CRF150F with CR85 fork spring rate ?

On my girlfriend CRF150F 2011 I gonna change the front suspension with a CR85R 2005 little wheel forks. I know the bike is really heavier so I can't rely on the different spring rate calculator website.

What spring do you recommend for my girlfriend

Novice, trail riding (smooth track soon)

Weight 120 lbs without gears

How much heavier is the bike?

80 lbs

If you add up the weight difference plus rider weight, 80 plus 120 you end up with 200 lbs. Does it mean one has to respring the cr85 fork like you would for a 200 lbs rider? If so, the recommended spring rate would be according to RT. stock .26 recommended .38

I thought this way too, but a lot say it's gonna be too stiff

Way too stiff. The fork springs must support the bike front wheel weight and only a fraction of the riders weight (most of a rider's weight is on the rear wheel). I would start by assuming the only weight increase is the difference in the bikes' respective front wheel weight. Honda springs for the 37mm USDs range from .26-.38kg, the stock spring for the CR80s was .28 (I suspect the CR85 is the same) and the CRF150R was .34 springs. The Honda Owner's manual for the forks will list stock and optional springs along with how the springs are marked. The Racetech website use to list target rider weight for each bike, might check there for the CR85.

I would suggest starting with the stock CR85 springs and then set static and rider sag.

I have those forks on a XR200 and found .34-.36kg springs about right for trail riding. The variables are: I weigh 175, the XR200 is lighter than a CRF150, I ride rocks and tree roots and need plush.

Thank for answer, I talk with FC and they sudgest .32 kg/mm . The fork I get for 50$ was never serviced so, I gonna replace everything inside and try a OEM set of .32

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