163 replies to this topic

[Jim Drago]

 

 

 

 

Well...I just know what I see and what some of the set up guys local lean toward...but not every car or driver likes the same thing or drives the same way. 

IMO the reason many run a stiffer rear bar is because they rake they car so much.. If you ever plot the roll centers of these cars, you would not see any reason to run positive rake. 

[Steve Scheifler]

Yeah, geometry is flaky when lowered so much without changing pickup points so “normal” rules may not apply. But I would normally expect more rake to increase the tendency to rotate which would be good if the car tends to push. Similarly a stiffer rear bar setting should tend toward oversteer. The two may be somewhat different in terms of where, when and how they change the balance but normally both should be in a similar direction. Having very little experience with NBs I’ve always been a bit surprised that so many people run flat or even negative rake and never go stiffer than minimum on the rear. I thought one of the knocks on them was a tendency to push? But again, everything about this suspension package is a compromise so real-world testing and results are what matter. In the 1.6 we always used rake to get a bit more rotation because a stiffer rear bar seemed more inclined to overheat the rear tires.

[Danny Steyn]

Beyond the order question(if everything is close to start last 2 steps aren't supper critical)...the NB chassis tend to run on the tight side. Odds are you will end up with a stiffer rear bar(turn in) and a ride height rake with the rear being higher. 

 

Ron, echoing Drago above, I would say that this is exactly opposite of what the fast guys run on the national circuit in NB cars. Just an FYI

[davew]

The order is really not important. I like to rough in the allignment and ride height, eyeball is good enough. Then you just keep going around the circle, cross, height camber, caster toe, repeat as often as needed. Every adjustment effects every other adjustment. So when you thing you are done, recheck everything again, as something may have changed.

 

I have found very often that people blame the set-up (make changes) based on poor driving and/or mechanical issues. Bad bushings, especially rear uppers can cause some weird handling issues. Look for bound sway bars. most importantly, if a SM pushes when the car is mechanically good, you are over driving the car. These cars should not push if you get them slowed down before turn-in. Foot should be off the brakes before turning the wheel, if not brake earlier.

 

Dave

[Ron Alan]

Ron, echoing Drago above, I would say that this is exactly opposite of what the fast guys run on the national circuit in NB cars. Just an FYI

So there is no misunderstanding on my part, more like first hole on rear sway bar(soft) and a flat to negative rake car? 

[DrDomm]

If we've accepted the "standard" rake and RSB setting, I'd like to hear people talk about camber settings.  I heard a wide variety of things last year, including at the Runoffs.  Just curious if there really is such a wide range (under 3 to over 4 degrees) amongst competitive drivers. 

[Jamz14]

These cars should not push if you get them slowed down before turn-in. Foot should be off the brakes before turning the wheel, if not brake earlier.
 
Dave

So are you saying that trail braking is a no no with these cars? Wouldn't trail braking and keeping weight on the nose help a pushy car?

[davew]

So are you saying that trail braking is a no no with these cars? Wouldn't trail braking and keeping weight on the nose help a pushy car?

 

No, the exact opposite. More weight means more work for the tire. Since a tire can only do so much, you end up with a push.

 

The fast guys will wear the left rear (clockwise track) faster than the left front. The weight is on the rear, because they are accelerating while you are still trying to make the corner.

 

The race from corner 1 to corner 2 will be won by the guy who accelerates first/most. If I get the car stopped and can be accelerating at turn in, flat before the apex. I will beat your trail brake every time (all things being equal).

 

Or think of it time wise. If you brake later and then trail brake, you will be accelerating on the incoming straight slightly longer. Let's say you accelerate 1 second longer. How much speed do you gain in 1 second at 100mph. Maybe 1 mph if you are lucky. And your advantage over me is for a very short (1 second) period of time. Now I get stopped and get on the gas 1 second before you do (it would probably be more like 2 seconds) at 50 mph. What speed will I gain in 1 second at 50mph. Probably more than 1 mph. But for arguements sake, let's call it 1 mph. But I gain 1 mph over the entire next straight away. Now I am 1 mph faster than you for the entire straight away, (let's say it is 10 seconds long) and you are faster than me the last 1 second. I would rather have that 1 mph advantage for 10 seconds than 1 second. Wouldn't you?

 

There are always a few exceptions, but at 99% of the corners, with 99% of the drivers; straight line brake, earlier to throttle will win 99% of the races. Again, all other things being equal.

 

I stand behind my statement, if a SM pushes it is either a mechaincal issue (i.e. allignment, bad part, binding suspension, etc) or the driver is over driving/trail braking.

 

Dave

[Jamz14]

Dave,

 

I don't disagree with you at all about which technique may be faster overall. Though I do think a case can be made that trail braking can be faster in more than 1% of corners. But strictly speaking about a car pushing and transferring weight to the front to help correct that: If transferring weigh to the front makes the car more pushy, then why is it that when people are learning to trail brake, or when they get it a bit wrong, it is the rear end coming around that happens and not nosing into the wall? I understand what you are saying about leaning on the front tires by braking and turning at the same time would cause the front to not have more traction available for turning. But the lightening of the rear end by trail braking seems to more than compensate for that and causes the rear end to come around if you get it wrong.

 

In regards to trail braking: If both techniques yield the same mid corner speed ( which in theory they should be able to ), then why is the guy that is coming to throttle sooner going to win to the next corner? All trail braking means is that you are still on the brakes to a degree after turn in. It doesn't mean that you aren't to throttle by the apex.

[Tom Sager]

Dave,

 

I don't disagree with you at all about which technique may be faster overall. Though I do think a case can be made that trail braking can be faster in more than 1% of corners. But strictly speaking about a car pushing and transferring weight to the front to help correct that: If transferring weigh to the front makes the car more pushy, then why is it that when people are learning to trail brake, or when they get it a bit wrong, it is the rear end coming around that happens and not nosing into the wall? I understand what you are saying about leaning on the front tires by braking and turning at the same time would cause the front to not have more traction available for turning. But the lightening of the rear end by trail braking seems to more than compensate for that and causes the rear end to come around if you get it wrong.

 

In regards to trail braking: If both techniques yield the same mid corner speed ( which in theory they should be able to ), then why is the guy that is coming to throttle sooner going to win to the next corner? All trail braking means is that you are still on the brakes to a degree after turn in. It doesn't mean that you aren't to throttle by the apex.

 

If our tires have 1.4G's of total grip available in a corner and a driver is still "consuming" a portion of that grip braking while turning, then the available cornering grip will be reduced by the portion of the grip used to slow down the car.  Under hard braking the front tires are loaded and after releasing the brake pedal it takes a split second for the braking G load to go to "0".  Stepping on the throttle shifts load to the rear and away from the front. 

 

The driver that brakes exceptionally deep and is still on the brakes during turn in is limiting turning grip to the apex and will be busy fighting the push while the driver who got off the brakes sooner can quickly steer to the apex is already on the throttle.  

 

Our cars slow down quickly when the wheel is turned and you are off the gas so the driver that can stop the "wheels turned and off the throttle" deceleration sooner in a corner is likely to have a higher exit speed.

 

Now if the earlier braking driver slows the car down too much before entering the corner, then that time lost will never be regained and the trail braking driver might win that one. 

[Jim Drago]

So there is no misunderstanding on my part, more like first hole on rear sway bar(soft) and a flat to negative rake car? 

thats where I set every car we drive or build to start

[Jamz14]

Dave,

I understand the friction circle. I think you are looking at this only from the front tire perspective. Why does a car not push out under trailing braking? Why would a car get oversteery super quick if you added only a front wing? Both things are doing the same thing: adding weight load to the front tires. These happen with the same tires on the car. I think considering the facts of the friction circle, what is happening is really we are taking away grip from the rear. Which makes the car oversteer. I'm not saying that taking away rear grip to make the car rotate is good or necessarily fast. But it will make the car rotate easier.

[davew]

Ok, I'll bite. Using your examples. You can only have 100% grip. Let's say perfect is 50-50 front to rear. Now add 10% to the front. I don't care how. Now you have 60% front and that only leaves 40% for the rear. You have an imperfect car that does not handle properly. The goal is balance, not total grip. Add 10% to both ends and you regain balance and go faster.

 

A trail brake car is not loose because it has too much front grip, it does not have enough rear grip to take advantage (balance) the extra front.

[Jamz14]

Dave, Tom,

 

Sorry I wrote Dave when responding to Tom.

 

Dave, I agree. That is what I said. We are taking away rear grip and the car oversteers under trailing braking. It does not push out. We agree that trail braking loosens up the car.

 

Now, if we both reach the apex at the same speed and both are on the throttle before apex, then would you agree ( all things being equal ) that both cars will have the same straight away speed and same speed into corner two? If that is true, then that minor second you were talking about that the trail braker gets on entry becomes important yes?

[Tom Sager]

Dave, Tom,

 

Sorry I wrote Dave when responding to Tom.

 

Dave, I agree. That is what I said. We are taking away rear grip and the car oversteers under trailing braking. It does not push out. We agree that trail braking loosens up the car.

 

Now, if we both reach the apex at the same speed and both are on the throttle before apex, then would you agree ( all things being equal ) that both cars will have the same straight away speed and same speed into corner two? If that is true, then that minor second you were talking about that the trail braker gets on entry becomes important yes?

 

If your foot is on the brake enough to cause the car to be slowing down, the car has less available grip for cornering at that moment.  Ideally if a driver can trail decelerate without using the brakes so that the car is traveling as fast as grip will allow during turn-in and as fast as grip will allow at apex and as fast as grip will allow post-apex (track out) while accelerating, then the theoretical maximum speed through a corner can be achieved (assuming also a perfect line).  We are essentially trail braking in our cars when we turn the wheel entering a corner with no pressure on the brake pedal.  The tires are doing the braking without the burden of the force of the brakes in the equation. 

 

We get to practice this all winter here up north as on an icy road where grip is really limited, the effects of braking even slightly when turning are quite noticeable.

 

Now some engineer might be able to argue or show that the added vertical force on the front suspension and tires when braking gives a momentary boost in grip to the front tires once the brake pedal is released and the nose of the car is still weighted.  

[Cnj]

Now some engineer might be able to argue or show that the added vertical force on the front suspension and tires when braking gives a momentary boost in grip to the front tires once the brake pedal is released and the nose of the car is still weighted.

Tom/Dave,

Given my recent finishing positions, I'm extremely hesitant to present myself as any type of expert on corner entry technique. However I AM a geek engineer and I love physics.
Nothing about either of your descriptions addresses vertical load and its relationship to slip angle or lateral traction. This has been well established in the literature and testing. See Paul Haneys book, or Millikens. Or here is a decent article on the subject:

http://racingcardyna...-lateral-force/

Daves indication of no turning before the brake is released contradicts what I see on video from our fastest drivers. It also is in conflict with the data I have seen, the multiple books out there on the subject, and with the coaching I have received by three different SM/MX5 national champions. Finally it conflicts with pretty much every form of racing that I watch, from F1 (which is in its own world...) to European series, to pro sports car racing. Who knows, maybe there is something I am totally missing or SM is a unique physics driving issue due to its slightly whacky suspension.....


Everything I have seen or heard is about increasing minimum speed in the corner, not about getting off the brakes before turning. In fact many of the very fastest pro drivers say that they let the car roll (coast) at some point with super gentle throttle application.

Now what is apparently different about our cars (to make them fast) is what some seem to call the "pitch and catch" approach which builds very rapid lateral load, and then allows pretty fast/early throttle application. But this still does not have drivers braking in a straight line. Personally I suck at this approach cause I can't seem to get my hands and feet to cooperate in the right timing, but its not a brake, get off brakes and then turn technique.

I suspect that we are all talking about very minor differences in brake/turning timing, but I did not want to let the conversation go on as if there was no other published viewpoints.


Of course (back to my recent finishing positions), maybe I'm all wet!

CNJ

[Tom Sager]

That looks like a very interesting article Craig.  Will read.  Just looked at a couple videos.  Definitely have my foot on the brake at turn-in for a corner here an there. 

[Martinracing98]

No, the exact opposite. More weight means more work for the tire. Since a tire can only do so much, you end up with a push.

 

 

More weight on the front due to braking will not make the front tires have to do more work. The front has to do work based on the amount of mass at the front end of the car. The weight shift, like a front spoiler or splitter result in the front being pushed harder in to the track and gives the front tires more traction. The problem is those same brakes end up taking some of that extra grip and uses it for the braking. And since more of the braking is in the front I suspect usually the net situation is is a push. I do not know since I have not driven the Spec Miata yet. 

 

A recent article identified being off throttle, using engine braking to help turn in by transferring weight to the front without the penalty of using the front wheels for braking. That makes since to me for helping if you find yourself needing to improve turn in. The downside to that for me is applying power after turn in means chassis handling change at the point of throttle application. Ideally when driving SRF3 I would apply power before turn in. I look forward to seeing if I can do the same thing with SM.   

[Steve Scheifler]

Wow! A LOT of over-simplification and misinformation here. It would take me pages to respond fully but the last posts by CNJ and Martinracing98 got things back on track. Read those again.

For now I will say that there is more than one way to turn a fast lap and the debate between trail-brakers and those who strive to be back on the power at turn-in has been raging for at least my lifetime. If I had to generalize, I would put it this way: They are both right, some of the time.

Obviously there are corners that open up, others that tighten up, on camber and off camber, critical corners and throwaways, all of which come into play when choosing the best approach. So we’re talking very general here. Assuming that you aren’t designing the perfect race car from scratch, then what you have to work with will influence how best to drive it. Even as good as the Miata is you will never get perfect balance in all types of corners. That said, for most front-engine RWD cars I would look for a setup which is just on the verge of too loose in the fastest corners, which (without provocation) will probably still leave it pushy in the tighest ones at tracks with both extremes. Hopefully those fast corners can be entered already on the throttle. Mid-speed corners may require a slightly slower release to maintain front bite while getting the nose to turn in, and the really tight ones might like a deep trail-brake to get enough rotation for the nose to be pointing the right direction at apex for a full throttle exit.

A lot of drivers who haven’t looked for it in their data and video will probably find, as Tom Sager just did, that they already trail-brake to some degree. Watch video from behind most of the fastest guys and you will see that they trail-brake to some degree in certain corners. DON’T watch F1, it will totally F with your head. They brake hard and downshift through several gears between turn-in and apex or beyond at almost every slow corner.

A good buddy of mine has long preached that the driver who “makes the most HP per lap usually wins”, meaning get back on the power earlier so you are spending more time accelerating. With data systems you can see % time on throttle. That’s very similar to what Dave W has been saying. Unfortunately it’s a lot more complex than that.

[gerglmuff2]

in autocross and TT we try to set up the car to have some steady state understeer, and then use the release of the brake petal on trail brake to load the nose and overcome that bias for turn in. basically you add searing and the same rate you are pulling off the brake. this allows you to get on the power sooner and be much quicker than a normal brake in a straight line, and then turn in after release. the line between over-braking (or holding onto the brake a bit too long) and thus inducing under-steer on entry, and getting it right, is tough, and i have not been able to do do so under race conditions. just too much going on. its also much easier to do in cars with slower set times, ie, stock suspension or near stock suspension. gives you a larger window because the nose unloads slower. my experience with miatas in general is they love a well timed trail brake, almost anything RWD should. 

fast driving is done on the edge of the friction circle, not on the two primary axis. that means you need to be mixing your steering with your braking, and your steering with you throttle application. you will be fastest if you use all the grip, all of the time you can. 

I too would like to have the conversation move to camber and toe. rake and bar settings is "agreed" on sounds like. the advice the previous owner gave me on camber was max in front (3.5-3.7 on my car) and maybe 3.2 or 3.3 in back. slight tow out in front, slight toe in in the rear (like most RWD cars).