether it meets the need. Tube axles look good; they're clean and simple. Also, the vendors assume that most of them will be used on cars that go straight ahead 99% of the time which is probably correct. I drove stock cars, off and on, for over 30 years and I learned (the hard way) what metal fatigue does to suspension parts. I try to give advice to other builders that will allow them build cars that they can corner hard and never have to worry about suspension failure for the life of the car (with normal maintenance).

On the rear radius rods, ladder bars, or lift bars where I use the rubber bushings, I use self locking nuts on the bolts and don't over tighten them. I tighten them just enough to take out the "slop", but they are not too snug or tight. Grab either end with a wrench and they will turn without binding. As for the rubbing inside the brackets, it's really not an issue; that is, I've never found any metal shavings or metal dust in between the brackets. The movement is pretty limited, so if there is wear it's negligible. If the possibility bothers you, you could allow some extra space between the brackets and put some nylon or neoprene washers in there.

Zandoz - 92 inches is doable. I've always thought Roth's Tweety Pie looked stubby, but an old friend of mine had a 92" wheelbase T-bucket that was really nice. If I can find the picture I'll scan and post it here for you.

 

[Zandoz]

Zandoz - 92 inches is doable. I've always thought Roth's Tweety Pie looked stubby, but an old friend of mine had a 92" wheelbase T-bucket that was really nice. If I can find the picture I'll scan and post it here for you.

Actually the original Tweedy had an 84" wheelbase, but I'm using an 8" stretched body, so I bumped my target to 92"...which also happened to bring the total length in at less then an inch under the 120" limit I have for shed storage.

 

[rodjr]

Thanks to all for the input, i will take every word under advisement as i move forward. Almost looking forward to work tomorrow, so i can order some stainless tube.

 

[rodjr]

As i continue to search, i ran across the idea of using shackel bushings at the frame ends of radius rods, front and rear, thoughts? I realize this would not be as forgiving as rubber on the axle end of rear, but it might be an option for the front axle to get some flex? I am also thinking the more inboard the rods are, the better. Wow much angle out from the frame to axle is considered the desirable minimum?

 

[roadmonster]

You really need to stick with tie rod ends and spread radius rods. Inboard rods with plastic bushings sounds like a recipe for disaster. I had the same idea at one time but was quickly talked out of it by those who know better.