Wednesday, Jul 13, 2016 at 13:15
" 1. With about 180-200 kg van ball weight, will the
Ranger need heavier springs or other
suspension support? "
No car should need any additional support that is not recommended by the car manufacturer. If the rear end is sagging then it is the owner who has done something wrong, not the manufacturer.
There are a couple of points to keep in mind before you start changing the rear
suspension design.
1. Have a look at all leaf spring rear suspensions. The linkage on independents work the same way. You will see the front eye of the spring has been mounted down at around axle height while the rear shackles are up a lot higher. The spring has a single front mounting point so the wheel can only swing up and down in an arc. It can not move up and down vertically.
When the car is fully and correctly loaded, the spring will be sloping up
hill to the axle. As it does this both wheels move forward towards the front of the car. When the car leans into a corner, the spring on the outside of the corner will compress a little more taking the wheel up closer to the chassis and further forward. The spring on the other side will have weight taken off it so the wheel will go down a little and further back towards the back of the car. The whole axle has now been turned slightly in the direction the car is going.
In the meantime the side stress on the tyres has distorted them forming an angle between where the wheel is pointing and where the tyre is pointing. That is known as the tyre slip angle. If enough side forces are applied to them they will let go and slide resulting in the car spinning.
By tilting the axle in towards the inside of the corner, you will reduce the tyre slip angle resulting in them hanging on a bit longer and hopefully enabling you to get around the corner. This is known as roll understeer and it is not the same as ordinary understeer.
If you overload the rear end of the car then lift it back up with heavier springs or air bags, you can very easily destroy this vital handling stability feature.
2. Go about two thirds down this page
understeer/oversteer and look at the drawing of the two cars understeering and oversteering. These two features are controled by the amount of weight that is placed on either the outside front or rear tyre in a corner. It is altered mainly by springs, sway bars and tyre pressures.
Just about all cars have been designed to understeer. By overloading the rear end and fitting heavier springs or air bags, you will quite likely change the car to oversteer.
Do you really want to be driving a ute with a big caravan and a
suspension that is now prone to swinging its tail out in oversteer and has lost most if not all of its roll understeer feature?
There are countless cars with modified rear suspensions towing big vans all over the country. Their owners will tell you they feel very stable and no doubt they do. The real
test of stability will come though if if you ever have to swerve suddenly at speed to miss a big hole in the road, another car, a cow or whatever or if the van is knocked off its straight ahead course by high wind or change in road surface. That is when your standard
suspension can instantly become a life saver or your modified
suspension your worst nightmare.
Don't play around with car suspensions unless you know exactly how they work in the first place.
This article
bent utes can be very useful when towing heavy loads with a cab/chassis vehicle. The problem is caused by too much weight too far back behind the rear axle resulting in the end of the chassis constantly flexing up and down. It can happen with 2wd utes in cities but is much more prevalent on 4wds on unsealed roads. The car does not have to be over or even up to GVM to do it.
AnswerID:
602370
Follow Up By: gbc - Thursday, Jul 14, 2016 at 05:36
Thursday, Jul 14, 2016 at 05:36
You give manufacturers too much credit. Commercial twin cabs are set up for driving around empty with an occasional load. Add bullbars
winches canopies towbars caravans etc, of course the
suspension is going to need changing if only to get back to normal trim. Dragging its arse down the street is not normal. I've never had a commercial ute that could handle constant load straight out of the factory. They all get tuned according to what they carry.
FollowupID:
871973
Follow Up By: splits - Thursday, Jul 14, 2016 at 19:45
Thursday, Jul 14, 2016 at 19:45
gbc posted:
" I've never had a commercial ute that could handle constant load straight out of the factory. "
I have never had any problems with the two that I have owned.
"They all get tuned according to what they carry."
That is where all the problems stem from because many try to take them up to maximum weight or beyond but the way they do it is outside their design limits.
Take the seats for example. You often see one carrying mum and dad with three kids of primary school age. There is nothing wrong with that except their combined weight may not be any more than 200 kgs.
One manufacturer that I contacted said they work on 85 kg per person plus 15 kg for clothing, brief cases and all the other things that people put in the cabin. That means around 500 kg in the seats before you start adding anything to the back.
That may not suit many people but it has to be that way. It is no use designing them to carry no more than the weight of five jockeys. There are countless families with a combined weight
well above that.
Maximum weight in a car means every load bearing area must be carrying its maximum share of the load.
Anyway how you load one is your business. All I have done is draw readers attention to a couple of basic
suspension design facts that you will find in any good
suspension book. If you want to put heaps of weight on the rear end then lift it up with stiffer
suspension, you will change the way the car handles but the difference may not become obvious until it is too late.
FollowupID:
871999
Follow Up By: gbc - Friday, Jul 15, 2016 at 07:53
Friday, Jul 15, 2016 at 07:53
We aren't talking "at the limits" or "right at the back".
A normal twin cab with 350 - 500 kg of constant load will not do that job properly without a spring upgrade. The exception might be the last dmax/Colorado which scored a wheelbase extension in cab chassis model. The rest are good enough to get out the showroom and not much more. You are trying to whip up hysteria when no one here has mentioned overloading or being anywhere near limits. I've seen the article you read, it's been trotted out before. Bottom line, a Px twin cab towing 2.3t and a 'normal' amount of holiday gear in the tray is going to look like a dog with worms and handle like custard. A 'normal' Spring upgrade will improve the rig in every way.
FollowupID:
872010
Follow Up By: splits - Friday, Jul 15, 2016 at 09:37
Friday, Jul 15, 2016 at 09:37
Bottom line, a Px twin cab towing 2.3t and a 'normal' amount of holiday gear in the tray is going to look like a dog with worms and handle like custard. A 'normal' Spring upgrade will improve the rig in every way.
That may be true but does the manufacturer claim it will tow a 2.3t caravan or anything else for that matter? They just list a maximum possible weight and that is usually for sealed roads only. It should be reduced for off road conditions.
I have yet to see any information from any manufacturer stating what their cars can tow. A 2.3t dog trailer for example would most likely put about 25 kg on the tow ball. One weighing the maximum towing capacity of the car could be much the same or maybe a little more. As long as the car can safely tow something that weighs the maximum then it has complied with the manufacturer's advertising claims.
If it can not do that then if is a case of false advertising and it is then up to the manufacturer to fix it. Do you really think a manufacturer would claim their car can tow a certain amount then hope some other company makes some parts to enable it to do it?
"I've seen the article you read, it's been trotted out before"
Do you mean this one by Maurice Olley?
chassis design If not then you will find what I said in it as
well as just about every other book on suspensions.
I suggest you read it. It is the one that all cars today are based on. You won't find any hysteria in it.
FollowupID:
872017