How much should front forks compress when rider gets on?

[Domantas]

Ok, my last thread was not very accurate and the search didn't give me any results. So I would like to know how much should front forks compress when rider gets on?

Or simply, how many milimeters should forks compress from the bike's weight and how many milimeters should forks additionaly compress when rider gets on?

The rear sag is very important. But just as we set rear sag, front sag is not less important. The forks should sit in the proper level of the stroke, right?

At the moment my forks compress 35mm from the bike's weight and additionally compress only 20 mm when I get on the bike. Full travel is 305mm. I believe that this is way too little, isn't it?

[Dwight_Rudder]

Approx 40mm static and about 76mm Rider sag. 35mm is not that bad if you have the correct rider sag. BUT you don't. What bike is this going on ? What is your rider weight (in Pounds please). Sounds to me like you have too stiff or heavy a spring rate.

[Domantas]

The bike is Honda CR 125 2002 and my weight is about 145 lb without gear

[KTM-Lew]

Do this: http://www.moto-pro.com/downloads.asp

Then carefully pry the dust wipers down from the seals and clean the area. Apply a finger swipe of fork oil around tube just below seals. Bounce the bike. Repeat several times. Slip dust seals back in place and re-check sag.

At 145 lbs you will need softer springs. But the forks have to move freely to check sag. Probably somewhere around .40 springs?

[Dwight_Rudder]

The bike is Honda CR 125 2002 and my weight is about 145 lb without gear

I would also guess your spring rate to be in the .38-.40 range. Probably in the .38 range on such a light bike and light rider. You want about 40mm static sag and rider sag of 76-79mm.

[Dwight_Rudder]

Do this: http://www.moto-pro.com/downloads.asp

Then carefully pry the dust wipers down from the seals and clean the area. Apply a finger swipe of fork oil around tube just below seals. Bounce the bike. Repeat several times. Slip dust seals back in place and re-check sag.

At 145 lbs you will need softer springs. But the forks have to move freely to check sag. Probably somewhere around .40 springs?

?

I like to use Silicone spray lubricate to minimize seal stiction while checking sag. But what Lew says is a great idea.

[Domantas]

Those are really good tips, will try them. Thank you guys for replies and help, now I see that softer springs are needed.

[Domantas]

And does anybody know how to construct any simple device for measuring fork spring rate at home?

[huskie]

An other trick is measure were your forks stay when riding flat terrain. Have a look at your forkleg protector. Keep in mind that you have to ride it with a half full tank to get the best estimate.

At a certain point on the protector i know what my sag is.

I ride at aprox 70mm.

The measuring device for fork springs can be done by putting weight on the spring and measure the difference when increasing the weight. A weight of a lifterweight is nice.

[kawamaha]

And does anybody know how to construct any simple device for measuring fork spring rate at home?

mine looks like this:

[Domantas]

That's a great device kawamaha ? It's a pitty I didn't see your post ealier. Today I went to the shop and bought two PVC pipes for the device which came to my mind. What do you think guys, should it work?

[mog]

it will yes, but you need a decent weight and not too much friction on the spring as it contacts the tube.

[kawamaha]

it will yes, but you need a decent weight and not too much friction on the spring as it contacts the tube.

I use approx. 20kg and for friction, I rotate the tubes and springs a bit...

[mog]

And do you find it accurate enough to tell between a 0.40 and a 0.42 as a example?

[kawamaha]

And do you find it accurate enough to tell between a 0.40 and a 0.42 as a example?

definately ?

when I measure stock springs, there's a max. deviation of 0.01kg/mm - but I guess stock springs have also some tolerance...

[mog]

yes they are rated at something like 3% anyway.

[Booger2]

I use approx. 20kg and for friction, I rotate the tubes and springs a bit...

What are you using for the weight?

Booger2

[kawamaha]

What are you using for the weight?

Booger2

two iron blocks

[Domantas]

I was looking for big weights which I could use for spring rate test and couldn't find anything. Then I thought that the car battery or two batteries would work. Just need to weigh them before test.

[kawamaha]

I was looking for big weights which I could use for spring rate test and couldn't find anything. Then I thought that the car battery or two batteries would work. Just need to weigh them before test.

perfect ?

just read a weight for a 72Ah battery as 17kg, that's enough