2013 KTM 250SX suspension help needed

Posted this in the KTM two stroke forum as well, I appreciate all your guys input with this, thanks!

 

Hi guys,

 

Recently purchased a barely used 2013 KTM 250SX. I weight 170 pounds and ride B/A level motocross only. The previous owner installed a 5.7kg spring in the rear and also went to the next stiffest spring in the front (he is still to get back to me to confirm whether thats a 0.48 or 0.49). My research on race-tech's website tells me that for my weight and skill level I should install the standard rear spring which is a 5.4kg, and likely a 4.8 or nearest spring rate in the forks. 

 

Research on MXA pretty much follows the same guidelines, see this link:

 

http://motocrossacti...-YES-8964.aspx�

 

Where they say they use a 5.4 for the shock and use 0.48 springs in the forks.

 

My initial plan was to go back to stock springs both front and rear, but now i'm thinking I'll just go back to the stock rear spring and leave the slightly stiffer fork springs in there and test.

 

What do you guys think and what has been your experience? 

 

Thanks a lot in advance!

 

Adam

Edited by adamdf

I weigh 150 and std springs felt reasonably balanced

Stock spring rates were 5.4 rear .44 front which is well balanced and good for up to about 170-180LB max.  I am 215 geared up and tried the 5.7 rear spring which unbalanced the front end and gave me bad arm pump. I had a set of .48 front springs which then unbalanced the rear since they were two rates up on the front. I put a 6.1 shock spring on and now the bike is great. I am at 32mm static and 105mm race sag geared up and the bike handles great.

 

 

I think for 170LB you would probably be borderline on the stock springs and better with the 5.7 rear and probably .46 fork springs which would be one step up on both ends.  If he only went up 1 rate front and rear, then you are probably already where you should be.  Personally if you are on the edge of spring rates, I usually find the stiffer spring with less pre-load gives a much better ride than the opposite.  Springs rates are a controversial thing between tuners, but IMO springs rates are not designated by rider skill level or agressiveness, but purely on weight. They serve to hold the bike in the correct geometry to handle as the bike was designed where the valving inside controls everything else and would be modified for skill level or rider preference.

 

 

What are your sag numbers looking like?

Stock spring rates were 5.4 rear .44 front which is well balanced and good for up to about 170-180LB max.  I am 215 geared up and tried the 5.7 rear spring which unbalanced the front end and gave me bad arm pump. I had a set of .48 front springs which then unbalanced the rear since they were two rates up on the front. I put a 6.1 shock spring on and now the bike is great. I am at 32mm static and 105mm race sag geared up and the bike handles great.

 

 

I think for 170LB you would probably be borderline on the stock springs and better with the 5.7 rear and probably .46 fork springs which would be one step up on both ends.  If he only went up 1 rate front and rear, then you are probably already where you should be.  Personally if you are on the edge of spring rates, I usually find the stiffer spring with less pre-load gives a much better ride than the opposite.  Springs rates are a controversial thing between tuners, but IMO springs rates are not designated by rider skill level or agressiveness, but purely on weight. They serve to hold the bike in the correct geometry to handle as the bike was designed where the valving inside controls everything else and would be modified for skill level or rider preference.

 

 

What are your sag numbers looking like?

 

Hi there, you are correct about the stock front springs being 5.4 on the rear but apparently its 0.46kg/mm on the front springs. Are you speaking of a 2012 or 2013?

 

Thanks for your input as well on this. 

 

I haven't messed with sag yet as I figured I would never come within range with the 5.7 spring, I will do that though and post figures in here once done.

Edited by adamdf

2013

 

The bike should have come with 4.4n/mm springs which would be .45kg/mm   (when I said .44 I was refering to 4.4n/mm)

 

The owners manual states the bike is set up for standard rider weight of 165-187 LB.  Most people are finding the owners manual to be soft by one spring rate when checking sag numbers.

 

From your manual

 

Front

 

143-165lb  4.0n/mm  (.41kg)

165-187lb  4.4n/mm  (.45kg)

187-209lb  4.6n/mm  (.47kg)

 

Rear

 

143-165lb  51n/mm (5.2kg)

165-187lb  54n/mm (5.5kg)

187-209lb  57n/mm (5.8kg)

 

That said, 4.4 fork springs and 54 shock spring are standard fit on these bikes.  I am running .48kg factory connection fork springs so they are technically 1 1/2 rates over stock based on the book, and I have a 61 rear spring which is the next available rate past the 57.

 

If yours has 4.6 springs then they are not stock.

 

Check your sag numbers and post back. Spring rates vary from what is marked on the springs so you cant always go by that number anyways. I find it easiest to set the static sag to 30mm, and then get on the bike and see what your rider sag (geared up) is.  If its less than 95 you need a lighter spring, if its over 110 you need a heavier spring. However many rates you change in the rear you should also change in the front to keep the bike balanced. I dont put too much stock into checking fork sag because there is too much friction on the fork legs to get any real relevant numbers. 

 

 

Also, FWIW....  

 

You ***CAN*** remove the shock on these bikes without taking the whole subframe/airboot off.   If you remove the lower linkage knuckle and the shock bolts you can drop the shock down inside the swingarm. Then you can angle it towards you in the opening on the side of the bike and lift up on the rear wheel/swingarm assembly. There is a sweet spot where the whole thing will slide right out without having to unbolt everything else. You might need to remove the seat and take the right side airbox plastic cover off to get enough clearance, but that still beats taking the pipe, subframe, and airboot off the bike.

 

 

Hi there, you are correct about the stock front springs being 5.4 on the rear but apparently its 0.46kg/mm on the front springs. Are you speaking of a 2012 or 2013?

 

Thanks for your input as well on this. 

 

I haven't messed with sag yet as I figured I would never come within range with the 5.7 spring, I will do that though and post figures in here once done.

Edited by newgensti

2013

 

The bike should have come with 4.4n/mm springs which would be .45kg/mm   (when I said .44 I was refering to 4.4n/mm)

 

The owners manual states the bike is set up for standard rider weight of 165-187 LB.  Most people are finding the owners manual to be soft by one spring rate when checking sag numbers.

 

From your manual

 

Front

 

143-165lb  4.0n/mm  (.41kg)

165-187lb  4.4n/mm  (.45kg)

187-209lb  4.6n/mm  (.47kg)

 

Rear

 

143-165lb  51n/mm (5.2kg)

165-187lb  54n/mm (5.5kg)

187-209lb  57n/mm (5.8kg)

 

That said, 4.4 fork springs and 54 shock spring are standard fit on these bikes.  I am running .48kg factory connection fork springs so they are technically 1 1/2 rates over stock based on the book, and I have a 61 rear spring which is the next available rate past the 57.

 

If yours has 4.6 springs then they are not stock.

 

Check your sag numbers and post back. Spring rates vary from what is marked on the springs so you cant always go by that number anyways. I find it easiest to set the static sag to 30mm, and then get on the bike and see what your rider sag (geared up) is.  If its less than 95 you need a lighter spring, if its over 110 you need a heavier spring. However many rates you change in the rear you should also change in the front to keep the bike balanced. I dont put too much stock into checking fork sag because there is too much friction on the fork legs to get any real relevant numbers. 

 

 

Also, FWIW....  

 

You ***CAN*** remove the shock on these bikes without taking the whole subframe/airboot off.   If you remove the lower linkage knuckle and the shock bolts you can drop the shock down inside the swingarm. Then you can angle it towards you in the opening on the side of the bike and lift up on the rear wheel/swingarm assembly. There is a sweet spot where the whole thing will slide right out without having to unbolt everything else. You might need to remove the seat and take the right side airbox plastic cover off to get enough clearance, but that still beats taking the pipe, subframe, and airboot off the bike.

 

newgensti,

 

I checked the manual, the fork springs for the 2013 European 250SX are 4.4N/MM but for the North American 250SX they have them listed at 4.6N/MM. I own the USA model as I purchased my bike in the US.

 

Which version do you own?

Thats interesting.. I just looked up the specs a second time to make sure i didnt mis-read.  You are correct that the 250sx US version shows 4.6 springs.  I have a 250XC model and it came with 4.4 springs.  Odd that they would use 4.6 springs only on american 250SX models, but use the 4.4 on all other 250/300 models here and around the rest of the world. I wonder if its a TYPO in the manual, or if they think for some reason american motocross riders need stiffer front springs? haha.

 

Either way, if you already have 4.6 springs and a 57 shock spring I would think you should be able to get good sag numbers and the bike should work pretty good for you.  Set the sag and see just for the heck of it.

Thats interesting.. I just looked up the specs a second time to make sure i didnt mis-read.  You are correct that the 250sx US version shows 4.6 springs.  I have a 250XC model and it came with 4.4 springs.  Odd that they would use 4.6 springs only on american 250SX models, but use the 4.4 on all other 250/300 models here and around the rest of the world. I wonder if its a TYPO in the manual, or if they think for some reason american motocross riders need stiffer front springs? haha.

 

Either way, if you already have 4.6 springs and a 57 shock spring I would think you should be able to get good sag numbers and the bike should work pretty good for you.  Set the sag and see just for the heck of it.

 

newgensti,

 

Thanks for verifying that! The 250XC would likely have softer springs than the SX models as that is mainly a cross country machine vs motocross which typically demands stiffer suspension for the large jumps etc.

Thats not entirely true though.. Like I said before, springs hold the bike at the correct geometry for handling. Valving controls bottoming.  That said, springs are selected for bike and rider weight and valving setup will determine how big of a hit it can take without bottoming out.   If anything, the heavier XC model with E-start, and extra fuel should require heavier springs than the lighter bike.  Also, why would the Euro motocross model come with lighter springs?

 

KTM does some funny stuff from time to time. Not sure what their thinking is on that move, but its not the right way to go about it. 

Hi adam df,

do you still have those 48n/mm fork springs? and poosibly the shock sping too?

 

Scott

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now