Rear sag for street riding W/aftermarket shocks

[Deleted member 452]

I've read every suspension thread on this forum and the Duke 390 forum along with some posts on other suspension forums and I'm still not sure where to start with rear sag on my YSS MZ456-300TR-38 shock due to conflicting recommendations. There are many other variables that we don't need to cover in this thread (shock length, spring rate, damping curves, etc..) but I'm just looking for a consensus on sag for street ridden 390's using aftermarket shocks W/O top-out springs. Please share your thoughts & experiences...

Static Sag Recommendations


YSS's generic recommendation for street use: 5-10mm
Race Tech's generic recommendation for street use: 2-17mm
KTM's recommendation for Duke 390: 15mm
KTM's recommendation for RC390: 15mm


Rider Sag Recommendations


YSS's doesn't offer recommended settings for rider sag
Race Tech's generic recommendation for street use: 28-37mm
KTM's recommendation for Duke 390: 50-55mm
KTM's recommendation for RC390: 45- 50mm

 

[Fangfactor]

I've read every suspension thread on this forum and the Duke 390 forum along with some posts on other suspension forums and I'm still not sure where to start with rear sag on my YSS MZ456-300TR-38 shock due to conflicting recommendations. There are many other variables that we don't need to cover in this thread (shock length, spring rate, damping curves, etc..) but I'm just looking for a consensus on sag for street ridden 390's using aftermarket shocks W/O top-out springs. Please share your thoughts & experiences...

Static Sag Recommendations


YSS's generic recommendation for street use: 5-10mm
Race Tech's generic recommendation for street use: 2-17mm
KTM's recommendation for Duke 390: 15mm
KTM's recommendation for RC390: 15mm


Rider Sag Recommendations


YSS's doesn't offer recommended settings for rider sag
Race Tech's generic recommendation for street use: 28-37mm
KTM's recommendation for Duke 390: 50-55mm
KTM's recommendation for RC390: 45- 50mm

For a start to keep the bike balanced I would measure your front suspension sag and set up the rear around 5mm less

 

[Deleted member 452]

For a start to keep the bike balanced I would measure your front suspension sag and set up the rear around 5mm less

I'll give it a try. I wonder why KTM recommends so much sag for the stock shock when all the aftermarket shock companies recommend so much less?

 

[CDN Duke]

Where do the KTM recommendations come from? I'm interested to know what's recommended for the fronts as I'll be redoing my forks tomorrow...

I'll be close to RC390 setup so looking for the 125mm travel numbers. Duke numbers will be different given the 150mm travel from factory.

 

[Deleted member 452]

It's listed in the repair manuals but they don't list sag recommendations for the forks because they're not easily adjustable.

 

[CDN Duke]

I'll give it a try. I wonder why KTM recommends so much sag for the stock shock when all the aftermarket shock companies recommend so much less?

I expect this may be due to fact that stock spring is progressive, with the secondary portio being quite a high spring rate relatively so you can afford to have more sag due to the remaining travel having to work against a stronger spring rate?

 

[Deleted member 452]

Just received this info from Race Tech...

1) We don’t worry so much about the static sag, this number is directly related to the preload number. We may even go stiffer or softer on the rear spring depending on the track, the same rider may run a stiff spring with light preload for higher speed or banked courses and a lighter spring with increased preload for a tight track. This is why our number varies, do what feels good.

2) RACE SAG, we are running 45mm on our track setups. I believe KTM’s recommendation is for street. 1/3 of the travel (143/3 = 47.66) is a good rule of thumb for sag. For your weight I would use a 12.5kg spring with 8mm of preload

BONUS ROUND) The bumper is part of the suspension. It acts like a spring as it gets compressed to create a rise in rate as the shock bottoms. This bumper will smash to nearly flat, set up correctly the bumper should engage in the last 30% of the travel. Expect the shock to touch this, especially when travel is limited like it is on street bikes.

 

[Deleted member 452]

And here is what Dave Moss (Dave Moss Tuning | Ensure your bike geometry, spring rates, hydraulic damping and tire size/compounds are in sync) said...

Any time I am testing a new shock, this is the procedure I use.

Static sag is generally at 8-12mm with a rider sag of 18-24mm. Your level of aaggression and skill will dictate smaller or larger numbers as a starting point. Perspective first......

If you don't get within 5 to 7mm of the bottom out bumper, you need more sag so soften preload 0.5 of a turn counter clockwise.

You ride the same road with different preload settings at your pace until you get the travel where you want it.

When that is achieved, change preload by +/- one turn to see how that helps or hinders static sag from a deceleration point of view.

Make it simple and subjective or a methodical process based on how you think.