sand rail design

[dsrace]

8.25" for the height measurement your asking and  6.62" on center in width. i run a 31-10.5x15 dirt tire and paddle tires are 1450's. they are advertised as 31" but are not. so say 30" tall - 14.50 wide x15" rim.

[Baloo]

right I have some numbers



the out put flange on the side of the gearbox id 5" in diameter  hanging below that is 3" of gearbox, I assume I don't want any gearbox hanging out the bottom as it will hook or smash on rocks, so if the bottom pivot is level with the bottom of the gearbox and I make the top pivot 3" above the flange so the driveshaft is in the middle height wise then I would have around 11" of separation between the top and bottom wishbone at the gearbox end, could stretch that to 13 or 14" if it was beneficial ?

at the wheel end of the wishbones I am going to have the height of the hub 9" ?  but then I have to leave room for the calipers
that might be 4" ?    so that gets us to around 17"  which is perhaps why the original car was on 18" dia alloys

length of the A arms would be around 24" if I make them to match the pivot points of the driveshafts  which  themselves have around 3" of plunge in them

do all those numbers sound plausible ?

Andy

[dsrace]

so from the last pic on your tablet......my answer is no. dont do it that way. you want to keep everything pivoting equally in the rear as in on parallel planes and all pivots at the same time. so you need to make a jig off the wheel bearing carrier including the cv mount and then bolt that to your cv trans side and weld the tabs to the frame so they match the carrier. this keeps all points pivoting equal in xny and g cooridanates. now if you feel comfortable and want to induce neg camber in the rear you can lower the upper a arm say 3/8" at the frame so its mounting points are 3/8" lower than the carriers upper point  ( in relation to its point from center of cv and center of bottom pivot) and this should get you close to -2 or -3 * camber change through the stroke. that statement is based on my front ends and at 22 to 24" wheel travel.

[dsrace]

so your a arms need to pivot on center equally with the center of the cv also.

[dsrace]

https://dtsfab.com/index.php?topic=5336.180

[Baloo]

so from the last pic on your tablet......my answer is no. dont do it that way. you want to keep everything pivoting equally in the rear as in on parallel planes and all pivots at the same time. so you need to make a jig off the wheel bearing carrier including the cv mount and then bolt that to your cv trans side and weld the tabs to the frame so they match the carrier. this keeps all points pivoting equal in xny and g cooridanates. now if you feel comfortable and want to induce neg camber in the rear you can lower the upper a arm say 3/8" at the frame so its mounting points are 3/8" lower than the carriers upper point  ( in relation to its point from center of cv and center of bottom pivot) and this should get you close to -2 or -3 * camber change through the stroke. that statement is based on my front ends and at 22 to 24" wheel travel.

not sure I understand all that   any pics  that might help me ?

[Baloo]

https://dtsfab.com/index.php?topic=5336.180

wow plenty of reading there, I better get started

[dsrace]

lets put it this way......using my wheel bearing carriers ( the ones i said i would give you for $1 pound) . they have an up and down center measurement of 8.25"  and 6.62" on centers ( of heims joints) left to right. i dont have one in front of me but lets say the cv is centered in the middle of all 4 of those points. you will want the same spaceing (mounting points) on the frame surrounding the cv joint. now with a wheel bearing and 930 flanged stub axle, those 4 point travel directly through the center of the cv joint so the center of the heim joint piovots on the same plane/ parrellal line as the heim. all pivot at the same time on the same lines. does that make more sense? i'm not good at explaining this, i just know it.  there are variations to this for different applications but what i descibed is the simplist way.

[dsrace]

in your drawing you show a spread of 11" on center at frame for the inside pivot points. at the wheel you show what looks like 9". if you do that you will wind up with major pos camber and i mean major. now major camber depends on amount of wheel travel of course.

[Baloo]

in your drawing you show a spread of 11" on center at frame for the inside pivot points. at the wheel you show what looks like 9". if you do that you will wind up with major pos camber and i mean major. now major camber depends on amount of wheel travel of course.

so are we saying  that the top and bottom wishbone need to be parallel to each other,  if they are 9" apart at the wheel end then also 9" where they join the chassis,   in which case I have to start with the hub plate ?

[dsrace]

yes and the cv location in the carrier needs to match at the frame as well.

[dsrace]

like this

[fabr]

Ds is taking good care of you. I've been quite busy but can't add anything to what he is saying anyway. He and I agree on all of it.

[dsrace]

starting with what i call the wheel bearing carrier and your calling the hub plate is the best and only way imo. with that being said, you do need to make sure you will have the room on the frame.  will you have enough room for tabs or some mounting bracket to bolt the heims to above and below the cv that all pivot on the same line through the center of the cv pivot point.

now if you really want to wade out into the deep end on your first attempt and want to develop ( i call induced) neg camber ( top of wheel leans in towards frame) for cutting and cornering then you'll need to get creative on the hub plate ( carrier) and/or mounting points at the frame. 

using my front ends as an example. the majority of my customers don't run front brakes. they run spindle mount rims so the center of the rim hub centers the tire on the spindle snout. so knowing that most run 6.75 tires ( maybe one size larger) i know where the scrub radius needs to be. i then know that on my spindles what the SAI needs to be to achieve positive scrub radius that i feel works best.  so now i know that with my un equal length a arms ,the neg caster i pre set and a lowered upper a arm pivot point on the frame , i can develop a -3* camber arc through a 24" wheel stroke. now when doing this as the wheel leans in the steering rack isn't going to move with it so it wants to push the steering arm out in to  toe out. the next step is to weld the a arms on the frame at a rake of such that send them back at an angle to off set that push, to alleviate  toe out which is bump steer. then if you throw anti dive into the mix it gets even more complicated and we won't touch that subject unless fabr has time for a debate  just kidding

so why am i saying this? well because this is another simple and easy way to develop neg camber in the rear ( less the tie rod and rack interference) and along with the right rim offset for a true pos scrub angle. i did not do this on my rear end as i didn't have the room around the drive flange at the trans and any kind of time frame to design a new way. i do plan on looking at doing this on my next frame. so i just pre set 1* of neg camber on my rears and it develops .5* neg camber through it's 23.5" wheel stroke also.  keeping it simple and straight will allow the tire to skid across the ground making it easier to drift but that can go to far if the front can't compensate by grabbing and cornering. that's where it get real fun imo and even more so in the dirt!!


something to read...

https://en.wikipedia.org/wiki/Scrub_radius

https://www.freeasestudyguides.com/included-angle.html

https://www.quora.com/How-negative-camber-provide-benefits-to-vehicle

https://en.wikipedia.org/wiki/Ackermann_steering_geometry

this is most important on the front end and i pre fer front steer in offroad applications.  a neg camber arc in the rear is beneficial but not a must have for all.

[Baloo]

   when you think about it  its pretty obvious the top and bottom arms have to be parallel to each other to get the hub to rise and fall vertically isent it,   I have made some plastic arms to play around with and see what happens when I move the mounting points

the new rear hubs I have have the fixing bolt holes at 4" centres which means they will fall half on and half off the holes in the centre of your wheel bearing carrier , not good   will ponder

how much is your front end kit ? and can I use it with brakes ?