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Thread: front ride height

  1. #1
    heloo all
    I searched the forum more than once and couldn't find an answer.
    a question for the front suspension.
    we are first year and we use 20" tire with 34 cm inside diameter of the wheel,simple substraction leaves you with the lower outer ball joint between 12 to 15 cm above ground,if i want my roll center to be a bit above ground than i need the inner lower ball joint to be at the height of the outer(or around it) which means very high front,i seen people connecting the lower a-arm to the most bottom place on the frame.
    I guess i'm asking what is your front height above ground?and some explanation would be very appreciated.
    excuse me for my lousy english
    last year in mech engineering
    Ben-Gurion UNI in Beer Sheva
    Israel

  2. #2
    heloo all
    I searched the forum more than once and couldn't find an answer.
    a question for the front suspension.
    we are first year and we use 20" tire with 34 cm inside diameter of the wheel,simple substraction leaves you with the lower outer ball joint between 12 to 15 cm above ground,if i want my roll center to be a bit above ground than i need the inner lower ball joint to be at the height of the outer(or around it) which means very high front,i seen people connecting the lower a-arm to the most bottom place on the frame.
    I guess i'm asking what is your front height above ground?and some explanation would be very appreciated.
    excuse me for my lousy english
    last year in mech engineering
    Ben-Gurion UNI in Beer Sheva
    Israel

  3. #3
    The upper a-arm also plays a big role in the location of the roll center...

    For '05 we were in the range you listed. Explanation is that those were the points that gave us the scrub, RC height and camber curve that we were looking for. A-arms are connected to the lowest point of the frame in that area of the car(shocks are below a-arms). Obviously the seat bottom is significantly lower...

    Do you have some sort of program that allows you to run iterations on points? It is fairly simple to write something in matlab and extremely beneficial.
    Rutgers Formula Racing 04,05, 06

  4. #4
    thanks for answering,of course the upper a arm has importance but i don't want to take the inner upper ball joint too high cause then my camber curve will be as my frame roll,i beleive one of the most importent things to keep in all times is outside tire negative camber,more importent than scrub(only my got feeling though)
    i'm using adams/car,it's not very friendly to me but i'm getting hold of it i think.
    did you see teams get their inner lower ball joint higher than the lowest point of the frame at that side?
    last year in mech engineering
    Ben-Gurion UNI in Beer Sheva
    Israel

  5. #5
    Two things to consider when trying to lay out your front suspension mounts...

    1. The side impact member must be between 11.8 and 13.8 inches off of the ground with a 170lb driver (aka, at ride height). You're generally going to want your upper suspension mount tube to be nodal with this side impact member.

    2. Your ride height isn't necessarily set by any one place. By raising the foot box you can still keep the engine and driver's cg's low, while getting the lower suspension mounts on the bottom frame member and improving the seating position.
    Kyle Jeffries

  6. #6
    thanks for the tips.
    I understand what you are saying and yet another question,when you model your suspension what are the max angles you take?i use 4 but have really no idea if i'm on the right direction,and what in bump and droop?i take 4 cm each side.
    here in Israel this sport is still illegal so there is no one in this country that has any experience designing race cars.
    different subject,the guys in my team who responsible to the seat wants to buy one and not to build,have you heard of teams indeed buying?
    last year in mech engineering
    Ben-Gurion UNI in Beer Sheva
    Israel

  7. #7
    The max angle is set by the ball/spherical joint that you choose.

    Buying a seat is an option, however, building one is not difficult at all and will cost less and package easier.
    Kyle Jeffries

  8. #8
    Well, you are required to have a minimum of 2 inches of suspension travel. So in terms of binding, that (or whatever amount of travel you end up running) is what you need to look at.

    In terms of dynamics, look at your wheel rate and calculate how much the wheels will be moving under braking, cornering etc... You are in the ballpark though.

    As Kyle said...you can buy, but building is easy and much cheaper unless you get a sponsor hookup. In '04 we did a 2 piece seat, using a garbage bag filled with expandable foam and an average sized driver. Once it dries, remove the garbage bag, lay up some carbon on there along with a method of mounting it to your car and you are done. '05 we went to a one piece seat, but it took significantly longer.
    Rutgers Formula Racing 04,05, 06

  9. #9
    <BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by adrial:
    Well, you are required to have a minimum of 2 inches of suspension travel. So in terms of binding, that (or whatever amount of travel you end up running) is what you need to look at.

    In terms of dynamics, look at your wheel rate and calculate how much the wheels will be moving under braking, cornering etc... You are in the ballpark though.

    As Kyle said...you can buy, but building is easy and much cheaper unless you get a sponsor hookup. In '04 we did a 2 piece seat, using a garbage bag filled with expandable foam and an average sized driver. Once it dries, remove the garbage bag, lay up some carbon on there along with a method of mounting it to your car and you are done. '05 we went to a one piece seat, but it took significantly longer. </div></BLOCKQUOTE>

    We did the same thing for a seat, except, we never took it out of the garbage bag (ours was STUCK to the bag) and we covered it in something similar to T-shirt cloth (it LOOKED like nomex.... )

    -Chuck

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