b454rat
I'm Awesome
My Tahoe doesn't have a rear bar, since I want to lower it and corner with it, thought bout getting one off a 3500HD in a yard near me. Dunno if it would fit, it is a MONSTER lol. Think it's like 2" thick lol.
Rear sway bars (anti roll bars) what got them and what didn't?
- Thread starter Pinger
- Start date
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Other dimensions affect the bar's stiffness also. Eg, shorter (across the truck) is stiffer and shorter 'arms' have the same effect. Where they mount on an axle or wishbone has an influence too (same as with springs).
Usually the diameter is used as comparator for the same fiitment as the other dimensions and mount points will be the same.
With European cars, I think the break point between being solid and hollow is around 25mm. Properly screws things up trying to compare them when they are or might be hollow.
Front bar on my C2500 Suburban is 32mm. Be interested to know what it is on one with a rear bar - and the same for the rear bar.
a Tubular bar is reacts as a larger bar in that it has 2 working surfaces I played with the idea of making a tubular bar for a 70 chevelle wagon I had using a rear bar from same era common Monte Carlo .Making out of .125 wall CRO/Mo tubing ended up being 2.5 times stiffer I also had a Sunbeam Tiger with a front bar that was made from Sched 60 water pipe & was a HUGE Difference on that car on a sprint car a torsion bar that is tubular works a lot better because it reacts quicker than a solid bar Just Some Thoughts Keep the Shiny Side Up 
1 3/16'' is 30mm - a touch thinner than the 32-33mm front bar on my C2500 Suburban which also is without a rear bar.
The difference must be due to either a Tahoe being lighter than a Suburban and/or yours being 4WD.
That's the first I've heard of different bar diameters at the front when no rear bar is fitted.
a Tubular bar is reacts as a larger bar in that it has 2 working surfaces I played with the idea of making a tubular bar for a 70 chevelle wagon I had using a rear bar from same era common Monte Carlo .Making out of .125 wall CRO/Mo tubing ended up being 2.5 times stiffer I also had a Sunbeam Tiger with a front bar that was made from Sched 60 water pipe & was a HUGE Difference on that car on a sprint car a torsion bar that is tubular works a lot better because it reacts quicker than a solid bar Just Some Thoughts Keep the Shiny Side Up
That's not how it works. It's the radius that increases the stiffness. It's only hollowed out to save weight at the desired radius as the centre is pretty much just dead weight. Same goes with prop shafts.
Wow, I don't check in for a day and the conversation runs away!
Even though Colin Chapman's backbone chassis looks flimsy compared to a truck frame, you have to remember the entire car weighed less than a ton. After Lotus came out with their backbone chassis, GM experimented with the X-frame, but on much larger cars. It was not successful. In '69 they went back to perimeter frames and fully boxed them on the Cadillacs.
Yes, the rear axle looks like a Jaguar rearend and also a Corvette rear end. It's a compromise over using dedicated suspension arms and a separate dedicated driveshaft, but Chapman was all about reducing unsprung weight, and in a light chassis like that it probably performs better than the Jaguar or Corvette versions.
I cut the bolt holes on the front of the sway bar brackets so they were just slots, then bolted them onto the exhaust clamps with washers on them and welded the washers in place. I just got the transmission back in on Friday, so hopefully I'll be able to start racking up some miles and see how it handles. I can already tell it has less body roll.
Even though Colin Chapman's backbone chassis looks flimsy compared to a truck frame, you have to remember the entire car weighed less than a ton. After Lotus came out with their backbone chassis, GM experimented with the X-frame, but on much larger cars. It was not successful. In '69 they went back to perimeter frames and fully boxed them on the Cadillacs.
Yes, the rear axle looks like a Jaguar rearend and also a Corvette rear end. It's a compromise over using dedicated suspension arms and a separate dedicated driveshaft, but Chapman was all about reducing unsprung weight, and in a light chassis like that it probably performs better than the Jaguar or Corvette versions.
Ain't that the truth!
I need to get under mine for a closer look. I was expecting a clump of a bracket on the axle but looking at HWB's photos, they are a lot more discrete than that. Maybe I already have (or close to) what is needed if I want to have a go at a rear bar. Won't be a GMT400 one though - I'll have to source locally.
Chapman made great claims about the rigidity of his backbone chassis but when it suited him he was a Grade A BSer! A brilliant engineer though who really understood the intricacies of suspension and weight transference better and before anyone else did.
That back bone was never meant to be a production chassis. The Elan was to be a fibreglass monocoque as per the (original) Elite and the backbone was knocked up as a mobile test rig for the mechanicals. When Chapman realised it worked well at a fraction of the price and complication of the intended monocoque - it was adopted. BTW, that Elan weighed closer to half a ton than a ton!
I forgot the Corvette also used driveshafts as upper wishbones. It dictates a very wide lower wishbone that has to be mounted very low to spread the loads. His hatred of conventional splined shafts (at the time neither the metallurgy or lubrication was up to the task) led him to mega expensive ball splines for the race cars when he moved to using upper wishbones.
Worth a few words - why the modern day trend is for a stout bar at the front and either none or a lighter one at the rear?
To stop a vehicle pitching (back and forth like a rocking horse) the spring rates (measured as frequency as it isn't only their stiffness that matters here but their stiffness in relation to the weight they support) have to be different front to rear. If they were the same, after a bump, the front and rear springs would be in sequence - fronts compressed when rears are extended then fronts extended when rears compressed etc, etc and an oscillation builds as the springs feed into each other. This can be seen on agricultural machines with no springing and same size tyres at the same pressures (their only 'springs') when the are on tarmac at any speed.
So, to avoid that the tendency is to have softer springs at the front than at the rear so that the frequencies front to rear are mismatched and pitching damps itself out within a few cycles rather than self feeds and builds. Typically, due to independent front suspension having low roll centres and softer springs there is little in the way of roll stiffness at the front - hence the stout bar up there.
On our trucks, the solid rear axle has quite a high rear roll centre so less roll is generated there. Which allows a rear bar to be deleted or if present, relatively (to the front one) thin. Sway bars have no influence on pitch. They can however contribute to diagonal pitching during cornering - so bars have to calibrated along with springs to control this.
The front bar exists primarily to add roll stiffness to a front end that has its springs soft to control pitch. That that permits the rear springs to be stiffer is beneficial because it is the rear that will see load changes more than the front will and initially stiffer springs can better cope with that. Just in case you were wondering...
To stop a vehicle pitching (back and forth like a rocking horse) the spring rates (measured as frequency as it isn't only their stiffness that matters here but their stiffness in relation to the weight they support) have to be different front to rear. If they were the same, after a bump, the front and rear springs would be in sequence - fronts compressed when rears are extended then fronts extended when rears compressed etc, etc and an oscillation builds as the springs feed into each other. This can be seen on agricultural machines with no springing and same size tyres at the same pressures (their only 'springs') when the are on tarmac at any speed.
So, to avoid that the tendency is to have softer springs at the front than at the rear so that the frequencies front to rear are mismatched and pitching damps itself out within a few cycles rather than self feeds and builds. Typically, due to independent front suspension having low roll centres and softer springs there is little in the way of roll stiffness at the front - hence the stout bar up there.
On our trucks, the solid rear axle has quite a high rear roll centre so less roll is generated there. Which allows a rear bar to be deleted or if present, relatively (to the front one) thin. Sway bars have no influence on pitch. They can however contribute to diagonal pitching during cornering - so bars have to calibrated along with springs to control this.
The front bar exists primarily to add roll stiffness to a front end that has its springs soft to control pitch. That that permits the rear springs to be stiffer is beneficial because it is the rear that will see load changes more than the front will and initially stiffer springs can better cope with that. Just in case you were wondering...
sewlow
Bitchin' Stitchin'
...along with, castor/camber/toe/Ackerman angles/bump steer/roll steer/Spring rates/Shock compression & rebound rates/Frame torsional stiffness/Suspension frequency cycles/Tire & wheel weight, sidewall size & stiffness, tread width & rubber compound/etc. etc. etc.
To make a vehicle understeer less, reduce front roll stiffness & increase it in the rear.
To make a vehicle oversteer less, do just the opposite.
Of course, that's considering that no other changes are made.
By tuning a vehicle for extremely high-roll stiffness—where it's difficult to notice cornering speed due to lack of body roll—you mask one channel of communication to the driver. Nobody wants to fly blind by masking roll; you're cutting off tangible communication. Instead, it comes down to understanding and predicting what's going to happen as cornering forces build to their breaking point and beyond.
Body roll is a primary, fundamental way to inform the driver about cornering and therefore a progressive indicator of grip.
The idea is to cook up a suspension absorbent enough to keep tires planted and talking to the driver as continuously as possible.
The hearts and minds of sporty car fans often relies on a game of numbers brewed in a cauldron of 0-60 mph times, quarter-mile figures, maximum grip numbers, lap times, and nutso horsepower.
Living by those stats adds up to one-upmanship that eventually leads down a rabbit hole of irrelevance.
Mix all those ingredients together and you get an automotive Dolph Lundgren—great on paper but lacking any real charm in person.
To put it another way, when is the last time you drove a spec sheet?
Grip in the form of lateral acceleration and breakaway character is the prime offender in the modern crimes against driving fun, and it's typically measured by the force of gravity in a lateral plane. In this dynamic, a car that can most quickly negotiate a 100-, 200- or 300-foot (30/60/90m) diameter skidpad in steady-state cornering in the least amount of time against others posts the highest grip.
Of course, grip on a skidpad proves only one thing: that tires stick well and the suspension keeps them mostly upright. That's not where the joy or art of driving live, however. Better grip may mean negotiating a steady corner faster, but if you focus only on grip in the chassis engineering phase, the enjoyment of driving plummets. The breakaway character of the car's and tires' cornering ability at maximum adhesion becomes unforgiving and hard to read for many drivers.
The real shame is that this is the exact point where enthused driving becomes a dance worthy of the effort. A superior handling vehicle can be as rewarding a partner as Fred Astaire or Ginger Rogers, but fit horrendously grippy sneakers, and grace falls flat on its ass. Put simply, tires and suspension engineered for maximum possible grip deliver what they're supposed to, but in inverse proportion to fun.
A lack of suspension travel is one of the most frequent causes of horrible handling.
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