Drz400 To Rm250 Fork Conversion


1 reply to this topic
  • john6169

Posted February 04, 2007 - 02:40 AM

#1

I have a 2001 DR-Z 400 and would like to know how hard it would be to convert the front forks to inverted forks off a 2002 or newer RM-250 ? What are some of the things I will need to look out for ?
Any help would be great, thanks.

  • KTM-Lew

Posted February 04, 2007 - 12:34 PM

#2

This has been covered here before:

Re: Triple clamp for upside down forks available?

Its been about 5 months since the last post in this thread and it is time to resurrect this post from the dead.

I will now add the research I have done to end all the RM USD Fork mystery forever I hope...... I thought about making a new post but figured its final resting place should be here in this post.

OK So here is a lot of info for those of you looking to put RM USD Forks on a DRZ.

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????)

The RMZ250 is a Kawi designed chassis so I will totally leave it out as it doesn't belong.

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.

Now for more on triple clamps....

OK so the main concern is to get a set of triple clamps with an offset that keeps the handling from being all twitchy and unstable. The answer is a special low offset triple clamp.

So you may have seen TAG Metals has a couple different special offset Matrix triple clamps on thier website as mentioned in this post elsewhere....

The 4506-M-21 which has an offset of 21.5mm and can be used on 47mm SHW or 46mm KYB forks.

The 4506-M-21F which has an offset of 21.5mm and can be used with a set of Showa Works Forks as Burned mentioned.......

"Showa Works Kit Forks" with all the goodies and Ti coatings etc. sold mainly by Pro Circuit or RG3 for like $5k with the shock. Turns out these forks are also usually a 49mm Showa USD Fork.

What this means for you and I is that a set of 49mm Showa USD Forks off a 1999-2000 RM will drop right in and work with this clamp. The dimensions are the same for the clamping area.

Using 47mm Forks.....

If you go with the 47mm forks you will be set no problems becuase you can easily obtain 22.5mm offset clamps. The TAG 4506-M-21 would be a little less offset but if you couldn't or didn't want to spend the money on the TAG clamps at least you would be close even if you had to settle with the 22.5mm

So now for the bad part and the sad part for the 49mm forks.....

When I went to purchase a set of 4506-M-21F last week I basically was told we don't have any more of those in stock and probably will never will make them again. Having just sold my only other set of clamps for my new forks which I had just had rebuilt I was kind of pissed initially with TAG.

You see I had just called a while back and the tech support guy measured some dimensions for me. So after doing some digging I found out some team snatched up the last few very recently and when I had called to get some measurements a while back they were on the last few.

Well turns out one of the guys there did a hunt for me and were able to find a last survivor. Thanks to him and the help of Brian Wilson @ TT my order is placed and they are on the way.

So what other options are out there for a 49mm fork???.....

Option 1. Turns out I read an old year 2000 back article on Dirt Bike Magazines website about "DRZ440 Race Edition" where they took a DRZ and made it into an MX bike....

They mounted a set of 49mm Showa forks off an RM to the bike in the project. They didn't like the handling however with the 24.5mm clamp so they had a shop here in CA make a special clamp with 21.5mm offset. Factory R&D (same guys that make the P38 thing for the FCR AP).

www.factoryrandd.com

OK so before I had found the TAGs would work for my fork I called up Ken @ Factory R&D (he is the owner). He did some digging and found me one of those special clamps he had leftover. So I told him I would let him know and he was gonna put them on the shelf for me. So why did I go with the TAGs you ask?... Came down to price basically. The Factory R&D clamp is pricey. But it is actually the only triple clamp out there that is lighter than the OEM clamps also.

Option 2. RG3...... RG3 has special offset clamps. They are very pricey. RG3 also sells showa works kits for $5k with clamps. (49mm forks remember).

So my guess is they have something avaliable. You wont find it on thier website but call and find out if you are looking.

Option 3. TAG..... well you can call TAG and bitch and see if they will do a run of the 4506-M-21F or dig and try to find a set for you.

Or you could buy a 4506-M-21 clamp and have a machinist bore it out 1mm diam over on all the fork clamping surfaces.

Well that about sums up my RM front end SAGA.







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