Tyre Pressures for Motocross Tyres

[Kenneth S (222)]

Hi Guys,

Lately I have been experimenting with tyre pressures and it occurred to me I don't have or never have had a baseline method of setting tyre pressures for my MX bikes.

I'm interested to know if any of you have a proven method you use or do you do it by feel like I always have?

Still love that word MOTOCROSS!

[JohnnyO]

I run 14lbs front and rear on a modern 4 stroke and 12 front and rear on all my vmx bikes.. Unless it rains then I'll drop it to 9 or 10.

[John Orchard]

Motocross Action swear by the process called 'rim clean' (Google it), how much the tyre flexes over the rim and rubs-off the dirt, it is too hit & miss for me.

I base my pressure by tyre flex and terrain I am riding on.  The amount of 'ply's' a tyre has greatly affects it's flex/distorsion, I can actually set my pressure by pushing on it with my hand.  Some Metzelers are 2 ply which require about 14 or 15 pound, Pirelli's that are 3 ply seem happy around 12 pound, yet 6 ply enduro tyres used for motocross (yeh I love that word too lol) would run about 8 or 9 psi.

Sure all the tyre manufacturers make tyres in different ply's; it is usually written on the sidewall of the tyre.  If I am riding in rocky terrain or crashing into logs I'd up the pressures by 2 psi.  I also take into account the tyre temperature; the tyre will flex more (you'll also get more rim-clean) when the tyre is warm & softer, vice-a-versa when cold.

I can spin my mates out by guessing the tyres pressures, to the pound, by pushing on it with my hand, once anyone gets use to it it is quite easy.

[Kenneth S (222)]

Motocross Action swear by the process called 'rim clean' (Google it), how much the tyre flexes over the rim and rubs-off the dirt, it is too hit & miss for me.

I base my pressure by tyre flex and terrain I am riding on.  The amount of 'ply's' a tyre has greatly affects it's flex/distorsion, I can actually set my pressure by pushing on it with my hand.  Some Metzelers are 2 ply which require about 14 or 15 pound, Pirelli's that are 3 ply seem happy around 12 pound, yet 6 ply enduro tyres used for motocross (yeh I love that word too lol) would run about 8 or 9 psi.

Sure all the tyre manufacturers make tyres in different ply's; it is usually written on the sidewall of the tyre.  If I am riding in rocky terrain or crashing into logs I'd up the pressures by 2 psi.  I also take into account the tyre temperature; the tyre will flex more (you'll also get more rim-clean) when the tyre is warm & softer, vice-a-versa when cold.

I can spin my mates out by guessing the tyres pressures, to the pound, by pushing on it with my hand, once anyone gets use to it it is quite easy.

John,
Thanks for this comment it was very helpful. This is a very interesting concept and exactly what I had hoped to learn about. I went practicing yesterday and using this method was able to find some noticeable improvement.
Cheers,
Ken

[TM BILL]

I run about 12 F+R but I doubt it makes much difference to me if there up or down a bit  im only a wobbler not like you professionals 

[oldyzman]

10 PSI if it rocky then 12 PSI

[oldfart]

12psi  front and rear on 2 strokes .... 14psi  on the tractors ( 4 strokes ) 

[firko]

Back in the early 90's I fitted a new rear tyre to my Maico for an upcoming meeting at Dargle and pumped it up to about 40lbs to pop it onto the rim. Something then distracted me and I forgot to let the air down to about 14lbs and it totally went out of my mind until about a week after the meeting. I hadn't noticed any difference between 14lbs and 40lbs, that how much of a mug racer I was.

[John Orchard]

I probably wouldn't notice the difference between 14 & 40 lb with a stiff carcas tyre, as I feel 14 is too high also, I would between 10 and 14.

I did the same thing as you with my Superbike one day, went out with 40 psi bead-seating pressure in the front, it opened my eyes to how a roadrace bike try's to stand-up under brakes with too little air in the front tyre and how precise the steering is with more air.  On the road I've lost the front & crashed with too low a pressure but not with too high a pressure ...... not that I ever made that mistake again!  :-)

[TM BILL]

On a road bike for sure I can notice the difference 

[Tim754]

We found on the 754 sidecar 12 pounds or slightly less (83 squillion kilo-pascals approx) was the go. Mind you we run 4 (yes four!) rim locks.

[JohnnyO]

None of the good modern motocross tyres have heavy duty sidewalls needing low pressures, trail and desert tyres are different.
For motocross 12 front and rear on a 2 stroke and 14 on a modern 4 stroke is the normal.

[80-85 husky]

"The Normal"
Every track is different? a greasy wet clay track i would go as low as 5 or less, on a hard packed fast track with square edges ruts you would want at least 14 - 15 lbs. anything in between.

In an enduro I've changed pressure up to 4 times in one event as the terrain changes.

face it, you should run the lowest acceptable pressure for the track your on as the tyre will give more grip  with less pressure.

[topari]

For typical trail bike riding, we usually sit on the bike and the tyres should spread out a bit and you should be able to see this. This means different pressure for a 120kg rider compared to an 80kg rider.

[JohnnyO]

"The Normal"
Every track is different? a greasy wet clay track i would go as low as 5 or less, on a hard packed fast track with square edges ruts you would want at least 14 - 15 lbs. anything in between.

In an enduro I've changed pressure up to 4 times in one event as the terrain changes.

face it, you should run the lowest acceptable pressure for the track your on as the tyre will give more grip  with less pressure.

We're talking motocross are we not?  And there was no mention of mud riding.
If it was a mud race I'd still never go below 8-10lbs or you'll pinch a tube landing off a jump or a square edge bump beneath the mud.
You don't run low pressures in good conditions, the front will push and wash out and you will pinch a tube hitting sharp edge bumps and jumps. Unless you're just out there cruising around...
I've had flat tyres running 12lbs so there's no way I'd go less than that on a dry track.