Re: ACCURATE SPEEDOMETER?
 

SnoMan wrote:
> On Mon, 17 Sep 2007 08:36:28 -0700, Tracie <brainart@upstate.edu>
> wrote:
>
>> Which would probably be somewhere in the neighborhood of 70-75 mph in
>> 6th at approximately 2500 rpms.
>
>
> Your speedo is way off.(big tires will do this) In 5th with current
> tires, 2500RPM would yeild about 74 MPH and 6th (.82 OD) 2500 would
> yeild about 91 MPH based on quoted tires sizes and axle ratios.
>
> Again you can do the math yourself
>
> http://www.snoman.com/HTML/axlecalc_5a.html
> -----------------
> TheSnoMan.com

Your site appears to be totally useless garbage.

No one 'knows' their freaking tranny ratio or their t-case ratio, most
do good to have their tire size and gear ratio.

'Comparing' tire sizes of old vs new to get a new speedometer reading is
garbage. The old tires were 'not' certified to have the correct speed
vs the gauge speed, so that is a GIGO situation. Garbage In Garbage Out.

If I punch in my numbers for how fast I should be going at 2300 rpm and
say my T-5 tranny in 4th is 1:1 and my Dana 300 t-case in high is 1:1
and my gears are 3.31 and my tires are 33", the 'calculator' gives me a NaN

If I put in my tire size and gear ratio I get infinity for a 'new' gear
ratio. Gee I thought gear ratios were set by the 'physical' gears, not
by some mythical number.

Care to explain?

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's - Gone to the rust pile...
Canadian Off Road Trips Photos: Non members can still view!
Jan/06 http://www.imagestation.com/album/pi...?id=2115147590
(More Off Road album links at bottom of the view page)

Re: ACCURATE SPEEDOMETER?
 

SnoMan wrote:
> On Mon, 17 Sep 2007 08:36:28 -0700, Tracie <brainart@upstate.edu>
> wrote:
>
>> Which would probably be somewhere in the neighborhood of 70-75 mph in
>> 6th at approximately 2500 rpms.
>
>
> Your speedo is way off.(big tires will do this) In 5th with current
> tires, 2500RPM would yeild about 74 MPH and 6th (.82 OD) 2500 would
> yeild about 91 MPH based on quoted tires sizes and axle ratios.
>
> Again you can do the math yourself
>
> http://www.snoman.com/HTML/axlecalc_5a.html
> -----------------
> TheSnoMan.com

Your site appears to be totally useless garbage.

No one 'knows' their freaking tranny ratio or their t-case ratio, most
do good to have their tire size and gear ratio.

'Comparing' tire sizes of old vs new to get a new speedometer reading is
garbage. The old tires were 'not' certified to have the correct speed
vs the gauge speed, so that is a GIGO situation. Garbage In Garbage Out.

If I punch in my numbers for how fast I should be going at 2300 rpm and
say my T-5 tranny in 4th is 1:1 and my Dana 300 t-case in high is 1:1
and my gears are 3.31 and my tires are 33", the 'calculator' gives me a NaN

If I put in my tire size and gear ratio I get infinity for a 'new' gear
ratio. Gee I thought gear ratios were set by the 'physical' gears, not
by some mythical number.

Care to explain?

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's - Gone to the rust pile...
Canadian Off Road Trips Photos: Non members can still view!
Jan/06 http://www.imagestation.com/album/pi...?id=2115147590
(More Off Road album links at bottom of the view page)

Re: ACCURATE SPEEDOMETER?
 

SnoMan wrote:
> On Mon, 17 Sep 2007 08:36:28 -0700, Tracie <brainart@upstate.edu>
> wrote:
>
>> Which would probably be somewhere in the neighborhood of 70-75 mph in
>> 6th at approximately 2500 rpms.
>
>
> Your speedo is way off.(big tires will do this) In 5th with current
> tires, 2500RPM would yeild about 74 MPH and 6th (.82 OD) 2500 would
> yeild about 91 MPH based on quoted tires sizes and axle ratios.
>
> Again you can do the math yourself
>
> http://www.snoman.com/HTML/axlecalc_5a.html
> -----------------
> TheSnoMan.com

Your site appears to be totally useless garbage.

No one 'knows' their freaking tranny ratio or their t-case ratio, most
do good to have their tire size and gear ratio.

'Comparing' tire sizes of old vs new to get a new speedometer reading is
garbage. The old tires were 'not' certified to have the correct speed
vs the gauge speed, so that is a GIGO situation. Garbage In Garbage Out.

If I punch in my numbers for how fast I should be going at 2300 rpm and
say my T-5 tranny in 4th is 1:1 and my Dana 300 t-case in high is 1:1
and my gears are 3.31 and my tires are 33", the 'calculator' gives me a NaN

If I put in my tire size and gear ratio I get infinity for a 'new' gear
ratio. Gee I thought gear ratios were set by the 'physical' gears, not
by some mythical number.

Care to explain?

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's - Gone to the rust pile...
Canadian Off Road Trips Photos: Non members can still view!
Jan/06 http://www.imagestation.com/album/pi...?id=2115147590
(More Off Road album links at bottom of the view page)

Re: ACCURATE SPEEDOMETER?
 

SnoMan wrote:
> On Mon, 17 Sep 2007 08:38:45 -0500, c <c@me.org> wrote:
>
>> As far as 6th gear is concerned, using only 5th gear will cause more
>> engine wear
>
>
> On a foot note, I do not know were this myth started. The engine is
> not going to wear out any sooner in 5th and may actually last longer
> if 6th is so tall that engine lugs. A few extra RPM never hurt any
> engine and lower RPM lugging is potentailly far more damaging and
> tough on bearings.
> -----------------
> TheSnoMan.com


Um, your statement is quite wrong. For instance, overdrive on my truck
reduces the RPM by 30% so yeah I am pretty sure my engine will wear out
sooner if I choose to never use it. I will agree with you on the lugging
part, especially if it causes pinging, but no, I will not sit here and
agree with you that my engine will last just as long turning 3000 RPM as
it does turning 2100 RPM. That's insane.

Chris

Re: ACCURATE SPEEDOMETER?
 

SnoMan wrote:
> On Mon, 17 Sep 2007 08:38:45 -0500, c <c@me.org> wrote:
>
>> As far as 6th gear is concerned, using only 5th gear will cause more
>> engine wear
>
>
> On a foot note, I do not know were this myth started. The engine is
> not going to wear out any sooner in 5th and may actually last longer
> if 6th is so tall that engine lugs. A few extra RPM never hurt any
> engine and lower RPM lugging is potentailly far more damaging and
> tough on bearings.
> -----------------
> TheSnoMan.com


Um, your statement is quite wrong. For instance, overdrive on my truck
reduces the RPM by 30% so yeah I am pretty sure my engine will wear out
sooner if I choose to never use it. I will agree with you on the lugging
part, especially if it causes pinging, but no, I will not sit here and
agree with you that my engine will last just as long turning 3000 RPM as
it does turning 2100 RPM. That's insane.

Chris

Re: ACCURATE SPEEDOMETER?
 

SnoMan wrote:
> On Mon, 17 Sep 2007 08:38:45 -0500, c <c@me.org> wrote:
>
>> As far as 6th gear is concerned, using only 5th gear will cause more
>> engine wear
>
>
> On a foot note, I do not know were this myth started. The engine is
> not going to wear out any sooner in 5th and may actually last longer
> if 6th is so tall that engine lugs. A few extra RPM never hurt any
> engine and lower RPM lugging is potentailly far more damaging and
> tough on bearings.
> -----------------
> TheSnoMan.com


Um, your statement is quite wrong. For instance, overdrive on my truck
reduces the RPM by 30% so yeah I am pretty sure my engine will wear out
sooner if I choose to never use it. I will agree with you on the lugging
part, especially if it causes pinging, but no, I will not sit here and
agree with you that my engine will last just as long turning 3000 RPM as
it does turning 2100 RPM. That's insane.

Chris

Re: ACCURATE SPEEDOMETER?
 

SnoMan wrote:
> On Mon, 17 Sep 2007 08:38:45 -0500, c <c@me.org> wrote:
>
>> As far as 6th gear is concerned, using only 5th gear will cause more
>> engine wear
>
>
> On a foot note, I do not know were this myth started. The engine is
> not going to wear out any sooner in 5th and may actually last longer
> if 6th is so tall that engine lugs. A few extra RPM never hurt any
> engine and lower RPM lugging is potentailly far more damaging and
> tough on bearings.
> -----------------
> TheSnoMan.com


Um, your statement is quite wrong. For instance, overdrive on my truck
reduces the RPM by 30% so yeah I am pretty sure my engine will wear out
sooner if I choose to never use it. I will agree with you on the lugging
part, especially if it causes pinging, but no, I will not sit here and
agree with you that my engine will last just as long turning 3000 RPM as
it does turning 2100 RPM. That's insane.

Chris

Re: ACCURATE SPEEDOMETER?
 

twaldron wrote:

Tracie wrote:

>>
>>
>> So, assuming that my speedometer is correct, running approximately
>> 2500 rpms in 5th gear at 65 mph will NOT hurt my engine or cause
>> increased engine wear? If I were to shift into OD (6th), what is the
>> approximate rpms that I should be running so as to not cause lugging
>> or increased engine wear?
>>
>> THANKS
>>
>
> Your minimal tire size increase likely made your speedo/odo more
> accurate as they tend to read high from the manufacturer. That way
> warranties expire sooner and manufacturers save money. I'd bet you are
> very close now. For fuel economy, use the highest gear you can while
> staying in the power band (not lugging). Lugging will become immediately
> apparent and you do it by feel, not by someone telling you what RPM to
> run. If you shift into too high a gear, you will notice a power response
> loss and ultimately your engine will lug. Downshift.
>
> tw

Jeep especially seems to like to have the speedometer high for some reason.

The largest stock tire that is listed for my 88 Cherokee on the sticker
is P225's, yet P235's make my speedometer accurate according to measured
'miles' and many GPS checks. The cops must think so too, because they
don't stop me.

Same for most TJ's. They 'do' list a 31 as the largest stock tire and
according to what has been reported here, that makes them accurate with
no t-case speedo gear change needed.

I don't know how it worked, but my 86 CJ7 is accurate with 33's. It was
4mph + off with 31's (reading 65, doing 60) when I got it.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's - Gone to the rust pile...
Canadian Off Road Trips Photos: Non members can still view!
Jan/06 http://www.imagestation.com/album/pi...?id=2115147590
(More Off Road album links at bottom of the view page)

Re: ACCURATE SPEEDOMETER?
 

twaldron wrote:

Tracie wrote:

>>
>>
>> So, assuming that my speedometer is correct, running approximately
>> 2500 rpms in 5th gear at 65 mph will NOT hurt my engine or cause
>> increased engine wear? If I were to shift into OD (6th), what is the
>> approximate rpms that I should be running so as to not cause lugging
>> or increased engine wear?
>>
>> THANKS
>>
>
> Your minimal tire size increase likely made your speedo/odo more
> accurate as they tend to read high from the manufacturer. That way
> warranties expire sooner and manufacturers save money. I'd bet you are
> very close now. For fuel economy, use the highest gear you can while
> staying in the power band (not lugging). Lugging will become immediately
> apparent and you do it by feel, not by someone telling you what RPM to
> run. If you shift into too high a gear, you will notice a power response
> loss and ultimately your engine will lug. Downshift.
>
> tw

Jeep especially seems to like to have the speedometer high for some reason.

The largest stock tire that is listed for my 88 Cherokee on the sticker
is P225's, yet P235's make my speedometer accurate according to measured
'miles' and many GPS checks. The cops must think so too, because they
don't stop me.

Same for most TJ's. They 'do' list a 31 as the largest stock tire and
according to what has been reported here, that makes them accurate with
no t-case speedo gear change needed.

I don't know how it worked, but my 86 CJ7 is accurate with 33's. It was
4mph + off with 31's (reading 65, doing 60) when I got it.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's - Gone to the rust pile...
Canadian Off Road Trips Photos: Non members can still view!
Jan/06 http://www.imagestation.com/album/pi...?id=2115147590
(More Off Road album links at bottom of the view page)

Re: ACCURATE SPEEDOMETER?
 

twaldron wrote:

Tracie wrote:

>>
>>
>> So, assuming that my speedometer is correct, running approximately
>> 2500 rpms in 5th gear at 65 mph will NOT hurt my engine or cause
>> increased engine wear? If I were to shift into OD (6th), what is the
>> approximate rpms that I should be running so as to not cause lugging
>> or increased engine wear?
>>
>> THANKS
>>
>
> Your minimal tire size increase likely made your speedo/odo more
> accurate as they tend to read high from the manufacturer. That way
> warranties expire sooner and manufacturers save money. I'd bet you are
> very close now. For fuel economy, use the highest gear you can while
> staying in the power band (not lugging). Lugging will become immediately
> apparent and you do it by feel, not by someone telling you what RPM to
> run. If you shift into too high a gear, you will notice a power response
> loss and ultimately your engine will lug. Downshift.
>
> tw

Jeep especially seems to like to have the speedometer high for some reason.

The largest stock tire that is listed for my 88 Cherokee on the sticker
is P225's, yet P235's make my speedometer accurate according to measured
'miles' and many GPS checks. The cops must think so too, because they
don't stop me.

Same for most TJ's. They 'do' list a 31 as the largest stock tire and
according to what has been reported here, that makes them accurate with
no t-case speedo gear change needed.

I don't know how it worked, but my 86 CJ7 is accurate with 33's. It was
4mph + off with 31's (reading 65, doing 60) when I got it.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's - Gone to the rust pile...
Canadian Off Road Trips Photos: Non members can still view!
Jan/06 http://www.imagestation.com/album/pi...?id=2115147590
(More Off Road album links at bottom of the view page)