Suspension tuning 101

[Matt Dyne]

So the theory is, with all these fancy adjustments on my Proflex, I should be able to get the most from them and get the Celica going even quicker...

There's bump, rebound, spring rates, valving etc.

All of which can contribute or take away from your performance.

Who's got some theory one how they all work, and how changing each part can yield differences.

Discuss.

M

[Mark]

Matt, The best advice given to me regarding suspension was: "Most rally suspension is set too hard". That's the first place to look.

Hand in hand with this: Read the instructions that Murray sends you. For bump settings, he recommends- I think- the lowest 8 - 12 settings out of the 21 - 24 clicks you can get out of the shock. Yet, some cars seems to be running settings outside this range i.e. stiffer, for road work - why bother if the designer of the shock has said to set it below that? Biggest problem, from a driving perspective, is then that it -the car- doesn't feel fast and tight because it is all setup 'soft' so you've got to trust the science rather than the driving feel?

So, why don't you get your hands on Murray's documentation first and see what he recommends.

Personally, I want the attributes in a suspension of grip in a straight line, good turn-in and something akin to manoeuvrability (nervousness so that I can change direction quickly when I frig up; the more I think about this attribute the more I think I've got to change the toe settings on the car to control it without compromising the suspension settings).

I guess my opinion on the above stuff is just what works for me as a beginner in a 4WD. And it comes back to your driving style and preference. Presumably the better you come, the more rebound and bump you dial in, the more support your car has through corners at the cost of maybe less grip but you're committing more so it doesn't matter...or something like that.

One thing that made a big difference for me was the difference between the settings on the front of the car and back of the car. If you've got 14 clicks on bump front and back, the little bugger is a bit resilient to turn I've seen in a few cases now. However, if you soften one end it seems to grip better at that end, doesn't it? Depends if you want the 'front end push' for the faster stuff or more RWD feel that I reckon provides a nicer feeling on turn-in.

Maybe it all doesn't matter: look at Ray in Bluetts, GAB suspension, not recce'd, no terraphone or terratrip

[tortfeaser]

The basics are that changes in bump damping are about stability, steering response, balance. Rebound damping is about traction and ride comfort. If you're thinking you need to go harder then go harder in bump and leave rebound alone to not affect grip.

I think the Proflex canisters you have have low speed bump on the canister. Rebound on the strut (at the bottom). More damping means more resistance to piston travel - in rebound, more resistance means less inclination to return - the big american car/falcadore wallow is because of lots of rebound damping. I reckon the Celica front end felt alright but the rear was loose but handles the hits OK - maybe lower rear rebound. My guess. Everything I've read always says keep lots of records on what you're doing, make sure all the non-damper variables are controlled - sort tyre pressures, make sure all the bushes are good, and when you're done go back to the beginning to see if you really were right.

I got the following from a DMS source (can't recall the source) (DMS 50mm has 4 clicks in rebound and 20 in bump):

Symptom
Correction

FRONT END
Front end bounces and/or hops
increase bump setting to hard ( towards 20 )


raise rebound ( towards 3 ) / lower bump ( towards 0 )

Steering feels loose
raise rebound ( towards 3 )

Oversteering
decrease bump setting to soft ( towards 0 )


Lower rebound ( towards 0 )

Understeering
increase bump setting to hard ( towards 20 )


Raise rebound ( towards 3 )

Front end dives
increase bump settings ( towards 20 )




REAR END
Rear end swings out
decrease bump settings to soft ( towards 0 )

Rear end hops
raise rebound ( towards 3 ) / lower bump ( towards 0 )

Rear end too soft ( rolls )
increase bump settings to hard ( towards 20 )


raise rebound ( towards 3 )

Rear end too hard ( uncomfortable )
decrease bump ( towards 0 )


lower rebound ( towards 0 )

Rear end bounces
increase bump settings to hard ( towards 20 )




GENERAL
Car hits bumps hard
lower tire pressure


less preload (lower height rings)


softer springs


softer bump settings ( towards 0 )

Hard to control ( twitchy )
verify alignment and tire pressure

[Ben Wilson]

Remember that damper settings are just one of a multitude of things which can change the handling of a car.

You've also got springs, sway bars, tire choice, tire pressures, geometry changes and wheel offset to think about. This is just off the top of my head, a simple change to camber, castor or toe can fundamentally change the way a car works.

Then there is the nut behind the wheel.....

[Matt Dyne]

Ben...my biggest problem IS the nut behind the wheel...hence my interest to date in setup changes (of anything) has been limited...my view has always been that I should lose weight and drive better both of which are in my control, and will realise a significant improvement over these other things.

However, I'm starting to realise that my driving ability is kind of plateauing...I don't reckon I'm getting any faster with more experience (whereas I was a few years ago)...therefore, starting to look at setup as improvements.

As to my car, one of the buggers is that with the recent strut top changes, Murray had to remove the rebound adjustment because they wouldn't work with the new tops...hence all I've got on the front is bump.

At the end of the day, I would much rather just get in the car and drive it the best I can, and not have to think about setup...I'm not an analytical guy at the best of times but I believe I can drive the car pretty fast with whatever setup I get...but having Marc with me (who is ANALytical) is starting to wear off and I'm thinking more.

[Kagan]

I am with Matt, I have very little idea when it comes to setting up a car, I just learn to drive what I have, and so far I have been lucky with a reasonably well handling car, which I believe others have done the developement on.

But having a car that was setup for me, I think would not only increase my speed a little, but will make the car easier to drive, although to be honest, there isn't to much about the Charade's handling i don't like.

[Matt Dyne]

I am also aware that even the top guys struggle with this...wasn't Chris Atkinson quoted this year as saying he was using a Solberg setup and customising it...so obviously it's a problem across the board.

M

[Kagan]

Was that a Chris thing or a Subaru thing though???

[fro]

Chris has had a few issues this year with set-up, the most notable being at New Zealand where, according to the TV coverage, he changed his anti-roll bar settings, and went backwards.

That said, in almost every WRC show I've seen, someone mentions that "Zey cannot vind ze zetting" or that they have "the good feeling".

[tortfeaser]

I think the good feeling is just Giles P talking about having a rub before a stage. Get in the car and drive it Giles. FFS.

[Kagan]

That said, in almost every WRC show I've seen, someone mentions that "Zey cannot vind ze zetting" or that they have "the good feeling".

Yeah but then again I guess that is the WRC version of I drove like a girl ~ Make excuses as to why you didn't do better, thats just human nature isn't it!!!

[Fiona McM]

I've read the book, watched the movie, spoken to other Familia drivers and am just waiting for Murray to send me the T-Shirt.
You should have a copy of the book Murray does, as I gave you some.

I started on the Michelins with the good grip at Oberon and the setup Murray dialled in. Car worked well but the rear was too hard with 200+ rear springs and a mid setting on the shock of about 12. The front did understeer a bit, but tyre pressure reduced this slightly.
Changed the rear to be softer, 2 clicks off dead soft and it worked better.

Before next event, Set the front to 11. Changed the rears to 180 and bumped up the rear to 6. Car worked well. Even helped me to good placings in Batemans with the Pirelli's I bought and on a relatively soft pressure. Had wheel alignment done.

Had the shocks serviced and changed the front springs. Made them a little harder. Seemed ok at Narooma, but it did skate a bit on some very tight corners. car was predictable until we caught dust and baged it into the tree.

In Canberra with the Dunlops the handling was woeful. The front bounced too much and it was like a pogo stick not really getting much grip and the rear was doing all the work. Changed tyre pressures with no luck. Car was no good on these tyres.

Changed the height and weight of the front springs and reset to 11. Changed the weight of the rear springs, and increased rear bump 2 clicks.

I have been playing with tyre compounds as well as settings and seem to have found a good setup.

Fitting the rear LSD made some changes and dropping the rear 1 click made it grip better.

Car does not have as much power as yours or Michaels, but can maintain more speed through the corners. A tweak to the antilag so it does not bog down as much will see it's launch out of corners improve.

Got a good alignment done by Chris, and Minidulla was a good setup run. Just trying to learn the car and try different things saw us not to far behind the leaders.

You would need to do some back to back runs.
first with your current setup and then try tweaking the bump/rebound and tyre pressures.
Get these to a point and reset them and then try sway bars and spring weights etc.

Take your info and combine.

Research spring weights and deflection rates to get a good idea.

Most WRC springs from what I have seen are now going fewer coils, but increased thickness.
Play with what you have and progress from there.

(smee)

[Spac]

The big thing is to work out what the car is doing wrongly/poorly. I know it sounds incredibly obvious, but that's where the real challenge lies: identifying the existing areas that can be improved.
The bike guys are big on video cameras - video the bike in action over a particular bit of ground and then go back and watch and analyse it.

Grossly insufficent rebound and the car feels like the shocks are rooted - this is usually easy to identify. Mildly insufficent rebound damping, and the car feels slightly wallowy, particularly on fast, undulating bits of road, but is much harder to indentify.

Excess rebound damping allows the car to "pack down" over successive bumps. Basically the excess damping means that the springs don't have the chance to restore the car to its proper height between bumps, and the suspension travel is "used up" after a few bumps.
This is remarkably difficult to identify in a rally car in competiton conditions, because you can never really know what the road is like.
Grossly excess rebound damping tends to make the car lift inside wheels and carry them for longer than it should.


Broadly speaking, high speed compression damping is for "choppy" bits of road (such as corners with embedded rocks in the surface) while low speed compression damping is more for "G-outs" through dips and similar. Obviously, there's a big bit in the middle where both adjustments interact with each other.
Remember that the "high speed" and "low speed" terms relate entirely to the speed the wheel moves at relative to the body, and have nothing to do with how fast the car is travelling!

Cheap shocks invariably have too much HSCD relative to the amount of LSCD which makes them less than ideal for rallying - rally cars need relatively little HSCD, and plenty of LSCD. In contrast, a circuit car basically doen't need to worry about HSCD, and it almost exclusively uses LSCD.
I'm pretty sure this is the main reason why rallying kills Konis - far too much HSCD once the LSCD is set right.


Spring rates are a product of the weight on that end of the car (and the motion ratio of the suspension) and should be fairly simple to calculate if you have corner weight figures. Ballpark damping values can then be calculated and valved in, based on the spring rates used there is no dark art to getting ball-park figures.
The real talent is then making it work for the car and driver in question...

[billdunn]

Matt;

Unfortunately, I dont think this is something that you are going to be able to solve by getting lots of advice of the forum, or phone for that matter.

When you are dealing with the best suspension reasnoble money money can buy, all you are getting is the hardware, it is expected that you will do the hard work - ie the set up.

I have used Drummond, Proflex, STA, JRZ, GAB, Tien and Ralliart gear.

I have the most time for the Proflex and STA gear (Also STA is the JRZ outlet). The reason for this is that both Murray and John are happy to work with me/you.

For the last couple of years, I have moved away from MUrrays Proflex, to the STA stuff. The reason is mainly because John used to work with me years ago, so I know how he works, and he is local, as well, he is far more upto date than the others, technology wise.

Construction wise, STA and Proflex are very similar, both are nearly bullet proof, both require minimal maintenaince.

What I like about tuning STA/JRZ stuff is the canister adjustment system, it beats any other system hands down, and every adjustment takes only seconds, and is very noticable.

TUNING SHOCKS

The only bits of worthwhile advice I can offer you is, one - contact Murray, and pay him to go out testing with you. This will short cut a lot of heart ach and time.
And two - working with John, I learnt to start the settings all on their minimum's, and work upwards, adjusting only the front or the rear, and only one adjuster per shock, each time, and not moving onto the next adjuster, until I was happy, then when moved on to the next adjuster, and you tune that, this gets you in the ball park, where you can then fine tune all the adjusters, at once, by minimal amounts - to suit fuel loads, tempretures, tyres, road conditions and weather etc.
Last piece of advise - write it all down, including all then parameters above. It is very easy to go backwards.

Just remember, one adjustment per time - takes ages, but it is hard to stuff up that way. And go test with Murray - thats my best advice, and learn from him. That is assuming you are still up in Brissie.

Best whishes and luck;

Bill

[Matt Dyne]

Spac...I think this is my biggest problem. I'm a huge fan of not touching anything if it's still working...unfortunately, my car preparation reflects this.

I also am still relatively inexperienced to know what the car is doing "wrong"...if at all.

Marc's got some views, but with all due respect, he's not exactly the experienced driver.

I think what would be good is to give it to somebody else, let them do some laps and tell me what they think. Neal would obviously be reasonably good at this, but he's down there, and I'm up here.

Some random thoughts:

Based on the results the car is getting, I'm thinking that it's pretty good given that it's underpowered (relative to Elf running Evo's) and overweight. As mentioned, I've got no rebound adjustment on the front, and bump is set halfway. I think it handles big hits pretty well, and it's high speed stability (more a function of the alignment possibly) is very good.

Spring rates would be worth looking at because I don't know what they are...Marc, do you remember the corner weights from ROC? also need something to test the existing ones.

The rear bottoms out with both fat bastards in on big dips...also, hit a grid in the QRC and the arse end flipped up enough for the nose to dig in...too hard at the rear?

I'd call it oversteery...but as Mark was saying elsewhere, I kind of like that...it makes it slower for sure, but more predictable in corners when it looks a bit pear shaped.

I've only got a rear LSD too, so that means open front and dodgy viscous centre, so that will be a factor in mid-corner acceleration.

I think it gets the power down reasonably well...front tyres are always more worn than than rears (like no edge and often way more wear generally) but that's probably a factor of weight. Has some low speed understeer.

M