Perhaps the higher profile tyres on some 4x4s would help a bit? Not the case for some of the newer ones with drug-dealer wheels though.
Slowing down might be the cheapest option of course ;-)
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USP of Citroens I would have thought?
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Espada III - well if you have a family and need a Lamborghini, what else do you drive?
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I agree about spray on tyres on huge steam-engine wheels. Hit a pothole hard and you will get a burst tyre and a bent alloy.
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, which incidentallyis to be replaced by a Panda 4x4 when Fiat pull their finger out and deliver it.
DrChris, Are you sure about this? I had one on hire a few months ago and it was *by far* the slowest thing I´ve ever driven. I was beaten away at the lights by cyclists. The 2wd is fantastic, but the 4x4 is, well, not good IMHO.
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It looked pretty good on last night?s Fifth Gear when it was embarrassing a new Range Rover
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Didn´t see it. I only get the BBC out here in Germany.
The one I tried was petrol. Maybe the diesel would be better, as the pettie version gave a whole new meaning to ´underpowered´.
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They timed the two of them around an off-road circuit and the Panda was leading until it was caught out by the final incline. Basically, it?s so dainty, it doesn?t break the surface tension of the mud. But you?re right, I wouldn?t want to use one daily on tarmac.
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Well almost all of my motoring is around Sunderland at 30mph and when it snows I have a very steep hill up to my house to negotiate. If we go any distance we take the wife's Jazz. So speed does not bother me one bit.
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In my experience 4x4's are better when it comes to forcing your way through a humpy borrows. But it's not about speed. I approach London humpfields in Toyota Hilux Surf with delicate freight strapped in the back, switch suspension to "soft" and then softly and delicately make my way over the traffic calming measures. Vehicle height and type of suspension means there are no hard hits and punches on neither begining nor end of hump mounting procedure, wheels don't knock on wheel arches with very heavy cargo and unlike van, 4x4 doesn't wobble like a scooner full of fish in storm with payload bouncing from wall to wall. Driving through humps is not enjoyable in any vehicle, doesn't matter if it's aircushioned Xantia, robust Landcruiser or handcrafted Maybach. But if I was to be driven to hospital with bursting appendix through mine fields of Chelsea I'd rather someone took me there in all terrain Toyota than regular ambulance.
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4X4s do offer more than just ground clearance. They have suspension components built like brick out houses and are far stronger and more resilient to the appalling road surfaces we pay so hansomly for. I agree that 4 wheel drive doesn't assist with speed humps but that is not the point is it? I don't know of any cars with suspension as strong as the average 4X4.
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\"Nothing less than 8 cylinders will do\"
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Dalglish,
Your repetitive and pointless stirring has been removed.
Get over it. Start it, or something similar, again and you'll be giving me an excuse to do something I have wanted to do for a long time.
Mark.
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Imagine an experiment, where you take a "normal" car, lets say a Mondeo and a 4X4, lets say a Discovery. Then drive them at a constant speed (quite low, say 10-15mph) over a "street circuit" which has, lets say 1000 speed bumps. At the end of 100 laps and 100,000 bumps, measure wear and tear to suspension
components on both. I'd bet that the Mondeo would lose by showing more wear than the Disco's.
If you were to increase the speed, the wear and tear on both would be greater but I'd reckon the difference would remain.
Now, conduct the same experiment but measure ride comfort instead, I'd guess, certainly at lower speeds, that the "normal" car would win due to the more compliant suspension. At higher speeds, both would probably be just as uncomfortable as each other, with perhaps the car marginally better off.
What's my point? If you negotiate speed bumps at lowish speeds (as they are intended to be) then most medium/large cars will be more comfortable than a 4X4. However the wear and tear would be greater to the car. At higher speeds neither is going to be particularly comfortable ........
We currently have 3 cars in the household; A Landcruiser, an Omega and a Yaris and I conducted my own little mini-experiment. At reasonble speeds, the Omega gives the best ride over speed bumps, with the 'Cruiser a close second and the Yaris third. Increase the speed and interestingly, though the Omega still wins, the Yaris pushes the 'Cruiser out to third place.
Make out of that what you will.....
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On some cars, Regular road cars, the optimum comfortable speed over traffic calming measures (humps to you and me) is actually faster than the prevailing speed limit.
I have a bit of 4x4 experience off road, and a bit of 4x4 experience on road, but quite a bit in a Bushi L200. It was HATEFULL over humps. It straddles cushions well, but the agricultural springing of the L200 (and most 4x4's are similar)
did not cope comfortably with humps at the same speed as cars.
My experience? A modern family saloon with well sorted suspension (and lets face it - thats most of them these days) is preferable. Dont forget humps have been around a while, and modern car suspension is designed to cope with them. Most 4x4's are not - but a compromise.
NOt driven cayenne/toerag - X5/3 - or XC90 New RR/Disco so cant include them in my summary.
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Guess work, but I suspect the many bushes in the suspension are the most vulnerable to damage. No doubt LRs and other real off-road vehicles are designed for repeated thumps, but boutique 4x4s?
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Funny you should say that RF. On the cushion type things in my Dad's car, driving at 40 over them pretty much irons them out but in mine makes it a lot worse.
Oh well.
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Adam
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What is the "recommended" speed for tackling these square speed bumps anyway? Both my car and my wifes are not happy at 20mph over the ones in our local road (30 mph area) and I tend to go over them at about 15mph (and get overtaken frequently as a result - idiots, it's because you drive like that that the bumps were put in) but as an experiment one night when the road was deserted I went over at 40, and they were almost undetectable (but I suspect that the suspension wasn't too happy at being worked so hard).
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Yes found exactly the same thing Mr Tower. On some humps 10-15 miles an hour over the prevailing speed limit irons them out niceley.
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I've noticed that. In a car the speed bumps seem easier at speed. Ditto a rough farm lane.
However, in the Landcruiser hitting a speed ramp at speed is horrendous and the first/last time I did it I was fairly sure that I must have caused significant damage.
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as an experiment one night when the road was deserted I went over at 40, and they were almost undetectable (but I suspect that the suspension wasn't too happy at being worked >> so hard).
IIRC (and it's long time since I did Applied Maths) the g-forces exerted on the suspension from a ramp/bump will increase exponentially(?) with speed. So by doubling the speed over the bump you'll probably increasing the load on the suspension by a much higher factor.
* Not sure whether it's exponential or not but it's certainly not linear from what I remember
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Limiting discussion to a simplified hump without any discontinuities, e.g. a raised cosine;
y=h*(0.5*[1+cos(theta)])
with h giving the height of the bump, and
theta being taken between -pi and +pi radians
increasing the speed that you go over the hump is equivalent to increasing the frequency with which you drive the input displacement at the tyre.
If unsprung mass is ignored,
At very low speeds, the car body follows the hump profile. i.e., the suspension does nothing!
At very high speeds, the car body remains in place, and the tyre only follows the hump. The maximum spring force occurs at the top of the hump, and is independent of speed. The maximum damper force occurs when the velocity is maximum, i.e. at -pi/2 and +pi/2 radians. This damper force is linear with frequency, hence, linear with speed.
If the unsprung mass is considered, the precedding is modified significantly. Owing to inertia forces on unsprung mass, the wheel can now overshoot at the top of the hump, and produce impact forces when it lands again.
Above, I talked about low and high speed - this is with reference to the natural frequencies of the car body. Predominantly those relating to bounce and pitch. This is the speed regime where most of find ourselves in when traversing these monstrous hinderances. If you go over a hump such that a) the frequency of the hump matches the bounce frequency of the car, or b) the time lag between the front wheels and the rear wheels going over the bump means that constructive forcing of the pitch mode occurs, then you get very large motion of the body. These are the types of (possibly amplified) motion that going faster over speed humps helps reduce.
Including discontinuities makes the whole discussion much more complex.
number_cruncher
Chad.R - I'm not sure if we are thinking about the same type of mathematical model for the suspension; but I can't think of anything exponential going on in the simple mass / spring / damper type representation that I am currently picturing. It is possible that you are also considering more non-linearities in the suspension components themselves?
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I think I'm getting a headache.
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N_C,
I'm not sure what would impress me more. The fact you knew all that off the top of your head, or the fact you spent hours researching it!
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Adam
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Please accept my apologies for being a bit too nerdy and geeky!
number_cruncher
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Don't apologise since no one is forced to read the posts. Thanks for the info, however, since I was discussing this very subject with a scientific colleague yesterday as our kidneys were getting their twice-daily bashing on the unmade roads hereabouts. The issue was why do corrugations form so readily once rain hits the sand roads and how fast should we go on the corrugations. While I don't follow your explanation fully, it goes some way to explaining why the corrugations form and why they vary in size when the majority of traffic is small bouncy motorcycles!
How fast do you go? We decided it depends on who is paying for repairs to the vehicle.
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Wow. I can't remember where I read the non-linear theory but I'll bow to your (obviously) much greater knowledge on the subject.
I wonder if progressive spings had something to do with it?
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One bit I missed from my post was that the inertia force of accelerating the unsprung mass is proportional to speed squared (via double differentiation w.r.t. time of the displacement input). I think this mainly affects the propensity of the unsprung mass to overshoot, because, as an inertia force, spread over the entire unsprung mass, it may not cause much actual stress - except in the spring as it compresses more during overshoot.
My suspension and dynamics knowledge is, technically, very limited - old hat, or strictly undergraduate, perhaps. My post discusses linear theory, which is, however, a very good starting point. Most dynamics papers of the last 10 years or so have moved on to consider non-linear aspects of suspension design, and, of course, active control of suspensions.
Discontinuities, for example, a triangular hump are difficult to deal with - but I'll have a go!
Via a theory which we owe to a Frenchman!, one can build up any shape (subject to some restrictions) by adding together a weighted sum of different sine, or cosine waves of differing frequencies. So, as you pass over a triangular hump, it is like traversing a whole set of cosine humps - all at different speeds! All adding together!
This is why triangular humps are, for their size, so nasty! There isn't a good (reasonable) speed to go over them, because you will always be hitting some of the many equivalent cosine humps at the worst possible speed.
number_cruncher
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Many off-roaders have non-independent suspension at both ends, which means they have a high unsprung weight. That means the wheels don't follow the undulations at speed as well as on an ordinary car, due to the inertia of the heavy axles in the vertical plane. So the bumps can get transmitted to the whole vehicle more.
When doing off-road trials in my late, lamented Land Rover 90, the rule of thumb was to always take it slowly and gently to avoid breaking anything or bouncing too much.
Cheers, Sofa Spud
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That reminds me. Managed to snap a leafspring on a Sportrak I had a few years back. Absolute hack of a car, used as a pick-up and towing vehicle that I could also sling muddy mountain bikes into and damp canoes onto.
Still didn't like speed humps though.
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My Range Rover has electronic air suspension which gives a very comfortable smooth ride. However, as per Mark, I too have hit a speed bump a bit too fast and the bounce was incredible. It felt like the rear wheels came off the ground and I wasn't travelling that fast.
The track of the car does allow me to straddle the square humps though which is useful.
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\"Nothing less than 8 cylinders will do\"
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