CASTER: How much do you have? Why?

[OLDE GUY]

We have this discussion going on the General Forum and thought that we would ask the serious trackers and racers to join in.

http://www.nsxprime.com/forums/showthread.php?p=371829&posted=1#post371829


Ponyboy: If you can lower it a bit more, you should be able to get more front camber. I've got mine to as much as 2.5 degrees with 10 degrees of caster.

Olde Guy: Thanks for responding and the input. I do think that the 3/8 inch front lowering helped increase the front camber from negative 1.3 to negative 1.6 degrees.

Does increasing the caster help gain additional negative camber? How has increasing the caster from 8 degrees to 10 degrees changed the handling of your NSX? What do you think that it accomplishes?

Ponyboy: I can answer the question in theory. The more positive caster the more negative camber the outside wheel gains in a corner - while the inside wheel gains positive camber.

I think this is an interesting question. Maybe if Chris or Seth sees this thread they can add to it.

 

[NSXDreamer2]

PLEASE, INPUT INPUT....

I'm anxious to learn more about the relationship between the caster, camber and toe...

 

[Edgemts]

Just my $.02
I dont know much about car suspension dynamics YET! but I went to Summit Point yesterday with my New to me '93 track NSX.
I had a 4 wheel alignment done to ~nsxr specs
will get printout and give you exact later.
Braking was good, turn in was great, much less understeer than my '94 set at ~stock nsx specs.
Biggest problem I had was with the rear, (Worn street tires so???) rear was very sensitive, I dont know yet if it was the tires or rear camber or???.
Drive out of turns was good, entrances and expecially off camber turns were very touchy.

 

[Dave Hardy]

The post is correct in stating that more caster leads to more camber when the wheel is turned. Think about the extremes - Assume you have 8 degrees of caster and 0 degrees of camber. With the wheels pointed straight you have 0 total camber. With the wheels turned 90 degrees to the right (impossible, I know) then your outside wheel (left) has 8 degrees of total negative camber and your inside wheel (right) has 8 degrees of total positive camber. Now back off of the extremes and look at it more real world. Let's say you have 2 degrees of camber and 8 degrees of caster. The wheel is turned 30 degrees. This causes camber gain. How much gain takes more math than this discussion warrents. You also have body roll that subtracts effective camber, which is the whole reason you need caster in the first place. The compression adds some camber, but not enough to counteract the body roll.

For an example of extreme caster, look at late model Mercedes. Those cars run a shitload of caster. Take a look at one that is parked with it's wheels turned sharply. You'll see that the tires are leaning into the turn. That's from the caster. They need all of that caster because they are softly sprung and have a lot of body roll.

The goal, as always, is to keep the tire in it's happy place. Caster helps it do that. Caster has side effects related to steering effort and track stability, but the primary goal is camber gain with the wheel turned.

 

[LJSB]

Nice explanation.

 

[Edgemts]

Question for Ponyboy
you say you are running -2.5 deg camber and 10 deg caster.
What are your thoughts on that set-up? Much better front grip?
What about braking, tire life, steering feel??

What are your rear settings to match front?
Thanks

 

[OLDE GUY]

Caster has side effects related to steering effort and track stability, but the primary goal is camber gain with the wheel turned.

David Hardy - Thanks for the excellent explanation.

Could you elaborate on the "side effects" of a large amount of caster? This discussion began on the other Thread about NSX-R suspension alignment. That suspension has about 600# of spring stiffness on the front and 485# on the rear thus greatly decreasing NSX body roll.

I assume that when you refer to "steering effort", you mean that once you have turned the steering wheel a little it become easier to turn because of the caster lean. What do you mean by "track stability"? My NSX has 8.7 degrees of caster and Ponyboy's as 10 degrees. Any thoughts on how much caster is helpful on the track (Driver's Education - not racing) for an NSX? Thanks for your help. Bill

 

[NSXDreamer2]

I also just check my alignment, and I'm having 6.5 degrees of caster.. I'm also wondering what I should expect if I raise the caster to say, 8.5 or 9?? Handling, tire life...etc?

 

[1BADNSX]

Ground control who are best known for their BMW suspensions have the best discussion I have seen about caster.

"Camber is the angle at which the top of the tire is tilted in, as viewed from the front of the car. As the front tires are turned left and right, the camber changes slightly because the pivoting points for the tire are not vertical as viewed from the side. If the car has positive caster, as most every racecar does, the topmost pivot is behind the lower pivot and this causes the tire to tilt in more at the top as the tire is steered inward. This small amount of negative camber gain is the most common reason for the popular misconception that a lot of caster is a good thing.

While it is true that most cars DO handle better with more caster than the factory spec, and many handle well with as much caster as possible within the limitations of the body structure, it is definitely a fallacy that "more is better".

The most confusing thing about too much caster is that the car can FEEL better, but actually be slower on the track. This is aggravated by the possibility that the car can feel so much better that the driver actually goes faster, even though the bumpsteer and corner weights are made worse. This occurence is the driver's problem for not going fast enough to begin with and there are books for that too.

Changing caster primarily affects four things, high speed stabilty, camber gain, bump steer characteristics and relative corner weights (wedge). There is no disagreement that high speed stability is a good thing, so extra caster is a plus there. Camber gain with extra caster just happens to be in the direction we want, more negative, so that's good too, however the amount is usually greatly overestimated as shown in the example below. Bump steer however is affected adversely, but this can be changed, however I have seen many racers get caught out by this one. Corner weights are the big problem with too much caster, as extra caster definitely affects an otherwise balanced racecar for the worse.

What occurs with extra ("too much") caster is that more and more weight is transferred off of the outside front and inside rear tires, while this may at first sound good because taking the load off the outside front CAN be good, the reality is that the outside rear tire will be doing too much work in the middle of the turn, so steps then taken to alleviate this will cause a corner entry push. Additionally, on any rear wheel drive car the inside rear tire will be light and won't come off the corners well. Remember we're talking about a well balanced car here, not a car where this extra caster covers up a sway bar or spring problem.

There's nothing like a good example so here are some actual numbers from the use of data acquisition, a set of electronic scales and an alignment machine. With caster + 3.5, camber -1.5,when the tires are turned 7 degrees as typical for sharp hairpin, the camber gain was 0.35 degrees (not much!) however the corner weights changed by 22 on just the outside rear tire. With caster +5.0, camber -1.5, and 7 degrees toe-in, the camber gain was 0.50 degrees (still not much), but the corner weight changed 35 lbs. on the outside rear tire, which is just too much. The most interesting item in these examples is actually how little the camber gain changed. "

For an NSX, I would run the stock caster to avoid changes to corner-weight, bump-steer and steering effort. Set the static negative camber high enough for track work. The ever stated advantage of negative camber gain due to caster is somewhat overblow.

Bob

 

[OLDE GUY]

" .....the camber gain was 0.50 degrees (still not much), but the corner weight changed 35 lbs. on the outside rear tire, which is just too much. The most interesting item in these examples is actually how little the camber gain changed. "

For an NSX, I would run the stock caster to avoid changes to corner-weight, bump-steer and steering effort. Set the static negative camber high enough for track work. The ever stated advantage of negative camber gain due to caster is somewhat overblow.

Bob

Bob - This is very useful information. Thank you. Bill

 

[Mark911]

Everyone has their theories when it comes to vehicle dynamics. As far as caster goes, there’s a direct relationship between it, kingpin inclination, scrub radius and any subsequent camber change. But I agree with Ground Control that the main effect on handling is in it’s ability to statically jack weight into the diagonal corners. In my opinion, the reason Honda designed in so much caster is to help in corner turn-in. At this point in the cornering dynamics, very little dynamic weight transfer is happening as significant cornering loads have yet to be developed. To get the car to start turning in requires that the inside front wheel be loaded and generating slip angles as soon as possible. That’s why Honda incorporates NEGATIVE front toe (toe-out), since it gets the inner front turned in more than and faster than toe-in. The down side is instability (darting) under breaking/bumps. Honda addressed that with the “front compliance mechanism” which reduces toe during breaking and/or hitting bumps. Very smart, although I see people “locking out” this feature which doesn’t make sense to me except for a full on race car. In addition, static weight jacking created by caster also unloads the inner rear wheel, another valuable dynamic for quick turn-in (have you ever tried to turn a vehicle with a solid rear axle)? Although not a sold axle, even the limited slip on the NSX contributes to pushing. By the time you really start to build up cornering forces, dynamic weight transfer overshadows most of the static weight transfer and unless your in turn 8 at Willow you should be unwinding the steering angle a bit in anticipation for corner exit. On corner exit you’ll be tracking the car out which unloads the outer rear a bit (very desirable on the NSX to prevent oversteer) and loads the outer front (again to reduce oversteer). The ability to statically jack weight (wedge) into the corners is a tool the NASCAR boys have used for years to get around corners, but with caster it works for both right and left hand turns! Obviously, the stiffer sprung you are the more pronounced the effect of caster created static weight transfer. Just my theory . . . .

 

[Ponyboy]

Wow...good posts here. 1BADNSX, you need to post more. I eat that technical stuff up like Frosted Flakes and whole milk.

Question for Ponyboy
you say you are running -2.5 deg camber and 10 deg caster.
What are your thoughts on that set-up? Much better front grip?
What about braking, tire life, steering feel??

What are your rear settings to match front?
Thanks

Good question but it's tough to answer. I'm running 4mm toe out and I hate it. Once the fronts hit a rut the car follows it like a slot car. I'm going to get it realigned with the stock toe settings and start with that as my baseline. I have had experience with camber and even with the 2.5 degree of neg cam I'm still wearing the outside edge of the front and rear tires. Next season I'll have a pyrometer to help dial it in but I see CTech front camber bushings in my future. Hopefully, I can get them to fit.

 

[OLDE GUY]

Ground Control who are best known for their BMW suspensions......What occurs with ...."too much" caster is ......the outside rear tire will be doing too much work in the middle of the turn..... and the inside rear tire will be light and won't come off the corners well. Bob

Mark911 - Thank you as well for your excellent comments which I think are more NSX specific.

1BADNSX and Mark911 - Regarding the above quote: what does "too much" caster produce - understeer or oversteer? What is the symptom that I should look for? Thanks again,,,Bill

 

[Mark911]

I’ve found that handling is in the eyes of the driver. In other words, five different drivers will come away with different assessments of what the same car is doing in the corners. And each corner has at least three distinct phases. Corner entry (or turn-in), steady state, and corner exit (tracking out). Entry and exit are transition phases where a whole lot of variables are constantly changing. In my opinion that’s where the fun is. Steady state is exactly that, the car is dynamically in equilibrium (not necessary balanced, just not changing). In some cases the steady state period is so quick for all practical purposes it doesn’t occur. A quick 2nd gear 90 degree turn for example. On the other hand some constant radius corners seem to go on forever, just ask the oval track guys. It helps when troubleshooting handing issues to identify what phase is giving you problems. Bottom line, the car must turn (rotate) about its Z axis so that after the process it’s heading in another direction (hopefully!). Where and how quickly (or slowly) this rotation occurs is very driver dependent, therefore cornering is very dependent on driver style. Although you can find dozens of books that say there is ONLY one correct way to drive I don’t buy it. Of course there are a handful of basic “Dos and Don’ts” that should be followed, but racing would be pretty boring if there was only one correct line and one correct way to drive and everyone followed it. So, in addition to figuring out what part of the cornering process is giving you problems I’d also evaluate your driving style. Are you more comfortable being smooth and precise or are you more on the ragged edge cut and thrust type? You can set up your car to work either way. Which way is faster (or more fun!) is a personal thing. As a general rule a driver that loves one style will hate the car setup for the other and vise versa. That’s why it’s not always very helpful to ask what other people feel is “the best” setup. It might be best for them, their speed, their track, and their style but it doesn’t always translate into what’s best for you.

 

[OLDE GUY]

Mark911 - I sense a lot of wisdom in your remarks. Fortunately for me, my NSX-R suspension is not adjustable since I wouldn't know how to adjust it - and therefore my decision. I have opted for the 1991 spec alignment (according to the Hunter machine) plus max negative camber and 0.45 degrees additional caster at 8.7 degrees.

........MY 1994 NSX..............................MAXIMUMS FOR ZANARDI/NSX-S....

FRONT: Caster: 8.7 degrees.....................................8.5
Camber: negative 1.6 degrees.................................-0.7
Toe: negative 0.07 inch.........................................-0.09

REAR: Camber: negative 2.3 degrees........................-2.2
Toe: positive 0.10 inch..........................................+0.10

I don't expect that the additional caster will make much difference but I wanted to learn more about it since it is the one spec I am uncertain about. I appreciate everyone's input. I learned a lot! Bill

 

[Mark911]

FRONT: Caster: 8.7 degrees
Camber: negative 1.6 degrees
Toe: negative 0.7 inch

REAR: Camber: negative 2.3 degrees
Toe: positive 0.10 inch

Are you sure about that rear toe? Most NSXers make it as far Positive as possible without grinding up the tires too quickly. This counteracts the natural tendency for the rear end to come around. It would be great for autocross, however.

 

[OLDE GUY]

Quite sure that the factory recommendation for the REAR in 1991 is total toe of positive 6 mm +/- 1mm and in 1993 it was changed to positive 4 mm +/- 1mm. My measurements are in inches because that is what the Hunter machine uses. The actual range on the Hunter for each side is positive 0.06 to 0.10" ; my NSX is at positive 0.10" for each side.

I am certain that the factory recommendations are toe out in the front for reasons which you explained and for toe in in the rear which helps the rear to turn into the corner as the weight is transfered to the outer wheel. My NSX is at the upper limit of the 1991 REAR spec range in inches which incidentally is the same as for the Zanardi or type S. The Hunter has the upper limit for caster for the Zanardi/type S at 8.5 degrees so my car is only 0.20 above that.

I have the FAQ on "The Factory Alignment Settings" in front of me.

 

[Mark911]

Right, you want the rears toed in. Maybe I'm getting my positive and negative backwards, it's been awhile. I could have sworn that positive was toe out and negative toe in. I must be getting old . . . .

 

[1BADNSX]

1BADNSX and Mark911 - Regarding the above quote: what does "too much" caster produce - understeer or oversteer? What is the symptom that I should look for? Thanks again,,,Bill

Due to the “wedge”, extra caster would cause the rear weight transfer to increase slightly relative to the front, which is an oversteering effect, but this would change as your steering is reduced from the apex to corner exit. This is why adding it may just be masking the vehicles otherwise unbalanced setup.

Read Don Erb’s excellent post at:

http://www.nsxprime.com/FAQ/TireWheel/alignment.htm

I agree with Don that anywhere near stock caster is fine. I would leave it near stock for two reasons, 1) why mess with the NSX’s carefully engineered bump-steer, and 2) the NSX doesn’t need any extra steering effort.

I'm running 4mm toe out and I hate it. Once the fronts hit a rut the car follows it like a slot car. I'm going to get it realigned with the stock toe settings and start with that as my baseline. I have had experience with camber and even with the 2.5 degree of neg cam I'm still wearing the outside edge of the front and rear tires. Next season I'll have a pyrometer to help dial it in but I see CTech front camber bushings in my future. Hopefully, I can get them to fit.

From my experience with a dual purpose M3 (street/racecar), extra toe tends to eat tires quicker than extra camber. I run -3.5 degrees of camber and do fine with street tires because the toe-out isn’t extreme. Yes, get a pyrometer and don’t let anybody tell you that you want the temperatures to be even across the tire. For maximum grip, the inside temperature should be 15 to 30 degrees hotter than the outside with a linear distribution.

Wow...good posts here. 1BADNSX, you need to post more.

Thanks, I only post when I have a worthwhile contribution. I would hate to be considered a post whore. I already have 223 posts since July of 2000.

Bob

 

[Edgemts]

I am confused-
Front toe is negative .07 inches or .7 inches(~18mm???)doesnt seem right.
Is negative toe in or out?

On a track only NSX, what is the best set up to start with to get the car balanced???
Should front camber be maxed out?

 

[OLDE GUY]

I am confused-
Front toe is negative .07 inches or .7 inches(~18mm???)doesnt seem right.
Is negative toe in or out?

I typed it wrong initially and corrected my posts. It is Front 0.07" on the Hunter machine for each side which is in inches.

I calculate that 0.07 inch equals 1.78 mm. The maximum upper limit for the Zanardi/NSX-R of 0.09" calculates to 2.28 mm. These measurements are for each side. When added together one gets the total toe which can be compared with the front Factory recommendations for ALL years of negative 3.5 mm +/- 1mm or a range of 2.5 to 4.5 mm. For the Zanardi/NSX-S the maximum total toe is just outside this range at 4.57 mm.

A negative measurement of toe is toe out.

 

[Dave Hardy]

Side effects of Caster - The GC site explained it well.

I'm running 4mm toe out and I hate it. Once the fronts hit a rut the car follows it like a slot car.

Yep - Front toe out helps turn in. The balancing act is that it hurts high speed stability. In my Civic Racer I run 1/4" (6mm) of toe out in the front, with the rear at zero. At autocross speeds, the turn in is helpful and there is no real ill side effect because I rarely see 70 mph. I took it to the strip to see what 1/4 mile time it would run, and it gets pretty squirelly at 80+. I never street it, so that is acceptable.

Ask yourself what you want out of the car. In general, the better the car handles on a track, the more dangerous it is on the street. Not things like ultimate grip, which is helpful in both scenarios, but things like turn in, balance, etc. I run completely different setups in the Civic Racer and the CRX Daily, even though they have near identical suspensions. The CRX is neutral. If pushed it will understeer, and in extreme maneuvers it will step out a bit, but overall it is very balanced. The Civic in comparison is very loose. It is ultimately faster with this setup, but if I daily drove the Civic, I would back it into something within a month while avoiding a cabby or red light runner.

 

[OLDE GUY]

On a track only NSX, what is the best set up to start with to get the car balanced??? Should front camber be maxed out?

For a track only NSX initially go to the 1991 settings with maximum camber. Or slightly more aggressively go to the Zanardi/NSX-S settings which takes the caster to 8.5 degrees - still with maximum camber.

On a stock suspension you won't be able to get much more than front negative 1.3 degrees and rear negative 2.3 degrees of camber.

If your suspension will lower the car, you can get more negative camber but then you are out of my league. Talk with 1badnsx, Ponyboy, etc.

 

[Barn Man]

FRONT: Caster: 8.7 degrees
Camber: negative 1.6 degrees
Toe: negative 0.7 inch

REAR: Camber: negative 2.3 degrees
Toe: positive 0.10 inch

Are you sure about that rear toe being positive? Most NSXers make it as far negative as possible without grinding up the tires too quickly. This counteracts the natural tendency for the rear end to come around. It would be great for autocross, however.

The NSX uses negative toe in the front to assist with turn in just like it uses a ton of caster for the same. The rear uses possitive toe to keep the back end planted in turns. Think of it like the rear wheels are trying to drive the back end into the turn. With negative toe, the rear would get nuts and the car would feel loose. It's kinda like a friend described his 911 Twin turbo after a shitty alignment. He said, "Going around a turn it felt like you were trying to throw a dart backwards...the rear of the car just kept coming out on me".
That's what negative toe will do for the rear of an NSX as well. He had the aligment rechecked, and set to his old race spec.....like he asked them to do in the first place, and it felt much better......much more predictable. He / I like to have the ability to drive with the throttle instead of trying to keep the back end under control. When I go around a turn in my Integra on the track, I can work the throttle to make the car "wiggle" around the turn. It's a cross between understeer and oversteer.....I kinda look at it like the car has MILD understeer until you work the car through weight transfer. If I had an all out track car, I'd probably set it to be more neutral....but my daily driver has to be predictable. Being able to make the car do what you want instead of what it wants is nice! No surprises!
Have a great day all,
Barney

 

[Dave Hardy]

I've never heard toe refered to as positive or negative outside of this forum. It's always been refered to as toe in / toe out. I believe you are refering to toe in as positive, but can you confirm?