2009 Toyota Land Cruiser Wheel Alignement and Kingpin Angle / Steering Inclination
Optimum scrub radius thread (2 Viewers)
- Thread starter highfructose
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I don't think anyone is saying factory scrub is zero. That's not the goal. But it is optimally correct given factory tuning and dynamics they've developed for the 200-series.
It's a baseline from which we're using to modify. To preserve factory qualities. Or not.
It's a baseline from which we're using to modify. To preserve factory qualities. Or not.
Good stuff i needed you to flesh out for me LOL.
Two things.
LX camber is done by my educated guess of highway stability due to ahc lowering at speed, which is awesome.
Part of the reason for any negligibility of scrub Is that the relationship between camber and caster during sweep will mean that an outside wheel will be gripping at the inner shoulder and inside the opposite as camber is further translated. These forces counteracting will hide things by being “balanced”, but generally not good for dynamic handling since the extremes are both exaggerated. That being said there are positives too such as track width considerations and aggressive appearance and perhaps wearing both shoulders more evenly as the inside shoulder does not get the same road friction in OEM geometry which both of my stock ahc LX exhibited. You will get less grip in corners but that can also be hidden by wider tires.
In my own plumb experiments, I've added about 7mm on my 100 in order to correct for 33" tires to reset scrub.
scottm
SILVER Star
Do 200s come with larger stock tires in other markets? I think the 80 did, and Slee sold a gear for the diff that corrected the drivetrain and speedo.
AFAIK, the TRD forged accessory wheels fitted with LT285/70R17 (C) ATs is the only optional offering. LXs had a forged 22” wheel as well, not sure of tire size on that. As it pertains to offset, the TRD wheels have 50mm positive offset.
I thought that 22” was a knockoff. Whered they sell that? Crazy fitment lol
Bringing this thread back up to the top as there's offset and scrub radius questions in other threads of late. The compromises and symptoms to aggressive offsets I think are clear. Understanding why might be a bit more difficult.
Re-using this picture, the zero scrub radius point at the tire contact patch is where the tire pivots as it steers. Besides that simple fact, this magical point has other qualities. Imagine the black line to be a piano hinge. One takeaway is that as you push on the spine of the hinge, the forces don't result in a torque or steering force. The further away from the spine or pivot that you apply that force, and there starts to be a lever arm creating steering forces.
That has consequence to the steering rack. As the front tires hit obstacles, normally it would just be absorbed by that magic pivot point which is the suspension kingpin structure. With more wheel offset providing a lever arm, those forces now have to be absorbed to a degree by the steering rack. And also to the drivers hand. This is why with poor offsets that there begins to be more feedback and undesirable push/pull when hitting uneven terrain, braking, or trying to put down power.
There are longer term consequences too. As the steering rack is absorbing more degree of forces, it is subject to increased wear and tear. The internal hydraulic pressures are higher too. This maybe why we're starting to see some racks in higher mileage wear out the power steering pump and develop leaks in the high pressure lines. Yes, wheeling and rock crawling puts more load on the steering so that's definitely a part of increased wear, but that's also compounded by aggressive offsets.
I get using low offsets for stance. That could be equally achieved with wide tires that push the outside of the tire just as far, while providing balance with more rubber on the other side of the zero scrub radius line to neutralize scrub radius impacts.
Re-using this picture, the zero scrub radius point at the tire contact patch is where the tire pivots as it steers. Besides that simple fact, this magical point has other qualities. Imagine the black line to be a piano hinge. One takeaway is that as you push on the spine of the hinge, the forces don't result in a torque or steering force. The further away from the spine or pivot that you apply that force, and there starts to be a lever arm creating steering forces.
That has consequence to the steering rack. As the front tires hit obstacles, normally it would just be absorbed by that magic pivot point which is the suspension kingpin structure. With more wheel offset providing a lever arm, those forces now have to be absorbed to a degree by the steering rack. And also to the drivers hand. This is why with poor offsets that there begins to be more feedback and undesirable push/pull when hitting uneven terrain, braking, or trying to put down power.
There are longer term consequences too. As the steering rack is absorbing more degree of forces, it is subject to increased wear and tear. The internal hydraulic pressures are higher too. This maybe why we're starting to see some racks in higher mileage wear out the power steering pump and develop leaks in the high pressure lines. Yes, wheeling and rock crawling puts more load on the steering so that's definitely a part of increased wear, but that's also compounded by aggressive offsets.
I get using low offsets for stance. That could be equally achieved with wide tires that push the outside of the tire just as far, while providing balance with more rubber on the other side of the zero scrub radius line to neutralize scrub radius impacts.
Which makes you wonder why a huge amount of the aftermarket 5x150 wheels out there are like +10 or +0. I really struggled to find a 17" wheel that was anything more positive than +25. Method has a few +35's and the Evo Corses usually seem to be +40. Other than that you are at <=+25.
Bros gotta Doze
@TeCKis300 would a change in tire diameter (larger) also result in a change in scrub radius?
Would that also need to be reflected in the choice of wheel offset to allow the red and black lines to meet at the pavement surface as intended?
Would that also need to be reflected in the choice of wheel offset to allow the red and black lines to meet at the pavement surface as intended?
Yes! @lx200inAR had a nice table earlier in this thread below.
+35 offset seems to strike a good balance for typical upsized tires between 33-35". It also makes clearance and fitment about as easy as possible for those sizes to drop in.
Another aspect to consider, the moment/torque forcing marginal toe-out during hard braking. In a derivative/static scenario, the tire center being one of the pivot points further out from the braking friction, creates a non-trivial amount of additional moment through the wheel. Spacing out of OE scrub spec has this consequence.
