Front forks: how much sag for best damping?

[Shuriken]

Working on suspension tuning...

Rear 412 progressive shocks are easy enough to configure but I find little discussion on front fork settings.

I inherited my front forks but have rebuilt them a couple time and they are in good shape with no leaks.

However, I have no idea about the details or rates of the fork springs and I think they are and have been misconfigured for my weight from the day I got them.

The installed spacers were about 5.5", which made the shocks very stiff. I have a spare set and have been ride testing each time I have shortened them. At about 3.5" lengths, there is no preload on the fork springs now.

When I sit on my bike in ride configuration and in gear, the front forks will sag about 1/4". I have configured the rears to sag about 1/3 of the travel length, which means the damping is involved pretty much at all times, and is what I want.

Can a few of you tell me how much front fork sag you observe on your bikes?

I believe for my weight, the springs I am using are too stiff, especially since removing the preload hasn't seemed to cause enough sag to activate front fork damping.

I believe the front forks are over sensitive and at highway speeds, steering inputs or bumps cause oscillations, which feel like both fork springs are fighting each other until they settle down. It feels like because the forks aren't pre sagged, that no oil is flowing through the damper rods. This is no good on the freeway.

If those of you with nicely configured forks tell me your front forks sag an inch while sitting on the bike, I think I'm moving in the right direction, especially in trying to match sag and damping between front to rear.

 

[MaxMidnight]

For the damping not to work the suspension would need to be locked up or the oil has turned to grease!

I wouldn't rely on other peoples settings as their preferences may be different to yours.
Race tech suggests a static sag between 25 - 35mm. Start by measuring the current sag and adjust the spacer length to get what you want.
I would start somewhere in the middle and if it is too soft add washers to lengthen the spacer or shorten to soften.

 

[one2dmax]

My suggestion is to cut spacers that are flush with the end of the fork tube with it fully extended. That way when you put the cap on you will end up with approx 1" of preload (the suggested amount).

 

[Shuriken]

Thanks guys.

I double checked everything again. Oil levels, spring configuration, and even compared to my spare set of shocks.

There is essentially no sag on the front suspension while I am sitting on the bike.

I believe this means the front end is too light / unloaded and doesn't become involved until uneven road or until riding 2 up. It is more stable with more weight.

I have tried 3, 2, 1in, and 0 preload and the less preload, the safer it feels. The springs, with 0 preload, yield no sag and I think are too stiff for my ride weight.

Maybe the previous owner installed heavy duty springs. It is possible and I would have no way of knowing.

I measured them at 19" in length and they are progressively wound.

 

[MaxMidnight]

I double checked everything again. Oil levels, spring configuration, and even compared to my spare set of shocks.

How did you check the oil level - forks compressed?

There is essentially no sag on the front suspension while I am sitting on the bike.

Are you saying that as you sit on the bike there is no suspension movement

I believe this means the front end is too light / unloaded and doesn't become involved until uneven road or until riding 2 up. It is more stable with more weight.

Unlikely. Unless you have done something radical to the front yours will have the same weight distribution as any other Max

I have tried 3, 2, 1in, and 0 preload and the less preload, the safer it feels. The springs, with 0 preload, yield no sag and I think are too stiff for my ride weight.

How much do you weigh with riding gear on?

Maybe the previous owner installed heavy duty springs. It is possible and I would have no way of knowing.

If they are progressively wound the that is unlikely.

With the wheel out of the bike and springs removed do you have free movement of the forks?
How much do the spacers extend out of the forks?

IMO if you have no sag then either the forks are locking up or you have too much preload.

 

[Shuriken]

How did you check the oil level - forks compressed?

Are you saying that as you sit on the bike there is no suspension movement

Unlikely. Unless you have done something radical to the front yours will have the same weight distribution as any other Max

How much do you weigh with riding gear on?

If they are progressively wound the that is unlikely.

With the wheel out of the bike and springs removed do you have free movement of the forks?
How much do the spacers extend out of the forks?

IMO if you have no sag then either the forks are locking up or you have too much preload.

I can jack the front end and remove the fork caps and can just lift the front wheel upwards and the forks will compress easily. Since I replaced the fork seals first and since they were empty at that point, I filled the forks based on measured oil volume from empty, not by oil level. 619ccs or about 20.1oz each fork of 10w is what the manual indicates.

However, upon rethinking things in consideration of what you and Sean said about too much preload, this has to be the issue. I've stated that the spacers are at 3.5" long right now and this places no tension on the fork caps when the front end is raised and forks are unladen. However, as the bike rests under its own weight, those spacers must still be placing preload on the springs.

So if there is no such thing as spacers that are too short, then I can still remove more preload from the springs by simply shortening the spacers further or removing altogether for testing.

This is where a discussion about safety is important. We are calling these things spacers but do they not fulfill 2 functions, spacer and preload? For example, if I have no spacer at all in the fork tubes and I wheelie the bike, the forks will extend fully. But when the front wheel comes back down, without spacers doing their job, the springs would fly through the empty fork tube voids up against the fork tube caps. No, I don't plan on doing intentional wheelies but are spacers even required? What if the rider is Pee Wee Gleason (RIP) at 130lbs? Are spacers even required or can they be omitted for lighter riders? For a 120lb or less rider for example, any preload may be too much.

 

[MaxMidnight]

If the spacers are that short then I doubt that they are applying too much preload.
With spacers omitted the forks would drop down and the springs would abut against the bottom of the fork caps.
It would mean that there isn't any preload on the springs and in your case shorten the effective length of the forks by some 3 1/2 ". This would significantly alter the steering geometry and may well allow the wheel to contact the radiator. To put it another way, no spacers is not a good idea.

Two further thoughts perhaps someone could measure the length of the OE springs?
Also make sure that the forks aren't twisted in the yokes causing them to bind.

 

[Shuriken]

[snip] 619ccs or about 20.1oz each fork of 10w is what the manual indicates.

Incorrect for my bike. More like about 453ccs / 15.3oz for the 85 forks....

So the good news is after a drain of the oil that I had used (some fork oil from an online purchase, presumably about 10w but....) and a careful refill to about 450ccs with 5w oil, the front forks are definitely moving. I can set the sag and now I can really tune the spacer lengths. Right now, the front end is more plush but definitely sags a bit much.

I know I didn't fill to 20oz previously because that amount of oil will overflow the forks. I actually believe the issue, for whatever reason, is that they were either binding or the 10w oil was too heavy for my weight. After a few ride tests, they are definitely not binding and are probably too spongy, now. Thanks fellas for the help.

I will place the OEM length spacers back in and test.

 

[El Canadiense]

Working on suspension tuning...

Rear 412 progressive shocks are easy enough to configure but I find little discussion on front fork settings.

I inherited my front forks but have rebuilt them a couple time and they are in good shape with no leaks.

However, I have no idea about the details or rates of the fork springs and I think they are and have been misconfigured for my weight from the day I got them.

The installed spacers were about 5.5", which made the shocks very stiff. I have a spare set and have been ride testing each time I have shortened them. At about 3.5" lengths, there is no preload on the fork springs now.

When I sit on my bike in ride configuration and in gear, the front forks will sag about 1/4". I have configured the rears to sag about 1/3 of the travel length, which means the damping is involved pretty much at all times, and is what I want.

Can a few of you tell me how much front fork sag you observe on your bikes?

I believe for my weight, the springs I am using are too stiff, especially since removing the preload hasn't seemed to cause enough sag to activate front fork damping.

I believe the front forks are over sensitive and at highway speeds, steering inputs or bumps cause oscillations, which feel like both fork springs are fighting each other until they settle down. It feels like because the forks aren't pre sagged, that no oil is flowing through the damper rods. This is no good on the freeway.

If those of you with nicely configured forks tell me your front forks sag an inch while sitting on the bike, I think I'm moving in the right direction, especially in trying to match sag and damping between front to rear.

Check out Dave Moss Tuning on youtube.

 

[Fire-medic]

I believe that with a rider in the saddle, something about 1/3 of the suspension travel is where you want to be. You can use a measurement with the front wheel off the ground, measured from the top of the slider to the end of the downtube at the top triple-tree bracket, then put on a snap-tie, lower the bike onto the ground, and sit on it w/no stand, just you supporting it while you get another measure from the bottom of the snap-tie to the top of the downtube in the top triple-tree bracket.

 

[Shuriken]

Just a sort of random observation and question....

I put some tape on the forks to help observe movement. With the bike on the center stand

I measured them at 19" in length and they are progressively wound.

So... the manual says the minimum front fork spring length would be 19.2" and I measured the springs at right about 19". Now that I have the forks working again after changing the oil, they are super soft. I will have to start over with them regarding sag and preload. Also considering the 11-1129 progressive springs as well.

With my bike on the center stand and the front wheel on the ground, wiggling the handlebars quickly back and forth a few inches causes a noticeable movement of the front forks. I used black tape on the forks to observe movement. No, I'm not sitting on the bike so it isn't fully loaded but this still seems a bit too sloppy. If the forks were to do this at 75, I could see how a wobble could be induced. Especially if it takes at least 6 or so oscillations to settle down.

Can one of you place your bike on the center stand and see if your forks move this much with a few inches of left and right inputs? I think I'm gonna start with a known quantity and grab some new progressive springs either way.

 

[MaxMidnight]

Have you set the static sag yet, if not then your observations are not that relevant.

 

[Traumahawk]

Setting the sag is the first thing to do to get the front end sorted. I always used a zip tie around a fork, it will move up so you can measure the sag accurately.

 

[Shuriken]

Actually, during my various tests, after changing the oil and restoring fork function, static sag is about right when using the 5.5" spacers. So the video I posted shows too much slop and is, as Steve says, not very relevant. One reason is I am waiting for progressive springs, which will mean I start the process all over again to set sag. I'll post back in this thread after I have the new springs installed an oil refilled.