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different sag question.

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I been trying to dial my suspension on my 05 kx250f I do harescrambles. I ride the A class. the bike has been revalved and sprung for my weight. question is when I go into corners the rear wants to slide out. my sag is at 100mm I need to go to about 105. How far can I go with out going to far to help the rear? I know I may soften the compression some to. my forks are also set at 5mm. also I've concentrated on rider position and I don't think its that.

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hey, yeah you have plenty of travel to work with, try going out to 103mm race sag on the shock about one turn of the adj ring and leave ur fork height standard yet u should have no problem running 105mm sag also

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I been trying to dial my suspension on my 05 kx250f I do harescrambles. I ride the A class. the bike has been revalved and sprung for my weight. question is when I go into corners the rear wants to slide out. my sag is at 100mm I need to go to about 105. How far can I go with out going to far to help the rear? I know I may soften the compression some to. my forks are also set at 5mm. also I've concentrated on rider position and I don't think its that.

You are assuming tht you have the correct springs but many times the tuner is just guessing unless he had you there when checking the same numbers.

Your shock spring preload should be less than 10mm on linkage suspension but not less than 5mm. You don't want to over preload a weak spring as you will just get a harsh ride that still will allow hard bottoming. I usually shoot for about 5mm preload on fork springs. If you have the right spring.

You can figure your correct sag numbers by using percentages. That way you can get the correct springs for you and your bike. Base these percentages on the available travel front and rear with a variance of + - 3 mm.

Front suspension static sag should be 14% ( available travel in mm X .14 = static sag in mm)

Front suspension rider sag should be 25% (X .25 = Rider sag)

Rear suspension static sag should be 11% of available travel (X .11 = static sag)

Rear suspension rider sag should be 34% of available travel (X .34 = rider sag)

Using these principles you can figure the correct sags for any bike and thus the correct springs without guessing and compromising.

With the correct sag rates the bike is not nearly as tall feeling. Much easier to throw a leg across. Turns perfectly and is very stable on straights. I am very happy with the results. Use the formula and you can get the perfect spring rates for you and your bike. Don't ride the bike till you are satisfied you have the correct spring rates as most shops will exchange unused springs for different rates. If you ride with them they will look used and can't be sold as new. I think you will be very happy with the results if you don't compromise.

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Nice formula. Is there somewere on here I can look up the exact amount of travel the bike has?

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Nice formula. Is there somewere on here I can look up the exact amount of travel the bike has?

Look up the spec sheet for your bike. It usually will give the travel .

On your bike it is:

Wheel travel rear 12.2" or (X 25.4) 310mm

Wheel travel front 11.8" or 300mm

So you want about 34mm static and 105mm rider sag on rear.

Front you want 42mm static and 75mm rider sag.

(Static sag has a variance of 2-3mm)

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Awesome thanks. On the front what 2 spots you measure from? Axle nut to bottom of top tube?

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You are assuming tht you have the correct springs but many times the tuner is just guessing unless he had you there when checking the same numbers.

Your shock spring preload should be less than 10mm on linkage suspension but not less than 5mm. You don't want to over preload a weak spring as you will just get a harsh ride that still will allow hard bottoming. I usually shoot for about 5mm preload on fork springs. If you have the right spring.

You can figure your correct sag numbers by using percentages. That way you can get the correct springs for you and your bike. Base these percentages on the available travel front and rear with a variance of + - 3 mm.

Front suspension static sag should be 14% ( available travel in mm X .14 = static sag in mm)

Front suspension rider sag should be 25% (X .25 = Rider sag)

Rear suspension static sag should be 11% of available travel (X .11 = static sag)

Rear suspension rider sag should be 34% of available travel (X .34 = rider sag)

Using these principles you can figure the correct sags for any bike and thus the correct springs without guessing and compromising.

With the correct sag rates the bike is not nearly as tall feeling. Much easier to throw a leg across. Turns perfectly and is very stable on straights. I am very happy with the results. Use the formula and you can get the perfect spring rates for you and your bike. Don't ride the bike till you are satisfied you have the correct spring rates as most shops will exchange unused springs for different rates. If you ride with them they will look used and can't be sold as new. I think you will be very happy with the results if you don't compromise.

Dwight do you know the theory/derivation of this formula? I see it posted a lot but would love to know the theory behind it. Not really wondering who developed it but how it was developed ,verified and proven.

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Time tested. I got the basic info from several respected tuners over the years and these are the ones that most tend to use. I have tested them myself and am amazed on how well the bikes work when setup to this formula. Others also have tried the formula and have been pleasantly surprised on how the bike handles. Damping is a personal thing and is typically set much stiffer for a MX / SX rider vs a Offroad racer. Springs are mostly the same.

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i have settled on 55mm for the perfect sag number on forks for mx for the majority of riders, but no formula can be used as cast in stone, its a start point.

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i have settled on 55mm for the perfect sag number on forks for mx for the majority of riders, but no formula can be used as cast in stone, its a start point.

Are you talking static or rider sag. I would think 55mm way too much static and way too little rider sag. The bike won't turn. I understand that MXers like to use berms but bike should be able to turn inside if need be. I have found that my formula will work for every bike. Some may need to tweak it slightly but not that much. I have ridden bikes with only 60mm of rider sag. It rode like a chopper. The front end pushed badly in corners. Pretty well sucked. Damping is the main difference in MX and Offroad suspension, not springs.

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sorry but i disagree with everything you just wrote...my personal bike has 45mm of rider fork sag and turns nearly as well as a ktm 85 big wheel i rode the other day....your ideas are not current and dont apply to mx on modern mx tracks.

We dissagree totally on this and wont agree , but i ride the tracks and conditions most mxers ride week in and week out, you ride off road and need a different setup for your riding style, your settings work for you, for 95% of the rest of the world they dont work or we would all be fitting 0.42 springs to 450s, i have measured a few bikes that handle really well and the rider sag was 55mm, at 75mm they would stinkbug and oversteer terrible.

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sorry but i disagree with everything you just wrote...my personal bike has 45mm of rider fork sag and turns nearly as well as a ktm 85 big wheel i rode the other day....your ideas are not current and dont apply to mx on modern mx tracks.

We dissagree totally on this and wont agree , but i ride the tracks and conditions most mxers ride week in and week out, you ride off road and need a different setup for your riding style, your settings work for you, for 95% of the rest of the world they dont work or we would all be fitting 0.42 springs to 450s, i have measured a few bikes that handle really well and the rider sag was 55mm, at 75mm they would stinkbug and oversteer terrible.

LOL, Not if they have the rear set correctly. You keep missing the point that both ends must work together. Glad you think a bike setup like a chopper will turn well for you. 95% of riders will not. Glad you know more about suspension setup than I do.

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Ok I was able to get my bike checked. The front was almost dead on with your numbers. The rear was barely out on the soft side by 3mm. Now I checked my compression and it was set at 10 clicks and I never bottom. And usually run my tires maybe 3 races at most. There michelin s12's. They hook great in softer dirt and mud but could that be a cause in hard flat turns and rock cause there not for that terrain?

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Ok I was able to get my bike checked. The front was almost dead on with your numbers. The rear was barely out on the soft side by 3mm. Now I checked my compression and it was set at 10 clicks and I never bottom. And usually run my tires maybe 3 races at most. There michelin s12's. They hook great in softer dirt and mud but could that be a cause in hard flat turns and rock cause there not for that terrain?

Was the 3mm from the "Perfect percentage" ? If so that will probably be OK. OR you might try a bit more preload to see if it will balance. If you are having a bit of a pushing problem then you need to pick up the rear a bit more to the stiff side. Be sure you have no more than 10mm preload on the rear spring. If you do you need a stiffer spring. :thumbsup:

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Yes it was. And the front works pretty good. I'll raise it a hair and see what the difference is. Also do you think my tire selection can be making enough difference to cause this?

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so dwight i dont know how to set the rear sag, i despair.....i dont think the bike turns well it does turn well....been riding since i was 11 and i am 38 now dwight, did the qualifiers for the british mx championships a few times, raced at expert level mx for over 20 years, countless trophies, setup and revalved hundreds of suspension from 50s to 450s, to 600cc road bikes, also tuned lots of engines, including a 37hp rm 125 that had the same power as jamie dobbs factory ktm which won the world championship in 2001...

but i dont know how to set the rear sag and what fork springs i should run....sad.....

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so dwight i dont know how to set the rear sag, i despair.....i dont think the bike turns well it does turn well....been riding since i was 11 and i am 38 now dwight, did the qualifiers for the british mx championships a few times, raced at expert level mx for over 20 years, countless trophies, setup and revalved hundreds of suspension from 50s to 450s, to 600cc road bikes, also tuned lots of engines, including a 37hp rm 125 that had the same power as jamie dobbs factory ktm which won the world championship in 2001...

but i dont know how to set the rear sag and what fork springs i should run....sad.....

no, no....my d@&k is bigger

Sorry to the OP, but could you guys just agree to disagree? As far as suspension goes, we all know there are many different techniques, theories, physics...etc. Some follow Dwight, some follow mog. I follow Dwight because I ride in the woods and honestly because I've heard others with this same theory as well. Not to mention that road racing was all about getting the "right" sag numbers AND then making adjustments from there as well, and honestly none the the spring calculators ever got me the "right" sag numbers.

I see both sides. Thank you both for your opinions. Please keep the arguing to a minimum in the posts.

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Play nice guys.

I just got off the phone with the guy that did my forks (04 250F forks valved for a BMW Dakar). I have my Rear sag set based on what Dwight was saying. My front is hella stiff and has 1 inch of stat sag and the same for race (aka it does not move when I get on the bike). He said this was fine. The forks have 11.5 inches of travel. Is he way off? Any pics of how to pull out preload washers.

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"HIJACK ON!!" So I dont agree with senseless arguing, but for the sake of learning I respect both Dwight and Mog for their knowledge and input and a debate is good cause we all learn from it, so lets share and learn

"HIJACK OFF"

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I just worry someone will try these very soft fork sorings and get seriously hurt , but at least they will have a good cornering bike :-(

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