Static sag

[bsharpish]

Messing with the new/upgraded suspension

78 GS1000c

At the back -
1100E arm
365mm YSS rear shocks
1100E back wheel running 130 tire

static sag at rear 55mm

At the front
82 1100E forks
anti-five blank off
15WT oil
racetech springs (.90kg)
4mm over stock length spacer
Tarozzi fork brace
10psi fork pressure
running position 2 on the preload and clik 3 on rebound

static sag at front 45mm

guessing I need to add preload at the rear and at the front and aim to get the two in line at about 40mm

appreciare any comments

[Dogma]

Static sag is usually recommended to be set as a percentage of travel for each wheel, so I'm not sure it should be the same front to back on your bike.

Other comments: I love my YSS shocks. No emulators up front? They're even better than the adjustable damper rod you're using. With YSS on the rear and emulators in the front, I no longer have any need or urge to stand up when I come to a RR crossing. It used to be nearly mandatory. Plush ride, but still better handling than I had before. I made no changes for track day.

[Steve]

If you are using Racetech springs, why are you still using additional air pressure?

Depending on your gravitational attraction and riding style, maybe the 1.0 springs might have been better?

If you remove the additional air and find that sag is more than 25% of available travel, put longer spacers in.

You might also want to reconsider the 15w oil. Oil viscosity will not prevent diving while braking, it only slows it down. It is spring rate that controls the dive.
I have found a MUCH better ride with heavier springs and lighter oil. I have 1.1 Sonic springs and 10w oil, the ride is fantastic.

General rule of thumb for determining proper sag is 20-25% of available travel.
Forks typically have about 5 inches of travel, so 1 to 1 1/4" of sag is good.
Shocks typically have about 4 inches of travel, so 3/4 to 1" is your target.
Since you are expressing your measurements in metric values, that would be 25-30 mm at the front and 17-25 mm at the rear.

.

[bsharpish]

Good point about the air .... brain fart on my behalf

I used 15W because it's factory spec

gravititational attraction ...... pretty significant:-)

[bsharpish]

PLus, at the moment, I'm trying to resolve the stiction issue caused by the tarozzi brace

I remember why I always preferred other brands in the 80's now

[RichDesmond]

Are you measuring static sag or "race" sag?
FWIW, I hate these terms, they're needlessly confusing. I prefer bike sag and total sag. Bike sag being the sag from just the weight of the bike, total sag being the sag of the bike with with the rider on it.

Some details on how exactly you're measuring would help too.

[bsharpish]

I always regard static as with you sat on the bike

front end I'm measuring by the usual cable tie trick - fully lift front wheel off the floor ... push cable tie to seal, sit on bike , amount tie moves= sag

rear end - again ensure wheel is off the floor , measure from axle centre to fixed point (use two in order to triangulate) ... sit on bike , remeasure and difference is sag

1100E has 6" of travel so aiming for about 1.25 on the front and rear shocks are actually 900F with nearly 5" of travel but 1.25" longer than regular GS so aiming for similar at that end.

FYI - not a track bike ...... just trying to dial in a slightly better ride than stock

[RichDesmond]

Static=bike sag, no rider.

If you're getting the sag numbers working alone you can't trust them, they are likely off. Need two people at least to get good ones.

Sag is harder to measure accurately than most people realize. The majority of numbers I get from people are physically impossible.

[mmattockx]

Static=bike sag, no rider.

I like unladen and laden, but there are lots of choices there.

If you're getting the sag numbers working alone you can't trust them, they are likely off. Need two people at least to get good ones.

Sag is harder to measure accurately than most people realize. The majority of numbers I get from people are physically impossible.

+1. Three people is even better. Rider sits in position, one holds the bike steady and one measures. Also good to mention is that you want to bounce the suspension you are measuring a few times to help with stiction. It's a good idea to measure 5-10 times and take an average, especially with these old bikes. If anyone thinks stiction is negligible, do a test for yourself. Lift the bike up and let it slowly settle to a stop and measure the sag. Then push it down and let it slowly rise to a stop and measure again. The difference between the two numbers is the stiction. It can easily be 5-10mm on our bikes when we are looking at a laden sag of ~40mm, so we can have upwards of 25% errors just due to stiction. New bikes are usually better, but it is still easily measurable with the same test.

Rich, didn't you recommend 28% sag for the forks on these old beasts a while back?


Mark

[RichDesmond]

Yeah, 28% is generally good. It's important though to measure actual travel, not what the spec sheet says.
Most street bikes have very similar amounts of travel, so if you just use 35mm total sag you'll be fine.

[azr]

This is why I give Sonic Springs as much business as I possibly can....