Tinkering has its limits.

[Gene_Starwind]

Spacer's Choice Edition only.

By that, I mean you cannot enhance any armor beyond level 50. You CAN raise a item's level beyond 50, but you get no increase in base defense. It's a waste of bits to do so.
Clothing has max rating of 30. Light armor/helmet is 90. Medium armor/helmet is 120. Heavy armor/helmet is 180. There are a few exceptions, such as the MSI Elite Armor you get from Sanjar, which has max base defense of 185. The Chinaera maxes out at 180.
One note is that there is a cap on the cost/level. It's 500,000bits. This does not count the special cap (Science skill 100+) on tinkering Science weapons, which remains at 200bits/level, all the way to level 104. I still have no idea why Employee Benefits remains the only weapon that can neither be tinkered, nor modified.