Some tips for the weekly forzathon.
For the 3 Street scene races. Stay in B class and use the easiest difficulty for an easy win.
For the speed trap. Use the Astmoor speed trap just south of the Mudkicker park. It's the easiest one. With some engine upgrade you will hit 140mph without problems.
For the 10 trading paints. Horizon solo. Go to highway and just hit all the traffic cars on the side. No need to be extra careful.
The Astmoor trap fells almost like cheating! I almost went crazy trying to find one, until someone mentioned it. I normally don't modify or tune my cars, but I had swapped the engine on my Mercedes truck , just because the stock one has an incorrect sound. That is more than enough to reach 140+ mph in Astmoor.
I managed to do the three street races in Expert. So long as you go for ones that don't have tight turns, you'll be fine. And I'm not embarrassed to admit, I used my truck's mass to... "clear" the road from other competitors.
I too didn't have too much trouble completing the MB Truck Weekly Street Races by dropping the difficulty somewhere around Above Average and keeping it on B class.
The truck will comply to the turn-in very well, but only at certain speeds, so I found it to be beneficial to just work with the truck than to make the truck work for me.
And the speed trap. Yeah that was fun. Never had to go searching for a trap that struck a balance between having a low-enough requirement, while having enough straight road to allow you enough room to build up the speed. All I will say is that these challenges are getting harder to complete, and this makes it feels less like an unrewarding grind.
You can definitely win on harder difficulty too. In fact on Costal Charge (west of Bamburgh Castle) you can win on unbeatable due to AI getting often confused along the way. Even in B class they often hit traffic cars, miss the checkpoint, brake on straight road, miss the bridge.. But than that is the only race where I can beat unbeatable regularly.
Also for some reason RWD tunes are way better than AWD ones, imo.