JohnnyCat

I was reading a breakdown on a Canyon road and came across this term: Diminishing Radious Turn.

Can anyone explain what this is and what the implications are for driving it?

negcamber

From my experience it is more commonly known as a decreasing radius turn. But that's semantic. Anyway, what it basically means is that the turn tightens as you travel further through the arc. Two other types are (1) increasing radius -- the turn become less tight as you travel the arc--and (2) constant radius -- the curve would form a perfect circle if carried for 360 degrees.

A decreasing radius turn can be tricky to negotiate as the first part of the curve allows a high entry speed. However, as the curve becomes tighter you probably won't be able to maintain that higher entry speed. An inexperienced driver may brake or drop the throttle when they realize that the turn is tightening beyond their ability to control the car at the entry speed. When this happens in an S2000, the result will likely be a nasty spin.

QPhox4

This may be total BS, but the way I understand it is: turns in hiways/roads/tracks are usually engineered using a radius, i.e. if it were a full circle it would be perfectly round, with a radius. The smaller the radius, the tighter the turn, with appropriate speed recommendations when the turn would require lowering your speed to safely make the turn, if less than the posted limit. I've read that pro racers can just about set the steering wheel going into a turn, and not have to adjust the steeriing until they roll out of the turn. A decreasing radius turn is one which starts at one "radius," but gets tighter (decreasing radius) as the turn progresses.

Charly

[QUOTE]Originally posted by negcamber
[B]However, as the curve becomes tighter you probably won't be able to maintain that higher entry speed.

Indecision

One should try to avoid getting too hot into the corner - keep in mind the golden rule "'slow in-fast out". Ease off the throttle slowly if you find yourself too hot, do not lift.

[QUOTE]

Charly

Indecision, that makes sense, but I must say, you're handle is the most worrisome part of your post for me.

STL

Yup, that is what I've always heard them called. There is a nice little road by the airport that has two short 90 degree turns one right after the other then a decreasing radius turn then a long sweeping turn...I love that road! Thank goodness the St. Louis airport expansion isn't taking my road!

WhiteS2k

There is one turn around my area that has a decresing radius (the 101N to 237W junction in Mountain View). I see cars driving off that turn all the time because they expected a constant radius turn and in the middle, the turn tightens and people don't expect it. The worse part about following the "slow in - fast out" rule is that once a driver gets into the turn, s/he expects it to be constant and start applying gas half way through to do a fast exit, just in time to find out the turn tightens. So they panic and lose control, either that or they just run right over the curb and into the bushes.

JohnnyCat

Palomar Mountain in San Diego seems to have alot of dimishing radious turns as well- I have gotten in trouble coming in too hot, but thankfully, I have been able to maintain.

Does the 50/50 weight distribution on the S help reduce throttle lift spin problems?

Alz2002

From all the talk, the S is one of the more susceptible cars to throttle lift spins out there. The problem with decreasing radius turns makes it worse, since there is a tendency to lift when you realize the radius is decreasing. A neutral throttle will allow some speed to bleed off, and gentle gradual steering input will avoid spin. Of course, it is a perfect opportunity to execute that perfect drift...