Tire pressure question

[Hogwylde]

Ok, for you woods guys...I have a question. How much air do you run in your tires?? I'm running local (Indiana) hare scrambles and the two closests GNCC's. After the first one, I'm wondering if I should lower my pressures to maximize tire contact or if I'll be asking for trouble. The first lap didn't seem too bad, but at the trail became more rutted and torn up....it just seemed like an effort in futility just to stay up on the bike let alone try to race someone and pick up positions.

I'm thinking about 5-8 PSI per tire as opposed to the manuels recommended 14 PSI would be good. I'm hoping it might give me some more sidewall flexibility and tire contact patch. Does this sound ok or am I asking for trouble from every root, rock and log that I will encounter???

 

[Jh85]

Is your bike set up for off road or MX?

 

[Hogwylde]

Originally posted by Jh85
Is your bike set up for off road or MX?

UMMM.......I'm sorry, wasn't it obviously CLEAR that I'm set up for woods in the first paragraph??? :think: And, if it matters what I'm riding......that's what the signature line is for.

Now I will admit that I do hit the local MX track with a buddy of mine. And, if I'm gonna be jumping over stuff on an MX track, I'll be worried about collapsing the tires and bending the rims on a landing without enough air. Funny thing is though, I ran the C moto at DW'01 with a rear flat and didn't know it until I loaded up the bike for the trip home. That 739AT has some pretty stiff side walls.

 

[wizard69]

I'm not positive but I think 8 is the lowest you should go in the woods.I'f I was you I would wait and see what the track or trails are like then if there wasn't to many hard landings or rocks to pinch the tires I would lower it a little I think 10 would be a good preasure to run it at that's what I run.

 

[Mac]

I run 10 to 12 psi here in rocky NE with heavy duty tubes. I wouldn't go lower than 8psi personally.

 

[Jeff Gilbert]

I ran 8 in both tires at the Amararillo s/f. Lots of rocky stuff and had no problems. I normally run anywhere from 10 to 12 in the rear and 10 to 14 in the front for mx

 

[TheGrinch]

I run about 13 on hard rocky terrain with heavy duty tubes, and 8 on muddy terrain. Any where between 10 -12 for intermediate terrain.

 

[agitt73]

i run 9 psi front and rear
but if its rocky you need to run about 12 psi
to keep from pinching tubes

 

[wardy]

how much do you wiegh? HOw hard do you hit the ruts etc. are you aggressive on logs and things or are you soft on obstacles? thats alot of what really matters. I would run 12-14 psi. but it also depends on the sidewall on the tires, if your running stiff tires lower pressures will work, but soft tires need a little more pressure.
I highly doubt that tire pressure will make that big of difference, I think from what you are saying there are other factors working here...

wardy

 

[Hogwylde]

Originally posted by wardy
how much do you wiegh?

I highly doubt that tire pressure will make that big of difference, I think from what you are saying there are other factors working here...

wardy

I'm 6'1 and tip the scales ~ 200lbs. I'm sure that the 739AT on the rear isn't the best, but this is also my play bike and I use it for everything from harescrambles to MX tracks to abandoned RR track beds to heavy clay farm fields and everything inbetween. I wanted a tire that would have some durability and this was my compromise. If I had the money to buy 4-5 extra's and switch them for play and race, I would.

Anyway, I was hoping that MAYBE by reducing the pressure alittle......I might be able to increase the flexibilty some and put some more of the power on the ground.

As far as how aggressive I am with obstacles, well....I'd have to say I'm soft. I'm just getting into racing for the first time and at 39, I can't afford to be too aggressive too soon. (gotta go to work on mondays, ya know?? ;) )
My goals are to 1)fininsh, 2) dont break the bike,3) dont break me. After my first race I can happily say I did all 3. And, a 13th out of 30 finish in my class isn't to bad either!! :D

 

[Okiewan]

Anyway, I was hoping that MAYBE by reducing the pressure alittle......I might be able to increase the flexibilty some and put some more of the power on the ground.

Generally speaking this is correct. But you have to consider rocks, other obstacles and tire design (sidewall, compound, etc as wardy was saying)... traction sucks with a flat. JIt's a compromise? The more the sidewall flexes, the more likely you are to get a puncture.

 

[dell30rb]

So true. In really soupy moto's I've seen guys using as little as 8 psi.

I like to run 12 in my front tire and 11 in my rear. I raise the pressure to around 15 psi When I ride in rocks, or trails. Some desert riders set their tires at 18 psi to avoid pinch flats. Its hard to avoid rocks at 60 mph!

 

[wardy]

39 on a KX 500, very good your in the club! LOL I would be 44 and on a CR500A/F.
13 out of 30 is cool! I haven't rode a hare scrambles type race in 20+ years I only have like 3 ahhh maybe 2 laps of MX in me at the moment!

play around with the pressure, but being your on the 500 i would also recomend using the clutch a little more so you power to the rear wheel is contained a bit. this will help greatly with that traction problem. ALSO
200lbs.........USE your wieght, what i mean is i have watched many 150 pound guys try like heck to get a bike to hook up, at 200 all you need to do is move on the bike more and get your wieght on the bike as you need it.......LOL at 240+ I generally just lean LOL!
wardy

 

[JPIVEY]

739AT is a good tire and with its thick side wall you could drop the rear presure down quite abit but I would stay between 10-14 maybe a little higher depending on the terrain for the front and like wardy said use your weight and the clutch to get that hookup.

 

[bud]

My experience is dropping the tire pressure can help traction, but I think of it as a last resort, something to try after new tires, fiddling with suspension and doing my best with body position and clutch/throttle control.

The effectiveness will depend on the tire and on the terrain, and it's certainly not without potential downsides, eg pinch flats and bent rims. Plus it cuts power and may not help traction at all.

Ftr, I usually run around 8 psi in the rear in muddy conditions. I use an s12 rear, which is the best in my terrain with HD tubes. As yet I've never had a pinch flat or dinged rim, despite numerous crunching contacts between rocks, roots and logs with no air between the tire and rim. With standard tubes and rims it would be more of a gamble.

 

[BSWIFT]

I'm 150 lbs. and on the 310 KX I have the same problem. I've learned to roll the throttle on to help prevent wheel spin. Jeff Freddete in his siminar at DW01 suggested that you remove the valve stem nut after mounting a tire. Add enough air to allow the valve stem to be pushed in 1/4 of an inch into the wheel. He said this is the "preasure" guage he uses. I've been using this technique ever since and have had real good luck with it. In real sandy condintions, I will lower the air preasure in the rear but I'm not running over rocks and roots so I'm not worried to much about pinch flats.

 

[Hogwylde]

Thanx for all the advice guys!! After todays MUDFEST though, I'm gonna get me a mud tire. Sloppy, greasy, YUCKY!!! A full day of rain yesterday made todays race ALMOST impassable after the first lap!! 12+ inch deep ruts, mudholes that would suck your bike down to a dead stop, and a rearend that I could just NOT hook into this Indiana clay soil!!! Still managed a 7th of 12 finish though. :aj: More points for a 7th fininsh, but worse statistically.

Any recomendations on a tire?? (19 inch 120+ width) I'm leaning toward a dunlop 756 or 752 or a maxxis Surcross or a Michelin S-12.

 

[ericruby]

run a bib mousse and dont worry about it

 

[danielst]

I'd recommend a Michelin S-12 Rear and an M-12 Front. I used to run various Dunlop variations but the Michelins are by far the best tire I have ever run. They wear great and they will find traction in just about any terrain.

FWIW, I run 12psi in them.

 

[Lorin]

IRC M5b is an excellent choice for your 500. I run a 140\18 on my wr500 and swear by it! It is considered an intermediate, sand \ mud tire, but works decent in rocks and wears exceptionally well. I manage to get around 9 to 12 months out of my rear tires.

 

[Jh85]

Ok, for you woods guys...I have a question.

Sorry I got the impression that you were trying woods riding and had been track riding with your bike set up for moto.

 

[Jeff Gilbert]

How much air do you run in your tires??

I thought this particularly funny after I got back from the races last week. This fella parked next to us at the track said he hadn't been on his bike in over 2 years and desided to fix it up and race it all on this one Saturday. After practice we were talking again and I asked him how he felt to be back on the bike after so long and he said "pretty good except I'm having trouble with my bike washing out in the turns." I asked how much tire pressure he was running and he said "I don't know, I just had the new tire mounted this afternoon." Being the good ole boy next door I offered my tire gauge so he could check and that's when he asked me if I thought 35lbs should be enough. That's what he was running in both tires :o

Now if I had been smart I would have told him ya but I didn't, he beat me in the 2nd moto :confused:

 

[soquel]

OK I'm confused, lets get things straight I've been hearing alot about lowering your tire pressure in muddy conditions and raising it for hard terrain, Is this just for off-road? The reason I ask is I am friends with pro level motocross mechanic, and he gives me adivice on tire pressure on race day, and he adivises that early in the day when the track is muddy run higher air pressure (14psi) the higher air pressure makes the knobbies stick out more so they grip the soft terrain better and don't get clogged up, and for later in the day to lower pressure to about 12.5 for the hardpack so that the knobbies flex to conform to the flat surface. So the theorys kind of contradict each other. I hope that makes sense, and provide some help.