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Discussion Starter #1
After reading BillaVista's coilover bible(sections one and two so far) I had a couple of questions about two of the rules of thumb used in the article.

1. For medium to high speed use, normally suspension frequency will be 10-20% higher in the rear than the front.

What kind of characteristics would be seen if the frequency front to rear was the same? or even up to 20% higher in the front than the rear?

2. Step-up ratios normally vary from 200-300%

I've seen people running higher SURs than 300%. What kind of tradeoffs would be seen if running 400-450% SUR? Would it mostly just be more jarring during transitions into the main spring rate? More difficult to articulate to full bump travel?

BTW Great article BillaVista, it's got me thinking a lot, I hope it also generates a lot of discussion.
 

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1. For medium to high speed use, normally suspension frequency will be 10-20% higher in the rear than the front.

What kind of characteristics would be seen if the frequency front to rear was the same? or even up to 20% higher in the front than the rear?
There are multiple considerations with this, but one of the biggest is that consideration which also often applies to passenger cars (ride frequencies around 1 Hz), which also will apply to crawlers or desert trucks running at some speed because we normally use low-ish suspension frequencies (1-1.5 Hz) due to having lots of suspension travel and traversing irregular terrain. At these lower ride frequencies the balance between the two freq. front and rear creates more noticeable effects than the balance of something like a race car that may have ride frequencies greater than 3 Hz. But, with the rear frequency a little higher than the front it helps keep the truck level and thus more in a heave mode when a bump or impulse is encountered by the front wheels and then shortly later by the rear wheels. It allows the rear to "catch up" so to speak and keeps the front and rear in phase so that excessive pitching doesn't occur. So that's the big thing it does, decreases the vehicle pitching (rocking you maybe could visualize) as it rides over some bump.

Also, the higher rear frequency is a 'buffer' that allows for an increase of load in the rear for things such as gear, tools, supplies, etc.

With equal or higher suspension frequency in the front, the pitching motion and out of phase front to rear motions will be more pronounced and the vehicle will have a tendency to pitch back and forth and not remain level after encountering some bump.

All this said, race cars and those vehicles that run higher suspension frequencies often run higher frequencies in the front than in the rear. It just all depends. Sometimes having the stiff front is better for keeping the front in some small range of motion for aerodynamic reasons. The difference in frequencies once you get into higher suspension frequencies isn't very pronounced because the amount of displacement and damping used in these cars negates the extended motions that may create pitching.

For something that sees some speed and runs frequencies less than 1.5 or so Hz, 10-20% higher rear frequency is a very good rule of thumb.


2. Step-up ratios normally vary from 200-300%

I've seen people running higher SURs than 300%. What kind of tradeoffs would be seen if running 400-450% SUR? Would it mostly just be more jarring during transitions into the main spring rate? More difficult to articulate to full bump travel?

BTW Great article BillaVista, it's got me thinking a lot, I hope it also generates a lot of discussion.
You've got some of the tradeoffs. The transition will be more jarring. You may not be able to fully stuff the shock during articulation. And the way all that happens may be just right for your rig!!

The SUR is something that is very hard to quantify until you test it. What you do with your rig, what terrain you see, how you prefer to 'feel' big hits in the cockpit, how your shocks are setup, etc. have a big effect. Heck, some people run no step-up rate and are more than happy. If it does its job for you I don't care if your SUR is 0% or 1000%.
 

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BTW Great article BillaVista, it's got me thinking a lot, I hope it also generates a lot of discussion.
No, thank YOU. Thank you for reading. Thank you for thinking. Thank you for asking. And thank you for helping generate discussion and the sharring of experiences.

I know I speak for both Benny and I when I say this is exactly what we had in mind for the article. i.e. hopefully it lays the groundwork from which we can have many an informed and educational discussion to our mutual benefit. No matter how much expereince and / or tech knowledge Benny and I may have or accumulate - it's great to hear the stories and opinions of others.

And your question sure beats the hell out of "what spring rate should I run...?"...it warms me heart, t'be sure now.
 

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No problem, glad I could help:D It seems the good discussions of old are few and far between these days.

I looked around a bit to see if there was a frequency comparison thread posted, but I haven't seen one yet(and my setups not done, so I don't have any input)

I can't wait until you get the portion done on valving. It's not well documented how people tune their shocks. Plus, I have some theories about free bleed and want to see what more experienced folks have to say about it.
 

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No, thank YOU. Thank you for reading. Thank you for thinking. Thank you for asking. And thank you for helping generate discussion and the sharring of experiences.
How about a link, to discussion threads like this, somewhere at the end of the article for easy future reference? I got overwhelmed when I first read part 1, this has given me a better understanding of frequency, after being able to read this, then go back to the article.
 

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i think my suspension frequency is about 20% more in the rear. it seems to pogo when going through big whoopdeedoos, small are pretty good. so i was going to add some weight to the rear to settle it down( spare tire), but now i am thinking i will investigate the frequency more. i had a "guy" do the math for my suspension frequency and recomend some coil rates, which i didn't get exact, but close. he said 165 front, i am at 175, then 155 rear, i am at 170.... these are just coils, not coil overs mind you. will too much rear frequency cause the pogo effect? i don't really want to go softer on the springs, so maybe a little firmer on the fronts? oh, 1 last thing, i know what my axles and tires/wheels weigh and what the front and rear weights of the jeep are, when i subtract axles and wheels for sprung weight, it is alot different of then when i use billavistas way, of taking the free length of the coil minus the static height times the spring rate.... how accurate is that method? i know you have to include 1/2 of control arms, shocks, driveshaft? am i missing something? i will just use the formula and trust it if it is accurate... thanks for all the info! this is a dream come true for newbie suspension tuners :)
 

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I'll try to speak from my limited understanding, this will be a good test for what I have learned.:D

The suspension frequency is setup to give the vehicle a tendency to react in a certain way to certain events. With the frequency setup correctly, there will be less 'bad' characteristics to be tuned out with shock valving. You don't want the shocks to have to fight the natural harmonics of the suspension while at the same time controlling events.

It seems to me that the pogo effect could have to do with shock valving. Do you have any video?

Anyone, feel free to correct me. They only way to learn is if the test gets graded.
 

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How about a link, to discussion threads like this, somewhere at the end of the article for easy future reference? I got overwhelmed when I first read part 1, this has given me a better understanding of frequency, after being able to read this, then go back to the article.
I've done this before... unless Lance is running a Content Management System (CMS) of which I'm unaware, that is almost guaranteed to generate a maintenance headache and broken links. :( As a work-around, you might suggest searching 'frequency' with the following authors: BillaVista, Bigger Valves, Beat95YJ....

Remember, the web can be almost forever.

Randii
 

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i think my suspension frequency is about 20% more in the rear. it seems to pogo when going through big whoopdeedoos, small are pretty good. so i was going to add some weight to the rear to settle it down( spare tire), but now i am thinking i will investigate the frequency more. i had a "guy" do the math for my suspension frequency and recomend some coil rates, which i didn't get exact, but close. he said 165 front, i am at 175, then 155 rear, i am at 170.... these are just coils, not coil overs mind you. will too much rear frequency cause the pogo effect? i don't really want to go softer on the springs, so maybe a little firmer on the fronts? oh, 1 last thing, i know what my axles and tires/wheels weigh and what the front and rear weights of the jeep are, when i subtract axles and wheels for sprung weight, it is alot different of then when i use billavistas way, of taking the free length of the coil minus the static height times the spring rate.... how accurate is that method? i know you have to include 1/2 of control arms, shocks, driveshaft? am i missing something? i will just use the formula and trust it if it is accurate... thanks for all the info! this is a dream come true for newbie suspension tuners :)
The first question, is how accurate are your numbers? I'll be the first to tell you it's disheartening to have all this good stuff only to realize how careful and accurate you need to be with estimates and measurements to get good results..

How sure are you of the rates of your springs?? Are they off a factory something or are they an aftermarket spec'd rate spring??

How are they mounted? I checked where you found the bit about estimating sprung weight from spring deflection and there's a little missing information there. It will be fixed soon. If your springs aren't mounted exactly vertically on the axle, you need to account for the installation ratio to guess your sprung weight.

If this is just a non-coilover setup I'm guessing it's pretty much vertical and on the axle, so that really isn't the problem. The first thing is how sure are you of the weights of your rig and how sure are you of the rate of your springs? If things are accurate the numbers should jive and not be miles apart. Where did the "guy" try to get your frequencies?
 

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With the frequency setup correctly, there will be less 'bad' characteristics to be tuned out with shock valving. You don't want the shocks to have to fight the natural harmonics of the suspension while at the same time controlling events.
That would be a very fine way of summing it up! :grinpimp:
 

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The first question, is how accurate are your numbers? I'll be the first to tell you it's disheartening to have all this good stuff only to realize how careful and accurate you need to be with estimates and measurements to get good results..

How sure are you of the rates of your springs?? Are they off a factory something or are they an aftermarket spec'd rate spring??

How are they mounted? I checked where you found the bit about estimating sprung weight from spring deflection and there's a little missing information there. It will be fixed soon. If your springs aren't mounted exactly vertically on the axle, you need to account for the installation ratio to guess your sprung weight.

If this is just a non-coilover setup I'm guessing it's pretty much vertical and on the axle, so that really isn't the problem. The first thing is how sure are you of the weights of your rig and how sure are you of the rate of your springs? If things are accurate the numbers should jive and not be miles apart. Where did the "guy" try to get your frequencies?
i am sure of the spring rates, they are currie 4 inch coils, 175 front, and the "light" rear coils,( they don't sell these anymore ) 172 to be exact, straight from Jon Currie....( i also calculated them to be within 1 or 2 of these numbers last year) the front and rear jeep weights are form a digital scale, front on , then rear on, then whole thing, usually ends up within 10 pounds ( i weigh it alot :) ) springs are vertical. maybe i am off on my axle weights, i will check numbers again and see how far off they are. i also didn't take into account 1/2 the weight of the suspension. the"guy" was the head engineer(owner) at nth degree mobility, seemed to know his stuff. i gave him my wheel base, front and rear weights, and sprung front and rear weights. maybe my sprung weight was off, if i estimated my axles light, then my sprung weight i gave him was a little heavy. i am still running a heavier spring then he recomended though. i run fox 2.0 rear shocks valved 40/80. i also was thinking some more rebound would help keep the rear from bucking. i also was thinking if the front shocks are too soft, it will glide over the bump then the rear hits it harder? this is a multi purpose rig, high speed bumps and jumps, hill climbs, slow rocks and street, right now my priority is whoops, so the comprimises will come in the other stuff.....oh, shocks are also vertical..... i will run the numbers again with the updated info, thanks !!!
 

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i will run the numbers again with the updated info, thanks !!!
Any updates?? What were your frequencies you tried to hit?

Another thing we should have brought up. Frequencies are not the answer to smooth jumps and landings. When you start hitting these very large whoops tons of things start coming into play and frequency bias may very well be the least of your worries. Getting a rally car to absorb a landing like they do is hard work. Getting them to take off correctly and fly like they do is a ton harder. I'm going to venture a guess that your largest problem now is CG, but that's just a wild ass guess. Let's keep this thread alive a lil longer.
 

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i didn't get a chance to get the numbers yet, but i think he was shooting for around 1 to 1.5 for the frquency. i did get a chance to rock the front corner of the jeep with no shocks, the rear settles down almost a second quicker then the front, this would mean a higher suspension frequency in the rear, correct? the center of gravity is estimated at the top of the bellhousing about 35 inches. front to rear is 55/45. for jumps and big whoops i would think 50/50 weight distribution is better, maybe even biased towards the rear? i will try to get some numbers next week, going out of town today. i was hoping the frequency would compensate for front to rear balance instead of weight. i really cant make the front lighter and i really don't want to add weight to the rear.....
 

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Getting a rally car to absorb a landing like they do is hard work. Getting them to take off correctly and fly like they do is a ton harder.
Great thread... elaborate if thats possible without writing a book:D

I think we are merging with other motorsports quickly, The rally guys have there shat together for sure. We've got crawling down, i think high speed is where the sport is heading. Articles like this are defiantly going to help the sport evolve.

Billa Vista's article couldn't have come at a better time for our sport. Most of us are using the right stuff... just a little better understanding of how to tune it is going to help push the sport in incredible ways.


makes me want to move west, hard to find dunes in the east. -Tim





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Haha, I think it may take a book. I don't really know everything they know and exactly how they do it. I know some of the things they concentrate on. I will be working on making my next rig fly a little and will learn a lot to go along with the theory.

I can tell you that weight distribution is extremely important as is the shock characteristics. I can also tell you they test with string pots on the suspension to collect velocity, acceleration, and displacment values to see how the car responds and reacts. That's tuning!

We are headed to more high speed. Those that take the time to understand what is going on will quickly leave the rest behind. There's a lot to learn and pick up from the pros in the rally and desert world. Be careful with the information you hear from the hobbiests though as they don't always get the ins and outs.

I see desert hobby guys buying up by-pass shocks and such and the same is happening to a lot of crawler guys. It's making a killing for the shock companies, but if you don't really know how to tune them you're wasting a ton of money. People don't need these things until they've tuned simple shocks and found for sure where they fall short for them. I see all the time guys selling bypasses after buying them cause they can't "get them tuned in" and all they do is blindly turn screws on the bypasses and never realize you still have to go inside the shock to get started just like every other shock on the planet. It's not a magic fix, nothing is. It's all in tuning and even the simplest coilover shocks at our disposal have an amazing ability to be tuned to exactly what one needs. I can't stress how important tuning is to making shocks, springs, and suspension work. Just a simple 2.0 coilover tuned right can do absolutely amazing things. Rally cars are a perfect example of this. Their equipment is fairly basic but their tuning is through the roof.

Oh well, off the soap box.
 

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Couple questions.

1)If the frequency in the front is say 1 then I would want the rear to be somewhere around 1.1 to 1.2?

2)Is this front to rear ratio more important for a shorter wheelbase rig like a samurai, Jeep, or baja bug?
 
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