Which rubber?

[Peter Seager-Thomas]

Several year back I made a few sets of tyres, primarily for the Bugatti slot conversions I was doing at the time. The last of these is the car featured in the past builds pre-war section, though this car is wearing some tyres I had made more recently.

There are many suppliers of very good after-market tyres, generally at pretty fair prices, with Wayne Allen in the UK supplying tyres at £1.00 each. The problem with these, and it seems all others, is that they are made in open moulds with one detailed side and one 'rough'.

I made mine in a two part mould with detail on both sides, but remember problems with the urethane used which melted the polystyrene wheels and the polystyrene Airfix track which I used at the time. The Bugs with these tyres ended up with ally rims.

Now I run Scalextric track in order that I can opt for Digital if I wish, so urethane is again an option.

So, would any members care to recommend a good Shore A30 compound? Ideally I would also like a less sticky compound for the front tyres.

Peter.

[Phil Kalbfell]

I have had good results with Smooth On Shore A 30 works well on our tracks.As for fronts I use a 75 shore product that is sold under a local brand name, it has little grip.

[bob]

To breath a bit of life into an older thread. I too use Smooth On products for my tires, I have been making them for a number of years now. I was selling them commercially, but as all hobbies , the business started to take over the hobby aspect, so I now only make what I need and am unable to find anywhere else.

The thing with urethane tires, be they single side formed or double sided, is the actual composition and shore as compared to the end use.
When running on wood for example vs running on plastic, or even smooth vs rough. These mixtures can vary greatly even with using a simple 30 shore mixture. The tires made at the same pour in the same environment can vary anywhere from 25 to 35 shore, just based on mix accuracy, curing temp, and dye percentage.

Humidity is also a big factor, and the air cure vs pressure or vacuum cure even changes the end results. I have used my durometer in checking tires made from different batches of the same shore, and have been able to vary the hardness by using a bit more of part A, than part B, and by using not just black dye or pigment, but mixing in some red also,the pigment also seems to affect the grip.

If you have a 15 mm wheel you want tires for, I machine wheels on my mini lathe that are 15 to 20% smaller in dia, but with the same ridge and shoulder dimensions. This way you get a good snap tight fit of tire to rim also. With very soft shore tires you will get more elasticity as the rpm goes up, so making the tire a tighter fit is an answer for this.

The tire making game is really one of mathematics and patience. I use about a 40 shore, actually 42 to 43 for wood tracks and narrow tires, and a 45 to 48 shore on the same track for wider tires. On plastic such as scalextric I run about 35 to 38shore, and on Ninco about 40 due to, the rougher nature. Carrera track can handle 30, to 35 shore easily.

A wood track surface also plays a big part in the mix. On a wood track painted with simple flat or satin latex I use the 42 shore, but on a shiny surface like polyurethane I go to a 48 to 50 shore.

It is not only a game of getting grip, but also of not getting too much grip. My stock of Smooth On consists of both Vitaflex and Reoflex urethanes, and shores from 25 to 60 which I can custom mix for my needs. I use only black pigment for the tires with some red mixed in, this gives me a black tire, but for some reason the red adds a bit more grip to the final product.

I have found that on wood, Vita flex gives better grip than Reo, but Reoflex is easier to get.

My durometer is used only one way for all hardness tests. I put the tire on the rim, and test the tire at the ridge, not the edge. I had a lot of fun playing around with these mixtures over the years, and have even developed a method for the brass chassis GT type racers where I can recap a sponge tire with urethane, and come up with a tire which performs as well as the original sponge for them.

Anyway I babble, but thought some of this may be of use to anyone still making their own tires.

All the best

Bob