Hi Tanggoman,
First of all I recommend Ric’s coaching services. I joined his Classic coaching package for 3 months (about 2 months ago) and I will definitely be signing up for another 3 months after this.
One good reason for doing the MAP test indoors is safety. When concentrating on producing power and trying to read the meter and remember watts and minutes it’s easy not to notice other road users, etc. Try to pick a place without traffic.
In my case, I first did my MAP test indoors but I was not satisfied with my results. I felt I could do much better outdoors on the road. Ric gave me the following instructions:
Warm up for 10-mins, then ease up to 150 W on a flat(ish) road. Over the next ~7-mins wind the power up about 25 W/min to arrive at about 330 W at the end of that *about* 7-mins make sure you are at the base of a hill, at which point, ride at a steady ~330 W for 30-secs (gives you time to change to your small chain ring) and then ramp it up 25 W/min again, until you cannot go any longer. The hill would need to be at least 7 minutes long and you should *generally* stay seated when going uphill (it's fine to occasionally get out the saddle but don't hammer the whole way up out of the saddle!).
FYI, my outdoor MAP was 446W compared with my indoor MAP of just 370W. Note that the starting wattage of 150W was set for me personally, you might want to start at 125W. Trying to get to the base of the hill at the right moment of the test is not easy. It helps if you check out your road beforehand to calculate how far from the base of the hill you should start your test.
I’d definitely go for an increase of 25 W/min rather than 5 W/12 seconds otherwise you will lose track of time and watts very easily, it’s hard enough with 25 W/m. For example, you will be trying to ride 325 W/min and your watts will jumping up and down and when you get to 50 seconds you will forget if you’re supposed to be at 325 W or 300 W or 350 W!
Good luck!