Update, September 2008: The Kennel Club has approved changes to the tyre and I have now constructed a new tyre jump that conforms to the following new regs.

Hoop-(Tyre) - Aperture diameter 533mm (1ft 9ins) minimum. Aperture centre from the ground: Large Dogs – 800mm (2ft 7.5ins). Medium Dogs – 550mm (1ft 9.6ins). Small Dogs – 490mm (1ft 7.3ins). The hoop to be of a consistent shape, constructed of an impact-absorbing material. The height of the hoop should not be lowered. The tyre/hoop must be directly mounted in a substantial frame structure which must be secured in such a way that dogs cannot knock the obstacle over from either direction; the frame shall not have a beam across the top. 

Training
If your dog is new to agility he or she will need to learn the tyre jump under the supervision of an experienced trainer. The best way to prevent accidents and injuries is to train under controlled conditions. I never place the tyre at an angle or at the end of a line of jumps and I don't let Sasha take it at full speed.  Have fun.
 

Making a tyre jump

First of all you'll need to buy something to make the hoop part of the new tyre.  I thought of buying a swimming noodle like the ones pictured right.  These could be bent into a ring shape with the ends taped together, or you can buy a connector that will do the job for you.  Unfortunately the Kennel Club changed the regs after the end of the swimming season, so I bought 2 metres of pipe insulation as shown on the far right. 

If you are constructing a frame for a tyre jump it needs to be fairly substantial so that it doesn't blow over in the wind or get knocked to pieces by a big dog like Jamie.   The design can vary according to the materials you have at hand but it mustn't have a crosspiece above the tyre.

To make the frame I used the same principle as in the simple jump construction shown left, but in the tyre jump the uprights are longer.  Mine measure 118cm.  

For our jump I've used slightly different feet but this is only because the uprights are lighter than in the original tyre and I needed some extra struts to give it strength.

The pipe insulation was easily bent so that the ends could be taped together to form a hoop.  I was a bit stumped as to how I should suspend the tyre as pipe insulation isn't as tough as a motorbike tyre.  At first I tried to suspend it on chains but the chain pulled through the insulation when I tried to tighten it up. As Sasha is the only one likely to use it I decided that I could simply tape it in place with duck tape.  

Finally I wound some of the tape round the bottom of the hoop so that a stray paw would be less likely to damage it.  After a lick of paint the tyre jump was finished and it was time to try it out on Sasha.  The trouble is she's so quick that we couldn't catch her actually going through it.  The finished jump is shown left and our attempts to catch Sasha going through it are shown below.
 

Weeeeeeee!!!  This is fun.  Have I really got to let Jamie have a go?
 

My go!!!  I can jump it at that height, yes I can, but if you insist I suppose I'd better look silly and do the tyre jump on its side.  Our humans never seem to know what they want these days.