Another Shock Preload Question - Static Sag

[rndlmn4]

I've searched, but haven't found exactly the info I'm looking for. I weight 220 lbs (100 kg) in my skivvies, in the morning before eating anything. Most of the spring charts suggest I need an 8.8 to 9.0 spring. I have an Ebach (RaceTech) 8.9 spring installed. However, rider weight isn't an issue at this point in my question. This is purely about static sag.

 

I checked the static sag on my 2021 T7, with pannier racks, empty soft panniers, and a loaded fanny pack sitting on a rear rack. At the first click out (CCW) from full CW, the static sag is 1-5/8" (41 mm). If I'm shooting for the unicorn 20mm, that's twice as much as it should be. That's with an 8.9 spring! This is just the shock holding up the motorcycle. How does anyone ever get static sag in the 20mm range? 

 

For reference, to check the affect of the preload clicker, at the 2nd click out static sag is 1-3/4" (44 mm), and at 4 clicks out it's 1-7/8" (47 mm). The height change per click is not linear though, because 8 clicks out resulted in static sag of 2" (51 mm).  I didn't test it any further, since it was going in the wrong direction. IF the height change were consistent, the change-in-height range would be 36 mm. It's hard to believe that's possible.

 

For tomorrow's ride, I set it at the 2nd click. There's not much use in measuring rider sag* at this point, since I don't have much preload adjustment remaining to work with. I'll have to judge my new setting by how it handles turning, and in any soft ground I encounter. Preload was previously set at 8 clicks out, which was determined without the panniers, racks, and tool bag. Since adding the cargo, I have not noticed any changes in the handling. I would have probably continued to ride it that way, but since I'm doing a longer ride tomorrow with some unknown terrain, I thought it would be good to recheck the sag with the cargo installed. 

 

* Although I did not measure rider sag with a scale, I did a visual check while sitting on the bike. With the bike upright and the kickstand out, there was maybe a 1/4" (6 mm) difference in the height of the kickstand foot off the floor, with and without me sitting on the bike. 

 

What's your experience been? Anyone else running an 8.9 or 9.0 spring... what are your static sag numbers... and at how many clicks out on the preload adjuster?

[AZJW]

@rndlmn4. Found this under Suspension and might be of help.

 

 

[TexasT700]

Disclaimer.... I no longer own T7.

I weigh only 5 pounds more than you and I found a 95nm spring about right. Topcase, center stand, so similar weight. While I had lowering links, 1 inch, it was difficult to get rider sag correct. If you have lowering links, good luck! I eventually removed lowering links and ride was greatly improved.

I never paid any attention to static sag, and I dont understand why static sag is important at all, and I dont get how it can be changed. Mabe someone more knowlegable can explain!

Eyeballing rider sag cant be very accurate, you gotta have someone help or get one of the sag measuring tools!

Rider sag IS important in telling you if your spring is correct, so stop eyeballing and guessing!

Imma betting you have lowering links, that would explain why so much preload with strong spring. I do know that correct spring that allows light preload vastly improves ride over cranked up preload.

Good luck, and share how you get it right...

 

[williestreet]

I am 220 without gear and run a 90N K tech spring.(very close to your 8.9KG)

I get pretty close to 20mm of free sag and 60mm rider sag with only 3-4 clicks of added preload from the  hydraulic adjuster.

 

The thing to be careful when buying a spring is the free length of the spring.

The stock spring is 240mm long.  The Ktech is 245mm long.  Rally raid is 235mm but they have a spacer that adds to the spring length to make it the same as stock.

 

I would be questioning the free length of the Racetech spring.  Racetech spring are usually made by Eibach and if my memory serves are 225mm  long. Therefore they require a 15mm spacer to make them work on our bikes properly.   I assume race tech sells an adapter with the spring to make this work on The T7.   Very possible the eibach spring and spacer combined is less length than the stock spring.  

 

My guess is your spring and spacer is 5-7 mm shorter than stock  and the reason for your issue.

I purchased the Ktech spring because there were no spacers required and it was just a few mm longer than stock therefore no adapters or spacers required.

 

Stock spring free length is 240mm long.  Installed with preload adjuster set at zero it should measure close to 226mm. (14mm installed preload)

eibach spring 225mm plus adapter 10mm?=235mm.  This equals 9 mm installed preload. 

 

5mm less than stock is a lot.  

 

Take your spring off and measure it's free length to find out for sure what is going on.

If short make a 5mm shim to get it back to 240mm total lengh or purchase a proper length spring.

 

 

 

 

 

 

 

 

 

[rndlmn4]

williestreet: "I would be questioning the free length of the Racetech spring.  Racetech spring are usually made by Eibach and if my memory serves are 225mm  long. Therefore they require a 15mm spacer to make them work on our bikes properly. "

 

I'll bet that's it! That makes perfectly good sense. I'll check the spring length, and if I need a thicker spacer I have plenty of machinist friends with lathes. The Eibach spring takes a thin spacer at the top and bottom because the spring's inside diameter is larger and doesn't sit on the shock's end plates. But, they are maybe 2 mm thick. That would still leave the spring 11 mm too short. 

 

For what it's worth for anyone following this thread, I started the day with my preload adjuster 2 clicks out from full firm. The front end wasn't overly twitchy, but on asphalt all I had to do was apply the slightest pressure to one side of the handlebars and it was moving quickly. Very quickly. When we got into gravel, the steering was very quick. It was almost to the point of being able to square off radiused 90 degree turns. At a rest stop, I cranked it out 4 more clicks. It was much better on the asphalt and it still turned pretty well on the gravel; just a tad slower to initiate the turn. I could live with it the way it is, but will look into the spring length as stated above. I'll also get a helper to assist with measuring rider sag.

[williestreet]

The stock spring at full preload was not enough when I first purchased the bike, so  I made a 10mm spacer to sit on top of the stock spring.   It allowed me to get 5mm more preload and proper sag until my new springs arrived.

 

If you have someone who can make you some spacers that is great.  I would try and set it up so you get proper sag with your preload adjuster at zero when the bike is how you normally ride.   That way you have the entire 10mm of preload available to compensate for passenger or when loaded up with gear.

Depending on how your bike is setup this will certainly vary, but for reference I am 220lbs without gear.

I have outback crash bars and skid plate.  A rear rack, but no side racks, and I always carry side bags with tools, tubes etc.  (Probably an extra 10-15 lbs on the rear )

 

I run a 90N Ktech spring (245mm) and still need to add another 2mm of preload to get my sag correct.

So if you are getting a spacer made I would suggest aiming for a total free length(spring and spacers included) of at least 245, maybe as much as 247mm.  

This should get you pretty close to perfect sag with the hydraulic adjuster at zero.  

 

Let us know what you find for measurements and how you get it fixed.

 

 

Edited May 21, 2023 by williestreet

[Tenerider]

Regarding static and rider sag: I also think that the static sag isn't of such a big significance. My sag measurements on the rear are spot on, but on the front I've more than 10% free sag.

In theory, it's possible to get perfect static and rider sag, the trick would be as follows: If you've got too much static sag, move to SOFTER springs and ADD preload.

Vice versa if you don't have "enough" static sag.

In my case, if I'd do it, I'd have to add lots of preload, probably around additional 20mm, on the front. I decided not to do it. The lighter spring would give a slightly more compliant ride probably (which can be achieved by less comp damping on harder springs, somehow) but it would be more susceptible to bottoming.

[rndlmn4]

18 hours ago, williestreet said:

Let us know what you find for measurements and how you get it fixed.

 

 I haven't had time yet to take the shock off the bike, but here is what I did do in the small amount of time I had.

 

With the preload adjuster at the '1' (full CW, and backed off to the first click) the static sag is 1-5/8" (41 mm).  At 24 clicks (full CCW) the static sag is 2-3/8" (60 mm). That means 10 mm of preload adjuster movement results in 19 mm of static sag change, at least at the point I measured it.  That equals a 1.9 ratio for adjuster movement-to-sag measurement. I'm using a Motion Pro sag scale that has a rubber cone to fit into the end of the axle.  I have it as vertical as possible using a point on the rear rack to measure against. 

 

At the first click out from full CW (I call it '1'. You call it '0'.), I need to reduce static sag 21 mm. That requires a change at the adjuster, of an additional 11 mm. Leaving the adjuster at the first click, a 15 mm spacer would provide 4 mm more than enough. Of course, that can be dialed back out with the adjuster.  If 24 clicks equals 10 mm, each click is worth almost .42 mm. To bring the static sag back up to 20 mm, it would require 9 or 10 clicks out at the adjuster.  So really, what you suggest about the length of Eibach springs, make perfect sense mathematically. 

 

Of course, this all teeters on what the spring actually measures on its own, AND when compared to the stock spring.  Again, I really appreciate you offering that information regarding spring length. That eliminates a lot of head scratching. I'll keep everyone following this thread, posted.

[rndlmn4]

16 hours ago, Tenerider said:

Regarding static and rider sag: I also think that the static sag isn't of such a big significance. My sag measurements on the rear are spot on, but on the front I've more than 10% free sag.

In theory, it's possible to get perfect static and rider sag, the trick would be as follows: If you've got too much static sag, move to SOFTER springs and ADD preload.

Vice versa if you don't have "enough" static sag.

In my case, if I'd do it, I'd have to add lots of preload, probably around additional 20mm, on the front. I decided not to do it. The lighter spring would give a slightly more compliant ride probably (which can be achieved by less comp damping on harder springs, somehow) but it would be more susceptible to bottoming.

 

Thanks for the feedback. I understand the sag measurement and spring selection process. I come from a dirt bike background and have uprated springs on every dirt bike I've owned... at least since becoming a heavy weight adult. What can I say; I like food. My bewilderment here came from numbers that didn't make sense. An 8.9 spring should have easily done the job for me.  If you read the ongoing conversation I'm having here with williestreet, you will see my problem is a matter of spring length.

 

Static sag is important because it represents the amount the bike's weight alone compresses the shock. By design (for the T7)* it's important that static sag be 10% of the travel and rider sag be 30% of the travel. That relationship is important to the function and efficiency of the rear suspension. As you said yourself, it's possible to achieve both numbers - in theory - with the correct spring and preload. 

*Note: Dirt bikes have slightly different targets. My KTM 300 had 310 mm of rear travel. Static sag target was 38 mm (12%) and rider sag target was 110 mm (35%).

 

I understand the challenge with getting front sag correct. Most bikes don't have preload adjusters in the fork caps. (My KTM dirt bikes did.)  With most, you have to remove the caps and add or remove spacers above the springs. I think it is more critical to get the rear sag correct, simply due to how the suspension works. The swingarm has a pivot point, a spring contact point, and a measured stroke point, aka the rear axle. The whole thing swings through an arc. And, the most weight transfer and load force is put on the rear wheel. The rider is shifting positions, you're landing jumps or striking logs during a wheelie, or adding and subtracting cargo during a ride.

 

The front suspension slides along a single line. Yes, you could say there are forces along the X (front impact) and Y (weight loading) axis, but all the movement and spring resistance is along the hypotenuse of the force triangle. It's also difficult to measure because just sitting on the bike doesn't make the front settle, the way the rear does. The way force is applied down the fork leg, it makes the bike want to roll. You almost have to measure front movement with the front brake applied.

 

I think most of us rely on the spring charts and advise of suppliers (i.e. K-Tech or RaceTech) to select the correct front springs. And then, just trust it. The rear is the place where we can actually measure things and see a difference. We tend to work on that, because it gives us a sense of accomplishment when we get it right.  : )

[Tenerider]

57 minutes ago, rndlmn4 said:

 

Thanks for the feedback. I understand the sag measurement and spring selection process. I come from a dirt bike background and have uprated springs on every dirt bike I've owned... at least since becoming a heavy weight adult. What can I say; I like food. My bewilderment here came from numbers that didn't make sense. An 8.9 spring should have easily done the job for me.  If you read the ongoing conversation I'm having here with williestreet, you will see my problem is a matter of spring length.

 

Static sag is important because it represents the amount the bike's weight alone compresses the shock. By design (for the T7)* it's important that static sag be 10% of the travel and rider sag be 30% of the travel. That relationship is important to the function and efficiency of the rear suspension. As you said yourself, it's possible to achieve both numbers - in theory - with the correct spring and preload. 

*Note: Dirt bikes have slightly different targets. My KTM 300 had 310 mm of rear travel. Static sag target was 38 mm (12%) and rider sag target was 110 mm (35%).

 

I understand the challenge with getting front sag correct. Most bikes don't have preload adjusters in the fork caps. (My KTM dirt bikes did.)  With most, you have to remove the caps and add or remove spacers above the springs. I think it is more critical to get the rear sag correct, simply due to how the suspension works. The swingarm has a pivot point, a spring contact point, and a measured stroke point, aka the rear axle. The whole thing swings through an arc. And, the most weight transfer and load force is put on the rear wheel. The rider is shifting positions, you're landing jumps or striking logs during a wheelie, or adding and subtracting cargo during a ride.

 

The front suspension slides along a single line. Yes, you could say there are forces along the X (front impact) and Y (weight loading) axis, but all the movement and spring resistance is along the hypotenuse of the force triangle. It's also difficult to measure because just sitting on the bike doesn't make the front settle, the way the rear does. The way force is applied down the fork leg, it makes the bike want to roll. You almost have to measure front movement with the front brake applied.

 

I think most of us rely on the spring charts and advise of suppliers (i.e. K-Tech or RaceTech) to select the correct front springs. And then, just trust it. The rear is the place where we can actually measure things and see a difference. We tend to work on that, because it gives us a sense of accomplishment when we get it right.  : )

Thanks mate for the detailed explanation!

My answer was more referring to @TexasT700 's post.

Definitely learned something about front sag measurement problems from your post - I have preload adjusters on the caps as well (but used spacers for coarse tuning), and in theory (based on mfg's recommendation) my spring rate in the front should match my weight.

Maybe I should try measuring sag with front brakes applied, then pushing hard on the bars, then slowly releasing. I don't have a lot of friction on the forks, but also had the feeling that they just don't settle correctly by just sitting on the bike and pushing down on the bars.

 

 

[williestreet]

15 hours ago, rndlmn4 said:

 

 

 

I think most of us rely on the spring charts and advise of suppliers (i.e. K-Tech or RaceTech) to select the correct front springs. And then, just trust it. The rear is the place where we can actually measure things and see a difference. We tend to work on that, because it gives us a sense of accomplishment when we get it right.  : )

My experience tells me to never trust what a spring or shock supplier suggests.

Sometimes they are correct or at least close.  Sometimes they are out to lunch and not even close to anything usable.

 

When I bought the T7 I measured everything.  Sag/free sag with zero preload,  sag/free sag with max on the hydraulic adjuster,  installed preload, measured and calculated the linkage ratio and after doing a lot of math came up with what I thought would be the correct spring rate.

Only then did I start to compare to suggested rates by Rally raid, Ktech , race tech and others.

 

I hate shocks with hydraulic adjusters like ours because they give you exactly the problem you are going through right now.  No ability to compensate for a spring length different than what is supplied stock.  For example A quality aftermarket shock with a threaded adjuster  like a Penske can be made to work with almost any spring length.  Just move the lock rings down the shock until you get the desired installed preload and you are good to go.

 

 

 

 

[rndlmn4]

21 hours ago, williestreet said:

My experience tells me to never trust what a spring or shock supplier suggests.

Sometimes they are correct or at least close.  Sometimes they are out to lunch and not even close to anything usable.

 

 

For a few years before they went to air forks, KTM used 4CS (four chamber) forks on their SX and XC model dirt bikes. They were a source of frustration for many riders and suspension tuners. The issue being mid-stroke harshness.  The best fix was to gut them and install traditional closed cartridge inner workings.

 

I had a KTM 300 XCW "6 Days" edition, which also came with 4CS forks. (It was suppose to be one of the included upgrades. ?) Because the fork valving was tuned softer for the enduro bike that the XCW is, the forks were actually pretty decent. My favorite feature was, one leg controlled compression and the other leg controlled rebound. Both were adjusted at the top with a easy-to-grip knob. When I was in the woods or in technical terrain, I had the compression at 14 clicks out. When I got to a long section of fast, whooped-out, or having jumps, I reached over and cranked the knob CW to 12 clicks out.

 

Back on topic... the alternate valving and less aggressive purpose of the XCW enduro model confused some of the suspension outfitters. They ignored the fact that the 6 Days had 4CS forks; recommending what they would for the normal "Explorer" fork. OR, they recognized the presence of 4CS forks (but not the softer valving) and recommended what they would for an SX or XC racing model. I ended up calling Slavens Racing and talking to them, in order to get the correct springs. 

 

First-World Problems, I know.

Edited May 23, 2023 by rndlmn4