Why is development going down?

This could be a common thing with the game that I haven't realised, but over time my level and speed of dev is going down. Last season, I was getting dev every 2 races (FYI they are daily) and I got it with 8% extra dev combined. Now however I only get it once every SIX RACES, and its only 6% comb. too. My thoughts about the percentages changing I think may be down to me running the minimal designers on each part needed to get it to arrive at a certain date. If you don't understand what I mean by that, I'm getting them with the minimum number of designers needed for them to come every 6 races. I have 77 total designers, with 11 for each part. It might be because I'm on my 3rd season, or it might be because I've got 52% dev which is more than normal. But if the last statement is the reason, why would it be preventing me from next season dev, that remains at just 7%, from going up as much? Guys just help me!

The higher this seasons design is, the more engineers you will need to design parts every 2 days. So instead of spreading your designers over all your parts, just focus on a couple and switch to other parts once you receive a new design.

Along with this seasons design, next seasons design also slows down. If for example you would focus completely on the next seasons design so that you can start with a 100% car, it would eliminate most of the progress for the season after that. Otherwise it wouldn't stop managers from developing a 100% car every season and that wouldn't be much of a challenge. Now you will either deal with the consequence of a high developed car and pay for it the next season or go with a balanced design that's possible to maintain throughout the seasons.

I for example have a similar design every season. I start with an average design which I develop such that I will reach 100% for this season at some point but also have the similar average design to start with for next season. It will hurt a bit at the start of the season but it's more or less the only way to go for performing consistent and certainly for maintaining a the ranking as a manager.

well thats a pain

but what about only getting 6% combined r&d combiuned each time?

car development is based on how high your current season is.  get close to 100% on this season and you will see as little as 1-2% total gains (if 100% this season you will mostly get 1% next season gains only).

The idea is to prevent someone from starting every season at 100% car.  It isn't a pain, you need to decide if you are running a "normal" development where you start each season in the 50-70% range or if you take the boom or bust stragegy where you start every other season with 100% car and are garbage the following season as you start with low to no development.