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post #1 of (permalink) Old 10-17-2000, 11:41 AM Thread Starter
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Some Dangers Of Suspension Modification


When you put over sized tires on a Jeep or any other vehicle, no one considers what happens to the rest of the suspension and drive line...

The first thing that happens is you over stress the lug studs trying to bolt those giant wheels on with 'universal' one size fits nothing lug nuts.
Then you stress the lug stud way past what it was designed to handle, and nearly twist it off trying to keep a wheel that is going to over stress the lug studs way past any acceptable limits time and time again....

The second thing that happens is the wheel bearings take a beating because no one gets the back spacing on the wheels correct, and the longer leverage line created by the taller tire and wheel combination multiplies the side loading on the wheel bearings, along with the lug studs and every thing else....
It's like pulling sideways on the bearings with a short handle ratchet, which the bearings were designed to hold back,, then putting another 18" longer breaker bar on the ratchet...
Suddenly the wheel bearings are taking up to 15 times the side load that they were ever designed to.
And instead of getting the very best bearings you can afford, you are buying Japanese junk at auto-jerks cause it's $1 less...

Then you have to consider the steering angles.
In one quick minute you just screwed up years of suspension design and testing...
The spindles, ball joints, steering knuckles, ect, were never designed to have the extra load the leverage the taller wheels and tires are going to produce.
Parts wear faster, parts fail, you get vibrations, the front end 'shimmy', the vehicle wonders all over the road, tires wear on the edges, or cup out, or feather edge, the steering won't center correctly any more, ect, ect,....
Mostly just damned dangerous to operate at highway speeds with all the wondering around...

All symptoms of incorrect front end suspension geometry, usually caused by oversized tires and wheels with incorrect back spacing.

Now, lets move to the brakes....
With the extra leverage that taller wheel and tire combinations give, the brakes take a beating!
With the increase of the leverage on everything else, you have to consider the increased leverage on the brake friction surfaces.
Longer distance between the centerline of the wheel, and the ground mean that you just gave the wheel a longer ratchet handle to pull on the brakes with.
Considering that the factory, like all factories, use the absolute minimum they can get away with in the first place, then you multiply the load, and it's a recipe for disaster.

Then add some lift, either body or suspension, to clear all that tire and wheel...
Without any regard for simple physics, you raise the center of gravity, and compound all the above problems, plus create more instability, and throw the suspension and steering geometry even further out of working specifications...

So, In the end, what I am left with,
(when it comes down to my life over yours, you will hear me say 'I' a lot...)
Is a oversized, overweight, over centered, top heavy, nearly uncontrollable vehicle, that has all suspension parts stressed way past acceptable limits, and can't even stop acceptably if something should occur, hurtling down the highway at me on nearly a head on collision course, at somewhere between 55 and 80 miles per hour, oblivious to the fact that he's endangering every life around him.

Anyone in the vehicle, and anyone on the highway... (namely, ME!!) are in the 'Stupidity Kill Zone'....

And people wonder why I keep my airbags serviced and wear my seat belts...
It's so they can find my body after some rambo wanna-be looses control and slams me head on....

"I Have The Body Of A God... Buddha"
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post #2 of (permalink) Old 10-17-2000, 12:00 PM
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Re: Some Dangers Of Suspension Modification

Yep. You are absolutely correct, sir.

Just a question though, aren't safety factors built into the engineering? You know, like a safety factor of 1.5, which is what we used during our design classes, or 1.9 when working on heavier vehicles.

I purposely went to larger axles with larger brakes for the Scrambler, stopping is a necessity. All the modifications are also to excess, so the rest of the vehicle will literally have to tear apart before my mods fail.

As to the rest, I drive my Scrambler, which is pretty heavily modified, to and from the trails, and it typically sees about 3,000 miles a year. It also does about 55 top end on the road. Is it dangerous? You bet, but then I don't drive it like a race car, I drive it a lot more cautiously than I do my motorcycle, because I realize it's a lot more dangerous than most vehicles on the road.

I also realize that with the larger tires it creates excess stresses on different parts, which is why it usually gets the once over at least once a year, when everything is torn down and looked over. As to tires, bearings, and joints, they're cheap to replace or inspect.

First and foremost on my mind is that I'm driving an altered vehicle, which I have altered. This means if I get into an accident it'll be looked over with a fine tooth comb to see if I screwed up somewhere. The state also has laws regulating the amount of lift and other important factors, so staying within those guidelines assures me a margin of safety.

A lot of the over the counter modifications are also "engineered" to be a direct replacement, so driveline angles are kept within specifications for that model.

You are absolutely right about the modifications though, they can be dangerous, and a lot of people just take them for granted, but not me.

'81 CJ-8 Scrambled!
GM151/SM465/NP205 twinstick/7" Lift/33" Swampers/REP 8000/RS9000's/Scout II D44's F&R w/4.10's & Lockrights
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post #3 of (permalink) Old 10-17-2000, 12:01 PM
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Re: Some Dangers Of Suspension Modification

good points TR but why the anger? something happen? just curious

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post #4 of (permalink) Old 10-17-2000, 12:03 PM
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Re: Some Dangers Of Suspension Modification

It should be noted that even stock vehicles are dangerous when driven incorrectly....just because the Jeep or Explorer or whatever has 4 wheel drive doesn't mean it can be driven down a slick road at 25MPH over the speed limit. On dry highway, it won't handle like a sport car; I wish some crazies would stop driving them like it was one....

It could very well be that some of the causes of the Explorer/Firestone rollovers are driver error.[img]/wwwthreads_images/icons/frown.gif[/img]

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post #5 of (permalink) Old 10-17-2000, 12:08 PM
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Re: Some Dangers Of Suspension Modification

I learned my lesson with wheel backspacing the hard way. It is so important to run as deep a backspacing (or as close to stock whatever the case maybe) as possible.

That is why I believe (all things considered) tall skinny tires are the best off road choice, especially if you are going to drive them daily.

So TR what do you drive?

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post #6 of (permalink) Old 10-17-2000, 12:08 PM
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Re: Some Dangers Of Suspension Modification

Thats a fact.
I have hundreds of hours and thousands of dollars in tghe modification of my YJ to a point where everything works well together.
The brakes have all been upgraded, with bigger booster, 4 piston race calipers in the front, discs inthe rear and high quality pads at all 4 corners.
The axles are moser high strength.
The steering is a custom made set up using high strength 3/4 " chromemolly tie rods ends from AFCO Racing, the tie rod and drag link are 1 3/8" chromemolly solid rod.And everything has been modified above the axle to maintane optimum angles.
Suspension has numerouse modifications to allow the lift be adjustable and controllable.
My YJ although lifted close to 8" and running 35x12.50 15 tires is actually very controllable on the highway, and is noot the nightmarich swerving ride sometimes related to this type of vehicle. But it has not been easy to get it to that point.
I also constantly have to check components and, I dont drive it like a race car on the road(or off, for that matter), I rarely ever drive over 65mph.
Im also not a good enough welder to trust my own welding on suspension and steering, modifications. So I only design and tack weld into place, then have either my structural steel welding pros, or local pro welders finish it up. My welding is getting much better, but I contain it to racks and other non life threatening peripheals(I would love to get a chance to train under a great welder, and really learn what Im doing).
TR is very correct though.
Its definitely not a matter of putting on some arched springs a body lift and big tires then your done. And even if done right common sense still is very essential when on and off road.Rollovers are very posiible.

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post #7 of (permalink) Old 10-17-2000, 12:17 PM
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Re: Some Dangers Of Suspension Modification

Absolutely Correct, Jeff, the most important part of any vehicle is the gray thing between the ears of the owner/driver!![img]/wwwthreads_images/icons/smile.gif[/img]

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post #8 of (permalink) Old 10-17-2000, 12:43 PM
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So.... What\'s yer point?

Some interesting informaiton there, and some points that should be brought up, but also a lot of assumptions, and incorrect things I would hardly call "fact" as you did.

So what is the point of that little post? Come on - offer up some suggestions, corrections, etc.

So you figured out what is "wrong"... nothing new there, that stuff has been hashed around a million times on every BBS and mailing list I have ever read... Tell us how to "fix" it and that is an accomplishment [img]/wwwthreads_images/icons/cool.gif[/img]

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post #9 of (permalink) Old 10-17-2000, 01:06 PM
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Re: So.... What\'s yer point?

I am more afraid of a loaded 18-wheeler with a driver that thinks that sleep is not an option.

TR, it seems the vehicle you described will not move forward with out falling over first.

I would hope that most of us are responsible enough to take some if not all of these factors into account when we are modifying our rig. If they don't, they should try.

I agree that we sometimes need to be reminded of safety issues associated with our hobbies and we all should consider the things that TR has said, but we have to be reasonable. A 31" tire and a 1" body lift is not going to cause a TJ to break in half and explode into flame.

I have BFG 35-12.5 15 tires and can still lock the brakes and skid all four tires on dry clean pavement with no brake mods. I agree that the leverage has change but I believe that I am still within limits.

Anybody that doesn't regularly service and check his or her wheel bearings etc. is asking for trouble no matter what mods have been done.

In all the years that I have been driving and all the different 4X4's, wheel tire combinations, race cars, and big hp engines, I have never had a failure related to tire size, rim back spacing, steering geometry, or any other part that I have modified to achieve a certain goal.

That's not to say that I haven't failures. I have blown transmissions, differentials, and an engine or two but it was certainly pilot error (ego). I can break anything if the old ego gets involved.

I guess that my code or creed is to stay on top of service and maintenance of my vehicles and try to consider all after affects when adding or modifying suspension parts or systems. A small bit of reason and common sense will go a long way to make things safer.

Drive safe.

post #10 of (permalink) Old 10-17-2000, 01:38 PM Thread Starter
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Re: Some Dangers Of Suspension Modification

I was an 'expert' witness a while back in a civil suit, and the judge in that case just subpoenaed me to testify as an independent witness in a new trial...
I just got the brief.

A moron took an old bronco, put 40 tall tires on it, a homemade lift kit, and no insurance, and lost control on an Interstate.
Side swiped another car, and that car lost control and caused a truck to crash into several other cars.

The guy in the bronco that caused it all didn't get hurt, but a 3 year old girl was killed, and 2 other people seriously injured (one with spinal cord injuries).

As far as I'm concerned, the bronco owner is guilty of vehicular homicide, (man slaughter).

It looks like he took an on ramp at about 70 miles an hour, and one of the steering knuckles gave way, launching him across three lanes of traffic going his way, and four lanes going the other way.


I guess the moral of the story is, Unless you have an education in engineering, don't attempt to do body lifts and change to grossly over sized wheels and tires unless you know what's going to happen...
And for crying out loud, drive like you have some sense....

It would be a really good idea if you took into consideration the application, and used the minimum size wheel, tire, lift, ect. you can get away with.
It will save you time, money, aggravation, and maybe your life, or someone elses life....

In this case, one 3 year old girl is dead, one man in a wheel chair for life, hundreds of thousands of dollars in damage and medical bills, three law suits, and a whole lot of other problems because some bone head wanted to be 'Cool'....

"I Have The Body Of A God... Buddha"
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