In order to sign a contract with a supplier, the commercials need to negotiate with the suppliers. Just like the sponsors, the suppliers negotiations progress needs to reach 100% to sign the contract. The better the conditions are for the supplier, the faster they will reach 100%. The negotiations will also go faster if the new season has started, and the team doesn't have a supplier contract yet. There are three quality agreement levels in the suppliers. The top two (works & partner) have a limit of teams that the supplier will want to supply. If the limit is reached, then the supplier will cancel all negotiations with the other teams that haven't reached 100% yet. The lowest level (normal) doesn't have such a limit.
The fee that you need to pay to the suppliers is spread out over the season and is paid in the week update. The cost per set is the cost you have to pay every time you order a new set of that type.
This is the best relationship you can have with a supplier. They will always provide you with the latest technology that is available. This also means that they expect a lot from the negotiations, and they will at least require a good sponsorship slot. This means if you offer them a spot, it's a spot less you can offer to the sponsors and the supplier won't have to pay for that slot.
The partner relationship is the second best relationship you can have. It means that you won't have the latest available technology, but that you will have the older technology. The technology improves over the season, but it won't be the latest state of the art technology as with the works deal.
The normal relationship is the lowest you can have, and therefore does not require a sponsorship slot. This deal means that there are no upgrades over the course of the season. Therefore the technology will always stay at the same level, and the characteristics won't improve.
The characteristics of suppliers is adjusted every season. This means that it's no certitude that the top level supplier will give you a good part. But the chance is much, much higher. The top suppliers also develop faster, so they usually catch up faster. But the top suppliers will cost the team more money than the lower suppliers. In the beginning of the season the characteristics are unknown. Once every supplier has done a certain number of kilometers/miles, the characteristics are revealed.
The speed characteristic of an engine defines how powerful the engine is. The more powerful the engine is, the more speed the car will be able to generate.
The acceleration characteristic defines how fast the car will be able to accelerate out of the corner.
How reliable the lifetime of an engine is depends on the reliable characteristic. If it's not reliable then the engine won't last as long, and the lifetime number will be not trustworthy.
The more grip a tire offers, the more grip the car will have in the corners. This statistic reduces heavily over the lifetime of the tire. At the end of the lifetime of the tire, the grip statistic will have reduced to the lowest stat.
The more reliable a tire is, the longer it will last and also the more you can trust the lifetime number.
Wet weather tires are a different kind of tires that are only used in wet races. The better a wet weather tire is, the more grip the tire will have. Intermediate tires are a combination of grip and wet weather characteristics, to define what the actual grip level is.
The higher the performance characteristic, the better the speed will be of the car.
The economical characteristic defines how much fuel is used per lap. A really high characteristic of this type will result in a lower fuel usage per lap.
The performance characteristic for brakes defines how well the brakes work when braking for a corner. The better this characteristic, the faster a car will be able to take corners.
The more reliable the brakes are, the more you can trust the lifespan number and the longer the brakes will last.