Threshold Braking + DCHT + stock pedal arrangement

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gizmo
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Threshold Braking + DCHT + stock pedal arrangement

Postby gizmo » Wed Jun 24, 2009 12:53 am

2009 Scion tC

Threshold braking + DCHT

I'm having great luck (accuracy) with it only it's slower than I'd like it to be. I've managed to get a motion going where I am not releasing the brake pressure as I rev match but it requires a very long and awkard heel raise/pivot/push; and by long I mean long comapred to a light braking DCHT. I know if I had a passanger in the car, they wouldn't sense the lengthiness of it but I also know I'd be hardpressed to sequentially DCHT to keep boost up like Gary does because of the length of the individual shifts. I have my light braking DCHT down to Gary's speed.

Just curious if some of the racers out there just accept this as a natural consequence of not custom configuring the pedals so that they overlap properly only under full braking (which is what's mainly done on the track)

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Re: Threshold Braking + DCHT + stock pedal arrangement

Postby LHOswald » Wed Jun 24, 2009 1:35 am

do you mean that its long and awkward because you have to bring your heel up past the gas pedal because your brake is floored so low because of the stock pedal arrangement? if thats the case i think your gonna have to either bend your pedals (such a great idea!) or get a new arrangement. i've never really "threshold braked...or broke?" and DCHT but under semi hard braking it is a little awkward. but i commend you for being able to keep the brake pressure the same. thats the only problem i have now on hard braking, but im trying to be nice to my new brakes and rotors for now so maybe ill test this later :)
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Re: Threshold Braking + DCHT + stock pedal arrangement

Postby ra64t » Wed Jun 24, 2009 8:21 pm

I'm not exactly sure what you mean by slow. but anyway, I don't have much problem with my stock pedals, but the foot placement definitely makes a difference. Shoes do too.

speed of the downshift is not necessarily that important anyway, as long as you get it done before the corner. And skipping gears is fine too, as long as you are good at rev matching.

It's quite surprising but a lot of racecar drivers don't do good rev matches. Even guys racing in pro series. Maybe the kids coming up now realize they likely aren't going to need to rev match in the future because either a computer will do it for them, or a car's propulsion will not have multiple gears in the future, so don't bother to learn it properly.

At racing schools it's quite horrid actually. Most people are all over the place with their footwork.
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Re: Threshold Braking + DCHT + stock pedal arrangement

Postby gizmo » Wed Jun 24, 2009 8:48 pm

My threshold braking DC is slower than the other types. Granted, if I just block shift, I have plenty of time to make the shift and the DC is usually close enough that I can dump the clutch without worry. I always know when I'm off, because the shifter doesn't go in smoothly, and depending upon how resistant the gate was, I slow clutch engagement accordingly. I'm not perfect with my shifts, maybe I should be, but I like to think that I'm pretty darn close a majority of the time.

My concern, and the reason for the post, was: if I had a turbocharged car, and wanted to keep it in boost, then I'd want to sequentially downshift whilst threshold braking. I'm not saying that I can't do it now, nor couldn't do it with practice, but it's undeniably more awkward and detracts from my "on the road" concentration. I think a bit of track time might mitigate this problem, but I don't want to corner myself in a situation where I can only effectively (maximally) drive a normally aspirated car.

To clarify, by awkward and slow, I mean that I need to get the brake pedal squeezed down to it's lowest point before I can even think about DCHTing. Under light braking, I'm used to just grabbing a shift whenever I feel like it. But with threshold braking, I need to get my foot almost stationary, so that I can "flex my calf", which brings my heel up while keep braking pressue steady, and than I can pivot that flexed calf onto the gas pedal and then drop it, however deep I need the rev match to be, and then the opposite to get off the gas and back onto the brake. With light/moderate braking, I just swing and stab, there's no thought or unusualy foot movement.

To be honest, even when I have the pedal down, I still believe I could be braking more effectively, but I've had bad luck with ABS kicking in, sometimes for no reason as far as I'm concerned, but I do believe if I didn't have to shift anything then I could probably brake slightly later and still take the same entry line but the difference is marginal at most? But marginality, on a race track, is anything but??

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Re: Threshold Braking + DCHT + stock pedal arrangement

Postby ra64t » Wed Jun 24, 2009 10:21 pm

whenever I make the downshift, I've already braked as hard as I'm going to brake anyway, and I can't think of any situation where this wouldn't be the case. Whenever you are braking, particularly threshold, you should hit you maximum brake pressure as fast as possible, and there's no need to downshift before this point, even if your trying to keep a turbo spooled or maximize engine braking or something. Obviously you still need to slow down before the downshift or you'll overrev.

I've only driven naturally aspired cars, but the theory behind keeping the revs up to keep the turbo spooled makes sense. I have no idea how significant doing this is though. If I wasn't fully comfortable with DCHT sequentially, I'd just do one block downshift and allow myself to concentrate on the other aspects of driving which are a lot more important. I'm guessing the time lost would be pretty marginal, could be wrong though.
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Re: Threshold Braking + DCHT + stock pedal arrangement

Postby gizmo » Thu Jun 25, 2009 12:08 am

I can think of a situation (I've had it happen)

Imagine you're coming down a straightaway and you engine is just about on the chip. You need to shift gears. So you shift. Now, as you approach the turn, you still have time, albeit very little time, to accelerate in this new gear before you take the turn. Thing is, you need to slow down for the turn, and in doing so, you don't need to slow much -- just enough so that the downshift will give you the pull you'd want out of the turn (for long enough that the downshift makes sense) but it all happens so fast that you literally need to make the rev match as the brake pedal is still traveling downward the brake (if you squeeze the brakes rather than mash them anyway). I couldn't do that with my current pedal arrangement without having to brake earlier and with less force (and the whole concept of threshold goes out the window for that turn). But maybe I'm too eager to downshift, but I know when I do, I always keep the gear for a long enough while that it makes sense.

And I've had instances like these where if I still drove in deep then I wouldn't be smooth the brake pedal and I would unbalance the car more than usual (maybe induce a bit extra push, or maybe release the stored energy in the springs too quickly, or maybe just cause the slip angles to build to quickly....). But then again, most people don't use a car like mine on a race track, they either supe it up first so that it actually makes respectable speed or they use a different car -- so maybe in another car situations like these could be avoided with more ponies.

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Re: Threshold Braking + DCHT + stock pedal arrangement

Postby ra64t » Thu Jun 25, 2009 4:42 pm

I can see how the situation can be common on the street, but on the racetrack, I still don't think it is a big issue because you should be hitting maximum brake pressure so fast - I don't have any data on me now, but the skip barber book has some good data samples. It's like a split second.

A few more things to take into consideration - if you're only pulling that gear for such a short period of time to be able to downshift safely without overreving - you might consider just stretching the lower gear and saving yourself the shift. The extra pull you get from the higher gear might be offset by split second it takes to complete the shift, and then you won't have to worry about the downshift either (unless you need to go two or more gears down). Also, if it's a fast corner that doesn't require slowing down a lot, you might consider lighter brake pressure over a slightly longer period - a lot of times the more gradual weight transfer could actually be faster. So with the lighter brake pressure you'll potentially be getting to your maximum brake still faster.

Just my opinion - others feel free to chime in - obviously there are various valid techniques in race driving.
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Re: Threshold Braking + DCHT + stock pedal arrangement

Postby gizmo » Thu Jun 25, 2009 8:51 pm

All interesting points.

My main experience is on a short track (circle track), where it's rare that you change gears outside of a restart (although some do).

And my road racing is limited to my "karting" -- if people are willing to consider that a form of road racing.

It would be interesting to see how it all plays out on a track, considering I rarely keep the pepiest gear for both gas reasons and longevity. I"m mainly using the bottom half of the engine, instead of the half I would need on a track.

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Re: Threshold Braking + DCHT + stock pedal arrangement

Postby GarySheehan » Fri Jun 26, 2009 12:55 am

This is DCHT in a Scion with a stock transmission, stock flywheel, stock-like clutch and stock pedals.

http://blip.tv/file/1559401/

If anyone knows how to embed bliptv, let me know.

Please excuse the driving errors. The car was VERY tail happy during my stint.

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Re: Threshold Braking + DCHT + stock pedal arrangement

Postby theholycow » Fri Jun 26, 2009 9:50 am

Can't embed blip.tv on this forum. I can help the administrator set it up, though, I just setup blip.tv embedding on another forum yesterday.
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Re: Threshold Braking + DCHT + stock pedal arrangement

Postby wannabe » Fri Jun 26, 2009 10:12 am

gasp. its gary!
Currently not driving anything - the escort died april 2014 and there's no funds to replace it

Crafting and stuff

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Re: Threshold Braking + DCHT + stock pedal arrangement

Postby watkins » Fri Jun 26, 2009 11:23 am

Looks like hes kicking ass too
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Re: Threshold Braking + DCHT + stock pedal arrangement

Postby wannabe » Fri Jun 26, 2009 12:54 pm

watkins wrote:Looks like hes kicking ass too

duh
Currently not driving anything - the escort died april 2014 and there's no funds to replace it

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Re: Threshold Braking + DCHT + stock pedal arrangement

Postby gizmo » Sat Jun 27, 2009 12:39 am

Gary, nice to see you again.


Thanks for your video, the first time I watched it I was impressed. If I may be so bold, I've learned a lot from your videos and your posts. If I may, I'd like to say that you are an invaluable addition to this forum.

Being a college student, with my car as my daily driver, I don't really have the heart (or the money) to beat on it. And the roads being no place for road racing, I really don't have the venue for it even if I did.

That being said, I'd like to ask a few questions if I may: 1) when you first started racing (I know you sat through about a 1.5 years of classes first) but once you actually started getting seat time, were you nearly as good with threshold DCHT as you are now? 2) what is your opinion of the stock pedal arrangements (do you find that you have to lift your heel higher or move it farther than other cars, does that make it any more difficult for you), and 3) are all your DCHTs butter smooth (the movement of the lever itself) or do you find the synchros occassionally doing work even though the clutch engagement itself is pretty smooth, and 4) are you basically dropping the clutch or are those quick but cautiously controlled releases/engagements?

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Re: Threshold Braking + DCHT + stock pedal arrangement

Postby gizmo » Sat Jun 27, 2009 12:40 am

Really, it's great to have you back.


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