downshift during course?

[bug killa]

hey guys I'm pretty new to autox'ing (been 2x love it), and I have a question. Do you guys downshift to 1st gear often when ur autox'ing to stay in lift? or do u basically keep it in 2nd? this question is for both gt and gts owners, but i'd like to specifically hear from gts owners.

thanks guys

[pitcrew]

You typically only downshift to 1st for a tight turn around pivot (a single cone or group of cones that you do a 180* around) Shifting is VERY slow, no matter how fast you are at it.

[NoCones]

Originally posted by bug killa
Do you guys downshift to 1st gear often when ur autox'ing to stay in lift?

I don't think you ever want to downshift if it's going to put you in 1st at over 6k...wheelspin galore. (I used to have a GT-S.)

I try to avoid downshifting because there's already enough going on and downshifting just multiplies the potential for error. Sometimes a turn is so tight that you have to though. I can't heel/toe or anything, so I just shift right before I need the power and go.

[bug killa]

yeah that's what I was thinking, especially since it's so darn hard to get our cars into 1st gear w/o double clutching.... cool guys thanks...

[00 scrub]

how do you gauge the number of revs you have to give the car when you want to downshift to 1st gear? I can double-clutch any downshift except 1st gear. I am too afraid to grind my gears if I rev it incorrectly. Which speeds correspond to what RPMs?

[nxracer]

In my many years of autocrossing I have found it's pretty much never a good idea to go back to first gear.

[pitcrew]

Originally posted by 00 scrub
how do you gauge the number of revs you have to give the car when you want to downshift to 1st gear? I can double-clutch any downshift except 1st gear. I am too afraid to grind my gears if I rev it incorrectly. Which speeds correspond to what RPMs?

Double clutching, while fun to do to impress your friends is totally unnecessary with today's full syncro transmissions (the gears will not grind), and a MAJOR time loser in competition. If I am downshifting to first on an AX course, it's because I'm at walking speed, so a slight slip of the clutch (think traffic lite changing green JUST before you completely stop) while adding throttle so as to not upset the car is usually all the rev matching I do.

[Phil C]

I've noticed the same thing that nx is talking about. Following advice I've gotten from this board and from the good drivers at the local events I've started to make every attempt to never go into first unless I've spun out and come to a complete stop.

Our first event of the year, 2 Sunday's ago, featured a 180 right hander around a single pivot cone with a sharp 90 degree left into a long no-option slalom 15 walking paces after the pivot. My first run I felt sure that this was a sure spot for a downshift to first so I did. I found that I was running out of revs as I was turning in for the first slalom cone and my shift to second put me far enough off balance, and my brain farted while trying to do too many things at once, that I hit the second slalom cone pretty much dead on with my inside wheel (there was no doubt I hit it since it was still in my wheel well at the end of the run). My second run I re-thought it and kept it in second and was able to enter the slalom MUCH faster without hitting any cones even though I took nearly the same line and entrance speed to the pivot.

I've taken to watching the really good drivers both FWD and RWD to see how they do the course, they all ran after me since I was first heat. Not a one of them downshifted for that pivot, just turn and rev it so that there was a bit of tire spin to keep the engine from bogging and go.

[traitor]

we have very tight courses in my area and at the last auto-x I went to 1st gear twice, I hate doing it though.

[nxracer]

Originally posted by traitor
we have very tight courses in my area and at the last auto-x I went to 1st gear twice, I hate doing it though.

After you have learned the course... Humor me and try it without downshifting.

Spinning the front tires does not make the run faster

[00 scrub]

ok the downshifting to first at walking speed makes sense. I can do that normally when driving. I have one technical question, you [pitcrew] say that double-clutching is not useful nowadays with syncro trannys, but why does double-clutching bypass the syncros in the engine? Why(inside the tranny) does one have to release the clutch in neutral, rev, push the clutch in, then select the gear? I have heard from some people that double-clutching is not nessaccary to save on syncro wear, but others have stated that you have to double-clutch inorder to prevent your syncros from wearing.
thanks to anyone who responds

[GTS LAID]

lets clear this all up...

the purpose of double clutching is to bring the next gear up to speed with the tranny output shaft which turns at the same speed as the wheels (or more accurately differential). In order to do this you have to understand how the gears attach to the engine. The gears are always spinning because they always meshed to the layshaft ... you can think of the layshaft as always being connected to the clutch.. which means pretty much that if the clutch is spinning then the gears are spinning.

The way you select a gear is by hooking up the collar of the tranny output shaft to one of the already spinning gears... now this can get ugly if the 2 arent spinning at the same rate.. so the synchronizers are used to match the speeds of the gear and the output shaft.

when double clutching what you do is first disconnect the output shaft from the gears by pressing the clutch in, putting the thing in N and letting go of the clutch... so now the output shaft is spinning happily with the wheels without touching the engine... the gears themselves are spinning at engine speed.. remember that pressing the clutch in actually disengages it because of the plate and springs. So what do we have after the first 'clutch' is the engine attached to the flywheel attached to the clutch attached to the layshaft which is always attached to the gears... so we have the gears spinning at the same speed as the engine now... so what do we do at this point....

we press the gas... this brings the engine speed and..... therefore the gear speed up to a certain range ... the right RPM for that particular speed in that particular gear. Once the engine is in the right gear ... we now have to connect the wheels (output shaft) to the gears... so we quickly push the clutch in and put the selector in the right gear before the gear slows down, this solves the problem of getting the gears matched up to the output shaft, but we have to quickly re-engage the clutch as well by letting go so that the engine speed doesnt fall down too much... if that happens then now you're going to have the clutch doing a lot of work to bring the flywheel (and engine) up to speed with the rest of the tranny and wheels...

so if you've followed with that you should be able to tell now why pressing the clutch in once and revving doesnt work...

so lets see why not and part review. the idea in the second rev match method is to press the clutch pedal in, disengaging the clutch plate, which disconnect the engine and flywheel from everything else... so now you have all your gears, shafts, and wheels spinning at the same (proportionate) speed. so while the clutch pedal is still depressed, you put the selector in N, this disconnects the output shaft *your wheels* from the gears.. .so you now have 3 separately spinning parts, the engine, gears, and wheels... you rev your engine... well if the clutch is depressed the engine isnt connected to the gears... so the gears are just gonna quickly slow down... even if you do this quickly remember that the gears are spinning at the speed of the old gear, now that you want it to spin faster (for a downshift) you have to speed up your gears by keeping them connected to the engine. you do that by letting go of the clutch, revving, then clutching again to place it in the right gear. with that you'll have a speed matched engine, gear, and output shaft...

by doing the half assed method (1 clutch only) you rev your engine thinking the gears are now up to speed and put the selector in the right gear.. well now the synchros have to actually do the work of bringing the gear up to speed.. and guess what .. since the gears have slowed down, the synchros have to do MORE work this way wearing them down even more than if you just downshifted normally... what about the clutch.. so you place the selector in the correct gear and your foot is still on the clutch pedal, so you THINK your engine is going the same speed as your tranny.. but thats not true cause as long as your foot was depressed the engine was only revving itself. so now that your engine is spinning quickly and your tranny is spinning quickly re-engaging the clutch will save it some wear...

that was long and convoluted but i hope it shed light on this whole controversy once and for all...

so a proper double clutch will save both A. your Synchros and B. your clutch.

[pitcrew]

Maybe cause it's early in the morning, or they call parts something different in your neck of the woods, but sorry to say I know how a transmission clutch and syncros work, I've had plenty of them apart, but I couldn't follow that explanation...
To simplify I hope:
All the gears in a modern transmission are meshed at all times. The gear ratio is selected by the shifter sliding couplers over matching corse toothed drive dogs on the sides of certain gears that, through a series of driven or free rotating gears and shafts couples the input shaft (connected to the clutch disk) to the output shaft (connected to the driveshaft in a RWD car, or the differential in a FWD) at a certain speed ratio depending on the gear selected. PHEW! It's much easier shown than described...
The sliding coupler is helped to engage the drive dog and match their speeds by a special aligning helper gear in between that can slip momentarily called a syncronizer, syncro, or syncro ring. It slips only momentarily as the coupler slides over it. The only strain on that syncro ring is the effort needed to bring the next gear up to the rotational speed of the coupler, since when the clutch is depressed during shifting the transmission is disconnected from the engine power, so there is no driving force on the transmission gears. Thanks to modern metalurgy and lubricating fluids, any wear on the syncro ring is neglegible.
Double clutching is a throwback to many decades gone by, first when simple transmissions of pre WW2 era actually slid the gears themselves in and out of mesh with each other, and their speeds needed to be matched for that to happen without chewing their teeth off, and then later (pre mid 60's) when first gear was still the only gear (besides reverse) not always meshed.
Double clutching today can accelerate wear on the syncro rings rather than reduce it. The faster the coupler becomes fully engaged with the drive dogs, the less work (slippage) the ring needs to do, plus the neutral reving up of the gears in the transmission are a LOT harder for the syncro rings to slow down than is is to speed them up.
Clutch wear is another issue entirely.

So as not to confuse any more, I won't discuss how us drag racers of the 60's would modify the drive dogs and couplers, throwing away the syncro rings entirely, that was the direct predecessor of today's clutchless shifting racing transmissions!

[GTS LAID]

Originally posted by pitcrew
Double clutching today can accelerate wear on the syncro rings rather than reduce it. The faster the coupler becomes fully engaged with the drive dogs, the less work (slippage) the ring needs to do, plus the neutral reving up of the gears in the transmission are a LOT harder for the syncro rings to slow down than is is to speed them up.


I agree with pretty much everything you said... SEE how hard it is to describe this stuff without pictures..hehe... anyway heres one part i'm not entire sure what you're saying in.

the speed of the coupler engaging on the dog teeth on the gear is directly proportional to how quickly you throw your shifter from N to the proper gear. Wear occurs when the speeds of the output shaft and the input shaft (and therefore gears) are different. So to minimize synchro wear you would want to bring those speeds as close to each other as possible... and put the shifter in the right gear quickly so that neither part has any time to slow down. So in a properly executed sequence with the 2 parts spinning at precisely the same speed you will now have any wear on the synchros since the relative angular velocity of the gear and the output shaft, collar, is zero.

The problem you're mentioning is if you OVERREV your engine, and therefore gears... at this point overrevving the gears causes the synchros to have to do more work cause now they have to slow down the gears. you're saying that if there was to be a mismatch between input shaft(engine) speed and output shaft (collar) speed then for wear's sake its preferable to have a lower input shaft speed... BUT in a porper double clutch you wouldnt even have to face that scenario cause there would be very little difference... certainly a smaller difference than you would see if you were simply shifting up or down without manually matching anything.

I'm really new to all this (less than a year) so excuse my lack of terminology and please correct me on anything wrong I've said... i'm gonna cross link this so that some of the autox people can elaborate as they're pretty technical.

[GTS LAID]

hahaha.. whoops.. we are already in autox..

[pitcrew]

LOL!
The gear ratios the engineers install in the transmissions, especially the six speed, are close ratios, so the speed difference is slight. The syncro ring actually uses the sheer strength of the oil to begin and cause most of the gear speed change, much like the way a torque converter works in place of the clutch in an automatic, so there is not real metal to metal contact. You actually can easily up shift your transmission without even using the clutch if you put only the slightest pressure on the gear shift knob after neutral with the car in a coasting state (neither acellerating or decellerating) until it drops into gear. Even though they are typically made of brass, I've never even seen a syncro ring with any significant wear on the "friction" surface, even on transmissions heavily used in drag racing. Like I said previously, double clutching can be fun and impressive to passengers, but there is no compelling mechanical reason to do it today. Professional road racers and Nascar drivers don't even use the clutch when shifting racing transmissions except when starting from a complete stop.

[GTS LAID]

i see what you're saying.. its using the viscosity of the fluid to actually do most of the friction work... so when they say your synchros are bad (like they did the other day about my 4th gear) ... what exactly are they talking about... too little fluid?

[pitcrew]

It usually means the tapered ends of the dog teeth on the syncro ring have become damaged or worn which causes the collar to hang rather than smoothly sliding completely onto the next gear. This will cause the shift to "hang" in neutral or grind. Evidently there is some issue with the rings in the six speeds.

[EndlessShock]

Hmmm... Food for thought... Thanks for the info guys :D...

[REdOX]

Originally posted by GTS LAID


I agree with pretty much everything you said... SEE how hard it is to describe this stuff without pictures..hehe...

Here ya go...

Picture of a clutch assembly (http://www.howstuffworks.com/clutch2.htm)