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if a motor suggests a 70~80 amp esc, can I use a 60amp?

Cecil Webb

No. You should not use it. If so, it will burn up the ESC.
Usually you should use ESC equivalent or greater than motor requirements.

ron_van_sommeren

Isn't that just he motor's maximum current rating? Or specifically an ESC rating advice?

Note that motors can handle any voltage, as long as rpm, actual current and actual power don't get too high.
The winding wire insulation/lacquer/resin can handle several hundred volt.

Yes. But only if you prop-load and voltage the motor to draw that current at wide open throttle (WOT).
Current drawn is proportional to pitch, voltage² Kv³ and prop-diameter⁴
All in all massively disproportional effects!
Some scary, some expensive realistic and some extremely silly examples, hopefully instructive as well.

Therefore always measure current in a new or changed power system.
A watt-meter will pay for itself, several times over, bigly.

ron_van_sommeren

Another thing to take into account ...
Power system derating
It is a good practice to have some headroom built in. Motor runs cooler, slightly more efficient too, and you have some leeway should things go south a bit.
About derating motors, controllers, batteries, electronics in general:

• Derating, starting at ... Then there is the 75% rule of thumb ...
  Questions and Answers.... - Page 928 - RCG
  
• About de-rating controllers and motors, starting at for everyone else:
  Questions and Answers.... - Page 290 - RCG
  
• Motorcurrent is proportional to voltage squared, and proportional to Kv cubed.
  A 10% change in battery voltage will give a 20% change in current, a 10% change in Kv will give a 30% increase. Not quite, because battery voltage will sag more due to higher current, but you'll get the idea.
  
• extra current with one or two cells added, simple table
  A.k.a. "Why did my motor and/or controller and/or battery go up in smoke ??? ¨.
  In depth discussion
  www.theampeer.org/ampeer/ampnov15/ampnov15.htm#ADD

Vriendelijke groeten Ron
• Without a watt-meter you're in the dark ... until something starts to glow •
• E-flight calculators • watt-meters • diy motor tips&tricks • Cumulus MFC •

ron_van_sommeren

Using a controller with a higher voltage and/or current rating is not a problem.
That only carries a mass and size 'penalty'.

A controller does not 'force feed' the motor with current.
Only pitch, voltage², Kv³ & gearing³ and prop-diameter⁴ determine actual current, as described earlier in post_#3 above.

The rules are almost the same for power drawn, voltage excepted.
Power is drawn is proportional to voltage³.

At full throttle the controller his little/no effect on current and power drawn, it just passes on what the power system demands, even if it would lead to its fiery death.

Prettig weekend Ron