So, here's a dumb noob question I know, but it's probably a REALLY good idea if I learn this

I'm often confused about the following.....say you are cruising along and all of a sudden whatever reason, you want a bunch of power. Yes I know you can just stomp on the accelerator, but if you want to go down a gear, how do you know when it's safe to go down a gear RPM wise? I'm just trying to make sure I understand what is safe and what isn't.....thx!

TH

 

I think it comes with experience and knowing your car. At highway speeds I've gone from 6th to 4th to make a pass. In town, I've gone from 4th or 5th to 2nd, but I'm only going 40-45mph when doing this. Obviously if you're in a gear and you're at 6000rpm or higher you dont want to down shift. I never downshift to 1st unless I'm coming to a stop. Hope that helps.

 

Below 3k RPMs you should be good to downshift into 3/4/5, but you can always let the clutch out a little to see what the tach is doing and how the engine feels/sounds before fully releasing. This is also useful when you're not sure if you hit the right gear with the stock shifter. You don't want to dump the clutch and find you accidentally went 6>3.

 

You need to learn your shift points by memorizing redline of each gear. Take a pen and pad and go find out.
That way you know how far you can go on a downshift in a passing/max power situation and choose the correct gear (I'm on mostly 2 lane mountain roads with limiting passing opportunities). I love reaching for 2nd (5spd), but I know I better be below 55mph, or the shift is wasted because it redlines @ 65mph (6500rpm). If its above 55, I reach for 3rd and can ride it all the way to 105 if I need to.
Also, since I know those, and out of decades of habit due to love for my synchro's, I double clutch and rev match with each downshift. Learning your shift points helps in knowing the correct rev match.

 

Okay, here is the simplistic answer. If you want max acceleration and you are going 45 or less, grab second gear and be prepared to shift to third fairly quickly. I'm assuming your second gear is good to near 60. If you are going much more than 45 there probably isn't enough speed left in second, so grab third. By the time third is ready to top out you will be going so fast you better be really lucky regards speeding tickets. If you are going too fast for third to help you, you probably don't need to downshift anyway.

If you are going less than 20 you could probably get away with going down to first. I've used SelectShift to downshift an automatic to first at near 20, and that box won't let you do a shift that can damage things.

 

On a semi-related note (and because it was just brought up), does double clutching do anything beneficial for a vehicle with synchros? I understand the concept, I'm just not grasping why the throttle can't be blipped while the clutch is pressed in during the gearshift.

So, why do clutch out -> neutral -> clutch in -> throttle -> clutch out -> downshift - clutch in, when you can just do clutch out -> neutral/throttle - downshift -> clutch in?

 

You're talking about an automatic...most are assuming the OP is referring to downshifting a manual transmission.

 

I double clutch on a down shift, may be pointless but it's a habit and the synchros don't work hard at all.

This all happens in a less than a second but here are the steps...

Clutch in, neutral, clutch out, rev to match, clutch in, shift to gear clutch out, go.

 

This whole conversation tickles me. My last manual was my 1st car - a 1989 Chevy Corsica. 5 speed stick and 2nd was good to about 25 (not 60). Speedo went to 85, but redlining in 5th prob got me to 95. Dunno cause the speedo was pegged (there was also no tach, so "redline" was where is sounded like RPMs were too high). Couldn't kill it thou...

 

No, I'm not. I'm talking about a manual except for the example I mentioned about my experience downshifting to first with an automatic. I'm assuming that in a six-speed manual first is probably good to 35 - 40, second is good to about 60, and third is good to perhaps 90 or better.

 

Why would you be shifting or downshifting in an automatic?
I could swear that make manual transmissions for that exact reason LOL

 

Autocross, spirited driving on tight twisty roads, long uphills. The SelectShift automatic works great in those conditions, and in normal driving (especially stop and go on a freeway) I don't have to shift if I don't want to. Manual transmissions are not the ONLY answer. I sold a Honda S2000 when I purchased my Mustang and I have no regrets about ordering it with the automatic.

 

Simple rev match only spins the engine higher. It doesn't spin the incoming synchro higher because you have the clutch in (trans disengaged).
Double clutching adds that step with the clutch out (trans engaged but gear in neutral) so you also spin the synchro (and gearset) higher. Then your downshift is nice and smooth on the synchro and you have rev match.

There it is:

 

No need, blipping the throttle gets you a nice smooth downshift.

 

Buy a Shelby. Second is good through 85.

 

I blip the throttle, rev matching, when downshifting. One of those things that are habit and dont think about doing it any more. You could say it's automatic

 

First .... I think you have your "clutch in"s mixed up with your "clutch out"s ???

As I was taught on the farm and as I always have read and said it ...
... "clutch in" means clutch pushed in towards floor ...
... "clutch out" means pedal released and out as in towards me.

The "why" you ask about is because reving in neutral with the clutch pushed in (disengaged) accelerates just a flywheel which is always turning crank RPM ...
... but does nothing to speed up front side of gear train in transmission to match the next lower gear.

 

By "out" I mean "disengaged". I didn't feel like writing that out each time and I figured everyone would get the idea.

 

Tbear has it correct - that is the standard phrasing - for gearheads and on the farm. Yours is backwards. "In" means "disengaged" (pushing in towards the floor).

I double clutch because I just like going the extra mile in caring for my transmission. My '83 F150 4X has 254k on the original transmission and it works great. It is a stiffer shifting trans (esp when cold) so I've just always been in the habit of double clutching. It has paid off!