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Spring rates from 4stroke to 2stroke?

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I have a 350 sxf right now and I just bought a 12' 300 xc. My 350 has SPI suspension with springs I used from a 11 yz450 I had. The fork springs are .54 custom wound from Canon and my shock spring is a 6.3. I had SPI make my 350 suspension very stiff (forks) so I know I just can't swap the suspension from one to the other with the 300 weighing 20+ lbs lighter than the 350.

So I went on race techs spring calculator to see what rates i should get and it calls for .54 forks springs and a 5.9- 6.0 shock spring. Now the shock spring calculation sounds right but .54's in the front?

What is the normal rate change for those that have went from a 450/350 to a 250 or 300 two stroke? Having the suspension dialed on this 300 will be very important, unlike a 4stroke you can get away with the suspension not being exactly the way you want it but on the two stroke its important to have the suspension a bit plusher than what id run on a 450/350 because the two stroke is so light it will deflect off everything if its too stiff. I can't find any other spring calculator so im just asking for riders opinions what they did when they swapped over to two strokes. Like how many rates did you drop? Did you run the same springs and able to get the ride free sag?Same springs 20cc's of oil taken out? Any info is appreciated, before I do any revalving I want the correct springs in there so I can get the feel of how the bike is and can relay that into a revalve on what exactly I need done.

Thanks!

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I have rarely found any spring calulator correct. I rely on setting static and rider sag to get the correct spring rates for my weight.

Using a .54kg fork spring you must weigh over 300lbs ?

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I have a 2012 350EXC-F and 300EXC and some WP aftermarket suspension - first step was to weigh front/rear wheel bias on both bikes and surprisingly the front wheel weight is pretty close on both bikes. So I transplanted the suspension from the 350F 1:1 onto the 300 and gave it a try. Bikes have same offset tripleclamps (in my setup). Overall I ended up with the same springs, +1 reb/-3 comp/same preload on the forks for the 300, -0.5bar nitrogen pressure/ -1/2 turn preload / same clickers on the shock for the 300. Keep in mind though that my suspension is pretty different from the stock components and reacts very sensitive to clicker changes.

Those are both PDS bikes vs linkage on yours, but in general I'd say it is comparable. Keep in mind though that I'm talking about the exactly same setup components on both bikes where as your shocks/forks will have a different valving. In the end on the 2012 chassis with the weight being similar and the weight bias making up for some of the differences 2 vs 4-stroke suspension loading I'd start with the same setup you like on the 4-stroke. Just my 2 cent.

BTW; I forgot. US spec linkage (SXF) 4-strokes have a shorter shock by 4mm. The SX linkage 2-strokes come with the Euro spec shock AFAIK. Measure the shock length, 4mm will make a big difference.

BTW2; just checked - the 2012 250/300XC have the US spec shorter shock with the exact same setup as the 250/350XC-F. The 250SX has the Euro spec longer shock.

Michael

Edited by Drehwurm

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I have rarely found any spring calulator correct. I rely on setting static and rider sag to get the correct spring rates for my weight.

Using a .54kg fork spring you must weigh over 300lbs ?

No not really im close to 6'4 and weigh around 250 and ride vet expert in motox I dont ride off road at all (id like to) . I run stiff front end on 4 strokes because the inertia and my weight on the front since I rode forward a lot, .52 never really worked out so last year I had canon make me some .54 fork springs and they work great on an 11 yz 450 and on my 350. Actually I tried just running springs on the 350 at first but noway the valving was way way to soft in the mid stroke like it was not even there, would just blow through. The shock I never had any complaints.

drehwurm,

Thanks for the info :bonk: I appreciate it. Im thinking even with my stiff forks springs and shock it may work out ok with how soft and plush the valving is on the 300 xc. Totally different feel even from a stock 350. Mine has that spi kit which I know for a fact will be way too stiff on the 300 or any bike for that matter. The 300 i could actually ride it fast on a moto track with stock suspension it was just on landing even downsiding them perfect it still would blow through but really was not BAD just so different from my 350. I may just try the springs I have since you broke it down and that is the way I took it?

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I doesn't take that much effort to just switch the suspension from one bike to the other and would give you a good baseline with some possible surprises included. If there is a 4-stroke that comes close to 2-stroke "dynamics" it would be the 350F ...

The stock XC valving in the forks is pretty "loose" with both a bleed shim on the rebound and compression side of the MV so keeping those 0.54 springs under control may create some problems. Now if you'd just remove (better only move down the stack on the comp side to keep the float the same) one or both of the bleed shims ....

Michael

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It isn't the springs fault if you are blowing through the stroke. Not enough damping. Springs are mostly to hold the suspension in the correct attitude so the damping can work correctly. I can't get a bike to turn unless the springs allow the bike to settle into corners correctly. I do ride mostly offroad but I bet you can't even turn unless there is a berm involved. Just for the fun of it I would be interested in knowing your static and rider sags. I would like to know how far off it is against what I think it should be per the sag method. Not saying you are wrong for you, just it for sure would be wrong for me. I know many MXers like stiffer springs , I just don't see how they turn. I watch SX on TV and I can usually pick out the rider who is going to turn inside another rider during the race because of how his suspension appears to be working.

No not really im close to 6'4 and weigh around 250 and ride vet expert in motox I dont ride off road at all (id like to) . I run stiff front end on 4 strokes because the inertia and my weight on the front since I rode forward a lot, .52 never really worked out so last year I had canon make me some .54 fork springs and they work great on an 11 yz 450 and on my 350. Actually I tried just running springs on the 350 at first but noway the valving was way way to soft in the mid stroke like it was not even there, would just blow through. The shock I never had any complaints.

drehwurm,

Thanks for the info :bonk: I appreciate it. Im thinking even with my stiff forks springs and shock it may work out ok with how soft and plush the valving is on the 300 xc. Totally different feel even from a stock 350. Mine has that spi kit which I know for a fact will be way too stiff on the 300 or any bike for that matter. The 300 i could actually ride it fast on a moto track with stock suspension it was just on landing even downsiding them perfect it still would blow through but really was not BAD just so different from my 350. I may just try the springs I have since you broke it down and that is the way I took it?

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Now isn't the reason they turn because even with very very stiff springs they will still compress enough to settle for turns? I mean with soft valving a suspension with stiff springs can still be way too soft corrrect?

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im just going to order .50 fork springs and a 5.9 rear shock spring and see how it works out. Race tech site is way off for the forks. I dont even want to waste time trying out the .54 fork springs in the 300 I just dont see it working. I like the stock feel of the 300 xc even at my size with .44 fork springs just want it to handle high speed bumps and landings but keep that initial plush feel. I was surprised that I could ride it bone stock and not really have issues other than high speed stuff. nothing seems to be open today so I will check into springs tomorrow.

Thanks

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I also have found Racetech and MX Tech to be light with their calculators. Both recommended springs 2-3 rates too soft, but I already had those springs and I couldn't get the sag right. I tried the Moto Pro calculator and it was more accurate. At least for my YZ, I can get my sag right with the springs they recommend. It's a good 3rd opinion if nothing else. ->http://www.moto-pro.com/mybike.asp

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I also have found Racetech and MX Tech to be light with their calculators. Both recommended springs 2-3 rates too soft, but I already had those springs and I couldn't get the sag right. I tried the Moto Pro calculator and it was more accurate. At least for my YZ, I can get my sag right with the springs they recommend. It's a good 3rd opinion if nothing else. ->http://www.moto-pro.com/mybike.asp

He is talking about the front forks springs not the rear. I find that they are 2 or 3 steps too stiff on front but soft on rear. The sags have to be correct if you want the bike to perform its best and handle correctly.

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He is talking about the front forks springs not the rear. I find that they are 2 or 3 steps too stiff on front but soft on rear. The sags have to be correct if you want the bike to perform its best and handle correctly.

Dwight that is pretty much how im looking at it. It calls for .54 or .56 forks springs for me and a 5.9-6.0 on the rear. Im ordering .50 for the forks and I have a 6.0 I can try out.. I checked my free sag on my 350 and its at 22mm lol Ya I know its way off but I run a softer spring in the rear so it squats and ive just gotten used to it. On the 2stroke tho I want and need it dang near perfect .

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