What RPM does 1st gear lockout?

I've been working on my heel-toe. But have not yet tried 2nd down into 1st. Once I master this it will be extremely valuable for some of the tight autocrosses I run.

 

Im not sure, I know that in the rx8 (same as my miata) its only easy to get into 1st from around 5mph-0mph....its a little harder from 5-10mph and damn near imposible above about 15 (those speed are what I think I see, if I remeber although i dont really pay much attention to the speeds....jsut the sound and feel).

 

Somewhere over 3k. I usually have to rev it way up to get it into the 15 mph range in 1st anyway (when heel toeing)

 

Try double-clutching. It makes the 2->1 shift significantly easier.

 

I have noticed that as well. I have to get my below 5mph to get it into gear without forcing it.

 

If you rev match correctly there should be no need to double clutch. Actually, I can't think of a situation where it would be necessary to double clutch. If you get it right you can catch first gear anywhere within it's rev range. Plenty of opportunities to practice that 2-1 downshift cruising around town-



Chops


Edit: Ok, maybe to get it into reverse or first gear from a stop on a car with sticky or abused syncros a double clutch would help.

 

There is no "lock-out." Just the inability of the synchro to engage 1st. According to the manual, 2->1 over 20mph can damage your tranny. If you shove hard enough, though, you can get the syncros to engage. And if you rev match you can get 2->1 all the way to 1 gear redline (which is like, what, 32?)

 

Exactly, there is no lock-out. Double-clutching eliminates the needs of the syncros to 'magically' speed up the layshaft in the transmission. I didn't say is way a necessity, but it does make the 2->1 shift at high rpms much easier. Any time you can reduce the load on the syncros, the shift will be easier.

 

Also, rev matching, when single-clutching, has NO EFFECT on the syncros.

 

Interesting. So if I am downshifting from 2 to 1 at say, 30mph, and I can sneek in a double pump, I can glide into 1st without rev match? Why?

 

You just dont need them. They still act as though they are doing their job, nevertheless.

 

I would disagree. With a double clutch you are trying to coordinate two clutch downstrokes, a shifter action, and a now delayed throttle blip. Not only is it slower, it is more movement to coordinate. All you have to do is tag the brake, clutch in, throttle blip, clutch out (shifter movement is in between) and you're on your way. The rev match is what makes things easy, their should be NO forcing involved. When you get it right, it should drop right into gear, no crunch and no forcing necessary, and it should be nice and smooth.

Chops

 

I didn't mean to imply that forcing was good. And I did mean to imply that rev matching removed need for forcing. Sorry for the lack of clarity. Forcing is bad.

 

The single-clutch rev-matching does not make moving the gear selector into first any easier. I agree that double-clutching is harder to perform, especially while braking.

Think about it: when you rev-match you are spinning up the engine. But the layshaft is still spinning at the speed it was before you pushed in the clutch. Pushing the gear selector into first causes the syncros to speed the layshaft up to the speed of the driveshaft. This is not made any easier by rev-matching. What you have done is eliminate the drive-line shock that comes when you release the clutch.

If you double-clutch, the rev-match portion of the shift is using the engine to speed up the layshaft to the speed it will be at when you engage first gear. This is much easier on the syncros. Also, if you can do this well, there is no need to use clutch AT ALL. That should emphasize how much easier this is on the syncros. I've done clutchless 3->2 shifts a number of times, although I don't think I'd try a 2->1 like that.

All I'm saying is that if you are having trouble physically moving the gear selector into first, the problem is that you are asking the syncros to do too much. Typical single-clutch rev-matching does NOTHING to help with this problem.

 

No, you still need to rev match. Here's what rev-matching does:

Single-clutching: eliminates drive-line shock/lurch when you release the clutch.

Double-clutching: eliminates drive-line shock AND matches the speed of the syncros, reducing the work they must do.

 

I dont understand this. How is a blip to the throttle to match engine RPMs affecting anything in the tranny when the clutch is disengaged?

 

Sorry. I understand you now. When you engage the clutch in neutral, everything is now at the same RPM. Nevertheless, I don't see (or feel) any need to double clutch. It is sufficent i my mind to disengage, blip, downshift, engage.

 

This is where I would factually disagree. You dont even need to disengage the clutch if you rev match. That doesn't get any easier. (when it works )

 

So If I stll need to rev match, then double clutching does...nothing.

 

Ok guys, here's how it breaks down:

engine-->clutch--->layshaft--->gear-selector--->driveshaft.

The clutch and the gear selector are what link the three pieces together. Now some of you may remember trans. w/o syncros. In those cars, when you downshift, the gear selector moves into neutral, decoupling the driveshaft and the layshaft. The layshaft is still spinning at the speed of the engine, say 5k. When you push the gear selector into the next lower gear, one gear spinning at 5k will grind with one gear spinning at the new rpm the engine will be at in the lower gear, say 7k. The gears will scream in protest and probably not mesh.

Ahh, so you say rev-match eh? Well since we've got the clutch in, lets give it a blip. Oh wait, the engine spins up to 7k just fine, but since we've got the clutch in, we haven't affected the layshaft in the trans. which is still spinning at 5k. We still grind.

Thus the double clutch. When you rev match with the clutch out and the gear selector in neutral, you have coupled the engine and layshaft, but decoupled the layshaft and drive-shaft. Thus both engine and layshaft spin at the same rpm when you blip the throttle, and moving the gear selector into gear is harmonious, because everything is spinning at 7k.

So in the same scenario with a syncro. trans, when we rev-match with the clutch in, we are NOT making it any easier to move the gear selector into gear (thus coupling the layshaft and driveshaft). The syncros still have to handle the same amount of work, namely spinning the layshaft up 2k faster as the gears approach each other so that by the time they meet, they are both at 7k.

If you rev-match with the clutch out in a syncro trans. you're still spinning the layshaft up to the same speed as the driveshaft, the syncros don't have to do much but maybe account for a few rpm.

So what is the point of the clutch then? Well, if you could match all three things perfectly, you'd never really need it except for starting. But since we have syncros now on our trans. we're in general, not too good at matching. The clutch allows the torque of the engine to be decoupled from the layshaft->driveshaft coupling. This removes the load from the gears, making it much easier to disengage one gear and engage another. If you manually pull the gearshift into neutral while trailing off the throttle, you'll see that you can do this easier if the load is not changing speed.

Yes you can shift without using the clutch on a syncro trans. but either you won't be able to rev-match, or you'll rev-match in neutral (which congradulations, is the clutchless version of double-clutching).

Finally, to confuse things a bit more, the Skip Barber school teaches on their Forumla Dodge cars (non-syncro boxes) to pull the shifter into neutral (without the clutch), blip, clutch-in, engage lower gear, clutch-out: the 'single-clutch' version of the double-clutch. So we see that double-clutch really just means rev-matching in neutral, with the clutch out, regardless of how many times you push the clutch in.

Oh yeah, one more thing: when we complain about hard shifts, what is it exactly that's the problem? Its hard to move the gear selector INTO the next gear! This means that we are asking the syncro's to do a lot of work (big difference in speeds between the two gears), or syncros cannot make the gears match, because of missing teeth, bent forks, etc. The syncros get the energy to match speeds thru the motion of the shifter into gear, so its natural that's where the resistance ends up.

 

Ok, that makes sense. But, again, in a realistic autocross scenario, thats alot o' movement to coordinate while screaming up on a tight ugly section. I've never encountered a difficulty in getting it to slot into first gear with my regular single clutch heel toe, so I guess I'm a bit skeptical about it's necessity on a car with this nice of a transmission to begin with. It's miles better than my first gen was! I can see the value of a double on a non syncro box, but other wise, seems like extra work-



Chops

 

Thanks tuj! Great writeup.

I can't really time myself...but I have double clutched heel-toe very fast 4th-3rd while practicing on a deserted access road. I think quick enough that if I can learn to do it second nature 2nd-1st it would be invaluable on an autocross.

Double clutching appeals to me for a few reasons (1) I grew up driving a Dodge Sport 3-on-the-tree. Although it was rumored to have synchros, you'd never know it, and my parents bought it new! (2) The idea of synchros is nice when I'm feeling lazy, but I got a manual to be more connected to the car, so sometimes I really want to feel like I'm doing all the shifting (3) In a few years I hope to get a Formula Ford or a Star Mazda (I WISH) for track use, and there's nothing wrong with getting techniques down now

 

Chops: hey, its its working for you then great! I personally can't get my car into first consistently above about 20 mph without double-clutching. The 2->1 is harder than any other downshift due to the amount of torque on the syncros.

 

Tuj,

I am going to copy this into a word doc and save it (if you dont mind, to avoid the mysterious thread deletions). Thanks. I'll consider and try it myself.

Hey, maybe you wont mind commenting on this question? https://www.rx8club.com/series-i-tech-garage-22/clutch-engagement-point-71794/

 

isn't it not recommended by the manual not to shift into 1st gear above 20mph?