Solved

Level 30 driver weight

BMI (Body Mass Index) is a function of height and weight. Ideal BMI is in the range of 18.5 to 24.9, so the taller your driver is the heavier he or she must be to fall in this range.

When you train a driver in iGP they will reduce weight (or increase if they're too light) until they fall somewhere in the ideal range. As soon as this happens the BMI indicator turns green and they will not change weight again no matter how many times you train them.

Johnny

Yes.

And the OP said...

This is incorrect, driver weight has no effect on speed but BMI does. 

I can assure you that driver weight is not active I’ve tested this myself. I’m confident that driver weight no longer has an impact on the pace of the driver. The BMI colour is the important factor.

Except for a brief period in early 2022 driver weight has always been disabled. It was turned on for a few weeks early last year, there was an immediate scrabble for tall female drivers and quite a lot of negative feedback from the community. So the Devs disabled it again then worked on implementing BMI instead.

BTW, the cost in tokens to promote a driver from your academy is 2 x Talent + 10. So a T30 driver should cost 70 tokens, if you were charged 75 you should raise a bug report, I'm sure Support will refund the 5 tokens you were overcharged.

Who suggested that to you?
Looks like you let the T30 contract expire and the game automatically assigned a low level retiring driver.
The good news, assuming nobody has since bought your T30 you will be able to re-sign them.
As for the retiring driver you will have to either let their contract run its course or buy them out.