The Tuesday Tune Ep 20: Preload Adjustment - Video

Nov 14, 2017
by Vorsprung Suspension  
Views: 4,825    Faves: 15    Comments: 0



Coil springs require a certain amount of preload to hold them in place securely, but how much should you run? This week on the Tuesday Tune, we go right back to the basics to take a look at the function of a preload adjuster and its purpose, as well as the carryover mentality of preload adjustment from the motorsport world to mountain bikes.

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64 Comments

  • + 18
 If you don't have command of the basics then the finer points are just a (potentially negative) distraction.
Thank you for another educational video.
  • + 13
 Hopefully now that Steve has said it, the world can start realizing that that trying to use sag to tune the fork is pointless!
  • + 4
 Haha yes, that is a pet peeve of mine. When people talk about things like "15-20% sag" for a fork, if measurements could be taken accurately and consistently, for a certain rider that sag range would be proportionally the same as the difference between a medium Fox 40 coil spring and the stiffest one they make. Obviously that is not a realistic range of spring rates, but even more of a confounding factor is that friction messes up fork sag measurements far too much for them to be consistent. It gets even harder if you start offsetting your measurements with substantial preload.
  • + 4
 @VorsprungSuspension: do you have a process for dialing in fork pressure/spring rate, or is just just something you have to dial in with feel/experience?
  • + 1
 I found something that felt right, grip/stability wise. No clue how much Sag I have...
  • + 0
 @bkm303: Thats my question as well. I use sag as a starting point and simply adjust from there.
  • + 1
 @VorsprungSuspension: Out of curiosity, what rear shock do you use . . . and have you given it some internal wizardry ?
  • + 2
 @Waldon83: all of them. And yes. Smile
  • + 1
 @VorsprungSuspension: Worst, and best response ever.

Aludes to nothing, but gives away everything
  • + 9
 The bit about setting sag was interesting. Glad I'm not the only one who thinks setting sag on forks is frustrating/pointless... my fork feels smooth on the trail (not a crazy amt of stiction), but if I hop on the bike and measure sag 10 times in a row the measurement will be all over the place. The only way I've ever found a pressure I like is to go for a ride and make adjustments until it feels right (whatever that means.... pedals well, no brake dive, etc), then write that pressure down for the future.
  • + 2
 I know what you mean!, my fork mfg, suggests 100 psi as a starting point for my weight, might as well be a rigid fork. i normally set it at 65-68psi, but when its park time it goes up 10psi.
  • + 1
 Agreed on fork sag. Just ride and keep it written down. Then it will change depending on the season.
  • + 2
 @VorsprungSuspension Your information is amazing, spot on, and extremely well explained, but of course you probably already knew all of that. Thank You for helping to verify many things i "discussed" with others even as rookie MTB'r (ti springs need different rate than steel springs = what a bunch of silliness), setting my preload to 0.5 turns, or found out the hard way (wasting precious time checking sag, hell i'm 52 yrs old and just need to ride or sleep) I ultimately said screw it I'm running the pressures/springs that feel right. The spring discussions really drove me crazy i'd only been a "field" mechanical engineer for 30 years, so i just wasn't gonna hear it. I'm now obsessed with full suspension bikes.

Thanks Again !!! can't say it enough .
  • + 1
 Hi Steve,

concrete example. I don't bottom out too frequently, my bike has good grip and feels really comfortable, front to back balance is pretty good, I'm 76kg with full gear on and rock a 2015 Boxxer Team with the medium coil installed (only drawback, the bike isn't super dynamic cause a little soft and I have to work a bit much to throw it from turn to turn).
I do have two preload spacers installed, one being the minimum otherwise there's slack.
One of my complaint is I find the front a little bit low in the really steep sections when my weight is completely over the front. As I'm not asking for more bottom out resistance, is preload a good solution to help keeping the front a bit higher as it adds a bit of resistance force (Obviously, It would be detrimental to small bumps sensitivity)? Would adding low speed compression be a better option?
I read that too much preload could lead to top out klunk when the wheel lives the ground. I can hear a slight top out sound nothing too bad really (and my rebound isn't that fast), is it normal?

Thanks a lot,

Benjamin.
  • + 2
 If your spring rate is where you want it to be and you don't like the way a firmer spring rides, you can try increasing the LSC although you may find it makes things harsher. If LSC isn't working for you though, a better solution than increasing preload is simply to raise your handlebar height - or in the case of a dual crown fork, you may be able to simply lift the crowns up higher on the stanchion if there's room.
  • + 1
 @VorsprungSuspension: I'll try that, thanks!
  • + 1
 Hi Steve!
Something else that I would like you to cover in a future episode is tires: how they can be used and tuned like a suspension and mostly how they interact with the rest of the suspensions found on a bike (fork and rear shock, just in case... ;-) )
  • + 1
 Question for you VS. I'll might be asking Santa for a 230x65mm metric coil shock for my 2017 Patrol seeing as I've been such a good boy this year. Most likely a Super Deluxe Coil unless more manufacturers bring out metric coils soon (I think it's just that, the CCDB and maybe some modified Push and Ohlins at the moment). 65mm = 2.56" stroke, so would a 2.5" spring work OK or are tolerances so tight that 2.5" means exactly 2.5" compression before the spring binds?

Or to ask it another way, if the 2.25" shock in this video was mounted with a 2.25" spring instead of 2.35", would any preload be possible without spring binding when the shock damper bottoms out, ie. do you always need a longer spring free stroke than shock damper stroke if you did want the option to run some preload?

Thanks.
  • + 1
 Like many others I had set the preload for sag adjustment; clearly not a good move and now I know why. Also with a 2.75 coil on a 2.75 stroke I was running the risk of the coil binding on bottom out which is not cool. Great video, back to basics always works best for me.
  • + 1
 If the stated stroke is 2.75 the spring will most likely have more than that IF it's any brand other than Fox. Fox specify the actual free stroke of the spring rather than just telling you what size shock it's for, which confuses people. If your spring is a RS/Cane Creek/whatever else, it's the right spring.
  • + 1
 How ironic, I was actually wondering just this morning if I could decrease preload, I feel like minimum to keep the collar tight is 1.75 turns, and it messes up the shocks ability to absorb chatter. I'm thinking of putting a very heavy duty piece of rubber between the coil spring and preload spacer but don't know if this will have any catastrophic unintended consequences.
  • + 1
 maybe try a very weak loctite, like the purple 222?
  • + 1
 @xeren: good idea. Hadn't thought of that
  • + 1
 If you can buy spare/replacement threaded collars then you could use a second one as a lock-ring like you would do on an automotive coilover unit?
  • + 1
 @gibbon-on-an-orange: that would work. I think marz makes their preload collars with a set screw.

I'm going to try a disc of rubber/plastic first, something to keep the spring from rattling around that won't get destroyed by the force involved.
  • + 1
 What about deciding between coil vs air rear shock besides just 'feel'? For a frame thats very progressive it would seem that a linear coil should would work great as you already have a progressive curve. Is adding a air shock in the instance overkill and too much progression in the curve possibly?

I'd imagine this is largely personal preference, but curious how you think about air vs. coil on any given bike if you had the choice...advantages vs. disadvantages
  • + 11
 This will be covered at some point in the future, there's actually quite a lot to consider.
  • + 3
 @VorsprungSuspension: Awesome. Thanks for doing these videos. You guys rebuilt my 40 and X2 this past summer and could not have been more pleased with the experience. Cheers!
  • + 1
 @VorsprungSuspension: Steve nice video. Always watch. I agree with your description of sag and a human power vehicle. Motocross bikes live and die by spring rate and sag, but they got +50 hp too. One thing with you saying more sag with more progressive susp. Designs may be better, but we find they wallow too much. Actually prefer a more linear design with a bottom out every now and then gives better control.
  • + 2
 @MX298: For sure, ride height is critical for all motorised vehicles. On a motorbike or car, adjusting preload is entirely legitimate - although there are tradeoffs like any adjustment, there is a very real reason to want to make small changes to ride height and geometry, and the heavier rigid sprung mass means the initial force offset required to move the suspension from topout is less of a concern. As far as how progressive is too progressive, that's another debate Smile
  • + 1
 question for VorsprungSuspension: regarding a DHX2 shock, sometimes I hear a clicking/clunking sound when the shock is compressed. fox racing said the noise is happening where the spring contacts the spring retainers. I removed the spring and compressed the bike and there was no noise. I replaced the spring and that improved the issue but I still get the noise. have you ever come across this kind of issue? Also, excellent video!
  • + 4
 Noises of all kinds are something we come across all the time, but trying to diagnose that from here is like trying to give a haircut over the phone - we'd need to see the shock/frame to work out what was causing it. You may even find that it's your derailleur's clutch engaging - this is a really common cause.
  • + 1
 @VorsprungSuspension: yeah...i here you. thanx! i did take off the chain to eliminate drive train possibility.
  • + 1
 No preload on my spring and no idea what my sag is lol

@VorsprungSuspension I was under the impression that preload only affected sag not bottom out force as once the force required to move past the preload the rate of compression is the same.
  • + 2
 Spring *rate* (slope of the force vs travel curve) is the same regardless of preload, but preload adds static force at zero travel - so if you add 1kN of preload at 0 travel, you'll add 1 kN of preload at max travel as well - the entire force vs travel curve gets moved up by the same amount. As he said in the video though, the increase in bottom out force using this method is not large enough to provide meaningful bottom out prevention, and comes with a huge penalty in terms of traction / initial force, because every time the wheel leaves the ground you'll have to overcome that static force again to make the shock move.
  • + 1
 @bkm303: cheers for the reply - you got the maths to show me that too lol
  • + 1
 @VorsprungSuspension: you should have mentioned that the breakaway forces on coil shocks are already quite high on most shocks and are indeed some sort of build in preload.
  • + 0
 My bike as a child had a RST rear spring that I preloaded the crap out of, and it bottomed out constantly, and eventually broke. Honestly if you don't want problems or cost, avoiding suspension can be the way to go in my opinion.
  • + 0
 Well first of all, I absolutely love the tuesday tune! Great work guys, keep it goin'!
I'm totally a bike nerd. mostly in suspesion- not only produts, but also philosophies behind linkage systems etc. However, and that is weird, i'm kind of every bike except mine kinda nerd, so I'm running 2006 26" XC bike, with full XT group and air shock. I even like my Avid SD V-brakes! (maybe cause i'm 125Ib guy, so almost everything locks my wheels and is powrful enough for the type of flat terrain i live in- Poland, 12 miles below the beaches of the Baltic sea). I switched to them from Hayes Nine and Simano deore brakes, that was too powerful in my opinion, and, as a poor engineering student I don't have money enough to buy some modern brakes with a proper modulation.
Getting to the point, I'd like to suggest You a topic, that is barely touched: shock stiffness/flex and how do links deal with unwanted forces, that are applied to the bearings/ Let me explain what i'm thinking about for some time now, and what i can only imagine, how works (i quit being a bike mechanic two years ago, when i found a job in automatics/teaching/programming and machine vision systems- I was at a hospital for two months, so i'm unemployed now, but i work on my engineer degree, so after few months i'll b bak on trail, probably with my wallets not so empty as now Razz )
We can see a whole sea of coplicated linkage systems, and the forces on links are being transmitted on the frame mostly through the shock. Thats right. But what we can see is that those links are in some angles, that varies, as shock goes through its travel, sometimes changes at those angles are about quarter of a turn, so that is rather much. As the back whel is sucked by roots etc it creates forces that not only alter suspension action, but also create stress on bearings, and of course, shock itself. What gives me some headache in comparison between those two above is this, that link, that compresses the shock almost never compresses it exactly in the straight line that can be drawn between eyelets, it almost always compresses the shock, with a force, that's vector is slightly (or more often not so slightly) rotated basing on this line. This causes stress on bearings, bushings, frame elements, and ofc shock itself. I know that we can alter some kinematics by making use of this, but it's a comromise between desired characteristics and material stress. And last: as we know, shocks are being compressed, but those frame elements, that links, that pushes them, are also kinda try to bend them in some way, cause forces go in a lot of directions. Air shocks have almost always wide shaft, while coil shocks has that few milimetres thin shafts. Im almostust sure, that it can be bent to some point (alloys are rather elastic, so it comes back to it's original form after compression). Is it true? How this can alter suspension performance/ I saw some old Yeti DH models, that compressed shocks in straight line with a weird kind of rail or sth. What can You say about this problem?
  • + 2
 Hi Steve, it may oversimplify dzenny's comment, but would you prefer to see a pull shock more widely used to counter(if it would) shaft flex? I think formula address this issue somewhat in their new forks With their Iinternal floating technology
  • + 1
 @Drover: Yes, it's one of my points. Plus, shaft in air shocks is wider than in coil.
Second thing: vectors of forces in frames cause some issues, as forces aren't parallel (or perpendicular) to them, so is there a way to avoid it? (bearings are being worn-out, stress on frame members etc.)
Didn't know that pull shocks are ridden because of counteracting a shaft flex, but it seems very clever (more than rail- based suspension designs
  • + 1
 I tend to have a few springs for a rear shox, one for free ride, one for DH and if I'm lucky ill have one for hammering the trails. ill even take it saggy for a bit then harden it up too depending what I'm up to.
  • + 3
 Steve, fantastic videos, please keep them coming. Every (tues)day is a school day ☺️
  • + 1
 I was trying to explain to a local mtb group that sag is pointless. Now I can use this as another example of why. Great video as always, keep it up.
  • + 0
 @VorsprungSuspension are all spring rates the same? Are all springs of different materials the same and how does weight or stress impact performance? Does coil rate change when they 'take a set'.
  • + 1
 Interested in this too. I'm struggling to find a Fox 500lb spring that's in stock. I can find CaneCreek ones which will fit the Fox shock, but reviews seem to suggest that a CC 500 feels more like a Fox 450. Is it a difference in measuring method? Or are the CC materials giving a more 'plush' movement within the wire's structure?
  • + 2
 @nicolai12 yes they are. Titanium, steel, whatever - they are all strain rate independent for the purposes of a spring, meaning that a given spring rate is a given spring rate. 500lbs/in from a steel Fox spring is identical to 500lbs/in from a titanium spring from elsewhere. If there is a difference in feel, it's from one of three things:
1. The stated rate on one or both springs is not accurate
2. Something was changed (preload, damper settings, tyre pressure, whatever) when the springs were swapped
3. Placebo. When you've paid $300 for a spring you're quite inclined to go looking for improvements whether they exist or not - plenty of people will tell you that their titanium spring feels plusher or whatever, but it just isn't the case.
  • + 1
 @VorsprungSuspension: Great point. I know that Fox states that they are within x % and that can be nearly 50lb off from rating. Can you comment on the rebound velocities of a given spring. If you have two identical spring weights but one weighs twice as much as the other, do they both have the same rebound characteristics? What if one has coil bind at one of the coils before allowing full stroke? Will that change the spring rate? Thanks again for all of the great feedback.
  • - 1
 Really interesting, I gave up trying to figure sag at rest, now I just go by how much the indicators read and adjust accordingly. And I think this guy looks more like a grown up Eddie Munster than Stevie.
  • + 1
 perfect timing of this video as I am experimenting with the correct spring weights on my sb6c and dhx2
  • + 1
 I run a DB Coil on my SB6c, my recommendation - use a spring calculator, and then go up by 15 to the next spring rate. I came in at requiring a 352 spring, so got the 350 Ti . . . Was great, but I felt after about 5 months that it was potentially just too soft making the bike track well, but far less playful. I upped to a SAR Spring at 375, best thing I did. Not too soft, playful and still tracks very well.
  • + 1
 @Waldon83: I found that pretty much all the current Yeti's need to go 25-50lbs heavier compared to all the online spring calculators to get correct sag, not sure why though. Holds true for SB6, SB55 and SB45
  • + 1
 Interesting advice about sag on the fork. Thanks for another great video!
  • + 1
 Facial hair belongs to urban lumberjacks
  • + 1
 Wow. I didn't even know I didn't know.
  • + 1
 Is it just me or does this man look alarmingly similar to steve smith
  • + 2
 If Steve Smith had been fatter, slower and more tedious, sure Smile
  • + 0
 It's Steve Smith's lookalike
  • + 1
 Love these vids!
  • - 2
 It would be more regular if they renamed it the Tuesday prune
  • - 2
 Please sound treat that room. Otherwise great videos as always. Smile
  • + 9
 Unfortunately it's not quite that easy - the room is a 1500sqft open plan workshop with heavy machinery in it. We'll do what we can to improve the sound quality though - microphone took some unintended swimming lessons in coolant and needs replacing anyway Smile
  • + 1
 @VorsprungSuspension: One line of egg carton on the wall in the same height as the microphone go a long way Wink

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