How do you down shift when multiple gears need to be dropped

[kary]

Good points, so it comes down to 3 easy downshifts vs 1 difficult downshift.

Amazingly, looks like complete consesus will not be reached on this topic, now thats something different on this forum....NOT

Interesting how such different, styles, cars and techniques can lead to virtually the same result in the end

I do not understand how it possible for a weekend warrior that a single downshift is so difficult as compared to three down shifts in this example. The only difference between the "rowers" and the "go direct" crowd is the time between braking and the actual shift. If drivers cannot be aware enough of the speed they are moving at as they prepare for a corner then I would be very worried about the drivers ability to be aware of others around them.

It seems to be nonsense that one can down shift three gears in the same amount of time one can brake and do a single downshift (thanks Mike for making that point as well).

Jad, I think your statement where you use the word "virtually" sums it up well, though virtual is not exact, just close.

I never started this thread to gain consesus, it was started to share information to make drivers faster and better at their hobby.

[Kim Crosser]

A couple of posts from people who I think of as "authorities" say that gearboxes aren't designed to shift from 5th to 2nd directly - that you should "row" through 5th-4th-3rd-2nd, but I haven't seen any posts as to why.

A question for one of you "techies" out there - is there any extra stress or wear and tear on the gearbox (especially the synchros) due to the extra speed mismatch on the input shaft (or gear rings?) in dropping directly from 5th to 2nd?

I am picturing the gears whirring at speed in 5th, and (even though the clutch is in) suddenly engaging the gears in 2nd. In a Boxster, that is a change from a 0.84 gear ratio to a 2.12 gear ratio - i.e., you are trying to spin up the gears by 2.5x. I would think that could put undue stress on parts of the transmission, as some parts would be rotating in contact at speeds potentially 2.5 times as fast as normal.

If you "row" through the gears, then the gear speed changes are 29% from 5th to 4th, 31% from 4th to 3rd, and 48% from 3rd to 2nd. A direct shift from 5th to 2nd requires a gear speed change of 152%.

Is my logic correct and/or is the extra stress/wear negligible?

[kary]

I am picturing the gears whirring at speed in 5th, and (even though the clutch is in) suddenly engaging the gears in 2nd.

Kim, the the "skip the gear method" there is nothing sudden about engaging nor shifting into the gear. When a car is at 140mph in 5th gear and approaches a 50mph 2nd gear corner, the driver should not immediately push the clutch in and shift the gearbox to second (with the clutch pushed in). There is plenty of time to allow the car to slow down in gear with the clutch out until the car slows some. Say 70mph of speed in this example can be bled off. Then the clutch can be pushed in and the actual gearbox can be moved into 2nd gear, all along still braking down.

Therefore, I do not see the gear speeds nor the ratio differences to be an issue. I to would be interested to understand in the scenario I just portrayed, what damage the gearbox is suffering?

[gulf911]

Well, I don't know how this happened, but I agree with Kary and Mickey G . Think logically gentleman, while its true there aren't that many 5 to 2 shifts, if you are approaching the corner in 5th, then on the brakes(threshold) until the desired speed is achieved, blip throttle, downshift ,clutch out , slowly off the brakes, turn in, and squeezing on the gas towards the apex. I think its obvious, if you are downshifing through all the gears there is more wear on those gears/syncro's, and there is no difference once you are at the right speed to downshift into 2nd from 5th. Its a waste of time IMHO. However your mileage may vary....

[kary]

Well, I don't know how this happened, but I agree with Kary and Mickey G .

I just got up off the floor and am marking the date and time so I do not forget this moment in time

[Mike]

A question for one of you "techies" out there - is there any extra stress or wear and tear on the gearbox (especially the synchros) due to the extra speed mismatch on the input shaft (or gear rings?) in dropping directly from 5th to 2nd?

If I row down or skip gears my shift to second will happen at the same car speed. I wait to shift directly to second at the same spot I do when I row.

I think it would be tempting fate to be on the brakes in second at a car speed that would mechanically over rev the engine if the clutch were released or if the clutch cable were to break.

Someone mentioned something about LSD and downshifting..
LSD question... off power in the brake zone does the LSD perform regardless if clutch is engaged or not?

[MikeD]

Someone mentioned something about LSD and downshifting..
LSD question... off power in the brake zone does the LSD perform regardless if clutch is engaged or not?

Yes, I asked about that. I do not believe the LSD will do any good if the clutch is engaged (but am willing to be corrected). So like Kary says leave it in gear (5th) until it's time to clutch+shift for 2nd.

I may not have articulated this well enough. But I "row" more for ME than the car. It really sucks being in 4th when you thought you were in 2nd . If I'm recalling correctly I brake hard -> engage clutch -> row down to 2nd -> blip+disengage clutch -> turn in -> power on. Well, at least that's my goal... sometimes I get it sometimes I don't...

[lowyder993s]

Here's a link to t-3 2x in the same race...rowing and not. Not a really good representation on the row, since I had all the time in the world and had to tip-toe thru 3.

http://easylink.playstream.com/jewelbox ... ontana.wvx

BTW...the5-4 sound is the car next to me...we both dropped down @ the same time.

[Bob Gagnon]

Someone mentioned something about LSD and downshifting..
LSD question... off power in the brake zone does the LSD perform regardless if clutch is engaged or not?

Good question. I think the pinions need to have tension on them to work the friction pressure plates in a factory LSD. So, if clutch is "in" the LSD is essentially non-functional since the only tension on the pinions is due to the friction within the clutch assembly and the inertia of the input shaft.

[Mike]

Getting a little off topic....
Thanks guys, here is a copy and paste of some LSD comments off of a Renn List thread. Interesting that the 911 trailing throttle oversteer may be tamed by the LSD.. this sound about right......

I did like your positive comments Kary on the same thread about off camber (T-5 BW) and the LSD.

anyways here's the paste.

To get the most out of a LSD you need to know how to drive with one. Most of the folks here are giving the positives of traction exiting a turn. There isn't too much to maximizing this benefit. Step on the gas!

To really improve your laptimes you want a LSD that will lock or approach lock on deceleration. This will induce a ton of understeer. Why is that good? Because it counteracts the oversteer you introduce by trail braking. Thus, if you're good, you can enter the beginning of a turn fairly neutral but trail braking. This should help your laptimes.

Porsche started getting clever with this and offered split ratio LSDs in the early 90's (all C2 Turbos have them). My LSD is only 20% on acceleration (works great with my 380 rwft/lbs turbo and helps keep the understeer under control when accelerating) but 100% on deceleration. She becomes a locker when you start to slow down. If you don't know how to handle this you will experience massive understeer. But if you understand what is going on you can fiercely trail brake. And survive.

Obviously the side benefit of the 100% lock, particularly in the beastly last single turbos, is that it helps control trailng throttle oversteer.

[Tim Comeau]

*My braking time isn't affected by my downshifts.
*Going through the gears doesn't make the braking take any longer.
*You cannot feel my downshifts.
*They don't affect the balance of the car at all when trail braking into a turn.

When I get into my lowest gear needed, you don't hear a change in revs, just a steady note, then accelleration. I'm not trying to be difficult, but I still don't see how you can "find" that perfect rpm in your lowest gear and be ready to accellerate out of the turn. Matching revs well isn't so important when you're not near the adhesion limit of the car?? Is that the missing piece of the puzzle?

In low ryders video, you can hear the engine chasing the tranny in the first version. He's not near the grip limit of the car or he would go into oversteer when this happened. This is why matching revs well is so critical.
In the second version, the driver is obviously being very conservative, probably due to uncertainties in traffic in what looks like the start of a race. In any case he takes way longer than neccessary to brake and downshift making this clip irrelevant.

I just launched a video clip to Kary. (At the Streets, coming down the hill into the skid pad) The video will need an introduction. After that you guys can tear it apart!! I hope he can post it.

After reading Chris Benbow's post, I watched my brake pedal more closely........Sacre bleu! It's pretty slight, but I do allow the brake pedal to move a little while downshifting. It's probably only decreasing from 95% braking to 85% momentarily, but I'll bet it's measureable on a G-meter. I'll try to be more sensitive to that at Fontana.
Something tells me there's going to be a ton of video shot at Fontana in the next couple weekends!!!!!!
I hope some of it makes it to our little classroom here on the forum.

[Mike]

*My braking time isn't affected by my downshifts.
*Going through the gears doesn't make the braking take any longer.

I do allow the brake pedal to move a little while downshifting. It's probably only decreasing from 95% braking to 85% momentarily, but I'll bet it's measureable on a G-meter.

That's honest Tim, my admission.
I never fail to execute perfectly my 5/2 downshifts, 80% of the time.

[Kim Crosser]

I didn't actually see any replies that directly answered my question above - all the replies seem to be focused on matching revs with the engine.

My question was more basic - take the engine completely out of the picture (i.e., assume the clutch is just in continuously and/or the driver is "perfect" at matching revs after the shift) and just think about what is happening inside the gearbox.

Is there any additional wear and tear on the gearbox from changing directly from a 0.84 gear ratio to a 2.12 gear ratio versus going down in sequence? If not, then why the earlier comments that gearboxes are designed for "rowing" down?

Also, I haven't heard any comments about "double clutching" when shifting - is there any advantage to that, or is the additional time it takes too great a penalty?

[kary]

*My braking time isn't affected by my downshifts.
*Going through the gears doesn't make the braking take any longer.
*You cannot feel my downshifts.
*They don't affect the balance of the car at all when trail braking into a turn.

When I get into my lowest gear needed, you don't hear a change in revs, just a steady note, then accelleration. I'm not trying to be difficult, but I still don't see how you can "find" that perfect rpm in your lowest gear and be ready to accellerate out of the turn. Matching revs well isn't so important when you're not near the adhesion limit of the car?? Is that the missing piece of the puzzle?

In low ryders video, you can hear the engine chasing the tranny in the first version. He's not near the grip limit of the car or he would go into oversteer when this happened. This is why matching revs well is so critical.
In the second version, the driver is obviously being very conservative, probably due to uncertainties in traffic in what looks like the start of a race. In any case he takes way longer than neccessary to brake and downshift making this clip irrelevant.

I just launched a video clip to Kary. (At the Streets, coming down the hill into the skid pad) The video will need an introduction. After that you guys can tear it apart!! I hope he can post it.

After reading Chris Benbow's post, I watched my brake pedal more closely........Sacre bleu! It's pretty slight, but I do allow the brake pedal to move a little while downshifting. It's probably only decreasing from 95% braking to 85% momentarily, but I'll bet it's measureable on a G-meter. I'll try to be more sensitive to that at Fontana.
Something tells me there's going to be a ton of video shot at Fontana in the next couple weekends!!!!!!
I hope some of it makes it to our little classroom here on the forum.

Tim I do not have accesss to my business servers right now but will look at it tonight.

[kary]

I didn't actually see any replies that directly answered my question above - all the replies seem to be focused on matching revs with the engine.

My question was more basic - take the engine completely out of the picture (i.e., assume the clutch is just in continuously and/or the driver is "perfect" at matching revs after the shift) and just think about what is happening inside the gearbox.

Is there any additional wear and tear on the gearbox from changing directly from a 0.84 gear ratio to a 2.12 gear ratio versus going down in sequence? If not, then why the earlier comments that gearboxes are designed for "rowing" down?

Also, I haven't heard any comments about "double clutching" when shifting - is there any advantage to that, or is the additional time it takes too great a penalty?

Kim, I understood your question but do not see the importance given my description of the series of events. The gears were slowing down given my scenario thus the speed of the gears and the ratio's are not a factor. If this is not true, then I am listening to other explanations.

Furthermore, I have not had any syncro issues moving directly between 5/2 and 4/2 (which happens 3 times per lap at the speedway). The only issues I have ever had was at SOW where it was seriously bumpy and the shifts needed to be timed with the bumps due to the tranny moving around. I guess I need to get those solid tranny and engine mounts in there soon if I am going back to SOW!