Transmission shifting with bigger tires?

[OrangeCrush]

In response to another post by a new member, he was asking about putting 39's on his H2.

It reminded me that I wanted some opinion from those that have bigger tires.

Obviously putting larger tires will give the same effect of reducing the gear ratio. I've noticed that around 45 mph, the trans can't stay in overdrive for long... the littlest incline or step on the gas pedal sends the trans downshifting into drive until it reaches the appropriate speed.

If I remember correctly, the trans is a 4le60 and shifts by speed, not rpms. Did anyone have their PCM reflashed to change shift points?

The speedometer with 38's is only off (according to those highway side portable radar units) 2-3 mph.

Anyone do anything about it or just leave it?

Thanks,

Mark

[OrangeCrush]

In response to another post by a new member, he was asking about putting 39's on his H2.

It reminded me that I wanted some opinion from those that have bigger tires.

Obviously putting larger tires will give the same effect of reducing the gear ratio. I've noticed that around 45 mph, the trans can't stay in overdrive for long... the littlest incline or step on the gas pedal sends the trans downshifting into drive until it reaches the appropriate speed.

If I remember correctly, the trans is a 4le60 and shifts by speed, not rpms. Did anyone have their PCM reflashed to change shift points?

The speedometer with 38's is only off (according to those highway side portable radar units) 2-3 mph.

Anyone do anything about it or just leave it?

Thanks,

Mark

[Hummertech]

The computer uses speed, and throttle position as it's main 2 inputs regarding shift timing. You are correct that changing your tire sizes will throw this off some. If you go a little larger than factory tires it's not a big deal. GM does not have many calibrations to reprogram for much larger tires. Unless the aftermarket has it, you'll have to live with the different shifting.

[PARAGON]

It does indeed use speed and rpm along with the throttle position as HT says. You can adjust the shift points relative to speed and RPM via a programmer, at least the Diablosport Predator anyway, as well as shift firmness for each shift.

There are actually two different ranges of setting also. There is a performance range where it is sensing the Throttle being mashed and you can make separate adjustments for that from a normal range.

[TXSUT]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by PhilD:
I used a SuperChips to program for the larger tire diameter and change the shift points (lower) and shift pressure (firmer). Very pleased with the overall result. </div></BLOCKQUOTE>

Same here.

[W1N]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by TXSUT:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by PhilD:
I used a SuperChips to program for the larger tire diameter and change the shift points (lower) and shift pressure (firmer). Very pleased with the overall result. </div></BLOCKQUOTE>

Same here. </div></BLOCKQUOTE>

Would you guys touch shift points when going from stock to 37" tires?

[TXSUT]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by W1N:
Would you guys touch shift points when going from stock to 37" tires? </div></BLOCKQUOTE>

Not sure I understand your question, but I went from stock tires to 37" tires and changed the shift points with my Superchips programmer as Phil described. Does that answer your question?

[W1N]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by TXSUT:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by W1N:
Would you guys touch shift points when going from stock to 37" tires? </div></BLOCKQUOTE>

Not sure I understand your question, but I went from stock tires to 37" tires and changed the shift points with my Superchips programmer as Phil described. Does that answer your question? </div></BLOCKQUOTE>

Yes, thanks!

Is it hard with the programmer? do you change the settings and then take test runs to find the optimum or how did you do it?

[kdio]

I have been running 37" tires for about 45,000 miles on my H2. I recently changed the gears to 4.56 and it made a huge difference. My H2 is running the Magnacharger and while it had a lot of power before the truck a lot better now.

[W1N]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by kdio:
I have been running 37" tires for about 45,000 miles on my H2. I recently changed the gears to 4.56 and it made a huge difference. My H2 is running the Magnacharger and while it had a lot of power before the truck a lot better now. </div></BLOCKQUOTE>

Do you have any idea what is the 0-60 range you can do with that set up of yours?

[kdio]

W1N,
I have never checked my 0 to 60 time, but my wife drived a Porsche Cayenne S and I can beat her off the line up to about 50 MPH before she starts to catch me. Most people are blown away how fast my H2 is when they ride in it.

[W1N]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by kdio:
W1N,
I have never checked my 0 to 60 time, but my wife drived a Porsche Cayenne S and I can beat her off the line up to about 50 MPH before she starts to catch me. Most people are blown away how fast my H2 is when they ride in it. </div></BLOCKQUOTE>

And this was with 4" lift and 37" tires? Do you have any pictures? I'm also interested of getting Rancho 4" lift...

Thanks!

[strongrhino]

Well why does a H2 have a 0-60 time of over 10 seconds and the Porsche Cayenne S (fastest suv) do it in 5.2 seconds....and you beat her? You are joking...right?

[W1N]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by strongrhino:
Well why does a H2 have a 0-60 time of over 10 seconds and the Porsche Cayenne S (fastest suv) do it in 5.2 seconds....and you beat her? You are joking...right? </div></BLOCKQUOTE>

First of all Cayenne S makes it 0-60 in6.8s. Cayenne Turbo makes it in 5.6s

Second, the guy has his H2 supercharged that's like 125 hp more to the stock plus all the other performance add ons...

[strongrhino]

You are correct...6.8 seconds. Still no way in hell a supercharged H2 can keep up. Come on now! My buddys whipple charged H2 with exhaust, cold air intake, and exhaust with stock wheels does 0-60 in just over 8 seconds and a 14.9 1/4 mile. Still not even close. Compare apples to apples!

[W1N]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by strongrhino:
You are correct...6.8 seconds. Still no way in hell a supercharged H2 can keep up. Come on now! My buddys whipple charged H2 with exhaust, cold air intake, and exhaust with stock wheels does 0-60 in just over 8 seconds and a 14.9 1/4 mile. Still not even close. Compare apples to apples! </div></BLOCKQUOTE>

Maybe it was the wife driving the porcshe

[TXSUT]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by W1N:
Is it hard with the programmer? do you change the settings and then take test runs to find the optimum or how did you do it? </div></BLOCKQUOTE>

It's very easy, the programmer walks you through the options, and only takes about 5 minutes. I'm not sure if how I have it set is optimum...I just did what PhilD told me to do. But yes, you can play with the settings and test drive until your heart's content.

[W1N]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by PhilD:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by TXSUT:
I just did what PhilD told me to do. </div></BLOCKQUOTE>Don't blame me But, yes, it is very easy to program. My 7 year old boy did it for me last time </div></BLOCKQUOTE>

Thanks guys!!!

How much of a difference does it actually make?