Setting Suspension Sag

[Scud]

Here's a place for us to help each other out on this important but oft-overlooked step. I am no expert, which might make me a good person to try to explain it. I've only done it a few times myself, and each time, it has noticeably improved the handling of the bike. Hopefully, some more experienced suspension guys will be along to add to the knowledge base.

 

To me, the best explanation is in the Ohlins manuals, which are available for download in the Fileshare section:  http://www.v11lemans.com/forums/index.php?showtopic=1427

 

The key is that you are looking for differences between pairs of measurements to be in the right ranges. The actual distances you measure are meaningless. The only thing that matters are the differences between fixed points under different load conditions.

 

You need three sets of measurements on the front and rear:

1) Wheels up

2) Bike on the ground without rider (balanced, not on sidestand)

3) Bike with rider (again balanced, not on sidestand)

 

So, you have measurements:

• Front:  F1, F2, F3
• Rear:  R1, R2, R3

Here's how I took the measurements:

 

 

 

 

I haven't seen any specs for the Marzocchi/Sachs setup, but I assume sag should be about the same as the Ohlins. The target sag ranges are as follows:

 

Free sag, without rider:  

• Front 25-30mm (this is F1-F2)
• Rear 5-10mm (this is R1-R2)

 

Race sag, with rider (and gear):

• Front 35-48mm (this is F1-F2)
• Rear 30-40mm (this is R1-R2)

Perhaps we can use this thread to share specs and help each other figure out if we need different springs, or can get ideal set-up by adjusting pre-load.  I'll start off with the work I just did today.

[Scud]

Today, I set up the Greenie's sag, which has Ohlins shock with remote pre-load adjuster on rear, and stock Marzocchi forks up front. I weigh about 165lbs and wore the minimum gear for my with-rider test: leather jacket, boots, helmet. Sometimes I also wear heavy leather pants and a backpack and sometimes a tank bag - rarely, if ever, do I load anything on the back or take a passenger.

 

Starting:

• F1=510mm
• F2=485mm
• F3=475mm

• R1=469mm
• R2=457mm
• R3=433mm

 

Free Sag

• Front (F1-F2)=25
• Rear (R1-R2)=12

 

Race Sag (with rider and gear)

• Front (F1-F3)=35
• Rear (R1-R3)=36

 

Conclusion - Front sag is at the lower end of the range, rear free sag is too much, and race sag is about the middle of the range. So rear is a bit too soft.

 

Action - add pre-load to the rear.

 

This is ridiculously easy with the remote pre-load adjuster (mounted on tab where I removed helmet lock). It is more complicated if you have to manually adjust the lock nuts on the spring.

 

After adjust the rear pre-load, I got:

 

Free sag

• Front:  24mm
• Rear:  9mm

 

Race Sag

• Front:  35mm
• Rear:  29mm

 

The race sag is at the minimum for both, so I conclude that these springs will work for me, and that when I wear more gear or carry some extra weight that I will still be OK. It leaves the springs on the stiff side of the acceptable range for solo riding, which is fine for me.

 

So, I luck out and don't need any new stuff. But hopefully this is an easy-to follow example for anyone else who wants to adjust sag.

[stewgnu]

Good stuff, i'd quite like a set of the ohlins.

I haven't checked mine but our local roads are awful and the bike hammers over them.

On good, smooth stuff she feels great though. What's a guy gonna do?

[Scud]

Stew - you might start by checking/setting sag. From there, you could verify that your compression and rebound are set to the original spots - and maybe loosen those a bit for the rough roads. When I got my Scura set up correctly and revisited a fairly rough road, it seemed like it had been re-paved compared to the previous trip.

[nobleswood]

Good stuff, i'd quite like a set of the ohlins.

I haven't checked mine but our local roads are awful and the bike hammers over them.

On good, smooth stuff she feels great though. What's a guy gonna do?

As someone here said ' best return on my money, when adding stuff to my bike, was always the suspension components'

[coreytrevor]

One other important thing to do, to compensate for friction in the suspension, is to get the correct sag number, is to take 2 measurements for each sag number you achieve. You probably need someone to help balance the bike and compress and extend the suspension while doing this. 

 

When doing free sag, you want to lift the bike and let it settle back slowly to where it stops dropping, then take a measurement. Then compress the suspension and let it rise slowly back up to where it stops, take a measurement. The sag number is halfway between the 2 numbers. Then do the same thing with the rider on board.

 

It's a lot more important with the front because the forks have a lot of internal friction, more than the rear suspension. If you just take one reading, you are really just measuring the point where friction stopped the up or down movement.

[Scud]

One other important thing to do, to compensate for friction in the suspension, is to get the correct sag number, is to take 2 measurements for each sag number you achieve. 

 

When doing free sag, you want to lift the bike and let it settle back slowly to where it stops dropping, then take a measurement. Then compress the suspension and let it rise slowly back up to where it stops, take a measurement. The sag number is halfway between the 2 numbers. Then do the same thing with the rider on board.

 

Good point. I remember hearing that before, but I didn't remember well enough to actually do it today. The post-compression measurement would show more sag than the "settle-down only" measurement. Since my measurements were on the short end of the ranges, the average-sag would probably be a little bit into the range.

 

Anyway, I went for a short ride and the bike feels great. Now I can play around with rebound and compression to fine-tune it.

[Chuck]

 

Now I can play around with rebound and compression to fine-tune it.

 

It'll be interesting to find out what you get compared to what I got..