Better turn in , and less understeer?

Folks , is it the rear ARB , or the front ARB one uprates to reduce understeer , and sharpen turn in? Or what else do ypo need to do? Its an 83 Campaign , all standard.

You stiffen the rear, reducing grip to the rear tyres as the car leans over. You can try changing the suspension angles first to give the front end more bite.

RedLexus said

Folks , is it the rear ARB , or the front ARB one uprates to reduce understeer , and sharpen turn in? Or what else do ypo need to do? Its an 83 Campaign , all standard.

Setting 0.5? of toe out (rather than the default 0.5? toe in) will do this.

I'd be tempted to keep stiffness the same front and rear. If you were going to only fit one uprated ARB, do the front. If you stiffen up the rear only, you will greatly reduce the margin between initial understeer and 'snap' oversteer, the back end won't gradually drift out it will grip for longer, but then suddenly lose grip once you reach a particular sideways force on it.

PS fitting lower profile tyres than 70 aspect ratio counts as stiffening, because you're reducing the amount of conical distortion that the tyre will display when its camber is changed (due to the body lean).

I'm running 185/60 14 Jetta steels , with a half degree toe out and about 3/4 to1 degree neg. camber (at a guess). Just the car seems "vague" on turn in , and power understeers on the exit of a corner.

RedLexus said

I'm running 185/60 14 Jetta steels , with a half degree toe out and about 3/4 to1 degree neg. camber (at a guess). Just the car seems "vague" on turn in , and power understeers on the exit of a corner.

What springs (stiffer)?
What's the ride height?
How heavy is the car?

OE Springs and ride height , only chassis mod is a fup' off steel sumpguard! needed for navigation rallies. It ties thefront legs together , and also attaches to the front crossmember. Car should be standard weight , no FRP panels or the like.

RedLexus said

OE Springs and ride height , only chassis mod is a fup' off steel sumpguard! needed for navigation rallies. It ties thefront legs together , and also attaches to the front crossmember. Car should be standard weight , no FRP panels or the like.

Do you need to retain standard ride height?

No , but tbh , the tracks are sooooo unbelievably rough at times , that any lowering would kill the car.

RedLexus said

No , but tbh , the tracks are sooooo unbelievably rough at times , that any lowering would kill the car.

Is it a road or dirt track you're driving on? Surely, if you are driving on dirt tracks, you'd not worry so much about the finer points of suspension tuning, but just use "the Scandanavian flick"?

It doesn't work like that. You need to be running a relatively standard ride height with plenty of underbody protection to be quick on a white.

yeha said

It doesn't work like that. You need to be running a relatively standard ride height with plenty of underbody protection to be quick on a white.

What's a white?

Its both  we could come off an "A" or "B" type road , and into someones farm track!

hi mate,

Stiffer arb's will INCREASE understeer, a good -ve camber angle will give better turn in (m3 csl's run 2 degrees -ve) and maybe SOFTER front suspension.

cheers bob.

bigbob said

hi mate,

Stiffer arb's will INCREASE understeer, a good -ve camber angle will give better turn in (m3 csl's run 2 degrees -ve) and maybe SOFTER front suspension.

cheers bob.

Ride height, and spring stiffness, will be determined by the roughness of the road you're driving on and will set a lower limit on both. Then, you need to compromise the setup of the car to one or other of the extremes your driving on: rough farm tracks or fast tarmac sections. I would suggest that you make the car faster on fast roads and don't worry too much if it slows you on the slower ones - from a purely track racing analysis.

During your analysis, you may find that you can run a slightly stiffer ARB, combined with slightly more supple springs, than would otherwise be optimal for tarmac.

Remember to keep the spring rates front and rear in proportion with each other, so your tarmac setup isn't compromised by oversteer on fast corners.

paul_c said

During your analysis, you may find that you can run a slightly stiffer ARB, combined with slightly more supple springs, than would otherwise be optimal for tarmac.

Remember to keep the spring rates front and rear in proportion with each other, so your tarmac setup isn't compromised by oversteer on fast corners.

Sounds good …. but a stiffer front or rear ARBto negate understeer?

RedLexus said

paul_c said

During your analysis, you may find that you can run a slightly stiffer ARB, combined with slightly more supple springs, than would otherwise be optimal for tarmac.

Remember to keep the spring rates front and rear in proportion with each other, so your tarmac setup isn't compromised by oversteer on fast corners.

Sounds good …. but a stiffer front or rear ARBto negate understeer?

Keep the proportion of stiffness at front/rear the same. As you increase (all round) stiffness, the car will be able to corner faster. For increasing speed during cornering, the car will tend towards oversteer.

In other words, if you want to reduce understeer, make the car be able to go faster around corners.

dude that doesnt really make sense!?!

yes you're right to go round a corner quicker it is best to eliminate as much roll as possible, (on track)
BUT the mk1 chassis tends to understeer on initial turn in of a corner when stiffened too much…
so you have to soften up the front of the car to 'grab' that initial bite when entering a corner.
I think this is more of an issue with uneven or unmade surfaces.

maybe using a higher profile tyre may help?

suspension geometry has a lot to do with it tho'. as we all know even on standard suspension and angles, the mk1 has a tendancy to bump steer slightly and this is eccentuated as you move the ride height about.

cheers bob.

bigbob said

dude that doesnt really make sense!?!

yes you're right to go round a corner quicker it is best to eliminate as much roll as possible, (on track)
BUT the mk1 chassis tends to understeer on initial turn in of a corner when stiffened too much…
so you have to soften up the front of the car to 'grab' that initial bite when entering a corner.
I think this is more of an issue with uneven or unmade surfaces.

maybe using a higher profile tyre may help?

suspension geometry has a lot to do with it tho'. as we all know even on standard suspension and angles, the mk1 has a tendancy to bump steer slightly and this is eccentuated as you move the ride height about.

cheers bob.

Which part of it doesn't make sense? Where is your experience that a car with stiffer suspension understeers more? Bump steer is an inevitibility of the (designed in) neutral steer characterisic if you have a puncture on a front wheel.

Suspension alignment is not a 'right' or 'wrong' thing. It is an adjustment away from optimal position during atraight ahead steady speed, which allows the wheel to be at an optimal position when cornering and/or acceleration/deceleration forces are presented on it. It is also linked to suspension stiffnes and ARB stiffness.

Ride height affects the distance between the centre of gravity and the roll centre, therefore the moment during cornering which puts the sideways force on the car.

Example: with the standard ride height, stiffness and camber (0.33? neg), the contact patch the actual camber the tyre has on the road will go from -0.33? through 0? and into a +ve? amount, perhaps something like 3-4?.

If you lower a car its roll moment is reduced as the distance between roll centre and C of G is reduced. If you also stiffen it (stiffer springs, stiffer ARB) it will lean even less on the sideways force applied. Then if you 'preset' the camber to -0.5?, as you corner it will go through a lesser range of camber, perhaps -0.5? through 0? through to 1?.

Now, this is the complicated part - when a tyre is subjected to a camber, it doesn't ride up onto its edge, like a solid metal wheel would. It distorts, into a conical shape, and this no longer rolls true but rolls towards its smaller diameter end. This is why earlier, I said lower profile tyres 'count' as being stiffer - they less easily distort into a different shape.

This tyre distortion also has another effect - the rubber runs a non-true path on the contact with the road, its contact surface distorts, it 'twists' on contact and returns to the tyre shape when not in contact.

Hence, any cornering force above a walking pace, produces some kind of non-straight behaviour - a sideslip.

So, sideslip is an inevitibility. What you want to do is control it to moderate levels, but much more importantly, preserve the relationship in sideslip front and rear. If you have more sideslip at the front than rear, the car understeers. If you have more at the rear than the front, it oversteers.

You would think that ideally you always have exactly the same sideslip both ends. But driving is not a mechanical computerised exercise, it is a feel and feedback interactive thing which means the driver wants to 'feel' how the car traverses a corner and wants repeated control inputs to produce predictable results. For most drivers, this means mild understeer on turn in and mild oversteer beyond the apex of the corner as it straightens.

IF YOU FIT AN ARB TO JUST THE FRONT OF THE CAR, OR JUST THE REAR, YOU WILL SIGNIFICANTLY ALTER THE RELATIONSHIP BETWEEN FRONT AND REAR SIDESLIP!

Holy Batmobiles , Robin! Now that's technical! 8O