If you have bigger tires... get the speedo fixed!

[yillbs]

So.. I've got 35" M/T tires, and my speedo has always been off by about 5 MPH, if I were going 70 on the dash, I'd really be going about 75, I was getting 11.6 - 12MPH regularly.

Finally got the hyper tech installed, and now I'm off by about 2 ( in the other direction ), so if I'm going 70, I'm really going about 68. This allows me to use 8th gear, and my RPM's are about 300-500 lower in any given gear. I'm seeing 15-16MPG now... I'm assuming most of you haven't left your speedo's like I did.. but in case you didn't, and you were curious, it's totally worth the money!!!!

 

[nateinva]

Yeah, I agree. I used my tuner to dial in 34.3"...it's still about 1 mph off and when I tried 34.0" the minor adjustment didn't agree at all with the 545rfe and it shifted like crap.

Minor adjustments related to tire size can make a significant difference...ie adjusting for size vs. just living with it and potentially not knowing things could be improved.

 

[H3MI UP]

The dealership did the lift and tires for my truck and they flashed the computer for me. Mine is dead on I have checked with 2 different gps

 

[Jershipe]

I agree. Shifts and drives way better with the speedometer corrected. I used diablosport tuner.


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[H3MI UP]

It makes a difference for sure

 

[mohemipar]

I'm wondering what a dealer would charge and if they'd give you any BS about it if youre under warranty. Anyone have any experiences?

 

[DannyMK2]

So.. I've got 35" M/T tires, and my speedo has always been off by about 5 MPH, if I were going 70 on the dash, I'd really be going about 75, I was getting 11.6 - 12MPH regularly.

Finally got the hyper tech installed, and now I'm off by about 2 ( in the other direction ), so if I'm going 70, I'm really going about 68. This allows me to use 8th gear, and my RPM's are about 300-500 lower in any given gear. I'm seeing 15-16MPG now... I'm assuming most of you haven't left your speedo's like I did.. but in case you didn't, and you were curious, it's totally worth the money!!!!

so you corrected your speedo, which resulted in you driving slower. am i understanding this correctly?

 

[69GWC]

That or the transmission shifting and shift points were affected by the speedo being off.

 

[yillbs]

I'm wondering what a dealer would charge and if they'd give you any BS about it if youre under warranty. Anyone have any experiences?

I'm under warranty, the dealer only has pre-set tire sizes they can use, if you just walk in with larger than optional tire sizes from dodge, they can't do anything.

The people that say the " dealer " was able to flash it, are incorrect. The dealer sends the truck out to a local off-road place. Every little town has a couple. Those guys can do it, not the dealer.

Warranty stays intact.

 

[yillbs]

so you corrected your speedo, which resulted in you driving slower. am i understanding this correctly?

I corrected the speedo, which resulted in the RPM to read properly. A side effect would be me going slower yes. It also effects the shift points, and engine RPM readouts. Obviously a lower RPM = better gas, and now I can actually go into 8th gear, where previously I was pretty much in 7th all the time.

 

[DannyMK2]

That or the transmission shifting and shift points were affected by the speedo being off.

having had a few trucks with larger tires, ive never really noticed a difference in the way the truck shifts having the speedometer corrected vs being off about 4-5 mph. as long as your aware how much your off at certain speeds and adjust accordingly, its usually fine. sure, ive encountered the truck not holding O/D in certain conditions, but thats a gearing issue.

I corrected the speedo, which resulted in the RPM to read properly. A side effect would be me going slower yes. It also effects the shift points, and engine RPM readouts. Obviously a lower RPM = better gas, and now I can actually go into 8th gear, where previously I was pretty much in 7th all the time.

correcting the speedo has nothing to do with the rpm. all you did was slow down. if you had slowed down in the first place, the outcome would have been the same is my point.


if you have the means of correcting the speedo, by all means do it. its always a good thing. but it making a drastic change in the way the truck drives (considering its the only different factor), im not seeing it.

 

[Ferro]

I'm under warranty, the dealer only has pre-set tire sizes they can use, if you just walk in with larger than optional tire sizes from dodge, they can't do anything.

The people that say the " dealer " was able to flash it, are incorrect. The dealer sends the truck out to a local off-road place. Every little town has a couple. Those guys can do it, not the dealer.

Warranty stays intact.

The dealer did my lift kit and calibration. Dealers can't do it I've watched him do it.

 

[yillbs]

having had a few trucks with larger tires, ive never really noticed a difference in the way the truck shifts having the speedometer corrected vs being off about 4-5 mph. as long as your aware how much your off at certain speeds and adjust accordingly, its usually fine. sure, ive encountered the truck not holding O/D in certain conditions, but thats a gearing issue.



correcting the speedo has nothing to do with the rpm. all you did was slow down. if you had slowed down in the first place, the outcome would have been the same is my point.


if you have the means of correcting the speedo, by all means do it. its always a good thing. but it making a drastic change in the way the truck drives (considering its the only different factor), im not seeing it.

You're not seeing it because you compensate for the changes, it's likely just become natural to you. As I said, the RPM was corrected now that the correct speed was displayed. I didn't say the RPM would change, the RPM is measured at the crank, not the wheel. However, when you look at it from the point of view of being off by 5MPH, you now don't have to focus on going slower to compensate for the higher speed. The RPM would be at the speed of 75, while I would only be going 70, from that point of view, when the speedo gets corrected, 2MPH in the OTHER direction, 70 is now 68 and true engine RPM is much lower. Based on that, you can see how much of a difference it would make, we're talking almost 10MPH difference, resulting in considerably lower engine speed ( RPM ).

I wasn't trying to say the RPM was actually altered. I assumed that was implied, sorry you didn't get it.

On another note, as I pointed up above, you likely don't notice a difference because you're used to it, or , because you compensate. I did not, not because I didn't want to, just a habit to not worry about it. This set of tires has less than 2k miles on them, wasn't something I was really " used " to yet.

 

[yillbs]

The dealer did my lift kit and calibration. Dealers can't do it I've watched him do it.

The dealer CAN NOT alter the revolutions of the tires manually, even if they did the math. The machine will -not- allow it, no matter how many people you tell it does, it doesn't, it doesn't for a very good reason.

you may have saw him use some sort of aftermarket piece of equipment. Likely what you saw was him lying to you, and him going up to the next available tire size. I know you'll say " nope, it's DEAD ON ", thats to be expected, but considering the 35" tires were never an option, there is no way it could be dead on without testing the math. So unless you watched him drive it around, and alter the revs per mile multiple times, he didn't do it, or he lied to you, and you believed it.

 

[Rzrman328]

My dealer told me can't be done as well....apparently "FCA" said f_ck no to dealerships doing it lol

Told me to buy a tuner....like a year ago.

Still haven't done it.

 

[DeathMachine73]

My dealer told me can't be done as well....apparently "FCA" said f_ck no to dealerships doing it lol

Told me to buy a tuner....like a year ago.

Still haven't done it.

Same here. They wanted to charge me almost 100 dollars for trying it only to be told after the fact that they couldn't do it. Told them I wasn't paying that when they didn't fix anything and eventually agreed on like 30 bucks so I could get the hell out of there. Still haven't fixed it, just got used to 51 being 55 and so on.

 

[Jershipe]

I bought a used tuner. But mine is a 2013. It's a bunch of money to do the 2015 up.


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[Ferro]

The dealer CAN NOT alter the revolutions of the tires manually, even if they did the math. The machine will -not- allow it, no matter how many people you tell it does, it doesn't, it doesn't for a very good reason.

you may have saw him use some sort of aftermarket piece of equipment. Likely what you saw was him lying to you, and him going up to the next available tire size. I know you'll say " nope, it's DEAD ON ", thats to be expected, but considering the 35" tires were never an option, there is no way it could be dead on without testing the math. So unless you watched him drive it around, and alter the revs per mile multiple times, he didn't do it, or he lied to you, and you believed it.

He did something cause My odometer is dead on. And I checked it with two GPS. And I had a police car check it with his radar gun. I guess they are all lying as well. Lol

 

[mohemipar]

Good info. Ive been debating if I should bother having the speedo fixed. I havent been quite ready to spend the money on a tuner. Why cant we just slap on mods without worrying about little **** like this lol. Boo to physics.

I have been thinking about going with a new set of Toyo's in 285/65/20. They are pretty light as well.

 

[sbarron]

Good info. Ive been debating if I should bother having the speedo fixed. I havent been quite ready to spend the money on a tuner. Why cant we just slap on mods without worrying about little **** like this lol. Boo to physics.

I have been thinking about going with a new set of Toyo's in 285/65/20. They are pretty light as well.

Because physics.

Edit to your edit: you beat me by half a second to physics. Lol


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