Spring length

[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.