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How to drive a FWD car in the rain:

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How to drive a FWD car in the rain:

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    How to drive a FWD car in the rain:

    Now that it’s winter, and most of us drive in the rain, or in the snow. I thought I’d share this with you all. Feel free to make any comments or corrections.
    Here are some things that I thought about after I reading a few Carroll Smith books, Race Car engineering books, and then later after some very long spirited driving with a FWD car on very technical roads in the rain.

    Keep in mind when entering a turn, weight will move to the front corner which is being loaded.
    Feel for the moment of understeer. Depending on the tires you have, and entry speed, etc…either the moment of understeer will occur quickly, or rather gradually.

    Gradual understeer will appear like you are not turning the steering wheel enough, and need to tighten up the turn.
    Power-on-understeer will be feel as though the car is moving forward only, regardless of steer angle. And the car will no longer have a continuously changing vector (i.e., steady state turning), but rather will just plow straight ahead, following the path of the rear wheels, rather than the steer angle of the front wheels.
    If it’s raining, and you are tuning hard, and suddenly increase throttle drastically, the front tires will be shocked, and the car will not change direction (which the steering tires are used for) and will track along the path of the rear tires.

    When the understeer limit is reached, especially when you are in the rain, the best thing to do it back off the throttle and ease on the brake.
    Engine braking will cause the front brake bias, which is further detrimental to stopping, because the rear is already neglected for its stopping power. Although engine braking in low traction condition will not cause wheel lock-up unlike brake calipers without ABS. This is due to the continuous rotation of the engines’ rotating assembly.

    Transferring heavy load to the front tires (or shifting the cars weight to the front) is also a bad idea in heavy rain, because this will cause the tires to reach front tire traction limits sooner.

    When cornering limits are reached while you’re driving, it is usually gradual. Initially it will feel as though the car is pulling inward (towards the inside of the turn) and while holding the steering wheel at that same steer angle, the car will FEEL like it is no longer pulling you towards the inside. (Of course this is assuming the consistency of the turn is a controlled variable.)
    Feel for the “hold” and “release” of the cars turning force. It will feel like a gradual climax, and then a drop off. (It will drop off suddenly is extra thrust is applied.)

    Keep in mind FWD’s car weight is in the front, (as well as the drive wheels in the front.) This makes the car a double loser, because the front wheel drive overloads the front tires too soon, as well as the front weight overloading the tires too soon as well.

    (Obviously: The capacity to take a turn faster, smoother, and shaper, lies within RWD or AWD cars.)

    When you are driving in low-traction conditions, try to drive as smoothly as possible. Especially if you’re pushing 200+ HP on the front wheels. You will meet power-on understeer VERY quickly.
    Also, when taking turns in rainy weather, if you are accelerating during the turn, up-shift, and then drop the engine speed to low-rpm’s, it is possible to clutch-burn brake, by balancing sitting in between neutral and full gear engaugement. (Careful though, doing this too much can burn your clutch—but the benefit to this is avoiding wheel lock-up.)
    Also, if your turbo’ed, be wary of boosting suddenly in the middle of a steady-state turn. (Steady state turn refers to a car turning without understeering or oversteering. And operating at a constant tire slip angle.)
    With less horsepower at little or no boost, throttle inputs are much more predictable.
    The opposite of this is holding the engine speed at 7,000 RPM’s, while at 0 boost, and suddenly in the turn (steady state), your right foot gets a little heavy, and 15psi of boost kicks in, causing power-on-understeer.

    Simultaneously, holding 6.5K RPM’s engine speed or so in the middle of the turn, can better prepare engine throttle and acceleration while exiting the turn.

    Bogging the motor to lower RPM’s in the middle throughout the turn in a low-traction condition will give predictable turning, due to less division of tire traction, between the vectors of TURN and THRUST.

    Keep in mind whenever you brake, turn or accelerate, you divide the traction of your tires. For example, a single front tire can only have 100% traction capacity. Your front tire on your FWD car, when entering a turn REALLY hot, and braking hard and late, you use 75% for braking. This leaves only 25% left for turning.
    A good driver will gradually make shift the job of the tire from 75% braking, more to turning, say 50%, and then 50% for accelerating.
    This is known as riding the traction circle.
    The traction circle (or traction capacity) is even less while driving in the rain.

    Given that your front tires do ALL the turning, accelerating, and almost 90% of the braking, your front tires will reach its’ limits VERY soon. Even sooner than usual when it’s raining.

    Often, with some front engine cars, (without ABS) upon hard braking, only the front tires will lock-up, and rear tires will keep rolling. This also depends on weight distribution, and dynamic brake bias.
    Depending on the distribution of braking power of your master cylinder, as well braking power of your rear brakes, it is actually helpful to PULL the E-brake, to boost the rear tires braking power, but NOT to the point of lock up.

    While braking while turning in the rain, A LOT of caution should be taken while pulling your e-brake to assist in braking power. Employing the rear brake more (but before the threshold of lock-up), will help lessen the braking effort needed for the front brakes.
    Keep in mind that only engine braking, causes 100% braking power to be on the front tires, and 0% braking power on the rear. This can cause brake bias, and when coupled with caliper braking, the front tires will lock up VERY quickly.

    Depending on the situation, the best way to utilize all components of brakes, tires, engine, and suspension, can be a combination of caliper braking, engine braking, and e-braking, as while turning the steering wheel, while feeling the car for it’s moment of understeer.


    A word about tailgaiting in the rain. (As well as in the dry.)

    Also, if you’re tailgating someone really close, your car had better be able to out-brake that car in terms of stopping distance.
    Say for instance, we take a 1400 lbs 1965 Mini Cooper, 305/50/13R sized tires on all 4 corners, with 6 piston AP Racing brake kits on all 4 corners. (Overkill, I know.) The car is driving 75 MPH on the freeway.
    Next to our Mini Cooper, is a 8,000lbs Lincoln Navigator SUV, and for some reason, he’s got 165/70/14 sized tires (the Wal-Mart special) on the behemoth. He also has stock brakes.

    These two cars are doing the exact same speed: 75 MPH.
    Suddenly the both slam on their brakes as hard as they car, both cars braking on the edge, right before lock-up.
    The SUV probably takes 50% more stopping distance than the Mini Cooper.
    Now for application. If this Lincoln Navigator is tailgating the Mini Cooper, he is a MORON. (The SUV will smash into the back of the Mini.)
    If the Mini Cooper is tailgating the Lincoln Navigator, he’s being an aggressive driver—let’s just hope his reaction skills are as sharp as his car.
    In this case, the Mini will slow, the distance between the two cars will increase, and SUV will maintain it’s momentum longer, and will stop LONG AFTER the Mini Cooper is parked.


    Moral of the story: ONLY TAILGATE, if you know your car can out-brake the car in front of you, and that your reaction skills are like that of a cat.



    Side note:
    The idea behind understeer and oversteer. If the rear tires break traction first, then the rear end of the car will pivot around the front end.
    If the front end breaks traction first, then your front end will pivot around the rear end. (Although, not nearly as much compared to oversteer, and rather the car will only slide straight, because the tire slip angles are increasing as understeer increases.)

    -------------------------------------------------------

    Anyhow...these are a few things I've been thinking about. And not everything here has been my idea. Alot of it is paraphrasing. (And congrats to you on reading the whole thing.) Let me know what you think guys. I hope somebody got something out of it. In anycase, be safe out there in the rain.


    -Andrew

    #2
    awesome. I like engine braking in the rain. I feel A LOT more in control, and a lot safer. I also find RWD cars WAY harder to drive in the rain. This being because the rear has no weight (unless the car is MR) and the tires stay over the "sheet" of water on the floor, causing loss of traction. I'd rather have my engine weight on my driving wheels to allow more traction.

    Comment


      #3
      Originally posted by ElBorintegra
      I'd rather have my engine weight on my driving wheels to allow more traction.

      buy a porsche. rear engine.


      or a new C6 vette. the transmission is in the back of the car.

      Comment


        #4
        Zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz

        Comment


          #5
          Originally posted by Schu
          Zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz
          Atleast offer constuctive criticism.

          Comment


            #6
            srry, but alot of that was really redundant, and knowledge i think ppl know already. But its gotta help somebody.

            ill sum it up. Drive slower in the rain, dont accelerate and break traction while you're turning. If you understeer, let off the gas, upshifting helps. Dont taillgate unless you can out brake the car in front and thats saying if you have a good reaction time too.

            Comment


              #7
              Originally posted by fantasya98
              srry, but alot of that was really redundant, and knowledge i think ppl know already. But its gotta help somebody.

              ill sum it up. Drive slower in the rain, dont accelerate and break traction while you're turning. If you understeer, let off the gas, upshifting helps. Dont taillgate unless you can out brake the car in front and thats saying if you have a good reaction time too.
              Ok. Thanks. Now explain how and why all of this occurs.

              -----------------
              As for what Elborintegra said, "I'd rather have my engine weight on my driving wheels to allow more traction"

              Actually, when you are accelerating, you DON'T have the weight over your driving wheels. Weight transfers to the rear of the car, thus the rear wheels are loaded, and the front wheels are unloaded. FWD cars, upon hard thrust lift up the wheels which are trying to put down power. This is the reason why our cars wheelspin so easily.
              When you do have weight over the front drive wheels, is when there is low acceleration, thus smaller amounts of load transfer. (Such as a FWD car outpulling a RWD car in the snow at slow speeds--but even in this case, the dices are loaded.)

              Comment


                #8
                Originally posted by UCSlugRacerX
                Atleast offer constuctive criticism.


                I wasn't even offering any criticism... I feel alseep reading your boring spout

                Comment


                  #9
                  i like what you posted, but i think rwd is harder in the rain, i have no problems with my car in the rain, i even did brake testing when it rain here and i braked hard going down this big hill i live on and it was better than i expected mainly because my tires are fairly new i think. RWD had like no traction while turning in the rain and those tires were bald on the 240sx so i dunno, i take precautions in the rain anyway

                  Comment


                    #10
                    I wasen't about to read the massive initial post, but some comments on the replies...

                    C5 vette has the trans in the rear as well

                    My engine is pretty much useless for engine braking, so I rarely do it.

                    Obviously the weight transfers off the drive wheels on a FWD car when accelerating. However, a) most of us won't ever have to accelerate as an emergency maneuver, and b) if you accelerate hard enough to get significant weight transfer in the snow you won't go anywhere no matter which end is driven.

                    Comment


                      #11
                      CSlugRacerX: I think you're trying to say RWD is better in Rain/Snow For some reason.

                      Go ahead, but I'd rather have my FWD. Even though a lot of weight transfers to the back, ALL of it doesn't...Thus, the car will have more traction in snow/rain.

                      Comment


                        #12
                        Originally posted by strikeback03
                        C5 vette has the trans in the rear as well.

                        i know punk.


                        c6 is sexier tho. :p

                        Comment


                          #13
                          Since I have a stock engine and tires with good wet traction I basically don't do anything special in the rain. Just drive like normal, maybe brake earlier if there is a lot of water. This article is geared more to racing in the rain, which I'll leave to the professionals and morons.

                          Now, driving in the snow, that takes a lot more precaution.

                          Comment


                            #14
                            haha

                            Comment


                              #15
                              I hope somebody found some this remotely helpful. (I figured it would be a more interesting thread than, "which ebay lowering springs should I get for $40.00?") I'm still perplexed as to why Schu must be such a dick--he's said so many other intelligent things before.

                              In anycase, RWD and AWD is obviously superior to FWD, usually in any circumstance. Although that wasn't what I was arguing in my initial post. I was trying to shed some light as to how a FWD car handles at the limit in the rain, and WHY.
                              Also, driving in the rain, is like driving with tires half the width of the contact patch in dry conditions. And driving in the rain is similar to driving at the traction limit in the dry.

                              (A few days ago, it was raining and I saw an RSX Type S totaled at the side of the road (on the outside of a turn). I doubt he was thinking about the understeer limit of his FWD car, as I'm certain it plowed wide.) Anyhow, be safe out there, even if you do drive fast in the rain.

                              My two cents.

                              -Andrew

                              Comment


                                #16
                                Driving in the rain isn't really all that hard as long as you have good tires. Most of the driving people do on the street will be fine for the rain, and many of the things you listed off are for driving under any conditions.

                                The braking distance case is exactly the same if the roads were dry, the Cooper would outbrake the SUV.

                                Heavy rain is a different story, but if you are speaking a drizzle to a light rain, there's not much difference as long as the roads aren't flooded.

                                Now, it is unwise to drive with any extra amount of speed on the first couple days of rain... This is because the roads build up oil and such things on them, and when it rains this oil collects on top of the water and creates a very slick surface to be driving on. But if it has rained the past couple days, you will have plenty traction to work with.

                                If you ARE driving spirited in the rain, know that you will have less traction that in the dry (duuuuh), if you want to find out the limits, take your car to a parking lot.

                                Things to watch out for on wet roads would be things that are slick, such as road paint (very slippery when wet) and if you can't see the texture of the road because there is a sheet of water on them, beware of hydroplaning.

                                Another problem with driving in rain is visibility, which is probably more dangerous than any road condition. When it's raining and the roads are wet, keep a good distance behind the vehicle in front of you because it will spray like hell. Spray is so thick that with the wipers on full blast it's still hard to see, not a good idea. Also, high-beams are anti-efficient in the rain, as the light just reflects back into your eyes (not good). Lines are harder (if not impossible) to see in the rain.

                                As for braking just be sure to not brake too hard, or you will skid and when you skid in the rain you have no directional control whatsoever. You won't skid directly foreward either, you will start moving to whatever side the road is slanted to.

                                That's about all there is to driving in the rain, unless it's fresh rain, or heavy rain, it's not that much different if you're driving on an all season tyre.

                                That's about all I have to say.

                                EDIT: Nevermind about all I have to say. FWD and RWD are very different in the rain.

                                Both WILL peel out because of loss of traction to the drive-tyres. The difference is what happens when you lose this traction. In a front wheel drive car, you get understeer which pulls you to the outside of the turn. Easy to correct, you just let off the gas. If you are going in a straight line nothing will happen, the car will just be skidding.

                                In a RWD car on the other hand, loss of traction in a turning acceleration will cause the car to massively oversteer, which is hard to correct for, resulting in a fishtail and possibly spinning out, ending up in the other lane, etc. Loss of traction in a straight line has the potential to do the same thing.

                                In a low-traction situation, a FWD car is much easier to keep under control.

                                If you wonder how I know all this - Extensive driving of both my Integra, a Mustang, a Volvo, and an Astro van. You would be suprised at how much rain-driving experience one can build up w/ 2 years of driving in Washington.

                                Comment


                                  #17
                                  Great info. Although you've left a few things out. It actually only gets more complicated from here. Often the coefficient of friction will change, as well as a reduction in heat saturation. (Due to the lower rubber compound temperatures.) Now as for tire slip angles, these change as well, due to the change in the coefficient friction.

                                  Comment


                                    #18



                                    Just kidding guys. Great job.

                                    Comment


                                      #19
                                      As for the FWD and RWD dynamics. Check this out when you've got the time. It's worth a read.

                                      http://www.corollaperformance.com/TechInfo/RWD.html

                                      Comment


                                        #20
                                        Originally posted by UCSlugRacerX
                                        Great info. Although you've left a few things out. It actually only gets more complicated from here. Often the coefficient of friction will change, as well as a reduction in heat saturation. (Due to the lower rubber compound temperatures.) Now as for tire slip angles, these change as well, due to the change in the coefficient friction.

                                        Comment


                                          #21
                                          I'm a little confused on some of the stuff stated on that website, seems like they are more than a little biased towards RWD cars. Better weight distribution? How does that work? More braking power to the rear wheels? What? How does having the rear wheels drive the car affect the braking ability? The weight bias is not that much different in a FF than a FR is it? I mean comon, a drive assembly can't weigh enough to really make too big of a difference can it?

                                          Comment


                                            #22
                                            Originally posted by Sam
                                            I'm a little confused on some of the stuff stated on that website, seems like they are more than a little biased towards RWD cars. Better weight distribution? How does that work? More braking power to the rear wheels? What? How does having the rear wheels drive the car affect the braking ability? The weight bias is not that much different in a FF than a FR is it? I mean comon, a drive assembly can't weigh enough to really make too big of a difference can it?
                                            Engine braking causes the rear wheel braking. (Thus RWD engine braking is 100% rear, and 0% front.) And yes, a drive shaft, plus a rear end is VERY heavy. Yes, RWD cars have better weight distribution, due to the engine ussually sitting behind the front axels, plus the transmission sits in the center, and a driveshaft and rear end weight down the rear.

                                            Comment


                                              #23
                                              Originally posted by UCSlugRacerX
                                              Engine braking causes the rear wheel braking. (Thus RWD engine braking is 100% rear, and 0% front.) And yes, a drive shaft, plus a rear end is VERY heavy. Yes, RWD cars have better weight distribution, due to the engine ussually sitting behind the front axels, plus the transmission sits in the center, and a driveshaft and rear end weight down the rear.
                                              Hm, that's right the transmission is in the back not the side. Forgot about that little detail. Gracias.

                                              Comment


                                                #24
                                                kinda iffy write up andrew. but none the less its detailed enough for us to know what youre doing.

                                                going into a turn lateral force is placed on the oppisite side of which you turning, more wieght isnt over the front drive wheels until you brake or light acceleration, that is the case with most of our cars, hence understeer. the cure? stiffer springs in the rear.

                                                or just dont push it so much down in santa cruz! those mountains are rough!

                                                Comment


                                                  #25
                                                  Originally posted by math labs
                                                  kinda iffy write up andrew. but none the less its detailed enough for us to know what youre doing.

                                                  or just dont push it so much down in santa cruz! !
                                                  That'll be hard to do Todd. In anycase, you're almost correct about the weight transfer, except that weight transfers to the rear of our car whenever accelerating.
                                                  Hey Todd, we should do some autoX together dude. Although it'll suck for me not being in a lower class. How are the Tein SS's treating you? I'll in Vallejo in this weekend.

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