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Proper fork offset

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I have a 2000 DRZ-400 S converted to SM. The front end consists of 49mm RM250 forks, and RM250 triples, with 17" excel wheels.

One thing I can't seem to 'get' is proper offset. Should I be running DRZ400SM triples? Or are the RM250 ones fine? What exactly is offset and how does it affect suspension?

Also what size are DRZ400SM forks?

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Matt,

You need to use the RM triples with the 49mm forks. Here is some info on USD forks for the DRZ that may help you......The offset on the SM's is 22.5. You will most likely not be able to tell the difference between 22.5 and 24.5, I couldn't. I am fairly certain that stock SM forks are 47mm, but you should verify that. So the 47's give you some offset options if you want to go that direction.

I've done the 49mm Showas on both my 400's, and they are awesome. Much of the info below is from another forum member that is no longer around, but his info and research lives on!

First off lets start with stock RM triple clamp offsets and the forks that came on each model.....

1999 - 2000 RM125 / 250 - 24.5 offset - 49mm USD Showa Forks

2001 - 2004 RM125 - 24.5 offset - 47mm USD Showa Forks

2001 - 2003 RM250 - 24.5 offset - 46mm USD Kayaba Forks

2004 RM250 - 22.5 offset - 47mm USD Showa Forks

2005 RM125 / 250 - 22.5 offset - 47mm USD Showa Forks

2005 RMZ450 - 22.5 offset - 47mm USD Showa Forks

(new axle and axle lugs on the RMZ450 fork may require different spacers maybe more to use a set of its forks etc. on a DRZ or other RM????)

OK Now for fork clamping area diameter measurements for the different forks :

47mm USD Showa Fork : 54.5mm upper 58.5mm lower

46mm USD Kayaba Fork : 54.5mm upper 58.5mm lower

49mm USD Showa Fork : 55.5mm upper 59.5mm lower

So basically an RM triple clamp whether 22.5 offset or 24.5 offset can be used to mount up a set of either 47mm SHW or 46mm KYB USD Forks.

As for the 49mm fork as what came on the 1999-2000 models you are stuck with a 24.5 at least as far as stock and most aftermarket clamps are concerned.

If you go for the 49's, try and buy them with whatever set of triple clamps they had........locating those triples can be a little tough. The 46 or 47mm forks will be more than adequate for the DRZ application, and they are easier to locate.

Try playing with the amount of fork sticking out the top of the triple a little, the 49mm forks are a little longer than the stockers, and if you are all the way out on the forks, you have effectively slowed down your steering by making it act like a chopper a little. The DRZ SM forks are shorter than the S and E models. So, my guess is that you need to lower the forks a little to help quicken the steering.

Also, you really need to make sure the rear suspension is sprung and the sag is set for your weight so that the bike is balanced front to rear. Did you respring the RM forks, or are they stock RM springs?

👍

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That's some fantastic information, thanks!

Does anyone know how much I have to lower the triples on my RM forks to get the proper rake?

I believe the RM springs are stock. .44 or .46 kg. I only weigh 145 pounds, and it seems about right.

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FWIW:

This is off-set. It's measured off of the steer tube center line and the fork center line. Less off-set places more weight on the forks and generally helps to make the front tire "stick" on corner entry.

Clamp%20Offset%20Disc.jpg

This is is trail (if anyone wondered). It's totally independent of the off-set but helps to give straight line stability over a rough surface.

Front%20Trail%20Description.jpg

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