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Steering and suspension:

Welcome back to the My Street Car project and Stage 3 of this build up where I will be concentrating on improving the chassis dynamics of this vehicle. Well, there is certainly is no question about the engine performance, its running great and is fun when driving in a straight line. However, the enjoyment soon fades once you start pushing through corners with the vehicle body feeling like its going to be thrown sideways from the suspension. You really have to hold onto the steering wheel for dear life as you start to lift off the seat and out the side window. Then comes the understeer...At that point you know its time to ease off or...Lets not even go there....!!

The basic suspension system on many domestic vehicle types is designed to provide a soft comfortable ride that will appease and satisfy your average grandpa driver, but that’s the end of it....!!! Heaven help if you find yourself in an emergency situation where you need to take abrasive action such as a high speed swerve or perhaps braking while cornering etc…. You quickly find yourself loosing control in a vehicle struggling for tyre grip.

The engine build was great fun, but the jobs not done until I am able to present this vehicle as a package that is a vast improvement in every aspect as compared to the Original Vehicle Design Specification. The fact is, the engine is out performing the rest of the vehicle and its now time to match the chassis dynamics up to our more powerful engine.

Is this possible...Absolutely...!! This is a Holden and in this country we have been graced with an abundant supply of quality after market products designed to enhance Steering and Suspension performance for Holden Commodores. Being associated with the Automotive Industry for more than 25 years and also owning a variety of Commodores over the last 15 years, I have experienced first hand the amazing transformation in suspension performance that is achievable with only some very basic suspension upgrades.

I personally love driving and there is nothing more enjoyable than driving a car that Handles...!!! Sports suspension and performance orientated chassis dynamics give you a feeling of power over your machine. You react and your vehicle reacts instantly with you and not against you...!!!

The suspension upgrades for My Street Car will not be super intensive or expensive. However, my focus is on making the upgrades very effective and I will also incorporate some minor upgrades that I have learnt from experience that will provide further worthwhile improvements.

The suspension system upgrade for My Street Car was carried out as follows:

Read on...!!!

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Photo 1: This photo displays the new front and rear lowered springs and shock absorbers.

 

The most effective method for reducing body roll and increasing a vehicles suspension roll stiffness is the fitment of lowered springs and upgraded shock absorbers. (Anti roll bars is also another effective means, more on that later). Whilst this is an easy upgrade, it is an area of modification that should be given some thought and forward planning first. All too often it is considered that super low with the vehicle slammed to the pavement is the way to go for ultimate cornering power. If you hold this believe, you might as well forget about setting your vehicle up for handling because at this stage you have probably crossed the point of no return with the only outcome being disastrous.

When considering suspension upgrades you must first ask yourself these questions:

    1. Budget: If you are like myself, cost will ultimately be a major factor towards the level of modification affordable.
    2. What level of handling you are trying to achieve??
    3. Intended usage. Eg. Normal road use with a measurable improvement in overall handling, spirited higher speed road use, tarmac competition or perhaps even off road rallying??


Whilst the end result may require a balance of several factors, it is only after a little forward planning and considerations that you are able to truly commence setting a vehicle up for your intended usage.

As My Street Car is to be an all round street car, I will be concentrating on a significant improvement in handling providing the capacity for higher speed spirited street use when required.

The springs fitted to My Street Car are Pedder’s Sports Ryder units which give a higher spring rate and an average ride height reduction of 55-65mm. This is about as low as you can safely go for a street driven vehicle whilst still maintaining satisfactory suspension travel.

The shock absorbers fitted are Pedder’s comfort gas. This level of shock absorber was selected to provide the best possible balance between ride comfort and handling. It may be argued that a heavier shock absorber would be more suited however, I have found that shock absorbers in the sports range tend to ride very hard to the point of frustration and discomfort on long journeys where road conditions are only average. Remember, it’s all about what level of handling you are trying to achieve.

Pedder’s part numbers are as follows:

Front Sports Ryder Spring: PN 2275
Rear Sports Ryder Spring: PN 2129
Front Shock absorbers R/H: PN 8985R
Front Shock absorbers L/H: PN 8985L
Rear shock absorbers: PN 8100


Photo’s 2 & 3: These 2 x photo's display before and after shots of My Street Car.

 

 

 

Photo 2 shows the vehicle at standard ride height. Photo 3 shows the vehicle after the fitment of lowered springs and shock absorbers. Check out the end result...!!! The car looks great now displaying some real street creed.

Photo 4: This photo displays the Commodore front sway bar links.

 

With the introduction of the VN Commodore way back in 1988, Holden implemented an interesting design change to the front sway bar links. Traditionally, the front sway bar links were attached to the lower control arm of the front suspension. With the VN model the sway bar links were moved to an attachment point high up onto the strut assembly at a point just below the lower spring seat. I believe the reason for this design change was to bring the sway bar into operation earlier with any change of steering input. The outcome of this design change gave the driver a more responsive turn in feel during the transition from straight ahead into vehicle cornering. Also, combined with the increased caster angle introduced into later model Commodores, the action of the sway bar links now resisting steering movement also improved steering self centering and stability.

As a negative spin off, attaching the sway bar using this method resulted in the sway bar links now being subject to high loadings and angle change during operation. A situation that caused these bushes to now operate at an angle well beyond their original design intent. As a result, these bushes and links have a high failure rate. It is common to find these bushes split in service and cupped washers pulled though their mounting nuts. In extreme cases of wear, links can be forced directly out of their mounting points. An early warning sign is a knock / rattle noise that will occur when driving over road bumps or speed humps etc.

For My Street Car I fitted the Nolathane Heavy Duty replacement sway bar link kit. I am blown away with the design and endurance qualities of this Nolathane part. The manufactures have clearly addressed the weaknesses and redesigned these parts to ensure greater component performance and durability. This replacement kit features 14mm attaching links that are bent to an S shape to reduce overall operating angles of the sway bar link. Polyurethane bushes are also used for extra endurance including hardened cupped washers preventing wear and distortion.

Nolathane sway bar link part number: PN 42997A

Be sure to follow manufactures instructions provided during assembly as top and bottom bushes are not interchangable and rods must be aligned upon installation.

Photo 5: Displays installed new front strut assembly, lowered spring and sway bar link

 

 

 

Photo’s 6 & 7: Photo 6 displays the original worn rubber panard rod bushes as removed from My Street Car. Photo 7 displays the new Polyurethane bushes fitted to the panard rod.

 

 

 

Moving on to the rear suspension now, a very low cost yet most effective upgrade involves the replacement of the panard rod bushes with heavy duty polyurethane parts. The panard rod of the rear suspension is designed to control lateral suspension movement and is attached from the rear axle along to a mounting point on the vehicle chassis. The original bushes are of a soft, high compliant design that suffer from a high wear rate in service. The subsequent vehicle loading actually causes the bushes to become elongated with the bushes soon losing their capacity to maintain satisfactory lateral support. On road, this will cause the vehicle to give the feeling of the rear end wandering at higher speeds and causing overall instability. A simple static check for panard rod bush condition involves pushing the vehicle at the rear from side to side. Worn bushes will result in excess lateral movement being noted. A second person observing movement from panard rod mounting points under the vehicle is also helpful when conducting this test. If you have a Commodore still fitted with original bushes, I am sure you will find excessive movement with replacement highly recommended. The fitment of heavy duty polyurethane bushes will result in minimal lateral suspension movement greatly improving vehicle stability and also providing increased service life. For My Street Car I fitted a Nolathane polyurethane bush kit.

Nolathane panard rod bush kit part number: PN 48002


Photo 8:
This photo displays Nolathane bushes fitted into the upper trailing arms

 

A very worthwhile and cost effective modification that will yield several benifits in rear suspension performance is the fitment of heavy duty polyurethane bushes into the upper trailing arms. The upper trailing arms not only locate the rear axle, they also prevent axle wind up (axle tramp) during acceleration. Axle wind up is the reaction caused by the drive force through the rear wheels of a rear wheel driven vehicle. During acceleration, the opposing action for the wheels transmitting force to the road way causes the axle housing to rotate clock wise lifting the front pinion housing. Axle wind up in extreme (High power output) will actually lift the rear wheels off the ground. With tyre grip lost, the wheels will fall back to the road way and if power is still applied the same action will occur with the wheels again being be forced clear of the road way. Of course, all this happens at a high frequency resulting in a tremendous vibration being transmitted though the complete drive train and vehicle.

A common problem with higher powered Commodore models featuring the 5 link live axle rear suspension was a significant vibration being transmitted through the vehicle during moderate to high acceleration. The cause of this vibration was axle wind up. This problem became most prominent in the VR-VS models. This was due to engines becoming more powerful in these vehicles and the trailing arm bushes becoming soft in the manufactures quest for reduced noise and vibration levels. Unfortunately, the soft bushes became poor locaters during acceleration causing these bushes to severely deflect and oscillate at a high frequency due to sudden loading and release actions.

A truly proven correction is the replacement and fitment of heavy duty polyurethane bushes to the upper trailing arms. The result and outcome from this installation is amazing. The inherent vibration caused by soft rubber bushes will be 90% eliminated and as an added bonus you actually achieve greater acceleration force as the soft rubber bushes become energy robbing parts with increased loading and resulting oscillation. As axle wind up in its extreme will cause reduced tyre vertical load, any means to reduce axle wind up will result in greater tyre grip. As for noise and vibration levels, the increase is minimal, if anything unmeasurable.

The transformation gained with upgrading of the upper trailing arms is something that I have proven time and time again. It really works and provides several benefits. No matter what level of modification you are trying to achieve, the replacement of these bushes will be worthwhile. For My Street Car I fitted a Nolathane upper trailing arm polyurethane bush kit.

Nolathane trailing arm bush kit: PN 46003

Note: Nolathane also have available complete replacement arms featuring polyurethane bushes that are a direct replacement bolt up. This is an attractive way to go if you do not have the required press tools available for the service and replacement of bushes into the original trailing arms.

Photo 9: This photo displays the fitment and overall shot of installed panard rod bushes, coil spring, shock absorber and upper trailing arm bushes.

 

Photo 10: This photo displays the Whiteline Automotive heavy duty rear sway bar ready for fitting.

 

At this stage of the suspension development, the vehicle handling is now in another league as compared to the suspension set up before modification. However, I feel that there is still room for some fine tuning before I close off this chapter of vehicle development. I feel the vehicle has a precise and responsive feel during turn in, no worry’s at this point. However, mid corner just still concerns me with the vehicle displaying a little to much roll at the rear which tends to unsettle the vehicle. As a driver, this consequent instability and imbalance is a little unnerving leaving you in a situation of trailing throttle with the vehicle feeling unpredictable until a save exit throttle can be applied.

As a means of now fine tuning the suspension, I decided to mildly increase the rear roll stiffness with the fitment of a larger diameter rear sway bar. The factory fitted sway bar to My Street Car is a 19mm diameter unit which is about the largest diameter factory fit you will find onto most Commodore models. The sway bar I have chosen for fitment is a Whiteline Automotive product with a diameter of 20mm. Whilst 1mm may seem insignificant, it should be noted that this will increase the effective sway bar rate torsion by a minimum of 20%. The actual increase in sway bar torsion is disproportional to the increase in bar diameter. This meaning, a small increase in bar diameter will result in a large increase in sway bar torsion.

To compliment the new sway bar fitment and to further increase the effective bar rate, polyurethane bushes are now fitted to all mounting points which include the 2 axle housing D type bushes and 8 x chassis link bushes. As a further positive spin off, the extra hardness of the polyurethane bushes will actually bring the sway bar into almost instant action during the transition from straight ahead into cornering. Soft rubber bushes rob initial sway bar effectiveness due to energy being wasted in bush compression.

Upon fitment of the new sway bar it was immediately noticed that this simple modification has resulted in a positive change in handling. The vehicle is now a pleasure to drive with mid corner performance now outstanding. Most notable characteristics include is a measurable decrease in overall body roll resulting in a much flatter cornering vehicle. As a driver, the vehicle feels balanced and so much more predictable with these attributes now enhancing cornering power and overall speed.

Whiteline Automotive sway bar used: PN BHR 16

For technical minded and interested persons, I might for a moment take a look at the theory behind sway bar (anti roll bar) operation and this components application to the motor vehicle. The sway bar is designed to increase the roll stiffness of a vehicles suspension while having no effect on the vehicles suspension spring rate while motoring in a straight line on a flat road surface. This is great news for a suspension designer as it allows the fitment of relatively soft suspension springs for domestic oriented motor vehicles with the fitment of sway bars providing a degree of vehicle anti roll during cornering. As the name suggests, the sway bar reduces vehicle body roll during cornering which greatly improves cornering stability. The sway bar is essentially a formed round bar that is fitted laterally across the vehicles suspension and is attached at various location points on the suspension and also to the vehicles body at points chosen by the suspension designer. This arrangement effectively ties the vehicle body to the suspension system. The effectiveness and power of the sway bar is generally determined by the diameter (torsional resistance) of the sway bar.

The application of the sway bay is considered a very powerful tuning tool by suspension designers and specialists due to its radical ability to change a vehicle's handling characteristics namely oversteer and understeer.

Definitions:

Understeer: Front tyres losing traction before rear. Vehicle pushes into corner. Without correction, front tyres will slip with vehicle sliding front end first off road way.

Oversteer: Rear tyres losing traction before front. Rear of vehicle begins to slide side ways. Without correction, vehicle rear tyres will slip with the vehicle sliding off the road way rear end first.

Upon cornering, the sway bar will become active reducing body roll. As a result, the reduced body roll increases side (lateral) force which inturn will cause the tyres to operate at greater slip angles. The slip angle of a tyre can be likened to a measure of tyre side wall twist between the direction the wheel is facing (steering input) compared to the actual travel path of the tyre tread (vehicle direction). The important fact to note hear is: greater the slip angle results in less tyre grip. Therefore, whilst considered scarificial tuning, the fitment of a large sway bar will cause reduced tyre grip on that end of the car which the sway bar is fitted. So for a vehicle that is understeering, the fitment of a larger rear sway bar should help balance the vehicle.

This is certainly just the basics and it should be remembered that every vehicle is different. There is no question that the fitment of a larger rear sway bar to a front wheel driven vehicle (which by nature of design will usually have loads of factory understeer) will deliver amazing results and is a mandatory upgrade for persons upgrading suspensions with these vehicles. However, a much more cautious approach must be taken when setting up rear wheel driven vehicles as oversize (bar diameter to large) rear sway bars fitted to rear wheel driven vehicles can have disastrous results and also create dangerous handling characteristics for inexperienced drivers.

There are two essential points that must be taken into considerations and they are as follows:

      1. Excessive rear sway bar rates may induce excessive oversteer. It should be noted at this point that all motor vehicles are designed to have a small degree of understeer built into them. Like it or not, understeer has been deliberately built into a suspension system for safety reasons. For the inexperienced driver who may approach a corner to fast, the natural driver reaction for an understeering vehicle (pushing into a corner) is to back off the throttle thus causing an instant front weight transfer, hopefully creating increased front tyre grip. The natural next reaction for an under steering vehicle is to increase the steering input (turn further into the corner) This combined increase in tyre grip and steering input should see the car back in control and on the right side of the road. However, an oversteering vehicle usually gives less warning for a vehicle about to break traction (loose control) with the oversteering vehicle requiring considerable driving skill to control. This is the reason understeer is considered desirable for all domestic vehicles. O.K back to excessive oversteer...Rear suspension sway bars that are to large may cause excessive oversteer. For all the reasons above it can be seen that such a vehicle in the wrong hands may end up with the driver constantly facing the wrong way as the rear end passes by out the side window.
      2. Excessive rear sway bar rates will reduce tyre grip during cornering which is a major problem during acceleration when you need all the traction you can get. During cornering, the outside wheel is pushed down compressing that side of the suspension. As the both sides of the suspension are now connected, via the sway bar, the reaction from the outside wheel is transferred to the inside wheel consequently trying to lift the inside wheel off the road way. This is bad news as once traction is lost the show is over...!!! A limited slip differential will save you up to a point allowing the fitment of larger sway bars. Anyway, I hope this information on sway bars help...!!!

    Conclusion:

    Well, that’s pretty much it for the suspension & suspension development, Stage 3 of My Street Car. I do understand that the market place is full of extra parts and components that would further enhance the work done so far. That’s the great advantage of owning a Commodore; there is just so much good gear out there. However, the fact is that I am content, I had a limited budget and I feel for what I have spent, the transformation has been amazing. I just love jumping into My Street Car for a drive. Its fast, stops well and hugs the corners nicely. The truth is...I wouldn’t own any other car at the moment…!!!

    Development notes:

      1. All suspension development was carried out on Michelin Energy XM1 205/65R15 tyres run at 40 psi (approx 280kpa). These tyres were as new on the vehicle upon purchase and they are best tyre of this size that I have ever driven on. Very impressive…!!! However, I can’t wait to get mags…!!! I strongly recommended running tyre pressures on the higher side of vehicle manufactures inflation specifications. Many manufacturers of domestic motor vehicles will recommended tyre pressures that are more suited to ride quality conscious persons and not performance orientated driving styles. Higher tyre pressures will generally increase tyre grip, provide less side wall flex, lighter steering, improved wear characteristics and even increased fuel economy. Feeling a few extra road bumps is a small price to pay for the many advantages to be gained with higher tyre pressures.
      2. Get yourself a good wheel alignment. Choose a reputable wheel aligner who is prepared to do more than just a toe in adjustment and will take into consideration modifications that have been carried out to your vehicle. Perhaps revised settings may be required etc. A switched on wheel aligner will know this information. A good wheel alignment will pay enormous dividends in the overall handling characteristics of a motor vehicle. All the good gear in the world will be wasted if wheel alignment angles are incorrect.
      3. Tyres Tyres Tyres…!!! Tyres are everything...I cannot emphasis strongly enough the importance of good tyres. It doesn’t matter if you are driving a family wagon or high performance street car, the best money you will ever spend will be on a Quality Set of Tyres correctly sized to your vehicle.
      4. Strut braces. During my research for suspension upgrades, I noted with some interest that there is a great deal of support and appears to be real advantages now for the fitment of front strut braces. (They look cool also). A strut brace is basically an adjustable support bar that bolts across the suspension strut tops inside the engine bay. The strut brace will eliminate body flex in this area of the chassis and are particularly suited to the VT Commodore and models built there after which, believe it or not, are manufactured with glued in fire walls. Holden revised vehicle manufacturing methods with the VT Commodore, for better or for worse, I really don’t know? However, if you have driven an ageing VT Commodore lately, especially a wagon, they really do seem to squeak, groan and move around a lot on the road. Something to perhaps consider for VT Commodore owners…!!!

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Stage 1
Engine & drive line

Stage 2
Brakes

Stage 3
Steering & suspension

Stage 4
Wheels, body & accessories