Wheel spacers' affect on rollover angle?

[andreylights]

Hey all! I am curious to see if someone with more knowledgeable of physics than I am could voice an opinion regards to the rollovers and the width of the wheelbase.

My setup is not ideal, as I believe I have a pretty high COG, since I ran a tall-ish lift of 3" front and rear, on some skinny pizza cutters and do have an RTT on the stock rails. Every time when I go off camber its breathtaking haha. I would think that increasing the distance between the wheels should make the vehicle more stable.

Question is: will 2.5" of difference (I think average wheel spacer is like 1.25"?) make a significant enough impact on stability to offset the price and potential additional wear on the wheel bearings?

PFA

 

[xtremewlr]

Hey all! I am curious to see if someone with more knowledgeable of physics than I am could voice an opinion regards to the rollovers and the width of the wheelbase.

My setup is not ideal, as I believe I have a pretty high COG, since I ran a tall-ish lift of 3" front and rear, on some skinny pizza cutters and do have an RTT on the stock rails. Every time when I go off camber its breathtaking haha. I would think that increasing the distance between the wheels should make the vehicle more stable.

Question is: will 2.5" of difference (I think average wheel spacer is like 1.25"?) make a significant enough impact on stability to offset the price and potential additional wear on the wheel bearings?

PFA

Won't hurt to be slightly wider but I don't think it will make a huge difference. There's actually not a ton of additional wear on the wheel bearings either.

 

[MrSeth]

I have noticed a difference with the feeling of being "planted", however, I do not have a RTT.

I'm running 1.25" spacers with a -12mm 9"wide wheel with 315's. I think that the heavier tire/wheelset might be helping me out, but my lift is also taller at 4" suspension and 1.5" Body.

Wide wheels, wide stance, I feel make it more proportionate when looking at dimensions of width vs height. Go taller? Go wider.

Almost done with a 12 hour shift, so that might not make any sense at all. :faint:

 

[RonJR]

So, lets make a couple of assumptions, and do some quick calculations.
a) assume COG is 30 inches above ground.
b) Track width stock is 63 inches.

In that case, theoretical static (ie, on a tilt table) roll-over angle is atan((63/2)/30)= 46.4 degrees
With the spacers, track width is 65.5, so roll-over angle is atan((65.2/2)/30) = 47.4 degrees.

So, not much difference. Notice a couple of things, though.
1) The static rollover angle is much higher than you think. Most of the weight of the vehicle is engine, transmission, frame, and axles, all of which are mostly well below 36 inches above the ground, thus the estimate of 30 inches for the actual COG. On a stock vehicle, it's probably closer to 26 inches or so.
2) DO NOT rely on these numbers for maximum safe tilt angle when offroading. Dropping your down hill wheels into a hole will start a rolling momentum that can carry you over at much more shallow angles, especially if you have a heavy weight, (i.e., RTT) on the roof rack. Computing the dynamic roll over angle is much more complex, and requires knowledge of moment of roll-over inertia, speed, road surface, etc. Not easy to predict.

I get nervous at about 25 degrees, and prefer not to push it further than that.

One thing I've noticed is that >20 degrees of tilt on the trail seems steep and uncomfortable. However, watching my tilt meter on the highway while going around sharp curves such as a roundabout, I regularly hit 20 degrees on the meter and think nothing of it. So a lot of it is a matter of perception.

 

[andreylights]

Won't hurt to be slightly wider but I don't think it will make a huge difference. There's actually not a ton of additional wear on the wheel bearings either.

AKA "you are overthinking this stuff"? seems like in your opinion its not worth it.

I have noticed a difference with the feeling of being "planted", however, I do not have a RTT.

I'm running 1.25" spacers with a -12mm 9"wide wheel with 315's. I think that the heavier tire/wheelset might be helping me out, but my lift is also taller at 4" suspension and 1.5" Body.

Wide wheels, wide stance, I feel make it more proportionate when looking at dimensions of width vs height. Go taller? Go wider.

Almost done with a 12 hour shift, so that might not make any sense at all. :faint:

You have noticed a difference after you installed the wheel spacers? Because 315 tires / new offset -- a lot of factors that could influence the judgement. I do agree, tho, wider stance makes the 4runner look so much better.

So, lets make a couple of assumptions, and do some quick calculations.
a) assume COG is 30 inches above ground.
b) Track width stock is 63 inches.

In that case, theoretical static (ie, on a tilt table) roll-over angle is atan((63/2)/30)= 46.4 degrees
With the spacers, track width is 65.5, so roll-over angle is atan((65.2/2)/30) = 47.4 degrees.

So, not much difference. Notice a couple of things, though.
1) The static rollover angle is much higher than you think. Most of the weight of the vehicle is engine, transmission, frame, and axles, all of which are mostly well below 36 inches above the ground, thus the estimate of 30 inches for the actual COG. On a stock vehicle, it's probably closer to 26 inches or so.
2) DO NOT rely on these numbers for maximum safe tilt angle when offroading. Dropping your down hill wheels into a hole will start a rolling momentum that can carry you over at much more shallow angles, especially if you have a heavy weight, (i.e., RTT) on the roof rack. Computing the dynamic roll over angle is much more complex, and requires knowledge of moment of roll-over inertia, speed, road surface, etc. Not easy to predict.

I get nervous at about 25 degrees, and prefer not to push it further than that.

One thing I've noticed is that >20 degrees of tilt on the trail seems steep and uncomfortable. However, watching my tilt meter on the highway while going around sharp curves such as a roundabout, I regularly hit 20 degrees on the meter and think nothing of it. So a lot of it is a matter of perception.

Thats a great post! Yeah, as I suspected the difference in math is not huge. And of course I fully understand the simplifications what went into the calculations (comparing to the real world), I wanted to know the scale of spacers effect and +/- 1 degree is pretty negligible I am assuming.