3rd gen caster

Just wondering what a good caster setting is. When I took my truck into get aligned they set it at 1 degree. Is it just me or does that seem too little. And if so what difference does it make? I am running 255/80r17 cooper st maxx's on raceline rims 0 offset. and 2.5" spacer lift.

 

Set it for what you need. Some people need more.

What are you trying to accomplish?

 

Well the my truck is in perfect alignment but still pulls off to the right. Im pretty sure this is because of the tread pattern on the st maxx's and obviously road crown. But it is pulling a little too much for my liking. Wouldn't adjusting the the caster to be more positive make this less

 

You would want more camber for road crown I think.

 

Really? wont that wear my tires unevenly tho?

 

It’s only a little bit of camber not enough to cause significant tire wear.

I think most people shoot for 2 degrees caster though.

 

More caster will give you more self centering effect in the steering, but if it's pulling, you generally have a caster differential problem. Most good alignment shops will set the left side about 1/2 degree less than the right to counter road crown. The vehicle pull toward the lower caster side. if your caster is equal right and left, that's your cause right there. I'd shoot for something like +2.5 on the right and +2 on the left or something in that range. It will depend somewhat on how much adjustment is available on your truck. The factory specs have a fairly wide range for camber but try to have that as neutral as possible or even a tick negative. Don't let any alignment shop tell you "It's within spec" and blow you off that way. There's an acceptable range in all the specs but you can easily be "in spec" and have it drive like shit if your alignment guy is lazy - like too many of them.

 

You should want between .3-.5 cross castor difference for road crown. I’ve got 3.0 castor cause clearance issues

 

Whenever I have had an alignment, I get the report that shows the red and green areas of each tire and am told it is within spec. Two questions: Is it possible to get each adjustment "dead nuts' on and, is there any advantage? Appreciate your thoughts. Stock '17 Limited.

 

I'm not sure what your asking? The closer to the actual recommended numbers the better but every vehicle is different. There are so many variables when doing alignments and one vehicle with certain numbers may drive great with no tire wear and another could pull and wear tires. Thing like tires, vehicle height, accessories installed, road crown differences form location and even the driver's weight can all effect drivability.

 

Castor is 2.2 for stock tires.
For 33s, you want about 2.8.
Here's a good primer on alignment.
http://aligncraft.com/terms/terms.html

 

A lot of lazy techs will show you that report and tell you it's "in spec". But you can have both sides in spec and, because there's a range to the spec, have it pull or otherwise drive weird or wear your tires more than it should. The exact caster number isn't as important as having the differential between left and right, with the left side (for RHD countries) being slightly less. Remember that the truck will pull toward the lower number side. That's what compensates for road crown. That can also cause it to pull very slightly on perfectly flat roads, but since most roads are crowned, alignments usually are set to compensate for that. You CAN get the number on both sides to be "perfect" but often that takes a lot of going back and forth and a couple of tenths of a degree simply doesn't matter. It might if your were racing but we're talking trucks here. You also have to be able to communicate with the alignment tech in a way that doesn't insult him or make you look like you don't know what you're asking. Rather that telling him what to do, ask if this might be possible. I often have them, incorrectly, tell me that having a very slight negative camber on my truck (minus .2 to minus .3 deg) will wear the insides of the tires. I just tell them I'll take my chances. It's really too much toe-in or toe-out that wears tires fast. The rear on my 911 are just over 2 deg. minus and even that doesn't cause excessive wear. The advantage of having it right is that, hopefully, it will drive better, be safer, handle better and even get slightly better mileage, assuming you're driving on pavement.

 

Not disagreeing with you at all but could you explain why more caster is better for larger tires? Thanks.

 

The way I wrote that, I could see why you came to that conclusion.
You actually gain trail(caster offset) when going to a taller tire. It's mainly to give an agressive tire with a longer footprint, a little bit more trail than stock. In that regard, I'm actually pretty conservative when it comes to suggesting caster numbers. I've never given number outside the green.

 

With our trucks, higher caster generally allows for larger tires because the wheel is shifted forward, giving more room to the cab mount.

However, caster means different things. You can have two trucks with the same caster but one truck may have significantly more wheel space than the other because of how the cam bolts were positioned.

You can actually have equal caster on a truck with one wheel more forward than the other. Seems odd right?

I have about 2.8 caster if I recall correctly and easily fit 35s, not because I have 2.8 caster but because I had the cam bolts positioned to shift the entire wheel and axle forward

 

This is the first time I've seen someone use the term "trail" in this regard. We've been using that term for decades in regards to bicycle suspension and how it affects how a bike rides and handles, but I can see how it applies just the same. And having just finished brazing up a hard steel fork for an old mountain bike I made, I'm acutely aware of it.