Synchros - Best Shift Point for Minimal Wear?

RogerPodacter · 11-25-2009, 12:03 PM

I was just thinking about my driving technique and the synchros on the manually trans. My technique when shifting is to let the RPM's drop close the next lowest gear before releasing the clutch. I always felt that this put the least amount of wear and tear on the synchros (since they are a friction mechanical component). But it got me thinking, is the transmission designed so that the synchros are made to be shifted at the top arc of the RPM shift point vs the bottom of the shift point?

What i mean is are the synchros designed with maybe some type of curveture design such that it perfectly pulls the dog collar onto the next lowest gear when shifted with the correct difference in RPM's from the current gear to the next gear? Or is it actually better to let the RPM's drop to get closer to the next lowest gear?

this is probably a way useless thread, and of course i know it doesnt really matter. but i was just curious. hope you guys understand what i'm talking about.

also does anyone know for the tsx 6MT, which gears only have just a single gear on the layshaft vs some of the gears that actually have 2 gears on the layshaft? hope that makes sense too.

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Itchytoe · 11-25-2009, 12:32 PM

Your synchros are out of the picture once you are ready to release the clutch. If you're revving up the engine, then hitting the clutch, then shifting from 1-2 (or whatever gear you're shifting to) then waiting for the engine RPM to match, then letting go of the clutch, you haven't saved your synchros from any wear by waiting. You're saving some clutch wear, but not synchro wear.
Your transmission is in gear once you've pulled the shifter down into gear, not when you release the clutch. When you release the clutch you're just connecting the engine with that transmission that's already in its gear.
Your synchros are between the gears and neutral. To reduce wear on them, you should rev up the engine, push in the clutch, take your transmission out of gear into neutral, then wait for the RPM to match the gear you're going into, then put it in gear as the engine RPM is at the correct speed for the gear you've selected, then release the clutch. Hopefully that made a little bit of sense to you.

RogerPodacter · 11-25-2009, 1:27 PM

I totally understand that. I realize that the least amount of synchro wear is matching rpm exactly before putting the shifter into gear. What i was asking is very obscure, basically for normal shifting, are the synchro's designed to have the optimal wear (ie minimal wear) at slightly above the proper shift point since that is the common place when a person would put the shifter into the next gear. Or is the optimal shift point really at the exact rpm do the next gear.

Its really a hard question to ask and very obscure, so there's probably no answer. But i totally understand how the synchro's work and how the clutch works. It was just a theoretical question.

Itchytoe · 11-25-2009, 1:44 PM

The wear increases as you get further from that perfect RPM match, either way. You probably get more wear if your engine is turning slower than it would if it were in the gear you're shifting into. Optimal wear means no wear, so a shift at the exact rpm is ideal if you're looking for optimal wear. If you shift like that though, you're basically double clutching and don't need synhros to do that. I'm lazy and don't mind using the synchros so I don't worry about matching them up. I don't force it into gear as fast as I can, but I don't pay much attention to exact matching.

*edit* Does that answer your question? Or did I miss it again?

RogerPodacter · 11-25-2009, 3:12 PM

Yeah thanks the end result is the minimal wear occurs the closer the rpm's are to the shift point. I had this random idea that maybe they engineered into the synchro's some type of tolerance since the average shift would be slightly above or below the optimal shift point at the exact rpm match. But that really makes no sense thinking about it. Thanks again:-)

11-25-2009, 12:32 PM	#2
Itchytoe Modding newbie Trader Rating: (0) Join Date: Nov 2008 Location: Down south where the food is good. Age: 27 Posts: 519	Your synchros are out of the picture once you are ready to release the clutch. If you're revving up the engine, then hitting the clutch, then shifting from 1-2 (or whatever gear you're shifting to) then waiting for the engine RPM to match, then letting go of the clutch, you haven't saved your synchros from any wear by waiting. You're saving some clutch wear, but not synchro wear. Your transmission is in gear once you've pulled the shifter down into gear, not when you release the clutch. When you release the clutch you're just connecting the engine with that transmission that's already in its gear. Your synchros are between the gears and neutral. To reduce wear on them, you should rev up the engine, push in the clutch, take your transmission out of gear into neutral, then wait for the RPM to match the gear you're going into, then put it in gear as the engine RPM is at the correct speed for the gear you've selected, then release the clutch. Hopefully that made a little bit of sense to you. __________________ UR Pulleys, Progress RSB, and K&N Drop-in. More to come when I get a little cash.

11-25-2009, 1:27 PM	#3
RogerPodacter So, do you like...stuff? Trader Rating: (0) Join Date: May 2002 Location: PA/NJ, now in CA (SoCal), USA Age: 30 Posts: 1,103	I totally understand that. I realize that the least amount of synchro wear is matching rpm exactly before putting the shifter into gear. What i was asking is very obscure, basically for normal shifting, are the synchro's designed to have the optimal wear (ie minimal wear) at slightly above the proper shift point since that is the common place when a person would put the shifter into the next gear. Or is the optimal shift point really at the exact rpm do the next gear. Its really a hard question to ask and very obscure, so there's probably no answer. But i totally understand how the synchro's work and how the clutch works. It was just a theoretical question. __________________ --CG/Ebony/6MT/Navi Delivered 05/17/03 --Navi conversion completed. --CarPC install completed. --Blue LED Door Lights --Blue LED Dome Lights --XM Commander installed in the "Not An Ashtray" bin compliments of Bass Mechanic

11-25-2009, 1:44 PM	#4
Itchytoe Modding newbie Trader Rating: (0) Join Date: Nov 2008 Location: Down south where the food is good. Age: 27 Posts: 519	The wear increases as you get further from that perfect RPM match, either way. You probably get more wear if your engine is turning slower than it would if it were in the gear you're shifting into. Optimal wear means no wear, so a shift at the exact rpm is ideal if you're looking for optimal wear. If you shift like that though, you're basically double clutching and don't need synhros to do that. I'm lazy and don't mind using the synchros so I don't worry about matching them up. I don't force it into gear as fast as I can, but I don't pay much attention to exact matching. edit Does that answer your question? Or did I miss it again? __________________ UR Pulleys, Progress RSB, and K&N Drop-in. More to come when I get a little cash.

11-25-2009, 3:12 PM	#5
RogerPodacter So, do you like...stuff? Trader Rating: (0) Join Date: May 2002 Location: PA/NJ, now in CA (SoCal), USA Age: 30 Posts: 1,103	Yeah thanks the end result is the minimal wear occurs the closer the rpm's are to the shift point. I had this random idea that maybe they engineered into the synchro's some type of tolerance since the average shift would be slightly above or below the optimal shift point at the exact rpm match. But that really makes no sense thinking about it. Thanks again:-) __________________ --CG/Ebony/6MT/Navi Delivered 05/17/03 --Navi conversion completed. --CarPC install completed. --Blue LED Door Lights --Blue LED Dome Lights --XM Commander installed in the "Not An Ashtray" bin compliments of Bass Mechanic