Most of the time overcoming your fear and weighting the front of the bike helps traction, cornering and control…

…except in greasy mud. Why is that? Answers to GCSE/A level physics standard preferred (degree level also accepted).

Cos you’ve got shit tyres

The tyre grips in the surface but the surface isn’t attached to the rest, also if there is hard under the surface then the tyre can’t bite into that but clogs on the mud.

Same thing happens on scree, but way more terrifying

The operative word is greasy. Normally increasing the pressure increases friction as we see in F1 and downforce. But if you lubricate the surfaces, and mud is a very good lubricating agent, then applying more force just causes loss of grip earlier.

because there is no grip to be had on greasy mud
So better to go light and don’t brake or steer
or if its on an off camber bend then foot out and hope for a miracle which wont arrive

GCSE 3/5 answer:

Most of the time there is more grip (friction between tyres and ground) available, so moving from unweighted to weighted helps.

In greasy mud, there isn’t any more grip available so weighting increases the force past what the friction of the tyres on the ground can provide.

Cos it’s slippy.

Yeah, I think I’m in the school of “there isn’t any more grip to be had”.

How about this for a sketch answer?

Usually weighting the front provides more grip, but also *demands* more grip to get the increased front weight round the corner. Fortunately you have tyres which increase contact patch as you weight them, so usually you get more grip than you needed.

In mud that doesn’t happen for reasons given above.

So how does getting to the back work then? I guess it means we demand less grip of the front so it generally does keep traction. (This works in normal conditions too but is not the best option as demanding and getting more grip gives better results). Steering the front therefore succeeds in turning the whole bike – rear and possibly front grip is lost in the process but usually catches up eventually after a period where the bike is pointing to the desired direction but not moving that way yet.

As a bonus, being at the back makes the occasional slide out less painful.

0/5 for gcse as I haven’t explained what it means to demand grip or even quoted F=uR but I guess we can all join the dots.

As a hi-jack/aside, does the above mean tyre choice is less important in really greasy mud?

Very very greasy xc race a few weekends ago, racing there again in a few weeks and wondering if i should put on mud tyres if it rains. Long steep fireroad drag climbs mean rolling restance important, but steep descents too. Will probably use rocket rons front and rear, but considering beavers if wet.

Also when is mud greasiest?

Back up the top there, my thoughts were the worst is the layer on hardpack. Summer with a hint of rain on a broken surface.

If you can get the bike down a slope while “letting it go” or “rolling/sliding with it” then go for it. Also pick where you are going to drop the most time, grinding up (yes) or running down (no)

when is mud greasiest?

Usually after Glastonbury.

MTB Marathon Rd 2 at Rhayader yesterday – most of the descents ended up being very greasy clay with ruts, best thing I did was let a lot of air out of my front tyre, dropper fully in, hang off the back and just hold on, trying to stay off the brakes, dabbing as required. Only came off once, proper over the bars, but it was soft and grassy.

It was harder trying to slow down so as not to just batter through those walking/going very slow, recovering from falls.

Most of the time overcoming your fear and weighting the front of the bike helps traction, cornering and control…

I wouldn’t say ‘most’ of the time.

This is a technique for open fast corners where your bike is in a steady position going round the bend. For twisty corners, UNweight the front. The closer your weight is to the rear axle, the less force required to pivot you and your bike around the rear wheel, which is how the bike changes direction when you steer.

However in fast long corners, not much force is required to pivot the bike, but much more is required to resist the centrifugal force.

Also when is mud greasiest?

Completely depends on the mud. Do this sport long enough and you’ll become intimately familiar with all the different kinds of mud there are and how they affect riding.

Interesting molgrips

Do you specificaly mean when you steer, as opposed to lean the bike or countersteer?