Re: Speedometer accuracy w/31" tires - did dealer lie?
 

On Thu, 23 Oct 2003 05:29:53 -0500, "Patrick Mills"
<plm1954R_E_M_O_V_E@ix.netcom.com> wrote:

>I happen to have a GPS, and, according to it, the speedometer reads slow
>by between 4 to 6 mph.


GPS is accurate to tenths of a mph, when you drive at a steady speed
for 10 seconds or so.... assuming the antenna has a good wide view of
the sky. Set the cruise control for 60 mph on a dead level road out in
the open and watch the readout (carefully).

Get the dealer to fix the speedo drive so it reads within 2-3 mph,
preferably on the high side. If you go a little larger on tire size it
will read close to dead-on and you won't have to do this again, and
you will be less likely to get a speeding ticket in the meantime.

John Davies
Spokane WA USA

Re: Speedometer accuracy w/31" tires - did dealer lie?
 

On Thu, 23 Oct 2003 05:29:53 -0500, "Patrick Mills"
<plm1954R_E_M_O_V_E@ix.netcom.com> wrote:

>I happen to have a GPS, and, according to it, the speedometer reads slow
>by between 4 to 6 mph.


GPS is accurate to tenths of a mph, when you drive at a steady speed
for 10 seconds or so.... assuming the antenna has a good wide view of
the sky. Set the cruise control for 60 mph on a dead level road out in
the open and watch the readout (carefully).

Get the dealer to fix the speedo drive so it reads within 2-3 mph,
preferably on the high side. If you go a little larger on tire size it
will read close to dead-on and you won't have to do this again, and
you will be less likely to get a speeding ticket in the meantime.

John Davies
Spokane WA USA

Re: Speedometer accuracy w/31" tires - did dealer lie?
 

On Thu, 23 Oct 2003 05:29:53 -0500, "Patrick Mills"
<plm1954R_E_M_O_V_E@ix.netcom.com> wrote:

>I happen to have a GPS, and, according to it, the speedometer reads slow
>by between 4 to 6 mph.


GPS is accurate to tenths of a mph, when you drive at a steady speed
for 10 seconds or so.... assuming the antenna has a good wide view of
the sky. Set the cruise control for 60 mph on a dead level road out in
the open and watch the readout (carefully).

Get the dealer to fix the speedo drive so it reads within 2-3 mph,
preferably on the high side. If you go a little larger on tire size it
will read close to dead-on and you won't have to do this again, and
you will be less likely to get a speeding ticket in the meantime.

John Davies
Spokane WA USA

Re: Speedometer accuracy w/31" tires - did dealer lie?
 

"Fred W." <Fred.Wills@ nospam myrealbox.com> wrote in message
news:l9Rlb.124490$qj6.7636690@news1.news.adelphia. net...

>
> It is completely normal for a speedo to read *high* by a few MPH, not low.
> The manufacturers would prefer to err on the safe side. Sounds like they
di
> not do anything and the larger diameter tires would explain the low
reading.
>
> -Fred W
>


I believe it's possible to adjust the speedo "gearing" on the '04
electronically. You could go back to the dealer and ask them to do that. Way
easier than changing the little gear on the t-case in earlier models.

They may want to chargea minimum labor fee, even though it's about 5 minutes
work with a terminal.

I changed out the stock 30's for 31's on my '97 Sport and now the speedo
seems more accurate, based on the displays around schools that the cops here
wheel around.

Doug

Re: Speedometer accuracy w/31" tires - did dealer lie?
 

"Fred W." <Fred.Wills@ nospam myrealbox.com> wrote in message
news:l9Rlb.124490$qj6.7636690@news1.news.adelphia. net...

>
> It is completely normal for a speedo to read *high* by a few MPH, not low.
> The manufacturers would prefer to err on the safe side. Sounds like they
di
> not do anything and the larger diameter tires would explain the low
reading.
>
> -Fred W
>


I believe it's possible to adjust the speedo "gearing" on the '04
electronically. You could go back to the dealer and ask them to do that. Way
easier than changing the little gear on the t-case in earlier models.

They may want to chargea minimum labor fee, even though it's about 5 minutes
work with a terminal.

I changed out the stock 30's for 31's on my '97 Sport and now the speedo
seems more accurate, based on the displays around schools that the cops here
wheel around.

Doug

Re: Speedometer accuracy w/31" tires - did dealer lie?
 

"Fred W." <Fred.Wills@ nospam myrealbox.com> wrote in message
news:l9Rlb.124490$qj6.7636690@news1.news.adelphia. net...

>
> It is completely normal for a speedo to read *high* by a few MPH, not low.
> The manufacturers would prefer to err on the safe side. Sounds like they
di
> not do anything and the larger diameter tires would explain the low
reading.
>
> -Fred W
>


I believe it's possible to adjust the speedo "gearing" on the '04
electronically. You could go back to the dealer and ask them to do that. Way
easier than changing the little gear on the t-case in earlier models.

They may want to chargea minimum labor fee, even though it's about 5 minutes
work with a terminal.

I changed out the stock 30's for 31's on my '97 Sport and now the speedo
seems more accurate, based on the displays around schools that the cops here
wheel around.

Doug

Re: Speedometer accuracy w/31" tires - did dealer lie?
 

It is important to be driving in a straight line when checking speed
with a GPS. The accuracy will be off when going around a curve in the
road. I find both of our cars (one Jeep, one car :-) ) to read 3 to
5 mph high when checked against my Garmin III+.

----

On Thu, 23 Oct 2003 07:33:09 -0700, John Davies
<johnedavies@comcast.net> wrote:

>On Thu, 23 Oct 2003 05:29:53 -0500, "Patrick Mills"
><plm1954R_E_M_O_V_E@ix.netcom.com> wrote:
>
>>I happen to have a GPS, and, according to it, the speedometer reads slow
>>by between 4 to 6 mph.
>
>
>GPS is accurate to tenths of a mph, when you drive at a steady speed
>for 10 seconds or so.... assuming the antenna has a good wide view of
>the sky. Set the cruise control for 60 mph on a dead level road out in
>the open and watch the readout (carefully).
>
>Get the dealer to fix the speedo drive so it reads within 2-3 mph,
>preferably on the high side. If you go a little larger on tire size it
>will read close to dead-on and you won't have to do this again, and
>you will be less likely to get a speeding ticket in the meantime.
>
>John Davies
>Spokane WA USA

Re: Speedometer accuracy w/31" tires - did dealer lie?
 

It is important to be driving in a straight line when checking speed
with a GPS. The accuracy will be off when going around a curve in the
road. I find both of our cars (one Jeep, one car :-) ) to read 3 to
5 mph high when checked against my Garmin III+.

----

On Thu, 23 Oct 2003 07:33:09 -0700, John Davies
<johnedavies@comcast.net> wrote:

>On Thu, 23 Oct 2003 05:29:53 -0500, "Patrick Mills"
><plm1954R_E_M_O_V_E@ix.netcom.com> wrote:
>
>>I happen to have a GPS, and, according to it, the speedometer reads slow
>>by between 4 to 6 mph.
>
>
>GPS is accurate to tenths of a mph, when you drive at a steady speed
>for 10 seconds or so.... assuming the antenna has a good wide view of
>the sky. Set the cruise control for 60 mph on a dead level road out in
>the open and watch the readout (carefully).
>
>Get the dealer to fix the speedo drive so it reads within 2-3 mph,
>preferably on the high side. If you go a little larger on tire size it
>will read close to dead-on and you won't have to do this again, and
>you will be less likely to get a speeding ticket in the meantime.
>
>John Davies
>Spokane WA USA

Re: Speedometer accuracy w/31" tires - did dealer lie?
 

It is important to be driving in a straight line when checking speed
with a GPS. The accuracy will be off when going around a curve in the
road. I find both of our cars (one Jeep, one car :-) ) to read 3 to
5 mph high when checked against my Garmin III+.

----

On Thu, 23 Oct 2003 07:33:09 -0700, John Davies
<johnedavies@comcast.net> wrote:

>On Thu, 23 Oct 2003 05:29:53 -0500, "Patrick Mills"
><plm1954R_E_M_O_V_E@ix.netcom.com> wrote:
>
>>I happen to have a GPS, and, according to it, the speedometer reads slow
>>by between 4 to 6 mph.
>
>
>GPS is accurate to tenths of a mph, when you drive at a steady speed
>for 10 seconds or so.... assuming the antenna has a good wide view of
>the sky. Set the cruise control for 60 mph on a dead level road out in
>the open and watch the readout (carefully).
>
>Get the dealer to fix the speedo drive so it reads within 2-3 mph,
>preferably on the high side. If you go a little larger on tire size it
>will read close to dead-on and you won't have to do this again, and
>you will be less likely to get a speeding ticket in the meantime.
>
>John Davies
>Spokane WA USA

Re: Speedometer accuracy w/31" tires - did dealer lie?
 

My Garmin EMap unit is dead on for speed.

I 'think' that 31" tires are right in-between two spedo gears for
accuracy.

MY CJ7 came to me with 31's and my spedo was reading fast of all
things. About 4-5 mph fast.

I went to 33's and my spedo is now dead on.

Same for our Cherokee. It reads dead on with P235's. Stock tire would
have the spedo reading fast.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's

Patrick Mills wrote:
>
> Hello,
>
> Got a new '04 Wrangler X in September. I plan to use this jeep for "fun"
> driving on-road in warm weather, occasional snow driving (on-road) and
> mild off-roading (no serious mudding, rocks or hill-climbing). It is not
> a daily driver.
>
> The vehicle is a stock Wrangler X with I6 engine and 3.73 gears. The only
> mod is a set of 31" AT tires (Dayton Timberlines, not BFG) and black
> wheels with faux beadlock-looking attachments - obviously for appearance
> only.
>
> I plan to gradually outfit this jeep with more trail-friendly gear,
> although I don't plan to lift it or use larger tires.
>
> My only question at this time is about speedometer accuracy. When I took
> delivery, they made me wait for about 45 minutes while the salesguy said
> they were making an adjustment so the speedometer would read accurately
> with the (dealer-installed) 31" tires.
>
> I happen to have a GPS, and, according to it, the speedometer reads slow
> by between 4 to 6 mph.
>
> Is a GPS a good way of measuring speedometer accuracy? I'm not sure if
> the dealer just gave me a run-around, did something wrong, or if my GPS is
> just not an accurate device for measuring actual vehicle speed (I use it
> for geocaching, and it's been very accurate for that).
>
> Thanks for any advice or comments. I enjoy reading this group.
>
> PLM
>
> --
> [ ]
> __OIIIIO__
> |||=oo=|||
> ||| |||