These are the campaign rules for, 'Ultra Lights' (mechs that weigh 10 or 15 tons)
Cockpit Weight ~> Standard 3 Tons ~> Ultra Light 1 Ton
Gyro Weight ~> Standard 1 Ton per 100 Eng Rating ~> Ultra Light 1/4 Ton per 25 Eng Rating
Jump Jet Weight ~> Standard 1/2 Ton per Jump Jet ~> Ultra Light 1/4 Ton per Jump Jet
Engine ~> Standard Starts with 10 heat sinks ~> Ultra Light starts with 7 heat sinks
Armor ~> Armor 1/2 Ton for 8af ~> Ultra Light Armor 1/4 Ton for 4af
Critical Space ~> Standard Mech Sheet ~> Half the Free Critical of Standard Mech Sheet {HD -1 crit ~ CT -1 crit ~ RT/LT -6 crit ~ RA/LA -4 crit}
'Blank' Ultra Light Mech
Ultra Light Mechs use 'small' cockpits, which apply a penalty to pilot skills.
Small character (with a Physical score of 2 or less) are not affected by this penalty.