Discontinued tires question.

[Mike_Yi]

I'd recommend changing them all. If you have different tires on the front and rear (or even the same kinds of tires but one set new and one used) you will have different grip levels front-to-rear.

[mikefocke]

will vary as we don't know your level of experience on the track, what kind of track you'll do (DE versus competition, length, speeds, etc), how much track you plan to do, how old the fronts are, what their tread depth is, etc.

I'm guessing that an experienced racer wouldn't be asking. So I'll answer with the safest answer for road use ... 4 tire change even if you have to go with cheaper tires. In CO you get weather and the deepest tread is the safest. For the track, there are such things as track tires and shaved tires that have more grip and are safer except in the rain.

Can experienced track folk mismatch per axle by design, sure. AXers sometimes do. But they know what the effect will be and are safer in handling the results.

(I know the $ feeling...just replaced my 4 because of age for $1060 or so.)