best static sag and ride height mesurements for the BRP???

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best static sag and ride height mesurements for the BRP???

Post  mortaygo on Thu Sep 23, 2010 11:42 am

I have searched and can not find the best Ride height and static sag set ups for the XR. I do trail riding and fast flowing Adv type riding with a bit of camping gear on board....

Joe BRP smile
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mortaygo
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Re: best static sag and ride height mesurements for the BRP???

Post  AURORA on Fri Sep 24, 2010 6:06 am

Compression damping controls the speed at which the spring is allowed to compress for a given force applied. Adding compression damping, the slower the spring can compress. Less compression damping, the faster it can respond. Rebound damping controls the speed at which the spring can rebound following compression. Again, more rebound damping means a slower spring decompression, less rebound damping means faster decompression. Determining the optimum suspension settings for your bike is as much art as science and has to do with your physical characteristics and riding style as well as the physics of the motorcycle's design.

To start with you need the right spring for you weight and the bike is in balance with the springs (front and back) and your riding style. I’ll say this a lot and not enough! It will be covered as we go. Bring a small screwdriver with you and make adjustments at your test track Getting the bike close for a rider that is starting out on a bike; I like to find a Table top that he can almost clear. For the XR650R that limit would be a 55 foot table top for most. For someone that has never jumped, a forty footer will do. Rear shock: Increasing your compression damping (the screw on the shock reservoir), will slow down the compression stroke and decrease rear end bottoming. Turn you compression adjuster "in" (clockwise) to reduce bottoming. If you never bottom, try turning your adjuster "out" (counter clockwise) to soften the compression damping and use more travel. Slight occasional bottoming is OK, but don't allow the bike to crash down when bottoming. As you jump you add compression control to stop bottoming and rebound control to stop the bounce. If either front or rear tends to kick up, (rebound), more than the other after landing from a large jump, then more rebound damping is needed at that end. Adjusting the rebound damper screw "in" or "clockwise" causes more damping, which causes the suspension to return more slowly to its original ride height. If the front end bounces up after landing from a jump, turn the slotted screw at the top of the forks "in" 1 click at a time to slow their return. If the rear end kicks up after landings, or kicks up side to side down high-speed whoops, turn the slotted screw at the bottom of the shock "in" 1 click at a time, to slow the rear wheel return. As you work on it and come close to clearing the jump, this is the spot you will bounce the most and make it the hardest on the your confidence. Stopping the bounce here with the bike not bottoming makes clearing the jump possible! Now you have a rider that would have never jumped a 55’ table top doing it with ease! Jumping a 55 footer on the BRP is a lot of air!

Getting the front and back in time through the whoops: The front forks have to compress enough to absorb the hit but, not bottom. The rebound has to let the front tire be at the next hit without slamming out. If it doesn’t get there in time you will start stacking. The shock has to have enough compression adjustment to not bottom and enough rebound to stop the bouncing that kicks you from side to side. You all know that feeling of the bike wanting to swap end as you go through the whoops. The bike starts to feel like a pogo! It is important to make all damping decisions with the suspension hot and to immediately test the change. Fork Rebound adjustment is on to of the forks in the center of the fork. The other brass screw is the bleed off screw. (That screw is to be taken out from time to time with the bike on it’s stand to let air build up out.) The Compression adjuster is in the bottom of each fork under a rubber plug. To slow the compression stroke and decrease front end bottoming. Turn your compression adjuster "in" (clockwise) to reduce bottoming. If you never bottom, try turning the adjuster "out" to soften the compression damping and use more travel. On the rear shock the Rebound adjuster is at the bottom where the shock bolts to the linkage. It is on the side of the mounting fork. (should be on the chain side) The Compression adjuster is on the top of the Nitrogen reservoir at the top of the shock. The trick here is as the rider gets faster he will move his butt back and this will change how you adjust the suspension! Run your rebound at both ends "faster" rather than "slower". When the bike in on the verge of, but not quite, kicking up after lands, the rebound is just about right. That’s one of the reasons you should never go by what some one else uses for adjustments on there bike. People ask me all the time and I’ll give them out but, it will only help for a ride or so. All bike suspensions are different (even if they are stock) and riders ride different. The best I can ever give out is a guess…a shot in the dark. Most of the time it’s more rebound to stop the bounce and that works enough for some to think I know something. But, remember too slow a rebound setting causes "stacking" because the suspension does not have time to rebound to its original ride height before you hit the next bump.

You got to love it……

Soft settings provide a plush mushy feel which works well for cross country racers trying to go straight and conserve energy. Stiffer, clicker "in", settings hold the suspension up and out of holes and provide more lift on jump take-offs. Additionally, body English and throttle changes transfer directly into the dirt instead of getting lost in a mush suspension.

--- What is your weight? What springs do you have? If you don’t know if they are stock this could be trouble. There is a chart below for the right spring for your weight. The stock shock spring is yellow but, then again I have painted lots of stock springs red.

Setting your race sag:

Starting out with your bike on a stand so, both tires are off the ground. Measure from the axle to just behind the side cover to the rear fender. This measurement will be close to 22~24 inches. Right that measurement down. Lets say it was 24 inches Now with the bike on the ground get on the bike ready to ride. That is everything; Helmet, boots, tools, drinking water…..everything. For the fuel you use, add half of the fuel weight for the springs. So, lets say you add 2 gallons of fuel that would be 2x6.42=12.84, 12.84/2=6.42 pounds. Springs are rated for riders weight + added weight to the bike. If you are carrying tools that could make a big difference if they are strapped to the back or front. Having someone balance the bike for you stand on the pegs while someone else gets another measurement. Let’s say that measurement is 20 inches, you have a race sage of 4 inches. Race sag should be between 3.75 ~ 4 inches (80mm ~ 100mm).

As for the front sag. With the right spring for your weight this should be right on. The spring length of the spring (with spacer if you are using one) should be 502mm ~ 506mm. This will give you the proper fork pre-load. More pre-load then this will make the front end ride to high and you will have a killer time stuffing the front end into a turn. What a mess if you are coming down a steep trail and you are way up on the tank and have to go into a rut infested tight turn! Arm pump will be outrageous if you are still on the bike. Then you hit rut after rut and your wrist will think you bought a MX bike not a trail bike. You adjust the front race sag by adjusting the rear shock's sag. Ok, before you all go crazy I'll say it again so you know I meant it. You adjust the front race sag buy adjusting the rear race sag. Getting the right springs for your weight and riding style is sooooo, important. Keep the front and back springs in the same range. In other words don't get stiffer fork springs to fix one problem, you will just make another. Example: if you weigh 240 pounds and the front end is bottoming but, the back is not.....don't buy .47kg/mm fork springs and leave, the stock shock spring. This will cause you to hate the bike. At 240 pounds you are right at the dividing line so, hard rider go .47kg fork springs and 11kg shock spring then set your race sage. Most riders start by riding to far forward on the bike as you get "faster" you will start to move back and "control the bike" instead of the bike controlling you.

RACE SAG



Make sure your forks are at the standard height in the triple clamps before starting any adjustments. 3mm down from the fork cap to the top of the triple clamp. Most run it 5mm for better steering.



Increasing the preload on your rear spring will decrease the Race sag. Most run 100mm of race sag on the rear. I run 85mm~90mm this is about 3.75". This will raise the rear of your bike putting more weight on the front wheel and reduce the front-end rake and be more like an MX bike. This will always make the bike turn sharper. If you tighten the spring too far it will make the bike unstable and make the bike prone to headshake.



Less preload on the rear spring will increase the Race sag at the forks. This will cause the front end to float and be light with hard acceleration. The back end will squat, putting less weight on the front wheel and causing it to ride like a "chopper". This will reduce head shake, making the bike go straighter and be more secure at high speed. The bad side of not enough shock pre-load is the bike will become hard to turn.



To fine tune the spring preload (Race Sag), start out with 4". The bike will pull the front end up sooner. Much easier to pull a wheelie. Try tightening the rear spring adjusting nut 1/2 turn down and mentally note how much easier the front end will dive into a turn and hold the inside line. Continue this spring tightening until the bike becomes twitchy and unstable, or it feels like you're always pulling up on the handlebars to get the front up in the whoops. Measure and record your Race Sag.



Then try loosening the rear spring preload (the bid adjustment collar and locking collar on top of the rear spring) 1/2 turn at a time and mentally note how the rear end "Squats" down and traction increases as you exit each turn. When you reach the point of excessive front-end lift (wheelies) and loss of steering, or you begin to have trouble holding a tight turn, the spring is too loose and you have too much Race Sag. Measure and compare these two extremes, then reach a compromise between them that balances "stability" and "tight turning".



Tune the front-end ride height to match the rear end!



If the Race Sag compromise you determined above is close to the typical (4"~3.75") measurements listed above, your fork height adjustment in the triple clamps is probably about right.



Raising the forks in the triple clamps will lower the front end making the bike turn sharper but will reduce high-speed stability. (Similar to increasing the rear preload.)



Lowering the forks in the triple clamps will raise the front end making the bike harder to turn, but will increase high-speed stability. (Similar to lowering the rear preload.)



I DO NOT agree with how stiff of springs Lindemann Engineering recommends! Or how stiff Race Tech Recommends! It seems they use a computer program that is setup for the MX track and/or bikes. XR's Only and the others are right on the money.

FORK & SHOCK SPRING RATE GRAPH / APPLICATION & RIDER WEIGHT






If you have Ever messed with Hydraulics and I know you have. If you push slow and steady on a shock all is well but, try and make a quick push and all stops. On compression of the suspension the Fast stack (smaller shims), allow the shims against the valve to bend just at the edge. But, if the jolt is quick enough there is not enough flow and for the time of the movement you hydraulic. Three things help over come this; Remove a fast stack shim (#1) (fifth one down, don’t do this), Thinner fluid, or allowing more flow. Thinner fluid allows more flow to a point but, opening up the valve ports is the way to go. The limit is #27 (.132) bit or mill out the ports indent. This will make it a lot like a gold valve. This will put, more force on the shims and allows for a more plush movement. How the shims bend has to do with the duration of the compression and time (frequency) for one compression to the next. Short compressions with short frequency, uses the most flow to be plush. The shims do not bend much and the forks knife, fighting the hit. You get that sharp reply that everyone complains about. 8” wide rut in second…bam, quick hit. If you could get the forks to move more on this hit there wouldn’t be that kick out, knifing effect. Longer compressions over longer time (Big Whoops and Jumps) Bends the larger shims way over. You have that steady applied force to keep the shims bent as the fluid flows. Adding shims here shows that flow down on the big long hits. For light weights that stay out of the stratosphere this won’t be necessary.



Big problem with fly weights is too much spring. It shouldn’t be out of the possibility to make the stock springs work for fly weights because if you are around 140 pounds and on this bike you are crazy….oh wait, that’s you! The problem is in that the static pre-load is off.

Usually if you are to stiff on your shock’s race sage it will push your front end down as you come off the first whoop but, with to much spring you really are not pre-loading the shock spring! The rule is for the rear sag is this:

If the rear end squats under acceleration along with too much front-end lift, and/or the bike doesn't want to turn sharp or easily enough: Adjust your rear sag to 3 - 3/4 inches.

But, at 140 pounds the spring adjustment is barely compressing the spring so, it’s light at first then gets stiff. So, if you 3.75” for race sage for you weight; This will push the front down into the next whoop….that is bad. Going stiffer on your compression adjustment on the forks and a little less on the shock will help get rid of this but, adding 2mm of shim to the fork spring will make a big difference and bring the front end back more into balance. Raise your forks in the triple clamps 5mm from the fork cap to the top of the top triple clamp. (For the tight stuff to get you quicker steering back)
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AURORA
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Re: best static sag and ride height mesurements for the BRP???

Post  Chris_w_65 on Fri Aug 26, 2016 8:32 pm

Hi Aurora

Nice write up

My bike is a motard and I need a starting point - Can I go with Bornyack weight/spring rates? or do I need stiffer for motard - He lists 3 styles of riding and the spring rates always stay the same but maybe motard is different.
Then I need to do the shimming and get the oil weight right so as not to have 11" of dive when I climb on the front brake - I am heavy on the rear brake to try and compensate for the terrible dive.
BTW, we ride motard on tar go-kart tracks, about 1000m tight circuits.
I weigh 90kg so that is 0.45 front and 10.0 rear according to Bornyack.

Thanks
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Re: best static sag and ride height mesurements for the BRP???

Post  BuRP on Mon Aug 29, 2016 9:26 am

Aurora........ where ARE you bru?
Looooong time zilch from you, hope you're well still! Bump
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BuRP
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