Just a thought ( over sized tires and mpg read out on dash.)

**** PLEASE USE SUBTOPICS BELOW FOR NEW TOPICS ****

Moderator: volvite

User avatar
Captain
Sponsored Member
Posts: 692
Joined: Wed Mar 19, 2008 7:41 pm
Location: S.w. Chicago

Just a thought ( over sized tires and mpg read out on dash.)

Postby Captain » Sun Mar 30, 2008 11:47 am

I did my search on the subject but all the threads were out of date. So I want to get a update on this subject. I see lots of you have changed your tire size. My question is

(I know all tires have fug factors of +/- 3 percent)

On my 08 PF Se with 265/65 17r tires there is not alot of choices for a good A/T tire. I want to run the BFG A/T ko's but they only come in 265/70 17r. when I do the math the 265/65 17 has a 30.56 diameter 680rpm and the 265/70 17 has a 31.65 diameter 657rpm so the change is 1/2" radius and -23rpm so my speedo reading 65 I will realy be 67ish.
I want to know with this mess up the dash computer as far as mpg read out and psi? I read on a nother post that all SE Pf are set to read the Offroad tire diameter of 265/75 16r what is a match for the 265/70 17. Is that true?


Gray
Posts: 750
Joined: Sun Aug 26, 2007 12:39 pm
Location: xxx

Postby Gray » Sun Mar 30, 2008 12:27 pm

I've read the same info; that the US built PF OR's with 265/75R16 size are about 31.5" diameter and that all of the other PF model odometers are set for that size, not sure if thats true though as I've never had these 245/75R16's checked in relation to odometer accuracy.

As an aside question do any know if tire diameters vary depending on the amount of air pressure in them.

.

User avatar
Captain
Sponsored Member
Posts: 692
Joined: Wed Mar 19, 2008 7:41 pm
Location: S.w. Chicago

Postby Captain » Sun Mar 30, 2008 12:49 pm

Greybrick wrote:I've read the same info; that the US built PF OR's with 265/75R16 size are about 31.5" diameter and that all of the other PF model odometers are set for that size, not sure if thats true though as I've never had these 245/75R16's checked in relation to odometer accuracy.

As an aside question do any know if tire diameters vary depending on the amount of air pressure in them.

.
well yes if you lower the psi down your footpring gets larger but your height gets a touch less as well.

Also look for Nissan all years of the R51
http://209.12.144.2/Products/Inline%20S ... r%20Module

instructions

http://209.12.144.2/media/manuals/aa/20 ... xterra.pdf

User avatar
blink32
Sponsored Member
Posts: 866
Joined: Wed Sep 13, 2006 6:38 am
Location: World Traveler

Re: Just a thought ( over sized tires and mpg read out on da

Postby blink32 » Sun Mar 30, 2008 4:47 pm

Captain caveman wrote:I want to know with this mess up the dash computer as far as mpg read out and psi?
PSI no, MPG yes. The optimal choice is to travel over a measured mile (if you can find one) that your local gub-ment utilizes to verify speedo's, or hit up one of the AAA events that do the same. Once you have that true MPH value you can extrapolate any other number you want from your display MPH/MPG.

Barring that if you could get your hands on a mobile gps such as the Garmin Nuvi 660 you could then "go for a drive". You could do it for just a short distance to get your true MPH or set it up then head off on a longer trip if you have a reason to. Then go ahead and extrapolate your numbers.

User avatar
Captain
Sponsored Member
Posts: 692
Joined: Wed Mar 19, 2008 7:41 pm
Location: S.w. Chicago

Postby Captain » Sun Mar 30, 2008 7:50 pm

I compared speedos with two other cars tonight and I found that my PF is off. At true 40mph my PF showed 37-38mph and at true the PF showed 62-63.

I check this with the tire size of my PF 265/65r17 and the Offroad 265/75r16 and my calculations are correct. my Se has the speedo calculations of the Offroad SE Pathfinder.

So this will show that my dash computer is off for MPG and Trip calculator.
This all still falls in the +/-5 or 6 percent fug factor from Nissan.

User avatar
Fofiddy
Moderator
Posts: 422
Joined: Sat Sep 02, 2006 6:40 pm
Location: New England

Postby Fofiddy » Sun Mar 30, 2008 8:45 pm

Captain caveman wrote:I compared speedos with two other cars tonight and I found that my PF is off. At true 40mph my PF showed 37-38mph and at true the PF showed 62-63.

I check this with the tire size of my PF 265/65r17 and the Offroad 265/75r16 and my calculations are correct. my Se has the speedo calculations of the Offroad SE Pathfinder.

So this will show that my dash computer is off for MPG and Trip calculator.
This all still falls in the +/-5 or 6 percent fug factor from Nissan.
I'm pretty much settled on the belief that all the computers are set to the SE-Offroad's 31.5" wheel size. My stock tires made the speedo disagree with my GPS for a 3+mph @60. Once I went to the 31.6" the two are just about equal.
As for tire pressue if your sticking with P rated tires keep em 35psi unless thats too stiff for you. Airing down your tires gives you nothing unless you have both flotation tires and conditions that necessitate their use.
Now LT tires are a diff story, 35psi doesn't cut it in most LT tires you'll be running those guys at 43-60psi depending on what you get and how you like your ride. If you do go with the LTs get the OME or a similar suspension. The Stock suspension isn't designed for LT's you'll really feel it beat up the suspension over time.

User avatar
Captain
Sponsored Member
Posts: 692
Joined: Wed Mar 19, 2008 7:41 pm
Location: S.w. Chicago

Postby Captain » Mon Mar 31, 2008 6:03 am

When the time comes Im going to go with BFg All terrain Ko. I had them on my Zr2 before I lifted it and I real liked them. they were 31/10.50 on 15r. When I do get them Im going to run them at 32-35 to keep them soft for the ride.

User avatar
NVSteve
Sponsored Member
Posts: 1985
Joined: Thu Feb 01, 2007 11:27 am
Location: Salt Lake City

Postby NVSteve » Mon Mar 31, 2008 9:28 am

Greybrick wrote:I've read the same info; that the US built PF OR's with 265/75R16 size are about 31.5" diameter and that all of the other PF model odometers are set for that size, not sure if thats true though as I've never had these 245/75R16's checked in relation to odometer accuracy.
I would really get it checked. I still can't believe the MPG numbers that you've mentioned, and really think the tires are coming into play with everything.

User avatar
phantom2
Posts: 81
Joined: Thu Dec 21, 2006 9:36 am

Postby phantom2 » Mon Mar 31, 2008 5:27 pm

Captain,maybe this will help you. http://www.miata.net/garage/tirecalc.html

User avatar
Captain
Sponsored Member
Posts: 692
Joined: Wed Mar 19, 2008 7:41 pm
Location: S.w. Chicago

Postby Captain » Mon Mar 31, 2008 6:16 pm

Thanks Phanton for the site I like to use Discount tires version. Its all the same calc. I also did a test with the trip computer on the speed dash compaired to the computer on the center dash and there the same. I also did the same test again last night and Im still off by 2-4mph I would like to connect a tech computer to see what tires are on the ecm

User avatar
NVSteve
Sponsored Member
Posts: 1985
Joined: Thu Feb 01, 2007 11:27 am
Location: Salt Lake City

Postby NVSteve » Mon Mar 31, 2008 7:17 pm

I kept an eye on the speedo and my portable GPS for about 1600 miles worth of driving the last week. I'd have to say they both reflect the same numbers. The GPS is just too accurate, which meant that I had to really position the speedo needle dead center of any of the tick marks in order to do a comparison. That's with 265/75/16s.

User avatar
Captain
Sponsored Member
Posts: 692
Joined: Wed Mar 19, 2008 7:41 pm
Location: S.w. Chicago

Postby Captain » Tue Apr 01, 2008 2:34 pm

NVSteve wrote:I kept an eye on the speedo and my portable GPS for about 1600 miles worth of driving the last week. I'd have to say they both reflect the same numbers. The GPS is just too accurate, which meant that I had to really position the speedo needle dead center of any of the tick marks in order to do a comparison. That's with 265/75/16s.
I think this is because you have a 31" tire not like me that has a 30.6".

User avatar
NVSteve
Sponsored Member
Posts: 1985
Joined: Thu Feb 01, 2007 11:27 am
Location: Salt Lake City

Postby NVSteve » Tue Apr 01, 2008 2:51 pm

Captain caveman wrote: I think this is because you have a 31" tire not like me that has a 30.6".
Yup. I just wanted to point out that it seems to be dead on with the 31".

User avatar
Captain
Sponsored Member
Posts: 692
Joined: Wed Mar 19, 2008 7:41 pm
Location: S.w. Chicago

Postby Captain » Tue Apr 01, 2008 4:06 pm

Well we will just have to wait to see when one of use with the 30.6" tires go to a 31.


Return to “2005-2012 Pathfinder (R51)”

cron