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reverse, reverse front a-frame, i think....


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ok then i hope you're sitting comfortably.... :rolleyes: my head has been melted with 1,2,3 and x-link front ends, i've had a bit of a brain wave/fart. basically we've been toying with using a rear a-frame on the front axle and using radius arms instead of hockey sticks. (this is on a 100" disco chassis, pure off roader with rads re-located, full hydro steering etc etc. now my limited understanding is you would normaly mount the two a-frames like this <> my thinking is mount the front one with the ball on the top of the axle like normal but.... you mount the other end to the chassis where the front crossmember is , now we'll have to remove the front crossmember, but as theres no rad or steering box there thats not a problem, we could also lose the panhard rod and front steering bar as we will be using the steering ram behind the axle.

now is this a stoopid idea born from too much reading and not understanding what i'm reading :wacko: or am i onto something?

let the tiddle taking begin!!!!!!

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I would think you will find you have two issues:

  • Getting clearance between axle pumpkin and engine/sump/front cover with the A-frame mount on the axle, plus height BJ and then A-frame.
  • You need to stop the axle rotating somehow, on the rear this is done with trailing arms mounted to the bottom of the axle tube

It is done, but the other way round, for some racers like comp safari, but then they are often mid engined so don't have engine clearance issues :) Often it is two Disco chassis rear half's welded together.

Other consideration is the strength of the front of the chassis, not sure it is designed to take those kind of loads...

Then there is whether the front is long enough for the a-frame in the first place, and whether you want to have any kind of approach angle at all... :)

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Are you proposing to have the A-frame mounted forward or behind the axle? If you have the A-frame forward, and the radius arms behind, vertical travel will likely make the axle rotate excessively, which you don't really want.

This thread could be moved to the new Modified vehicle builds and special projects section.

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The system you are suggesting allready exists on a producion 4x4, the Auverland A3

In the A3 It works very very well but there is a deceptive amount of complex geometry involved in getting right.

Why not go for a single (or double) triangulated 4 link, well trodden path.

Have a go at the 4 link calculator on pirate if you know enough of the variables.

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phew no tiddle taking!!! soo it could be done ....... the points covered above became glaringly obvious when i went and looked at the front of the trayback... gonna have a mooch around pirate this evening as well, might get some more daft ideas :i-m_so_happy: thanks for the pointers.

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why not do an inverted a-frame setup?

So like the Land rover rear but the other way up on the front.... ball joint mounts on the bottom of the axle and other two arms mount on the top.

Seen quite a few rock crawlers with this setup and you could even use the a frame as a sump guard/slider

you will still have same problem as the land rover rear where the axle steers as it travels through its arch.

like this http://www.pirate4x4.com/forum/land-rover/961915-d90-spidertrax-9-609-build-6.html#post15072062

I would do my links different to this example but you get the idea and its even on a land rover chassis :)

paul

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why not do an inverted a-frame setup?

So like the Land rover rear but the other way up on the front.... ball joint mounts on the bottom of the axle and other two arms mount on the top.

Seen quite a few rock crawlers with this setup and you could even use the a frame as a sump guard/slider

you will still have same problem as the land rover rear where the axle steers as it travels through its arch.

like this http://www.pirate4x4.com/forum/land-rover/961915-d90-spidertrax-9-609-build-6.html#post15072062

I would do my links different to this example but you get the idea and its even on a land rover chassis :)

paul

we did discuss the ball under the axle like the above, can't remember why we dismissed it tho? so if they are rock crawling with this then it must be awful strong to withstand the bangs and scrapes off the rocks, not sure that's the way i'd go. head melted looking at stuff this evening :wacko:

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so if they are rock crawling with this then it must be awful strong to withstand the bangs and scrapes off the rocks, not sure that's the way i'd go.

It really does not need to be any stronger than if it was the other way up.

Its just a different way of looking at it and with front end layout in a land rover it looks like it helps with the packaging.

If your hitting rocks with any force any suspension part or link is hard to keep straight :D

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I think that triangle joint at the bottom is not a very good design for a few reasons:

-big hits from a front wheels are not being tranfered to the chassis as you would like, it is trying to rotate the axle and bend the triangle.

-the roll centre is at the lowest point, meaning it will lean in the corners (and sideslopes) very badly.

I would have links to the axle in a straight line and a third link on top of the axle, offset to clear the engine. Then a panhard or watts linkage at the front.

I did read the banter on the pirate thread about a KOH car that had it like this, and worked, but as usual, there were no solid arguments to explain why, like it works because such and such, but just that car worked so its a good system. Maybe the car worked because of other things, but there wasnt much informed knowledge going on there. Internet chat at its best....

Daan

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As the owner of three A3's (one of which Dan has played with) I can tell you the main problem with this set up is the front overhang needed to mount the 'A' frame to. On the A3 the front 'A' frame is shorter and is curved to shorten the overhang but it still causes issues with approach angle. Mind you in standard form you get 13" of travel and that's with the limiting staps still on; added to which an A3 simply won't run big tyres without a T box change...

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Assuming you use a standard length a frame and radius arms, for the first 10" of axle droop, the axle will roll 18 degrees (back of an envelope calculation). In the next 10" droop, the axle will rotate to 48 degrees. These assume that the vertical separation of the front & rear links is 9".

Even 18 degrees is a problem, but at 48 degrees it's just silly! Hydro steer to some extent will protect you from the worst effects, but the camber change from normal -10 deg to +8 or even +38 deg will mean that as soon as you apply the slightest lock, it will try to wind on full lock in that direction. I think you will really struggle to control it even at slow speeds.

Si

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I would also work on the 'if it works why mess around with it concept' The A3 is the only light 4x4 vehicle I have come across in 30 years that is mass produced with 'A' frame front and I've yet to see more than a couple of engineered specials (and they were carp).

These days you can't turn round for falling over 1 links and they are so simple if you can do the maths and fab

Also what do you want it for? And why?

The A3 that Dan and Jez worked on is up for sale and it's almost finished - I believe the owner wants £1k for it. It's less than 1000kgs is beautifully traybacked and challeneg winged and has a sweet 1.9TD in it

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I would also work on the 'if it works why mess around with it concept' The A3 is the only light 4x4 vehicle I have come across in 30 years that is mass produced with 'A' frame front and I've yet to see more than a couple of engineered specials (and they were carp).

These days you can't turn round for falling over 1 links and they are so simple if you can do the maths and fab

Also what do you want it for? And why?

The A3 that Dan and Jez worked on is up for sale and it's almost finished - I believe the owner wants £1k for it. It's less than 1000kgs is beautifully traybacked and challeneg winged and has a sweet 1.9TD in it

Do you have any pics?

i wonder if i'd get a discount, i never did get paid for the "sweet 1.9td" :(

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Do you have any pics?

i wonder if i'd get a discount, i never did get paid for the "sweet 1.9td" :(

Did you not! Did you tell Mark? He's all wedded and fathered up now so has no time for anything... He has a possible buyer but if it falls through I think a discounted offer might work

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I'd be a bit concerned about fitting a trailing system for the front axle, as per the A3 - the vehicle will dive when braking and this configuration will reduce front tyre grip under braking, increasing braking distances and giving more pronounced understeer.

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I'd be a bit concerned about fitting a trailing system for the front axle, as per the A3 - the vehicle will dive when braking and this configuration will reduce front tyre grip under braking, increasing braking distances and giving more pronounced understeer.

Please feel free to educate us on how you arrived at that conclusion.

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The A3 does dive like a bitch under heavy braking but that is due to it's massive front bias and ****ty back brakes. The fronts are C25 calipers and discs and the rears are escort Mk3 drums. The handbrake works (if that is a word I can use) off the rear drums. As for handling , it's astonishing once you get use to the roll. I took class wins in a number of european endurance events (sub 2.0lltr diesel NA) where due to the lack of power speed was maintained by getting round corners quick. Once you fit a decent turbo lump in them the A3 is a hoot on the road and you can use that rear wheel drive and LSD to its maximum advantage - hell even the NAD is damned quick. It's all about weight balance, springing, shocks, wheelbase and CoG

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Please feel free to educate us on how you arrived at that conclusion.

The standard LR front suspension system causes the weight of the vehicle to act in a thrust manner on the radius arms, pushing back along them into the chassis. The nose dip is reduced, and the tyres are forced down into greater contact with the road. A trailing system would allow much more suspension flex under heavy braking, much of the force being stored in the springs rather than forcing the tyres against the road. It'd be more like how a Series vehicle, whos front axle is essentially trailing on the leaf springs, on soft parabolics behaves, and they do lock up front brakes and under steer much, much more than a Defender, RRC or Discovery - I know because we have a 109 (which now has LR discs all round), a 90, an RRC and have just sold a Lightweight! I also used to own a very comprehensive book about 4x4 suspension design and modification that I studied thoroughly before converting 110 axles to fit my 109.

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Two books I'd recommend:

1. Chassis Engineering by Herb Adams

2. Theory of Ground Vehicles by J.Y.Wong

The latter is very technical and theoretical - but good stuff. The former is more practical and easier to read!

Si

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There's nothing stopping you from creating a trailing system for the front with the right geometry to have the right AS. Should probably even be possible with the standard LR a-frame, would need to run it through the link calculator to see what needs changing though, but I'm guessing more vertical seperation at the chassis end would be a nice start.

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The standard LR front suspension system causes the weight of the vehicle to act in a thrust manner on the radius arms, pushing back along them into the chassis. The nose dip is reduced, and the tyres are forced down into greater contact with the road. A trailing system would allow much more suspension flex under heavy braking, much of the force being stored in the springs rather than forcing the tyres against the road. It'd be more like how a Series vehicle, whos front axle is essentially trailing on the leaf springs, on soft parabolics behaves, and they do lock up front brakes and under steer much, much more than a Defender, RRC or Discovery - I know because we have a 109 (which now has LR discs all round), a 90, an RRC and have just sold a Lightweight! I also used to own a very comprehensive book about 4x4 suspension design and modification that I studied thoroughly before converting 110 axles to fit my 109.

Sorry for the blunt question,

I read the OP's proposed suspension as retaining lower arms mounted behind the axle and an upper A frame mounted forward of the axle,

Having all the suspension arms as you sugest in front of the axle would cause all manner of problems.

Do you know the title and author of the book about 4x4 suspension, i haven't come across anything writen specifically for 4x4's.

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I can't remember the name of the book, and I gave it to a mechanic friend once I had gleaned what little information was relevant to me (anti-roll bar issues). all I remember is that it is an American book, so mostly concentrates on US vehicles, but it covered most suspension types, even though no LRs were featured.

There was certainly one comment about using standard forward projecting radius arms and a trailing A-frame, but it was already pointed out that spring compression would cause massive forces to rotate the axle, and with standard arms resisting that, I suspect that something would break (A-frame ball joint or the radius arm bolts or the axle bracket they fix to). I had understood the next idea was to use trailing arms in conjunction with a trailing A-frame, but may have misunderstood.

The inverted A-frame has the most technical merit of the proposed solutions, provided that it clears the engine and chassis, but it will produce ground clearance issues and is likely to catch on rocks and stumps. Still, it seems far easier to buy or fabricate one of the off-the-shelf kits, and a kit should at least have been tested to make sure it all works and handles well and safely.

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