4.10s &37s what speed are you hitting 8th?

[BigRed97]

I looked in some other threads and couldn't find an answer....

Sport S w/max tow, 425 miles

I just put on 37s yesterday (Speedo adjust with Tazer) drives great....

This morning was the first highway speed run on my way to work, I have about 2 miles of 70mph. (All flat, at sea level)

So got going steady at 70 and thought it was reving high, clicked it over to M and it was only in 7th, shifted it to 8th and Rpm was where I expected. Back to D and it dropped to 7th again

So my question is why is keeping me in 7th, at 70mph? What speed are you all seeing 8th ?

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[BigRed97]

Anyone?

 

[Jeep Rookie]

Trans and gears are not set up for that tire size. You basically have a 7spd now.

 

[BigRed97]

Respectfully, I disagree on the gearing. In my experience 4.10s &37s are fine for street use(Wich is what I do)

Correct me if I'm wrong but what I've gathered 7th is the same OD ratio as the older jk(wich I had 37s and 4.10s on my 18) .84:1 I believe?
Wich put me right about 2200rpm @70

When I manually put it into 8th it drops to just below 1800rpm..Wich should be a perfectly good cruise rpm ... And once it's in 8th it drive fine. No lack of power or trouble maintaining speed..

Just not sure why it won't allow 8th at that speed

 

[Greg@RME]

You have too much resistance, rolling and wind, to get it to stay in 8th with 4.10 gears and 37's. The 8 speed does a pretty good job of making up for bigger tires with 4.10 gears, but no matter how you cut it, at the end of the day your final drive ratio is off... and the final drive ratio is really all that matters. You need to regear to get the engine back into it's optimal RPM range to get it to stay in 8th gear. The gear ratio for 8th gear is massive, .67... you can't compare a JK to a JT, the transmissions are totally different.

Disagree all you want, you made a big change with the 37's versus stock tires and you're ignoring the need to regear the axles to make up for that.

 

[smoverland]

Drove from Tennessee to Virginia for overland Expo. 38" Milestar Pats, stock 4.10s, and shift points corrected via Superchips Flashcal. I was in 8 the majority of my highway miles (70mph) and averaged over 21mpg.

 

[BigRed97]

Actually running Milestar pats ATs.
I haven't gotten it over 70 to see when it will shift to 8th yet.

 

[TennesseePA]

I have 37 KO2s on my LE and I hit 8th gear with a trailer attached. It doesn’t pull very hard in 8th and will drop down on any sort of an incline but goes up to 8th and coasts as long as it can. In my opinion 8th gear is not a cruising gear it is to get the rpm as low as possible while the engine isn’t under load.

 

[Ted Striker]

On my highway commute back and forth to work, I go over some overpasses but most of it is level terrain. At 70 mph, it can hit 8th but as soon as one of the overpasses comes up, it drops to 7th and if it's a large one or if there is a headwind, it drops to 6th. Honestly haven't been able to keep it in 8th very long so it mostly stays in 7th. Mine is a Rubicon with 37" Ridge Grapplers and speedo adjusted by Tazer JL Mini.

Also, FYI - you don't have to drop it in Manual to see what gear you're in. There is a selection on the dash info screen that allows you the see the gear number next to the D at all times.

 

[BigRed97]

...
Also, FYI - you don't have to drop it in Manual to see what gear you're in. There is a selection on the dash info screen that allows you the see the gear number next to the D at all times.

Thanks! I did just find this out the other day and it does help me get a better handle on what the trans is doing.

So I DO in fact hit 8th over 60mph if the conditions are right. I'm satisfied with the way it behaves on the highway now that I see what is going on more accurately

 

[Oscar Indy]

 

[wanderer]

Where is the selection on your dash I found it on my jlur. But can’t find it on the jtr

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