Cut Front Fork Springs?

Has anyone thought of, or tried, cutting the stock fork springs?

I'm looking to increase the rate to .50 kg/mm. Stock appears to be .47 kg/mm per Racetech.

I did a pile of math, even wrote a spreadsheet, and determined that removing 2 coils would get me to .50. The stock spring appears to have 3 coils "extra" with regards to fork/spring travel.

I've searched high and wide. NO ONE offers springs for the WR250R/X, and no one even offers a .50 in the 41mm diameter we need close to 450mm in length.

I've spoken to Rich at Sonic Springs (www.sonicsprings.com) and he could make me a custom set of springs for ~$140. I might go that route if cutting is a REALLY bad idea.

ac

Don't know what you're looking for exactly.

Generally speaking the stock springs are pretty wimpy and soft.

What exactly would cutting them do for you?

Cutting a spring to a shorter length actually stiffens it's rate because it will then be harder to compress.

It's like holding a 12-inch ruler flat on a table and hanging 9 inches of it off the edge of the table and then bending the end downward, noting how much effort was involved.
Slide the ruler back so 4 inches hang over the edge and try bending the end downward - more effort involved because there is less leverage.

A spring is a steel wire that gets bent when the fork compresses, only the steel wire is wrapped around an axis.

Well, I did it.



Springs cut:



I made some custom spacers/top hats to make up the cut length and keep the spring oriented properly:


The result has been great. The bike really works MUCH better with proper springs for my weight.

ac

Your spacers look great.

I had a local dealer/shop cut mine down 1 inch and make a 1 inch spacer to go on top of the stock spacer, it just looks like a thick washer.

I had them do this as I dont have a torch to heat and bend the top coil flat after cuting it off.

I decided to go this route after talking to race tech on the phone, they told me to buy .48s (the stiffest they offer) and shorten them 20 mm for my weight, I instantly thought why not just shorten the stock .47s lol.

I decided to go this route after talking to race tech on the phone, they told me to buy .48s (the stiffest they offer) and shorten them 20 mm for my weight, I instantly thought why not just shorten the stock .47s lol.[/quote]
------------------

-by way of curiousity, what rider weight did you tell them (or what spring rate did they indicate you'd get) when they recommended 20mm?
-the notes on the R.T. website say they can shorten springs to be .55kg max.

i took out 30mm from the stock spring (two turns exactly, closed and ground the coil),and added 30mm spacer cut from a heavy-wall PVC coupling. (you don't need the machined flange on a thick-wall spacer, it's located by the fork cap and fork internals anyway, )

at 30mm shorter, i'd say it's at least .55 now-(judging by sag measurements) -and a  bit more than i needed. Also, fwiw,  with heavier spring rate, if anything, the the preload should be reduced a bit as well...-i reduced the 30mm spacers by 6mm to get a bit more sag (more correct ride height.)

(the stock springs are only correct for about a 140 pound rider max!)

with the correct spring rate, the the oil level needs dropped 10mm...-the stock oil height makes the total fork rate VERY progressive (so that the  wimpy stock springs won't fully bottom out when they're badly overloaded by a heavier rider.)  
-just becouse the stock setup doesn't bottom on every bump doesn't mean the stock spring rate is close-enough for 200+ pound rider ...and, the overall fork function/handling will still be way off.

I told them im 240lbs and they recommend .51 fork springs for my weight.
You still need a spacer with their set up as you cut the .48 spring down 20mm then add about a 10mm spacer for the right amount of preload as their springs are 10mm too long. Im going off memory so thse #s could be of a few mm.

I dont know the exact spring rate I have, its probley .50-.52, if .48 springs with 20mm cut off are .51 then .47s with 25mm cut of should be about the same.

You can only cut so much off before the spring will coil bind before you bottom out.

Cutting the stock springs down 20-30mm seams safe and you would have to be about 300lbs to want them stiffer than that.

I have no desire to go stiffer as its a touch stiff on small stuff now but works great when riding it aggressively, I also have gold valves with a setup for a fast aggressive guy.

I run the oil height at 110mm, I will drop it to 120mm next oil change as its a touch stiffer than it needs to be now that I dont race my wrr anymore.

Its hard to get a good sag measurement on forks, theres too much friction in the fork seals messing it up, thats why its not brought up much and I dont worry about exact fork sag #s.

thanks, that seems about what one would expect-( BTW, i said the  flange on the spacer is unecessary, not that the spacer is unnecessary) also, fwiw,the stock spring are .46, (not .47)....you can measure fork sag  using race techs' procedure-(averaging the uppermost and lowermost points of 'stiction" to get the accurate sag numbers.)- as i mentioned, it looks like from my pip[squeak sag numbers (only anout 1 inch different between loaded and unloaded) that cutting 30mm from the stock (.47) springs put them somewhere in the .55kg range-which seems in keeping with what they told you....and still well short of coil-binding the spring.....if i had another set of stock springs handy , i'd re-do them at 25mm.....thanks for the deat's

A quick comment on the reason I decided to make my own top hat/spacer custom.

I have had bad experiences in the past with using heavy wall plastic pipe. I forget which bike I was working with, but the plastic pipe had managed to get damaged. It cracked and pieces broke off. These pieces clogged up the valving and the forks needed to be pulled apart.

Since I had the means, I decided to just make a proper solution for myself.

It is true that the internals of the fork will work to control the buckling of the spring, but I do like a top hat to help orient the end. Every time the fork buckles and touches the aluminum of the upper fork tube we get wear. This is the metal you find in the fork oil when you change it.

A 2nd quick comment. I swapped to SKF seals/wipers to help reduce "stiction" in the fork. I am not sure if it works while riding, but on the bench there is certainly less stiction than a stock set of seals/wipers.

I've actually INCREASED the amount of oil I'm running. I was still bottoming out the forks regularly with my cut springs. I don't know the height I am set at any more. My oil level is now "whatever Racetech suggested + 10ml in each leg".

Happy tuning!

ac

[quote="avc8130"]A quick comment on the reason I decided to make my own top hat/spacer custom.

I have had bad experiences in the past with using heavy wall plastic pipe.  I forget which bike I was working with, but the plastic pipe had managed to get damaged.  It cracked and pieces broke off.  These pieces clogged up the valving and the forks needed to be pulled apart.  

It is true that the internals of the fork will work to control the buckling of the spring, but I do like a top hat to help orient the end.  Every time the fork buckles and touches the aluminum of the upper fork tube we get wear.  This is the metal you find in the fork oil when you change it.
=======

not pvc pipe, i described using a heavy- walled pvc coupling- it's about 3 times the thickness of pvc pipe and as thick as your machined spacer, just without the flange-since  the stock metal washer with flange then  goes below the spacer and locates the spring- ( same as stock setup. )
-there's no change in the wear or alingment of the spring...fwiw, the silver debris in fork oil is typically from the cheif wearable parts-(the fork bushings-) -which wear from sliding while supporting the full load of the bike-  the springs conduct relatively little contact or force on the tubes ;-)

Might wanna do some more "analysis" and include some dynamics with both compression and rebound damping so that you get the "suspension" suited to your riding style and activity. For instance, you might want the soft spring for the first few inches of travel so that bumps don't hit so hard but keep the load at large travel high so you don't bottom out. In any event the damping characteristics will play a huge role in the suspension performance... probably more than the 1-3% change in the spring rate.

check it out before you cut.

If your too heavy for the stock springs and try to valve it stiff so it doesnt bottom you end up with a pretty rough riding bike as you are riding too low in the stroke without the right springs which puts you into the stiffer part of the travel.

I had stock springs with gold valves setup kinda stiff for 1 year and now have the right stiffer springs, it feels softer on small bumps with the stiffer springs as its riding higher up in the soft part of the stroke now.

As all tuners will tell you, not that im one lol, you need the right springs for your weight first before messing with the valving.