Alot of confusion about Slow In Fast Out (SIFO) technique.... and no it is not something that weenies do. In specific situations it results in better lap times.

Essentially on any turn the drivern can trade off between entry and exit speed by varying the line (apex). This decision is based on which one gives you the best payoff....

Assume a 400 foot segment length turn that has a a max speed of 60MPH if you take the apex at the geometric center. If I reduce my speed by two MPH for the 200 feet entering a turn by taking a late apex, and get 2 MPH more exit speed down a 1000 foot straightaway that is a 5:1 win, even though my average speed through the turn was the same.

A road course is basically a dragstrip with turns stuck in it. Wide Open Throttle (WOT) is still the goal in both cases, but on the road course I have to slow down and accellerate.

Assume two identical cars with 90MPH max speed, that accellerate 1MPH every 10 feet, and decellerate 5 mph every 10 feet. They are racing down a 2000 foot strip. At the 1,110 foot mark there is a laser speed trap. They must be going exactly 60MPH at the speed trap. It takes the driver 20 feet to transition from brake to WOT and the car slows 2 MPH in that space.

Driver A late brakes at the 1,040 foot mark and is going exactly 60MPH at the speed trap, coasts 20 feet, and at 1,120 feet is at 58MPH and goes to WOT

Driver B brakes at the 1,000 ft mark, gets off brake at the 1,060 mark, and is going 58MPH at the 1,080 mark when he goes WOT, accellerating to exactly 60 mph at the 1,100 foot mark.

Both drivers execute the braking maneuver exactly the same way, but Driver B carries two MPH of extra exit speed down the second straight.

OVer the 2,000 foot course Driver A's average speed is 66.7MPH, Dri ver B average speed is 67.1 MPH... Driver B wins.

If however, the turn were at the end of a straight, and led to a bunch of low speed twisties, I would reverse the process.... using late, heavy trail braking and taking an early apex to extend the straight, since exit speed in this case is a liability, because I have to slow down anyway.

 

The problem with slow in fast out is not being at 60 mph at the corner.

The problem is that a slow in fast out often means to a driver

"Take it easy on the way in and go like stink on the wayout"

Well that is slow because you really need to be going like stink on the way IN as well as on they way out.


This is not an excuse to outbrake youself and shoot past an apex point. The basic concept to not slow down as much on the way in. Most novice as they learn to drive learn the basic line and the ability to modulate the throttle on the way out of a corner. This actually quite easy. Instuctors teach slow in fast out because it safer and the natural tendancy is for drivers to "charge" a corner barely make the through and result in a slow exit and white kunckles.

As drivers learn to control the car on the way out they can master how much throttle it takes to get out of the corner. The only way to get faster is to address the part of the corner they did not focus on when starting. That is corner entry.

I learned alot from switching from 250 hp 951 to my 150 hp 944. What I learned is that my 944 was darn slow and had no hp, but it could grip like hell.
So the only way to make the car keep-up to guys did before was to not slow down. If I slowed down just a bit too much then I never make it down the next straight.

So I learned to use less brakes in the braking zone. I learned to go faster on corner entry since if I used my 951 entry the car would be slow. Putting power down was easy and I needed get it down ASAP and slow down as little as possble. So my focus was dead set on not slowing down in corner entry.

That did not mean late braking. In fact that usally meant to me to brake sooner and lighter and turn in a little soon to try to get the max raduis on the corner. A late apex was fine for high hp 951, but in my 944 NA I did not need to be going dead straight to apply power. So turn in sooner and take more geometric line. I found myself applying power long before I did in the 951 and slowing the car much less. I found myself trailing on the brakes at turn in in attempt to get the car to rotate more so that I could carry more speed at turn in.

Then I started braking a little later. Then I found myself braking after others start. Turning in before they did and braking after turn in to an overall higher speed at mid corner and thus more speed at throttle application which just happend to be sooner than everyone else. Result... I could stay with a number 951's at the track as long as I was not too close and get stuck behind then as they went "slow in" to the same corner I barely slowed for. Think they go down two gears and I went down just one.

Hmm slow in .. nope fast in fast out.

Of course there are still a few corners were you have to "go slow" to go fast. Places were it does not help to carry speed into corners. Of the tracks I have been two there is at most 1 corner like that on each track. At other none like that. Just about all the corners benfit from carrying speed on the way in however. The trick to this is that if you carry to much speed it can slow you down either by going off track or my missing your apex point.

 

M858, I think that the 951 and your 944 are both correct - if the 951 sacrifices just enough entry speed to use its excess power earlier than it could with the 944 line, it will gain more on the straight than it loses at turn in, as per JCP. The difference is probably fairly subtle at the limit. Most 951's (mine included), give up too much entry speed. The correct way to determine the right line would be to use the 944 entry with the 951, slow it slightly to get on full power earlier, and measure segment time to the next turn in. There will be an optimal combination. Stewart, Senna, and co. probably arrived at this optimum in three laps. Have you been back to the 951 after your 944 experience?

 

Too often, these discussions proceed on the assumption that we are all at about the same point on the learning curve. Anyone with any amount of instruction under their belt knows that beginners typically overcook entrance speeds, particularly on slow corners, and then tip-toe through faster corners. For almost all novices, a slow-in, fast-out approach is the best way to learn.

Later on, of course, you start to work on increasing your entrance speeds. But the fact that a good juggler can keep seven objects in the air doesn't mean that a novice juggler should look at starting with three as some sort of compromise.

 

JCP and M75 - There's another aspect to the slow in fast out legend that's rooted in the 911. Given rearward weight distribution, a racer could usually outbrake his front engined competitor into a corner and then get on the gas sooner exiting said corner. Not every corner mind you but often enough that it became sort of a Mantra. I think over time it became a requirement for DE since, as you have written above, it was also a lot safer that way. Fast in and faster out is the way to win races though.

Best,

 

Hmm,
I do not think this really a 944 vs 951 type discussion. My point was that with less hp I was forced to use more of the car at turn in to be at same speed as in the 951. With 951 I could use the stop, turn, and go approach and still reasonably fast with respect to others in the group. With lower hp car I had to use it entry speed as I could not rely on hp to anything for me.

Fundamentaly I believe that new track you first work on the exits of corners. (This assumes an experienced driver at a new track) You should attempt to fine how soon you can get on the power coming out of each corner. This will be different in cars with varried grip vs hp ratios. So see how soon you can get the power down and still stay on track. That is step 1. Now when you are doing this corner entry is not huge deal since you are working on corner exit.

Once you have that pretty good you move to braking points and corner entry. You then want to maximize your speed on way into a corner while attepting to maintin that optimal power start point. Now in some cases you may choose to move the power out point farther down track to maximize speed in if it helps overall lap times. On the cases you simply cannot carry that much speed in to corner since it throws you past the optimal power point. So what you do in each corner is dependant on alot factors.

Personally for me when I switched from a stock 951 and moved in to stripped our R compund 944 NA qucikly learned that my 951 corner exit power points were far too late. In essense I was apexing too late for the car since it was not on the traction limit on the way out of the corner. So I applied power sooner and sooner gaining a little speed back. Of course where the real speed of the car was to be found was in corner entry. I never maximized corner entry in my 951. Why? I was already passing alot folks in my DE group so "seemed" pretty quick. Same technique in my 944 was down right slow. I learned alot. Example my fastest lap in 951 100% stock on street tires PIR (1.5m course) was 1:19. My first drive in my spec car down 3-400 lbs with R-tires was 1:21 best lap. Now with only a few minor tweaks my best is 1:12.9.

I have not been back with 951. I did do a track event another track with 951 and don't have any lap time to compare, but I held my own quite well vs a group of instructor 99% on R-tires. I was still on streets. I was not even pushing the car hard although in retrospect much harder than I ever did before. The difference was my definition of hard has gone up 10x from racing.

 

Jack to you point. Currently I am a Club Racer with about 40 racer under belt and quite a few class wins.

My transition from 951 to 944 occured when I was still learning to drive. I was solo at the time and could easily find my way around the track, but was not one of the fast DE guys. I was solidly intermediate. Good enough to be out there and safe, not good enough to be fast. My transition to low a hp high grip car was what I needed to begin the process of seeking the next level of speed and start experimenting with advanced techniquies. It was during this time that I progress into the instructor ranks.

 

M758, I didn't mean to imply it was inappropriate for you to talk about increasing your entry speeds. It was offered in the context of the recent CC threads, where this line of thinking would immediately go to why CC would need to start out his driving career by invoking ABS all the way to the apex of most turns.

In fact, I look at the thread and there's (thankfully) no ColorChange content at all.

What a relief.

 

I wonder if maybe the term "Slow in, fast out" is confusing. I don't think of it like M758 said "stop, turn, and go". But more of a "give up some entry speed, so that I can maximize exit speed." I try and go just slow enough so that I can hit my apex and get back on the gas ASAP. It's still "Slow in, fast out" as I am entering the corner "slower" than I am exiting it.

I agree that a lot of people over slow for some corners, and it may (or may not) be a direct result of instructors pounding on them to go "Slow in, fast out". But that doesn't mean the concept is bad, just some implementations (and even explanations) of the concept.

Just my thoughts.

 

I have spent some time with professional drivers from Skip Barber (people who set the comparison laps) and have heard an interesting take on things - they teach that there are 3 keys to being really fast. 1. Be on line 2. Exit Speed 3. Entry Speed

They say the first two are pretty easy. In a simplified way, you put the car in the right place and accelerate from the apex out. Even with exit speed, sliding and drifting out are not that scary - you always have control with your right foot.

Entry speed is the scary one. To slide a car into an apex takes some work. Being able to get the car in and to the right point, at the right angle is tough - even tougher when your on the edge. The difference is only 2-3 mph, but it ends up huge.

Everyone likes the facts that 1 mph at the beginning of a straight is some multiplier more at the end. The same is true in a corner. A few mph more in results in a few more out.

Matt

 

What a great thread. Good dialog, well though out points, and respectful disagreement. And here's mine...

I have always felt that there is a point in the turn, usually in the first 1/3 where the car is at it's maximum cornering G's and you are moving from the brake to the gas. I have refered to this point as the transition point. I feel that this, being the slowest part of the corner, the connection between braking into the turn and accelerating out of the turn, really divides the turn in half. You can brake early for the entry to the turn and still come out every bit as fast (classic DE training). You can fly into the turn, and overshoot (or overspeed) this point, and pay for it with lower exit speeds.

The challenge is knowing exactly where this point is, and flying into it, and powering away from it. Car setup, HP and grip all influence where this point is, and it is unique to every corner. If it is farther into the corner, then you may want to hard trailbrake down to it. If it is earlier in the corner, you may want to bend into it while releasing the brakes. And in almost all cases, you want to floor it at that point and accelerate all the way out of the turn. So fast in does not necessarily mean fast out. You have to hit the transition point properly to tie entry speed and exit speed together.

 

Jack... No problem I actually should have given my post a context of experience.

Mike... I understand your reasoning, but just like Matt's post points out if you are at all giving up anything at corner entry you will be givng up speed. The corners where you SHOULD do this exist, but are not common.

Matt... Right on!

Larry. My take is that those here that say fast in is bad are those that are thinking it means going in too hot. There was one corner at local track that was great for trail braking. I would typically trail brake and double apex it. Well one day I had little too much understeer. Turned out my rear sway bar had been shifted when I got the car off the trailer. To compensate I tried to trail brake harder and deeper to get the car to rotate. Well I proceeded to struggle to keep the car on track and was slower since I was past my power out point still working on getting the car to rotate just right ammount. Later I noticed my problem and reset the sway bar. I also slowed down a just bit and went faster overall. So really the key was the right balance of how deep to go. In that corner the traditional DE line says to brake straight and get the car slowed down. Then turn the car and wait to a late apex to apply power. Now that was I call slow in slow out.... At least it is safe.


In reading your post I think you have i backwards (or maybe its just me)

For example
If you have very tight exit to a corner you will want to late apex that corner. To do this you want to late brake and slow the car dramaticly. You take a slow in concept since the late apex line required a tigher turn radius and therfore slower speed. You can if you would like trail brake to make this happen, but not always. The critical point is the to exit the corner you need to get the power down ASAP. Since the exit is tight the nees to be pretty straight thus you need a greater percentage of the turn done before you being to power out.

If by contrast you have corner exit with lots room you can get the power down much sooner. You can apply power and unwind the wheel so as the speed goes up the radius the car makes increases. Here you want to brake early and turn early and may be able to carry speed on the way in. You lose speed however if you attempt to carry speed causes to you be late on your early power application.

 

I think that we are on the same page. With respect to early and late apexes, if your transition point is farther into the corner (as it would be with a later apexing corner) then you would want to trailbrake a lot so you could brake later and all the way to that point. If the transition point was early in the turn (like with a fast, increasing radius turn) then you would be doing very little trailbraking, if any.

 

I'm not entirely sure I understand. You may have to speak slowly and use small words. I understand that if you are WOT when you turn-in chances are that you over slowed. But what I don't get is when/where/how you would enter the corner faster than you would exit the corner.

This is probably not a good example corner, but the corner that comes to mind for me in this discussion is T1 at Willow Springs. Through some work and time I have been able to get to the point where I can brake later (the very last cone), softer, and carry what feels like a ton of speed through that corner. I could probably still brake less and turn in a little later (as I have more track out) but it scares me (there I admitted it).

I can't seem to comprehend how I could change the way I'm taking that corner so that I am not doing "Slow in, fast out."

OK, so after all that what you are actually trying to accomplish is to enter the corner as fast as possible so that you can hit your marks (apex and WOT point), but no faster as you will be out of shape for the exit and straight. Right? Which in theory is "fast" -- as fast as possible, but in reality may be slower than the exit speed (or even apex speed depending on the type of corner) or it may not?

M758: Are you going to be at PIR this weekend? Maybe we can pick a corner and you can walk me through it there (if you have time).

 

Hmm... you know what. It just occured to me. I may not be at the right level for this conversation. I do a little trailbraking. But nothing near as extreme as you guys probably do. I may just lurk for a while, but should probably duck out now...