Downshifting in Autocross

[smg1138]

Just curious how many of you downshift to 1st during Autocross runs? I've been told different things from different people about it. I sometimes have trouble deciding; especially when going around a pin cone or on extra technical courses. Considering our cars don't have a lot of low end torque, I think it probably makes sense in many situations. I guess it really comes down to possibly chugging in 2nd vs the time it takes to make the downshift. I'd like to hear some feedback from you guys and what you find works best in your experience.

[renfield90]

1st gear isn't really tall enough to justify it. We top out around 35 - to make the shift worthwhile, the time you spend downshifting + the time you spend upshifting must be less than the time gained by extra acceleration in 1st gear.

I'd say as a seat of the pants guess that around 15mph of headroom (apex speed 20mph) is where it starts becoming worthwhile. Also it's a VERY tall hill to climb to get back into first in terms of rev matching. Last but not least you increase the risk you spin the car if you're applying throttle mid corner; usually it's a lot easier to stay in a higher gear and just get on the gas sooner and more aggressively.

Typically the cars that go back to first have a super long 1st gear (AP1 S2000, first gear winds to about 45mph) and they are more likely to see speeds below the threshold where it's actually faster to downshift.

[Shark_Bait88]

You have to be going really slow, like under 10mph, to make a smooth shift into 1st. At least my trans is notchy enough that the car doesn't like it. Like renfield90 said, the time saved vs time spent probably won't be in your favor.

Or the simple answer, not me. haha

[Frost]

Originally Posted by renfield90

1st gear isn't really tall enough to justify it. We top out around 35 - to make the shift worthwhile, the time you spend downshifting + the time you spend upshifting must be less than the time gained by extra acceleration in 1st gear.

I'd say as a seat of the pants guess that around 15mph of headroom (apex speed 20mph) is where it starts becoming worthwhile. Also it's a VERY tall hill to climb to get back into first in terms of rev matching. Last but not least you increase the risk you spin the car if you're applying throttle mid corner; usually it's a lot easier to stay in a higher gear and just get on the gas sooner and more aggressively.

Typically the cars that go back to first have a super long 1st gear (AP1 S2000, first gear winds to about 45mph) and they are more likely to see speeds below the threshold where it's actually faster to downshift.

I have an AP2 but even then first is usually a waste effort.

See attached video below - I had a great downshift to 1st with the exception of 1 run where I botched it at the end.
[ame="https://www.youtube.com/watch?v=kf-owZPzmCg"]SPDA Advanced Driving Clinic - 2nd Day - April 24, 2016 - YouTube[/ame]

I kept it in second for most of it and it was so much better except for the last sharp hairpin.

[renfield90]

Originally Posted by Frost

I have an AP2 but even then first is usually a waste effort.

See attached video below - I had a great downshift to 1st with the exception of 1 run where I botched it at the end.

I kept it in second for most of it and it was so much better except for the last sharp hairpin.

AP1 at 2013 nats, six downshifts to 1st.

[ame="https://www.youtube.com/watch?v=RuFqiftsr-s"]2013 SCCA Solo Nationals East Thursday STR #180 77.861 sec - YouTube[/ame]

His license plate is "DWNSHFT"

[renfield90]

Originally Posted by Shark_Bait88

You have to be going really slow, like under 10mph, to make a smooth shift into 1st. At least my trans is notchy enough that the car doesn't like it. Like renfield90 said, the time saved vs time spent probably won't be in your favor.

Or the simple answer, not me. haha

I have actually tried a couple 20mph rev match to 1st shifts on the street lately. It takes too much effort and concentration to get it right. It's a possible reward of 1-2 tenths but with a risk of a 5 tenths mistake.

Last year at nats I rev matched very poorly on east course, which was uncharacteristic given how much I practiced it. I tried taking a run with no shifts to 3rd and ran an identical scratch time. Given how much time was spent in third gear on the previous run, that should tell you how much of a penalty it is to bork a heel-toe. You're increasing that potential penalty going to first.

[Lynxis]

I find my shifter just doesn't want to go into 1st when I'm travelling faster than about 8km/h no matter what. I don't really want to force it so I just leave it in second, on the courses around here, everything is fast enough that going to 1st is a waste.

[Frost]

Originally Posted by renfield90

AP1 at 2013 nats, six downshifts to 1st.

His license plate is "DWNSHFT"

Man, I wish there were more large autocross events like that up here. Ours is soooooo much smaller.

[GeorgeJFrick]

The transmission doesn't seem to like it, and it doesn't seem to help (for previously mentioned reasons). There is also a speed academy episode where they talk about jamming the car into 1st (and they proceed to replace the transmission). I've considered trying to get better at it; but from the video it sounds like you would be turning the tranny into a season disposable item.

[renfield90]

Originally Posted by GeorgeJFrick

The transmission doesn't seem to like it, and it doesn't seem to help (for previously mentioned reasons). There is also a speed academy episode where they talk about jamming the car into 1st (and they proceed to replace the transmission). I've considered trying to get better at it; but from the video it sounds like you would be turning the tranny into a season disposable item.

Some cars do not have a syncro for first - and then yes, the transmission becomes a wear item unless you double clutch it.

Ours is synchronized. But it's a big ask from the syncro to go 2-1 at appreciable speed. I consider all syncros to be wear items, even in street cars, but this will definitely wear it out faster (whereas if you're actually careful, you could get syncros to last most or all of the life of the car).

[chaoskaze]

O.O I can't say much but changing the fluid to motul really helps? Atleast I know I can down shift into 1st @20-25miles smoothly no problem. But then again I got 36k on the car now... >_> Lets say it's all done with breaking in now...


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[jamomatt]

I run really tight gymkhana courses over here n am in first for every turn. Going from second to first is just a matter of rev matching... You'll get used to it.

[ame="http://www.youtube.com/watch?v=TmoZ5VV73oo"] typical gymkhana run in Singapore[/ame]

A typical course is like the one above. I guess it really depends on how slow or tight the turns are.

[rx3]

Here's an example of a relatively fast course where I needed to downshift to first-gear 3 times:
[ame="https://www.youtube.com/watch?v=y2SGdUB6hmk"]Dry Autocross/Hillclimb - YouTube[/ame]

And here even 7 times:
[ame="https://www.youtube.com/watch?v=zfOjgMslR4I"]Rallye-Autocross - YouTube[/ame]

No need to rev-match since you have usually much more time to shift when you decelerate/brake than when you accelerate.

[renfield90]

Originally Posted by rx3

Here's an example of a relatively fast course where I needed to downshift to first-gear 3 times:

And here even 7 times:

No need to rev-match since you have usually much more time to shift when you decelerate/brake than when you accelerate.

First off, very nice driving given there was no room to make mistakes. Wish we could drive stuff like that here but the lawyers would say no.

Next, I looked at your speedometer for all your 1st gear downshifts in the second video to approximate apex speed:

0:50 - 39kph = 24mph
1:06 - 30kph = 19mph
2:30 - 40kph = 25mph
2:49 - 35kph = 22mph
2:56 - 45kph = 28mph (note: too much power on exit, caused oversteer and loss of time)
3:14 - 36kph = 22mph
3:30 - 43kph = 27mph

Also, looking at video 2, at 1:19 there was a right hander you stayed in second gear for. Apex speed on the dash was 50kph (~31mph in the Land of Silly Unit Systems). 31mph would be about as slow as the slowest turn at a "normal" US autocross. Didn't Wilmington have a 29mph corner last weekend that EVERYONE complained about?

So maybe my 15mph buffer is a bit high. Still I'd say 10mph minimum buffer (25mph apex speed) to make the shift worthwhile. At 2:56 you could've stayed in second gear which would've made the car easier to drive on exit and maybe not caused you to lift and correct the car.

To me, once you have the fundamentals down autocross is all about damage control and limiting your own mistakes. Where possible, I preach that you shouldn't create opportunities for yourself to make a mistake especially when the payoff is small.