Sag?

[Guest captain nemo]

Is the difference between the height of your saddle without rider compared to the height of the saddle WITH rider referred to as SAG? If so, then my bike 'sags' about half an inch. That is the difference say on the height of the tail pipe between straddling the bike and sitting down on it. that seems about right to me. How is it for you guys? When I first picked up this bike you could not budge the front or rear end no matter how much you jumped on it. Would not BUDGE. And that guy was my weight. No wonder he wasn't happy.

[dlaing]

Sag refers to the drop of the bike relative to the axle when both rider and bike weight are applied, as measured from bike suspended.

Ideal sag is roughly one third of total travel.

So, 1/2 inch of rider only sag is probably too firm, as it probably implies that your bike only sag is also less than 1/2 inch, and your total sag is probably less than an inch, while it should be more than 1.5 inches and less than 2.0 inches.

But then again you are riding far up on the bike and you are not extremely heavy, so it may be ok.

To measure sag you might try putting a plastic zip tie on the shock's shaft, gently put your weight on the bike in your riding position, on tip toes, then dismount, then lift the weight of the bike up so that the tire is suspended, and then measure the distance from the zip tie to the shock.

The shock travels at about one inch for every inch of wheel travel, so double your measurement and you will get a fairly accurate sag reading.

The tricky part is to lift the bike and suspend the tire, if you do not have the right tools.

[Lex]

Just to add another opinion, I've been taught to use a bit less sag than seems to be the standard advice on this site. The rule of thumb, as I learned it, is 20 to 25% of total travel. That would be about an inch for our bikes. Thirty percent sounds, to me, more like a dirt bike number. They have 10 to 12" of travel to work with and need more extension for holes, drop offs and such than street bikes.

 

I don't think this is an issue of right or wrong, just what works for a given rider. In other words, I'd try both and see what works for you.

 

Cheers,

 

Lex

[al_roethlisberger]

.... nah, you're just wrong

 

And hey, maybe some of do take our bikes off-road?

 

Just kidding

 

 

I'm attending "Doc Wongs Suspension Clinic Part2" this Friday, so might have some more to add later on the subject.

 

http://www.docwong.com

 

Great guy. He sponsors classes, rides, etc... all for free

 

 

al

 

P.S. ...and no jokes about the name

[docc]

Suspension set-up is a black art. Largely because we stay up all hours of the night messing with it. And because of what it can do to you if you get it all out of sorts.

 

I've always heard 25% sag (preload) of total travel (bike + rider) for a sporty street bike.

 

This assumes your spring is right for your weight.

 

Now, I was under the impression that the wheel travel was substantaially more than the shock travel. As in 4 inches of wheel travel to 2 inches of shock travel. Such that we are looking for movement of the shck plunger about 1 inch .

[Guest Brian Robson]

Yeah, right, thats where I would head to if I wanted to learn about suspension, a Chiroquakter

[docc]

Drat! Does it show??

 

Here I thought I picked all this crap up from reliable sources (all of you).

[dlaing]

Here I thought I picked all this crap up from reliable sources (all of you).

I thought I got it from you guys too, but maybe it was one of these sites...

http://www.tsrltd.com/sag.htm

this site says,

"Street bikes run between 25 and 33 percent of their total travel, which equates to 30 to 35mm. Roadrace bikes usually run between 25 and 30mm. "

But their math is a little off, because 25 and 33 percent of 120mm would be 30 and 40mm.

30 and 35mm would be 25 and 29%.

So, I would go with what Lex says.

Lex also informed us of how it is important to not have too much preload, and that getting the right spring and fine tuning with preload is the solution for proper sag, rather than just cranking up the preload.

I hope I phrased that right, it has been a while since Lex posted about it.

[docc]

The plot thickens:

 

The front travel is 120 mm . The rear is only 64mm.

 

The stroke of the shock is 1/2 of the axle travel ( 32 mm).

 

The shop manual specifies spring preload of 11mm.

 

 

(This is an open book quiz)

[Paul Minnaert]

Doc,

The rear travel isn't that short. The ohlins manual states 70mm travel for the shockabsorber, so 140 mm wheeltravel. Guzzi states on their website 128mm for a le mans, so that shock is doing 64mm travel.

 

I my experience, the spring on guzzi's were allways to stiff. But I'm running an old bike, never driven a v11.

[docc]

Paul,

 

I'm wishing I do have more travel. The 2000 sales brochure states the 64mm "stroke". But my Sachs is lying on the bench and I am mesuring the stroke until the 'bumper' is hit: 32 mm .

 

Also, my swingarm is off the bike and I measure the distance from the pivot to axle: 40 mm . Pivot to shock mount ~20 mm. This ratio makes me believe the axle travel is two times the stroke of the shock. (This is for 2000 sport).

 

So, what gives?

[Guest Jeff Kelland]

Just a minor detail, sag is measured from the suspension topped out to loaded ride height.

[dlaing]

But my Sachs is lying on the bench and I am mesuring the stroke until the 'bumper' is hit: 32 mm .

Youch! It sure is a big bumper. I think I am going to shave mine down a bit if I go to a firmer spring.

[Mike Stewart]

Also, my swingarm is off the bike and I measure the distance from the pivot to axle: 40 mm . Pivot to shock mount ~20 mm. This ratio makes me believe the axle travel is two times the stroke of the shock. (This is for 2000 sport).

 

Doc,

 

I believe your measurements are cm., not mm. It is still a two to one ratio for the rear suspension. Just double the shock travel and that will be your suspension travel. Yes the travel on the stock sucks shock is very limited (total travel with bumper compressed 60mm.). I have been told by LE that the rubber bumper will compress to paper thickness. I find this hard to believe and had cut my bumper in half on my old Sach shock. It did feel better but still not as good as the Ohlins shock. By the way, the Ohlins shock has a longer stroke with bumper compressed(70mm.) so the rear suspension has more travel. On the Penske, the stroke is less than the Sachs shock (50mm.) and Yes, I do like the Ohlins better so far!

 

Mike

[docc]

Mike,

 

Right you are on the pivot distances 20CM vs 40CM.

 

I'm surprised the Penske is shorter. Is the Ohlins longer overall, raising the ride height?