Sag and correct spring rate

Louie112
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Louie112
I used RaceTech’s spring calculator to figure out I should have .44 fork springs and a 4.3 kg shock spring at 140 pounds with no gear. I’m a C-class motocross rider on a KTM 350sx-f.

I just changed the spring and greased the linkage and all that. When I went to set the sag, the preload collar is all the way loose and I’m only getting 91mm of race sag. A local suspension tuner told me based on that information, a 4.3 kg shock should be correct.

Any ideas why I’m not able to get the correct sag? I sat near the front of the bike when measuring which is where I would say I am a good portion of the time riding. Maybe I should sit more towards the middle? Or is there something else it could be?
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kb228
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kb228 6/22/2019 6:32pm
6/22/2019 6:32pm
are you measuring from a good spot? If youre too close to the swing arm pivot it will make the measurement less.
Louie112
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Louie112 6/22/2019 6:42pm
6/22/2019 6:42pm
kb228 wrote:
are you measuring from a good spot? If youre too close to the swing arm pivot it will make the measurement less.
Think so. On the KTMs, there’s a spot that says SAG on the rear fender so I just put a mark right under that. Maybe my help just measures incorrectly?

Does that sound out of order? A 4.3 kg shock spring for a 140lb C-level Moto rider?
Cadpro18
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Cadpro18 6/22/2019 8:12pm
6/22/2019 8:12pm
I ran a 45 N/mm (4.6 kg/mm) spring on my 350 @ 105 sag and 40 free sag. I weigh 155 lbs. I think I had 7 mm preload on the spring.
Paw Paw 271
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Paw Paw 271 6/22/2019 8:56pm
6/22/2019 8:56pm
Sounds like the spring may be marked incorrectly, due to the static sag number.

Paw Paw

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NeedMoto
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NeedMoto 6/22/2019 9:21pm
6/22/2019 9:21pm
Paw Paw 271 wrote:
Sounds like the spring may be marked incorrectly, due to the static sag number.

Paw Paw
Agree with Paw Paw.

My suspension tuner test each and every spring he works on, as he has found a fair amount that are not what is claimed on the spring. Sometimes two rates different.
chump6784
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chump6784 6/23/2019 2:46am
6/23/2019 2:46am
I've found racetech's calculator to be on the stiff side, moreso on the shock than the forks. Did you edit your first post? I can't see a static sag number there
Louie112
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Louie112 6/23/2019 5:05am
6/23/2019 5:05am Edited Date/Time 6/23/2019 5:05am
Paw Paw 271 wrote:
Sounds like the spring may be marked incorrectly, due to the static sag number.

Paw Paw
NeedMoto wrote:
Agree with Paw Paw. My suspension tuner test each and every spring he works on, as he has found a fair amount that are not what...
Agree with Paw Paw.

My suspension tuner test each and every spring he works on, as he has found a fair amount that are not what is claimed on the spring. Sometimes two rates different.
Hmm that’s interesting. So what did you guys do in that spot? Just remove the spring and send it back? Seems like it is a costly mistake as a spring is easily over $100

I bought a FC spring. Are there any companies that are generally more accurate than others with their rates?
Louie112
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Louie112 6/23/2019 5:08am
6/23/2019 5:08am
chump6784 wrote:
I've found racetech's calculator to be on the stiff side, moreso on the shock than the forks. Did you edit your first post? I can't see...
I've found racetech's calculator to be on the stiff side, moreso on the shock than the forks. Did you edit your first post? I can't see a static sag number there
I bought the suggested one for my CRF250R a couple years back and it felt really good so I thought it would be fine this time as well but maybe they sent me a bad spring as mentioned above?

I didn’t include a free sag number because I was unable to get the correct race sag even with the preload collar backed all the way out.
aees
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aees 6/23/2019 6:02am
6/23/2019 6:02am
Louie112 wrote:
I used RaceTech’s spring calculator to figure out I should have .44 fork springs and a 4.3 kg shock spring at 140 pounds with no gear...
I used RaceTech’s spring calculator to figure out I should have .44 fork springs and a 4.3 kg shock spring at 140 pounds with no gear. I’m a C-class motocross rider on a KTM 350sx-f.

I just changed the spring and greased the linkage and all that. When I went to set the sag, the preload collar is all the way loose and I’m only getting 91mm of race sag. A local suspension tuner told me based on that information, a 4.3 kg shock should be correct.

Any ideas why I’m not able to get the correct sag? I sat near the front of the bike when measuring which is where I would say I am a good portion of the time riding. Maybe I should sit more towards the middle? Or is there something else it could be?
Whats the statics sag?
Louie112
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Louie112 6/23/2019 6:16am
6/23/2019 6:16am
I didn’t even bother checking it since I couldn’t get the correct race sag with the preload backed all the way out. Is it worth it to check the static sag at that point?

I figured I may be measuring it wrong but I’ve watched 3 different videos just to make sure and I don’t think that’s the case. Should I sit more towards the middle of the bike to measure? I was sitting more towards the front since I feel like I’m up front the most.
garagedog
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garagedog 6/23/2019 6:43am
6/23/2019 6:43am
Sit more middle over foot pegs like you are putting through the pits.
Paw Paw 271
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Paw Paw 271 6/23/2019 1:04pm
6/23/2019 1:04pm
If you have no preload on the spring, then your free sag is incorrect and thus your race sag will be way off.
The spring you have is just too stiff for you. I have also found some errors in the Race Tech spring calculator over time. I know my Husky showed as rate even higher than what I had and it was too stiff. I went to another company to get the correct spring.
Call Race Tech and speak with a tech for his opinion.
When you do your race sag....Wear all your gear and sit the middle of the bike. After you get this set where you want it, check your static sag to make sure it falls within range.

Paw Paw
m21racing
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m21racing 6/24/2019 8:15am
6/24/2019 8:15am
A 2018 350 for 155lb rider we calculated at 39nm. Basically one rate and a half down. KTM/WP recommends different preload settings on different models. I would agree that some recommended rates are off. The KTM chassis are sensitive to changes, so I'd look to more than one source on spring guidelines. Also, I set race sag with my riders standing straight up on pegs for more consistency from the varying heights in riders.
duckdog77
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duckdog77 6/25/2019 6:55am
6/25/2019 6:55am
I had read a lot of concerns with race techs system being 1-2 spring rates off (To the stiff side) and I would agree. I just set my bike up with race tech and used one spring softer than recommended. And also helped a buddy with his and used one spring softer (due to him being a big guy and not having a stiff enough spring) and both our bikes are good to go.
T-Fish
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T-Fish 6/25/2019 4:52pm
6/25/2019 4:52pm
FC, Race Tech, and Powerband all suggest different rates front and rear for me and my 350. I’m left very confused.
m21racing
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m21racing 6/25/2019 5:01pm
6/25/2019 5:01pm
T-Fish wrote:
FC, Race Tech, and Powerband all suggest different rates front and rear for me and my 350. I’m left very confused.
The key is correct preload on spring to get desired race sag. You should be 5 to 8mm, but as stated before, ktm wants different numbers on different models. 140lb on a 350sxf i think 38nm would be ballpark. Call factory services dealer. Mx tech i believe is one.

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