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front fork springrate for supermoto/street use

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As said in the title, I am going to use my 87 XR600 on 17inch wheels and on the streets. the stock springs are very very soft and I have a lot of dive under hard braking.. What would be a good springrate to replace them with? Im pretty heavy myself, with gear and all around 100kilo/220pounds

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The dive is a compression characteristic. Along with a better spring you should play with different viscosities of oil. Ive only seen springs up to .47 and i bet there a whole lot stiffer than thirty year old springs. Also you can raise the forks in the clamps lowering the front end. Also theres a bolt on lowering link out there fairly cheap. Lastly adjust sag in the back correctly cause it might wanna catapult you during a soft forks dive.

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I'm not certain about 1987 forks, but they may be the design that has small (100 mm or so) long springs on top of the normal much longer fork springs.  If so, remove those small springs and replace them with a solid spacer of the same or slightly longer length. 

 

Whether or not you have the small springs, putting small spacers (maybe 20mm tall) on top of the main fork springs will preload the springs, increasing the spring rate in the first part of the fork's compression.  You can experiment with different heights of spacers.

 

Your forks don't have adjustable rebound damping. So if you put in dramatically stronger springs, you'll find the handling very poor or possibly dangerous over rough roads. Your bike will act like a car with blown out shock absorbers.  A crude solution is to use heavier (thicker) viscosity oil in your forks, which increases damping in both compression and rebound.

 

If you can get 1992 or later XR600 or XR650L forks and triples, they will bolt on and have much better performance.  Your 1987s are damper rod forks, which are known for having poor low compression speed damping (the brake dive you feel) and excessively stiff and harsh damping on higher speed impacts such as rough roads.

Edited by heart_of_darkness
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The dive is a compression characteristic. adjust sag in the back correctly cause it might wanna catapult you during a soft forks dive.

its not a nice feeling when u have just overtaken a car on the highway and are now speeding when a car pulls out of a driveway on the crest of the hill (yer they do roads like that in aus) :crazy:  and then u jam on ur breaks and have no idea if ur gonna stop of hit him as all u can see it the tarmac   :thinking:

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You would be around a .47-.49 spring normally.  Makes a big difference. But as noted damper rod forks don't handle brake dive or sharp hits like potholes very well.  Springs and thicker oil, or more of it as appropriate help.  Valving help like Gold Valves help a bunch beyond that.  Ideal is sending them off to be tuned for you and your riding style.  For motard they often take out mid-range dampening completely so as you corner the bike drops down on the suspension and stays down through the turn, where a dual sport setup will try to bring the bike back up during the turn, not ideal for hard core handling.  Springs are $100 new, sending them off for spring and tuning of the valving can be done for $250+++. 

If you have interest in them anyway, street use is to me the ultimate use of USD.  My 03 CR125 forks came with .47 springs (i'm 225) and are just phenominal on the street.  They soak up potholes like they aren't there (the motocross valving works exceptionally well here) and don't dive 50% of the XR forks.  Just love them on road.  On my 85  (has a 19" front wheel now, NICE on the street)

 

I spent about $400 on the USD and CRF wheel and brake rotor and other parts needed for that swap. I sent my XR400 forks out to be sprung and tuned for me and they work every bit as well and cost $250 (that's cheap in the tuning world, stay away from the big guys in the market, this ain't rocket science  ;)

 

WP_000134_zpsf7b559f6.jpg


its not a nice feeling when u have just overtaken a car on the highway and are now speeding when a car pulls out of a driveway on the crest of the hill (yer they do roads like that in aus) :crazy:  and then u jam on ur breaks and have no idea if ur gonna stop of hit him as all u can see it the tarmac   :thinking:

 Steer steer steer. 

Edited by MindBlower
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I'm not certain about 1987 forks, but they may be the design that has small (100 mm or so) long springs on top of the normal much longer fork springs.  If so, remove those small springs and replace them with a solid spacer of the same or slightly longer length. 

 

Whether or not you have the small springs, putting small spacers (maybe 20mm tall) on top of the main fork springs will preload the springs, increasing the spring rate in the first part of the fork's compression.  You can experiment with different heights of spacers.

 

Your forks don't have adjustable rebound damping. So if you put in dramatically stronger springs, you'll find the handling very poor or possibly dangerous over rough roads. Your bike will act like a car with blown out shock absorbers.  A crude solution is to use heavier (thicker) viscosity oil in your forks, which increases damping in both compression and rebound.

 

If you can get 1992 or later XR600 or XR650L forks and triples, they will bolt on and have much better performance.  Your 1987s are damper rod forks, which are known for having poor low compression speed damping (the brake dive you feel) and excessively stiff and harsh damping on higher speed impacts such as rough roads.

Have thought about a forkswap, Only issue is there are no 650L's over here (Netherlands). Although I do have a 650L rear shock, must be from Belgium or Germany :D

 

So searching a 1992 or later forks would be the only option (don't really want to spend upsidedown money), and finding a 92 or later wheel, since those have a 17mm front axle right?

 

I'll see what I can find and what happens next. Will update after findings and progress.. (current forks are polished, would have to repeat :cry: )

 

Greetings

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I think 1992 was the transition year to more modern shim style valving on the XRs.  Possibly 1991.  You will also need triple clamps to match the new forks.  However, be aware that while the newer forks are a better design, they still will not be perfect for street riding.  They will still not have correct rebound damping if you swap in much stiffer springs.  They will still exhibit some degree of brake dive.  The better design is more tuneable, however tuning them correctly requires a suspension shop, Race Tech gold valves, or a lot of research to learn how to revalve forks yourself.

 

By the time you buy newer XR forks, new springs, and pay someone to revalve them, you're equal to the cost of a USD fork swap.  Factory stock forks from a CRF450R will come with stiff 0.47 rate springs and valving that will have very little brake dive.

 

Yes, it's much easier to just buy a 1992+ front wheel.  It's possible to convert an earlier front wheel, but doing it correctly requires a custom made spacer.

 

How did you fit a 650L shock on a twin carb bike?

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 Steer steer steer. 

haha nowhere to steer its a 1 lane bush rd either pray it stops or "steer" into oncoming traffic lol luckily i stopped about 1 foot off his rear bumper  :ride: 

i blame the under sprung/valved suspension for poor braking as u have to wait for the front to dive and the rear to raise before any braking actually happens  :banghead:  (wont have that problem this time round) already has CR500 USD's and re-sprung and re-valved before purchase  :goofy:

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I think 1992 was the transition year to more modern shim style valving on the XRs.  Possibly 1991.  You will also need triple clamps to match the new forks.  However, be aware that while the newer forks are a better design, they still will not be perfect for street riding.  They will still not have correct rebound damping if you swap in much stiffer springs.  They will still exhibit some degree of brake dive.  The better design is more tuneable, however tuning them correctly requires a suspension shop, Race Tech gold valves, or a lot of research to learn how to revalve forks yourself.

 

By the time you buy newer XR forks, new springs, and pay someone to revalve them, you're equal to the cost of a USD fork swap.  Factory stock forks from a CRF450R will come with stiff 0.47 rate springs and valving that will have very little brake dive.

 

Yes, it's much easier to just buy a 1992+ front wheel.  It's possible to convert an earlier front wheel, but doing it correctly requires a custom made spacer.

 

How did you fit a 650L shock on a twin carb bike?

 

make it a single carb bike :D

 

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