Revisiting understeer


Frankster left a comment on my previous post regarding understeer and looking where you want to go, and I thought it interesting enough to post here:

“Look where you want to go” does not apply to understeer. You are already looking and steering in the direction you want to go, but it’s not happening because you’ve lost front end traction.

If you continue look in the direction you want to turn and steer that way (around the curve) you will continue or even increase the understeer situation. You need to momentarily steer LESS in the direction you want to go until the front wheels regain traction.

Good point, Frank, I should have been a bit more clear. I didn’t mean you can look where you want to go and you will magically go there without any other actions. Obviously you need to consciously use the throttle, brakes, and steering.

But from a racing perspective, I don’t agree completely with what you’re saying.

In an understeer situation, there are theoretically two ways to correct it – either reduce the steering angle as you point out, or reduce throttle. Let’s look at both of these in more detail.

Reducing steering angle will obviously reduce understeer, and in the Safeway parking lot, this will work great. However, on the track, if you reduce steering angle, you will drive off the track…remember, we’re at the limit here, and we were already planning to exit the curve with about 12 inches or less to spare between the car and the edge of the track. In some cases the edge of the track is dirt, but in other cases it’s a concrete wall. There’s no room to open the steering wheel.

The other option is to reduce throttle. This shifts weight forward, onto the front tires, increasing their grip. Understeer is thus reduced, and the line around the turn tightens. We’ve lost some time by lifting off the throttle, but we’re still on the track. Don’t get crazy with the lift, though, or the car will start rotating – you’ll go from understeer to oversteer in a heartbeat. More on this below.

So what does this have to do with where you’re looking? If you’re looking where you want to go, and lifting off the throttle to keep the car on the track, you will naturally tend to lift just the right amount. Too little, you drive off the track. Too much, you’ve lost more time than you had to. And at the same time, you’re making steering corrections – definitely look where you want to go.

Incidentally, when most folks start understeering, their natural reaction is to lift off the throttle. This is why most street cars tend towards understeer when you drive them off the lot – it’s generally safer for the average Joe in most situations.

Of course, you can also forget the steering correction altogether, and use throttle to kick out the rear

Frank wasn’t specific about how to use the throttle in this case, so let’s look at both possibilities.

First, you could stomp on the throttle. If you have lots of horsepower, you might be able to break the rear end loose, and go from an understeer situation to power oversteer. This could work in some situations, but in most cases at the cornering limit of the car you will bump up against the laws of physics and go flying off the track.

Second, you could lift off the throttle to “kick out the rear end”.  Definitely possible – if you do an abrupt lift in mid-turn, the rear end of the car will get very light (remember, all the weight shifted forward) and typically start coming around. The trick here is to get back on the throttle at just the right time and the right amount to get weight back on the rear tires without breaking them loose, or you just might loop it all the way around. That said, a quick lift like this is often a good way to clear up a mild-to-moderate understeer with minimal time loss under racing conditions. I say “under racing conditions” because during qualifying, the lap is probably shot. And on the street, just lift slowly and carefully. :-)


4 thoughts on “Revisiting understeer

  1. joe

    yeah, thanks for the explanation! Understeer can be a scary thing, especially to an inexperienced 16 year old driver in his Mom’s fifty thousand dollar BMW! Just Watch that corner round the other bend if you lift hard off the accelerator and the tail swings out, or before you know it you’ll be all over the show then completely off the road or track. If you do drive a low powered car, just be careful if you stab the accelerator during understeer because most of the time it will just make that horrible understeer even worse! Tahnks

  2. Don Ross

    As a first time reader, I have always wondered how the driving characteristics of a FWD and a RWD differ from each other at the APEX of a curve. I know that at the apex if you give gas to a RWD it will wash out (start skidding)at the back end over the driven wheels (makes an oversteer) and the back end will push off of the OUTSIDE of the curve. This actually helps point your nose in the direction that you want to go at the vertex. However, what happens when you give gas to a FWD vehicle at the vertex? Anybody know?????? Don

  3. Harvey McFadden

    Let us look at 3 cars:

    We will assume that each car has a weight of 1,000kg

    It will have front traction (FT) and rear traction (RT)

    Traction is calculated as weight x the adhesion of a tire and we will give a standard all season radial a value of 1.

    CAR 1 1000kg 49% of weight on front, 51% on rear

    The theoretical perfect car: It exists as sports cars and race cars. It has a split of 49% weight on the front and 51% weight on the back. (FT=490 RT=510) It has very predictable behaviour and if it starts to get out of control it will be felt on the front end first and will tend to go straight ahead and braking or slowing down will bring it back under control.

    If I put radial tires on the front axle (A=1)and belted tires on the rear axle (A=0.6) then FT=490 and RT=306. At this point I have broken an MTO law and made the car susceptible to oversteer and if it goes out of control it tends to go sideways and roll over or veer into other lanes of traffic.

    CAR 2 1,000kg

    Front wheel drive 65% of weight on front, 35% of weight on rear

    FT=650 RT=350 with new tires

    After driving it 10,000km I rotate the tires; now FT=650 RT=315

    Or I put snows tires on the front and partially worn all seasons on the back; now FT=975 RT=210

    This car is very unpredictable and given to roll-overs and lane changes and even an experienced driver can easily over correct and loose control. see further information attached

    CAR 3 1,000KG

    Front wheel drive 65% of weight on front, 35% of weight on rear

    4 new tires FT=650 RT=350

    At this point this is the same as Car 2, however for winter driving if we put front tires on that feel fair on pure ice at about 50kph, which I have found to be about 6 months old all season tires with a value of about 0.8 so FT=520 and on the rear, softer ice-snow radial tires which will give the rear a value of RT=525 (FT=520 RT=525)

    This car is very predictable and can out perform even an all wheel drive in some conditions. If it starts to get out of control you just brake, it slows down and you regain control.


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