REVERE THE STEER - Rubicat Going Wide with 72.5" Dynatrac XD60 / PRO 1550 Front Axle

[JK_Dave]

Is there any way to come up with a calculation of 1" of scrub radius = __ ft of extra turning radius on a JKU?

 

[JAGS]

Nice turn testing. [emoji106] So this is all as a result of the scrub radius. And no rubbing at full turn on Rubicat because the axle is wider though the BS is less, yes? That's some top notch made in the USA science right there!

 

[chitown35]

Is there any way to come up with a calculation of 1" of scrub radius = __ ft of extra turning radius on a JKU?

Nice turn testing. [emoji106] So this is all as a result of the scrub radius. And no rubbing at full turn on Rubicat because the axle is wider though the BS is less, yes? That's some top notch made in the USA science right there!

Turning radius and scrub radius are completely different, and for the sake of discussion, unrelated. Turning radius is the tightest circle the car can turn in without backing up and doing a multi-point turn. The number is typically published as part of the vehicle technical specs by the manufacturer. Rarely is scrub radius published.

Front wheel end geometry does have an effect on the turning radius of the vehicle, but other things (non-axle related) have a larger impact. We did not test the turning radius on Rubicat before or after the axle was installed, but maybe Eddie can chime in with his impressions so far.

We will publish more info on this at a later date.

No, as Dynatrac posted the scrub radius is not related to the turning radius. The factors that influence turn radius are wheelbase, axle width, wheel backspacing.

The scrub radius is helpful for some other things though.

 

[wayoflife]

Is there any way to come up with a calculation of 1" of scrub radius = __ ft of extra turning radius on a JKU?

LOL!! I have no doubts that there is and I'm sure an engineer will come on with one soon :crazyeyes:

Nice turn testing. [emoji106] So this is all as a result of the scrub radius. And no rubbing at full turn on Rubicat because the axle is wider though the BS is less, yes? That's some top notch made in the USA science right there!

No, as Dynatrac posted the scrub radius is not related to the turning radius. The factors that influence turn radius are wheelbase, axle width, wheel backspacing.

The scrub radius is helpful for some other things though.

I spoke with Dynatrac about this yesterday and they were cautious to say one way or another whether or not scrub radius has any effect on turning radius but for the most part, it wouldn't. If you try making a full u-turn in Rubicat and Moby back to back, you can definitely feel resistance in Moby but a lot of that would have to do with ackermann.

 

[DP1120]

Thanks for the real world test. Only downfall i see is the selection of good wheels with that backspace that i like.

 

[wayoflife]

Thanks for the real world test. Only downfall i see is the selection of good wheels with that backspace that i like.

That is the downside to doing this but of course, there aren't many wheels available because there hasn't been an axle option like this available in the past and therefore, there hasn't a demand for them. Perhaps that will change now. :yup:

 

[chitown35]

Thanks for the real world test. Only downfall i see is the selection of good wheels with that backspace that i like.

Or ponying up the money for a weird length spare shaft. But hopefully with this setup you're not breaking those shafts.

 

[wayoflife]

Or ponying up the money for a weird length spare shaft. But hopefully with this setup you're not breaking those shafts.

THAT ^^^ is a legit concern. Granted, the whole point in running something like an XD60 is to have confidence that things like that won't be a concern. :yup:

 

[jeffj]

I went from a stock axel with 3.5 back spacing with hydro ass connected to the tie-rod to a pro rock 60 with the psc connected to the knuckle and it seems it doesn't turn as easy compared to my other rig and its really hard to steer with my front locker on compared to my other one. Does this make sense? I know I have 40 now and wider axels and I'm sure it has to do with what this thread is talking about, but I'm not an engineer so I'm just try to understand this a little better.

 

[wayoflife]

I went from a stock axel with 3.5 back spacing with hydro ass connected to the tie-rod to a pro rock 60 with the psc connected to the knuckle and it seems it doesn't turn as easy compared to my other rig and its really hard to steer with my front locker on compared to my other one. Does this make sense? I know I have 40 now and wider axels and I'm sure it has to do with what this thread is talking about, but I'm not an engineer so I'm just try to understand this a little better.

Yup, makes total sense that it's harder for you to steer your ProRock 60 with lockers on especially being that it has Pro 60 steering knuckles and the back spacing on your wheels is most likely significantly less. They will dramatically increase your scrub radius and that will cause your tires to scrub their way around as they turn. This scrubbing or resistance will make it harder to steer. The stock axle on your other rig still uses factory knuckles with unit bearings and should have measurably less scrub radius. While a ram that is too short or improperly setup can limit your steering range, how it's mounted up shouldn't make a difference in your ability to steer.

 

[jeffj]

Yup, makes total sense that it's harder for you to steer your ProRock 60 with lockers on especially being that it has Pro 60 steering knuckles and the back spacing on your wheels is most likely significantly less. They will dramatically increase your scrub radius and that will cause your tires to scrub their way around as they turn. This scrubbing or resistance will make it harder to steer. The stock axle on your other rig still uses factory knuckles with unit bearings and should have measurably less scrub radius. While a ram that is too short or improperly setup can limit your steering range, how it's mounted up shouldn't make a difference in your ability to steer.

Great, its making more sense to me now. This really seems like revolutionary changes are going on.

 

[chitown35]

I went from a stock axel with 3.5 back spacing with hydro ass connected to the tie-rod to a pro rock 60 with the psc connected to the knuckle and it seems it doesn't turn as easy compared to my other rig and its really hard to steer with my front locker on compared to my other one. Does this make sense? I know I have 40 now and wider axels and I'm sure it has to do with what this thread is talking about, but I'm not an engineer so I'm just try to understand this a little better.

Did you first add the 40s when you did that change too?

 

[jeffj]

Did you first add the 40s when you did that change too?

No, I actually bought a new to me jeep that had the 40's and 60's so it was pretty neat having them both at the same time for a little while.

 

[chitown35]

No, I actually bought a new to me jeep that had the 40's and 60's so it was pretty neat having them both at the same time for a little while.

I guess my question was, are you comparing the steering on two jeeps that both have 40s?

 

[jeffj]

I guess my question was, are you comparing the steering on two jeeps that both have 40s?

Ah ok, sorry. No, I had 37's on my old jeep with stock axels and 3.5 back spacing. So it was a different set up all together, but was interesting to compare the difference between the two.

 

[JeepFan]

Reading through this thread inspired me to do some testing of my own. Thanks Eddie!! :crazyeyes:

Since I have a stock 2015 JKU and a 2009 Modified JKU I thought it would be cool to do a turning radius comparison.

Here's what I found...

According factory specs, a stock JKU has a turning radius of 41.2'. Here is what I found....


As a starting point, I lined up the Jeep close to the end of the white line. Next, I turned the steering wheel all the way to the left and began slowly moving the Jeep until it completed a 180* turn. I marked the ending point at the right front tire outer edge close to the center line of the tire contact patch. I measured between the two points on a diagonal and this is what I found...


The stock Jeep came in at 500" (41.6') Of course this is not an exact measurement but, not far off from stock.


Next up...My 2009 JK with stock axles, ATX Beadlocks with 3.5" BS and Toyo MT 37x13.50 tires. 83" wide It measured out at 537" (44.8'). A 3.2' difference!


Here's a picture for reference. My daughter Cristina is standing at the starting point. Seems like a mile away. LOL!!

Hope you find this info useful. I must say this is a confusing subject. There's Curb to Curb, Wall to Wall, and turning radius. Factor in scrub radius and you have a recipe for insanity. :cheesy:

I think I'll stick to scrubbing the dirt off my Jeep.

Speaking of scrub radius, here are some picks of the tires scrubbing the concrete...


2009 Jeep.


Stock Jeep.

 

[TrainWreck618]

All too fascinating. I have been enjoying seeing everyone's findings!


Sent from my iPhone using WAYALIFE mobile app

 

[wayoflife]

Awesome!! Thank you so much for posting this up Tony! [emoji1303]


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[WJCO]

Reading through this thread inspired me to do some testing of my own. Thanks Eddie!! :crazyeyes:

Since I have a stock 2015 JKU and a 2009 Modified JKU I thought it would be cool to do a turning radius comparison.

Here's what I found..

So you're the dude who's been chalking up my parking lot......

 

[JeepFan]

So you're the dude who's been chalking up my parking lot......

LOL! Funny you mentioned that...We did get some strange looks from Home Depot Employees and customers. :shock: