had a quick look for something already up but couldnt see anything.
i have always wondered why it is easier to skid on a smaller gear? is it something to do with the ratio between the gear size and the length of your cranks? or something else? happy to have a technical description.
cheers
Harder to start pedalling = harder to stop pedalling…?
basically, the smaller the gear ratio, the more leverage you have, so the more force you can exert via the rear wheel. more force = easier skidding.
likewise, longer cranks give you more leverage, so same argument.
I’ve often wondered that myself. This is how i see it:
When you skid, you need to quickly reverse the momentum of the spinning wheels.
You need to do this by moving your legs only a set distance, say half a crank turn.
To move your legs a set distance, you need to apply a certain force over a certain time.
A high ratio means a greater force, over less time, for the same distance.
A low ratio means less force, over more time.
Since it all happens so quickly, the time taken is very short either way, hence it’s easier with a low ratio.
thanks for all that makes a lot more sense now. 
its simple force and leverage.
if you need to apply less force then its easier.
a bigger leaver makes it easier.
a smaller front ring/bigger rear cog means it takes less force etc
Icecream and roxby get the points.
The whole drivetrain is four levers.
The length of each lever determines the ratio of pedal force to tyre contact patch force.
For a skid with just one leg (order of operations is left to right, as you read it):
Pedal force = Tyre grip force * tyre radius / sprocket radius * chainring radius / crank length
For a double leg skid with equal leg forces, halve that crank force.
The initial force is higher than just the skidding grip force because there’s also torque required to brake the wheel’s rotation and the tyre has a higher coefficient of friction when it’s not skidding (esp in the wet).
In other words, low gear = low leg force, high gear = high leg force, which you hopefully already know intuitively.
what about the same gear ratio but in different sizes???
i’ve run a 46/16 = 2.9 ratio & also a
44 / 15 = 2.9 ratio at various times
and it turns out 55 / 15 was sooooo much harder to skid on