08 yz450f stiffer shock spring

[Jim813]

I'm pretty sure the stock shock spring for an 08 yz450f is a 5.5. I need a stiffer spring. I weight 195lb in street clothes and around 220lb in all my gear. I have a des tank and other off road add ons that make the bike a bit heavier. When I've tried to to the Race Tech spring calcutator, is says the stock rate is 5.3. My other problem is race tech and factory connection offer a 5.6 rate and a 5.8 rate, which should I chose? I know also Eibach makes odd number springs( possibly a 5.7?). I am not sure of my current sag with all my gear on but in my street clothes a have 27mm of static sag and 111mm of race sag. Can anyone help on what spring to buy?

[grayracer513]

Yamaha lists your standard spring at 5.5kg/mm.

Rule of thumb, if you set your race sag to 100mm (at your riding weight) and you have less than 25mm of free sag, it an indication that your spring rate is too low. I think I would say 5.7/5.8 would be close to right for you, but suspension isn't my strongest suit, either.

[08YZ450Derek]

I have been dealing with the same issue, I have read that as long as you have 18-25mm free sag you are ok. I have set my bike up at 100mm sag rate, and I have 19-20mm of free sag. The bike is working well so far, but I might need a stiffer spring also.

[xtreme165]

Just go to www.racetech.com and enter your weight. According to there site the stock spring is 5.3? If you enter your weight with out gear as it say's to do then the stock spring rates should be perfect for you. I think the 5.8 will be to stiff as that is for 250lb rider range according to there site. First thing is to determine weather the bike has a 5.3 or 5.5 stock shock spring. Race Tech test's all there springs so they say so maybe the Yamaha ones are under sprung from what they say they are stock?

[osheen]

Yamaha lists their springs in N/mm instead of Kg/cm. The manual doesn't mention it but on the parts fiche they are listed as N/mm. The stock 5.5 N/mm spring is really a 5.61 Kg/cm when doing the conversion.

This also applies to Yamaha fork springs.

I find variances in both race tech and mx-tech's spring calculators when it comes to what the bikes actually come with. Therefore I don't trust either one. I have a local suspension guy test my shock springs so I make sure what I want is really what I get and if nothing else at least using the same tester I know if one really is stiffer than the other.

For what it's worth, he tested a race tech and a factory connection spring and they were both pretty much exactly what they were indicated to be.

[grayracer513]

Yamaha lists their springs in N/mm instead of Kg/cm. The manual doesn't mention it but on the parts fiche they are listed as N/mm. The stock 5.5 N/mm spring is really a 5.61 Kg/cm when doing the conversion.

You're observant to have noticed that the parts book lists spring rates as N/mm. What you did not notice is that the standard 1C3-22212-50-00 rear spring is listed as having a rate of 54N/mm (whole numbers, no decimal) and that the manual lists the same spring at 5.5, which would indeed be kg/mm (not kg/cm).

But I do wonder about the veracity of the spring calculators, nevertheless.

[osheen]

Ooops...I don't know why I had "cm" on my mind instead of "mm".

It's confusing that Yamaha would choose to use N/mm in the parts fiche and Kg/mm in the manual. The manual doesn't even specify what units the springs are. Given the conversion factor it makes sense that the manual would be Kg/mm though.

I measured the stock spring to be 5.6 Kg/mm. Which being off by +/- 0.1 is within the manufacturer's tolerance I'm sure.

[grayracer513]

I measured the stock spring to be 5.6 Kg/mm. Which being off by +/- 0.1 is within the manufacturer's tolerance I'm sure.

Or the unit you used to measure it, eh? ?

[Drfletcherdc]

I'm pretty sure the stock shock spring for an 08 yz450f is a 5.5. I need a stiffer spring. I weight 195lb in street clothes and around 220lb in all my gear. I have a des tank and other off road add ons that make the bike a bit heavier. When I've tried to to the Race Tech spring calcutator, is says the stock rate is 5.3. My other problem is race tech and factory connection offer a 5.6 rate and a 5.8 rate, which should I chose? I know also Eibach makes odd number springs( possibly a 5.7?). I am not sure of my current sag with all my gear on but in my street clothes a have 27mm of static sag and 111mm of race sag. Can anyone help on what spring to buy?

I weighed around 205 and got a 5.6 spring from Factory Connection. It made a night and day difference. Metal springs are only a $100 so go with the 5.6. If you gain weight over the next couple of years then buy the 5.8.

[Jim813]

I weighed around 205 and got a 5.6 spring from Factory Connection. It made a night and day difference. Metal springs are only a $100 so go with the 5.6. If you gain weight over the next couple of years then buy the 5.8.

Are you 205 in street clothes or in gear? and can you get the correct rider sag ( 95-105mm) and stay in the correct static sag ( 25-40mm)?

Thanks