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Hi everyone,
As you all know, Coffee (Dean) passed away a couple of years ago. I am Dean's ex-wife's husband and happen to have spent my career in tech. Over the years, I occasionally helped Dean with various tech issues.
When he passed, I worked with his kids to gather the necessary credentials to keep this site running. Since then (and for however long they worked with Coffee), Woodschick and Dirtdame have been maintaining the site and covering the costs. Without their hard work and financial support, CafeHusky would have been lost.
Over the past couple of weeks, I’ve been working to migrate the site to a free cloud compute instance so that Woodschick and Dirtdame no longer have to fund it. At the same time, I’ve updated the site to a current version of XenForo (the discussion software it runs on). The previous version was outdated and no longer supported.
Unfortunately, the new software version doesn’t support importing the old site’s styles, so for now, you’ll see the XenForo default style. This may change over time.
Coffee didn’t document the work he did on the site, so I’ve been digging through the old setup to understand how everything was running. There may still be things I’ve missed. One known issue is that email functionality is not yet working on the new site, but I hope to resolve this over time.
Thanks for your patience and support!
Fork Oil Quantity and Weight for 74 Mag Forks
- Thread starter Gord
- Start date
Ron
Husqvarna
AA Class
Hi Gord. I believe the factory recomends 7.5 ounces of 10 to 30wt oil. I would probably start with 15wt.
Now I'm no suspension expert, but here's how I understand it.
I use use the Race Tech spring rate calculator on their website www.racetech.com to determine the proper spring rate to use.
Their calculator allows you to specify the bike, your weight and riding ablilty to determine a suggested spring rate.
I'm sure they have some sort of sliding scale, but I don't how they came up with it. Lots of testing and experience I suppose.
After selecting a spring rate, each set-up gets personal.
Some guy's like their suspension very plush, while others do a lot of jumping and need more resistance to bottoming.
With a stock conventional damping rod your only adjustments are oil viscosity, oil volume and spring preload.
The trouble with a conventional damping rod is that you can not isolate the compression function from the rebound function.
If you change to a higher oil viscosity to increase compression damping, you will also increase the rebound damping.
This is where you will have to find the best compromise for your own personal riding.
Once you have determined the oil viscosity, changes in the amount of oil will allow you to do some fine tuning.
When there is a set amount of oil in each fork leg, an air chamber is created between the oil level in the fork leg and the space above. When the fork is compressed this chamber is decreased and builds pressure.
By adding oil to decrease the chamber volume, the presuure will rise faster and give you additional resistance to bottoming, but will have little affect on slow speed damping.
The other adjustment you can make is to add preload to your springs.
Because springs compress at a fixed rate, each additional inch of compression requires addtional force.
By adding preload to your spring, you raise the amount of force required to compress the spring.
This allows you to adjust the static sag, how much the fork compresses under the bikes weight and free sag, how much the fork compresses with the rider aboard.
This also controls the way the forks feel, plush or stiff.
Generally, and depending on how much travel you have available, you would want the static sag at about 3/4" inch and free sag at about 1-1/2" inches (measured from fully extended).
If you have to add more than about an 1" inch of preload to achieve the proper sag, your spring rate is to soft for the bike and rider.
Adding additional preload does not change the spring rate and does not compensate for a spring that is to soft.
If you can not achieve the static sag or free sag with no preload at all, your springs are to stiff.
The other thing is to keep good notes and only change one thing at a time, otherwise you won't know what caused the effect.
It's an oily messy job and will take some time and experimenting, but worth it in the end.
Hope this is helpful,
Ron
Now I'm no suspension expert, but here's how I understand it.
I use use the Race Tech spring rate calculator on their website www.racetech.com to determine the proper spring rate to use.
Their calculator allows you to specify the bike, your weight and riding ablilty to determine a suggested spring rate.
I'm sure they have some sort of sliding scale, but I don't how they came up with it. Lots of testing and experience I suppose.
After selecting a spring rate, each set-up gets personal.
Some guy's like their suspension very plush, while others do a lot of jumping and need more resistance to bottoming.
With a stock conventional damping rod your only adjustments are oil viscosity, oil volume and spring preload.
The trouble with a conventional damping rod is that you can not isolate the compression function from the rebound function.
If you change to a higher oil viscosity to increase compression damping, you will also increase the rebound damping.
This is where you will have to find the best compromise for your own personal riding.
Once you have determined the oil viscosity, changes in the amount of oil will allow you to do some fine tuning.
When there is a set amount of oil in each fork leg, an air chamber is created between the oil level in the fork leg and the space above. When the fork is compressed this chamber is decreased and builds pressure.
By adding oil to decrease the chamber volume, the presuure will rise faster and give you additional resistance to bottoming, but will have little affect on slow speed damping.
The other adjustment you can make is to add preload to your springs.
Because springs compress at a fixed rate, each additional inch of compression requires addtional force.
By adding preload to your spring, you raise the amount of force required to compress the spring.
This allows you to adjust the static sag, how much the fork compresses under the bikes weight and free sag, how much the fork compresses with the rider aboard.
This also controls the way the forks feel, plush or stiff.
Generally, and depending on how much travel you have available, you would want the static sag at about 3/4" inch and free sag at about 1-1/2" inches (measured from fully extended).
If you have to add more than about an 1" inch of preload to achieve the proper sag, your spring rate is to soft for the bike and rider.
Adding additional preload does not change the spring rate and does not compensate for a spring that is to soft.
If you can not achieve the static sag or free sag with no preload at all, your springs are to stiff.
The other thing is to keep good notes and only change one thing at a time, otherwise you won't know what caused the effect.
It's an oily messy job and will take some time and experimenting, but worth it in the end.
Hope this is helpful,
Ron
halffast
Husqvarna
B Class
I did a lot of expeimenting with my MAG forks . The original springs were progressive wound , sacked out , and way too soft . Got a set of straight wound replacements from AMS Racing but they were way too long ( stuck up out of the fork tubes about 2 inches . I kept cutting them down until I achieved the preload and sag I wanted as Ron described . Went through a lot of oil but settled on the 7.5 oz of 30wt . The forks were great at soaking up jumps but harsh on small bumps and wouldn't stay down at all in the turns causing the front wheel to push . Then I got a set of fork emulators from Race Tech . They simply are dropped in on top of the damping rods before you install the springs . You do have do drill the holes out bigger in the bottom of the damping rods and drill out another set of holes too ,but this is well described in the instructions and is no big deal .I also had to cut the springs down a bit more due to the extra thickness of the emulators , to achieve the correct preload . I used 20 wt oil and filled the collapsed forks to about a 5.5 in. air gap if I remember correctly ( I'm going to change the oil soon so I'll check that and get back with the actual # ) . Be sure to stroke the forks a few times to eliminate any air pockets before taking the air gap measurement . The emulators act as a metering system to allow oil to flow more freely on small bumps but slows it on bigger hits so you aren't bottoming all the time . They also have an adjustable spring to fine tune their damping characteristics . The difference was amazing . Now I can go across stutter bumps without numbing my hands and blurring my vision . I can take bigger vintage friendly jumps without immediate bottoming unless I get real frisky . The bike also handles much better in the tunrs as it doesn't want to pop up and push as much as it did before . It is not yet perfect ( and probably never will be to me as I am a constant tinkerer ) but are far better than what I started out with . What has worked for me may not be ideal for you as so many things can affect the outcome . Your weight , riding style , the terrain , where the forks are clamped in the triples , tire selection , rear suspension setup , etc. can come into play . The emulators were one of the best mods I feel I've made to the bike . Good luck and have fun experimenting .
Ron
Husqvarna
AA Class
Hi Halffast,
I also run Race Tech emulators in my 77 250CR Husky.
What spring are you using on the emulators and how many turns of preload.
I heard somewhere you shouldn't need more than 15wt with emulators to get adequate rebound damping, although mine feels like I could use a little more rebound damping
I'm 220 lbs and my current set up is .48kg Race Tech springs, 8 ounces of 15wt with the blue springs and 1 turn of preload on the emulator.
I agree the ajustability is almost infinite and I'm a tinkerer too! So I guess I'll never be totally happy either.
Ron
I also run Race Tech emulators in my 77 250CR Husky.
What spring are you using on the emulators and how many turns of preload.
I heard somewhere you shouldn't need more than 15wt with emulators to get adequate rebound damping, although mine feels like I could use a little more rebound damping
I'm 220 lbs and my current set up is .48kg Race Tech springs, 8 ounces of 15wt with the blue springs and 1 turn of preload on the emulator.
I agree the ajustability is almost infinite and I'm a tinkerer too! So I guess I'll never be totally happy either.
Ron
Gord
Husqvarna
AA Class
Thanks guys. This information is exactly what I'm looking for. To help with weight and riding style; I'm 150 pounds and am an intermediate rider. My bike is a 73 WR250 with CR transmission, CR pipe, CR tank, taller rear shocks, Mag forks and set up for Motocross. My 73 forks never really worked well and topped out something fierce. I was told to try the 74 Mag Black legs, so that's why I asked these questions. I just finished reassembling them, from a complete disassembly, cleaning, repainting and putting in new seals. I will probably try them out as they are (stock), so I'll have a better idea how the Race Tech Fork Emulators change the set up.
Thanks again, Gord
Here's a photo of the bike from the Vintage Restoration Projects page. And I now have the correct air cleaner.
http://www.cafehusky.com/threads/1973-husqvarna-wr250.15769/page-2
And here it is when I brought it home.
http://www.cafehusky.com/threads/1973-husqvarna-wr250.15769/
Thanks again, Gord
Here's a photo of the bike from the Vintage Restoration Projects page. And I now have the correct air cleaner.
http://www.cafehusky.com/threads/1973-husqvarna-wr250.15769/page-2
And here it is when I brought it home.
http://www.cafehusky.com/threads/1973-husqvarna-wr250.15769/
Ron
Husqvarna
AA Class
Gord,
Race Tech's spring calculator recommends .42kg springs for your bike and 150 lbs rider weight.
The available rates are .40kg and .44kg. If you like your bike to ride high in the front, go with the .44kg springs.
Otherwise go with the .40kg springs, they will let the front end dive a little deeper going into the turns.
Remember, you control your forks bottoming with damping, not springs. If you decide to add emulators, you will be able to adjust your damping for both compression and rebound seperately. You can't do that with a conventional damping rod.
I never thought about painting an earlier frame white, but it looks pretty cool. Nice job!!
Ron
Race Tech's spring calculator recommends .42kg springs for your bike and 150 lbs rider weight.
The available rates are .40kg and .44kg. If you like your bike to ride high in the front, go with the .44kg springs.
Otherwise go with the .40kg springs, they will let the front end dive a little deeper going into the turns.
Remember, you control your forks bottoming with damping, not springs. If you decide to add emulators, you will be able to adjust your damping for both compression and rebound seperately. You can't do that with a conventional damping rod.
I never thought about painting an earlier frame white, but it looks pretty cool. Nice job!!
Ron
halffast
Husqvarna
B Class
Can't remember what color spring I have on my emulators but they are the ones that were already installed and I didn't go to the other set included ( which I cannot seem to find at the moment ) . 1.5 turns of preload on them . I go about 185 lbs before gearing up ( always wondered what I weigh in full gear but never took the time to check ) . I'm fairly content with the rebound using the 20 wt. but will probably play with the air column a bit more . I have air caps on the forks but only use them to release built up pressure after a ride .
Saw a MAG at a Portland , MI AHRMA race that had high pressure plastic tubing ( like used on automotive air shocks ) that ran from each fork cap to two small sub tanks mounted under the seat . When the owner came by I asked if that was legal . He turned a bit red and pushed the bike further into staging . Didn't seem to want to talk about it . The guy won the class . Still don't know if it would be AHRMA legal .
Saw a MAG at a Portland , MI AHRMA race that had high pressure plastic tubing ( like used on automotive air shocks ) that ran from each fork cap to two small sub tanks mounted under the seat . When the owner came by I asked if that was legal . He turned a bit red and pushed the bike further into staging . Didn't seem to want to talk about it . The guy won the class . Still don't know if it would be AHRMA legal .
Ron
Husqvarna
AA Class
Both sets I have came with a blue 40 psi springs and the additional set is yellow 60 psi.
I think the idea is, if you have to have more than 4-5 turns on the blue spring, it will hurt slow speed damping, because of to much preload.
With to much preload your blue 40 psi spring takes more than 60 psi to get the valve to open, even though the forks may feel good landing big jump. By going to the 60 psi spring, you can back off the preload and get some of the slow speed action back.
If you like yours at 1.5 turns, I wouldn't mess with the emulator springs.
I think the AHRMA tech guys only check for safety items and suspension travel fo the class your riding.
I think you would have to protest the guy with the pressure balance set up to get AHRMA to make a legal ruling. And even then, they tend to lean toward period correct. If others were doing it back in the day, it's legal.
I can't see where it would help much, but it probably looks trick and could have pysch-out potential. LOL
I think the idea is, if you have to have more than 4-5 turns on the blue spring, it will hurt slow speed damping, because of to much preload.
With to much preload your blue 40 psi spring takes more than 60 psi to get the valve to open, even though the forks may feel good landing big jump. By going to the 60 psi spring, you can back off the preload and get some of the slow speed action back.
If you like yours at 1.5 turns, I wouldn't mess with the emulator springs.
I think the AHRMA tech guys only check for safety items and suspension travel fo the class your riding.
I think you would have to protest the guy with the pressure balance set up to get AHRMA to make a legal ruling. And even then, they tend to lean toward period correct. If others were doing it back in the day, it's legal.
I can't see where it would help much, but it probably looks trick and could have pysch-out potential. LOL
Parh 474
Husqvarna
AA Class
I could use some emulator advice. I've got them in my AJS Stormer and am getting tank slappers though bumps that I didn't get before I installed them. This is accelerating through bumps and deccelerating through braking bumps on the same straightaway. Would too much compression damping cause this?
Ron
Husqvarna
AA Class
I would think you don't have enough compression damping.
Without adequate compression damping you may be using to much fork travel. Compression damping slows the rate the forks can compress.
When your forks compress your steering angle (rake) decreases, causing your bike to steer quicker, transfer weight forward and loose straight line stability. The back-end will feel loose (like it wants to swap ends).
Not enough compression damping could also cause over-steering when cornering (forks knifing in).
A bike with a long wheel base and lots of rake will go straight like a freight train, but will be more difficult to turn.
It could also be your springs are to soft or sacked out?
Tells us your set-up? What oil weight, what color springs do you have on the emulators and how much preload.
What is your static and rider sag?
Without adequate compression damping you may be using to much fork travel. Compression damping slows the rate the forks can compress.
When your forks compress your steering angle (rake) decreases, causing your bike to steer quicker, transfer weight forward and loose straight line stability. The back-end will feel loose (like it wants to swap ends).
Not enough compression damping could also cause over-steering when cornering (forks knifing in).
A bike with a long wheel base and lots of rake will go straight like a freight train, but will be more difficult to turn.
It could also be your springs are to soft or sacked out?
Tells us your set-up? What oil weight, what color springs do you have on the emulators and how much preload.
What is your static and rider sag?