Suspension suggestions?

[Jonald]

btw brendan, empty your inbox bro!

[Limbo]

if your gonna only drive on the road save your money and get a decent brand shock & spring combo. Try finding something that has already been matched as they usually ride alot better.

Coilovers are crappy rides, they are mainly for track where you need to be able to adjust your height in a hurry.

ALso since your new it could take you forever to even know what settings to adjust your coilovers to. If you adjust it wrong you will hate them for the wrong reasons.

[JohnL]

teh_mechanic hit it on the head. I have the koni's on stiffest setting because of the scrub issue. I had it on sports setting(which i believe is middle turn) and with just me in the car, no scrub... Once i had a passenger it was burrrrr. Put it on stiffest, i can get 4 ppl in the car before it starts to burrr.

The only other time it will start scrubbing as you said is it really uneven roads and while turning hard. But the koni's have definately helped my scrubbing issue

Understand. My point is that while this may help alleviate the symptom it's really the wrong medicine for the illness. The side affects will affect handling and ride characteristics, maybe in a a good way but maybe in a bad way. If it works well enough for you and the side affects are good or indifferent then I suppose it's a legitimate 'treatment'. The only way to completely cure the malady with no side affects is by surgery, i.e. panelwork.

Personally, I like my Konis on the stiffest setting, but only because of how it makes the car handle (though I am probably attempting to make up for the too soft standard springs, with stiffer springs the 'best' damper setting may well be softer, i.e getting the desired handling responsiveness from stiffer springs rather than overly stiff damper settings). To get this responsiveness I'm happy to put up with a harsher ride, though it's only a real issue on broken surfaces.

The good side affect in my car's case is that this lessens how often the rear suspension bottoms out with a back seat full of passengers / bootfull of crap, which is a bit strange because the adjustment is supposedly only for rebound, which you wouldn't think would affect this problem as stiffer bump valving would?

It may be that there is some 'crosstalk' in the damper, i.e. in theory the rebound adjustment is independant from the bump valving, but in practice the rebound adjustment may not be 100% independant from the bump stiffness. This is apparently quite common with adjustable dampers (i.e. a change to either bump or rebound having some unplanned affect on the other setting), but more so / often with lesser quality brands than Koni (though I read that it's very hard to completely eliminate this from an adjustable damper).

[JohnL]

ill probably appear noobish by saying this, but normally bigger wheels means lower profile tyres, which means less air required for same tyre pressure and more responses from bumps on the road, so in that regard it could affect damper choices, altho not by much. i went from 13s with high profile grippy tyres to 15s with low profile grippy tyres and the response difference when you go over a bump is more noticeable, with the 13s and the bigger tyres being more floatier, and the 15s being more responsive and slightly annoying on bumps.

All else being equal, I think it's less the volume of air (i.e. the size of the air cavity) inside the lower profile tyre than the shorter side wall being inherantly stiffer (than with a higher profile tyre) that increases response to steering input as well as increasing harshness over bumps etc.

Tyre profile (and psi and sidwall stiffness generally) affects overall spring rate because the tyre is effectively the first of two springs in series (the tyre, then the coil spring itself), but it's hard to predict what the affects of increasing tyre stiffness might be for damper rates because the tyre is an undamped spring that is typically very much stiffer than the coil spring, which is damped.

Note that in F1 cars and similar, that the tyre is the major spring in that it's usually (always?) softer than the coil and accounts for the majority of the 'suspension' compliance.

[string]

JohnL have you actually dialed down your Koni's to a softer level and tested the "handling". Steering response is far from a good gauge.

Also, if you wanted something with more bump damping you shouldn't have gone with Koni's in the first place. High rebound is all part of the Koni experience.

[Jonald]

I forgot to mention that i agree with what you mean JohnL. It does give me better handling. All the points you mentioned i agree with.

[JohnL]

JohnL have you actually dialed down your Koni's to a softer level and tested the "handling". Steering response is far from a good gauge.

String,
Yes, and I do know good handling from bad. I used to have a 'clubman' style sportscar that would out-steer and out-corner almost anything on the road (out accelerate and brake most too), an Alfa Romeo which was just really sweet in it's handling (had Koni 'reds'), and I raced karts for years and was fairly good at it. I've also owned quite a few fairly ordinary handling cars as well as some real shitboxes...

I've had the front Koni's just about everywhere from full soft to full hard. Of these settings I prefer the full hard, really disliked full soft. The rears are more problematic to adjust, you tend not to do it just on a whim because they need to come out to make any change. I first installed the rears at 1 turn from soft (which was good), then tried full soft (which I did not like), now at full hard (best yet).

I really like good steering response, so long as it doesn't also mean erratic or unstable handling. I may possibly be giving up some outright grip with the stiff damper settings (may not, grip is pretty good considering the cheap hard tyres I'm running, surprisingly so), but when there are a lot of potholes it's nice to be able to just twitch the steering wheel a little this way and that and have the car go just where you want it when you want it to (an important part of this is getting the pressures right for the tyres you're running). For me it's a major part of the enjoyment of the driving experience, more so than pulling really big Gs around corners (what can I say, I'm getting older!).

My car's handling is very good considering the springs are way too soft, those tyres, and that it could really use a stiffer rear ARB (it's getting close to neutral because of some other tweaks I've done but a bit less understeer would be nice, and it does still roll a bit too much in longer corners). At first I was wary of full stiff, I more than half expected it would make the car twitchy and hard to deal with at speed on bumpy sirfaces, but this hasn't turned out to be the case.

On full stiff it's very well damped / controlled in roll and also provides rapid weight transfer in transitional states (which is what gives the good steering response, that and properly high tyre pressures, and / or better tyres), but it's also remarkably compliant over more savage bumps. I can only assume Koni has the low shaft speed input vs high shaft speed input damping well sorted.

Koni uses a 'digressive' damper curve, meaning that the damper is effectively stiffer at low shaft input speeds (for better control of low speed inputs such as body roll, and speeds up the rate of weight transfer for faster response) than it is at faster shaft speeds (to allow adequate compliance over larger or sudden bumps).

To be clearer, a digressive damper isn't actually softer at faster shaft speeds, but if you draw it out on a graph with shaft input speed on one plane and damper resistance on the other plane, then the resistance component of the curve will flatten off as shaft speed rises, compared to a 'linear' damper where the 'curve' will be a rising straight line, or a 'progressive' damper where the curve will rise more steeply as shaft input speed increases.

Also, if you wanted something with more bump damping you shouldn't have gone with Koni's in the first place. High rebound is all part of the Koni experience.

What would you suggest then? There's bugger all around better than the Koni, except perhaps a Koni fitted with a bump stiffness adjuster as well (they can be retro fitted for additional $). The problem is you don't know what you've got until you have it on the car, but having said that I'm very happy with them, they just 'feel' a little soft in bump (fronts more so than rears). If I were to have stiffer bump valves fitted, it might not be so good, I really have no way of knowing without trying it. I suspect stiffer springs would probably help by adding more resistance to bump forces.

[SeverAMV]

All else being equal, I think it's less the volume of air (i.e. the size of the air cavity) inside the lower profile tyre than the shorter side wall being inherantly stiffer (than with a higher profile tyre) that increases response to steering input as well as increasing harshness over bumps etc.

Tyre profile (and psi and sidwall stiffness generally) affects overall spring rate because the tyre is effectively the first of two springs in series (the tyre, then the coil spring itself), but it's hard to predict what the affects of increasing tyre stiffness might be for damper rates because the tyre is an undamped spring that is typically very much stiffer than the coil spring, which is damped.

Note that in F1 cars and similar, that the tyre is the major spring in that it's usually (always?) softer than the coil and accounts for the majority of the 'suspension' compliance.

sorry if my explanation seemed vague but that was generally what i was implying. a higher sidewall profile means that more air will be required for the tyre to reach the same pressure, thus making the tyre seem more bouyant/floaty as there is more air between the tyre and the wheel, thus making response slightly dull. but the other stuff you mention is interesting.

[JohnL]

sorry if my explanation seemed vague but that was generally what i was implying. a higher sidewall profile means that more air will be required for the tyre to reach the same pressure, thus making the tyre seem more bouyant/floaty as there is more air between the tyre and the wheel, thus making response slightly dull. but the other stuff you mention is interesting.

I doubt it's actually the volume of air in the higher profile tyre that causes it to be "slightly dull" and "bouyant/floaty" compared to a lower profile tyre. I think its more likely that it's the sidewall compliance itself that causes this. The problem with seeing the difference is that the two tend to go hand in hand, i.e. low profile and less air volume, easy to mistake the affect of one for the affect of the other.

The sidewall stiffness of a low profile tyre tends by necessity to be stiffer than sidewall of a higher profile tyre. But, if the sidewall stiffness were the same with both kinds of tyre, then both kinds of tyre would 'compress' to the same degree for the same loading or impact on the tread and behave more or less the same up to a certain point, but after that point the tread on the lower profile tyre would 'bottom out' against the rim before the tyre with the higher sidewall would. This would cause an instantaneous and very harsh impact on the rim itself, causing an effective abrupt increase in the tyre 'spring rate' (to infinity) that could cause handling issues as well as rim damage. The issue is the distance from tread to rim and sidewall stiffness, not the air volume.

In reality the sidewall of the lower profile tyre is very likely to be significantly stiffer than that on the higher profile, at least partly to avoid this potentially catastrophic problem (though some higher profile tyres will have quite stiff sidewalls, rally tyres for instance). As a consequence of this an increased loading or an impact to the tread will be absorbed with greater resistance by the stiffer sidewall of the lower profile tyre than with the softer sidewall of the higher profile tyre. The occupants of the car will feel this as the tyre being less 'dull or 'bouyant/floaty'.

I hope I'm being clear, it's harder to explain than you'd think!

[SeverAMV]

I doubt it's actually the volume of air in the higher profile tyre that causes it to be "slightly dull" and "bouyant/floaty" compared to a lower profile tyre. I think its more likely that it's the sidewall compliance itself that causes this. The problem with seeing the difference is that the two tend to go hand in hand, i.e. low profile and less air volume, easy to mistake the affect of one for the affect of the other.

The sidewall stiffness of a low profile tyre tends by necessity to be stiffer than sidewall of a higher profile tyre. But, if the sidewall stiffness were the same with both kinds of tyre, then both kinds of tyre would 'compress' to the same degree for the same loading or impact on the tread and behave more or less the same up to a certain point, but after that point the tread on the lower profile tyre would 'bottom out' against the rim before the tyre with the higher sidewall would. This would cause an instantaneous and very harsh impact on the rim itself, causing an effective abrupt increase in the tyre 'spring rate' (to infinity) that could cause handling issues as well as rim damage. The issue is the distance from tread to rim and sidewall stiffness, not the air volume.

In reality the sidewall of the lower profile tyre is very likely to be significantly stiffer than that on the higher profile, at least partly to avoid this potentially catastrophic problem (though some higher profile tyres will have quite stiff sidewalls, rally tyres for instance). As a consequence of this an increased loading or an impact to the tread will be absorbed with greater resistance by the stiffer sidewall of the lower profile tyre than with the softer sidewall of the higher profile tyre. The occupants of the car will feel this as the tyre being less 'dull or 'bouyant/floaty'.

I hope I'm being clear, it's harder to explain than you'd think!

yeah, your explanations are understandable. im just not too good with the mechanical explanations you post in the other threads. my mechanical knowledge is quite limited compared to my physics knowledge.

but back to the start, i believe the bridgestone adrenalin tyres (forgot to mention earlier) use a softer sidewall than most high performance tyres from what im hearing. so it is rather similar to using higher sidewall profile tyres made out of an equally soft compound. but swapping to a bigger rim size can bring out more of the steering quirks outta the suspension setup. since the swap to low profile tyres and bigger wheels, i can notice the tyres going over every bump and the places where i would be able to 'float' over with the high profiles now trigger bump steer. but thats probably more due to dead shocks and increases in responsiveness of the tyres thats causing it. should be sorted out shortly once i can sort out the problems with my coilies.

[JohnL]

yeah, your explanations are understandable. im just not too good with the mechanical explanations you post in the other threads. my mechanical knowledge is quite limited compared to my physics knowledge.

IMO an understanding of the basic first principles of physics is essential to any meaningful understanding of chassis dynamics, Newton will take you far if you apply him thoughtfully!

but back to the start, i believe the bridgestone adrenalin tyres (forgot to mention earlier) use a softer sidewall than most high performance tyres from what im hearing. so it is rather similar to using higher sidewall profile tyres made out of an equally soft compound. but swapping to a bigger rim size can bring out more of the steering quirks outta the suspension setup. since the swap to low profile tyres and bigger wheels, i can notice the tyres going over every bump and the places where i would be able to 'float' over with the high profiles now trigger bump steer. but thats probably more due to dead shocks and increases in responsiveness of the tyres thats causing it. should be sorted out shortly once i can sort out the problems with my coilies.

My bet is that while this tyre may have a softer sidewall than other tyres in it's class (and I don't know, I'm accepting your description), it will be relatively softer, but still likely to be significantly stiffer than most high profile tyres. A harsher ride is to be expected when changing from a higher to a lower profile tyre.

You say "bump steer" and "since the swap to low profile tyres and bigger wheels". Does this also mean a significantly wider tyre than standard? If so then an increase in what may seem like bump steer isn't to be unexpected. Assuming this isn't actually bump steer (and it probably isn't if it wasn't there before with the high profile tyres, though it could be...), it may be torque steer associated with effective 'scrub radius'. You don't need to be accelerating hard for torque steer to occur, anytime some power (with a front driver) or braking is being applied and you encounter an irregularity in the road surface it's possible to experience significant torque steer if the steering geometry and / or tyres makes the car susceptible to it.

Scrub radius is defined as the 'lateral distance from the point at which the steering axis intersects the ground to the nominal centre of the contact patch'. Note that I placed 'nominal' in italics, and also note that the centre of the contact patch really means the point that represents the average point of loading of the contact patch, which may not be in the geometric centre of it. E.g. if you have say neg camber then the 'centre' of the contact patch will be somewhat toward the inside of the contact patch, being the 'centre of loading', and would be toward the outside with pos camber.

The problem is that the 'centre of loading' is not static, it moves across the face of the contact patch as camber changes or you traverse bumps and undulations (anything that causes more weight to be carried on one side of the contact patch vs the other).

So what does scrub radius do, I hear you ask. It causes the steering axis to be offset from the centre of contact patch loading so tyre forces are fed into the steering from a laterally offset point. I.e. it creates a relatively small virtual 'lever arm' through which tyre forces are fed into the steering axis, and has the affect of causing the wheel to pull one way or the other, depending on whether SR is pos or neg (pos SR is when the centre of loading is to the outside of the steering axis, and neg when the centre of loading is to the inside of the steering axis).

It adds some weight and feel to the steering, but on a smooth road the forces it induces are in balance side to side, so the car doesn't pull to one side but tracks straight. For most front drivers the nominal (on paper) SR is zero or very close to it in order to minimise torque steer effects, but that's not the whole story.

Here's where 'nominal' comes in. The actual SR isn't static, the effective SR changes if the centre of loading changes (bumps etc), and when this happens on one wheel the affect becomes unbalanced side to side and the car will momentarily pull to one side. This is normal, and gives some 'feedback' to the driver, but you don't want it to be excessive or the steering will get twitchy and torque steer under hard accelration will become problematic on less than smooth roads (try driving a Camira with wide tyres, it can nearly rip the wheel out of your hands on poor sufaces!). However, when you put substantially wider tyres on the car the range of possible effective SR change increases, more so the wider the tyres are. This means that problems associated with torque steer can increase beyond what is comfortable for the driver.

[kraiye]

has anyone tried KYB's ?