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Ever Decreasing Circles
A Rider's View
By Colin Richardson

Former rider Colin Richardson responds to Ken Nicholson's recent article - Ever Decreasing Circles and explains why race times haven't decreased to the extent that may have been expected.


The analysis is very well thought out but the variable which you haven't taken into consideration is the tyres and carburettors which have been used to slow the sport down.

I was racing in the seventies when you had a choice of two engine suppliers, essentially JAP's and Jawa and also two types of tyres, Dunlop or Barum. However the tyres had treads in some cases nearly twice the depth of the Barum tyres used today. We would then cut the tyres by hand with sharpened hacksaw blades or electrically heated tyre cutters to get down to the canvas.

The Track surface was in the main Arbury Shale, if you remember it was deep red, heavier then today and in most cases the track guys would bind it together with used engine oil dumped on the track surface and mixed in to bind it, not exactly environmentally friendly but very effective. The tracks made grip the and tyres had the capacity to put the horsepower on to the track more efficiently.

The engines revved at a much lower level and the power band output peaked at say 5,000 rpm, the engine would rev to say 7,000 rpm so we as riders played with the throttle to get the optimum power down without over doing it and getting handfuls of wheel spin because you could pass through the first power band and the engine would continue the increase in power and if you could get it right the tyre would maintain to put it onto the track.

The 4 valve engines changed the way power was produced and raised the game. Circulatory engines introduced further changes inadvertently by producing backpressure, the engines did not over rev so easily and in turn the engines put the power onto the track easier.

The tyres continued to develop up until the 80's with Pirellis tyres to its zenith when Briggo introduced the American Carlisle tyres. Speeds had increased to such a point where the riders couldn't handle the grip and the ruling body changed the rules:

Reduction in tyre tread depth
Rubber compounds were changed
Tyre treatments to soften etc were banned
Pre warming of tyres on and off the track banned
Carburettors were restricted to 34mm from 42mm

The tracks no longer have the red shale, they are clay based and the advent of laydowns has meant that engines are now like formula 1 engines and tuned for specific purposes, deep tracks, slick tracks, big tracks, small tracks.

Hence the new phrase of set ups, something which in the 70's and 80's was restricted to tweaks in tyre pressure or jetting or engine timing, is now engine, clutch as well as all the other settings.

Riders now rev the engine to its capacity 12,000 rpm and the if the engine is not set up correctly for the size or surface the set up is lost.

The loss of Arbury shale and secondly the measures taken to artificially restrict the performance of the bikes, have resulted in the mechanics of the bike evolving to compensate and the riding style has changed, including the riders now attacking the circuit with the throttle flat out and adjusting the bike to suit the track surface.

The bikes are totally different but what would be great to see would be grab a Carlisle tyre, bore out the carb to 42mm, add proper shale and oil and see where it leads you!!!! You could see the records fall very quickly.


This article was first published on 30th April 2009


  • Dave Beecroft:

    "What a fascinating article. Basically I don't understand a word of it but at the same time it all seems to make perfect sense! I believe that there have been debates/controversies like this throughout dirt track history, was there not a famous attempted forced change of tyre formation in the late 40's or early 50's? I believe the great leg trailer Oliver Hart, for one, threatened to retire unless the old tyre returned, which I think it did. Someone out there must remember?"

  • Ken Nicholson:

    " It is good to read Colin's points on the technical aspects of speedway. Tyres seem to be a mystery to those of us who do our racing from the terraces. I recall there was a huge controversy in 1996 when solid block tyres were introduced by the FIM and the following year when there were teams accused of softening them with solvents. But other than that, not much seems to have been written about them in the press. The same is probably true for most other technical aspects of speedway, which makes Colin's points all the more interesting and important. The idea of needing to attack the track more nowadays is very interesting also. I wonder if this has led to more complaints from riders about a track being inconsistent (which every rider seems to say when interviewed!) or rain-offs becoming more commonplace."

  • Tony Richardson:

    "I agree with Colin's reply especially about the track. I rode as a junior in the mid 80's to 1990 when at first the engine oil was put on the track during the racing. The track surface was better to ride and break up, when they changed it to having a tank/bottle to catch the oil the tracks started to rut up and the shale flew about more. That in turn brought the dirt deflectors which to me cause a lot of the first bend crashes now. I was talking about this last night at Redcar if they somehow used the old oil (or something else) to bind the shale together more the dirt deflectors could be a thing of the past."

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