[grampa_ss]

Originally Posted by Yosh6

Actually, the transmission shifts by MPH AND RPM. The shift is a two-step process that is MPH Initiated and RPM Completed. The shift tables require both parameters. I pay a lot of attention to shift points and log every run on the drag strip to tweak the tune shift points (See Log, an example from last weekend at the Texas Speed Syndicate Quick 30 in Houston).

On the right side is the tune indicating RPM and MPH loaded in tables. On the left side is the RPM actual in the run. The / separates the initiation RPM and the completed RPM. The middle figures are MPH initiation and completion.

You can see that the shift is initiated at the MPH number in tune (can vary 1 MPH) and completed at the RPM number in the tune (again this can vary by 50-75 RPM or more). Think of it as "nominal" 6500 RPM if that is the target.

For example, you can see the 2-3 shift was initiated at 45 MPH and completed at 6543 RPM (50 MPH). 3-4 shift initiated at 72 MPH, 4-5 shift initiated at 94 MPH.

The 4-5 shift illustrates that the shift will not initiate until the target MPH is reached and if the RPM already exceeds the parameter in the tune the shift will complete almost immediately. In this case initiated at 94 MPH, completed at 95 MPH with only 33 RPMs between initiation and completion.

As for tires, the computer looks at tire height (measured with tire on car sitting on ground) not diameter. There is a place in the tune for that number and it affects the transmission shift points and speedometer. IF you put a taller or shorter tire on the car and don't change that parameter in the tune it will not shift correctly, as grandpa_ss said.

I don't want to question your tuner or you grandpa (and this could be just a matter of semantics), but I would not want lower shift points to fix the problem, I would want the correct tire height parameter changed in the tune.

Of course, that would mean one tune for your street tires and another one for the drag strip.

I do have 2 tunes. Yes, it uses both. But MPH is first. So the new tune had the correct tire size and lower mph shift points. we left rpms the same. A 26" tire will have a lower mph at the same rpm vs a 28" tire. So, regardless...if you adjust the tire size...the mph shift points need to be lower for a 26" tire.

If you want to shift at 6800 for every shift...then why can't we just leave the mph like at 20 and just set the rpm for every shift at 6800. That's what you're saying. Ok, we hit the required mph (20) so lets initiate the shift and then complete it at 6800. I don't think it'll work. I think it'll short shift.

I'm no expert by any means. I think the shifting is more complicated than initiate at a set mph and complete at set rpm. If it was that simple..we could just set the shift points by rpm we wanted and leave the mph at the low stock setting. I think you want your desired shift mph and rpm to be as close to accurate as possible so the shift happens quick.

[laynlo15]

With my Camaro we always short shifted out of low at 6400 rpm and then 6800 on out. My car made about 800 lbs of torque so get out of 1st quicker at a lower rpm and it kept the car from wanting to break the tires loose in second. I'd want the tallest tire on a A10 as possible, just my 2 cents worth.

[cerino2000]

Originally Posted by grampa_ss

Close, but not quite. It's the exact opposite. These A8/A10 shift by MPH, not RPM. If the car is programmed to shift at lets say 60 mph (6500rpm) with the stock tire. If you use a shorter tire, it'll take maybe 6800 rpms to reach 60 mph and you'll bounce off the limiter by the time the shift actually happens.

I know this because I went to the track with shifting set at stock tire height, but at the track I switched to my 26" DR. I hit the limiter on my 1-2, 2-3, 3-4 shifts. Informed my tuner and 1st thing he said was "are you using a shorter tire?". He sent me a new tune with lower mph shift points.

But that would be relevant to where the speedometer reading is coming from. If read off the front tires, then that would be correct. Actual 60 mph would be more revolutions of the back tire than stock (since tire is shorter) thus higher RPM. where is the MPH read from? If coming off the output shaft on the transmission then that ties wheel RPM and engine RPM together directly as my theory above. Still trying to wrap my head around it really.

[cerino2000]

Originally Posted by Yosh6

Actually, the transmission shifts by MPH AND RPM. The shift is a two-step process that is MPH Initiated and RPM Completed. The shift tables require both parameters. I pay a lot of attention to shift points and log every run on the drag strip to tweak the tune shift points (See Log, an example from last weekend at the Texas Speed Syndicate Quick 30 in Houston).

On the right side is the tune indicating RPM and MPH loaded in tables. On the left side is the RPM actual in the run. The / separates the initiation RPM and the completed RPM. The middle figures are MPH initiation and completion.

You can see that the shift is initiated at the MPH number in tune (can vary 1 MPH) and completed at the RPM number in the tune (again this can vary by 50-75 RPM or more). Think of it as "nominal" 6500 RPM if that is the target.

For example, you can see the 2-3 shift was initiated at 45 MPH and completed at 6543 RPM (50 MPH). 3-4 shift initiated at 72 MPH, 4-5 shift initiated at 94 MPH.

The 4-5 shift illustrates that the shift will not initiate until the target MPH is reached and if the RPM already exceeds the parameter in the tune the shift will complete almost immediately. In this case initiated at 94 MPH, completed at 95 MPH with only 33 RPMs between initiation and completion.

As for tires, the computer looks at tire height (measured with tire on car sitting on ground) not diameter. There is a place in the tune for that number and it affects the transmission shift points and speedometer. IF you put a taller or shorter tire on the car and don't change that parameter in the tune it will not shift correctly, as grandpa_ss said.

I don't want to question your tuner or you grandpa (and this could be just a matter of semantics), but I would not want lower shift points to fix the problem, I would want the correct tire height parameter changed in the tune.

Of course, that would mean one tune for your street tires and another one for the drag strip.

Why would you not want your shift initiated and completed at the same moment in time? Regarding MPH, in your one reference you have the shift initiated at 45 and completed at 50. What is physically happening between these two MPH points? Lastly, isn’t that short shifting? I feel like my A10 2-3 shift is about 60mph.

[Yosh6]

Originally Posted by grampa_ss

I do have 2 tunes. Yes, it uses both. But MPH is first. So the new tune had the correct tire size and lower mph shift points. we left rpms the same. A 26" tire will have a lower mph at the same rpm vs a 28" tire. So, regardless...if you adjust the tire size...the mph shift points need to be lower for a 26" tire.

Yep, semantics. Your original post didn't mention the new tune having the correct tire size, it just said "lower mph shift points". Agreed, you did the right thing. Cheers.

[Yosh6]

Originally Posted by cerino2000

Why would you not want your shift initiated and completed at the same moment in time? Regarding MPH, in your one reference you have the shift initiated at 45 and completed at 50. What is physically happening between these two MPH points? Lastly, isn’t that short shifting? I feel like my A10 2-3 shift is about 60mph.

First off, let me make the same claim as grandpa_ss - I'm no expert by any means. What I know about this comes from the limited material you can find to read about the 8L90 and conversations with my tuner, who by the way, IS the expert. There is a lot of room for misunderstanding and speculation about what MPH Initiated and RPM Completed actually means. It does not mean the shift begins with one and ends with the other in terms that would result in a long, slow shift. It has NOTHING to do with how quickly the transmission shifts from one gear to the next. The 3-4 shift in my car that initiates at 72 MPH and completes at 75-76 MPH hits like a sledge hammer, it is not a slow shift and neither are any of the others. What happens in that time interval? What is the transmission doing? I have no idea. All I know is the Trans Current Gear PID in HP Tuners turns from 3 to 4 at 72 MPH, so something electronically happens but nothing mechanically happens that I can detect. At 75-76 MPH (6543 RPM) the transmission makes the 3-4 shift crisply. Honestly, logging the shift initiation RPM is probably a waste of time. What we are all after is a target shift completion at a certain RPM and/or MPH. I like to see as much data as possible; that's not for everyone. Short shifting, in my view, would be getting either a completed shift sooner than you want or an intentional shift earlier than "normal". As for initiation being short shifting, since nothing really happens at initiation in terms of a mechanical gear change; no, don't think you can call that short shifting.

[cerino2000]

Good info. Thx. I’ve got a 10 speed so my shift points would be different.

Originally Posted by Yosh6

First off, let me make the same claim as grandp_ss - I'm no expert by any means. What I know about this comes from the limited material you can find to read about the 8L90 and conversations with my tuner, who by the way, IS the expert. There is a lot of room for misunderstanding and speculation about what MPH Initiated and RPM Completed actually means. It does not mean the shift begins with one and ends with the other in terms that would result in a long, slow shift. It has nothing to do with how quickly the transmission shifts from one gear to the next. The 3-4 shift in my car that initiates at 72 MPH and completes at 75-76 MPH hits like a sledge hammer, it is not a slow shift and neither are any of the others. What happens in that time interval? What is the transmission doing? I have no idea. All I know is the Trans Current Gear PID in HP Tuners turns from 2 to 3 at 45 MPH (6295 RPM) and nothing else happens. At 50 MPH (6543 RPM) the transmission makes the 2-3 shift crisply. Honestly, logging the shift initiation RPM is probably a waste of time. What we are all after is a target shift completion at a certain RPM and/or MPH. I like to see as much data as possible; that's not for everyone. Short shifting, in my view, would be getting a completed shift sooner than you want. Since nothing really happens at initiation, no, don't think it is short shifting.