You don't want a wheel falling off your trailer. That could be one very bad day. Besides a wheel bearing failure you could easily have the lug nuts loosen. The next thing you know the trailer wheel passes you as you go down the road. 

The torque setting for your trailers wheels is generally greater than it is for your car or truck. Plus the trailer nuts loosen easily. On your car or truck the wheels actually turn as you go around a corner. OK - at least the front ones turn. Your trailer wheels are fixed in place. This means that when you go around a corner the wheels actually flex. This loosens the lug nuts, for bolts. 

You can't just tighten the lug nuts with a bigger wrench because you might break the wheel stud. That's an even bigger problem. The solution is to tighten them correctly and do it several times. 

People say you should do it until the nuts actually stabilize. I'm suggesting that you do it after 50, 150 and again at 300 miles. You should be fine then until the next time you remove a wheel. Then you get to do it all over again.

If you're taking a decent size trip with your trailer it's not a bad idea to go around the trailer and check all the lug nuts on the trailer before you leave on any trip.

Torque Specifications*

M10 - 50 lb. ft. 
M12 - 75 - 95 lb. ft.
M14 - 85 -100 lb ft. 

7/16" UNF - 70 -80 lb. ft.
1/2"   UNF - 90 - 120 lb. ft.
9/16" UNF - 120-140 lb. ft. 
5/8"   UNF - 190 - 210 lb. ft.

Torque Specifications for Alcoa aluminum wheels*

1/2"   UNF - 90 - 100 lb. ft.
9/16" UNF - 130-150 lb. ft. 
5/8"   UNF - 140 - 160 lb. ft.

*Always refer to your trailer or wheel manufacturer's recommendations for actual torque values for your application. The above specifications were compiled from multiple sources and may not be appropriate for your application.

Standard Steel
Bolt Torque Specifications

Bolt Size
(in.)
Coarse
Threads/ inch
Standard Dry Torque in Foot-Pounds
SAE
Grade
0-1-2
74,000 psi
Low Carbon
Steel
SAE
Grade 3
100,000 psi
Med. Carbon
Steel
SAE
Grade 5
120,000 psi
Med. Carbon
Heat T. Steel
SAE
Grade 6
133,000 psi
Med. Carbon
Temp. Steel
SAE
Grade 7
133,000 psi
Med. Carbon
Alloy Steel
SAE
Grade 8
150,000 psi
Med. Carbon
Alloy Steel
1/4
20
6
9
10
12.5
13
14
5/16
18
12
17
19
24
25
29
3/8
16
20
30
33
43
44
47
7/16
14
32
47
54
69
71
78
1/2
13
47
69
78
106
110
119
9/16
12
69
103
114
150
154
169
5/8
11
96
145
154
209
215
230
The above chart is taken from the Engineers Handbook.  Most trailer axle studs are Grade 5.