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Hi, new to the Forum. I have a 2020 KTM 250tpi 6 days with standard shock and springs.
As I weigh in at around 85kg without kit I rode the bike for a while to see what it was like with standard springs (about 35hrs) in mixed terrain and noticed it was very soft and was near bottoming out on even small obstacles and minor enduro/trail jumps.
I've recently bought the next spring/s up for back and front. Pretty straightforward job to swap the springs over.
However, when I set the new shock spring preload to 10mm on the bench (225mm free length to 215mm preloaded) I then wound down further to aim for 110mm race sag after fitting, the static sag is way now under at about 20mm instead of the manual's 37mm. With 37mm I had a massive 135mm of rider sag instead of the prescibed 110mm. The old and new springs are the same length unloaded, The printed number on the old spring is 60-63-66 225 F/P, the new spring is 63-66-69 E/Y. What do the last letters refer to? I'm confused! The bike was very unbalanced when you stand alongside and weight the pegs and the back end is very soft compared to the front. I reinstalled the original spring and went for a ride which was better at the front end, but the back end needs to match. I'm having to put loads of preload on the original spring to try and match the heavier springs in the front so the bike compresses at an even rate.
Any thoughts you experts?
 

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So you put 10mm preload on the spring.... then you added more to get race sag correct?

The spring is too soft
 

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Don’t forget those three number springs are the three stage springs. Progressive I think they are called. I didn’t like prog springs. Went to straight rate and felt better. You might need to go up two to get the feel/geometry you want?
 

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Hmm, I noticed on my old 250 EXC that it was so soft on the back when sat to 35mm static sag, and what I thought was 110mm with me on it. I re-did the sag measurement and wound a bit more preload on (static sag to around 32mm).....made a massive difference to rear end feel / firmness, could hit stuff hard and it was great. I'm 85 kg and in the end was happy with the standard spring, but obviously static sag was a little less than recommended.
 

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Don’t get hung up on sag. Get it near then tweak for feel. A better feeling bike is worth a lot more than just a number written down as a guide.
 

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There’s a rough rule of thirds in spring systems... designed to operate in the middle two thirds so that you have some travel either side for anomalies / safety. Static sag is to keep it working in the upper part without unloading. Riding sag more critical for handling of the bike.

Like Pindie says... you’ll get a feel for it. Get a friend to help, take lots of notes.
 

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Don’t forget those three number springs are the three stage springs. Progressive I think they are called. I didn’t like prog springs. Went to straight rate and felt better. You might need to go up two to get the feel/geometry you want?
yeah but 20mm of preload instead of 10 points to something being wrong
 

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Yes, shit progressive spring and internals on the stock shock😂

I agree though. A different spring may well be needed but without seeing the rider on a bike it can be tricky. Sometimes just how/where people sit/stand can really screw up setting things up. I for one run my bars well forward and have soft fork springs as I like a lot of movement in my fork. This means I use more fork preload than most, l like the feel. This makes my rear really light so I get away with a very light rear spring which is great for traction. I love this odd feel but others would say it’s a mushy mess. It’s like a trials bike.
 
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