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    Suspension Questions
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    Hello everyone I hope the big man in the red suit treated you all well. I got lucky and got a version of TurboCad so now its time to get all the ideas I have in my head into the computer. I have read numerous threads over and over again and I think Im ready to do this. I do have a few questions that I have seen answers for but Im hoping to get them all here again instead of searching through the over 300 threads I have subscribed to. The car will be a full unequal length A arm car both front and rear shooting for between 12 and 15 inches of travel but I may not even need or get that much. I have studied alot of designs and Im going to pull ideas from them all. I think trying to do rear swing arms on my first one will cause more trouble then I need.

    Front Rake - Im thinking between 5 and 7 degrees and I will try to build it into the frame. Im not sure I like the idea of a frame prebent so maybe design it into the mounts for the arms and the steering rack. I know you will get the caster right away with mounting the arms on this same degree angle so I will have that built right into the front end.

    Ackerman - This is where I need some help with building some into the spindles. Is there a certian or average number I should be looking for? I know how to check it in the drawing just not sure how and how much to build in. I know I want the mounting point of the rack to be centered in the distance between the arms on the spindle, just dont know how far back off the spindle or how far in towards the rack.

    Droop - This is where Im a little lost. I think I saw some where that ride height should be set somewhere around 30 percent of droop. Is that right or close? Again I have an idea on the wheel tire combo so I can figure that into the design as well.

    If I have left out any info to help with answering these questions, please let me know what info would be needed. Nothing I am thinking of is written in stone so I can change any idea if Im way off base on any of my thoughts or ideas.

    Ok guys flood me with info and help to make my head spin just a little faster and longer then it already does .....

    ALW
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    Re: Suspension Questions
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    Millenium Member nutz4sand's Avatar
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    Quote Originally Posted by ALWX65 View Post
    Hello everyone I hope the big man in the red suit treated you all well. I got lucky and got a version of TurboCad so now its time to get all the ideas I have in my head into the computer. I have read numerous threads over and over again and I think Im ready to do this. I do have a few questions that I have seen answers for but Im hoping to get them all here again instead of searching through the over 300 threads I have subscribed to. The car will be a full unequal length A arm car both front and rear shooting for between 12 and 15 inches of travel but I may not even need or get that much. I have studied alot of designs and Im going to pull ideas from them all. I think trying to do rear swing arms on my first one will cause more trouble then I need.
    I know you might reallly want to design but the Edges Barracuda already has this. I am just saying. Its a proven design and they work very well with a few mods to the plans. IF this might work Doug Heim can set you up better than you know.

    Now that I have said that if you reallllly want to build it yourself thats also really great. But it WILL be a lot more work but it sounds like you are more than aware of that. So lets see if I can aid you a tad.

    Quote Originally Posted by ALWX65 View Post
    Front Rake - Im thinking between 5 and 7 degrees and I will try to build it into the frame. Im not sure I like the idea of a frame prebent so maybe design it into the mounts for the arms and the steering rack. I know you will get the caster right away with mounting the arms on this same degree angle so I will have that built right into the front end.
    The frame prebent offers one great thing. A ramp if you will IF the frame ever hits the ground) . Like the front of a sled tries to lift itself out.
    You want something there that is bent up. With a nice skidplate. If not the frame then an under the frame bumper setup to push you u[p and over bad things.

    Rake is a matter of preferance. Till you have drove both ends of the spectrum you will not really know what you really like. Your numbers are recommended by many and will make you happy likely. But short of desinging a setup that will allow you to dial in no rake to massive rake for "testing" you will need to build one with more and one with less to see what YOU like. Of course different rake numbers work different with different tail ends. So the tail end would have to be the same to really see a differenace to each person.

    Quote Originally Posted by ALWX65 View Post
    Ackerman - This is where I need some help with building some into the spindles. Is there a certian or average number I should be looking for? I know how to check it in the drawing just not sure how and how much to build in. I know I want the mounting point of the rack to be centered in the distance between the arms on the spindle, just dont know how far back off the spindle or how far in towards the rack.
    RcTek - Radio Controlled Model Car Handling Main Section Page

    That link is good to see the differances and can show you the different ackerman angles very well. Go find its link there and check out the pics and examples.

    Quote Originally Posted by ALWX65 View Post
    Droop - This is where Im a little lost. I think I saw some where that ride height should be set somewhere around 30 percent of droop. Is that right or close? Again I have an idea on the wheel tire combo so I can figure that into the design as well.
    Some say 30% and some say 40%. It really depends on you and the higher it sits the better in a straight line but cornering suffers some. How and what you drive on determines this a good bit. You like to corner hard or just float along in a straightish line?

    Also AN IDEA of the tire/wheel combo is iffy. You should KNOW what you will run to get it where you want it. MANY say get the wheels and tires you will run and build INWARD from there for a reason.

    The KPI (king pin inclination) is determined by the size of the tire and rim and the rims offset. If this is not right the rest of the suspension will tend to fight itself. The KPI angle will also affect a lot of the other angles directly so it should be determined first so later you do not have to alter/compromise others to fit.

    That scratched the surface! :] Hope I helped some!
    Now that NOBAMA has PROVEN he is the absolute WORST president in the history of history Jimmy Carter can thank him for stealing the dunce crown.

    Lets hope the next guy repeals NObama care along with the rest of the stupid crap this blight on our windshield has done.
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    Re: Suspension Questions
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    I was gonna answer, But I knew Nuts4sand would so I just kept quiet..
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    Re: Suspension Questions
    #4
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    Nutz, thanks for all the great info you supplied. You gave me some things to think about that I wasnt and thats always a good thing. I never looked at the angled frame that way. I saw builders who have done this and thought is was all about the rake they were trying to get. I will be honest I have really thought of getting Rorty's R11 plans and go from there, but what I may do could take out some of the things he has learned and designed into it. The briggs cars are also where I get some of my ideas. I was thinking I could find something in between the two. The car I want, want being the key word here, to build is for fun, not intended to race, but driven just as hard still.

    I read somewhere that designing a car is a comprmise in everything. Im just trying to limit the most mistakes I can from the begining. Just because it looks good on the chalk board in my brain that doesnt mean its going to work. I know you went over everything I asked but if there is more food to feed the beast in my head, serve it up. That goes for anyone else looking to feed it.

    ALW
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    Re: Suspension Questions
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    A few thoughts:
    Rake does not effect caster in any way. In relation between upper and lower ball joints determine caster. I suggest a few degrees of rake for the reason listed above (and sport atvs use it, it must work..lol.)
    For setting up droop, (for designing purposes) I find the rolling outer ball joint placement. Then establish a ride height (chassis height with lower arms as close to level as possible.) Next figure your height under full compression (Usually 4-6" for me.)
    Subtract your compression travel from the total travel you desire and you have droop.
    Have fun designing, thats what its all about.
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    Re: Suspension Questions
    #6
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    Ok I thought that rake would give you caster or am I thinking about it wrong? I did a quick and some what laim picture in paint to show what Im thinking. Black lines are the a arms and the red is the spindle looking at it from the side.

    One of these days I will figure out how to put the picture here ...

    ALW
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    Re: Suspension Questions
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    Admin Gene's Avatar
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    I disagree with Evan. Rake will create caster and your picture proves it to be true.

    My first car uses the same principle to create 6* of caster. Doing this on my car made for not only a good ride, it allowed steering to return to neutral when letting go of the wheel. Without caster you practically have to return the wheel to neutral by hand.

    My second car has no rake and caster is induced by turning wishbone heims. With zero caster it is very twitchy and with caster it settles down. My first car is not twitchy at all.

    IPSO FACTO my first car has caster equal to the amount of rake. If it had zero rake it would have zero caster. It has 6* of rake and thus it has 6* caster.
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    Re: Suspension Questions
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    At first glance, what you are saying makes sence. However, If you move the upper a-arm forward, or lengthen the rear/shorten the front of the upper a-arm inboard to bring the upper a-arm outer balljoint forward, you have any amount of caster you want. You could do the opposite and create more caster. You could also make the upper have more "rake" then the lower, creating anti-dive. The downside of anti-dive is a caster change though the cycle. Hope that clears things up. oh..Just remembered, r.c buggies / trucks (ie rc10t3) have lots of "rake", if I remember right, about 30deg. Caster on them is something like 10deg
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    Re: Suspension Questions
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    Yes, what is being said is if the front arms had zero caster, and you raked it 10 degrees you would then have 10 degrees caster, You always have to measure from the floor..
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    Re: Suspension Questions
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    Oh to add to that, more caster harder to turn, yet more straight line stability, Less is just the opposite, easy to turn, less straight line stability..
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