Tyre pressure help

Hey all ,

I just got a set of knobblies for my WR250R tyre size are 120/100/18 rear and 90/100/21 front (i think). My question is what pressures do I run.
I currently have 16PSI in both but It just feels spongy and kind of feels as tho the rim is rolling from side to side in the tyre at times.
also should I be running rim locks?

The type of riding is I do is off road only and pretty causios no jumping ect. as i've only been riding for about a month.

This is the first time I have run knobblies so is it just me.

Something I should add is the inner tube in the rear is abit small for the tire 100/100/18 (standard) I have read its ok to go 10-15mm either way. Could this be my problem?

thanks for your help everyone

Mat

I've found 18 rear and 22 front to be good for me in most circumstances. If it is real wet with roots etc I will drop to 15 rear but only for as long as needed. All tires are not created equal there are knobs I will not run and some I like more than others. I usually run MT21's and have for years, D606 one I'm trying on my XR650R now. Air pressure is like oil--run what works best for you.

Sinfull wrote:

Hey all ,

I just got a set of knobblies for my WR250R tyre size are 120/100/18 rear and 90/100/21 front (i think). My question is what pressures do I run.
I currently have 16PSI in both but It just feels spongy and kind of feels as tho the rim is rolling from side to side in the tyre at times.
also should I be running rim locks?

The type of riding is I do is off road only and pretty causios no jumping ect. as i've only been riding for about a month.

This is the first time I have run knobblies so is it just me.

Something I should add is the inner tube in the rear is abit small for the tire 100/100/18 (standard) I have read its ok to go 10-15mm either way. Could this be my problem?

thanks for your help everyone

Mat

Ditto on that pressure. I run that as well on all the knobbies I've had. Go to rim locks if you go below 13 on either end. The rear tube, if it's the same size as it was stock, will be fine; I've got 110's on the back of mine (140) and no problems. The lower pressure you go, the more squishy it's gonna feel, but you get better traction in the loose stuff. Hardpack you want to run higher.

At the pressures you are now running I seriously doubt the tire is rolling. You are probably just feeling the flexing of the knobs which you are not used to since you are new to knobbies.

I have never run more than 12 lbs in any knobby. I'm currently down to 7 front and 6 rear on 606s BUT I'm running the Tubliss system.

I've found a BIG improvement in handling between 12 and 8 pounds on rocks. Less bouncing and more traction. But my riding is in MD/PA/VA/WV amd not high speed desert stuff.

At the pressures you are now running I seriously doubt the tire is rolling. You are probably just feeling the flexing of the knobs which you are not used to since you are new to knobbies.

Yami calls for 18/25 - front/rear with stock tires. What am I missing here? Do you drop them that much for knobbies?

You can. It really depends on the terrain you're riding on and the tires and inflation system you are running. Lower pressures will allow the tire to flex more, meaning (up to a point) the tread can absorb bumps better and grip the terrain better. Go too soft and you'll lose precision, too hard you'll lose traction. Every tire has a happy place that varies based on conditions and setup. Thin tubes will need different pressures than thick HD tubes or a tubliss setup.

I agree with Skierd.

The Yami recommendations are based on being TOTALLY safe at a sustained speed of ~75 mph in severe desert heat on pavement for road use and almost total freedom from pinch flats in high speed off road use.

For real off road use in the east coast terrain it would be unusual to use more than 15 PSI with even the smallest softest tires.

ok so it sounds like my pressures are ok. what about the inner tube size difference. tyre is 120/100/18 but tube is 100/100/18

do you think it would have much effect on bike handling?

skierd wrote:

Thin tubes will need different pressures than thick HD tubes ...

Great stuff skierd. Can you be more specific on HD tubes (up/down)? I'm running them now.

I found I need to run less pressure to get the same effect as regular tubes as the HD tube effectively stiffens the tire with its added thickness. YMMV, give it a shot and see what works for you and your bike.

The tube size probably won't affect handling, most tubes are sized for a broad range of tire sizes. They're fairly flexible rubber and inflate to fill the cavity inside the tire/rim. I've personally watched a 21" front tube set the bead on a 17" street tire, and then survive about 50 miles of pavement limping the bike closer to home, which is when I realized that exactly proper sizing isn't all that critical so long as its close. That being said, it will probably have some small effect on handling and optimum pressures but what that will be and whether or not its noticeable I have no idea.

I guess it comes down to playing around. find what you feel most confortable driving with and then ulter slightly for condition