Jump to content

Axle wrap/tramp control


Snagger

Recommended Posts

Now before i say anything, i want to make it clear that A: i do not want to reignite this into a snuffle and B: where i cannot claim that i know all, and that everyone else is wrong.(because to be honest, im only 20 and theres a lot more technically minded poeple out there that have been doing this stuff longer than ive had hot dinnerrs) BUT, i have studied steering and suspension geometry at university quite in depth and can offer my input as to what i have learnt.

"How have you not lost ground clearance by lowering the spring seats? Drive down a set of deep ruts and see how much your U bolts dig in!"

something i would quite agree after having a few different sets of leaf springs under my truck, all of varying depths from the bottom of the axle tube.

The spring plates are slightly lower than before, but still higher than they would be with standard leaf springs - parabolics are much thinner in the middle.....

.....Losing about 1/2 clearance under the springs compared to before makes little difference - the diffs are still by far the lowest points...

the first bit there is a fair point, using parabolics does decrease the cearance issue by around 2-4 inches on the front

however from past experience i know that 1/2" clearance loss under the spring hangers can make the world of difference in an off road situation. i have ample experience where i have followed a 90 or 110, on the exact same size tyres, down the same ruts, and not made it. this is because while the diff is the same height, and therefore not a problem. the way the ruts have been carved out by the more common coiler vehicles, means you have to dig/skim your own clearance for the spring plates and this can be a real problem, especially as they are shaped to dig in!

so already, regardless of what springs you have, theres a disadvantage, and while you could argue that the front radius arms are roughly in the same place and therefore would plough for you, thats not really the case, as they are set out wider than land rover leaf plates, and even then, they are smoothly curved and tend to slide over obstacles much more than those darned anchoring spring plates!

can you tell i dont like these spring plates yet? But on standard axles at least, there is an advantage over stock springs to be had with parabolics, and even more of an advantage should you work out how to minimise the profile and anchoring properties of those plates without hindering the spring curve properties

......As for the Ackerman issue, it's basic physics. On a mostly road going vehicle, it's a benefit to have it, otherwise it wouldn't be incorporated in the design of cars. I don't need to experience neutral Ackerman to know it's not a good idea, just like I don't need to experience jumping off a cliff to know that's a bad idea too.

This is not strictly 100% true. according to my studies (both in books such as hilliers fundimentals, and my previous experiments when we had a steering circle issue on our off road buggy that we built) the ackermann geometry is not there to improve the cornering performance or stability per say, who knows, it might be an added benefit, but was brought up to reduce tyre scrub whilst turning at low speeds, and also dramatically reduce the turning circle of the vehicle as a result of this.

i have read this in books, and seen it in real life.

the amount of ackermann angle is not too crucial on something like a land rover or an off road buggy such as the one we made, but the optimum changes in relation to the length of the vehicle wheelbase. i.e. the construction lines of the angle should intersect each other at the centre point of the rear axle. whether the arms point forward or backwards is irrelevant, HOWEVER. it is not irrelevant if the arms are designed to point backwards but have been turned round. this will result in more steering lock on the outside wheel and less on the inside wheel. dramatically increasing the turning circle and tyre scrub.

not something too obvious at low speeds round a yard in an old land rover, but try having reverse ackermann on a go kart, you would constantly be in the tyres.

just my 2p :)

Link to comment
Share on other sites

I'll be coming down there for a week in October with the family, Grem. Get the sprinklers on in September, will you?

I will try.......good we can meet up over a beer for some LR chat..........you can also still swim as the sea is lovely in october.

G

Link to comment
Share on other sites

The Ackerman bit is pretty much what I was saying - I need a tight turning circle, and the Ackeman not only helps that but also reduces wear and tear while doing it. And like I said, the steering arms need to be divergent ahead of the axle or convergent behind, so fitting a track rod ahead of the axle was not going to work well for me.

I take your point about the spring plates. Every solution is a compromise, though, and there was no way for me to fit the new axle with slimmer saddles without both notching the axle case for the right spring to sit into the neck of the diff housing and fitting that frontal track rod with the associated issues that would cause. To that end, the compromise of having the spring plates about 1/2" lower than with the previous axles, which was higher anyway than with standard springs, is not a bad one. Considering that it's really for roads and tracks, not heavy off-roading or rock crawling, it won't affect me much. By trimming off the excess of the U-bolts to minimise the protrusion, you can help reduce the problem, and you could fit some sort of profile to the front edge to try to stop it digging, if you find it causes trouble in your use of the vehicle, though they'll never be as low resistance as radius arms. But without a coil conversion, I can't get rid of the plates, so it's an issue that will have to stay. Thankfully, it hasn't had any effect on me anyway.

Link to comment
Share on other sites

The Ackerman bit is pretty much what I was saying - I need a tight turning circle, and the Ackeman not only helps that but also reduces wear and tear while doing it. And like I said, the steering arms need to be divergent ahead of the axle or convergent behind, so fitting a track rod ahead of the axle was not going to work well for me.

I take your point about the spring plates. Every solution is a compromise, though, and there was no way for me to fit the new axle with slimmer saddles without both notching the axle case for the right spring to sit into the neck of the diff housing and fitting that frontal track rod with the associated issues that would cause. To that end, the compromise of having the spring plates about 1/2" lower than with the previous axles, which was higher anyway than with standard springs, is not a bad one. Considering that it's really for roads and tracks, not heavy off-roading or rock crawling, it won't affect me much. By trimming off the excess of the U-bolts to minimise the protrusion, you can help reduce the problem, and you could fit some sort of profile to the front edge to try to stop it digging, if you find it causes trouble in your use of the vehicle, though they'll never be as low resistance as radius arms. But without a coil conversion, I can't get rid of the plates, so it's an issue that will have to stay. Thankfully, it hasn't had any effect on me anyway.

just out of interest, if your running coiler hubs, and series springs, how do you get on with the rear track rod system, as i have coiler hubs on series axles, and i have series steering arms. i then cut off the rearward track arms as they hit the lower shock mounting eye. so lock was seriously reduced. does your track rod clear the shocks or are you running a different setup?

Link to comment
Share on other sites

I used 88" rear spring plates to move the dampers forward, close to the axle case - since the swivel mounting flange is now well outboard of the dampers, you can afford to move the dampers forward like this for track rod clearance. As it happens, their aft end droops less than the 109 version, so my ground clearance is ever so slightly better too. ;) Everything is clear of everything else, even at full lock.

Link to comment
Share on other sites

The U bolt spring plates can be flipped and swapped left to right and fitted on top of the springs instead of below and be welded to the spring saddles. Square U bolts ala Hilux can then be fitted from below the spring with the nuts above. To gain 3/8'' or so under the springs when doing this, I used to cut a rectangular shaped hole in the spring plates and recess them over the spring saddles. I made different upper shock mountings for longer stroke shocks anyway, so the higher lower shock mounting below the axle didn't create shock bottoming issues. The slightly increased effective spring saddle length may actually reduce axle wrap too.

Link to comment
Share on other sites

  • 1 month later...

I've done the engine mount, so the prop won't contact it any more. I might take it to the MoT test centre to put on their rolling road to see how much of the diff movement was from wrap and how much from spring compression - the rollers will only produce the wrap effect, after all. What I have now should be similar in effect to what I I had before the axle swap - the leaf springs would have allowed wrap under braking, with the associated steering and transmission effects it had. I don't think the disc brakes are much more powerful than the drum brakes, so the wrap should be comparable, and the third leaf on the front springs must be helping. I don't have any witness marks on any steering or suspension components of parts contacting each other - it was just the prop and engine mount.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...

Important Information

We use cookies to ensure you get the best experience. By using our website you agree to our Cookie Policy