Wheel back spacing???

Redneckryder549 · Jan 18, 2017

I am building a set of spidertrax 9's with there ultimate knuckles and unit bearing. My question is if there is a draw back to making the WMS of the housing wider and using a wheel with more back spacing as compared to a shorter wms with a less offset wheel? For example would it be ok? Better? Or worse?? To run a WMS of 67" and a 6.5" backspaces wheel or a 62"wms with a 4" back spaced wheel? Either would put the tires in the exact same place. The wheel mounting surface to the center of the knuckle is 5.375".

mcutler · Jan 18, 2017

Re: Re: Wheel back spacing???

Redneckryder549 said:
I am building a set of spidertrax 9's with there ultimate knuckles and unit bearing. My question is if there is a draw back to making the WMS of the housing wider and using a wheel with more back spacing as compared to a shorter wms with a less offset wheel? For example would it be ok? Better? Or worse?? To run a WMS of 67" and a 6.5" backspaces wheel or a 62"wms with a 4" back spaced wheel? Either would put the tires in the exact same place. The wheel mounting surface to the center of the knuckle is 5.375".

All depends on how much room you have for scrub radius and your steering angle.
For example; (my build has 66.5 wms, 4.75 bs, 86 overall width)... in my case because I'm trying to keep my 40" tires between the door jamb and grill header, I needed the least amount of scrub, which hurt my overall steering angle (41° now, capable of 48, still better than a 60...) due to interference wth the lower links. All depends on what your building...buggy- run a less bs, more scrub, max steering angle; full body rig- use what fits. Have to do it all at the drawing board first if possible, It's a complete system; knuckles, shafts, lower links, bs, ram throw, tire size, fender opening...cascading problem.

Matt

Redneckryder549 · Jan 18, 2017

Won't more scrub radius throw the tire more towards the center of the vehicle when the wheel is turned all the way? It is in a buggy and the lower link is all that it would ever rub on, they are angled wider on the axle and narrower on the chassis. My over all goal is to keep the width as narrow as possible, while still main ting as much steering angle as possible.

Redneckryder549 · Jan 18, 2017

This is looking from the top down, where the top and bottom links are the skinniest side to side is 17" back from the center of the axle housing and 27-1/2" between the two points side to side. I am going to run one of 2 tires at this point, either a set of 42 Boggers or a set of 40" Treps.

Redneckryder549 · Jan 18, 2017

Theoretically what is the advantage of having more or less scrub radius?

mcutler · Jan 18, 2017

More (positive scrub) moves the tire away from the king pin, therfore away from the lower link; but also causes the outside corner of the tire to swing in a larger radius: this being the reason I used as little scrub as possible to keep the tire from interfering wth the body. But keep in mind the down falls off positive scrub; more effort to steer, more leverage on the spindle/bearings/kingpin-uniball- ball joint, and probably more issues than I'm versed in.

Matt

mcutler · Jan 18, 2017

Another thing to consider; inner axle shafts...are you going to run custom, or stock length? -this could determine your wms for you.

Matt

Redneckryder549 · Jan 19, 2017

It will be custom length shafts, trying to keep it as narrow as possible so I believe a neutral or negative scrub radius would help keep it out of the links, just seeing if there is any disadvantage or what they are before I pull the trigger.

mcutler · Jan 19, 2017

Re:

Spidertrax, ctm, or rcv, 300m?

Matt

Rokcrler · Jan 19, 2017

Re:

What are you building for? Trail, cone dodging? Racing?
That will help determine some of your points.
I loved full width tons with 5.5bs, then 3" narrower front D60 with 4.75bs.
Lay out your links, plan for neural scrub or close as positive scrub will push thru turns.

Redneckryder549 · Jan 19, 2017

Trail, maybe a lil racing, keeping small, it's a Sxs replacement AKA the Rzr hunter!

Redneckryder549 · Jan 19, 2017

How does having a negative scrub radius effect things?? Looking at race lines beadlocks and could go as far as 6.5" back spacing.

Redneckryder549 · Jan 19, 2017

Links are already done and mounted, just trying to figure out where to cut the axle tubes to set the Wms and what back spacing wheels to get.

Rokcrler · Jan 19, 2017

Re: Re: Wheel back spacing???

Redneckryder549 said:
How does having a negative scrub radius effect things?? Looking at race lines beadlocks and could go as far as 6.5" back spacing.

Negative puts you in the links, positive puts you outside of the king pin/ballhoint causing push.
Set the inner shaft to off the shelf shaft length...down time getting a replacement sucks.
Measure the swing of tire to links and rock out.

What's your outside tire measurement goal? Get wheels that puts you there