Gentlemen, time to publish all that knowledge base on 'How to Modify your Rubber Cones' that was lost on the last forum. Discuss coil overs somewhere else?

1. Pros and Cons of drilling versus machining

2. How many holes and where to drill them.

3. Are proprietry springs that replace the rubber cones worth the extra cost and how do they affect the character of the ride?

I have never done this as I went to coil overs but I can tell you that when I bought the Coupe it had the GTM modified springs on and they were machined not drilled.

The problem with modifying the rubber cones is that they are an unknown quantity. Unlike steel they are rising rate in the first place and once you start modifying them you have no idea what effect each modification has on the spring rate. At least with steel springs you can calculate or measure the rate so you have a starting point.

In all my years of racing we never touched them as you could not be precise enough to gaurentee a sufficient result, I would personely steer clear of modifying them and either buy new ones or replace with the new spring type. This is my own opinion.

I put 6x 10mm holes thru the rubber at about 45 degees to horizontal at the front - It now feels like the suspension is working over big bumps as opposed to just jarring over them.

I think Malc Jones may be able to shed a little light on this, unless my memory is playing tricks

Did you have any difficulty drilling into the rubber, I would imagine it doesn't cut that cleanly?

My coupe has machined front cones,

One day i will get doughnuts onto a tester and test them scientifically, espcially if i can get use of a machine at work.

from articles i have read also the size of the pad on the trumpet has an effect onteh rate, and if you compare original hilos to std trumpets you will notice the pad is larger efectively increasing the spring rate, and i can see how this can be possible.

With my car i feel the rear may actually be too soft compared to the front, as the car does porpoise on one road which has a very bad surface for this around oxford, its the only road i have exprianced this on. It will be on my test when i go coilover. my views on coil overs/rubber will be saved for another day

WEST

Yes Malc, your input is requested. I know you have been quoted in the past, could we have the benefit of your experience please?

Thanks so for to the replies, interesting to hear so many different points of view. I think there are two more questions to add here.......

4. What is the best method of drilling? does a wood drill work better than HSS bits and what speed works best?

5. Has anyone compared the difference between a standard aluminium cone, a Ripspeed Hi Lo, a Minisport Lo Hi and these machined trumpets which either come from the UK or China (allegedly)

This last I can answer.
The cheapo "hi-lo's" have a very small contact area and quite sharp corners.
The standard front trumpet has a larger contact area and the edge curves over quite gently.
The original Ripspeed Hi-Lo's have about the same contact area as the standard trumpet with a similar curve at the edge.
The Moulton Smootharide trumpets have an even larger contact area with a nice curve at the outside edge.

Just to add a different one into the pot though - the Mini rear trumpet has pretty much the same contact area as the cheapo "hi-lo's" but with a radiused edge. I assume this is another method that BL used to change the effective spring rate whilst actually using the same spring (the lever ratios are also very different between front and rear).

I did some work on a set for a friend where I turned the flange off a set of Mini cones and made it's rear face flat. I then cut the step a little deeper on a set af cheap "hi-lo's" so that the Mini flange would fit over the "hi-lo". This gave him the adjustment whilst retaining the curved surface of the original Mini item.

Iain

Interesting, So was there a noticable change?

I had a set of rear trumpets with a larger than usual flange a while ago (possibly off a van?)
Unfortunatly I didn't do any back to back testing, but the Mini they went in certainly handles nicely.

Not really, used a very blunt HSS bit, stabbed it thru, then kept it turning for a few seconds while it fetched/burnt the unwanted stuff out of the hole. It smoked a bit, and if you don't stand firmly on it, it hurts your wrist when it tries to escape.

Yes, i'm a cowboy

Not at all, someone once described me as a shadetree mechanic, a much nicer way to describe that sort of technique I feel!!

Is that THE REAL SLIM SHADETREE MECHANIC ????

There's quite a bit about this including diagrams showing where and how to modify the cone (by Malcolm Jones from 1991) in the Technical Manual that I bought from Bob Hadlington for a fiver I believe that he has some left.

I thought that you got a tech manual free when you joined the club?
Are you not a member?