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04 Yz250f Question

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the stock front springs are .43 and stock rear is 4.7, using the racetech spring chart, with my weight i should go up to .441 in the front and 5.0 in the rear. since the front is so close, is it possible to go to a heavier oil or increase the oil amount in the front to get the same effect?

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What kind of riding style did you put into the racetech charts? Motorcross I hope. I would say that you try a 7wt oil instead of the 2.5-5w oil that is in it as a cheap test. Too heavy a weight will not allow the valving to work correctly due to the oil not being able to go through the holes quick enough or as the valve was designed for the lighter weight oil to do. A lot of people like to run their suspension a little softer than recommended even some pros. The rear I would say go with the correct spring. I just changed my 05 YZ250F springs from .44kg front to 0.40kg rate and the rear I went from a 4.9 to a 4.6 rate. Made a world of difference on handling. I had to turn my rebound down about 8 clicks on the rear to get it to where it wasn't so "springy" though. BTW I weigh 135 and I used what racetech's website showed for the motorcross style of riding. The front was recommended at a 0.41 which I couldn't find (discontinued) so I went down to the 0.40.

A buddy has Jessica Patterson's old practice KX125 and at the time I know she weighed around 140-150lb and she was running a 0.38 rate spring!! Talk about soft. You may not even have to change the oil, may want to play with the compression/rebound settings on the front to get it to handle properly. Another thing to remember is that if the rear is not set up properly (i.e. the spring) it will affect how the front end is handling. Get the new spring in the rear and then see how the bike handles before messing with the front.

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I wouldn't suggest running a higher oil weight. I never change oil weights any more. Back in the days of fixed orifaced pistons this was a very important tuning tool. Now with variable oriface pistons (aka valving) it doesn't offer the same reaction that it would in a fixed system. Thicker oil effects the performance of the suspension as much as a few clicks of the compression and/or rebound adjuster.

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i factored it for motocross. sometimes on big hits the the front end bottoms out. i've been increasing the compression about 2 clicks per ride just. now i'm getting to the point where it seems like the front end is starting to push in corners. i will mess with it more on my next practice day. to see what happens. what about increasing the oil a bit?

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always worth a try but if it is bottoming out that bad and that much you may want to just go ahead and go to a stiffer spring. I believe you can call racetech, factory suspension, ect. and talk to them about what they suggest. I don't think increasing the oil will help that much though but I am not a suspension expert by no means. Maybe someone else could help you there or you may get your answer by calling on of the suspension companies.

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it doesn't bottom out that bad, just on hard landings (over jumping/hard landings). that's why i would like to see if i can fix it without spending the money.

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I would add oil. It's cheap and will make a big difference in bottoming without stiffening the first part of the travel.

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how much should i add? 10mm in depth or a certain cc to start?

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First off why do you want to change out the springs?

2nd, do not confuse what was done on an 05 model with and o4 model.

Two completely different forks. The ICS springs add to spring rate so in most cases you can go down on the main springs in the 05 models.

You change springs to match the ride hieght for your wieght, with ability and type of riding factored in.

If you are riding to low in the stroke than going to heavier oil will just make things worse.

Try MX-TECHS calculator. It is generaly a little softer than Race Techs but I find it more accurate for lighter riders.

Check your sag numbers, static sag, free sag, and race sag, front and back before you make any changes.

If the sag numbers are not correct than springs will be a must.

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First off why do you want to change out the springs?

it's not that i have a problem changing the springs, it's just i would rather keep the $100 bucks in my pocket. my only problems is with the front, it bottoms very little on on big hits (but it still bottoms out), the spring calculator from racetech increases the spring rate by .011. if i can get close to the same effect by adding a little oil to it and save the money, i will do that. the rear is a bigger difference being off by .3 i will change that.

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just bottoming

here is the trick with the springs.

I don't find the spring rates on production springs to be very accurate.

the best bet would be to test your stock springs first to see what you have. They could be significantly stiffer or softer than stock.

what is your oil hieght right now??

where are you clickers set at?

I think the minimum oil hight is 80mm.

stock I think is about 130mm

10mm makes a big difference in bottoming.

If your oil hight is maxed out at 80mm switch to some Mobile 1 synthetic ATF at about 140mm to start with.

It is about 8wt but it has less stiction than normal fork oil so it works nicley for testing things like this.

probably need to turn the clickers out to around 13 on the comp to start and 2 more out on the rebound.

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spend some serious time just measuring your current oil hieghts and work with that.

If it's 130mm go to 120mm and test. then add 10 more mm and test.

oil hieght changes will really surprise you!

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Start by adding 5 cc's of oil to your forks. Use a small syringe and go in through air bleed screw in the fork cap. You might need to add more but start slow. It's easier to add some then it is to take some out.

doc

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