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Bowie69

Thoughts and musings on the Ineos Grenadier

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On 5/1/2020 at 1:50 PM, WesBrooks said:

Final question on the handling characteristics though (it does fasinate me but not had the time to find a decent affordable book to read) is beam axles do have their own perculiar handling characteristics compaired to the run of the mill road car right?

Absolutely. Came across this post yesterday that's also very interesting: https://www.reddit.com/r/cars/comments/felfna/2018_ford_f350_death_wobble/fjp3ypm/

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2 hours ago, Snagger said:

A lot of older road cars have live beam rear axles, and I think most US muscle cars still do.

And they're renowned for their handing :lol:

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Yeah, a lot of economy UK/EU front wheel drive vehicles have (not live) beam suspension at the rear too. It's the front that causes most chaos with the road manners.

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49 minutes ago, WesBrooks said:

Yeah, a lot of economy UK/EU front wheel drive vehicles have (not live) beam suspension at the rear too. It's the front that causes most chaos with the road manners.

Witness a lot of pickups & vans - independent front (usually from a car) and a beam rear with leaf springs.

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3 hours ago, FridgeFreezer said:

And they're renowned for their handing :lol:

That why the US had to build straight roads and grid iron cities! 😜

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He he yes, I dodged that comment. Random citations in US marketing such as peak G forces a vehicle can exert when going around a corner, rather than a far more real dynamic test.

I Apologise for dragging this off track! 😄

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12 hours ago, WesBrooks said:

Yeah, a lot of economy UK/EU front wheel drive vehicles have (not live) beam suspension at the rear too. It's the front that causes most chaos with the road manners.

Not just economy models , the sport models are usually a beam rear too 

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Big thing about beam-axles at the front is the 'unsprung mass' - the combined mass of the wheels/tyres/discs/calipers/suspension-swivels/halfshalfs/CVs/diff/axle-casing and a proportion of the propshaft-weight - which gets slung-about whenever the wheels hit bumps/potholes.

The suspension-damping/steering system then has to handle a couple of hundred Kg mass that's now moving in something other than a nice predictable vertical up-and-down motion. Hence the dreaded "Death-wobble" when you drop a wheel into a pothole while going round a corner.

Try catching an entire LR front-axle, complete with wheels/tyres when it's thrown at you to understand the 'unsprung mass' issue.

Proper independent front-suspension means that the suspension only has to handle the oscillating mass of the tyre/wheel/hub/hub-carrier and half the mass of the driveshaft. So it can react much more effectively to road-events that cause wheel deflection, largely because it's not having to calm-down the bouncing of a load of lumps of iron.

Same goes at the rear: lots of 'rough' roads in US/Australia have ridges that trigger oscillations between the vehicle-mass and axle-mass at certain speeds: back in the days when RWD US 'estate-cars' were still popular some of them had four shock-absorbers - two vertical, two at something like 35-45 degrees to the horizontal - to try and control the axle-tramp on such roads.

Independent suspension - with intelligence - reduces unsprung-mass and allows the computer to tweak the damping in real-time to 'catch' a wobble/tramp before the driver gets to know it's happened.

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Posted (edited)

I did catch a few interesting articles on unsprung mass a while back including some that mentioned in some cases the weight of the axle could make the tyres work a little more at absorbing road vibrations (at some frequencys) before they are transferred to the body. I guess for us that's countered a bit by heavier duty tyres and additional vibrations from aggressive treads!

I'll look up the death wobble closer as I've seen that mentioned many times. I guess it's almost as effective as ice for one end of your vehicle sliding out if you catch it on a corner.

Edited by WesBrooks

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Death wobble is caused by vehicle defects, not by live beam axles, so can affect any vehicle.  Unsprung mass is higher on live beams as you said, but for utility trucks, does it matter?  We’re not racing and don’t need ultra sharp handling.  Claiming ECU adapted damping rates as a benefit of independent suspension is misleading - if you wanted to, you could have automatic tuning for dampers on live beam axles too.  But the Grenadier is supposed to be getting back to basics and dumping all this expensive and inessential electronic complexity, so you’re missing the point if you think live beam axles are a detractor of this vehicle.  Do live beam axles fare worse on washboard roads than independent suspension?  Is suspect it has more to do with spring and damper rates than independent suspension or unsprung weight, but instead of complex adaptive systems to deal with it, how about changing your speed to avoid harmonic frequencies - seems cheaper and more reliable to me, and doesn’t continue to hammer the wheels and hubs. 

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1 hour ago, Snagger said:

how about changing your speed to avoid harmonic frequencies - seems cheaper and more reliable to me, and doesn’t continue to hammer the wheels and hubs. 

But requires a certain level of driver skill and understanding what the problem is...

Independent suspension will, all other things being equal, perform better on a washboard road simple because there's less unsprung mass to control. But the engineers have to look at the bigger picture and work out what will do the best job for the vehicles overall intended uses.

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... which in this case is beam axles.  They are generally much better for most off road situations, especially for working vehicles.  That describes Grenadier pretty accurately, as I understand it.  
 

As for changing speeds to avoid harmonics needing a level of skill or understanding, if people can’t work out that being shaken about and having control issues means you need to slow down, then they shouldn’t be driving!

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Death wobble can occur at any speed even with a well maintained vehicle, in my experience.

Obviously more threatening at higher speeds :) 

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5 hours ago, Bowie69 said:

Death wobble can occur at any speed even with a well maintained vehicle, in my experience.

Obviously more threatening at higher speeds :) 

Put slightly oversized tyres and/or offset rims or spacers on a coil-sprung Land Rover/Range Rover of beam axle vintage and then take the steering damper off and you could very easily discover how scary that wobble is and how suddenly it comes on (I've also had it on a leaf-sprung Series 3 but there is less "play" to amplify the effect with leaves).  For me, that steering damper kills the handling so I have removed it on various vehicles, out of interest - and reinstalled it very soon afterwards!  We used to call the phenomenon "tank-slapper" in motorbike days.  In either case, it is both unnerving and potentially quite dangerous.  

The dynamics are well understood now and good design means it shouldn't happen on a properly maintained vehicle.  We shouldn't forget all those huge trucks and trailers running round on beam axles and staying confined, for the most part, to a narrow part of the road.  It's pretty much vital the Grenadier has beam axles, so it's a very good thing that the system is sorted!

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Must admit I’ve never had any kind of death wobble, even when pressing on and for almost the entire time the truck was on the road I never ran a steering damper either. 

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It's occurs more in my experience when the wheel is unloaded a little, and you hit a bump.

So, when pressing on, you tend to be loading up the suspension pretty well, so less likely to happen.

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And when there is insufficient preload on the swivels. The spring scale is very important.

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Yep, though I get better result by feel.

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8 hours ago, Gazzar said:

And when there is insufficient preload on the swivels. The spring scale is very important.

IMHO this is the most common reason for LR wobbles, but as per a previous comment due to lack of maintenance or understanding during rebuild.

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Those are the points I was making.  Set the swivel preload and have the correct steering damper, which is part of the standard design, and death wobble doesn’t happen.  In 23 years of regularly driving my 109, even for the first few years with absolutely knackered swivel pins and bushes, and 15 years of driving my RRC, I have not once experienced it.  I’ve had worsened effects of hitting pot holes, the exacerbation of offset rims or spacers (both something I learned to hate), but never death wobble, because my tyres and rims were relatively standard size and mass, because the steering damper was always correctly functioning, and because I tried to eliminate the play in the steering system (even though in the early days I didn’t understand about the criticality of the swivels).

Almost every question on these forums and others relating to death wobble involves a vehicle with oversized and very heavy wheels and tyres.  That spinning mass has a huge effect, much more than the suspension parts or choice of live beam versus independent suspension, on how the vehicle responds to the road.  Think of those gyroscopic forces and how increased mass and increased radius exponentially increases them.  Fit oversize wheels to a vehicle with independent suspension, add a little wear and take out the steering damper and I’m sure you’ll find nasty effects there too.

As a slight digression, because of the mass and also the gyroscopic effects of bigger tyres, anything larger than standard should be accompanied by an appropriate increase in steering damper rate.  Retaining the standard damper with 35” bog tyres on 8” rims is clearly inappropriate.

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Pah, death wobble ! Wait until you get the steering hammer from a knackered Panhard bush. That's sixpence - half a crown territory 😂

Mo

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i haven't encountered death wobble on my 90 at all so this is a bit puzzling for me. I regularly drive on various road surfaces at speeds from 20 - 70mph, i'm fairly sure my swivel pre-load is wrong, my dampers are sh*tpart as are my springs and steering damper and i've got steel modulars with standard tyre sizes. Is this a common occurrence in defenders?

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19 minutes ago, paime said:

i haven't encountered death wobble on my 90 at all so this is a bit puzzling for me. I regularly drive on various road surfaces at speeds from 20 - 70mph, i'm fairly sure my swivel pre-load is wrong, my dampers are sh*tpart as are my springs and steering damper and i've got steel modulars with standard tyre sizes. Is this a common occurrence in defenders?

Only if you don't do any maintainance.

I've never had it either but I have seen the white face afterwards.

Mike

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I don’t know if weak suspension dampers would affect it, though clearly they’re not good for most handling issues.  But I haven’t heard all that much negativity about Britpart dampers anyway, in fairness - maybe they’re one of the product lines they get right (or right enough).  But 7” modulars are a standard Lr size - that’s what all the alloys and the Discovery 1 steel five-spokes are, so those with normal tyres don’t seem to cause the problem.  I had similar 8spokes and 7.50s on my 109 with truly terrible swivel pins and no trouble.  Then again, it was using a worn out 2.25 petrol when I bought it and a 12J later, so maybe a lack of speed was also responsible.

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Face it, most LR owners wouldn't notice if you replaced all the bushes with soft cheese and unbolted the dampers entirely, they're usually just happy the damn thing's working today and that the MOT man didn't see the cardboard and bathroom sealant "welded patch" on the chassis.

Number of cars you see driving along with one almost-flat tyre and no-one notices that, I think finer subtleties of handling are lost on most of the population.

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