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Old 03-24-2013, 12:53 PM   #1
neepuk OP
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A question for off road suspension gurus.

I'm interested to know the basic set up differences between two-stroke and four-stroke KTM exc bikes from the 04-05 era suspension. My current bike is an 04 250 exc, the forks and shock came off my 05 450mxc. I swapped out the suspension from my old 450 before I sold it because it had been totally revalved, sprung and set up to be smooth as silk by a very reputable suspension shop. The suspension that was on the 250 was well maintained but totally stock inside, it felt a bit harsh under me and didn't suck up the small bumps and washboard anywhere near as well as the suspension off the 450. It's been a long winter and it's almost riding season out here again and I'm finally going to be able to put some miles on the 250. I realize there's about a 15 lb weight difference between the bike my suspension came off and the bike it's on now, and in all reality I've probably made up for that weigh difference in my own weight... Are there any obvious changes I will likely be making to keep this stuff as plush as it was on the 450? Are there any big differences in two-stroke vs four stroke setups? FYI, the shock and forks that are now on my bike were completely serviced with new oil and seals before I left Santa Cruz and moved out here so they have almost no rides on them, just a little buzzing around and maybe 1/2 hour on a fire road.
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Old 03-24-2013, 03:33 PM   #2
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Damping should be fine. Spring rate may need adjustment (new springs) but only a ride or two will answer that.
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Old 03-25-2013, 05:14 AM   #3
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I'm fairly certain the forks were identical save for the changes you made. Id run them, see how they feel then make changes. I can't imagine 15# is that big of a difference where you will be surprised
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Old 03-25-2013, 05:48 AM   #4
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Valving should be close and the springs are likely 1 rate stiffer assuming they were correct for your weight on the 450.

The 05 is a much better design (fork and shock) than the 04.
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Old 03-25-2013, 10:42 AM   #5
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Thanks for the input guys. I could tell the shocks were a different design when I swapped them out because they were different externally. I was also reading some info that I "googled" and there's a brief description on the Bruce's Suspension page that talks about the differences in the shock and how they should be set up initially. It's not an incredibly detailed description so I'm not exacly just how much different/better the 05 Is vs the 04 but is sure worked great on the 450. Based on just about everything I read about this suspension shouldn't have felt at good as it does because it was technically under sprung for my weight on the 450, and still is on the 250 but not as much. I think that the forks are the same between the two bikes except the ones I swapped on have one step stiffer springs than the 250 stock springs, and they've been totally revalved...
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Old 03-25-2013, 11:04 AM   #6
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Originally Posted by neepuk View Post
Thanks for the input guys. I could tell the shocks were a different design when I swapped them out because they were different externally. I was also reading some info that I "googled" and there's a brief description on the Bruce's Suspension page that talks about the differences in the shock and how they should be set up initially. It's not an incredibly detailed description so I'm not exacly just how much different/better the 05 Is vs the 04 but is sure worked great on the 450. Based on just about everything I read about this suspension shouldn't have felt at good as it does because it was technically under sprung for my weight on the 450, and still is on the 250 but not as much. I think that the forks are the same between the two bikes except the ones I swapped on have one step stiffer springs than the 250 stock springs, and they've been totally revalved...
The 03/04 forks have 3 bushings that cause binding and a stiff feeling. In 05 they went back to a conventional 2 bushing setup that everyone else uses.

The 03/04 shocks have a top out spring that caused confusion for most people when trying to set the sag. They also have a less progressive needle.
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Old 03-25-2013, 11:28 AM   #7
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Quote:
Originally Posted by neepuk View Post
Thanks for the input guys. I could tell the shocks were a different design when I swapped them out because they were different externally. I was also reading some info that I "googled" and there's a brief description on the Bruce's Suspension page that talks about the differences in the shock and how they should be set up initially. It's not an incredibly detailed description so I'm not exacly just how much different/better the 05 Is vs the 04 but is sure worked great on the 450. Based on just about everything I read about this suspension shouldn't have felt at good as it does because it was technically under sprung for my weight on the 450, and still is on the 250 but not as much. I think that the forks are the same between the two bikes except the ones I swapped on have one step stiffer springs than the 250 stock springs, and they've been totally revalved...
While I don't have experience with the 250s vs 450s, I am a suspension guy so I just wanted to chime in. I agree that it doesn't sound like you need to do anything, given that it seems the fork dimensions are the same and the shock mounts are the same.

FWIW, if the shock mounts on the rear were different between the two bikes, then the spring and damping would have to be adjusted accordingly to get the same ride performance. Given a shock length, the distance along the swingarm and the angle of the shock determine the total suspension travel on the rear and whether the geometric rate (the wheel rate) is progressive, digressive, or linear (for the majority of the travel). If that wasn't considered when changing suspensions around, then it could lead to big problems that would likely show up at the worst time, like when hitting a huge whoop unexpectedly.

As far as being surprised about an having a good ride with an under sprung suspension setup, it's actually a matter of riding conditions, riding style, and preference. I haven't read the Bruce's Suspension site, but I'm not surprised at all. A good suspension is one that soaks up bumps with minimal accelerations on the rider, and without hitting the end stops. Hitting the end stops is the biggest thing to avoid, and as long as your machine doesn't do that, then you're set up well. If you ever start to bottom out, then more spring (and more damping) are where you have to go...at the expense of ride comfort...unless additional travel is available, but that's a whole other ball of wax...

Hope that helps...

-R
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Old 03-25-2013, 11:32 AM   #8
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Cool! Thanks for the details, good to know. Now I just need to find an available neighbor to take some sag measurements for me...
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