| Do It with Dermot
Healy - Corner Weights
I sold some lever arm corner weight gauges and had to do an instruction
sheet .....so here it is in case it is of use to others
Preliminaries
1. The usual sign of a car with a significant cornerweight problem is
premature locking of a laden front wheel under braking. Obviously many
cars will lock a front wheel on turn in as it becomes unladen, but if
one front wheel consistently locks prematurely before turn in then corner
weights need checking.
2 You need a decent flat surface…..scrutineering areas in the paddock
often have a flat patch where they check ride heights etc
3 Do the corner weights last…after you have set everything else
& adjusted ride height/rake as these adjustments will affect cornerweights
4 Use the wheels/tyres that you intend to race on & inflate tyres
to correct pressures. It is worth measuring the cirumferance of each set
of pair of tyres as sometimes there can be significant differences between
tyres of the same nominal diameter especially if you are using secondhand
rubber of indeterminate origins.
5 Disconnect rollbars (…just one end of the link will do!)
6 If the car has not been used (and the suspension has been apart) jump
up & down on the car to ensure suspension/springs etc are seated properly.
7 Check that the front suspension appears correctly set – eg pushrod
lengths appear equal, spring platforms in similar positions, no obvious
distortion of rocker arms/wishbones. No obvious wear at the point pushrods
meet wishbones. etc
Using a lever type Cornerweight Gauge
1. Adjust the gauge so that the lifting tab is roughly in line with
the top of the wheel rim. There are several different holes in the gauge
uprightthat allow you to adjust as required
2. Position lifting tab under top edge of wheel rim – some wheel
designsmay make this difficult, in which case you may have to fabricate
a small metal clip that will connect with holes or spokes in the wheeland
provide a location for the gauge lifting tab
3 Lift the wheel several times to break any stickiness between wheel and
ground & then insert a sheet of thin card/or thin metal under the
wheel. Lift the wheel slowly with the cornerweight gauge until you can
just release the card & record the gauge reading. Repeat the process
a couple of times to confirm a consistent reading.
4 Repeat for all four wheels – the absolute values are unimportant.
What you are looking for is a situation where the readings across each
pair of front or rear wheels are broadly similar.
5 If there is an imbalance it will appear in the form of one diagonal
pair of wheels showing low readings – eg LH front 140lbs RH front
180lbsLH Rear 280lbs RH Rear 230lbs
6 An imbalance in any other form suggests something very odd – most
likely an error in the cornerweighting process/uneven floor/things embedded
in tyres preventing the card form sliding out, or something simila.
Correcting an imbalance
1 The adjustment necessary to correct an imbalance will depend on the
suspension design. You will either adjust a pushrod (most F3, FR &
modern FFs), adjust a spring platform (most older cars FFs,FVL,FVJs)or
on some cars with appropriate dampers you will make use of an adjustment
on the damper mounting.
2 There will be a single mode of adjustment appropriate for each car –
eg you should never find yourself adjusting both a pushrod and a coil
platform on a single car
3 ALL adjustment is done at the rear. Adjust the rear corner which is
giving the LOW reading. By raising the coil platform/extending the pushrod
or whatever you will encourage that wheel to take a greater interest in
proceedings. This will automatically correct the low reading of the opposite
diagonal front wheel
4. Quite small adjustments of a coil platform or a pushrod should make
significant difference to the imbalance. If your adjustments are not having
any effect…..then something is wrong with the adjustment process/cornerweighting
process/ or ….the car (it is bending in the middle as the engine
is not really connected to the tub?)
5 By adjusting the corner with the low reading you ensure that your adjustments
are least likely to reduce the ride height. However to correct a severe
imbalance you may need to adjust both rear corners (one side up &
one side down)in which case beware that ride height/rake may be affected
adversely.
6 This adjustment procedure assumes that the front suspension is not significantly
misaligned. If it proves impossible to secure anappropriate balance by
this adjustment process then you should look carefully to see that the
front suspension pushrod lengths are equalized & that rocker arms
have not distorted unduly or damper or pushrod mounting points worn or
elongated.
7 You DO NOT need to seek perfection. If you consider the loads on the
suspension when racing, and the fact that even the smoothest circuit surface
will not be totally flat and free from undulations, there is no special
benefit to be gained by trying to secure 100% balance. A situation where
readings across pairs of wheels show a difference of less than 10% will
probably suffice for most purposes (unless your name is Tristan).
Other thoughts
1. When extending pushrods DO be sure that there remains sufficient
thread in the pushrod to ensure its security. As a rule of thumb you would
not wish to have less that 1.5 times the diameter of the rod end thread
remaining in a collar or pushrod. Pushrods are very highly stressed &
failure could be unpleasant
2 Make sure that the rod ends & thus the pushrods can rotate after
adjustment – ie that the rose joints at each end are not binding
in their housings but are properly centralized. If you cannot rotate a
pushrod slightly, then it is likely to be under severe additional stress
in use and you run a risk of failure
3 It is worth checking corner weights regularly & the convenience
of the lever arm cornerweight gauges make this easy to do at the circuit.
A change in corner weights will alert you to wear and damage that might
otherwise go undetected. Eg- rocker arms (esp on FVLs) will start to bend
and distort, Damper mounting points will elongate, distort and fracture
(eg FVJs) whilst lower wishbones will wear due to high stress at the point
where they connect with pushrods (F3s FRs)
4 Don’t forget to reconnect the roll bars.
Dermot Healy
Disclaimer: The above represents only the unofficial view of
the writer and not of the Monoposto Racing Club in any way whatsover.
Subheadlines and captions are not originated from the named author.
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