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offset obviously increases or decreases track (how far appart the wheels are from the left and right hand side of the car) usually increased track is good in most circumstances but if it becomes too wide, the car wont be as nimble.
similar principal applies for wheel base front and rear
Here are a few things off the top of my head.Quote:
Originally Posted by 89lude
Offset affects the scrub radius, with a more negative offset giving a more positive scrub radius and a more positive offset giving a more negative scrub radius. A positive scrub radius will have more steering kickback and less steering effort at low speed, whereas a negative or zero scrub radius will have high steering effort at low speed but the steering will tend to wander less because the tyre exerts a smaller moment on the steering axis. This will have a significant effect on feel through the steering wheel when on the limit of the tyre's grip.
Offset also changes the motion ratio ever so slightly in some suspensions which makes the spring/damper effectively slightly softer or harder depending on whether you are increasing or decreasing offset. Offset also affects the location of the roll centre very slightly since the centre of the contact patch which is part of the geometry which defines the roll centre is changed. This affects roll effects in a corner but I don't full understand how, but I don't think anything less than a 2" change in wheel offset would have a measurable effect.
In addition to what I posted above the wheel offset affects the track (distance between the centrelines of the wheels) which will change the amount of load transferred across the chassis to the outside tyre from the inside. Think of it like this, a cornering force produces a roll moment in the car because the lateral force at the tyre is offset from the centre of gravity (CG). Somewhat like a seesaw but in a vertical situation, the tyres push on one end and the mass of the car pushes on the other end. The CG is trying to push its way to the outside of the corner because an object in motion likes to stay in the direction it is going. It is the lateral force at the tyres that forces the car to go in an arc.
Since the lateral force at the tyre is at ground level and the CG is higher up the car tries to rotate or roll (about the roll centre but that is not pertinent to this point). This rotation must be resisted by a vertical force at the outside tyre and the further the outside tyre is from the CG the less significant this force needs to be and hence the less heavily the outer tyre is loaded. So for example in an ideal situation a car with X track (where X is a given constant) will have an outer tyre twice as heavily loaded as a car with 2X track assuming they are in a steady state corner of the same lateral Gs and both cars have the same mass.
If this isn't clear I can draw a picture and scan it.
The way this affects handling is roughly like this: A tyre develop increasing levels of grip as they are loaded vertically, EG. a heavier car car has more grip (friction between the tyres footprint and the road surface) on the same tyres. However an twice the vertical load (weight) on a tyre doesn't give you twice the grip. There is a diminishing return, so if a tyre is initially loaded vertically by say Y Newtons and gives X Newtons amount of peak lateral grip before it breaks away that same tyre when loaded twice as much to 2Y Newtons might only give 1.7X Newtons of peak lateral grip before it lets go.
So if you have less load transferred from the inner tyre to the outer tyre you have more total grip at that pair of tyres. Another way of thinking of it is that your car will never generate as much grip as it does when it is parked :). So vertical load transfer to the outer tyre is to be avoided, and a wider track brought about by lower wheel offset is one way to achieve this. The amounts of offset that are usually discussed here though may not be significant enough to produce a noticeable change in lateral grip available, the effects could be masked by a myriad of other factors. Also aiming for optimum peak lateral grip is only one consideration in setting up a race car, although a fairly significant one.
Sorry for the long rambling/offtopic post but I remember seeing a post regarding wheel offsets and their effect on handling and intended to put together some good thoughts on it and post but never got round to it.
If anything isn't clear in this post then let me know and I will try to clarify.
Wow thats exactly what i was looking for when i posted my thread askign that question! But yeah the concept is crystal clear now. So i would assume that since the effects of offset takes place between a pair of wheels - means that if i have a set of wheels with a higher offset for the rears in comparison to the fronts, that only taking this one factor into account (since the front has a wider track) i would have a marginally grippier front end?
Yeah you're right but my post above really only considers one pair of tyres. Once you start considering a full four wheeled car things start to get a bit more complex as you have to consider how the front and rear suspension, and particularly the roll stiffness, will interact.Quote:
Originally Posted by 89lude
Say for example that the desired effect is less understeer/more front grip so you put some 25mm spacers on the front end it is possible that this will increase the front roll stiffness, so whilst you would expect more grip from that end of the car since there is less load transfer to the outer tyre due to the wider track, that effect might be slightly mitigated by the front roll stiffness increasing relative to the rear. If you then consider that when the front and rear roll stiffnesses of a car interact generally the stiffer end loses grip first due to overloading the tyres, so it would seem that the change to a wider track has effects that could produce both understeer and oversteer. Most likely the positive effect of the change will be more significant than any understeer due to higher front roll stiffness and the net effect will be a grippier front end.
For some anecdotal evidence I run anywhere between 10-15mm lower offsets and 1" wider wheels at the front on my DC5 and it still understeers more than it did previously when I ran very worn semis on the rear and passable ones on the front. So wheel offset is just one tuning tool and it probably isn't nearly as significant as spring or swaybar rates.
HERE is the thread on honda-tech that got me thinking about it. Take anything meb58 says with a massive grain of salt but I think beanbag is on the right track. The guys on the RR/AutoX section on Honda-tech seem to have forgotten more about this than I will ever know so it is a good place to start reading.
how about the putty road....thats pretty twistyQuote:
Originally Posted by bennjamin
nsw has some nice roads leading from the west to the blue mountains, Manly is also a good drive as well as the drive to Kiama, yeh haa :)
and what Nigs mentioned also is a great point :)Quote:
If you want a decent setup... your better of going coilovers from the start. You will have good height and damper adjustability.
For a decent starting set up: Coilovers, sways bars front and rear, strut braces, and alignment and some good tyres on some 15inch wheels. Possibly look into reducing the weight of the vehicle too.
Will this car still be your daily?
spend money on bushes (if your car is beyond 160,000ks on stock ones time to upgrade :))
*check for wear in tie rods/rack ends as well (will make a world of difference to your steering and alignment if these are in good condition)
*decent dampener/spring combo (alot of good kits from Koni with springs included to suit most vehicles with a moderate drop in height (mine was nearly 30mm in height over stock), but the abilty to tweak the dampening makes the ride alot better)
*rear trailing arm bushes
*front and rear strut braces
*rear sway bar (ek4/em1) or ek9 with asr kit (if it's an ek civic anyhow) any is better than none, best per $ mod around
*15x6.5" 38 offset, they don't rub scrub or anything but work well for how you want to drive on a surface that's not perfect
*single direction tyres (tried a good dozen on my car most manufactures as long as theyre good in the rain will suit your daily needs)