YZ250F Where can I get the right shock spring for my weight

[dirtboy88]

where do I find the spring for my weight. 2019 yz250f. 140lbs. Static sag was like 50mm race sage 104mm. 

[Kaw751]

Go to the race tech site, they have a spring rate chart

[dirtboy88]

1 hour ago, Kaw751 said:

Go to the race tech site, they have a spring rate chart

Ok so I found it says mines 5.5kg an i need 5.2kg is this gonna make a big difference or? If so like how so? 

[mlatour]

A spring of the correct rate will get you about 25-35mm of static sag at the same 104mm of race sag.

a 5.5kg/mm is listed as stock, the RT calculator suggest a 5.2kg/mm for a 140lbs rider.

 

Keep in mind the forks should ideally also get softer springs to balance the chassis.

Again from the Race Tech page, .47kg/mm (stock)  .43kg/mm recommended 

Edited August 1, 2020 by mlatour

[lucgallant]

What I can tell you is not to buy the Race Tech springs, because they are too short and without using spacers you will not have the adjustability you want. 

Buy a spring that is 275mm rear and 497mm front. Stadium Suspension sells them in Canada.

[dirtboy88]

46 minutes ago, mlatour said:

A spring of the correct rate will get you about 25-35mm of static sag at the same 104mm of race sag.

a 5.5kg/mm is listed as stock, the RT calculator suggest a 5.2kg/mm for a 140lbs rider.

 

Keep in mind the forks should ideally also get softer springs to balance the chassis.

Again from the Race Tech page, .47kg/mm (stock)  .43kg/mm recommended 

Why don't I just gain 3 lbs. Guess that makes total sense. Didnt think about it but yeah im gonna have to do all of it. I dont think its bad enough riding wise for me to do it but I don't know what it should be like since my sag is 104 an static over 40. I read 102 sag was best. Its definitely not bad riding it. Wish it was set up right though cause I wanna know how it'd perform then. Think ill try to gain 3 to 5 pounds then it would be right I think

[mlatour]

'by the book' spring rates and sag values are suggested 'known to be in the ballpark for most' settings.

Ideally is to experiment what works best for you no matter what the numbers say.

In your case, it's actually the opposite of many riders which are heavier than the manufacturer's target weight (160-180lbs)

thus require stiffer springs otherwise their suspension rides too low in the stroke and is mushy and harsh at the same time.

Having slightly stiffer springs than 'ideal' and running less preload is much more preferable than the opposite.

 

Before buying springs or gaining weight (not a bad thing if you do it thru exercise / muscle gain, not by eating more burgers!)

try running 100mm of race sag, that will probably get you closer to 45mm of free sag.

If you find the front end too nervous/lack of stability, instead of increasing the sag, lower the fork tubes flush with the top clamp.

Reducing spring preload on the forks isn't easy, you'd have to have the spring perches machined down a few mm's.

 

Edited August 1, 2020 by mlatour

[dirtboy88]

4 hours ago, mlatour said:

'by the book' spring rates and sag values are suggested 'known to be in the ballpark for most' settings.

Ideally is to experiment what works best for you no matter what the numbers say.

In your case, it's actually the opposite of many riders which are heavier than the manufacturer's target weight (160-180lbs)

thus require stiffer springs otherwise their suspension rides too low in the stroke and is mushy and harsh at the same time.

Having slightly stiffer springs than 'ideal' and running less preload is much more preferable than the opposite.

 

Before buying springs or gaining weight (not a bad thing if you do it thru exercise / muscle gain, not by eating more burgers!)

try running 100mm of race sag, that will probably get you closer to 45mm of free sag.

If you find the front end too nervous/lack of stability, instead of increasing the sag, lower the fork tubes flush with the top clamp.

Reducing spring preload on the forks isn't easy, you'd have to have the spring perches machined down a few mm's.

 

So I've gone a turn or so in both directions. On the spring. I wind up around 104 sag an 50 static sag. Whats happening is the rear end is swapping around an i have no traction. At 104 it seems to be better. Definitely not bad at all BUT my whole thought process here is to make it on point an right so I have a bike that is set up for my weight, experience, track i mainly ride so I can get the best performance out of it. Sou do like its going to be something ill have to have done. Like pay the pros to do it. I cant redo the inside of the forks. Shock spring, raise or lower fork tubes i can. But yeah the easier option to do is gain weight. Yz250f suspension is very good as is. 

[mlatour]

 

28 minutes ago, dirtboy88 said:

the rear end is swapping around

 

I have these notes in my how-to files, have a friend watch you to figure out exactly what the bike is doing.

 

SWAPS SIDE TO SIDE

- BOTTOMS OUT = TOO SOFT
- PACKING = REBOUND TOO STIFF
- BOUNCING =  REBOUND TOO SOFT
- HIGH SPEED COMP TOO STIFF / DEFLECTING

POOR TRACTION

- LOW SPEED REBOUND TOO STIFF
- LOW SPEED COMP.  TOO STIFF
- WRONG TIRE PSI
 

Edited August 2, 2020 by mlatour

[lucgallant]

12 hours ago, mlatour said:

 

 

I have these notes in my how-to files, have a friend watch you to figure out exactly what the bike is doing.

 

SWAPS SIDE TO SIDE

- BOTTOMS OUT = TOO SOFT
- PACKING = REBOUND TOO STIFF
- BOUNCING =  REBOUND TOO SOFT
- HIGH SPEED COMP TOO STIFF / DEFLECTING

POOR TRACTION

- LOW SPEED REBOUND TOO STIFF
- LOW SPEED COMP.  TOO STIFF
- WRONG TIRE PSI
 

Using the slow motion video feature available on most cell phones can be very useful also.

 

See this after the 3 minutes mark...

 

 

[mlatour]

Those look to be extremely nice trails Luke, exactly the type terrain I would look for. (but ridden at a slower pace)

Sold my CRF250X trail bike recently to concentrate on MX only, perhaps will venture back into off-roading in a few years.

[GP]

Luc, my stuff is very much like that.  Almost all of it has some kind of ledge/step, wall, boulder, rock hill, multiple logs, or other similar obstacle.  What I can see is your not using your travel, on the uphill attack of the step you only use half, and rebound rapidly, on the downhill you use more of course but still have a few inches left.  In the beginning, on that slow negotiation of that step, your up in the travel and spinning the tire.  Stock bike setup is all wrong for that stuff. 

I've been saying for a long time video is one of the best ways to diagnose suspension. 

[lucgallant]

You're talking front or back? What timestamps? 

And it is not stock suspension though a story best saved for another day....

You're talking front or back? What timestamps? 

And it is not stock suspension though a story best saved for another day....

[GP]

19 minutes ago, lucgallant said:

You're talking front or back? What timestamps? 

And it is not stock suspension though a story best saved for another day....

You're talking front or back? What timestamps? 

And it is not stock suspension though a story best saved for another day....

Back looks a little stiff going up the step to me, but if it works for you then good.  No idea what you had done, and I haven't looked at my own current setup yet.   I think the linkage ramps up quicker on these than say on my Beta, feels like it.

[lucgallant]

Ya I've seen it stiff in that way.

I've resprung to a 5.4 kg/mm rear and 0.44kg/mm front. Valving in the works.... ... ...

I had a slightly different configuration for the rear previously but it would bottom far too easily so I like it a little bit more stiff, but I do agree that the rebound on occasion seems potentially little bit quick. I find a factor that makes it difficult to compare is varying body positioning on the bike and amount of gas that's being given, can really affect the weight distribution. The slow motion is definitely so essential because it does allow you to see some of these intricacies.

I bought a little tripod with flexible legs and I can hang the camera in any tree and on any branch.

[mlatour]

In my experiences for this type of terrain, unless you are riding at crawling speeds

if you adjust the suspension to use up all the available travel, it will ride mushy and the handling will suffer.

In my last valving experiments before I sold the bike, I've gotten the plushest ever results by using up only 3/4's of the travel front and back.

[GP]

We are working with two FXs now, different valving configurations.  One overall slightly softer than the other.  The problem is because of Covid, no racing on faster more moderate terrain courses, so testing has been limited to stuff like in Luc's video.  My buddy with the softer setup, also did get an MX practice day in and said it wasn't bad with the adjusters pretty far in.  I'm guessing my stiffer setup will be very good for general HS racing here especially on rocky courses, and is good for what I do now, but not optimal.  Once we can get some faster riding on both I will figure where we want to be for the best compromise.   Honestly though, IF all I wanted to do is cross training drills on more extreme obstacles with my obsessed neighbors, never out of 2nd gear, I'd just ride my Beta which is much better for that.  But, I'm too short to be really effective at a lot of that stuff, and enjoy a little more flow, while keeping it tough enough for a good workout, how I like to ride these days.

What can get you more initial compliance and rebound control from the rear is using the MX Tech piston band(less stiction), and adding three face shims to the rebound stack to allow, running the reb adjuster 15-20 out.  Plenty of adj range in and added comp bleed.  This I have on both FXs and we agree it works well.