Drilling Radius Rods for Castor - Prelude, EF Civic, Accord

**McChook** · 24-06-2004 11:30 PM

Hey guys

Now, you all read my fantastic copy and paste article on Castor - "Technical suspension Definitions". If not READ IT NOW. Well, now you learn how to get it. How, well, read on and I shall show you.

Before we start
I OR OZHONDA CLAIM NO RESPONSIBILITY FOR YOUR OWN ACTIONS AS A RESULT OF THIS THREAD - DO SO AT OWN RISK

DO NOT ATTEMPT UNLESS YOU HAVE ACCESS TO A DRILL PRESS

WHEEL ALIGNMENT IS NECCESSARY AFTER ADJUSTIG THE CASTOR

So, the time came to get some castor...

Firstly, I payed a visit to the firiendly guys at HONBITS, in Smithfield. I found myself (yes, I looked for them myself, since I kinda work in the field ya see) a pair of Honda Prelude 97 model raidus rods (SeeAPENDIX A for what radius rods are and do).

I recomend you buy yourself a second pair of radius rods incase you stuff it up, and don't use the set you have on the car - coz if you stuff up, no driving your prelude til you get some. I CAN SUPPLY THEM SHORTLY, but they can be very cheap or very expensive....

So, Took them home.
This is what you start with

1 pair of your average radius rods...

Now, on the 5th gen rod, measure 19mm from the centre of the bottom hole to BELOW the hole. This gives you enough room on the flat piece of iron to work with before it rounds off. I suggest you use a whole punch or paint marker to mark centre of the whole. Use a PILOT HOLE to drill the centre whole. I suggest you use RP7 or WD40 to lubricate all holes drilled.

Drill like so....

then drill with the correct size drill to atch original holes like so

Now, double check you have drilled in the centre of the rod - if you haven't, that is not problem, just make sure the same whole on the OTHER rod is exactly the same, and mount hole which has the shortlest distance the outside wheel....
If all is good, repeat on the second whole. End result SHOULD be like this

So, then, repeat the above steps on the other rod, and you have 2 re-drilled radius rods.

Great, but what the hell does it do??
Well, the act is basically shortening the length of the radius rod, thus pulling the wheels firther forward, and change the Shock absorber angle. The result is that the wheel must now follow the axis of the lower control arm and top of shock absorber (for a clarification see Castor Explained - only difference to the pictore is that we are moving the LOWER pivot fowrard, not the top pivot backwards

Next step is to use Urethane Bushes - a step I will add to this post
Final step is installation and testing the fruits of your labour and WHEEL ALIGNMENT IS NECESSARY.

I will also do a write up of how to do your own wheel alignment, and how to measure how much castor you have.

Remember, this can be applied to ALL PRELUDES, from 1st to 5th Gen, they all have radius rods....

Castor will result in MUCH beter turn in - That's right, LESS UNDERSTEER. Exactly how much I will review AFTER they are installed and aligned

All words and pictures by Matt Cook. If you wish to duplicate, ask me.
APPENDIX A
Radius rods are simply a rod of cast iron. The connect to the Lower Control Arm, and are held in place to the Front Crossmember. Basically, it hold a constant radius between the cross frame and the wheel when it turns. A very simple and cheap device, and very effective - not used by honda anymore as it can be one less item to replace in repair of accident, as there are many other ways to control the LCA - however, in the Prelude case, Radius Rods are a GREAT THING.