i am just in the process of fitting some WP USD forks to my yamaha xt600 and was wanting to find out how i work out what strengh springs to fit with this being heavyer than the bike they came from. any tips ?

have a read up from the following link:
http://www.horizonsunlimited.com/hub...049#post301185

question is, what WP forks do you have or got, like a 43mm or 48mm and there are difference in the length of the diving tube..
well they are all marked to identify which one it is...
have a look on the top, near the tiny air bleeding screw... there is a number stamped in...

as a sample:
WP fork "1418W711" is a 48mm from a LC4 ADV 2002 and has springs with 4.4n/mm
a "0518W714" is a 43mm from a LC4 Enduro 2002 and has springs with 4.2n/mm
a "0518W722" is a 43mm from a LC4 SM 2002 and has springs with 5.0n/mm but a shorter diving tube and less travel length.

just to give you an idea, not to mention the size of the axle clamp and mounting brackets of the different brake callipers...
the easiest and cheapest is to change springs if you got the right fork legs in the first place to start a conversion.

so my advice... have a good look on what sort of forks you came along first, before starting converting it...
it's all depending on what sort of riding style you are after for... are you in need for a suspension for travelling, racing or SM-style... all factors matters.

have a look at the WP markings first, it can tell you the type and year of manufacture... post the number here and I can have a look what you got to guide you through.

__________________
The trouble is that he was talking in philosophy, but they were listening in gibberish.

my forks are the 48 mm forks from the 03 exc. they are now fitted to a xt600e

I cant imagine you will need more than 4.4 n/mm Dave

I have 4.4-5.8 progressive springs in my WP 05-06 640 Adv forks .. and have not bottomed them out. your EXC forks probably have longer travel than my 275mm. I also have a 6-7 kgs on the front of the bike with the front fairing and all the bikes electronics there.

Do you know what the suspension travel is on the forks? If its 275mm then go for the Hyperpro progressive spring - I like them a lot for touring. If its 300mm I would try a 4.4 WP spring first and see how it feels.

As mentioned above ... have you worked out what you are going to do about a front wheel / axle clamps yet? If you go for the WP forks and triple clamps, you might as well go for a KTM front wheel as well. And if you are starting with a blank slate, then go for one of the larger axle sizes and axle clamps ... 26 or even 30mm. Bigger axle is stiffer and spreads the bearing load better.

__________________

yes that's right !

I have no manual or parts book of a EXC to check it out, but yes they have 48mm fork with the longest stroke from all the KTM's... but.. regarding this are mainly used for jumping, offroad and used by youngsters up to 75kg of weight.. they have the softest spring as well. the EXC fork fist or axle clamps use brake disks of 260mm for there clipper.

for parts check this online parts books, you can download them as pdf:
Mike's Cycle Suppy (Main Parts Fishe)

and as colebatch is mentioning... get as least a set of 4.4N/mm or better a 4.6N/mm springs fitted to your forks while doing the overhaul.
a set of springs cost about 120-Euros over here.

I did converted my forks from 43mm with 4.2N/mm to a set of ADV forks with 48mm and 4.4N/mm... still I'm changing them over to 4.6N/mm springs of the later model ADV regarding the higher cargo weight for travelling, big tank and so on... my calculation is a cargo weight of 150Kg for me and the luggage for my suspension setup. That is 4.6N/mm on the front and a 75/260 spring on the back to even the whole thing up, without making the bike hard and bumpy like a stiff donkey.

about the rear springs... well the whole suspension want to be put right front and back need to match up to get it right for your purpose... to change the front only and not doing the rear is only half of the job, just keep this in mind.

__________________
The trouble is that he was talking in philosophy, but they were listening in gibberish.

KTM has used several forks at the EXC and the spring-recommendations varies among the forks. Some examples:

For my EXC (with a 14187C06 fork):
4.2N/mm -> 65-75 kg rider
4.4N/mm -> 75-85 kg rider
4.6N/mm -> 85-95 kg rider

For 14187C29:
4.4N/mm -> 65-75 kg rider
4.6N/mm -> 75-85 kg rider
4.8N/mm -> 85-95 kg rider

Edit: But you will probably have to use more preload then normal. You can buy spacers at your friendly KTM-shop or make someone yourself.

thanks for the tips so far guys. i now have 2 more questions .i what will be best .my nisin brake with a 320mm disk or just go for the brembo that the ktm use ? and 2 what rear shocks are the strongest/longest lasting .that can be custom made it needs to be a littel longer than the OE xt shock.it has to be a good price and im not to arsed about lots of adjustment settings.i will be going for the ktm front wheel and then a 18" excel on the rear.11 welds and a few chinese spokes (4 for a $1) in my wheels now so iv had me use haha.

with your EXC fork you will be stuck with the single 260mm front brake disk, as found an all SXC as well, the axle clamp is the key there and has the thread drilled diferently to the rest of the other models to fit the calliper.
The Enduro has a 300mm disk and the ADV-2003 forks with single disk use 320mm disk and have the same mounting distance for the calliper, the SM has 320mm disk, but the ADV and the SM share the same calliper, so that they have the space for the 320mm disk.

__________________
The trouble is that he was talking in philosophy, but they were listening in gibberish.

when i was asking about the brake i was thinking more about the power.i can make a bracket to make most things work.the nissin is the easyest to make for a bigger disc.