i find it much harder to skid the rear wheel on my bike than my girlfriend's bike. which of these do you think is the biggest culprit?

1. wheel diameter: 20" vs. 700c
2. tire width: 35mm vs. 28mm
3. tire material (??): irc metro vs. continental grand sport
4. gear inches: 75 vs. 70
5. geometry: swift folder vs. kona paddy wagon

hopefully not 1 or 5, because i can't change those. but if you think it is, i'd still be happy to get a good explanation for why.