CIH's Training Thread

[Tony]

not sure what you mean ?

 

What happens to the chassis at the end of the straight when the power is removed?

[CIH]

weight is transfered to the front ? such as when the brakes are applied ?

[CIH]

oh while I remember how do I convert Toe from mm to minutes ?

[Tony]

oh while I remember how do I convert Toe from mm to minutes ?

 

9' = 1mm

[CIH]

can we still go through roll-oversteer ?

[Tony]

You have the Roll Center, which is the exact instant center that the sprung mass will rotate about at the given position of the individual front or rear suspensions. The Roll Center, itself, is an Instant Center meaning it moves up and down, and even side to side, depending on the geometry, as the suspension cycles.

 

Then you have the vehicle roll axis, which is the line connecting the two roll centers. This basically depicts how the entire spring mass will roll, at a particular position of the suspension. Remember, since the Roll Centers move, so will the vehicle roll axis.

 

Finally, with live axle suspensions, you have the individual suspension roll axis. This depicts how the axle will "steer" relative to the longitudinal vehicle axis as the suspension articulates. This effect is called "roll steer". Depending on the orientation of the suspension's roll axis, the axle will steer different directions, either in to or out off a turn, if you will, as the body rolls. Like the two previous variables, the suspension roll axis changes as the suspension cycles and it is quite possible for a suspension to vary from roll under steer to roll over steer as the suspension cycles. Generally, neutral or roll understeer geometry is preferred over roll oversteer as it provides a more consistent feel to the vehicle when cornering.... normally

[CIH]

How does all this impact upon Scrub radius (SR) ?

[Tony]

How does all this impact upon Scrub radius (SR) ?

 

There's obvious migration of the SR but this is within the suspensions expected articulation cycle, even on lock, transition and lat acc... The perfectly calibrated chassis would maintain the contact patch.

[CIH]

so how does changing camber impact upon all this movement of mass, given that camber itself adjusts how much weight is pressed upon the SR ?

[Tony]

so how does changing camber impact upon all this movement of mass, given that camber itself adjusts how much weight is pressed upon the SR ?

 

A well balanced chassis would be tuned to the inertia moment so that the transitional forces are within the suspensions articulation. It would be assumed the SR migration falls within the same geometric calibration if this moment is during yaw. In the event this situation is purely the moment of inertia then the SR is nothing more than a spectator.

[CIH]

I don't follow how transitional forces could be beyond suspension articulation ? Isn't most/all of the transition prompted by the articulation ?

[Tony]

You have lateral acceleration, particuarly if you go beyond grip limits and you have applied thrust, neither of which are directly involved on the suspensions articulation.

[CIH]

is it fair to say roll-oversteer could be compaired to a pendelum (effect) ? with the movement of mass almost taking on a life of it's own (so to speak).

[Tony]

is it fair to say roll-oversteer could be compaired to a pendelum (effect) ? with the movement of mass almost taking on a life of it's own (so to speak).

 

I suppose that's one way of looking at it.... Remember though this would be lateral across the roll couple.

[CIH]

how does rear-toe impact on a FWD chassis ? I was quite happy with toe-tendencey on the front of that lowered Civic I spoke to you about today but was pretty lost on the rear (forgot to ask when I was on the phone duh).

[Tony]

Normally the trailing wheels would have a zero tendency subject to any play in the bushings. On FRD cars most have a live rear axle or I-beam axle depending on your terminology, on these the toe is more or less beside the point hence the absence of adjusters.

 

Multi-link does have a tendency and since it's not live so this tendency would need to be controlled hence the adjusters, but there's always exceptions, the Civic type-R has a live axle and toe adjusters

[CIH]

but limited dynamic infulence, unlike RWD (or 4WD ?) This '98 civic was IRS and had toe adjustment

[Tony]

but limited dynamic infulence, unlike RWD (or 4WD ?)

 

Very much so.... Look at something like the Land Rover axle's, what you got you keep whatever action the suspension takes, obviously the modern example needs to be a little more agile but the principle's the same.

 

4WD cars have little or no static toe, the wheels are not being pushed or pulled so the bushing compliance should be uniform, there is a tendency though albeit small.

[CIH]

Did a late model 525D on non-rft tyres today. T'was nice. Camber & toe, front and rear with no corners-cut in 40mins.

Tell ya what, a zero-offset wrench is awesome for those pesky upper track-control arm eccentrics on the rear.

[Tony]

Did a late model 525D on non-rft tyres today. T'was nice. Camber & toe, front and rear with no corners-cut in 40mins.

Tell ya what, a zero-offset wrench is awesome for those pesky upper track-control arm eccentrics on the rear.

 

Well done, was the front camber "wheels raised"... Also do you think you are simply more confident now and find this type of calibration run of the mill?

[CIH]

Yeah I go straight to wheels-raised as a matter ofcourse unless it's on eccentrics.

Run of the Mill ? Yeah I guess so. Unless it's modified (very rare for KF) most are fairly straight forward. Except maybe when OEM data is poor but that seems to be quite rare.

 

I agree it's much more frought trying to account for tyre wear, as apposed to handling traits.

[Tony]

Yeah I go straight to wheels-raised as a matter ofcourse unless it's on eccentrics.

Run of the Mill ? Yeah I guess so. Unless it's modified (very rare for KF) most are fairly straight forward. Except maybe when OEM data is poor but that seems to be quite rare.

 

I agree it's much more frought trying to account for tyre wear, as apposed to handling traits.

 

But you are becoming the law of your own example.... meaning you now have the insight to determine what settings work and what won't..... I'm proud of you.

[CIH]

aw shucks you're makein' me blush :angry:

[Mark H.]

So, When does WIM North open then? :angry:.

[CIH]

lol that had already occured to me!

 

I just spent the last 3 hours going through all the Geo reports I'd kept from the past few months and matching them up with the phone-camera picture I got of the corresponding car. I'd gotten a bit lazy keeping a portfolio but have "rationalized" most of it today- kinda.