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Discussion Starter #1
Put gas in the wifes titan today and i noticed that in 4th gear @ 1500rpm i was goin' about 51mph. I then did the same trip in mine. At 1500rpm i was only doin 41ish. Would this be the size of the tire or different gearing?
245/75/17 - hers
265/75/18 - mine
 

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the 18s are bigger tires in diameter, but do both titans have big tow package or neither or one? in mine 1500rpm is bout 51mph and my titan has the big tow package and the 17in off road rims, i cant remember the size of the tires but they are the original tires. if 1 has the big tow package it makes a difference in speed i think. i have never driven another titan but mine so i have nothing to compare to.


O, and when you did this test did you let the torque converter lockup into overdrive?
 

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Nissan_Kid said:
Put gas in the wifes titan today and i noticed that in 4th gear @ 1500rpm i was goin' about 51mph. I then did the same trip in mine. At 1500rpm i was only doin 41ish. Would this be the size of the tire or different gearing?
245/75/17 - hers
265/75/18 - mine
I notice in your sig you have a 4x4, I'm assuming hers is probably a 2wd. The difference is in the gears her's 3:73, while your's is closer to 4:10 that's taking into consideration the tranny reduction. Just my .02 I have the 4x4 and I believe mine is about the same, I usually just try to get the torque converter to lock up and keep it just within over-drive range.
 

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Let's assume your wife's Titan has standard transmission gears (1st - 3.827, 2nd - 2.368, 3rd - 1.519, 4th - 1.000, 5th - 0.834). Further, assume she has the standard rear axle ratio of 2.940.

Since she has 245/75-17 tires, the standard diameter would be about 31.470 inches. At 1500 rpm, she SHOULD be doing 47.77 MPH in 4th gear. Close enough to 48 MPH.

Let's assume YOUR Titan has the Big Tow package with 3.357 rear axle. Your transmission has the same gears and you are running 265/75-18 tires with a nominal tire diameter of 33.650 inches. At 1500 RPM in 4th gear, you SHOULD be running 44.73 MPH. Close enough to 45 MPH.

So, I see maybe a 3 MPH difference, 4 at the outside, assuming your tachometers are correct and your kept constant throttle when you switched to the speedometer from the tachometer. If you went a little fast in hers and little slow in yours, then you are pretty close to what you saw.

It would be more accurate to run side by side at the same speed in the same gear. Ask her to note the RPM and you do the same. We could go from there.
 

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dang, you're good greg, how did u find out what speed he would be going?
gears confuse me sometimes, i can under stand the rear end that the pinion has to spin 3.357 times to get the ring gear to spin 1 time. but when there are 2 gear ratios i get confused.
 

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TITAN DOHC V8 said:
dang, you're good greg, how did u find out what speed he would be going?
gears confuse me sometimes, i can under stand the rear end that the pinion has to spin 3.357 times to get the ring gear to spin 1 time. but when there are 2 gear ratios i get confused.
There are online calculators where you input all the info (tire size, gear ratios, final drive, etc) and it figures it out for you.

Here's a simple one ----> http://www.f-body.org/gears/

Top speed one --------> http://www.catherineandken.co.uk/sti/tyres.html
 

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Discussion Starter #7
Both the trucks are 4x4 and both have the tow package. Next time my brother in law comes over i will have to try the side by side thing.
 

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I made up an Excel spreadsheet that calculates it all.

If anyone wants it, PM me.

Or, my home email is [email protected]. I'll send you the file. It's in Excel 2002, but I could easily save it in an earlier format if needed.

Tires are easy. A 285/70-17 is 285 mm wide, which is 11.22 inches. The tire sidewall is 70% as high as the tread, which is 7.854 inches. So, the wheel is 17 inches with 7.854 inches all around, so the diameter is 32.71 inches in diameter (17 + 7.854 (on bottom) + 7.854 (on top)).

The cicumference of a circle is pi times the diameter, or 3.14159 * 32.71 = 102.7552 inches around for one revolution.

From there, you need to know the transmission gears, the transfer case gears, and the rear axle and you can get speed at any rpm.

For my 2007 Titan:

Transmission:

1st = 3.827
2nd = 2.368
3rd = 1.519
4th = 1.000
5th = 0.834

Transfer case:

Hi = 1.000
Lo = 2.596

The rear axle ratios are:

Normal = 2.940
Big Tow = 3.357
 

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cool, i will try using those sites to compare to the spedo and tach on my titan and other cars.

thanks, maybe i will figure out how gear ratios all work now.
 

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TITAN DOHC V8 said:
the 18s are bigger tires in diameter, but do both titans have big tow package or neither or one?
Actually, the outside diameter of the 18 inch wheels is smaller. The OEM Goodyear Wrangler 265/70-18 is 32.6". The outside diameter for the OEM BF Goodrich Rugged Trail 285/70-17 is 33".
 

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Nissan_Kid said:
Put gas in the wifes titan today and i noticed that in 4th gear @ 1500rpm i was goin' about 51mph. I then did the same trip in mine. At 1500rpm i was only doin 41ish. Would this be the size of the tire or different gearing?
245/75/17 - hers
265/75/18 - mine
i was going off of these tire sizes, i went to a online tire calculator and the 18s were bigger. the width of the 18s is 265 vs. 245 and the sidewall is the same at 75 plus on a bigger rim.
 
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