when ppl say eg 50% tread - how is this measured ? how deep should it be (how much of a penny should fit)?

 

if there is less tred left than the distance from the edge of a penny to the top of lincolns head on a penny you will fail your safety test. 50% tred left just means relative to how much the tire started with there is half as much now.

 

THere is no real way to determine this. If the original tread height is 8mm, and there is 4 mm left, you would be at 50% roughly. (Keep in mind most smart ppl do not run down until they have 0 tread)

They sell tread depth measuring tools,- but I would say that anything over 2-3mm is good.

 

yeah there are little tools which you stick in the thread (between the tread blocks) and have the "base" rest on the top of the thread and it measures the thread depth.. you can also measure the thread depth and see what percentage it is to the tires original thread depth when new (would have been in the tire brochure.. or the manufacturers website if you don't have the brochure)...

if your talking about when people sell rims w/ tires.. I think they are for the most part just guessing.. I doubt they actually go measure the tread depth..

 

New is typically 10/32", and the wear-bars are typically 2/32". So 50% would be 6/32". Most people don't measure it when the tires are brand new, so they guess...