Fork sag
#1
09-02-2011, 03:17 AM
Fork sag
Seeking some input here:
I replaced the fork springs on my '07 250s with the recommended .42 kg springs from MotoPro. Things feel firmer up front but I measured my sag (push down and let rise - measure; pull up and let settle - measure. Average measurement) and I got 56 mm, which is about half of what I've read is recommended. The front end feels kind of jacked up and when I go pretty fast on the freeway I start to get a wicked headshake, a symptom, I've read, of too little sag in the forks. I'm tempted to go back to the stock springs but I like that firm feel up front.
Does anyone else have stiffer fork springs but still an appropriate amount of sag?
FWIW I haven't changed out the rear springs. They are stock. I also weigh 190 lbs without gear.
I replaced the fork springs on my '07 250s with the recommended .42 kg springs from MotoPro. Things feel firmer up front but I measured my sag (push down and let rise - measure; pull up and let settle - measure. Average measurement) and I got 56 mm, which is about half of what I've read is recommended. The front end feels kind of jacked up and when I go pretty fast on the freeway I start to get a wicked headshake, a symptom, I've read, of too little sag in the forks. I'm tempted to go back to the stock springs but I like that firm feel up front.
Does anyone else have stiffer fork springs but still an appropriate amount of sag?
FWIW I haven't changed out the rear springs. They are stock. I also weigh 190 lbs without gear.
#5
09-02-2011, 03:52 AM
And even so, wouldn't I end up with too little sag at both ends with a stiffer rear spring?
#6
09-02-2011, 04:26 AM
Guido, I'm 190 too, and most of the spring calculators I've seen for our '06/'07 KLX recommend .46's. I went with .44's, as I like a softer setup. The .42's you have there should be super soft. Are you sure there's not some kind of stiction caused by a bent fork leg or bushing issue?
#7
09-02-2011, 10:32 AM
A call to John at motopro will help. IF its just too much sag, there may be a spacer needed to adjust the preload.
Too much sag in the front will change your bike geometry. Maybe even cause the headshake.
What is your rear sag?
Front should be .25 to .33 of total suspension travel. IF you have 10" of travel in the front, then 25% of that would be 2.5" or 63 mm sag fully loaded.
David
Too much sag in the front will change your bike geometry. Maybe even cause the headshake.
What is your rear sag?
Front should be .25 to .33 of total suspension travel. IF you have 10" of travel in the front, then 25% of that would be 2.5" or 63 mm sag fully loaded.
David
#8
09-02-2011, 03:12 PM
Guido, a couple of things and questions. You don't say exactly, but I'm guessing your 56mm is the fork sag with you on the bike, right?...not a static sag with just the weight of the bike? If so, then yes, that's not optimum sag.
However, here's the problem with trying to determine fork sag as opposed to setting rear sag. Front forks are notorious for having some natural stiction caused by seals, bushings, and just the angle of the front wheel to the steering head. The fork/front wheel moves in a telescopic manner without any real leverage advantage like the rear suspension. Plus, we're sitting more over the rear, and our weight tends to yield a better, truer number of sag. The front end is less loaded at rest and has more inherent drag working against its compression. Once you're moving this changes a bit, and the fork starts stroking more smoothly and normally. The bottom line is that obtaining really accurate sag numbers for a fork while sitting still is a little difficult. You almost just have to try to get into the ballpark first and then ride the bike to observe small bump compliance and full travel performance. Most of us are looking for good small bump compliance, attaining full travel, and without too much brake dive and/or wallowing. Both spring rate and damping work hand-in-hand to achieve this.
Rear sag is much more easily attained while sitting still, as the dynamics of the rider's weight and the leverage working the rear shock are closer to how the bike performs while it's moving. The fork not as much.
I would suggest trying discern your fork's sag and travel more as you actually ride the bike. A small zip tie or careful observation of your "dust line" will be more accurate as to your forks performance if done correctly.
One other thing, have you bled your fork's air valve on each fork when you're trying to measure sag? Make sure all air is out of the fork. This affects static and "at rest" sag measurements greatly, and it's a bit surprising how much air gets built up in these forks. Get the fork off the ground and bleed each valve.
However, here's the problem with trying to determine fork sag as opposed to setting rear sag. Front forks are notorious for having some natural stiction caused by seals, bushings, and just the angle of the front wheel to the steering head. The fork/front wheel moves in a telescopic manner without any real leverage advantage like the rear suspension. Plus, we're sitting more over the rear, and our weight tends to yield a better, truer number of sag. The front end is less loaded at rest and has more inherent drag working against its compression. Once you're moving this changes a bit, and the fork starts stroking more smoothly and normally. The bottom line is that obtaining really accurate sag numbers for a fork while sitting still is a little difficult. You almost just have to try to get into the ballpark first and then ride the bike to observe small bump compliance and full travel performance. Most of us are looking for good small bump compliance, attaining full travel, and without too much brake dive and/or wallowing. Both spring rate and damping work hand-in-hand to achieve this.
Rear sag is much more easily attained while sitting still, as the dynamics of the rider's weight and the leverage working the rear shock are closer to how the bike performs while it's moving. The fork not as much.
I would suggest trying discern your fork's sag and travel more as you actually ride the bike. A small zip tie or careful observation of your "dust line" will be more accurate as to your forks performance if done correctly.
One other thing, have you bled your fork's air valve on each fork when you're trying to measure sag? Make sure all air is out of the fork. This affects static and "at rest" sag measurements greatly, and it's a bit surprising how much air gets built up in these forks. Get the fork off the ground and bleed each valve.
#9
09-02-2011, 04:00 PM
Guido, a couple of things and questions. You don't say exactly, but I'm guessing your 56mm is the fork sag with you on the bike, right?...not a static sag with just the weight of the bike? If so, then yes, that's not optimum sag.
However, here's the problem with trying to determine fork sag as opposed to setting rear sag. Front forks are notorious for having some natural stiction caused by seals, bushings, and just the angle of the front wheel to the steering head. The fork/front wheel moves in a telescopic manner without any real leverage advantage like the rear suspension. Plus, we're sitting more over the rear, and our weight tends to yield a better, truer number of sag. The front end is less loaded at rest and has more inherent drag working against its compression. Once you're moving this changes a bit, and the fork starts stroking more smoothly and normally. The bottom line is that obtaining really accurate sag numbers for a fork while sitting still is a little difficult. You almost just have to try to get into the ballpark first and then ride the bike to observe small bump compliance and full travel performance. Most of us are looking for good small bump compliance, attaining full travel, and without too much brake dive and/or wallowing. Both spring rate and damping work hand-in-hand to achieve this.
Rear sag is much more easily attained while sitting still, as the dynamics of the rider's weight and the leverage working the rear shock are closer to how the bike performs while it's moving. The fork not as much.
I would suggest trying discern your fork's sag and travel more as you actually ride the bike. A small zip tie or careful observation of your "dust line" will be more accurate as to your forks performance if done correctly.
One other thing, have you bled your fork's air valve on each fork when you're trying to measure sag? Make sure all air is out of the fork. This affects static and "at rest" sag measurements greatly, and it's a bit surprising how much air gets built up in these forks. Get the fork off the ground and bleed each valve.
However, here's the problem with trying to determine fork sag as opposed to setting rear sag. Front forks are notorious for having some natural stiction caused by seals, bushings, and just the angle of the front wheel to the steering head. The fork/front wheel moves in a telescopic manner without any real leverage advantage like the rear suspension. Plus, we're sitting more over the rear, and our weight tends to yield a better, truer number of sag. The front end is less loaded at rest and has more inherent drag working against its compression. Once you're moving this changes a bit, and the fork starts stroking more smoothly and normally. The bottom line is that obtaining really accurate sag numbers for a fork while sitting still is a little difficult. You almost just have to try to get into the ballpark first and then ride the bike to observe small bump compliance and full travel performance. Most of us are looking for good small bump compliance, attaining full travel, and without too much brake dive and/or wallowing. Both spring rate and damping work hand-in-hand to achieve this.
Rear sag is much more easily attained while sitting still, as the dynamics of the rider's weight and the leverage working the rear shock are closer to how the bike performs while it's moving. The fork not as much.
I would suggest trying discern your fork's sag and travel more as you actually ride the bike. A small zip tie or careful observation of your "dust line" will be more accurate as to your forks performance if done correctly.
One other thing, have you bled your fork's air valve on each fork when you're trying to measure sag? Make sure all air is out of the fork. This affects static and "at rest" sag measurements greatly, and it's a bit surprising how much air gets built up in these forks. Get the fork off the ground and bleed each valve.
#10
09-02-2011, 04:20 PM
Ride on
Brewster