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Everything is a compromise...But IFS is less compromised than a beam axle when turning both directions, as well as on the street as noted below. I suppose that your axle might be level to the road, and that this trait might be desirable...IF tires were rigid objects. However, they are not. As load transfers and the tires deflect, the outside tire will compress more than the inside (just like a spring), causing the axle itself to 'camber' the wrong way. Additionally as the tires deflect, they roll under on to the edge towards the outside of the turn, increasing the 'camber' problem. These are the same problems fought by drivers of poorly designed (from a performance perspective) strut suspended economy cars. So now you camber your solid axle. While an IFS will send both the inside and outside wheels cambering the desirable way to at least some degree proportional to the amount of cornering force experienced, the solid axle will now only be cambered in a fixed manner such that only the outside wheel is cambered in the desirable direction. This does not maximize grip. The solid axle can however be setup with both wheels cambered for a singular turn direction only, such that both wheels are cambered the correct direction. This is precisely why the solid front axle isn't used anywhere in modern road racing classes, but makes for an easy and effective design on circle track cars like Supermods.

NO BUILDER should base their geometry on pure-bred racing vehicles (Supermodified, F1, SCORE, etc) as they all make compromises specific to their constructed purpose, and within a given set of rules (often prohibiting better solutions) which street cars don't have to adhere to.

That being said: A well setup lesser technology is capable of being as good ,or better, for many purposes than a poorly setup superior technology. That is the case for anything. And yes solid front axles appear to be a fairly simple device to build and setup such that it could make for a fairly decent vehicle right out of the box with somewhat less planning, effort, and design work than an IFS. These attributes could certainly suit some builders quite well!

A poorly executed design is a poorly executed design. Period. There are plenty of poorly executed solid axles setups out there too. Big deal. See above comments on the "compromise" a solid axle must makes for anything other than unidirectional turning. It may offer 95% of its potential out of the box, but even at 100% potential is not capable of offering similar multidirectional capabilities to a 90% potential IFS...For which the information needed to build is readily available to those willing to put the time and effort into researching it. Admittedly because there are so many variables, it does mean that there is no simple/singular 'best' solution to the IFS geometry, which does make it more challenging to design and a little bit of a black art to dial in.

Above you mention the superiority of IFS on bad roads, yet ignore the fact that most Locosts are street driven on less than ideal roads. Unsprung weight may be over emphasised by some people, but is certainly not 'over rated' for our needs either. The lighter the car, the greater of an impact unsprung weight has...And these are some of the lightest cars out there. Sure a custom solid axle sized specifically for the car could be lighter than an IFS using production components from cars 2x-3x the weight. But your argument fails to hold water when you start comparing apples to apples.

I'm not saying that the solid axle is necessarily a bad way to go, depending on the wants and needs of any specific builder...Especially if it's reasonably well executed. But the decision of which path to take should not have to be based on potentially misleading information from either side of the debate.

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-Justin

"Orville Wright did not have a pilots license." - Gordon MacKenzie

How many solid axle street rods have you seen at an autocross or on a track?

Of those you have seen how many handled well?

Are they known for being able to turn right and left well?

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mobilito ergo sum
I drive therefore I am

I can explain it to you,
but I can't understand it for you.

That sure explains a lot of the dorked up IFS setups on Locosts....


I'm too old and slow to go any faster than 95% anymore. And all of the hardened veterans of the Grand Theft Auto driving school are probably never going to drive that hard either.


You are correct. It's a very important consideration on a solid axle in this case. Makes a difference in the feel of the car when you do hit a pothole. But again, my experience has been that unless you have a very well calibrated butt, you won't be able to tell the difference in a pound or two either way. I say, if given a choice, lighter is better for our purposes. On a solid axle 4x4 rock climber, big deal. But as cheap racer said, you can get the unsprung weight into the same ballpark as an IFS.


Well said. Same is true of IFS.

Now, back to the original point of the thread.....What's a reasonably good way to execute a beam axle?

This is like the system on the rear of my 32. It works very well in that application and the same style layout could be adapted to the front.



Or a panhard bar with parallel bars

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Jack Collins

Here's a couple of examples going right AND left. Actually these are Austin Seven specials and are probably somewhere in the Locost evolutionary chain.





and this is kind of amusing. http://www.youtube.com/watch?v=V8Wb-3OI5R4

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Jack Collins

Nice single dimension thinking there but you're simply and absolutely 100% wrong - It's called caster, in turning it gives camber gain on the outside tyre and camber loss on the inside to offset any tyre compression/slight tilting of the beam issues and adjusted in seconds - not so easy for a IFS when simple changes also change a few other things at the same time. Caster is used very successfully as a camber adjustment tool for the same purpose on thousands of Formula Vees around the world for the last 50 years.

Name a modern racing class that would use a beam and find an improvement by decreasing the all important aero efficiency or allowed in the rules - there is also the question of basic design of which cars have been developed around the engine front, low and central not allowing anything but IFS.

Ahh we come back to Supermodifieds, 800hp and low to medium speeds so aero isn't a worry like a 120hp Formula Ford but maximum grip is as they spend half their time turning.

FWIW Ferrari tried a DeDion tube on an F1 car in the 70's but the packaging issues and again aero's don't allow successful designs.

don't use hot water when washing cars, they shrink!

Maybe they should have washed and dried the driver as well...

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Jack Collins

Parallel 4 link is almost unavoidable but theres a number of lateral locating devices that can be used at the front panhard rod and this thread are the two best options viewtopic.php?f=5&t=8371

Another way is 2 rollers running up either side of a metal slide.

You can't run a Watts because of clearance problems,

Caster is mostly useful at higher steering angles...Which means an increases in effectiveness as at-the-limit cornering speeds decrease. It has absolutely zero cornering force dependence, unlike the camber gain on an IFS. Caster is a life-saver when it's the only tool in your box...But a suspension system that can successfully utilize both traits, when needing to turn both directions, is at an overall advantage relative to a suspension system that is limited to only the one of the traits. Either way IFS and solid axle cars both are able to be set up with similar amounts of caster, so it's pretty much a moot point in regards to a discussion of the differences between the two systems...Which is precisely why I didn't bother bringing it up in the first place.

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-Justin

"Orville Wright did not have a pilots license." - Gordon MacKenzie

I don't know much about whether triangulated 4-links are viable at the front, or how it might be best set up with the steering geometry and whatnot, but I do have a fondness for the triangulated 4-link...At least on the rear. However I would probably put the bottom links as the triangulated pair rather than the top links as shown in this photo, due to the lower roll center. The reason for this is that the virtual intersection of the angled links is your roll center for that axle.

Edit: With a tube frame car I also would consider reversing the direction of the triangle, such that the forward attachments are towards center and the rearward attachments are towards the outside. Fully supporting the axle as close as reasonably possible to the wheels should provide better support to the axle when dynamically loaded.

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-Justin

"Orville Wright did not have a pilots license." - Gordon MacKenzie

Actually a simple 4 or 3 bar setup with a panhard bar would be the lightest and the simplest. Roll center in the front could be immediately adjusted provided you allowed for it in the construction. Honestly the non parralell 4 links used in the rear of a lot of street rods are only used because of space issues. In a race or handling situation 3 links with either a panhard bar or a watts linkage are most commonly used.The upper link in a seven could run over the trans tunnel ( or in it ).

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The biggest thing in motocross.

A parallel 4-bar in the front would be very easy to do and it would be a piece of cake to add a panhard that was height-adjustable to move the roll center. It's just not possible to move the RC below ground, however. Advantage IFS.

I would steer it with one of these - a one sided R&P built for hot rods with straight axles. The cross steer arrangement practically eliminates any bump steer issues and mounting is dead simple.


One of the cross tubes could double as a torsion bar housing instead of using coil overs. 1/4 elliptic springs??? Those would be easy to package.

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Jack Collins

The Austin 7 is the grandpa of the Lotus 7 and of course Locosts.

Since the original question was for a Locost to be driven daily on the street, I'm thinking of cars driven on the street/roads in most of my commentary here.


Driven5 wrote:
Everything is a compromise...But IFS is less compromised than a beam axle when turning both directions, as well as on the street as noted below. I suppose that your axle might be level to the road, and that this trait might be desirable...IF tires were rigid objects. However, they are not. As load transfers and the tires deflect, the outside tire will compress more than the inside (just like a spring), causing the axle itself to 'camber' the wrong way.

That's one shitty axle in that case. I have an idea that the tires would be sliding long before the axle would flex enough to affect the handling. We had to chain the axle down and use a huge press to bend them even a small amount after an accident.

Additionally as the tires deflect, they roll under on to the edge towards the outside of the turn, increasing the 'camber' problem. These are the same problems fought by drivers of poorly designed (from a performance perspective) strut suspended economy cars.

I would think that the tire patch on the ground gets so small that the tire looses traction before it can bend an axle. And strut cars generally lean so much that the camber angle goes + at the same time anyway. Have you looked at the suspension geometry change of an old Mustang in bounce? I'd sure rather run a solid axle than that IFS! And most stock IFS of even slightly older cars aren't much better.

So now you camber your solid axle. While an IFS will send both the inside and outside wheels cambering the desirable way to at least some degree proportional to the amount of cornering force experienced, the solid axle will now only be cambered in a fixed manner such that only the outside wheel is cambered in the desirable direction. This does not maximize grip. The solid axle can however be setup with both wheels cambered for a singular turn direction only, such that both wheels are cambered the correct direction. This is precisely why the solid front axle isn't used anywhere in modern road racing classes, but makes for an easy and effective design on circle track cars like Supermods.
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[Getting back to street/road driving.]
I found that on the open highway if you are really pushing a souped up flat head '40 Ford in a turn you can induce a very controllable "power slide" [oversteer] condition and most of the theory about tire roll under etc isn't something that mattered all that much. Once all four wheels are sliding the car handled differently than if you tried to drive the thing around the turn at a what would be the maximum "drive it" speed. The difference was ~50 mph vs 75-80 mph. I used to take the small yellow truck caution speed signs and double the number and add 10 mph for starters! [DON'T try that on a reverse camber turn!!!]

To show that tire theory and IFS vs solid isn't all that matters, I had to keep the windows closed so the air could build up pressure on the side of the car to help stabilize it in a Banzai run in the twisties. You aren't going fast enough at an autocross to do that in the small amount of time you are in the small turns they use.

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"My junk is organized. At least is was when I put it wherever it is." -olrowdy
Completed building GSXR1000 CMC7, "Locouki"
Website: http://projekt.com/locouki/

Driven 5 isn't referencing the axle flexing, he's assuming the axle (or locating mechanism) is infinitely ridged like you do with most suspension theory. He's refering to the fact that the Tires themselves are flexible, springy elements that deform quite a lot under loaded use.

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MG midget bodied Locostish car in progress

Driven5 wrote:
"Everything is a compromise...But IFS is less compromised than a beam axle when turning both directions, as well as on the street as noted below. I suppose that your axle might be level to the road, and that this trait might be desirable...IF tires were rigid objects. However, they are not. As load transfers and the tires deflect, the outside tire will compress more than the inside (just like a spring), causing the axle itself to 'camber' the wrong way. Additionally as the tires deflect, they roll under on to the edge towards the outside of the turn, increasing the 'camber' problem."

After re-re-reading the part of his post above I agree. I'm sure he means that the outside tires radius will decrease some due to weight transfer which would cause the axle to assume a slight angle to the road. This would change the camber towards + on the outside tire.

OK, let's look at that a minute. The track of the old Ford (from memory) was something like 57". So how much would a tire change radius in hard cornering. I'll take a dumb guess ....... 3/4"? 3/4" over 57" is ~3/4° change. And that is with no complicated computer aided suspension geometry calculations to set the axle up. As one poster said, "right out of the box".

Anyone want to play with the same numbers with a 57" tread IFS considering body roll, bounce/rebound, camber change due to braking etc etc. None of those things directly affect a solid axle. I can look at my computer graphs but it's past my bedtime and the dog is cross eyed because he wants to go out.

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"My junk is organized. At least is was when I put it wherever it is." -olrowdy
Completed building GSXR1000 CMC7, "Locouki"
Website: http://projekt.com/locouki/