Suspension Options and Setup for B Series Ts

[Smoke them tyres]

Erko,

The info on the spring rates in this sticky has been very useful to me....many thanks.

The stock fronts being 450in/lb is ok, but looking at the other rates:

-the 520in/lb King and Tein "street" spring rates don't seem to be a big enough jump in rate to me

-however, the Tein 670in/lb "performance" rate may be too much of a jump for street tires

I'm thinking of somewhere between the 2 uprated rates. Any thoughts?

I have managed to get some extra camber and caster that the front end has really responded to along with poly bushes throughout. I have also taken the standard rear sway bar off to soften the rear and gain some "dynamic camber" via the effect/benefit of double wishbones. The tyre contact patch at both ends is far better and it doesn't hammer the outside edges of the tyres anymore.

Chassis balance is still quite good but I realise that some stronger front springs are needed with the increased grip, just a question of where to start. My other old Falcon () has 750in/lb springs with Global West upper control arms and it is a perfect rate for that. Was going to use the motion ratios for both to calculate out the BF spring rate that would be a match.

PS: Fulcrum now has poly blade link bushes available for $230 approx. The std one's are a joke!!!!!

[qik1]

Thanks for taking the time to write this up erko its a very interesting read. Its one of the last frontiers I havent been through with the T so its all new to me. Have been looking at my options lately as im after a slightly lower stance & something abit more positive as far as cornering under power (love our local ranges) as it feels abit like a boat almost unstable.

I dont do any track racing but would like to feel abit more confident when im giving it hell. The rear end is reasonably stable due to the fact I run semis but there is too much body role & understeer. Would the combination of SL King springs (front) & SSL King springs(rear) with 27/22 non adjustable sway bars help as well as lower it enough to see compared to the standard setup to make it asthetically better.

Dont really wont to spend the $'s on the adjustable gear.

[Smoke them tyres]

Here's a link or two that's worth a look for a better understanding of suspension setup:

http://eibach.com/cgi-bin/htmlos.exe/08755...156895600030177

http://home.scarlet.be/~be067749/58/c2/index.htm

[Smoke them tyres]

Sorry, forgot to ask also if the Tein springs will fit an original/non Tein BFII damper?

Edited 08/05/09 01:40 PM by Smoke them tyres

[Smoke them tyres]

No.

[Smoke them tyres]

Erko and guys,

I recently decided to further upgrade the front suspension of the BF (Dec05 build) to make it perform like a double wishbone setup should. I had already replaced all the soft std bushes for poly at the front but still had the std springs and dampers. Even at this stage, the improvement in tyre life was good (no chopping out the inside of fronts from toe out load under braking). The front felt generally more tied to the car and steering was much more responsive to inputs. So the next logical step was to look at the shocks and springs.

I had previously dialled more camber and caster into the front end. The specs of the wheel alignment are 2.5 degrees camber with another 2-2.5 degrees of caster. This is more what it needs to stop it falling over on to the outside edge of the tyre under cornering. The centre of the current tyres looks good, but due to everything previously being std, the inner and outer edges look second hand, but for different reasons!

The rest of the car:

-std rear end springs, dampers and bushes (tyre life good)

-rear bar removed to improve rear weight transfer and to take some load off the front when cornering

-27mm adjustable Whiteline fitted to front (inner pivot point tried and too stiff).

After looking at all the shock possibilities for the stiffer springs (Tein...too dear, Bilstein....no experience with), I decided to fit Koni reds (no yellows available for our cars). I had previous positive experience with these, so these seemed to be the go. Koni reds were purchased.....$650.

I initially had some 600lb/in linear springs made by King Springs to replace the std 450lb/in units (all springs at std XR ride height) and the Koni's were fitted. Thanks Erko for the specs in this thread. The new rate was an "educated" estimate/calculation at what I would need for the increased grip I now had. This was midway between the 2 rates for the Teins, but stiffer than the originals. I thought this would be ok, but it proved too stiff and had two major effects when cornering:

-insufficient load transfer to the front end meaning less grip than what it could have. The tyre seemed to have more slide at high loads.

-too much diagonal weight transfer to the outside rear tyre by the unloaded front spring. You could definitely feel the outside rear squat under cornering. Did not do anything unnerving, but definitely didn't feel right.

After deciding that the 600's were too stiff, I fitted some King 520lb/in units. Now the spring rate was right.....D'oh. Now it was at this point I decided that the Konis were definitively underdamped, particularly in the low speed rebound. This now opened up what has transpired. Overall, I have had these units in and out 9 b$**#y times in this whole process either to revalve or adjust them.

The first shock dyno graph shows damper piston speed on the x axis and the newtons force on the y axis. Compression damping force is above the middle line, and rebound below. Basically, the compression force is kept to a minimum as it is only there to stop the unsprung weight of the suspension overshooting on compression. This is even less with stiffer springs as the stiffer spring takes more to compress on bump and is less likely to "overshoot".

The low speed rebound is 0-100/125mm per second of shaft speed, mid range is from there up to about 250mm/sec, with high speed above that.

The main focus for me was the low speed rebound (this is where the shock spends much of it's time....ride quality). All the other rates bar the low and mid rebound were fine, but the low speed rebound was just ABYSMAL. There was no way it was anywhere like strong enough (even for std springs). It had a definite bouncing boat feel like lowered ricers do....uhhhh. Definely NOT an improvement over the std units! For $650 I would have thought it would have been better. (Apparently Koni don't do the yellows in these because the radiator overflow bottle is above the driver's side shock and not enough height is available (this is crap....see further in this post).

Now inside these units is:

-rebound piston (8x2mm holes) and a "restrictor" piston below that. This is what is wound in and out on the bottom of the rebound piston to adjust rebound.

-compression foot valve and shim stack (effectively the only shim stack in these units.

Now we can see from the first revalve attempt both the std Koni damping and the revalve rates.

The std rate at the 100mm/sec is 800-1000n. After the revalve we have 800-1700n.....still not enough....grrrr. Out they come for revalve 2. Also notice that the rebound curve is linear in shape, not like the digressive curves after revalves 2 and 3. The linear rebound means that when it is ajusted, very little is added as one curve is basically above the other.

Now the second revalve has the digressive curve. Much better. This was done by a new piston that had only 6 holes (force rises by the square of shaft speed). It now has 1000-3100n at the 100mm/sec. Better, but still had the boat feeling, even when set on max. GRRRRR, out they come again for another revalve.

The third attempt. It now had enough low speed rebound. Now only 5 holes in piston. These rates were now suitable. 1800-3700n. Springs were now controlled in low speed rebound. Happy, or so I thought. At this stage, the limitations of the old design Koni's were starting to show. Because the only shim stack is on the compression valve, very small rebound oscillations couldn't be damped by the piston. It would feel jumpy over small movements, like when going slowly across a rutted intersection.

It was at this point I had lost all faith in these units being able to do the job of both normal speed ride quality and high speed work.

Back to the net for some more research.

After cooling off, I managed to come across these on the KYB Australia website....

KYB_AGX 50%.BMP

They aren't rebuildable, but are KYB quality and 4 position adjustable from the top of the piston rod (farkin' hooray....no need to remove them to adjust them like the Koni's).

After searching the available part numbers, and talking to Jason last week on their sales and tech line, the only ones available that might fit are

KYB_AGX_AU_part-number 50%.bmp

The AGX's are not done for the BA/BF because of the radiator coolant reservoir on the drivers side.

I ordered the AU units as the front suspension is basically AU. Comparing them to the std BF's, the only differences are:

-the shock body itself is about 30mm longer

-the shaft where it goes through the upper spring mount is approx. 1mm larger in diameter.

This means that the BF upper shock mounts can't be used BUT AU ONES CAN....now were getting somewhere. These "pair" to these dampers so that std wheel travel is maintained.

After going to the wreckers, the upper mounts were fitted....same stud pattern (AU mounts are prefitted to damper unit as an assembly, so the whole damper unit has to be bought unless they will separate them).

This car is now soooooo much better than before. The adjustment is on 3 out of 4 (further capacity if required), with good control AND ride of the the stiffer springs of which the std and Koni's can only wish for . Cost of these units was about $700.

The shock shaft does stick out further through the inner guard, but there is still plenty of clearance to the bottom of the overflow tank......why can't they make them for our cars????????

Would I buy Koni's again? Well, I have to say they have been a disappointment in my case which has surprised me given previous positive experience. For cost and performance effectiveness, I would buy the KYB's again.

Note: std spring height was moved up/shortened in the BFII in 2007, so earlier springs will be needed to fit these AU units.

It has been a long post, but I hope that it saves others and adds to the excellent info that Erko and others have already posted in this sticky..........

[DesFlurane]

Did you only fit new shocks and springs to the fronts?

[Full Monty]

Great write up. You definately know your stuff regarding shocks, but I think your asking too much from dampers alone.

But wow, you must like understeer! (removed rear bar altogether and added stiffer rate27mm front bar, along with going up in front spring rate). What was done to the rear dampers / spring rates? To re-establish neutral handling?

The standard geometry and corner stiffness already provides plenty of Understeer, if you want more neutral handling, try going to a slightly stiffer rear spring, To improve the standard front to rear ratio / corner weight.

My understanding is the main tuning needs to be done via spring rates and anti roll bars to get a good even corner weight balance and front to rear distribution of mass. The Dampers need to be adequate to control the spring rebound and control oscillations etc, to maintain tyre contact with the road. The Dampers can effect cars balance during transitional phase, and initial steering input response. By slowing one end of the car over the other during bump / rebound

From everything I have read / experienced, Your Dampers aren't going to limit "total body roll" in cornering, I.E under maximum cornering force at the apex of the corner.

Their job is to slow, or increase the rate of Yaw and roll, however the car will still reach the same amount of roll under full cornering loads.

They can however be used to change cornering transition traits, and initial input response.

Changing the fronts to stiffer bump and rebound valving for instance, will increase transitional speeds - during change of direction, by placing more cornering load through the tires at the initiation of a turn (car feels more responsive on initial steering input).

Edited 22/11/09 10:50 PM by Full Monty

[Full Monty]

Did you consider going the Tein route with the EDFC module, that would have been right up your alley, you can tune to your hearts content, with the push of a button.

From soft / comfy highway cruising, to teeth jarring hard, and anywhere in between.

I'd love that setup oneday. (maybee on my next car).

[Smoke them tyres]

Hi Monty and Des,

This stage only involved the shocks and springs to the front as I had previously done the camber/caster and the poly bushes there. This is where I have concentrated my efforts so far and it has yielded good results IMO, but it has been a "journey" with the/those Koni's.

Agree that the dampers are there to only control the spring/spring rate. Also that it will help in transition and that final position of suspension under load will not differ. But it did need stiffer front springs (520's). The 600lb/in front springs did tell they were too stiff (don't know where you would use the Tein 670lb/in rate????....must ride like a Flinstone mobile), and that weight transfer between the front and rear of the car (particularly diagonal) does have a major effect on handling so you would be on the right track, hence the excessive rear squat under cornering load when they were fitted. And yes they did seem to have more slide at the front at the limit....less weight transfer.

BUT, the current setup with the 520's and no rear swaybar as described is neutral grip up to the limit, a touch of understeer at that limit as a warning, and then a nice and controllable 4 wheel drift.......perfect.

The way I look at it is:

-one of the outcomes of the rear bar is to stiffen the effective spring rate in roll. This stiffer rate means that there is less weight transfer to the back and more load that the front has to carry. The front has insufficient camber and caster in std form to carry this load, so it understeers and hammers the outside edge of those tyres, while the rears get a relatively easy life. Hence, the std setup with the rear bar fitted will actually induce understeer....IMO.

-the decreased rear suspension compression would also cause the load point on these tyres to be the same as the front......on their outer edge (no dynamic camber gain from the double wishbones to combat body/suspension pivot outwards roll), and neutral handling would be restored, but at a lower ultimate grip level and a higher wear rate on the outside edges (but not as bad as the fronts). I have found that after removing the rear bar that the rears were wearing more evenly across their entire surface than the std setup. Bonus.

Also, I figure that the rear spring rate and geometry is good (seems like a well sorted piece of engineering right out of the box.....diff centre mounting TOTALLY excluded).

-the front is where most of the weight is carried and it's C of G is higher. Also that it is the end actually trying to turn the car (yaw). The 520's are only 70lb/in up on the std fronts or 15.5%....not a large increase. The front 27mm sway bar from the Whiteline webpage (they have a swaybar stiffness comparison table there....bloody marvellous) is up 60% from the std 24mm...sufficiently stiff without being excessive. Good match for the increased camber and caster. (I tried the inner point of this bar and it felt like a 30mm bar.....a 144% increase on std.......definitely tooooo stiff).

Couldn't agree more on the Tein's.....they would be fantastic to tinker with (and would love to), but I just can't see coughing up $2.5k for the fronts plus the EFDC.......nice to have a goal though. But then I would also want the rears!

It's gets harder to hide the spend from the "minister for war" at that level.