Shift points are terrible with 305/55R20 tires
- Thread starter Keebler
- Start date
Starrs
Member
The AEV procal takes care of that for you. Just input the size tire into the chart and then set it up in the procal. Will change your shift points. Easy fix
Wayne Reel
New Member
Is using the tuner to adjust shift points an acceptable alternative?
Starrs
Member
The procal is what you do when you go up in tire size. You can change gears, but would be a bit overkill. What size tires?
geez just saw it in the title! Do you have 3.21, 3.73, or 4.10 right now?
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Waste of money. The Procal does not even half the stuff the J-Scan app does. The J-Scan app does everything the Procal does and so much more, and costs $16 plus about $20 for the Bluetooth adapter. Not to mention it's an app, so you already have a phone.
Procal is obsolete anymore if you ask me.
To my knowledge you can not change shift points with any of the tuners, including HPTuners (which is the most comprehensive full access tuning solution I know of).
Starrs
Member
It changes the shift points, changes gear ratios if you change gears, will change your light settings for headlights/fog lights, sets your PSI threshold for your tire settings. Just to name a few things. Does what it is intended for...changing the shifting points when you go up in tires, and all you do is plug it in. Seems like a no brainer to me. But if somebody wants to download an app to reset shift points they can too I suppose.
Wayne Reel
New Member
So I guess the next question I have is I’m going with a 35x12.50r17. Stock on mine was a 255/75r-17. Which should be a 32” inch tire if my math is right. I know I have the 3.73 rear gears. That’s a 9% increase in tire diameter. Is it necessary to re-gear with such a small increase? Or would the jscan app and adjusting the speedometer be sufficient. If I had 3.21’s I would jump up to a 3.73 or even a 4.10 since I was already changing them.
IndominusHuman
JK Enthusiast
I would definitely regear. I imagine that will feel very sluggish running 35s. Just my opinion though.
The app does the same thing the Procal does (and way more), costs way less, and can be easily updated on your phone. I've used both first hand, and can tell you the Procal is 100% obsolete compared to J-Scan. I'm not the only one who seems to think that either. If you read around, you'll see J-Scan has really taken the Jeep world by storm.
It should also be noted that I've read into this extensively. The Procal (and J-Scan) do not actually change shift points. You can update your tire size and gear ratio,
If you re-gear then change the ratio setting on the Procal (or J-Scan) to match it will make your transmission shift at the correct speed / RPM for those new gears. However, you still have no real control over your shift points, and what it comes down to is that if you want to have the right shift points for bigger tires like this, you need to re-gear, then use the J-Scan or Procal to tell the computer you're running new gears and larger tires, at which point it will update your shift points for the new gears.
But again, none of this is possible without re-gearing.
Yes, with 35s it's going to be sluggish. No ifs, ands, or buts about that.
I ran with 4.10s and 315s (which technically measure out at 33.3") for a long time, and it felt about perfect. However, if you were going to run a true 35", you'd actually want a 4.56 gear, believe me on that. That would be the perfect gear ratio for a true 35". It's also better to have a gear that is slightly deeper as oppose to one that isn't. While you could get by just fine with a 4.10 and a 35", if you are already going to re-gear anyways, the 4.56 would be the better option.
Adjusting the speedometer for the tires via J-Scan will only update your speedometer. You really don't want to run the 3.73 gears with true 35" tires, it will be less than ideal. But, don't feel you need to re-gear right this moment. If you don't have the money, live with it for a while, then re-gear when you get the funds.
Wayne Reel
New Member
Thank you for the input! It is appreciated! I did some studying last night and figuring things out. I would say I would eventually go with the 4.56’s. Budget is a little tight right now. Anyway that’s what the wife said 
. I did want to share some ratios and information I figured out. This was figured using the w5a580 trans and the nv231 ratios. First pic is with 255/75r17’s with 3.73 gearing on the left column and 35’s with 4.10 in the right column. It comes out virtually the same. The second one is with 35’s on each side. Left side is 4.56 and right is 4.10.
. I did want to share some ratios and information I figured out. This was figured using the w5a580 trans and the nv231 ratios. First pic is with 255/75r17’s with 3.73 gearing on the left column and 35’s with 4.10 in the right column. It comes out virtually the same. The second one is with 35’s on each side. Left side is 4.56 and right is 4.10.
Thanks for sharing that. You could go either way, but I promise you that you'll enjoy the 4.56 gears more with 35s. 4.10s aren't bad, but the 4.56 is really going to be perfect.