When I raced in the 80's we got our cars as light as possible since weight takes power to move and more weight takes more power. We geared based on if we could finish the race or not and not on motor temperature or necessarily the best gearing for the track based on speed. It was definitely a game of strategy and trade-offs. Motors and batteries both ran super hot and we needed heat sinks on the motors to help them stay cool. Motors got cleaned out after each heat which helped cool them. Brushes got resurfaced or replaced. Batteries got the discharge light bulb hooked up to them and were then thrown right back on the quick 15 minute charger while still hot to get it charged in time for it's next use. This was tough on batteries and motors. A 5 minute main was an eternity!
Today motors and esc's stay cool. I can get a half an hour of runtime and still be able to touch my motors. The problem is trying to keep the car together for that long on our harder modern tracks. We actually do vary race and qualifying lengths based on attendance. If there are lots of people with many heats to run, we'll do 5 minute qualifiers with a 7-8 minute main. If we get a slow night with less people then we may run 7-8 minute qualifiers with a 10 minute main. Sometimes we have 2 qualifiers and sometimes we have 3. We've even had a 15 minute main. Most prefer to keep it to 10 or under. Keep in mind that some places follow ROAR rules (at least some here do) and they have rules for heat lengths.
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