TTopJohn

Is there any downside to maxing out caster? This would be somewhere between +4 and +4.5 given stock suspension I believe.

I know increasing + caster increases your high speed stability. But is there any downside?

This caster would be run with the ususal recommended -.5 to -.7 Camber, and a bit of Toe In (.1?) in an attempt to make the car run the interstate like a freight train - or at least track as true as possible with 245 tires.

Cal

iTrader: (1)

Nope, already a lot of people running that range for caster. I would set the toe to zero though, otherwise you'll be chewing up your front tires.

TTopJohn

So increased caster doesn't have any downside at all?

Toe - it looks like I'll need a bit of toe in to avoid hunting and wandering. My commute puts me on a lot of uneven road surfaces, and if it's possible, I want the car to track dead straight and I'll trade away a bit of turn in response to get that.
Most factory alignment specs call for a bit of toe in, and don't result in undue tire wear - is .1 toe in too much?

Jason98Zee

Actually caster will affect the rate of your turning radius.. its called Camber Roll.. If you adjust it in effect your car will not turn as good, or it could be better.. but should have no effect on tirewear. however EVERYTHING you adjust effects toe.. so make sure you adjust that after everything else is where you want it.

Cal

iTrader: (1)

I doubt you need any toe in to avoid hunting and wandering, althought you could try a small about if your having those kind of problems already. A narrower tire will help with this more than anything else. I recently went from 3/32 toe in to 1/32 toe out and didn't notice any increased wandering. Most autoXers max out both the castor and camber to improve low speed turning, as I have done.

TTopJohn

Regarding Toe
Running stock size 245/50/16 Firehawk SZ50 EPs right now. That's as narrow as I'm willing to go given the weight of the car and the amount of traction I desire. I realize that in 1986 when they first put this size tire on IROC-Zs it was considered a wide low profile tire, inherently more likely to follow ruts than say a 235/60/15. But now we've got wider, lower profile tires as OEM on C5 Corvettes, and they seem to track dead straight down the interstate.

In any event, according to general suspension theory, a bit of toe in will reduce the inherent tendancy of a wide low profile tire to hunt and wander over truck ruts in the road. Are you saying that in your experience this is not true?

Regarding Caster, you say maximizing caster improves your low speed turning ability. But Jason above you says it increases the turning radius, makeing the car harder to turn(presumably at low speeds)? I'm a bit confused now.

Cal

iTrader: (1)

Yeah I had one of the first IROC-Zs' (an '85) and that thing was all over the road following every crevice. It had the 245's from the factory. For some reason, the 4th gens are much better about this.

Yes, a bit of toe in will help, I'm just saying you don't need it on a 4th gen; I have zero problems running up to 1/32 toe out, and that's with 275's on the front. Try it at 0.00" and see if you like that before going to toe in. I ran 3/32 of toe in for some Land Speed attempts, and left it that way; my tires were soon chewed up.

Caster makes the tires tip into the curve whenever you turn, so that's more positve camber on the inside tire and more negative camber on the outside tire which gives the tires more lateral grip. The increased caster increases turning effort some, but with power steering you don't notice it. I think most autoXers agree that it's more important to get as much negative camber as possible, but you can max out the castor with what's left over. For this type of wheel alignment, you don't even need a caster/camber gauge; you can just go to the outside of both slots. But then you've got to reset the toe for sure! I had about two inches of toe-in after doing this!!

TTopJohn

Thanks Cal,

Caster - you confirmed my plans to more or less max out negative camber, which should be about -.7 since I'll be at stock ride height less 3/4inch with the lower perch on the Konis) and then max out positive caster with whatever adjustment room is left.

Toe - Okay, I think we're chasing two different things here. I think you're right that there's no problem running 0 toe, the car will track fine. But I'd like to make it better. I'd like it to have that Mercedes/BMW(and to a certain degree - Cadillac) ability to track so dead freight train straight that at triple digit speeds it speeds it feels as if you could take your hands off the wheel. If this is possible without compromising tire life, I'll do it. Basically, I want your land speed record stablity any time I get a wild hair to go over 100mph.

3/32nds of toe in chewed your tires up, so perhaps 1/32nd of toe in? It's within factory specs. GM uses 1.8mm toe in on the Saab version of the WRX to enhance on center feel and straight line stability, I presume they wouldn't do that if it was going to chew up tires within the warranty period.


Or does running that toe in work fine if you use all factory alignment specs, but become a problem when combined with Max + Caster and Max - Camber? Seems that with those settings, at 1/32nd toe in the tire is experiencign more negative camber than it would be at 1/32nd toe in with factory (lesser) camber and caster settings. Which would increase tire wear, though the toe setting remains the same.

Cal

iTrader: (1)

I think your tires would be safe from excessive wear at 1/32 toe-in, but I would still try 0-0 first if you aren't paying a bunch of money for every change (i.e. doing it yourself.) I believe some of the Open Road Racing guys are running 0-0 toe-in, and they are at around -0.5 camber. These guys spend a lot of time everywhere from 100 mph to 200 mph on different road surfaces.

At the time I chewed up my front tires, I had about that camber along with the 3/32 toe in. At present I've got 1/32 toe out (total, 1/64 each wheel) along with -1.7 camber and max caster (haven't measured caster but it's maxed out) and that seems to be the sweetest setup yet. I autox as well as drive fast on the freeway from time to time.

I had 1/16 toe out (total) for a while and straight line stability was still excellent; I could let go of the wheel at 100 mph no problem . . . BUT, if the car ever hit a bump, the suspension felt unsetled. So based on my experiance, any toe-in is overkill for stability, but you don't want much toe-out either unless you never go over 100 mph.

The best thing you can do IMO is get some good alignment tools and knowledge, and do your own alignments. That way you can find out what is best for your car and the way you drive it. Wheel alignment makes more difference than most people think, and the factory wheel alignment is very crude.

mitchntx

iTrader: (14)

John ... you graduated LSU in an engineering field didn't you ...

TTopJohn

LOL at Mitch - nope, Business Administration. And while I attended LSU, I graduated from SMU.

Cal,

See, that's the thing - I don't currently have the facilities to set my own alignment. Buying the needed tools (for one I need a new jack) would cost 4x more than what I'm going to pay for this alignment, and I'd still be doing it in an apartment complex parking lot. They get pissy enough about me doing oil changes out there

So if the general consensus is that I can get away with a touch of toe in, I'd like to go ahead and set it up that way.

Now if 1/32nd is "a touch of toe in", Is that total (1/64 toe in per tire), or is it 1/32nd toe in per tire?

Cal

iTrader: (1)

You could have 1/32" per wheel toe in for a total of 1/16" if you wanted. While castor and camber setting require specailized tools, you can do toe in without anything fancy. Just a couple of straight pieces of metal to hold against the tires, a tape mearsure, and a couple of helpers.

jRaskell

iTrader: (1)

Caster, Cal. Caster. Castor is what you use on kids who've drank something they weren't supposed to drink (or when you're just feeling a little sadistic. We all get those feelings from time to time... don't we?)

Cal

iTrader: (1)

Whoops, well I spelled it right in a couple of my other posts above . . . hey I've drank that stuff before, talk about nasty! And that Mag-Citrate crap isn't any better IMO.

jRaskell

iTrader: (1)

Ya, I noticed it was just a slip up, but I couldn't resist the castor crack.

Cal

iTrader: (1)

I think I've caught myself trying to spell it that way several times, I need to work on that! LOL

The best use for castor oil IMO is to put in two-stroke premix fuel for model airplane engines, not to drink! And even as premix lube, synthetic oil is cleaner.

jRaskell

iTrader: (1)

Found an older post where you used Castor in the Road Racing forum Cal. About a month old. I was tempted...

And do you fly model airplanes? I have a duraplanes 60 trainer that I fly from time to time. I just use airplane fuel bought at the hobby shop though.

This is a pic about 97% built. Just had the ailerons to finish up. It's looking a bit rougher now, having taken a few emergency brush landings, and a little patching up here and there.

Cal

iTrader: (1)

"Found an older post where you used Castor in the Road Racing forum Cal."
Oh no I'm busted! Guess that shows I've spent too many years with model fuel.

Hey that plane is a familiar sight! My trainer was a "Sturdy Birdy," a very similar design only a tail-dragger. I loved the downspout tubing fuse; could buy it cheap in 10 foot lengths from the hardware store. Must have rebuilt that thing 100 times. I've built many rc planes, but my favorite was a 40 sized "Ugly Stick" fitted with a Super Tigre 90 engine. Could hang on the prop and do vertical take-offs at half throttle! Finally started flying helicopters and ended up with a JR Vigor, a 60 sized heli; very challenging but rewarding also. Due to the high cost of heli fuel, I got into mixing my own. For the last three years I've just been working on cars, but miss RC and will get back to it some time for sure.