When your talking control tires, why not put it to a tender process. Say different importers submit products for evaluation and a group/commitee votes on the results. That importer then gets the contract for x amount of time (1-2 years etc) at a fixed price which is all submitted at time of tender. That way the importer knows rough quanities he needs of the particular tire over a set period of time and also stops him jacking up the price once winning the tender. If he does, he should lose the contract and it all starts again. Same at the end of the contracted period.
It may sound a little complicated but can be made very simple which I feel could be very effective in helping to reduce costs.