Spring length

[W2racing]

This might be a dumb question, but does coilover spring length matter? IE 10 or 12 inch on front , 12 or 14 on rear. Or do u just use whatever length u have that is the rate u want?

[MasterSbilt_Racer]

This might be a dumb question, but does coilover spring length matter? IE 10 or 12 inch on front , 12 or 14 on rear. Or do u just use whatever length u have that is the rate u want?

It only matters if you will coil bind the spring during use . Or get close enough that the rate changes in a way you do not want. Or you cannot set ride height because you cannot get the adjuster nut high or low enough on the body.

[Dirt Man]

So basically your saying it does matter!

[Matt49]

That's not what he's saying. He's saying avoid situations where coil bind becomes part of your setup and it won't matter. As long as you aren't in a coil binding situation due to travel, spring length has no effect on performance. A 12 inch spring and a 14 inch spring of the same rate behave the same way until they bind.

[Dirt Man]

I understand what you are saying, however with current set-ups and current front end geometries the difference between a 10" spring and a 12" spring is a very relavent tuning tool.

[MasterSbilt_Racer]

I understand what you are saying, however with current set-ups and current front end geometries the difference between a 10" spring and a 12" spring is a very relavent tuning tool.

Not really. Coil bind shouldn't be used to tune.

[DirtRacer9x]

Not really. Coil bind shouldn't be used to tune.Go tell cup teams this. But the springs are also $1500 a piece. Just saying.

[MasterSbilt_Racer]

Go tell cup teams this. But the springs are also $1500 a piece. Just saying.

Cup teams are not allowed to do anything compared to us. They race street stocks. There is always a better way, rules permitting.

[hucktyson]

If you do anything more than slightly touch coil bind you will immediately shear the contact patch and push. That even happens with too many shims in your bump stop and coil bind would be much more harsh

[Dirt Man]

This is a widely used practice. If possible, take a look at some data sheets.

[MasterSbilt_Racer]

This is a widely used practice. If possible, take a look at some data sheets.

Severe surface stress on springs results. Failure and rate change follows. Monoleafs were once a widely used practice.

[7uptruckracer]

Cup Teams do not coilbind the only series that do are Bush, Trucks and K&N because they aren't allowed bumpstops. Cup teams are on 15,000# springs at short tracks and 55,000# at Plate Tracks. They have no Ride Height rule and Aero Is far more important the Mechanical so they only use them for static height and with not having a height rule its raised the rate a lot I have some pictures if your interested. Sounds crazy but its true

[hucktyson]

Coil binding reacts like a bump stop in a coil loader. The rate increases in the last little bit
Before coil bind then naturally goes to infinity. If your just barely touching coil bind it might not break the contact patch but if it's a big hammer down half mile where you drive the car straight you WILL know when it coil binds just like you will know if you have too many shims in your bump stop. If your running like 1000lb of zero point and you just ride around coil bound it might not take off like that especially if the track is perfectly smooth. I've never tried that though ...

[DirtRacer9x]

Cup Teams do not coilbind the only series that do are Bush, Trucks and K&N because they aren't allowed bumpstops. Cup teams are on 15,000# springs at short tracks and 55,000# at Plate Tracks. They have no Ride Height rule and Aero Is far more important the Mechanical so they only use them for static height and with not having a height rule its raised the rate a lot I have some pictures if your interested. Sounds crazy but its trueWe run bumps on the cup cars and Rentons coil binding in K&N cars. I've never once seen a 55,000lb spring near our shop or any shop I've been in.

[Matt49]

Given the ability to run a bump stop or a dual-stage spring setup (both of which are almost infinitely adjustable), why would you ever want to run a coil bound setup which provides no adjustment AND eventually ruins the spring and lord knows what else when you eventually pancake a wall?
Makes no sense to me but a lot things don't...

[drtrkr244]

I have had very good success using Bob Bolles' software. It requires you to measure from the top of the spring to the ground to determine the roll angle. I cant say that I have tested different length springs to determine their effectiveness but I do believe spring length is critical to dlm setups.

[grt74]

its all about dynamic tire load with in the rules giving to you,but its a ton of time and testing, just because it looks good on paper doesn't mean it will work on the track,but spring sizes do not matter to me except to give me the adjustments i may want on the coil overs(room to put rounds in or out)coil bind is something else all together and in the dirt world in my opinion should never be used, there are to many other options for us

[Matt49]

I have had very good success using Bob Bolles' software. It requires you to measure from the top of the spring to the ground to determine the roll angle. I cant say that I have tested different length springs to determine their effectiveness but I do believe spring length is critical to dlm setups.

I don't care what the software says, it is completely inaccurate that the sprung mass of a vehicle has any idea where the top of a spring is within a coil-over.

You're either misunderstanding the variable it is asking for or the software is rubbish or some combination of the two.

My guess is that this question is being asked to calculate rear roll center location but the question should be asking where the top of the shock mount (assuming coil-over) is located, not the top of the spring. Load on any coil-over is felt (input) at the ends of the shock, not the ends of the spring. This fundamental fact of physics is why spring length has ZERO effect on vehicle dynamics. That is until coil binding comes into play which no software is going to take into account because it is dependent on way too many variables regarding the spring construction all the way down to how much powder coat they put on it.
If you want proof, go buy or rent yourself a spring smasher and do the homework. Don't trust software written (supposedly) by a guy that has been writing the same 4 tech articles for the last 20 years.

[7uptruckracer]

We run bumps on the cup cars and Rentons coil binding in K&N cars. I've never once seen a 55,000lb spring near our shop or any shop I've been in.

From Martinsville, I don't imagine you would see this on a K&N it's totally different. They don't use the springs just for ride height. Like the Cup cars. I guess you haven't been in many shops this year, I don't know what other way to put it but if you're in Charlotte anytime shoot me a PM and you're more then welcome to come by.

[W2racing]

I don't care what the software says, it is completely inaccurate that the sprung mass of a vehicle has any idea where the top of a spring is within a coil-over.

You're either misunderstanding the variable it is asking for or the software is rubbish or some combination of the two.

My guess is that this question is being asked to calculate rear roll center location but the question should be asking where the top of the shock mount (assuming coil-over) is located, not the top of the spring. Load on any coil-over is felt (input) at the ends of the shock, not the ends of the spring. This fundamental fact of physics is why spring length has ZERO effect on vehicle dynamics. That is until coil binding comes into play which no software is going to take into account because it is dependent on way too many variables regarding the spring construction all the way down to how much powder coat they put on it.
If you want proof, go buy or rent yourself a spring smasher and do the homework. Don't trust software written (supposedly) by a guy that has been writing the same 4 tech articles for the last 20 years.

If you're referring to the original question I asked, you're giving me way too much credit as far as understanding how a dirt late model actually works. The reality is that the little I know about them equates to "I don't know squat". In actuallity , I need to buy some springs and I wondered if there was any particular reason to use one length over another. I really am enjoying reading all the responses from you people who really do understand this stuff. Thanks to all for your responses.

[7uptruckracer]

Most builders will provide you with a baseline sheet and it includes spring heights. Normally its 10" LF 12" RF 12"RR and 14"LR The shorter the spring for the same given rate the less available travel it has before bind.

If you're referring to the original question I asked, you're giving me way too much credit as far as understanding how a dirt late model actually works. The reality is that the little I know about them equates to "I don't know squat". In actuallity , I need to buy some springs and I wondered if there was any particular reason to use one length over another. I really am enjoying reading all the responses from you people who really do understand this stuff. Thanks to all for your responses.

[drtrkr244]

I don't care what the software says, it is completely inaccurate that the sprung mass of a vehicle has any idea where the top of a spring is within a coil-over.

You're either misunderstanding the variable it is asking for or the software is rubbish or some combination of the two.

My guess is that this question is being asked to calculate rear roll center location but the question should be asking where the top of the shock mount (assuming coil-over) is located, not the top of the spring. Load on any coil-over is felt (input) at the ends of the shock, not the ends of the spring. This fundamental fact of physics is why spring length has ZERO effect on vehicle dynamics. That is until coil binding comes into play which no software is going to take into account because it is dependent on way too many variables regarding the spring construction all the way down to how much powder coat they put on it.
If you want proof, go buy or rent yourself a spring smasher and do the homework. Don't trust software written (supposedly) by a guy that has been writing the same 4 tech articles for the last 20 years.

I think you might be misunderstanding what his software is trying to calculate. Its not calculating loads on/off each corner. Bob believes unbalanced setups come from unbalanced front and rear suspensions.In other words, the roll angles of each are too far apart causing ill handling. He has to be partially right as dlms are rolling more and more on the rf, getting closer to matching the rr. Im not an engineer, but I haven't seen someone prove his theories are wrong.

All I know is that I have used his software on lms, mods, 3/4 lms, and hobby stocks. It has always improved the handling on each one. Bob told me at Volusia last year that all dlm chassis builders were using his software now. It would be interesting to know if they are designing their suspensions around his software.

[setup479point2]

On the RF , if running a 400 lb spring a 10" should be fine . When I get to 300 or softer I like a 12 , just because of a possible coil bind situation . LF a 10 or 12 is fine . RR 10 , or 12 is fine unless really soft 150 or under ( not common ) . LR 14 or 12 is normal .

[Matt49]

I think you might be misunderstanding what his software is trying to calculate. Its not calculating loads on/off each corner. Bob believes unbalanced setups come from unbalanced front and rear suspensions.In other words, the roll angles of each are too far apart causing ill handling. He has to be partially right as dlms are rolling more and more on the rf, getting closer to matching the rr. Im not an engineer, but I haven't seen someone prove his theories are wrong.

All I know is that I have used his software on lms, mods, 3/4 lms, and hobby stocks. It has always improved the handling on each one. Bob told me at Volusia last year that all dlm chassis builders were using his software now. It would be interesting to know if they are designing their suspensions around his software.

Just as an example, what did his software teach you that improved the car's handling characteristics?
I'm not trying to be argumentative but I will say this: You're asking for someone (in this case me) to prove his theories wrong. As the person proposing the "theories", the burden of proof is on HIM. BB has made a living on taking very simple concepts and putting a lot of words around it. Blend in a little "pit knowledge" from days gone by and you have yourself a real cutting edge race engineer. Not TRYING to cut him down but I am...his stuff is 5 years behind and recycled before it is even printed.

[fastford]

I like bob, but I have to agree with matt here, I really haven't seen anything hes done lately, especially with the dynamics of the two stage or bump stop right front that's the hot ticket right now, I think these new setups kind of makes some of the old way of thinking obsolete , JMO

[7uptruckracer]

He still swears by a Right Hand mounted Jbar.....

[MasterSbilt_Racer]

He still swears by a Right Hand mounted Jbar.....

I have actually had recent success with that.

[fastford]

He still swears by a Right Hand mounted Jbar.....

are you talking about on the pinion or the frame?

[7uptruckracer]

Right Hand Frame, I've never had success with it, tried it on asphalt too.

[DirtRacer9x]

Right Hand Frame, I've never had success with it, tried it on asphalt too.Asphalt is mostly on right side frame mount. Dirt guys tried it and found the car easier to drive on the tack but dry you don't stand a chance.

[7uptruckracer]

The Asphalt right hand frame mount Jbar just seemed to make the car to ill on entry. We mostly stick to long bars with reverse rake and bumpstop on the Asphalt mods. They aren't really traveling the cars as much once it goes down it stays down. We suck the LR in laterally which helps free entry and middle and then also places more weight on the LR for exit and engage the bumpstop. Its alot easier to setup asphalt but your fighting for smaller gains it seems.

[7uptruckracer]

To kinda go along with the original post on this car it runs conventional coil springs. We run a 325 and a 275 in the front with bumpstops. You normally see 9.5" tall springs as the standard height but a spring that height and that soft you run out of travel and it coilbinds. So you go to a 5" x 11" or 13" tall spring in the front and reset it to the same ride height and you have more travel before it binds. It still has the same rate but to make that rate at that height it has different coil spacing between the coils and different diameter in some cases so you can travel it more before bind. Height makes no dynamic difference just moves your collar to a different spot.

[drtrkr244]

Just as an example, what did his software teach you that improved the car's handling characteristics?
I'm not trying to be argumentative but I will say this: You're asking for someone (in this case me) to prove his theories wrong. As the person proposing the "theories", the burden of proof is on HIM. BB has made a living on taking very simple concepts and putting a lot of words around it. Blend in a little "pit knowledge" from days gone by and you have yourself a real cutting edge race engineer. Not TRYING to cut him down but I am...his stuff is 5 years behind and recycled before it is even printed.
My success with his software was on conventional setups. I don't know if it applies to dual stage or bump setups. Im certainly not an engineer or computer guy, but I have worked on dirt cars for 20 plus years. I really would like a chassis builder or top tier team to test his theories and see if they apply. I do think that you need the front and rear suspensions to be working together instead of fighting each other. It seems to me that all the technology is applied to one end of the car most of the time. Now days , it seems everyone is working more on the front end, even Mark Bush, stated this in one of his tech articles. All I can say is that his software has helped my customers that are on conventional setups.