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2013 KTM 250SX suspension help needed

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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 4.8 or 4.9). 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://motocrossactionmag.com/Main/News/HOW-TO-BUILD-THE-ULTIMATE-KTM-250SX-TWOSTROKE-YES-8964.aspx

 

Where they say they use a 5.4 for the shock and use 4.8 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

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Yea, I think the 5.4 in the rear and .46's in the front, will work fine for ya. Thats actually what my 2013 250SXF came with and it weighs 20+ lb more then your bike does.

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Yea, I think the 5.4 in the rear and .46's in the front, will work fine for ya. Thats actually what my 2013 250SXF came with and it weighs 20+ lb more then your bike does.

 

Hi Tye, im going to remove the 5.7 rear spring and install the 5.4 tomorrow. I will leave the heavier front springs (4.7/4.8/4.9 - still to be confirmed by previous owner!) installed and see how it goes after a test ride. I'm thinking the sightly heavier fork springs may not be such a bad thing. Thoughts?

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Yea, spring rates are critical and you'll know if its too much simply by riding the bike and seeing how much of the travel is used up. My guess is, you'll have a solid 20 - 30mm of travel NOT being used with the .48 spring with your weight. Throw a zip tie on the fork bottom to check travel, see what ya get! You can also get a buddy to help you measure fork sag, it should be around 60mm.

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Yea, spring rates are critical and you'll know if its too much simply by riding the bike and seeing how much of the travel is used up. My guess is, you'll have a solid 20 - 30mm of travel NOT being used with the .48 spring with your weight. Throw a zip tie on the fork bottom to check travel, see what ya get! You can also get a buddy to help you measure fork sag, it should be around 60mm.

 

So your thinking along the same as me? Maybe test the 5.4 with the slightly stiffer front springs. Over in the suspension forum theres a guy saying that for my 170 pounds the 5.7 rear spring and slightly stiffer fork spring may be ideal for me an that I should just set the sag. This can get quite confusing! I have to admit I didn't set the sag before my first ride on it as I figured the springs would need changing, maybe I should just do that first and see where i'm at. On the other hand, MXA says they recommend a 5.4 on the rear and 0.48KG/mm springs in the forks, Race-tech calculator also recommends roughly the same thing for my weight. Hmmmm

Edited by adamdf

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Well, I have the same chassis with a MUCH heavier motor and weigh about 165 with my gear and run a 5.4 rear and feel its perfect. So subtract 20lb (motor weight difference) and then you got your weight difference. In terms of the front, I too like a stiffer spring because I feel they give better pop on jump lips. If you don't weigh enough to get the spring to compress, it will feel more harsh. That to me is the only detractor and it does depend on your riding style. The .46's may be a TINY bit too soft, but I feel the .48's could be a tiny bit too much.

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Well, I have the same chassis with a MUCH heavier motor and weigh about 165 with my gear and run a 5.4 rear and feel its perfect. So subtract 20lb (motor weight difference) and then you got your weight difference. In terms of the front, I too like a stiffer spring because I feel they give better pop on jump lips. If you don't weigh enough to get the spring to compress, it will feel more harsh. That to me is the only detractor and it does depend on your riding style. The .46's may be a TINY bit too soft, but I feel the .48's could be a tiny bit too much.

 

Thanks Tye - i'll test the stiffer fork springs that are in there now and just install the stock 5.4 spring for now and see how it goes and will report my findings.

 

Out of curiosity - what type of riding do you do? Mainly MX?

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All MX, all the time :)

Ohh and don't forget to set sag, 105mm rider, 35mm static. Try to get close to those numbers. If you CAN, then the spring is spot on.

 

Same here - strictly MX.  Thanks again man!

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I got a 13 sx also.... I am on my second revalve and third spring combo I weigh 215 no gear. Tried it stock bike was awesome till you found bumps or track got rough. Went with a local guy and mx tech spring calc factory connections weight tested those spring and rear was 591 and forks 50. Bike rode about the same just a little better but was never living up to it potential. I was still enjoy riding and racing my old four stroke all the time.

After a ride one day came home pissed to have a brand new bike I didn't like riding. Took suspension off and sent it into factory connections... Let them have there way revavled and put a 61 in the rear and 4.7 in the forks. I questioned it. After riding I truly enjoy it. Best money I have every spent on a bike... I would call them and see what FC is putting in them! Got to keep a clear mind and realize no local tuner or smaller company can spend the money and hours trying different combos on your model bike... First time I have tried fc i have always used many local guys and they have done great. But all that testing of combos they try are epic! Good luck!

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I measured the static sag last night with the 5.7 spring on there, it came to 32mm. The rider sag was 97mm! Yikes, for me to get 105, I think the static sag will be way off. I have to make some more time today to go through it when I get back from work.

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All MX, all the time :)

Ohh and don't forget to set sag, 105mm rider, 35mm static. Try to get close to those numbers. If you CAN, then the spring is spot on.

 

Just got done taking some measurements. With the 5.7 rear spring installed the measurements are as follows:

 

Rider weight without gear (170 pounds)

 

Ride sag = 105mm

Static Sag = 37mm

 

Last weekend when I rode it for the first time, I was way off, ride sag was 97mm. Now I am contemplating whether I should ride the bike one more time this weekend with these new measurements (Sag set to 105mm) or just go back to the 5.4 spring tomorrow. Thoughts?

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Those numbers look good. Can you weigh yourself with gear? You may weigh 185 - with gear... that spring sounds WAY too stiff to get those numbers. 

 

Also, can you measure how much preload is on the spring. 

 

Also, measure sag HOT, not cold in your garage. 

Edited by tye1138

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Those numbers look good. Can you weigh yourself with gear? You may weigh 185 - with gear... that spring sounds WAY too stiff to get those numbers. 

 

Also, can you measure how much preload is on the spring. 

 

Also, measure sag HOT, not cold in your garage. 

 

I will try to weigh myself with gear. And I did take the measurements cold.

 

I had my brother take the measurement twice to be sure. I'd also like to note the spring is a race-tech spring. Will I really get drastically different numbers HOT? 

 

I'll take the measurement HOT again at the track this weekend. But according to MXA, faster riders can get away with the 5.7, that's a vague statement as well but am I one of those riders? Maybe, barely? Who knows? My initial thoughts before my actual test are telling me that the 5.7 is do-able but will be a bit on the stiff side.

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I think maybe if you're 185lb with gear on and a fast rider, yea that may work. It does seem like a lot to me, I would say 5.6 at absolute most at that weight. I wonder how much preload you have on it.

Here is the scoop on hot vs cold. The shock has more stiction when cold, so you can unscrew the damping entirely from the shock and measure sag in a different way by getting 2 numbers per sag measurement. So an A and B unloaded measurement and an A and B loaded measurement. Then find the average of the A and B numbers to give you an accurate sag number. So perhaps A is 20 and B is 30 then the average is 25.

The other solution is to get the shock nice and hot (through riding) and you'll find the sag numbers to be MUCH more accurate because the shock has a lot less stiction when the oil is hot and flowing better. But you still need to unscrew the damping to get the best measurement.

I'd also like to know your preload number, that would kinda put the pieces together. I'm betting its like 2 or 3mm at most.

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I think maybe if you're 185lb with gear on and a fast rider, yea that may work. It does seem like a lot to me, I would say 5.6 at absolute most at that weight. I wonder how much preload you have on it.

Here is the scoop on hot vs cold. The shock has more stiction when cold, so you can unscrew the damping entirely from the shock and measure sag in a different way by getting 2 numbers per sag measurement. So an A and B unloaded measurement and an A and B loaded measurement. Then find the average of the A and B numbers to give you an accurate sag number. So perhaps A is 20 and B is 30 then the average is 25.

The other solution is to get the shock nice and hot (through riding) and you'll find the sag numbers to be MUCH more accurate because the shock has a lot less stiction when the oil is hot and flowing better. But you still need to unscrew the damping to get the best measurement.

I'd also like to know your preload number, that would kinda put the pieces together. I'm betting its like 2 or 3mm at most.

 

Tye, when you say unscrew damping, do you mean back off on the compression? And just on the shock? I've never heard of that technique before, I guess only a few tuners recommend that. 

 

About the COLD method, I did measure it more than once (although i didnt back off the damping) and the numbers remained the same, give or take 1MM if so much?  I'll try the hot method at the track though.

 

Regarding the preload - For me to get that measurement I would have to remove the shock, however with the preload ring backed nearly all the way out, static sag was 41mm and rider sag was 121mm, after turning it in a couple times (maybe 4 or 5 turns), I managed to get the rider sag to 105mm and the static to 37mm. Based on that i'm with ya, my preload may only be 4-5mm.

Edited by adamdf

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Tye, when you say unscrew damping, do you mean back off on the compression? And just on the shock? I've never heard of that technique before, I guess only a few tuners recommend that.

Yea, because the shock has a lot of stiction and the difference between 35mm and 45mm is a lot in terms of results, but in terms of how much more the shock has to move to get those numbers, its not that much. So if I'm forced to work on my bike in the garage and not at the track, I back off the damping (compression/rebound) which will help the shock loose some of the stiction.

Also when you measure static sag, you need to push on the rear end and get it to compress then let it come back up again on its own. Some people just lightly push on it or others not at all. Its important to try and cycle the rear end in order to get an accurate static sag reading both with static and rider numbers. I take two readings when I do sag... one is me sitting on the seat center of the bike. I will bounce on the seat a few times. Then I also do a standing sag reading, I find those to numbers to be different and I take the average of them, which will be my accurate sag number.

Regarding the preload - For me to get that measurement I would have to remove the shock, however with the preload ring backed nearly all the way out, static sag was 41mm and rider sag was 121mm, after turning it in a couple times (maybe 4 or 5 turns), I managed to get the rider sag to 105mm and the static to 37mm. Based on that i'm with ya, my preload may only be 4-5mm.

You need a Sag tape measure to measure the spring preload. Its kinda tricky on the bike, but a piece of cake with the right tool. If you even have a ruler, that would work, all ya gotta do is find a fixed point on the bike somewhere and measure how much preload it takes to compress the spring and get those numbers.

So far the numbers all sound great, even if you think 4 or 5mm of preload, thats not too bad either. (scratching head) LOL :)

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Yea, because the shock has a lot of stiction and the difference between 35mm and 45mm is a lot in terms of results, but in terms of how much more the shock has to move to get those numbers, its not that much. So if I'm forced to work on my bike in the garage and not at the track, I back off the damping (compression/rebound) which will help the shock loose some of the stiction.

Also when you measure static sag, you need to push on the rear end and get it to compress then let it come back up again on its own. Some people just lightly push on it or others not at all. Its important to try and cycle the rear end in order to get an accurate static sag reading both with static and rider numbers. I take two readings when I do sag... one is me sitting on the seat center of the bike. I will bounce on the seat a few times. Then I also do a standing sag reading, I find those to numbers to be different and I take the average of them, which will be my accurate sag number.

You need a Sag tape measure to measure the spring preload. Its kinda tricky on the bike, but a piece of cake with the right tool. If you even have a ruler, that would work, all ya gotta do is find a fixed point on the bike somewhere and measure how much preload it takes to compress the spring and get those numbers.

So far the numbers all sound great, even if you think 4 or 5mm of preload, thats not too bad either. (scratching head) LOL :)

 

Ye I did the measurements both sitting and standing, they both returned the same result (or so I was told by my assistant). Also, for static sag I pushed down on the seat a few times and bounces it before I took the measurements, so we are pretty good there.

 

Your note regarding the preload measurement and how to do that, kinda has me confused though, lol. Can you elaborate a bit on that? 

Edited by adamdf

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