jelanier

I have been reading a book published by Barber Racing School about race driving. The book discusses braking and downshifting in 2 separate sections but does not specify what I am asking. (unless I missed it)

Situation: I am traveling at 120 MPH on a straight entering a brake zone where I will go from 5th to 3rd gear.

Question:
When I start my hard braking, when do I disengage the clutch? Do I only disengage when I have slowed enough to downshift? Do I disengage immediately when I apply the brakes?

I would think that an early disengage would require a double clutch because the input side of the tranny would have slowed considerably.

Here are 2 possible scenarios. Are these correct?

1. Disengage immediately and go into neutral then release clutch (prepare for double clutch blip). Blip, press clutch, go to 3rd, release clutch.

2. Keep engagement and slow to intermediate shift speed for 4th followed by fast downshift and blip (no double clutch) repeat for 3rd.

Any help from experienced track drivers would be appreciated. (BTW, I read where D. Sullivan said he never double clutched in his life. Larger blips and parasitic clutch drag I guess)

Thanks,

Jim

aCab

I honestly don't know exactly what I do. I just do whatever feels right and isn't going to unsettle the chassis. Don't over think it. So many times with driving people over analyze it and sych themselves out.

Here's a video that shows what I do. - http://vimeo.com/26854290 When the revs stop climbing, I'm pretty much on the brakes (no coasting).

Good luck!

dan_uk

don't push the clutch in till you are ready to move the gear shifter
if I am downshifting more than once I usualy let the clutch out at least a bit between shifts to engine brake a bit

you don't have to do that I think it helps me and I don't like to skip gears because I'm worried about overrevving

robrob

I've read a lot of performance driving books and several downshift techniques are recommended. I went with pushing in the clutch at the beginning of the braking zone and leaving it in until I'm ready to heel-and-toe to select my corner entry gear. I regularly go from 6th to 2nd at the end of Summit Point's front straight. Keeping the clutch in keeps the engine from fighting the ABS and also keeps you from accidentally hitting the accelerator and fighting the brakes. For 99% of people this will allow you to maximize your braking by letting you focus on threshold braking because most of us do release some brake pressure when we blip the throttle.

I realize the syncros will have to spin up the transmission input shaft for the shift but that has not been a problem for my S with 100+ track days.

Leaving the clutch engaged during the entire braking zone will allow the input shaft to slow with the drop in road speed. To get the input shaft up to the speed needed to match a proper downshift you will have to double-clutch as mentioned above or downshift through every gear.

For a description of how I downshift and heel-and-toe see: http://robrobinette....2000HeelToe.htm

My shifting technique can be seen here: http://www.youtube.c...h?v=5FkTlSR8dVA

ZDan

I've never seen this recommended. Source? Seems like very poor form, I always instruct students to keep off the clutch unless shifting.

You can skip gears doing the "normal" technique of keeping the clutch engaged until shifting. You just wait until when you'd be doing the last downshift anyway. No biggie, I do this all the time. I would probably go 6-4 and 4-2 rather than 6-2, though.

??? ABS will take additional drag at the rears from compression braking into account. I've never felt the engine and ABS were "fighting" each other.

??? If you're accidentally hitting the accelerator, i clutching all the way through the braking zone might be a band-aid, but surely improving technique to avoid this is preferable!

I disagree, and I think that having the clutch disengaged for the entire braking zone takes away a lot of info on when exactly to downshift. Keep it engaged, and you will have more input, as you'll know exactly what rpm you're in from road speed in the given gear, much better idea when is the best time to downshift.

???? No double-clutching required, nor downshifting through every gear. You will have to match input shaft speed to road speed whether you keep the clutch engaged or disengaged. In fact if you declutch as soon as you start braking, presumably you're just at idle until you need to shift, so a much greater rpm disparity to get to the appropriate rpm for the next gear down vs. leaving the clutch engaged.

Obviously you *can* drive a car this way, but in my opinion it is not a good idea, poor form, and nothing to be gained by it, and info on drivetrain speed vs. road speed is lost. Clutch should be engaged at all times except while shifting.

vanDiemen

shhhhhh. stop giving away secrets please..

dan_uk

here this is how senna does it I say copy him and you'll be allright:
http://www.youtube.com/watch?v=8By2AEsGAhU

WynnS123

^^ He heel and toes while rowing through all the gears. That is the only way that feels natural to me.

robrob

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Source?

I'm out of town right now but I'll post the source when I get home.

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Keeping the clutch in keeps the engine from fighting the ABS

??? ABS will take additional drag at the rears from compression braking into account. I've never felt the engine and ABS were "fighting" each other.

With the clutch engaged the engine will try to turn the rear wheels and fight the brakes to keep the wheels turning. When ABS engages the wheel has stopped turning, something the engine is fighting against.

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??? If you're accidentally hitting the accelerator, i clutching all the way through the braking zone might be a band-aid, but surely improving technique to avoid this is preferable!

Accidents happen, and keeping the clutch in can prevent one. With the clutch disengaged you'll know if your foot accidentally hits the accelerator (you'll hear the engine rev) and you'll quickly learn how to keep from doing it. I've seen my students accidentally add throttle while max braking with the clutch engaged and it's very similar to brake fade. Suddenly you're not braking enough to make the normal turn-in point. You won't hear the engine rev because the brakes keep the rpm down. I actually diagnosed this problem by having a student keep the clutch disengaged and sure enough the engine reved to redline in the next brake zone. He was wearing big-ass sneakers and covering both pedals. This is much more common than you would think with students learning to heel-and-toe.

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For 99% of people this will allow you to maximize your braking by letting you focus on threshold braking because most of us do release some brake pressure when we blip the throttle.

I disagree, and I think that having the clutch disengaged for the entire braking zone takes away a lot of info on when exactly to downshift. Keep it engaged, and you will have more input, as you'll know exactly what rpm you're in from road speed in the given gear, much better idea when is the best time to downshift.

Are you looking at the freakin' RPM gauge while threshold braking? Can you hear your engine exhaust on track at idle throttle and low rpm? You don't gain any feedback from having the clutch engaged.

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Leaving the clutch engaged during the entire braking zone will allow the input shaft to slow with the drop in road speed. To get the input shaft up to the speed needed to match a proper downshift you will have to double-clutch as mentioned above or downshift through every gear.

???? No double-clutching required, nor downshifting through every gear. You will have to match input shaft speed to road speed whether you keep the clutch engaged or disengaged. In fact if you declutch as soon as you start braking, presumably you're just at idle until you need to shift, so a much greater rpm disparity to get to the appropriate rpm for the next gear down vs. leaving the clutch engaged.

I think you're confused about the input shaft. With the clutch in and in neutral the input shaft is disconnected and spins on its own and slows due to friction. Engaging the clutch while in neutral (double-clutch) will match the input shaft to engine speed. Rowing down through the gears also engages the input shaft to keep it spinning. I don't do either, I allow the syncros to match the input shaft to the transmission during my one downshift (this happens with the clutch disengaged and the shifter is snicked into gear).

My engine is at idle at the end of the braking zone but a good heel-and-toe blip matches engine speed to transmission speed no problem.

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Obviously you *can* drive a car this way, but in my opinion it is not a good idea, poor form, and nothing to be gained by it, and info on drivetrain speed vs. road speed is lost. Clutch should be engaged at all times except while shifting.

What's your published source for keeping the clutch engaged? I disagree with your opinion, The gain comes from not having to waste braking energy to overcome the drive of the engine and ensuring you're not mixing throttle and brake.

My technique works. I turned a 121.7 lap at Summit Point Main with a stock engine/transmission/gearing and I've never had any clutch, transmission or differential problems.

View my video above and witness the fastest S2000 lap ever videotaped around Summit Main.

Sukeetoshyoo88

how do you guys blip the throttle with the top part of your foot?
and with your heel on the floor? (from another thread)
are my feet just not wide enough? cause I have to step over and hit the throttle with the side of my heel