Coil-overs > Torsion bars: answered at last!

[Grim Jhaixus]

So I've been around here asking about things like why our cars have torsion bars and if the coil-over kits are truly superior and wasn't satisfied with the responses I had received, so I put the question on a shelf. Now that I'm finally pulling the 318 out I renewed my query to find it answered on a Porsche forum, so I'll share the important bit here with a link to the page because even though its a different car they make a lot of solid argument on this issue.

My favorite part (complete with authentic typo) :

"Absolutely true that coil-overs require chassis reenforcement to work properly, however once reinforced the ride quality with coil-overs will be better than torsion bars all else being equal. This is the result of lower loads on the trailing arm bushings and hence lower friction in the pivots.

A coil-over spring puts spring force on the trailing arm very close to the wheel axle. The result is a load path the goes from the spring almost directly to the hub and wheel. This puts very little bending moment on the spring plate and hence very little load on the bushings at the spring plate.

With torsion bars the opposite is true- the spring plate carries a lot of bending force, as the load is on one end (the wheel) and the spring force is on the other. The bushing reacts to this force, meaning it is very highly loaded with torsion bars. Since friction is proportional to load the torsion bar suspension has higher friction. High friction results in poor ride quality and lower suspension performance.

This might not be a big issue if there were quality bearings at that location, but unfortunately we have bushings, even the best of which are relatively high friction.

The same problem occurs both front and rear, and I feel it is primarily responsible for the improvement in ride-quality found with coil-overs (unless the important bushings have been converted to bearings)."

The link to the page for more context on the issues and arguments and experiences of the people involved:

http://forums.pelicanparts.com/porsche-911-technical-forum/524474-ride-quality-coilovers-springs-vs-torsion-bars.html

It's a good read.

[Mike DC]

Bushings -

I don't know how the Porches in question are set up, but on Mopars the LCA pivots don't get that kind of major league friction they seem to be discussing.   The LCA doesn't pivot direction on the rubber bushing.  The bushing's inner metal insert rod thing pivots inside the K-frame's metal mounting tube.  Different deal as far as friction is concerned.



Reinforcing the unibody for coilovers -

IMO this is something that everyone seems to misunderstand.  The torsion bars don't put the upward pressure on the T-bar crossmember but rather on the LCA pivot point.  That is not exactly the same place that a coilover conversion would put the force, but it's also not 3-4 feet farther back in the chassis like many people talk about.  The T-bar crossmember is subject to (significant) twisting force but that's it.  It's not being pushed up/down to hold the front end of the car off the ground.

If the longitudinal T-bar layout was really putting the upward stress (holding up the front end of the car off the ground) on the crossmember end in the chassis, which is so often assumed, then how could antisway bars work correctly?  If this was how things worked then any twisting force introduced into the antisway bar by a LCA would push up the opposite side of the front end from that LCA!  This is not how things work.

Bottom line - coilover conversions that mount directly onto the stock front shock towers do call for some reinforcing.  But the switch does not move the front spring force several feet farther forward on the chassis than the T-bars were putting it.  (BTW, the RMS K-frame setup would hardly even move the loading around at all thanks to those little coilover mounts added to the K-frame.  It would take the twisting loads off the T-bar crossmember and otherwise leave things basically the same as stock.)

   

[Grim Jhaixus]

Actually the length of Porsche 911 T-bars was something I overlooked while reading the article, and it has since been explained to me that our T-bars work better because they are longer? I don't know enough about Porsche but I guess having a drastically shorter t-bar in relation to the wheelbase would cause a lot of stress.

What I do know is that T-bars were installed on our cars because they could absorb shock with less bounce and that was life/death important on the track, back when performance at the track was used to sell cars (or so I read, the Age Of Power had been dead 17 years before I was born).

What else I know is that every time I happen upon a 3rd gen with any suspension mod at all its a full tubular k member with tubular arms and coil overs (it's been 50% that had 4 links in rear too) and when I ask I always hear that the car turns tighter because the coil system dampens better on the inside of turns and eliminates a massive percentage of wheel travel.

The final reason I repost a version of this thread every so often is because if T-bars were truly the way to go even after 40+ years why are all modern performance cars coils? NASCAR is all coils now, Porsche went all coils right after the 911, and the most glaring is that I see torsion-to-coil conversion kits but not coil-to-torsion kits with the specific exception of lifted 4WD pickups.

So which would you consider superior? I'm here to learn the best ways to make my car stronger, and share what I've heard with others, that's all. I've already decided that if I go coils it will be later on, this engine swap will only see new bushings on the factory T-bars and new shocks.

[Scaregrabber]

Unsprung weight, adjustability, I'll keep my Mopars all Mopar and that means T-bars for me.

Sheldon

[HPP]

I'm sure there are some engineering reasons why Chrysler chose torsion bars, but there was also marketing advantages they had starting in 1957. I'll relate what I know specific to Mopars as I don't know squat about Porsche. FWIW, my late 80s Honda CRX had torsion bars in it as does my new Suburban and so do some other models of newer trucks/SUVs. So, I'd say they haven't been abandoned by the industry as an inferior spring choice. The also are still in use on many modern sprint cars in competition so again, they are out there being abused every weekend.

The torsion bar puts the weight of the spring lower and further back in the chassis than a coil spring. This locating provides improvement in both the center of gravity height and the moment of inertia for rotation. IE, they have impacts on handling performance. Granted, these are impacts that can probably only be seen by the hands of a stop watch and the typical butt dyno probably won't notice them, so they aren't huge gains, but they are part of a package that can contribute to performance.

The reason why so many new competition cars have moved away from them is not that the torsion bars aren't a good spring choice, but it becomes a scale of economics in both cost and time. Changing a coil spring can be done quickly. A great variety of spring weights can be carried around very easily. Since so many people use them, the market has responded by supplying them in 50# increments so you can almost infinitely tune them to a very specific application. When winning can be cut into tenths of a second, sometimes that 50# difference can make that  difference. Torsion bars did not have the selection to provide that finite a way of slicing the rates plus as series such as Nascar have moved away from stock platform builds to fabricated chassis, it became much easier to design in the simplest and easiest tuning tools. FWIW, the jack bolts designed to crank in wedge into a chassis for tuning are already in place in a stock Mopar t-bar system and were never part of the stock offerings on coil spring cars.

Additionally, as the speeds and loads have increased in racing applications, the rates required have gone up as well. Back in the day, t-bars could be had  up to 1.66 for speedway applications. This is a 1450# wheel rate. Wheel rates on banked tracks have gone well up over the 1500# rate on even short tracks, never mind a super speedway, until recently when shock technology has caught up enough to start softening those rates. But now that everyone uses coils, there is really no reason for premier levels cars to go back to t-bars now. Add to that the fact that a t-bar system require specialized bar sockets, cross members, and control arms to support t-bars in those sizes, and you had additional hardware requirements that don't lend themselves well to competition where they have to carry additional parts, or the street where the stock parts now become inadequately sized.


In my conversation with guys who have aftermarket suspension under their cars, the one glaring point I always find is that  the vast majority of them went with the rates the manufacturer recommended and they now rave about the increase in handling performance. I contend that if these individuals took the time to understand the math that could be used to dial in the stock system to similar wheel rates or spoke to someone who could make those recommendations, they could experience a similar jump in performance out of the stock system. While there are some geometric reasons why coil overs perform smoothly, a torsion bar system can be cleaned up to be very close as well.

Unless you are in a position where you race in a class that allows these mods and you need the lighter weight of a coil over and you need the ability to rapidly change spring rate, these conversions in a street car are more for a lot of Wow! power. Especially if you are a driver that wants to set it and forget it. That isn't to say that if you feel you want to have a system like this that you shouldn't get it,  I mean really, who needs 572 cid of Hemi on the street either, that you shouldn't get one. I doubt most street drivers can extract all the performance potential out of these systems over the stock set up, so I don't now that I'd say any one is superior.

Over the last 100 years, there have only been 4 ways to spring a vehicle; leaf, coil, torsion, or air.  That's it. They all have advantage and disadvantages. The fact that a lot of manufacturers and competition have gone coil doesn't necessarily mean they are superior, just that they are now easier to design in with all the available selections and due to their prolific nature, cheaper, and because of package, can be made smaller and lighter, and you have a perfect storm where they are seen almost everywhere.

[Mike DC]

The vast majority of aftermarket coilover R/P front ends are sold because owners see them as an easy plug-n-play fix for a stock front end that needs overhauling and improving.  

It's arguably cheaper & better to rework the stock front end.  But that still takes some money, more work, and more understanding of the whole subject.  



I personally wouldn't run one of the RMS K-frame conversions but IMO it's not a bad setup.  I think Rick Ehrenberg's criticisms of it are basically valid, although the vast majority of the cars in the hobby will never see enough hard miles to suffer for it.   

[Grim Jhaixus]

Awesome awesome.

Okay, I have finally located a BB k-frame, I'm doing all new bushings for the T-bars and by years end I hope to have the power rack and pinion.

Coil-overs was a "someday, one day, maybe" project anyways, but now my question is how do I get maximum performance out of my existing system? I'll search the forum for an existing thread but if one of you guys have a link or opinion handy I'd appreciate it.

A side note here; over on FBBO I see threads about rear sway bars causing oversteering? Does anyone here have this issue?

[myk]

Awesome awesome.

Okay, I have finally located a BB k-frame, I'm doing all new bushings for the T-bars and by years end I hope to have the power rack and pinion.

Coil-overs was a "someday, one day, maybe" project anyways, but now my question is how do I get maximum performance out of my existing system? I'll search the forum for an existing thread but if one of you guys have a link or opinion handy I'd appreciate it.

A side note here; over on FBBO I see threads about rear sway bars causing oversteering? Does anyone here have this issue?

Hotchkis.net.  It's the best you'll ever do with strictly bolt-on parts.  I'm running some of their pieces now and couldn't be happier.  Some here have their full systems and are completely satisfied.  Throw in a modified steering box and you'll have quite a driver...

[RallyeMike]

I love the response from the guy who said "ride quality has improved because now with coil overs your chassis is flexing". Classic! 

The vast majority of aftermarket coilover R/P front ends are sold because owners see them as an easy plug-n-play fix for a stock front end that needs overhauling and improving. 

Great comment that I agree with 100%.

[HPP]

Okay, I have finally located a BB k-frame, I'm doing all new bushings for the T-bars and by years end I hope to have the power rack and pinion.

If you considering adding a bolt in Unisteer R&P, I'd recommend against it. Not only do they reduce your turning radius, they increase bump steer characteristics that will make the car very unpredictable on any less than a perfectly smooth road. A Firm Feel staged box or one of the rebuilt Borgeson units will give significantly improved feel and feedback while avoiding the conversion problems.

Coil-overs was a "someday, one day, maybe" project anyways, but now my question is how do I get maximum performance out of my existing system? I'll search the forum for an existing thread but if one of you guys have a link or opinion handy I'd appreciate it.

I'll second myk's recommendation of Hotchkis and also throw out Firm Feel. The guys at Firm Feel have been building handling Mopars for 30 years now and are hugely helpful in making recommendations if you take some time and talk about your goals with them. BTW, as a 3rd gen, do you have the solid mount front end or the isolated front end? This could be a factor in what parts are available to you.

A side note here; over on FBBO I see threads about rear sway bars causing oversteering? Does anyone here have this issue?

I don't have that issue because of my component selection, but it is entirely possible. In the simplest terms, the end of the car with the most spring rate will be the end that slides first. If you have the stock suspension under your car and you  add super stock springs to control that new big block and then put in a big rear sway bar under it, you have significantly stepped up the rear rates compared to the front and when pushed to the limit, the rear will slide first. Conversely, leaving the stock 4 leaf rear springs and adding big t-bars and a 1.25 sway bar, the front will now understeer. BTW, in stock form, most of our cars were designed to understeer. This is because an understeering car still maintains its basic direction heading and must be slowed down to allow the driver to regain control. A good combination for inexperienced and underskilled drivers. By contrast, an oversteering car will turn completely around and face you the wrong direction. Controlling this slide before you swap ends takes more skill and possibly throttle to avoid the situation.

[ODZKing]

Unsprung weight, adjustability, I'll keep my Mopars all Mopar and that means T-bars for me.

Sheldon

And I also agree with MYK. Hotchkis.net. I saw the demo at Carlisle and these are quite impressive.
If I needed the front end on mine to be more response, I would go with these in a heartbeat.  

[Grim Jhaixus]

The rudder and triple dog bone steering in my car now scares me. It makes my brain upset. You guys talked me out of coils but the rack is going to happen, and I thank each of you for your input because that input is specifically why I come here.

This is the rack I am/was going to get, I dunno if it's the "Unisteer" kit HPP says is no good:

http://www.speedwaymotors.com/1968-74-Mopar-B-Body-Rack-and-Pinion-Kit-B-B-Engine,38452.html

I came to Mopar after primarily being a Ford guy and the steering is the one thing I miss most (IME Fords of comparable years had better wiring and I loved the twisting ring style brake light switch versus the plunger everyone else had, but the steering racks are awesome) and I know we are a ways off the original topic here but spare me from starting a new thread and I'll be satisfied for now.

If that rack is undesirable what rack should I look for?

[HPP]

Unfortunately, that is a Unisteer derived rack. You can tell by the large bolt in brackets that replace the steering box. Sadly, when you put a R&P in a rear steer position ( steering is behind the centerline of the front axle), they don't produce perform as well as a front steer application. This is why aftermarket suspension set ups, like Alterkation and Magnumforce, put the rack in a front steer position. Additionally, in a classic Mopar, because the torsion bars and rack position compete for the same space, most bolt in racks produce bump steer conditions worse than the factory set up. I'd still suggest keeping the recirculating ball box and upgrading it to a Firm Feel Stage 3 or a Borgeson unit. While these are not R&P units, both of these will feel more like a late model in steering effort with improved precision of motion without all the over assist of the original unit.

I also looked at our profile and notice your Charger is a '73. This means you have the added burden of having an isolated K frame, isolated t-bars, and I believe a rag joint in the steering shaft. All of these are additional factors in the mushy steering you are dealing with in your car. You can get solid  or urethane bushings to firm up the K frame and t-bar mounts. You might also look at  options for replacing the rag joint arrangement, if you have one. I honestly forget when those become standard issue. If you have the older pot style coupler, it likely needs rebuilt as well as that also contributes to drifting feeling steering also.

[Mike DC]

  
Caster is another thing to consider in this conversation.  Caster is what makes the steering in newer vehicles naturally begin to straighten out whenever you let go of the steering wheel while the car is rolling.  Whereas older cars have more of a "motorboat" floaty feeling.  This is a different issue from the amount of slop in the steering gearbox/linkage.  

No steering box or R/P - NONE OF THEM - will change this by itself.  This trait is a product of the front suspension geometry/alignment rather than anything directly in the steering system.  The standard habit of raking the car's stance a bit (down in front/up in back) also makes the problem worse.  



Somebody can correct me if I'm wrong here but I think the RMS K-frame should give more caster than stock.  The RMS setup converts to a rack/pinion and it also replaces the stock spindle & control arms and some of the geometry.  It's not the R/P itself making that difference.

The stock front suspension can be given more caster by using offset bushings in the UCAs or aftermarket UCAs (a better method) with the ball joint location moved slightly rearwards.  


 

The stock setup can feel quite "tight" compared to how it originally came if you make the right changes.  rebuild the sloppy parts, replace the springs/shocks/sways, use a tighter steering box & couplings, and do one of the caster fixes to the UCAs.  This setup will also probably remain more cushy on bumps & impacts than the aftermarket K-frames because it doesn't ditch all the rubber bushings. 

Plenty of modern vehicles have WAY tighter steering than 45yo muscle cars and still have rubber bushings for ride smoothness.  The two things are not mutually exclusive. 

[Grim Jhaixus]

Oh yes, I do have the '73-itis. The rag joint is probably my single least favorite thing on this entire car.

I've spent a lot of time on Magnumforce's page staring at their k-frames for the '73+. It's specifically why I started this thread and the threads I made before it over the years I've been here. It's their coil-overs I ask about, the ones they send with the tubular frame and control arms and rack and pinion.

Maybe if I use their spindles I can use their RNP? I guess I'll send an email.

[ODZKing]

I also looked at our profile and notice your Charger is a '73. This means you have the added burden of having an isolated K frame, isolated t-bars, and I believe a rag joint in the steering shaft. All of these are additional factors in the mushy steering you are dealing with in your car. You might also look at  options for replacing the rag joint arrangement, if you have one. I honestly forget when those become standard issue.

HHP, the rag joint was in 72 and 73 C bodys and 73 B bodys only.  It was supposed to reduce the vibration that came up through the steering wheel. Yuh, right!
I replaced mine with a solid piece that I purchased from Bouchillon. I thought I posted about it here before but I can't seem to find it.
In any case, it is a solid piece powder coated and replaces the rubber piece. I feel the steering now but it eliminated the slop. I also plan on getting tighter steering box when money permits, similar to the one in my 67 which I purchased from Firmfeel. Both of those will improve steering considerably.
This is the new piece and what was left of the old one.

[Grim Jhaixus]

I like that.

[HPP]

I'll second Mike DC's comment about caster. In the  process of upgrading your system, you will want an alignment with as much positive caster as possible. Yes, the RMS system has a lot more caster than stock along with revised geometry. Since they started with a clean sheet design, they have changed it to eliminate the stock caster/camber problem and optimize the suspension motion while using the R&P and a bunch of new components.

I've spent a lot of time on Magnumforce's page staring at their k-frames for the '73+. It's specifically why I started this thread and the threads I made before it over the years I've been here. It's their coil-overs I ask about, the ones they send with the tubular frame and control arms and rack and pinion.

Maybe if I use their spindles I can use their RNP? I guess I'll send an email.

Magnumforce parts are nice looking. However, I would be reluctant to use their kits without the additional inner fender bracing. This because their kit puts the new coil over loads into the shock towers, which were not designed for that much stress. Without the additional support, it will slowly bend you car until the hood wont close well any more.

Which spindles are you talking about? MF offers a dropped spindle for regular mopar ball joint applications, but the spindle used in their conversion kits is actually a Ford piece. The two are not interchangeable. However, the use of the drop spindle with a bolt in R&P is a recipe for major geometric trouble. This is because the drop spindles in an of them self alter geometry and make bump steer worse. So does the addition of a R&P. Add them both, and you'll be off the charts for dynamic changes.

In all seriousness, call the guys at Firm Feel and discuss you goals with them. They can give you a recipe of upgrades that you can do piece by piece to avoid breaking the bank, but over time step up the performance of you ride.

[Grim Jhaixus]

Can do.

I will point out tho that RMS doesn't have a kit for the '73, and as mentioned earlier in this thread the RNP system will actually perform worse than stock unless mounted forward of the frame. Magnumforce also used round tubes. My brain likes it better. I wish I had a more technical argument.

But yeah since a stock k-frame is going back in I'll leave the T-bars alone (new bushings) and put in a firm feel steering gear. I'f they have better dog bones I'll change all of them too.

It does seem like for this car to do what I want it to do MagnumForce has the product. It can wait til after I get a bigger motorcycle tho.

I'd like to thank everyone for their input, but I feel this thread is done. I'll start another soon and as always you guys are the best 

[HPP]

No, RMS doesn't list a kit for your car. They don't list kits 76-80 F bodies either, but I know they have made them. If/when you get the point of actually doing a conversion, a call to RMS and a discussion of the ability to adapt one of their kits to you chassis may yield positive results.

Good luck with the upgrades and modifications.