83 XL600R how much fork air pressure


23 replies to this topic
  • markd89

Posted March 11, 2008 - 09:22 PM

#1

Hi,

I want to stiffen up the forks a little. I know that I can run thicker fork oil, but I'd rather not take the forks apart. I heard zero PSI is the stock setting, but I'd imagine that I can add some air and make them stiffer. I don't have the owners manual so I'm not sure how much is safe.

Any suggestions?

Thanks
Mark

  • Krannie McKranface

Posted March 11, 2008 - 09:33 PM

#2

Define 'stiffer':

- To raise the fork stroke higher up
- To prevent bottoming
- To handle weight
- To slow down the 'action' of the fork

Adding air will make the fork very 'uncompliant' over small bumps, but prevent bottoming better.
What works best is springs that are higher in spring rate. Everything else is a band-aid that compromises the ride.

  • martinfan30

Posted March 12, 2008 - 04:03 AM

#3

I wouldnt use any air... Like Krannie said, it'll make it feel really bad!

Get the right springs for your weight.

  • Coolidge

Posted March 12, 2008 - 04:08 AM

#4

Owner's manual for my 97 XR600R says 0-15psi. Use a bicycle pump, w/frt wheel off the ground. Unlike CR/F frt ends, you dont bleed off air, the XL/R are supposedly air adjustable. When I had stock forks, they bottomed out like crazy desert riding w/"0"psi and Im only 150lbs. They were much better @ 5-7psi. I have since gone to USD forks, and find these to be waaay better. Again, this info is from 97 XR600R Owners manual (not repair manual) Good luck. ~Guy

  • pwrpapa

Posted March 12, 2008 - 04:15 AM

#5

Add 7psi of air.

  • sportbiker929

Posted March 12, 2008 - 05:47 AM

#6

ambiant air with forks extended

  • markd89

Posted March 12, 2008 - 06:23 AM

#7

Thanks for all in the input. I weigh about 185 pounds, 5' 11".

I am getting back into riding and had the front bottom out. I was riding on the street, went downhill, then over a decent (but not huge bump). It just feels very soft.

Thanks,

Mark

  • Kenzo

Posted March 12, 2008 - 06:48 AM

#8

My Clymer Manual states:

Front Fork Adjustment Specifications

XR600
Air Pressure
Standard...0 psi (0 kPa)
Maximum...15 psi (98 kPa)


XR650L
Air Pressure
Standard...0 psi (0 kPa)
Maximum...7 psi (40 kPa)


The primary difference between the ratings appears to be a lower reccomended oil level in the XR600's forks by 20mm (125mm VS 145mm)...

Over on the KLR boards use of air pressure preload is a great debate(ur gunna blow ur seals...ur gunna put ur eye out, etc...) even though there is a manufacturers sticker stating the maximun preload air pressure of ~35 psi...go figure :thumbsup:

These oldskool forks are designed to allow air pressure preloading. A preload spacer or even changing the spring rate may be a better choice in some applications. BUT air pressure preload does have its place.

On my XR650L with my ~200lbs rider weight I find 5psi in each fork prevents front end dive on hard braking onroad and prevents bottoming the forks offroad with a trade-off of a slightly harsher ride transmitted to the handlebars from small bumps and road joints.

i hope this helps.

:eek:

  • Denn10

Posted March 12, 2008 - 06:49 AM

#9

start low and see how it feels, i would prefer to say 0 psi also but if you have to then start at like 3 and try it, the less the better so dont just rush into 7 psi and leave it. Remember as the temps change the psi will also go up and down so you have to check it like you do tire pressure, dont want to set in in the cold evening and then in the heat of the day have it be high and blow some seals or something.

  • cleonard

Posted March 12, 2008 - 06:55 AM

#10

The air will help a little. It's worth a try.

With the old damper rod design you do not have to take anything really apart to change the oil or install stiffer springs. All you need to do is remove the drain screw at the bottom and the top for cap.

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  • Kyron

Posted March 12, 2008 - 07:03 AM

#11

the XL forks are way diffrent than the XR forks.

You really need to open the forks (way easy on those) and get stiffer springs. If you increase the air pressure the seals will fail quicker...... sure go ahead and put like 8 psi in them and when the seals start to leak do the stiffer springs then, you have nothing to lose :thumbsup:

I had a 86 XL600 that I put stiffer springs front and rear, it was a huge improvment!!

  • Kenzo

Posted March 12, 2008 - 07:31 AM

#12

blown and leaking seals from adding air pressure is a bit of an "old wives tale"...

when ur forks fully compress without any air preload they develope over 100 psi (SWAG)...additional preload air pressure within specs is not a problem...

if ur forks leak they wud have leaked anyway...if u blew out ur seal (VERY UNCOMMON) it was installed incorrectly most likely the spring clip wasn't seated correctly or overfilled oil level...also the few psi developed due to temperature change is insignificant.

when i load and strap down my bike the forks and shock is nearly fully compressed and not a drop of oil has leaked...next time i load it up i will check and report back on the pressure developed...

:thumbsup:

  • Denn10

Posted March 12, 2008 - 09:01 AM

#13

blown and leaking seals from adding air pressure is a bit of an "old wives tale"...

when ur forks fully compress without any air preload they develope over 100 psi (SWAG)...additional preload air pressure within specs is not a problem...

when i load and strap down my bike the forks and shock is nearly fully compressed and not a drop of oil has leaked...next time i load it up i will check and report back on the pressure developed...

:thumbsup:


not really an old wives tale its more stress on the forks, thats why they went away cuz they werent that good of a way to add compression and stiffen the forks.

check your forks psi with 0 psi static and then 10psi and see what you come up with when there loaded down to the same position. use something to measure how far the forks compress and make sure its at the same level and let us know what the differences are, im sure its gonna be noticable

  • Kenzo

Posted March 12, 2008 - 09:24 AM

#14

not really an old wives tale its more stress on the forks, thats why they went away cuz they werent that good of a way to add compression and stiffen the forks.

check your forks psi with 0 psi static and then 10psi and see what you come up with when there loaded down to the same position. use something to measure how far the forks compress and make sure its at the same level and let us know what the differences are, im sure its gonna be noticable


yes, they are an older design being replaced by newer technology/design with multiple adjustment in some applications...

...isn't ur rear shock gas charged (i.e. pressurized nitrogen) like modern race bikes???

yup...a 10psi difference

:thumbsup:

  • Denn10

Posted March 12, 2008 - 10:15 AM

#15

of course shocks are nitrogen charged but not the whole shock chamber, its contained in a bladder and the movement of forks vs shocks is alot different. but todays forks are long gone away from using air/nitrogen pressure to compensate for compression. Shocks only move a few inches vs 12 inches on forks. Give us some good info on your fork pressure readings with the 0 and 10 psi when compressed down as far as you can to an equal length. Im sure its a fair amount of difference but till you do some testing for us we will never know. not bagging anyones opinion just inputing mine and really wanna see some solid info, would be great if you did that. Always good to learn more and im sure very few can give you actual numbers on the difference as most would never think the PSI gets that high in a fully compressed fork tube.

  • markd89

Posted March 12, 2008 - 12:59 PM

#16

Cool, I will measure the fork pressure compressed. It will be a few of days as I have some things apart right now.

For pumps. If I am going to put only a few psi, I need a bicycle pump with a sensitive guage. Any suggestions on brand/model?

Thanks again,

Mark

  • chakaxr650l

Posted March 12, 2008 - 01:12 PM

#17

I believe the 100PSI at ful compression. Think about your piston. It is atmospheric at BDC and over 100 at TDC. The fork leg is the same principle.

I would like to see the numbers as well. No idea on a brand. Maybe a mid level digital tire gauge.

  • Kenzo

Posted March 12, 2008 - 04:21 PM

#18

For pumps. If I am going to put only a few psi, I need a bicycle pump with a sensitive guage. Any suggestions on brand/model?


i just give mine a "shot" of air from a compressor and use a TannerRacing dial gage 0-60 psi with a built-in bleeder and bleed them down to the desired pressure...it's accurate to 1/2 psi for setting tire pressures for cage racing...

of course shocks are nitrogen charged but not the whole shock chamber, its contained in a bladder and the movement of forks vs shocks is alot different. but todays forks are long gone away from using air/nitrogen pressure to compensate for compression. Shocks only move a few inches vs 12 inches on forks. Give us some good info on your fork pressure readings with the 0 and 10 psi when compressed down as far as you can to an equal length. Im sure its a fair amount of difference but till you do some testing for us we will never know. not bagging anyones opinion just inputing mine and really wanna see some solid info, would be great if you did that. Always good to learn more and im sure very few can give you actual numbers on the difference as most would never think the PSI gets that high in a fully compressed fork tube.


i'm not really stating my opinion but rather science as far as it being only 10 psi higher...

http://en.wikipedia....i/Ideal_gas_law

i'll repete myself...adding a little air pressure may not be the best solution...half the people who try it like it the other half hate it BUT adding air pressure within spec will NOT blow the seals, will NOT cause them to leak and will NOT put ur eye out. :eek:

the specs for the pressures are in the manual(s)...argue that the manual is incorrect if u must but keep in mind that these forks are 1990's technology(if not even earlier) EVEN on the 2007 model year.

also keep in mind if/when u increase ur fork oil fill level ur only decreasing the volume of air over the same stroke length (i.e. volume)...this is VERY simular to adding preload air pressure(but not exactly the same)...it's all based on pyhsics.

:thumbsup:

  • pwrpapa

Posted March 12, 2008 - 04:49 PM

#19

I have an 83 XL600 an run 7psi in the forks an like the ride it gives me.
The seals have never blown out from the added air pressure.

  • martinfan30

Posted March 12, 2008 - 08:49 PM

#20

of course shocks are nitrogen charged but not the whole shock chamber, its contained in a bladder and the movement of forks vs shocks is alot different. but todays forks are long gone away from using air/nitrogen pressure to compensate for compression. Shocks only move a few inches vs 12 inches on forks. Give us some good info on your fork pressure readings with the 0 and 10 psi when compressed down as far as you can to an equal length. Im sure its a fair amount of difference but till you do some testing for us we will never know. not bagging anyones opinion just inputing mine and really wanna see some solid info, would be great if you did that. Always good to learn more and im sure very few can give you actual numbers on the difference as most would never think the PSI gets that high in a fully compressed fork tube.


I like the idea of maybe trying the nitrogen in the forks. I have a "generator" at work. Maybe I'll put 1-3 PSI of the stuff in my forks for the April ride and see how it works. It wont reallly increase in pressure with heat like comp. air will.... Maybe it could work?





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