If you live in the US then you are spoilt for choice of materials. The silicone of choice for me is Vagabond, then it is a close run thing between Alumilite and Smooth-On. Here in the UK it is difficult to get these but there are routes!! (if you have any problems try looking here

If you have read Jack Stinson's article, (see the section under) making a tyre that is "straight and true" depends on drilling a perfectly perpendicular hole through a thick flat base, (to get the axle "square") and then getting the base plate exactly level so that the depth of silicone is even around the tyre circumference. This really requires quite expensive machinery to achieve, or a degree of skill, so it's out for me!! In trying to get around this problem, it has also been possible to cast a sidewall, it goes like this:-

NOTE: I just looked at Jack's page and I think he has removed the article refered to above

Assemble an axle, wheel, and tyre (I always cast in pairs of course..... who wants one silicone?). Place it (them) onto something flat and smooth, tyre downwards, axle sticking up in the air. I use a piece of plasticard as my "something" and cut it about a quarter of an inch larger than the tyre diameter (this will give you a reasonable thickness to the walls of your mould). It will now look much like Photo One.

At this point, a few things need thinking about !!

Firstly, we intend to cover the tyre and wheel in resin to make our mould, when we do this, the resin will pick up any sidewall detail that might be on the uppermost face of the tyre, BUT, the upper most face is the "back" of the tyre,so we turn the tyre around on the rim to get the detailed sidewall facing upwards. Almost all rims have a raised section (or depression) which is centrally placed so that the tyre can be reversed without being "off-set". (If you want to do one with an offset centre section, it's possible, but this is
not the place or time to go into it !).

Secondly, we need to make a retaining wall around our plasticard base to contain the resin (fairly obvious that !!) I use 2" masking tape made for 1:1 cars. As the resin will have a viscosity of between 1 and 10 (water is 1) , the join between the plasticard base and the masking tape needs to be watertight. I generally sand the edge of the plasticard to remove any sharp edges and then wrap the masking tape around the edge, tucking the lower part under the plasticard to assist the seal.We want to cover the tyre and about a quarter to a half an inch of the axle so depending on the width of the tyre , you probably want about one inch to inch and a quarter above the plasticard to make your wall.

Thirdly, when we pour the resin into the mould, the tyres will become bouyant and try to float in the resin. We must prevent this by gluing the tyre/wheel to the plasticard, but we don't want it to be permanant !! I either use two tiny drops of superglue on the tyre (it is the rear face, so doesn't matter too much, or, I use Bostik , smeared around the tyre wall which peels off afterwards quite easily. Although, I have found that the tyres from early Airfix and MRRC cars can melt when in contact with Bostik.

Fourthly (are you still here?!) the resin will stick to just about anything , so we need to make sure that we can get our assembly out again afterwards. You can get mould release agent to spray over the wheel /tyre/axle but it's expensive. I use a light vegetable (sunflower) oil to coat everything sparingly. One of those spray containers works well, but you can just brush it on (the condition of the tyre that you are trying to copy is important here, a good soft tyre requires little oiling but an older dry one is best rubbed over thoughly beforehand).

Dont forget to oil the axle stem too !! Look closely at the wheel, you dont want the resin to get in any "nooks and crannys". If it is a spoked wheel the resin will encase it. I use something like plasticine/bluetack to stop up any "holes" and smooth the rear (uppermost) face of the wheel if required.

You should now have something like PhotoTwo .............Still awake???

Now you just mix your chosen resin and pour it slowly into the mould and wait a couple of minutes while it sets. If you haven't got a watertight seal with the tape, it is at this point that you will panic! Once set you can peel off the tape wall, turn the thing over so that the plasticard is on the top and peel the plasticard off ( that's why you don't stick the tyre down too securely ), you should now see the two tyres sticking out of the resin. Push the axles up from underneath and your wheels and tyres should come out of the mould.

What we have now is a perfectly "straight " mould. The top of the mould is level with the tyre edge and as straight as the originals were on the axle (dont say it!) If you look inside the mould you will see all that lovely sidewall detail. Now take the original tyres off the wheels and push the axles/wheels back into the mould. All you need to do now is support the mould with the top face level (you can use the discarded plasticard base, cut in half, and used as "legs". I put mine in the top of a beaker) See Photo Three.( This is a picture of a different set of wheels- Scalextric Mini ones- I couldn't find the mould for the yellow wheels! )

The very obvious next step is to pour your silicone into the space where the original tyre used to be. When it has cured (usually several hours), push the axle up from underneath, as you did before, and your new silicone tyres will come out of the mould with sidewall detail on the "wrong" face.
Simply reverse the new silicone tyre on the rim and you are done.

..........hello............HELLO !!!!!! (lol)

There are loads of other bits of trouble shooting and hints and tips if you want to hear them, E-mail me, but I'm getting well into the rambling stage now.

Just remember, I was as sane as the next guy 'til I started listening to Jack Stinson !!!!!!!!!!