Solved

Slower after pitting

In every race I've watched so far after pitting i'm doing laps like 2 seconds down on what I was doing before and I only start matching the times again towards the end of the stint? How do I overcome this?

its because your car is much heavier after pit stop. The weight comes from the fuel.

ah thanks

To try over come it, you need to consider the length of your stints against the number of stops you are doing.

If you losing lots of time for lots of laps compared to everyone else, you might consider short shorter stints. I know a lot of people try to avoid carrying more than 50l of fuel for example for this reason. I am not sure what the "ceiling" is for fuel weight in this new release.

A bit more detail would be nice on the problem, examples; amount of stints, tyres used in each stint, how much fuel you had and perhaps what your thoughts were on the strategy?

Could be your tire temps are too low which means either you need to get your driver to push in the driver orders for a short time, doing so will expend the drivers health more rapidly and tyre life as well. however if managed well the tyre temps will come up without too much risk.
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your got a set of tyres on that don't work in colder temps (make sure to check under "next race" page, "race tab" "weather forecast" button to get an idea of the track temps), for example hard tyres on a 16'c track? they are likely to remain stone cold, try switching to another set like mediums or softs as these work in those temps and have more grip at the expense of tyre durability, meaning how long they last. however be aware of the amount of tyre wear the track in question produces, it's usually in the "next race" page under the "race" tab. the last one on the list, the more black in that bar the higher the tyre wear is, meaning if a track produces a lot of wear and so the amount of tyre life taken from each lap is higher than a track with lower wear. so you may need mediums at the very least unless you are planning on doing a 4 stopper or even a 5 stopper and could risk soft tyres for these stints, it depends on you.

Having the right tyre and the right temps in those tyres if you are watching from the live viewer is essential to maximizing your ability to race on track and having consistent lap times.

I wouldn't suggest a 1 stopper unless your car is so fast you can run around on the hard tyre and a full fuel load. with the changes to the design side of things just recently, it may not be the best option to have. but if you can manage it without taking too much tyre life or driver health over the duration, you could make it work for you.

How much does the weight of the driver factor into this, it seems that if I have identical amounts of fuel in my cars, the drivers are about as fast or the heavier driver is faster (probably because he has better stats), but it also seems that 10 unit difference in fuel makes a HUGE difference in speed but same amount of difference in driver weight seems to be meaningless.

In the real world, a kg is worth a few tenths to a Formula car, in the game i have no idea if weight is as bigger factor or not.