I'm having some fork spring confusion

robl

Member
Feb 24, 2004
64
0
Hello everyone,

I plan to order some fork springs for a 97 KDX, but have a question. Jeff Fredette recommends a .38 spring for someone weighing 200 lbs or less. I weigh 155 without gear. The Race Tech spring calculator recommends .40. Does Jeff rate his springs differently than Race Tech does? Does anyone of a similar weight have any experiences they're willing to share concerning either the .38 or .40 rate FRP springs? I tend to ride fairly rocky trails and TRY to go fast. My last bike was setup by the prior owner, with the 3 rate RT springs. I THINK they're set to .4, so I was leaning toward the .4 FRP springs.
I'd like to get it right the first time since they're $70.

One last question: Is there any advantage to using the XR400 springs over the FRP springs? The XR springs are longer, right? Anybody have experience with both?

Thanks guys,

Rob
 

kmccune

2-Strokes forever
LIFETIME SPONSOR
Jul 3, 1999
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I weight 155 and use .40 spring s from FRP. I think he uses a lot of preload?
 

captbly99

Member
May 30, 2005
117
0
I know, I am in the same boat you are with the rear! I weigh 145 w/o gear, Jeff recommends the 5.0 rear and staying with the stock .35 front springs. So, I ordered the 5.0 rear, should get it tomorrow, the shock is off and getting serviced right now, so I am hoping to have it back together by Friday. Test run it over the weekend. I am alittle worried about it feeling "mushy", but am thinking it will be better balanced.
I ride a lot of single track, which the bike handles great in. My problem is higher speed, more open stuff, I don't feel comfortable hitting any water breaks, the bike(suspension) just doesn't handle a jump well at higher speeds, not motocross jump, the small fun little water break jumps.
Does that make any sense? I don't really know how to describe how it feels.
Oh well, good luck!

I have read that if you are not happy with the spring rate you get from Jeff, he will exchange them for you, probably just the cost of shipping.
 

Rhodester

Member
May 17, 2003
549
0
The stock shock spring is a 5.0kg. It works great for me at my weight of 230+lbs. 5.2kg was just flat too stiff for me. If I was 145lbs I'd be looking into a 4.6kg spring. Good luck.

Jeff did my shock. It came back with way too much high speed compression damping.....even after I sent it back a second time. I decided at that point to tear into it myself. I got some tips locally on which shims to remove to reduce high speed compression. My winter project will be to tear into it yet again to reduce it some more. When I get it where I want it I'll put my specs on the site if anyone cares. Again, good luck.
 

captbly99

Member
May 30, 2005
117
0
I'm sorry, I am must have been half asleep or something when I posted.

yes, stock rear is 5.0, Jeff recommended 4.6, that is what I ordered. DUH!
Rhodester, are you removing stock shims, or did you have RaceTech or something put in it when Jeff did your shock?
I wondered if there was some kind "free mod" like the front forks with removing 2 shims? But the rear has all different sized stock shims in the stacks? The front stock shims are all the same.
Thanks
 

StuckinJersey

Member
May 11, 2005
111
0
I'm 6 ft / 180 lbs. and I had the FRP .38 they were an improvement but still got a ton of nose dive
in the turns and down hills. Went to the .42 that Race Tech suggested and it's a lot better but
also have 30 pounds on you. I'm also riding really rocky crap so I tend to notice every time the fork
reacts poorly. FRP includes a section of PVC with the springs to make custom preload spacers, race tech only sent me the springs I think and it was much more expensive ($110 I think). Good Luck with it.
 

KTM Mike

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Mi. Trail Riders
Apr 9, 2001
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FWIW - the pre 95 KDX stock rear springs were a lighter rate (4.6??? not sure). I found it pretty easy to find a used pre 95 stock rear for sale cheap when I wanted to lighten up my son's KDX rear rate. (it seems you can find plenty of used stock rate stuff out there, not much in heavier rates)

That was just a year ago, and in that time that kid put on 20 lbs and about 5 or 6" in height - so I plan to go back to stock rate for him. (he is around 155 or so...and growing - only 12 yrs old!) That 4.6 sure seemed soft though - even with ample preload, mega static sag. (which he needed to get seat height down - or least he did a year ago!)
 

robl

Member
Feb 24, 2004
64
0
Thanks for the responses guys. That's correct about the earlier models having a lighter stock rear spring. It's a 4.7 rate. I had a Race Tech 5.2 or so on the rear instead on my 91 KDX. And like I said, I think the front 3 rate was set to .40. The available range was .40 - .46. I still need to find out for sure from the previous owner of that bike. So, I was thinking of using that combination for the 97 I just got.

The feeling I'm getting here is that the FRP recommendations seem to be a little on the soft side. If .42 seems to work well for 180 lbs, then .40 may work for me then. I would rather lean toward too stiff than too soft. I too ride pretty rough/rocky trails up here in the inland northwest, and need the fork to respond well to high speed hits. On that front, I'm also going to be removing 2 shims from the stock valve stack, but that's another story.

So, it sounds like .40kg/mm fork springs from FRP then.
(155 lb / aggresive riding / rough trails)

Any other thoughts on this?

How about the FRP VS. XR springs? I'm just curious since using the XR springs seems to be such a popular thing to do, and I'm wondering why since Jeff offers springs for sush a great price.

Thanks everyone,

Rob
 

seancza

Member
Apr 22, 2003
83
0
I put in XR springs. You can usually get them pretty reasonably priced from someone on thumper talk. Those folks are usually upgrading their springs as well.

I chose XR springs because they are longer. Simply because I'd rather have spring in my fork than spacer. I can't compare to FRP springs though.
 

Red_Chili

Member
Nov 30, 2005
79
0
I'm going with used stock XR springs because they are $30, frankly (a tad high for used, but the only ones local I can find). .39s, I weigh ~180 and ride some of the slow to moderate technical stuff with the occasional boring MX track during the frozen months... :ahhh:

I'll probably do the free shim removal trick too, mebbe with Mobil1 ATF. The rear seems tol' able.
 

John Harris

Member
Apr 15, 2002
552
0
I too like the XR springs, just because there is more spring and less spacer. I am old and slow, but the 0.38? ones I have are much, much better than the stock ones. I am sure FRP's would also be a substantial imporvement also. FRP and Race Tech give you more choices than XR does (at least in the used category). Which ever springs you use, they will be an improvement over stock! Cheers John
 

robl

Member
Feb 24, 2004
64
0
Well, the FRPs (.40) are now ordered, along with a few other nifty items. I'm excited to see how they work.

Thanks everyone for taking the time to post your opinions.

Thanks,

Rob
 

kmccune

2-Strokes forever
LIFETIME SPONSOR
Jul 3, 1999
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:cool:
 

Rhodester

Member
May 17, 2003
549
0
Captbly99, I just had Jeff do a revalve I assume using just the stock shims. Here's how the stack looked after the second time back from Jeff:
34mm low speed comp
34mm o " "
34mm x " "
34mm " "
24mm transition shim (?)
34mm o high speed comp
34mm x " "
34mm x " "
34mm " "
32mm x " "
30mm o " "
28mm " "
26mm " "
24mm " "
21mm " "
x = shims I removed with my first modification (BIG improvement)
o = additional shims I'm going to remove with my next modification.
 

robl

Member
Feb 24, 2004
64
0
That's interesting, thanks. Although that doesn't look like the stock stack though. I'll find out for sure as soon as I tear into my forks here pretty quick, but I believe the stock stack consists of 10 shims of equal size. The common free modification of the stock stack that has been discussed here is to remove 2 of them. Apparently, it works surprisingly well. I can’t wait to find out for myself.

Rob
 

StuckinJersey

Member
May 11, 2005
111
0
Robl,
The reason it looks different is because a dicussion on rear suspension got start on your thread.
You are right on the money, but try removing one shim at a time and make sure after you install
the heavier springs to set the clicker on the bottom of the fork to the softest setting before tuning the forks. Also since the older KDX forks have no rebound adjustment (stock I feel the rebound is too quick) that a 5 or 7 wgt. fork oil will slow down your rebound and help handling greatly. Most cats use 5 or 2 1/2 because it allows the piston to move easier with in the fork but the rebound is crazy fast. Good Luck and Enjoy it!
 

Rhodester

Member
May 17, 2003
549
0
As far as I know the piston is stock. When I was building the shim stack I failed to mic the shims for size. If I remember correctly the 34mm shims in the low speed stack were quite thick....thicker than the smaller shims (diameter-wise) in the high speed stack. Next time when I'm into the shock I'll take care to make note of the shim thicknesses. I'll also post a report as to the performance of the new valving.
 

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