VIDEO : SCRUB RADIUS - What it's All About & The Dynatrac PRO 1550 Knuckle

wayoflife

Administrator
Staff member
While wheels with very little back spacing are all the rage, widely available and will push your tires out far enough to help clear things like steering and suspension components, it does so at the expense of your ability to steer and at the cost of putting significant stress on your ball joints, wheel bearings and even tie-rod. The more you push the center line of your wheels out, the more you increase your scrub radius and in this short video, you'll get to hear Jim McGean, the owner of Dynatrac explain what all this means, why you don't really want it and see how their XD60 front axle with Pro 1550 steering knuckle allows you to run a wheel like a Trail Ready bead lock that has 5.5" of back spacing to virtually eliminate it. Please note, this is just a raw, impromptu video and so I apologize for the screen scan that you'll see.


For more information regarding the Dynatrac XD60 front axle and PRO 1550 steering knuckle, please click on the link below:
REVERE THE STEER - Rubicat Going Wide with 72.5" Dynatrac XD60 / PRO 1550 Front Axle

Also, more videos like this are coming your way so be sure to check back soon :cool:
 

WJCO

Meme King
Refreshing to see it explained so simply. I've read about SAI and scrub radius many times in books over the years without being able to easily wrap my head around it. This explanation was much easier to understand.
 

wayoflife

Administrator
Staff member
Refreshing to see it explained so simply. I've read about SAI and scrub radius many times in books over the years without being able to easily wrap my head around it. This explanation was much easier to understand.

LOL!! I totally agree. It's one thing to read about theory and it's another to see it explained in a practical application. :yup:

I'm seriously impressed with this whole design. I was looking over your pictures again earlier, and it's crazy the improvement made. I'm looking forward to seeing videos in the rocks

The design of the XD60 and PRO 1550 really is impressive. We hope to get videos out on the rocks as soon as we can :yup:
 

FuriousDz

New member
Refreshing to see it explained so simply. I've read about SAI and scrub radius many times in books over the years without being able to easily wrap my head around it. This explanation was much easier to understand.

Im still having a little trouble wrapping my head around it. :idontknow:

So is it the design of the knuckle combined with the BS that allows such a small scrub radius? Does the BS alone change the scrub radius on say a stock axle?

Awesome info by the way!
 

jeeeep

Hooked
well hell...

I just added spacers on the pr44 but I've got Dynatrac BallJoints so I'm going back into my "it's all good" safe place lol

in all seriousness I'm considering going back to stock knuckles, not sure why my steering changed so much after installing the Rancho knuckles
 

wayoflife

Administrator
Staff member
Im still having a little trouble wrapping my head around it. :idontknow:

So is it the design of the knuckle combined with the BS that allows such a small scrub radius? Does the BS alone change the scrub radius on say a stock axle?

Awesome info by the way!

While the PRO 1550 steering knuckles alone will help reduce scrub radius and therefore improve steering, running them WITH a set of wheels that have 5.5" of back spacing will virtually eliminate scrub radius, vastly improve steering, protect your steering components and help them to last a lot longer. :yup:

well hell...

I just added spacers on the pr44 but I've got Dynatrac BallJoints so I'm going back into my "it's all good" safe place lol

in all seriousness I'm considering going back to stock knuckles, not sure why my steering changed so much after installing the Rancho knuckles

By adding wheel spacers, you have effectively pushed your the center line of your wheels out and by doing that, you have INCREASED your scrub radius. Unless there is something I am not aware of on your new knuckles, I wouldn't think they would cause a change. Of course, I have no experience running them so I couldn't say for sure.
 

WJCO

Meme King
Im still having a little trouble wrapping my head around it. :idontknow:

So is it the design of the knuckle combined with the BS that allows such a small scrub radius? Does the BS alone change the scrub radius on say a stock axle?

Awesome info by the way!

Scrub radius is where the center line of the wheel/tire meets the SAI line. So if they don't meet, scrub radius is the space between those two lines. The closer the better. So yes it is a combination of both the knuckle design and the backspacing of the wheels.

The way I'm reading it is that the new knuckles allow you to run wheels with more backspacing and not have rubbing issues, etc, and achieve a better scrub radius at the same time.
 

highoctane

Caught the Bug
That last few seconds where he explains how it's difficult for a tire to roll with the locker engaged really sums up what might be the biggest advantage of the decreased scrub radius; easier turning on obstacles with the locker engaged.
 

WJCO

Meme King
in all seriousness I'm considering going back to stock knuckles, not sure why my steering changed so much after installing the Rancho knuckles

Unless there is something I am not aware of on your new knuckles, I wouldn't think they would cause a change. Of course, I have no experience running them so I couldn't say for sure.

Not to hijack too much, but what issues are you having with the Rancho knuckles, Jeeeep? Mine have been fine. My steering improved, but then again, I wasn't running high steer prior and should have been.
 

FuriousDz

New member
While the PRO 1550 steering knuckles alone will help reduce scrub radius and therefore improve steering, running them WITH a set of wheels that have 5.5" of back spacing will virtually eliminate scrub radius, vastly improve steering, protect your steering components and help them to last a lot longer. :yup:

Scrub radius is where the center line of the wheel/tire meets the SAI line. So if they don't meet, scrub radius is the space between those two lines. The closer the better. So yes it is a combination of both the knuckle design and the backspacing of the wheels.

The way I'm reading it is that the new knuckles allow you to run wheels with more backspacing and not have rubbing issues, etc, and achieve a better scrub radius at the same time.

Thanks for the clarification!
 

NFRs2000NYC

Caught the Bug
Jim did a great job of explaining something fairly complex in a manner which is easily understandable by the layperson.
 

chitown35

LOSER
well hell...

I just added spacers on the pr44 but I've got Dynatrac BallJoints so I'm going back into my "it's all good" safe place lol

in all seriousness I'm considering going back to stock knuckles, not sure why my steering changed so much after installing the Rancho knuckles

The instructions for those knuckles provide guidance for adjusting the steering stops (they come intentionally long), take a look.

www.reidracing.biz/JK001RL.pdf
 
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