Wrong Gear Ratio Factory Installed 35’s

[Gladman]

Interesting tidbit here on dealers flashing for tire size corrections in Canada. It is forbidden by transport Canada according to my dealer when I asked for it!

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[ShadowsPapa]

This is true.

This thread title is misleading. The correct gears were installed, but the Jeep was modified. This does not make the gear ratio “incorrect”. Would lower gears be better? Sure. Are they required for 35s? No.

OP- Buy a device to correct your speedometer and enjoy your Jeep.

Yeah, I read that - no way it's a factory installed lift and 35's. That's AFTER factory, dealer or owner installed and no a dealer does what you ask, they don't swap gears unless you ask and that's on YOU since that is your request.

You bought a truck with the 3.73 ratio. You had the dealer install bigger tires and a lift. Those are accessories, not factory. So why would a dealer make a gear change? It's not part of any package and not even a factory option.
If you want different gears, it's on you.
Dealer told me months ago if I went to different tire sizes they'd reconfigure the truck - for a fee, or they'd sell me the tools to do it and I'd then have the tool forever and for future tire changes.

It ain't on them. You have to tell them what you want or want done.

 

[Jeeperjamie]

I used JScan on mine to correct the speedo and shift points after I added 35's to mine. As far as getting the dealer to correct your gear ratio, that's going to be on you 100%. You should have realized that with 3.73 gears and 35's it's not going to get the MPG that it would have on smaller stock tires. Did you test drive it before buying it. A good 30 to 45 minute test drive would of told you that the 35's were going to be like a dog with 3.73 gears. Not trying to make you feel bad or stupid about it just don't worry about it to much. It's not going to hurt anything other than your mpg. I wouldn't worry about the torque converter, but if it does fail under warranty then they will fix it under warranty.

 

[ShadowsPapa]

What is your actual tire size you are currently running? At what speed is the speedo 5 mph off?

Also curious what lift did they put on it? The mopar is 2” not 2.5”... is this an actual Jeep dealer?

This install is highly suspect merely because they didn’t recalibrate the Speedo. Hey maybe they over looked, it, but it’s also like dropping your guitar off at the guitar store to change the strings and they didn’t tune the guitar. Highly suspect...

Here is a great tool to compare tire sizes and how distance/speed is affected:

https://www.tacomaworld.com/tirecalc?tires=265-75r17-315-70r18

You hit on a good point - speedometer being off is a percentage, not a given. It will be 5 off at xx speed and 3 off at a different speed and so on. The difference as far as being off in MPH will vary with the speed. Bigger difference the faster you drive as again, it's a percentage, not a solid number in MPH.

 

[MrZappo]

I have a mojave with 4.10 and 33's.

I understand that many people are saying it won't blow up and everything will be fine but I gotta tell you, I can't imagine running like that.

Mine is just about tolerable. But close to bugging me as is. It shifts out of 8th a lot on the highway if there is any incline or wind.

I was considering 35's but after putting 5000 miles on the 33's, I would not think of it without regearing one or 2 steps.

I like my vehicles to run "as intended" and driving in 6th on the highway (although not damaging) would drive me absolutely nuts. Not to mention that towing would be severely diminished.

The argument that "it won't blow up but if it does they will cover it under warranty" does not seem like sound reasoning to me for a vehicle that I want to last a long time.

My opinion. And worth well, nothing I guess.

 

[Jeeperjamie]

I have a mojave with 4.10 and 33's.

I understand that many people are saying it won't blow up and everything will be fine but I gotta tell you, I can't imagine running like that.

Mine is just about tolerable. But close to bugging me as is. It shifts out of 8th a lot on the highway if there is any incline or wind.

I was considering 35's but after putting 5000 miles on the 33's, I would not think of it without regearing one or 2 steps.

I like my vehicles to run "as intended" and driving in 6th on the highway (although not damaging) would drive me absolutely nuts. Not to mention that towing would be severely diminished.

The argument that "it won't blow up but if it does they will cover it under warranty" does not seem like sound reasoning to me for a vehicle that I want to last a long time.

My opinion. And worth well, nothing I guess.

I'm running 35s with 410 gears and my Jeep hardly ever hunts for gears and I live in the Piedmont Foothills area of North Carolina. I average between 18.1 and 19 miles per gallon and as high as 21 on some long trips. When I go to 37s I still want considered regearing.



My statement was meaning that the warranty would cover it either way, if you had 35's, 37's or whatever size tire. Your not going to have to worry about something happening to the jeep, especially with 4.10 gears. I've also towed 5,000lbs of rock that felt effortless. Gas mileage was around 15 on that 45 minute trip which was as expected. I also got a Max Tow not a Mojave which apparently makes a difference based on others comments on this forum a gas mileage and shift points etc....

 

[Kevin_D]

You hit on a good point - speedometer being off is a percentage, not a given. It will be 5 off at xx speed and 3 off at a different speed and so on. The difference as far as being off in MPH will vary with the speed. Bigger difference the faster you drive as again, it's a percentage, not a solid number in MPH.

Depends on the vehicle...
My Metric Cruiser (motorcycle) speedometer is off by 10mph over about 30, but the odometer is dead on. The manufacturer has it built like that on purpose to try and get riders to slow down by making them think they're going fast !
My last sedan was the same, but the difference was only about 4mph on the speedometer.
The Jeep is dead on.
But, that being said, differences due to tire size will be a percentage.

Kevin

 

[Renegade]

I have a mojave with 4.10 and 33's.

I understand that many people are saying it won't blow up and everything will be fine but I gotta tell you, I can't imagine running like that.

Mine is just about tolerable. But close to bugging me as is. It shifts out of 8th a lot on the highway if there is any incline or wind.

I was considering 35's but after putting 5000 miles on the 33's, I would not think of it without regearing one or 2 steps.

I like my vehicles to run "as intended" and driving in 6th on the highway (although not damaging) would drive me absolutely nuts. Not to mention that towing would be severely diminished.

The argument that "it won't blow up but if it does they will cover it under warranty" does not seem like sound reasoning to me for a vehicle that I want to last a long time.

My opinion. And worth well, nothing I guess.

You know that 6th gear is the 1:1 drive ratio in the automatic, right? They are double-overdrive transmissions. There is actually less going on in 6th than any other gear, and it’s totally appropriate.

 

[Renegade]

Interesting tidbit here on dealers flashing for tire size corrections in Canada. It is forbidden by transport Canada according to my dealer when I asked for it!

And you believe the dealer? I don’t trust much of anything a dealer says. You know FCA actually put out instructions to their dealers on how to correctly program for tire size, along with the number of labor hours to charge the customer?

 

[Jeeperjamie]

And you believe the dealer? I don’t trust much of anything a dealer says. You know FCA actually put out instructions to their dealers on how to correctly program for tire size, along with the number of labor hours to charge the customer?

Yeah a lot of dealers just don't want mess with it for whatever reason and lie to their customers, not sure what the logic is there. Hendricks told me they would flash it for free if it's under warranty if I decided to add larger tires. I had already added the tires and got the JScan before I knew that. They did however flash it for the led bulbs I put in the tail lights to turn the turn signal light out warning light off the dash at my last oil change and did it for free.

 

[Gladman]

And you believe the dealer? I don’t trust much of anything a dealer says. You know FCA actually put out instructions to their dealers on how to correctly program for tire size, along with the number of labor hours to charge the customer?

Yes, FCA can do whatever they like in the the US according to US regulations.
However, in Canada it is FCC and they must follow Transport Canada Regulations.
In this case I do trust the dealer. The sales manager I dealt with has a 2020 Wrangler with larger than factory tires and referred me to an aftermarket shop that sells the Tazer. That is how she got her tire sizes adjusted.
The field for adjusting tire sizes in the factory software provided to the dealer is greyed out.

 

[wvyankee2]

I have 488's with my 35/11.50/18 and am getting 15-16 MPG. Much better performance too. Tazer lite installed.

 

[ShadowsPapa]

Depends on the vehicle...
My Metric Cruiser (motorcycle) speedometer is off by 10mph over about 30, but the odometer is dead on. The manufacturer has it built like that on purpose to try and get riders to slow down by making them think they're going fast !
My last sedan was the same, but the difference was only about 4mph on the speedometer.
The Jeep is dead on.
But, that being said, differences due to tire size will be a percentage.

Kevin

My last bike was a Yamaha Maxim 750 shaft drive, jet black. Old school. Both odometer and speedometer got the same "input". When you were going 75 you WERE going 75. Wife or kid on the back kept my speed in check, LOL - no need for the factory to do so.

 

[ShadowsPapa]

And you believe the dealer? I don’t trust much of anything a dealer says. You know FCA actually put out instructions to their dealers on how to correctly program for tire size, along with the number of labor hours to charge the customer?

The part I like about a dealer doing it - charge or not - is that there's a RECORD should anything happen - like warranty claim question on mileage (you are really close to the end) or some other legal BS. It's on record, they did it. And MOPAR seems to agree according to your post here.
My dealer said they would do it - or sell me the thing to do it, my choice. I've not changed tire sizes really (32.2" stock Overland and 32.8" stock Rubicon tires didn't seem to change mine according to GPS comparisons) so, so far, I've not had need but if I do change tire sizes, I will talk to the dealer first even though I do have the ability with jscan or AlfaOBD either one. That way it would be on record, sort of like having them add the passive entry sales code - it's then part of my VIN forever.

 

[PDiddy]

I have 488's with my 35/11.50/18 and am getting 15-16 MPG. Much better performance too. Tazer lite installed.

yeah I’m on 488s and 35s. It’s a lovely combo. I have not reprogrammed mine for the gears or tires. So not sure if my mpg, since it isn’t accurate. I need to get it into the dealer foe the reprogram.

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