Tire size & Shift Points
Post Fiend
Joined: Jun 2004
Posts: 9,293
Likes: 10
From: Parker, CO
My understanding of this has always been that it was speed related when it comes to transmission shift points, but it didn't occur to me that the VSS signal is split between the ABS module (speedo calibration) and PCM (trans shift strategy).
So on a side note that now gives me a new idea for something to check out in the tuning.
I guess hard headed folks like me can take a lernin' to new stuff every now and then. For some reason my head wouldn't wrap around what was happening until I knew where the signal itself was going, and I just had to take a step back and start over again to have it explained where I would understand. Thanks for the explanation and having patience with me. Not sure why I couldn't figure it out but now it makes sense.
Elder User
Joined: Sep 2011
Posts: 979
Likes: 4
From: Vancouver
Thank you Mark for explaining this - it is actually making sense now. Sometimes we get a certain idea and it can be difficult to understand what the actual sequence or logic is when it comes to these "simple" diesels. It makes me really like the old hit and miss engines and the diesel powered pile drivers where the ram is just a giant diesel powered piston. No brains needed to understand how they work.
Laughing Gas
Joined: Nov 2013
Posts: 868
Likes: 1
From: SoCal
Sorry to dredge up an old thread, but I’ve been talking to Akcooper in here and comparing AutoEnginuity to Forscan as it pertains to correcting tire size. It appears that AE changes the tone ring size while Forscan changes the revs per mile. Akcooper has been in contact with Forscan and they’re working on a version that’ll change the tone ring and/or rev per mile. After correcting for my 35s in AE, I found that Forscan displayed an error in my as built data because Forscan was expecting to see 120 tooth tone ring, but AE had reprogrammed it to 111 teeth. This is more of an FYI, but with the back and forth about axle speed vs. vehicle speed, I would imagine that revs per mile has no effect on shifting, but changing the tooth count on the tone ring would.
Laughing Gas
Joined: Oct 2016
Posts: 1,074
Likes: 91
From: DFW, Texas
Good questions. Anyone have any thoughts on this?
Laughing Gas
Joined: Jan 2017
Posts: 1,216
Likes: 94
How do I get that forescan setup to change tire size? A mechanic replaced my PCM 2 years ago and didn’t reprogram the tire size. The truck drives fine justness annoying for me and the speedo. Found out he didn’t reprogram the hard way when I got pulled over going 77 while having the needle at 70 Thanks
Laughing Gas
Joined: Oct 2016
Posts: 1,074
Likes: 91
From: DFW, Texas
How do I get that forescan setup to change tire size? A mechanic replaced my PCM 2 years ago and didn’t reprogram the tire size. The truck drives fine justness annoying for me and the speedo. Found out he didn’t reprogram the hard way when I got pulled over going 77 while having the needle at 70 Thanks
The public version doesn't support this yet unless you know how to edit hex values.
New User
Joined: Mar 2019
Posts: 7
Likes: 1
4.88
I have a question I had 4.88 put in front and rear and now when I hit 75 on the speedometer my truck starts jerking and such . Feels like maybe I hit the speed limiter early unsure what's going on with it didnt have this problem with the 3.73 speedometer is only 5mph off by gps on my phone
FTE Stories
Ford Trucks for Ford Truck Enthusiasts
Top 10 Most Expensive Ford Trucks Ever Sold on Bring a Trailer
Joe Kucinski
2027 Ford Super Duty Buyer's Guide (Every Model, Engine, & Package)
Brett Foote
Top 10 Ford Truck Tragedies
Joe Kucinski
AEV FXL Super Duty - the Super Duty Raptor Ford Doesn't Make
Brett Foote
Lobo Vs Lobo: Proof the F-150 Lobo Should Be Even Lower!
Michael S. Palmer
Ford's 2001 Explorer Sportsman Concept Looks For a New Home
Verdad Gallardo
10 Best Ford Truck Engines We Miss the Most!
Joe Kucinski
2026 Shelby F-150 Off-Road: Better Than a Raptor R?
Brett Foote
2027 Super Duty Carhartt Package First Look: 12 Things You NEED to Know!
Michael S. Palmer
It's a Van Gogh
Joined: Feb 2010
Posts: 7,809
Likes: 1,334
From: Elk Grove, CA
Only speed limiter on my 2002 is my fear of worn out S rated tires blowing up. You have a commercial/gov't rig? What year?
Could be you simply have a tire or 4 out of balance. With 3.73's that might show at 85 mph, but now it's showing at 75. Recommend you post up more info on your own thread so it will attract more eyeballs.
Still I'd get that speedo recalibrated. With it off like that you have no way to argue with a speeding ticket.
Could be you simply have a tire or 4 out of balance. With 3.73's that might show at 85 mph, but now it's showing at 75. Recommend you post up more info on your own thread so it will attract more eyeballs.
Still I'd get that speedo recalibrated. With it off like that you have no way to argue with a speeding ticket.
Butt-Head
Joined: Apr 2004
Posts: 9,437
Likes: 2,925
From: Reed Point, MT
Hi mark
I have a question I had 4.88 put in front and rear and now when I hit 75 on the speedometer my truck starts jerking and such . Feels like maybe I hit the speed limiter early unsure what's going on with it didnt have this problem with the 3.73 speedometer is only 5mph off by gps on my phone
I have a question I had 4.88 put in front and rear and now when I hit 75 on the speedometer my truck starts jerking and such . Feels like maybe I hit the speed limiter early unsure what's going on with it didnt have this problem with the 3.73 speedometer is only 5mph off by gps on my phone
Yes, it's monitored and the PCM cares about it. However, you should be able to do at least 90 MPH (3200 RPM in overdrive with 4.88s with any tire taller than 33") before the driveshaft speed gets to that speed. Tell me your PCM code or current calibration hex code and I'll look up the factory speed when I get home from work.
USUALLY the speed limiter doesn't create a jerking sensation though. Power output simply tapers off before the max speed limit and acceleration just stops.
Thread
Thread Starter
Forum
Replies
Last Post
schmiddw
1967 - 1972 F-100 & Larger F-Series Trucks
13
Mar 10, 2019 09:04 PM
49fordfiretruck
1948 - 1956 F1, F100 & Larger F-Series Trucks
4
Jul 13, 2010 01:44 PM