This Is Why It's Difficult To Downshift Into First Gear
Changing gear can become an automotive art form when practiced and fully understood, forming a smooth relationship between ratios, engine speeds and differing shaft speed. Although first gear is generally only engineered to get a car off the line, hairpins and sharp corners can necessitate a change down from a higher ratio to the first cog.
If you have tried this before, you may have noticed just how difficult it can be to slot back into first gear, sometimes requiring a mechanically-unsympathetic shove. The most common situation that this occurs is when drivers are slowing down for a traffic light and pre-empt a downchange into first to get going again.
The problem is that the difference in ratios between second and first is large. So considering the job of a synchromesh is to bridge this gap, the synchromesh for first gear has to work a lot harder than in the rest of the transmission.
A synchromesh is almost like a small clutch that sits on the output shaft between gears, slowing or increasing the required gear’s relative speed to perform a perfect meshing of teeth within the transmission. So when trying to downshift to first, the relative speed difference between the output shaft and input shaft will be large compared to the other less-aggressive ratios.
Let’s take a 2016 Honda Civic’s transmission for example. The ratio for first gear is 3.6:1, meaning that for every 3.6 full rotations of the crankshaft, the gear rotates once. Second gear has a ratio of 2.1:1, third is 1.4:1, fourth 1:1, fifth 0.8:1 and sixth 0.7:1. As you can see, the difference in gear ratio gets smaller and smaller as you go up the gears, meaning the transition between each of them gets easier for the synchromeshes to perform.
The stiffness encountered when changing from second to first gear can also be experienced when committing the blasphemy of selecting second gear from fourth, skipping third gear. The difference in the speed of the input and output shafts of the transmission will be large, forcing the required synchromesh to work harder.
Solutions to help downshifting into first are double clutching and rev-matching. These will allow the transmission the chance to match the speed of the crankshaft, lessening the load applied to the synchromesh for first gear and aiding smoother shifts. Despite this, we wouldn’t recommend regular downshifts into first due to the strain it can put on the components within the transmission. So next time you feel that first gear is necessary to launch out of a corner, make sure you think about the required pedal inputs to perform a smooth shift.
Comments
“Shift to R for maximium speed!” - A non-car guy, year unknown
Fast and furious seems to have no trouble at all..
‘R’ means ‘Racing’.
R means rocket!!lol
Would this also happen if I were to go to 1st from 17th?
“Engine has became a petrol bomb. To prevent fatalities, please leave the car immideately”
Meh that’s still way to close to each other… Would probably start occuring when you shift from first to 42nd
You’re not supposed to shift down into first gear in normal driving anyway. It’s only there to set the car into motion, after that you can drive in second gear. Nearly any car can start in second gear as well, it just needs a certain lack of mechanical sympathy.
True, most people that do decide to shift down to first are normally doing so in the run up to a stop sign or traffic light. Or - like in the MX-5 video - when 2nd gear isn’t aggressive enough out of a hairpin!
I started a car in 5th gear once…
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I know this is kinda off-topic, but it’s so annoying when you’re driving in a city and the traffic is moving slowly and you try to use the 1st gear, but it’s too short, and when you change into second the car nearly stalls and you need to slip the clutch to keep it moving. Like c’mon people, step on the gas or stop completely.
Every 4AGE guy ever!
Sounds like there are a ton of automatics in your city.
Sam problem here, this is why we got traffic jam everywhere. Because they’re too damn slow.
Amen to this.
Right? Stop making us compensate for your inability to drive
Actually downshifting to first is only interesting in traffic and in that conditions I like to rev match it to keep the car smooth and quick
When stopping on the traffic lights I mostly press the clutch, change into first, but not depress it, untill I’m starting to move again. Downshifting in first is just raping the car.
I use it a lot when rolling to a red light i rev match downshift because 1. its tricky and therefore fun 2. no brakes needed making it kinda amazing. also feels so satisfying when i get it 100% right..
Holding the clutch pressed is not good for the clutch as well
That is very bad for the clutch release bearing, and very bad for the crankshaft main bearing. So, why are you doing this is beyond me…
yeah shifting down to 1st on the move is not the easiest, especially if the syncros are bad, but who uses 1st gear during normal driving anyway xD
I do, redline the sh8t out of first before you redline the sh8t out of second
I always rev match to downshift when i downshift to accelerate or to slow down the car but its super tricky when braking at the same time .. hardly possible.
This, my friend, is what heel and toe is for. I’m sure you’ve heard of it. I had the same issue as you until I gave it a whirl. It takes a bit of practice, but once you’ve got it, you’ll be downshifting like a champ and impressing anyone who gives a damn. (Trust me on that last point)
You’re getting downvotes bud ahaha