XR250 suspension question

[B0000M]

my mate has one, and the front end is soft as, we're wondering what most other people are running as fork oil weight in these, he weighs about 70kg and the bike is mostly used for trails / light mx style riding. its a 96 so has no compression adjustment

[merv]

Is it soft in the springs, or damping or both. Heavier weight oil can fix the damping - I'm similar weight to your mate (should be lighter but I'm getting old eh!) and have always used auto trans fluid in the forks (which is quite light) and that's good for me. You should be able to adjust the damping as well - look under the bottom of the fork legs and has it got click adjusters there? If the springs are too soft you can fit a preload spacer to stiffen them up a bit or buy stiffer springs - progressive springs are a good option for the XR - soft at low load and they stiffen the rate as they compress under load like if you land off a jump.

[B0000M]

dont you usually use fork oil in forks?

ive seen different fork oils- 2.5wt, 5wt, 10wt, 15wt etc, this is what im talking about, the springs will be ok, its just a damping issue.

so what i mean, is what weight to use?

[merv]

If it is just a damping issue try adjusting the compression damping on the forks - you reckon its got none but look up the bottom of them and there should be little rubber plugs to pull out and the hex adjuster is under there - wind them on a few clicks. Try that first before you change the oil.

[B0000M]

arent they the rebound adjusters?

[Danger]

No they are compression. Fork oil weight has more effect on the rebound damping than on compression. The fork springs in that bike are too soft for your friend too.

[Brian d marge]

Google fork set up

I am with Danger here , ( except oil viscosity , effects both comp/rebound ,, just most dont notice the comp )

1. set sag , using approx 15mm of fork preload . ( inside the fork~)
2. check spring rate.( most likely you will need stiffer springs
3 ,If stiffer springs are fitted , then the rebound will have to be slowed,
oil is a cheap way , but the better way is to revalve it
Basic revalving , in cartridge forks isnt difficult ..( if you can get em aprt!! ) but damper rod type forks require a bit of metal work.

All that wil happen if you try to mask the set up by adding say heavier oil , is that you will slow the fork travel down But the springs will compress more for a given load , bottoming on things like whoops, those stutter bumps in to the braking area etc,,,,if yo jack up the preload , to try and get the correct sag no

it will kick, ie , when going round a corner with the bike layed over ,,,the front will be washing out and you will have to stand the bike up ..

Compression /rebound adjusters on older Jap bike only changed the slow speed circiuts , they didnt adress the mid to high speed circuits

A member here on KB , hade a set of springs made by national springs in AUK for around 120 NZ ...if I remember


Stephen

[tysonzane]

I had a XR250 once upon a time. I would strongly reccomend not putting anything higher then 10W oil, my old man made a big mistake of putting 10W oil in and it made it ride like a pig esspecially when it was wet. Since i imagine you dont want to spend a truck load of money, you could either get someone else to give them a decent rebuild or put about a 15mm spacer between the springs and put some new 5W oil in.

If you are lucky you could look out for some XR400 forks as they are supposed to be a really good upgrade. Im not sure why, maybe the valving is different etc.

Failing that, buy some new springs and get the whole shock overhauled. I didnt remember my XR250 having damper adjusters on the front forks...

[Danger]

Most people will try to adjust compression damping with oil weight. When you consider that you have the weight of the rider combined with the weight of the bike and the force of the impact compressing the forks and only the spring making them rebound, then naturally the oil will have a greater effect on rebound than on compression.

[Brian d marge]

Most people will try to adjust compression damping with oil weight. When you consider that you have the weight of the rider combined with the weight of the bike and the force of the impact compressing the forks and only the spring making them rebound, then naturally the oil will have a greater effect on rebound than on compression.

Dont worry we are saying the same thing ( though the oil viscosity has the same effect wether is compression or rebound , The forces MAY be different and the effects more or less noticeable ,
but the oil give the same shaft retarding force ( for want of a better way of saying it ) in either comp or rebound, due to the viscosity of the fluid ,

As you say most people slow down the shaft speed by using oil , which then , causes tracking probs ,

Stephen