SaKaNa Posted October 1, 2007 Share Posted October 1, 2007 (edited) I've been experiencing *extremely* long shifts for some time now, to the point that you basically NEED to ease off the gas to let it shift, otherwise its going to stay in gear revving forever, and while my mechanic is pressing out my old bushings and putting in new ones, I told him to take a look at it, he said the transmission is fine, and he suspects the extremely extended shifts are from going 235 to 265 tires... Does this sound right to anyone? Is there a way to do anything about this other than a regear? Edited October 9, 2007 by SaKaNa Link to comment Share on other sites More sharing options...
XPLORx4 Posted October 1, 2007 Share Posted October 1, 2007 extended shifts are from going 235 to 265 tires... Does this sound right to anyone? Is there a way to do anything about this other than a regear? Yep, that sounds about right. No way around it except to lighten your right foot a little or regear. Link to comment Share on other sites More sharing options...
blamtro Posted October 1, 2007 Share Posted October 1, 2007 Yep, that sounds about right. No way around it except to lighten your right foot a little or regear. Could you elaborate on that? That doesn't make sense to me. Link to comment Share on other sites More sharing options...
FUELER Posted October 1, 2007 Share Posted October 1, 2007 (edited) Could you elaborate on that? That doesn't make sense to me. I'll elaborate It sounds right that you experience this from your heavier tires. I had the same thing when I swapped to 265/75/16 BFG all terrains. All the added rolling resistance makes your car rev up and shift way high like it's going up an eternal hill (but you're really on flat ground). Lighten your right foot: let off the gas pedal a bit, don't accelerate too rapidly. You'll notice that when you drive like a grandma, the tranny will shift more smoothly. Regear: If you have the 4.3's, you could help by swapping to the 4.6 That's all your choices for regearing Edited October 1, 2007 by FUELER Link to comment Share on other sites More sharing options...
XPLORx4 Posted October 1, 2007 Share Posted October 1, 2007 Fueler has it right. The higher gearing (numerically lower @ 4.363:1) with larger tire sizes not intended for use with the higher gears will force the engine to work harder than it used to. The transmission programming and gearing is designed to shift at certain TPS position, RPMs and/or certain engine loads. With the engine working harder to turn those bigger tires the higher gears, the engine load is higher for a given RPM, so it will take longer for the engine to reach the pre-set engine load value to trigger the transmission to shift. If your right foot is lighter while accelerating, then the engine load will be lower, triggering the tranny to shift at lower RPMs. Regearing will compensate for the larger tires, so the engine and tranny can be restored to pre-tire-size-increase performance. Link to comment Share on other sites More sharing options...
kmgar99 Posted October 1, 2007 Share Posted October 1, 2007 Can you reset the computer and have it re-learn new shift points based on the new speed and RPM range? I added 32x11.5x15's and haven't really had the problem. But right after i had the tires installed, i drove home....about 1 mile....and had to work on the emmissions system so i disconnected the battery for 3+ hours. I hooked it back up the next day and drove it back and forth for work....about 50 miles one way. That was over a year ago. It definitely rev's higher, but still shifts at the speeds it used to shift at. Maybe i'm talking out my exit only hole..... Link to comment Share on other sites More sharing options...
Nissan3 Posted October 1, 2007 Share Posted October 1, 2007 I was wondering if anyone knew if you could program the PCM to tell it that ur running a certain size tires and if it would help with the shifting issue. I remember when I was working at chrysler, one of the mechanics had me programming the ABS system and the DRB scanner asked what size tires was on the vehicle. Link to comment Share on other sites More sharing options...
SaKaNa Posted October 1, 2007 Author Share Posted October 1, 2007 I was thinking the same thing as kmgar99, can you reset the trans comp to allow a relearn so it does it earlier? I was considering just leaving my battery unplugged overnight, but I know I'll forget and have no idea why its not starting. I just had someone do the upper and lower rear bushings today, and I've gotta say, driving feels so much more safe and stable now, my Pathy is as sure-footed as a mountain goat. Link to comment Share on other sites More sharing options...
XPLORx4 Posted October 1, 2007 Share Posted October 1, 2007 (edited) Unfortunately, the Pathy ECM (Engine Control Module) and TCM (Transmission Control Module) cannot be reprogrammed to compensate for larger tires. Resetting the computer won't help, since the computer isn't aware of the more-difficult-to-rotate-with-stock-gearing tires. It only resets the fuel trims, it doesn't change the fixed programming of the TCM and PCM. All it knows is that it's now harder to accelerate. It doesn't know WHY it's harder to accelerate. The effect is actually not much different than towing or carrying a lot of heavy cargo. That's why my initial response said "lighten your right foot or regear". The description matches exactly my experience after converting from 235/70R15 tires to 31x10.50R15's. I noticed that my truck could barely even get into overdrive and stay in overdrive at 70mph on level ground. That's what motivated me to regear. Edited October 1, 2007 by XPLORx4 Link to comment Share on other sites More sharing options...
FUELER Posted October 1, 2007 Share Posted October 1, 2007 Xplorx4, just noticed that you have dual ARB in your signature. Are you fully locked? Link to comment Share on other sites More sharing options...
XPLORx4 Posted October 2, 2007 Share Posted October 2, 2007 Are you fully locked? Yes. Link Link to comment Share on other sites More sharing options...
FUELER Posted October 2, 2007 Share Posted October 2, 2007 That is absolutely bad ass. I'd be happy with one ARB locker, it must be titties to have 2. That is such an important piece of equipment... 100% of the time I get stuck is due to open differentials. Link to comment Share on other sites More sharing options...
88pathoffroad Posted October 2, 2007 Share Posted October 2, 2007 I don't see why bigger tires would change the shift points like that. The TCU is set to shift at XX RPM's and XX speed, why would changing tire size change the shift points to XX++ at XX++? I went from 31's to 33's and it still shifts at the same places it used to. Link to comment Share on other sites More sharing options...
XPLORx4 Posted October 2, 2007 Share Posted October 2, 2007 I don't see why bigger tires would change the shift points like that. The TCU is set to shift at XX RPM's and XX speed... No, the TCM isn't set to shift at certain RPM's and certain speed, it's set to shift at certain RPMs, and certain engine loads, in addition to other factors such as the VSS and the TPS values. That's why if you accelerate gently, the transmission will shift much earlier than if you accelerate rapidly. Bigger tires with unchanged gears increase the engine load for a given RPM and TPS value input. Link to comment Share on other sites More sharing options...
SnowSurfLax Posted October 2, 2007 Share Posted October 2, 2007 Interesting. So he added 30cm on his tires and his shift points are all off. What's the difference? i.e. how much short is his speedo now w/ the bigger tires? Is it going to offset the shift point difference? Link to comment Share on other sites More sharing options...
csutke Posted October 2, 2007 Share Posted October 2, 2007 (edited) how much short is his speedo now w/ the bigger tires? (New Tire Diameter / Old Tire Diameter) * Speedometer MPH = Actual MPH 31.6/28.9(stock)*60 mph = 65.6 mph 65.6/60=1.093 off Edited October 2, 2007 by csutke Link to comment Share on other sites More sharing options...
XPLORx4 Posted October 2, 2007 Share Posted October 2, 2007 65.6/60=1.093 off aka 9.3% off. That translates to a 9.3% reduction in power to the ground, 9.3% increase in engine load for a given rpm, etc. etc. I'm sure the % error isn't expressed as simplistically as that, but you get the point. Did you ever notice if you carry around 4 passengers in your truck that it feels more sluggish, tends to accelerate more slowly? Well, that's a lot what changing tire size without regearing is like. The bottom line is that an increase in transmission shift times after a 9.3% increase in tire size is completely normal. Link to comment Share on other sites More sharing options...
02silverpathy Posted October 2, 2007 Share Posted October 2, 2007 (edited) aka 9.3% off. That translates to a 9.3% reduction in power to the ground, 9.3% increase in engine load for a given rpm, etc. etc. I'm sure the % error isn't expressed as simplistically as that, but you get the point. Did you ever notice if you carry around 4 passengers in your truck that it feels more sluggish, tends to accelerate more slowly? Well, that's a lot what changing tire size without regearing is like. The bottom line is that an increase in transmission shift times after a 9.3% increase in tire size is completely normal. No doubt, just moving to a size of 255/70/16 made my VQ change its thoughts, very aggrevating, watching it hold RPM's at like 3K for no reason, then falling back after a 1 MPH improvement...I see re grearing in my future, although that rear end looks scary to me. Do you think that the tranny points get moved around due to say an LSD instead of opens? *snatch topic* if you are regearing, from 4.36 to 4.63, would you reccommend getting the factory LSD or adding a Detroit locker? (This is on a daily driver) Edited October 2, 2007 by 98silverpathy Link to comment Share on other sites More sharing options...
csutke Posted October 2, 2007 Share Posted October 2, 2007 *snatch topic* if you are regearing, from 4.36 to 4.63, would you reccommend getting the factory LSD or adding a Detroit locker? (This is on a daily driver) didnt know that they made a detriot, i thought the only option for a locker was ARB? Link to comment Share on other sites More sharing options...
02silverpathy Posted October 2, 2007 Share Posted October 2, 2007 I am really curious, I am moving to the garage to finish the topic of Lockers ... Link to comment Share on other sites More sharing options...
XPLORx4 Posted October 2, 2007 Share Posted October 2, 2007 Do you think that the tranny points get moved around due to say an LSD instead of opens? No. The transfer of power from one side of the axle to the other has no relevance to the final drive ratio (and therefore, the tranny shifting behavior). Link to comment Share on other sites More sharing options...
chappy Posted October 2, 2007 Share Posted October 2, 2007 Is upsizing tires from stock harmful to your engine in the long run with out regearing? Link to comment Share on other sites More sharing options...
XPLORx4 Posted October 2, 2007 Share Posted October 2, 2007 Is upsizing tires from stock harmful to your engine in the long run with out regearing? No. It's no worse than installing 600 lbs of misc off-road equipment and 32" or larger tires. Link to comment Share on other sites More sharing options...
SaKaNa Posted October 7, 2007 Author Share Posted October 7, 2007 So I can just ease off the gas to allow gear changes and I'm not going to fry anything internal? I was worrying that the transmission was on its last leg when it was taking so long... But this is a real relief! Link to comment Share on other sites More sharing options...
KLL Posted October 8, 2007 Share Posted October 8, 2007 pathfinders sold here were equipped with 265/65/15 tires by nissan... as described above even it is not climbing, it requires to light your foot to make it shift. It is completely normal. Fitting larger and heavier tires are causing more friction on surface. Acceleration is worse, fuel consumption is higher but handling and braking is better. Actually i am thinking to switch to 255 or 245 from 265 now. Link to comment Share on other sites More sharing options...
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