Compression damping vs. spring rate???

[Rcannon]

If you guys dont mind, why do we need both?

Could a person have a stiff enough spring that made the compression damping unnecessary?

On the other side, if a spring is too soft, why not just increase the damping?

Truly, I do not understand. My YZ 250, 97, feels soft up front. Do I use a heavier spring or have it revalved?

I am not trying to start a business or anything like that. I am curious for my own sick mind. I do no tmind spending a few bucks to fix this, if needed! Thanks again...

 

[James]

You can try a heavier spring first and then if it isn't stiff enough go with valving. You can also try raising your oil level which will stiffen the last third of the travel.

The springs primary job is to support your weight and the weight of the motorcycle while making sure it rides at the proper height.

Too soft springs with damping to compensate would ride too low in the travel and in an extreme example, if you sit on the bike and it sinks through 3/4 of its travel, there won't be enough suspension left to soak up bumps.

If the spring was stiff enough to absorb all impacts by itself, then you would bounce around like a pogo stick. Would ride way too harsh.

 

[JTT]

The idea of damping is to control the movement of the spring. Spring rate is an entirely different animal. Picture the wheel moving along at a good speed, it hits a bump. The force compresses the spring, but without damping, the inertia of the wheels upward motion would carry beyond the top of the bump. Compression damping is there to control that excess movement. Have you ever seen a car go down the road with real bad shocks? :scream: ...the wheels are constantly bouncing off the ground...as would your bike.

The common problem here is that many people misunderstand the concept of damping. You cannot effectively compensate for too soft springs with damping. All you will get is harsh suspension. Spring rate is dependant on your weight for the most part, with some fine tuning for partcular preferances and conditions.

My suggestion would be to make sure you have the proper springs for your weight, both front and rear (don't overlook the balance aspect), then work from there on tuning the damping to suit your needs.

 

[Rcannon]

Thanks for taking the time to respond to this. I believe I am starting to understand.

Holding a new automotive shock made me think of it. Despite the shock being made for a 1 ton ford van, it was fairly easy to compress. Much easier than a set of forks.

 

[WorldWideRacer]

The 97 YZ250 was notorious for haveing a problem with the midvalve. I would suspect that yours has never been revalved/rebuilt. Dont you just love that metal-to-metal "CLANK!" when you bottom that sucker out? Mine bruised the palms of my hands before I got them rebuilt.

 

[DEANSFASTWAY]

Paul if youyre a normal sized guy @175 lbs on MXfast offroad you might try like 43 or 44 springs up front . The compresiion damper sort of only works around a certain parameter , if you runningwith the compression all the way in , a switch to firmer springs will hold the bike up and you can turn out the compression adjuster and the bike should feel more plush .

 

[Rcannon]

Worldwide, my wrists are what is bothering me. The hands have finally became tough enough to handle it!

The clank is great! It keeps the 4 wheelers from cutting in front of me. Well, at least that is what I tell myself as I am saving up the $$$ for a revalve!

 

[Jeremy Wilkey]

Soft settings at the bleed (adjuster) and allow the chassis to be unplanted by sesawing back and forth. Also the bike can be sucked into holes which casuse the rider to feel more of thr bump. JTT really sumed this one up well. As we've learned more and more it seems really that stiffer valing (To the proper Degree here don't take this to far) and softer springs actually produces the best ride.

Its generally a mistake to go up in rates if they are not needed.


BR,
Jer

 

[Papakeith]

I thought that the purpose of the springs was to simply support the sprung weight of the bike and rider. If you go with lighter springs, wont you end up riding lower in the stroke of the piston?

 

[MACE]

Yes, unless you run more preload. Preload is really a somewhat misleading term. What we call preload is really ride height adjustment. For offroad I'm thinking it is worth an experiment to run light springs without extra preload an a low oil level. Let the fork sag. A lower ride height is an advantage in many tight technical areas. Lowering the oil level will reduce the rapid air spring rise that I believe is what causes "midstroke harshness" in bikes ridden by magazine writers.

Yes you need to balance the rear ride height...

Don't forget to question authority. ;)

 

[Papakeith]

Wont letting the fork sag effectivly change your rake angle? Is that the advantage you are talking about in the tight stuff?
Honestly I never quite understood running a lighter spring then preloading it to the hilt. What's the difference between doing that, and running a heavier spring with less preload.

 

[marcusgunby]

Until recently i went down the softer springs with low preload and it hanged down in the stroke and was harsh, and it didnt seem to steer that well as small bumps knocked the front wheel off line.I have since added 4mm of preload and its alot better.I say go for a spring rate thats within one rate of what the generator says to run.On the rear of the CR i have had to goto a 4.3 as the 02 seems to have a stiffer linkage ratio-at least at the start of the travel.

 

[WoodsRider]

The comment I have (and Jer may want to jump in), after Jer re-did my 45 'zokes they worked awesome in sand whoops. Unfortunately another job transfer brought me to the land of New England rock gardens. The 'zokes did not perform well at all until I replaced the springs with the stock springs that are technically way too soft. With these springs the bike turns great in the tight stuff, but the front has a tendency to tuck in when turning in soft soils. I also know it's riding lower in the stroke as the front still deflects badly off roots.

After playing around with these forks I came to the conclusion the stiffer springs had too much pre-load (approximately 20mm). I've reduced this, with a shorter bushing, to approximately 4mm and will try it out Sunday.

 

[Eric82930]

Another thing to consider is that the spring alone does not determine the ride height. The compression and reboud damping adjustments can also affect ride height. The reason is because on a dirt bike the suspension is almost always moving, so by slowing down the movement up or down will make the average ride height higer or lower. Extreame use of the adjusters can cause adverse affects such as packing. It amazes me how all the different parts of the suspension needs to be considered to get the end result you want. This is why it requires lots of experience to be a good suspension tech.