Track Testing the Honed Roll Centre Correction Kit

An exciting new Honed product is our suspension geometry correction kit for  ’88-’00 Hondas. This kit will be made up of three sub-products; adjustable tie rod kit, front roll centre correction ball joints and rear roll centre correction brackets.

This kit, when matched with a quality coilover will maximise the mechanical grip and driveability of a Honda Civic, Integra or CR-X.  Like all our products we take our time to ensure the components are fully tested before release and  we’d never offer a product we wouldn’t fit to our own cars.

So with that ethos in mind we sourced a second set of knuckles and trailing arms for our EF Civic and then fitted them with our front roll centre correction ball joints and a prototype set of rear roll centre correction brackets.  The idea being that this will allow us to compare the EF’s performance (with corrected front and rear roll centre heights) against some laps we did recently with the standard geometry (low roll centres).

The trailing arms were stripped and powdercoated black, then we installed the rear roll centre brackets.  Installation of the brackets is a straightforward process, the new bracket simply bolts to the original lower control arm pickup point;  The original welded nut on the trailing arm is cut off, then an extra hole is drilled for the upper mounting bracket of the roll centre correction bracket.  Bolt it up, torque to spec and the install is done.

The front roll centre correction ball joints were installed as per the standard ball joint replacement procedure

We design our parts for hard track use at Honed, so our first stop after the wheel alignment was Winton Raceway.  Since the last event at Winton we’ve fitted the suspension geometry kit and swapped the Rival S tyres on to wider 15×9 and 15×8 6ULs.  Ideally we would have only changed the geometry for a true back to back test.  However the Rivals had to go onto the wider wheels in preparation for Vic Time Attack with the CR-X the next day.

Test car specs:

1989 Civic 25XT – The bare bones Japanese model, with the D15B4 motor
Modifications:
Honed roll centre geometry correction kit front and rear
Tie rod end kit for bumpsteer correction
Brake air guides
Koni sport shocks with GC sleeves
14kg/mm rear springs and 9kg/mm front springs
15×9/8″ 949 Racing 6UL with 225/205 Rival S
Momo steering wheel

The bold items on the list are the changes since our last event.

Our driving impressions following testing are excellent; we cut more than 2 seconds off the previous best lap time.  Turn in is crisp and responsive, and the cornering attitude of the car is much more adjustable mid corner.  Part of that is down to the much wider wheels, but the change in handling matches the great experience we had with Grant’s DC2 which featured an early version of this same suspension geometry concept.

Here’s a short video of one of the better laps for the day, a 1:44.5.  Comparing this video and the earlier video here you can see the difference in driving style required.  With the roll centres corrected with our geometry kit, initial steering inputs are smaller and more precise; mid corner understeer is much less prevalent.

Data Analysis

The graph below shows a comparison our best lap of 1:44.3 with our previous best.  A couple of points of interest stand out:

• The full throttle point in each corner is consistently earlier (1).  This isn’t just the wider wheels at work; even with the 7″ wide wheels the Civic has basically no power understeer. The well worn D15 can’t overpower the grippy Rival S.  The car turns in much better and has substantially better mid corner balance, so the exits of the corners can be straighter and throttle applied earlier.
• The wider wheels produce consistently more lateral Gs in the longer corners (2) with bigger peaks in the short corners.  The Rival S definitely work a lot better on a wider wheel, no surprise here.
• Despite better mid corner speed, straight line speed hasn’t improved much, so the extra mass of the wider wheels and possibly an increase in rolling resistance are playing a role here.  Or maybe it’s just a sign that the old D15B is about ready for retirement.  Oil consumption getting excessive, but we think that’s part of the joy of doing track events in a car that’s had an interesting life full of many neglectful owners.

We’ve got a hill climb event up next where we’ll be swapping back to the OEM geometry.  Following that we’ll be making some further tweaks to the Civic.  The goal is to see how far we can push our lap times the old D15 motor.  We’ll also be installing the geometry kit on the CR-X and a number of our other development partner’s cars. 

Thanks to the good people at Gripshiftslide for the pics.

Honed Roll Centre Correction parts are available from our online store: