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Circuit Owner
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Hi Petestrike,

I have used MBFG for my tyre making stuff in the past.

Use the general purpose silicone mould making rubber. I used to use this but actually bought my last batch from another supplier because it was a bit cheaper.

For the tyres themselves I have used the Polytek T Flex 20 and PT Flex 50 rubbers BUT they have hellish short curing times so don't mix more than 40 grammes in TOTAL or it will thicken and set before you finish pouring.

Using a syringe to put the urethane in the moulds makes life a little easier BUT the pot life is too short to make it easy.

My next batch will be done using urethane mould making rubber from a different supplier - this has a pot life of 15-20 minutes rather than 2 minutes and will be far less stressful.

If you do mix only 40 grammes then the best way to measure the pigment is to dip a lolly stick about 10mm into the pot then lift it straight out - this tiny amount of pigment will give you jet black tyres. Make sure you pre-mix the pigment thoroughly into the correct part before combining parts A and B of the urethane.

If you are making small superslix - do not go softer than Shore A 40 - I made some in Shore A 20 and the tyres peel from the rims under cornering and acceleration - urethane stretches more than standard rubber. Shore A 40 or 50 is perfect for these little tyres.

If you make large superslix then Shore A 20 is great - the tyres are really thick so the tyres do not peel off and they are super sticky and actually quite controllable on the edge of adhesion.

I am going to order my next batch of stuff from tiranti.co.uk as they have some shore A 40 slow curing urethane rubber that will make the whole casting process a little less rushed (I hope!) and they are cheaper than MBFG for the stuff I want.
 

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Circuit Owner
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Hi Petestrike,

You are most welcome!

You are right - the silicone mould making material is not particularly critical - a high tensile strength is handy because that makes it more resistant to tearing.

The silicones I have used are all around Shore A 25-27 and are all billed as general purpose mould making material.

On my first attempt at making a mould I forgot to shake the red catalyst. I sweated on it for days before taking the plunge to take the moulds out of the mould boxes only to find they were perfect!!! It seems the red stuff that settles at the bottom is only pigment because the silicone came out white not pink and I have used that mould at least 10 times with no problems. Better to shake it properly though, and I have not forgotten since!!! Silicone seems to be quite forgiving.

The urethane is less forgiving - if you don't make a perfect mix you can get some tyres that don't set properly and ooze out of the mould


This is why I am switching to urethane mould making rubber (rather than urethane casting rubber - it seems to be what most of the professionals/semi-professionals use for tyre making.

By the way - apparently urethane rubber contains alcohol and water and finished tyres can sometimes appear to become "wet" some time after casting - this is normal weeping from the urethane and is not an indication of a problem.

If you use softer urethane - store the tyres side down flat and not in a pile - I shoved about 12 NASCAR tyres into a tub after they were a few days old (fully cured so I thought) and a few weeks later some of them had taken on a distinctly kinked oval shape!

Have fun Pete - and let us know how you get on (preferably with photos) - the urethanes will transform your escorts, zeds and minis on Sport Track. No magnets required.
 

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Circuit Owner
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Hmmm - interesting idea.

Initial thoughts in response......

Getting the wheel perfectly central and parallel to the tube will be tricky - the less central - the more truing will be required.

Depending on the wheel (some hubs/spinners stick out further than the rim so you couldn't do this) you might try this;

Get a sheet of glass.
Cut down the plastic tube to the desired tyres width. Cut the tube as square as possible and sand the edges as smooth as you can.
Spread PVA glue (white wood glue) thinly on the glass.
Stick the wheel, outer rim down, onto the glass.
Stick the plastic tube down around the wheel with the wheel as central as possible.
Wait a couple of days for the PVA to fully dry.
Mix your Urethane and pour into the mould around the edge of the wheel. Use a syringe if you have one and make sure you dribble the urethane in so the air can get out.

Once the urethane has set remove the tube and pull up the wheel/tyre combo.

Wait a couple of days for the urethane to cure properly.

True the tyre and sand the edges to your desired radius.

Now use the tyre as a master to make a silicone mould so you can make more.

Extra thoughts;
If you want the tyre outer edge to be slightly proud of the rim (sticking out wider than the rim) simply make your tube a bit deeper and add a shim on the inner rim to build it up a bit, then turn the tyre around on the rim (inner edge becomes outer edge) and sand it back when truing. Of course I am assuming your wheel has an inner hub that stops you laying it inside edge down - if you can lay it inside edge down then you don't have to turn the tyre around. Just be careful not to damage the rim when sanding the tyre.
 
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