Bike is a 2023 KX450
I'm 5'10 currently weighing 228lbs naked. I'm already on a 6.2 shock spring yet I'm all the way at the end of the threads on the shock to get 104mm of race sag and static sag is like 35mm. I have no idea what brand the shock spring is as I know they vary and some brands are more accurate than others.
After putting in my info into RaceTech's calculator, it recommends 6.10 kg/mm. I'm really puzzled, shouldn't a 6.2 be money at my current weight, especially for a stiffer feel? Yet I'm fighting with this shock constantly messing with my sag, and now I'm out of adjustment. With so much preload cranked on this thing already (There's literally no threads left to add more like I said) it feels like a damn springboard off of jump faces when I want a more dead feel.
Should I go to the RaceTech 6.3 or would that be crazy stiff? Factory connection also makes 6.1.
Are RaceTech and FC the best springs?
Thanks!
Don’t worry about the amount of threads left for preload. Some springs are shorter than others. If you can get 104mm sag with 35mm static, you are good. If you run out of threads, race tech makes a spacer. I use Diverse Springs. They make good chrome silicone springs that rival titanium.
This number you quote : 104 and 35 sound good, but then you imply you've got a shedload of pre-load on the spring ( and your 'springboard' comment implies what you get from a heavily pre-loaded spring.
But, as willbilly wrote, we could take it as just being a short spring - a common route a manufacturer may take to achieve a spring rate - eg : a shorter spring, like a shorter rod / bar requires more load to deflect the same distance than a rod of the same diameter / metal composition, thus achieving a heavier spring rate..
And, once again, the OPs number indicate it is a good setting. Though, other things, like a 'sticky' linkage / pivot point(s) can really create 'issues'.
So, Do You Have a Lot of pre-load in place?
You can have a spring tested for it's Actual rate, to know exactly what you are starting from.
I personally, prefer minimal pre-load, on Any bike - just nudging towards the 'too heavy a spring' zone. But, that's me - I hate the initial harshness of a (overly) pre-loaded spring.
When you go way up on spring rate from stock you need a revalve or the bike may feel like a spring board when leaving jump faces. You also need to put stiffer springs in the fork to maintain bike balance. You can try turning in the rebound clicker but it can only do so much.
The shorter spring or rod being stiffer can be demonstrated by holding a ruler of off the edge of the table and flicking it to make it bounce.
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103-105 is where I want to be for my race sag because that's what works well with this chassis. I was kind of implying that 35 static is way off.
However, according to Bones from Pro Circuit 30-40 is where you want to be. I thought around 25 was the sweet spot for some reason...
https://motocrossactionmag.com/bare-bones-how-static-sag-can-help-you-choose-the-right-spring-rate/
AS A RULE OF THUMB, FOR BIG BIKES STATIC SAG SHOULD BE BETWEEN
30mm AND 40mm. IF AFTER SETTING THE RACE SAG YOUR STATIC
SAG IS MORE THAN THE RECOMMENDED 40mm, YOUR
SPRING MAY BE TOO STIFF FOR YOUR WEIGHT.
I thought I was getting 35 static but maybe it was lower, which would make sense. I'll check it again when I get home and get my facts straight. My apologies! Race sag is definitely 104
Are you confusing kg/mm with N/mm rates? 1 kg/mm is equal to 9.81 N/mm.
It sounds a lot like your shock is binding when it compresses.
I bet you have a measurement error on Static sag.
No. Talking strictly kg here. For the shock at least....
Hey guys, so just an update I ended up buying the 6.3kg RaceTech spring. Before I swapped it I checked my static sag one more time and it was at 25. We threw the new spring on and set my race sag to 104. I was able to take a bit of preload out from where the previous spring was but not much, which I was a bit bummed about. There's maybe 4 threads exposed now versus none.
Tried it out last Saturday and initially felt zero difference. Still felt like I was riding a 2009 Honda and all my weight no matter what was forward. And still getting the springboard feeling off of jumps.
I fucked around with clickers all day and was frustrated as hell. I've been on this bike for three years and the thing has always handled like a dream!
Finally, I dropped the forks down (Previously had them at the first line below the top cap which is roughly 3-5mm down I believe) in the clamps so they were flush with the top caps, which is actually how this bike comes stock. MUCH MUCH better. I could actually ride and steer the damn thing without almost tucking the front every turn! Sucks that it took me all day to get comfy and by then it was 100 degrees and the track was about to close. Hoping to do more testing this weekend.
I'm hitting the scale at 229 and still surprised I'm down that low on the threads with this heavy of a spring. Is my best option to keep losing weight so I can lower the shock?
Thank you to all of you for the help!
I suspect you may be measuring your race sag incorrectly.
Just for shits and gigs, I'd try taking preload off the spring so that your static sag is closer to 40mm. Then ride the bike, adjusting preload 1-2 spins either way to dial in your race sag.
Side note, did you get a revalve for the heavier springs? It will make the bike handle like crap if the valving doesn't match the spring rate.
What is the correct way? I stand because I think it's more consistent than sitting. We have a sag scale in mm, had it for years.
I zero out the scale while bike is on the stand holding the scale almost vertical from axle to fender
I hop on the bike, bounce a bit to remove stiction then measure while someone holds me up.
Honestly I was thinking the same thing. Who cares about the number, maybe just turn it in to take some preload off and see how it feels.
My bike was valved to go with the heavier 5.3 fork springs and 6.2 shock spring by an old school tuner who's valved all of my bikes. If I continue down this rabbit hole I may have him tweak it, but I don't think valving is the problem.
Sounds like you have the process dialed but the amount of preload required still draws concern.
I'd probably try with a tape measure and see if I got the same measurement.
Yeah that's the part I'm not understanding either.
Your going from a marked 6.2 spring to a marked 6.3mm spring , with the discrepancies/ inaccuracies Most springs have, may have meant you achieved Nothing.
Which, is an expensive Bummer.
I've always checked springs for their true rate.
And, even if both springs were true to labels, or, indeed, the new one was the one point up from what you've got, it's a buggerall change in spring rate.
Now, after writing hat - have you checked the shock - if oil is aerated, piston rings worn / sticking, body worn in a section of the bore, you can be chasing your tail, ever and anon.
Same goes for the linkage, well, Any pivot point bearings.
A while back, a mate of mine didn't take my advice to Not get a particular Linkage Bearing kit, and, soon after he installed it, his bike became almost unrideable. It was, quite frankly, Frightening to ride, when I had a go on it.
Turns out, one of the Needle bearings in the linkage, had the needles 'cock', thus, intermittently Jamming the rear end!
Just a 'poofteenth' off with the needles or their case is all it takes - I didn't bother to really measure things, I just Hoicked the Absolute Garbage, and installed OEM bearings.
Result - back to a fine handling rear end for my mate.
There's a whole bunch of potential 'failures' that can Really give you Headaches / Hurt You - I'm just trying to offer some help.
The new spring at least got me in the window of proper static sag, so I wouldn't say it achieved nothing. The old spring I was completely maxed out and had no more threads left.
Linkage was cleaned and greased right before I started having issues, everything looked great. I usually go no more than 25 hours on bearings before going through them.
I replaced the oil in the shock about a month ago, however I just went through the compression stack hole to empty, refill and bleed. I didn't fully disassemble it to check everything out.
I checked my static sag again last night, it's at 38. I'd be happier with this number if I were more in the middle of the threads. I'd say I have about 4-5 threads showing. I imagine if you go past 40 it means you have so little preload that the shock isn't compressed enough and your spring is too stiff. But I have too much preload. I don't understand!
The area of the threads is shorter than I imagined.
I could see a normal preload being near the bottom of the threads, especially if you have the axle slid back.
Pit Row
That makes sense. It does seem shorter than the other bikes.
Hey guys, I went riding Saturday and the bike was definitely better. Fortunately a few buddies of mine were there hanging and not riding, so they were able to watch, film and give me feedback. Initially we left the forks alone and and went two out on rebound, one out on low speed comp on the shock in hopes of it sticking to the ground better instead of deflecting. I could see that it looked stiff and loose coming into high speed sweepers in the footage. I think I rode most of the day on that setting and played with the forks later on. By end of day I also tried turning my rebound out on the fork and I think that helped with the square edge chop.
I'm still getting this cab-forward stink bug feeling no matter what I do however. Also still feeling that annoying last second rebound kick off of jump faces too that I've been struggling with for awhile. Later that night I even had my dad help check sag, hoping it would be close to 100 so I could finally take some pre-load out of the shock. It was still at 105, which is where we set it two weeks ago and should be the sweet spot for this bike. I'm glad it's consistent but bummed I don't have more of a window of adjustment to work with.
At this point, should I have my valving looked at and adjusted or...... Am I just a head case? Have I been hanging out with Chase Sexton too much!? Lol!
I appreciate all the help from you guys!
I've also downloaded the REP AI tuning app on my phone. It recommends Keefer's settings which I think I will try. I also need to record my clickers and see where I ended up Saturday.
One thing I didn't mess with this weekend was high speed comp. Would turning that out help with that kick I'm getting off of jump faces?
Keefer's settings and MXA recommend having it only 1 and a 1/4 turn out. But I think that's with stock valving.
I'd keep reducing sag until the bike corners better. 1 rotation makes a big difference.
Don't get hung up on ___mm sag, it's just a measurment to help you return to the setting you like.
After getting the sag where it feels good, then I'd slow shock rebound if getting a kick. (It would make sense to slow your rebound after moving to the stiffer spring, I wouldn't be surprised if you have rebound 3/4 of the way closed)
From the sounds of things you want to go in on your rebound a few clicks and out on your high speed comp. You've established your sag numbers are correct even if the collar is close to the end of the threads. Less high speed will let the shock ride lower and more rebound will stop it unloading which will intern get the front end higher.
How many mm of shock preload do you have? That’s a number I would be concentrating on more than sag.
Really? I was thinking of adding sag/taking pre-load out so I'm more in the middle of the threads and my shock isn't so long, then riding it just to see what it does. I don't need the bike to corner better, I need it to be balanced. Riding feels so sketchy and uncomfortable because all of my weight is forward. Or at least that's what it feels like.
Yeah, that's the real question. That's exactly what the RaceTech rep I spoke to about the spring told me too. They said they're going away from measuring static sag because linkage designs are so different bike to bike these days. Spring preload is the real measurement.
I haven't taken the time to take my shock off and measure that. And I can't get in and measure with it on the bike.
Yeah if that's what youre feeling then go for it.
My thought was 105 is in the high range for OEM's, they usually recommend ~90-100mm.
Your rebound kick and bike being unbalanced could be because you have too much sag and are riding too low in the stroke, but on the flip side also could be from riding too high in the stroke.
If you're feeling too much front end bias then reduce preload and do a few laps. If it feels better then reduce more, keep going until it feels worse, then work back the other way. When it gets hard to tell if it's better or worse, then you've found your sweet spot, take a sag measurement so it's easier to find again in the future.
You should be able to measure with a small measuring tape. I do it all the time.
If you know the standard spring length you can at least get an aprox.
I just got a new GasGas and my static and race sag numbers look pretty good but I’m running 12mm of shock preload with 105sag.
I’d really like to be closer to 6-7mm and I’m sure I would be just going up one rate.
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