Tire Size Question

Yep another one,
A friend has a 2.5L TJ X, 5 speed tranny,with standard OEM tires 215/75R-15,
he wants to put 31s on it. His question to me how bad will his mileage
suffer? He averages about 17-18 MPG now with gas the way it is he uses the
TJ as the daily driver and drives 120 miles round trip to work each day.

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Coasty
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If he has a X, it is the 4.0. The 31's won't hurt it that bad, he just
won't be using 5th gear much. When I put 31's on my 2002 X, i found I was
running 70 in 4th at 2000 rpms. It still had get up and go. That was with
the 3.07 gears which are stock in the X.

Patrick
Ô¿Ô

"Coasty" > wrote in message
...
> Yep another one,
> A friend has a 2.5L TJ X, 5 speed tranny,with standard OEM tires
> 215/75R-15, he wants to put 31s on it. His question to me how bad will
> his mileage suffer? He averages about 17-18 MPG now with gas the way it
> is he uses the TJ as the daily driver and drives 120 miles round trip to
> work each day.
>
> --
> Coasty
> SEMPAR PARATUS
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>

Proably not a lot. It will depend more on exactly what speeds he runs on
his commute. The tire change will move him over about half a gear (old
effective gear ratio is about in the middle between two new effective
gears). If that means the engine is overreving or lugging, mileage will
sink rapidly. It also means that 5th gear is not going to be very useful
most of the time.

A TJ doing 120 miles a day with $2.39 gas is not a happy combination.

Coasty wrote:

> Yep another one,
> A friend has a 2.5L TJ X, 5 speed tranny,with standard OEM tires 215/75R-15,
> he wants to put 31s on it. His question to me how bad will his mileage
> suffer? He averages about 17-18 MPG now with gas the way it is he uses the
> TJ as the daily driver and drives 120 miles round trip to work each day.
>

Before the 31"s my Brother-in-law's '94 YJ four banger could go any
speed he wanted on the straight and level, and got a ticket for ninety,
after the extra weight limited that to seventy miles per hour and that's
with a tailwind: http://home.att.net/~taschers/beach03.jpg
God Bless America, ßill O|||||||O
http://www.billhughes.com/

Coasty wrote:
>
> Yep another one,
> A friend has a 2.5L TJ X, 5 speed tranny,with standard OEM tires 215/75R-15,
> he wants to put 31s on it. His question to me how bad will his mileage
> suffer? He averages about 17-18 MPG now with gas the way it is he uses the
> TJ as the daily driver and drives 120 miles round trip to work each day.
>
> --
> Coasty
> SEMPAR PARATUS
> (ALWAYS READY)
>
> Remove The SPOOGE To Reply

I read somewhere that every lb of unsprung weight is worth 10 lb of sprung
weight ; don't know if that's true or not.

Dave Milne, Scotland
'91 Grand Wagoneer, '99 TJ

"L.W. (ßill) Hughes III" > wrote in message
...
> Before the 31"s my Brother-in-law's '94 YJ four banger could go any
> speed he wanted on the straight and level, and got a ticket for ninety,
> after the extra weight limited that to seventy miles per hour and that's
> with a tailwind: http://home.att.net/~taschers/beach03.jpg
> God Bless America, ßill O|||||||O
> http://www.billhughes.com/
>
> Coasty wrote:
> >
> > Yep another one,
> > A friend has a 2.5L TJ X, 5 speed tranny,with standard OEM tires
215/75R-15,
> > he wants to put 31s on it. His question to me how bad will his mileage
> > suffer? He averages about 17-18 MPG now with gas the way it is he uses
the
> > TJ as the daily driver and drives 120 miles round trip to work each day.
> >
> > --
> > Coasty
> > SEMPAR PARATUS
> > (ALWAYS READY)
> >
> > Remove The SPOOGE To Reply

Hi Dave,
To keep something turning takes more horsepower the heavier it is,
that's why the drag racers use a thirteen pound aluminum flywheel and
lighter rims and tires. Of course, that flywheel also stores energy,
that will made the stock V6 buick power CJ with it's fifty pound
flywheel easily crawl over rocks that would easily stop a couple of
hundred more horsepower in a 350" Chevy V8. I know taking your hundred
pound girlfriend with you down the drag strip will cost you a tenth of a
second. As far as sprung and unsprung weight, all I know is it makes a
great deal of difference in their ride and cornering ability, like road
racers need independent suspension to win.
God Bless America, ßill O|||||||O
http://www.billhughes.com/

Dave Milne wrote:
>
> I read somewhere that every lb of unsprung weight is worth 10 lb of sprung
> weight ; don't know if that's true or not.
>
> Dave Milne, Scotland
> '91 Grand Wagoneer, '99 TJ

The reason you use a 13 pound flywheel is to allow maximum ACCELERATION
of the engine. The reason for lightweight tires is to allow
ACCELERATION. The reason to not take your girlfriend along is
ACCELERATION So what does weight have to do with steady state? (other
than the additional wear on the bearings?)

L.W.(ßill) Hughes III wrote:

> Hi Dave,
> To keep something turning takes more horsepower the heavier it is,
> that's why the drag racers use a thirteen pound aluminum flywheel and
> lighter rims and tires. Of course, that flywheel also stores energy,
> that will made the stock V6 buick power CJ with it's fifty pound
> flywheel easily crawl over rocks that would easily stop a couple of
> hundred more horsepower in a 350" Chevy V8. I know taking your hundred
> pound girlfriend with you down the drag strip will cost you a tenth of a
> second. As far as sprung and unsprung weight, all I know is it makes a
> great deal of difference in their ride and cornering ability, like road
> racers need independent suspension to win.
> God Bless America, ßill O|||||||O
> http://www.billhughes.com/
>
> Dave Milne wrote:
>
>>I read somewhere that every lb of unsprung weight is worth 10 lb of sprung
>>weight ; don't know if that's true or not.
>>
>>Dave Milne, Scotland
>>'91 Grand Wagoneer, '99 TJ

Horsepower, or imagine the the force you would need to peddle your
bicycle, now put your Jeep tire on the bicycle and peddle. E=mc². The E
stands for energy. The m stands for inertial mass, which is similar to
(but not the same thing as) weight. C squared stands for the speed of
light multiplied by itself. I would say Lance Armstrong bike wheel are
very light right about now in france, not like his mountain bike.
God Bless America, ßill O|||||||O
http://www.billhughes.com/

RoyJ wrote:
>
> The reason you use a 13 pound flywheel is to allow maximum ACCELERATION
> of the engine. The reason for lightweight tires is to allow
> ACCELERATION. The reason to not take your girlfriend along is
> ACCELERATION So what does weight have to do with steady state? (other
> than the additional wear on the bearings?)
>
> L.W.(ßill) Hughes III wrote:
>
> > Hi Dave,
> > To keep something turning takes more horsepower the heavier it is,
> > that's why the drag racers use a thirteen pound aluminum flywheel and
> > lighter rims and tires. Of course, that flywheel also stores energy,
> > that will made the stock V6 buick power CJ with it's fifty pound
> > flywheel easily crawl over rocks that would easily stop a couple of
> > hundred more horsepower in a 350" Chevy V8. I know taking your hundred
> > pound girlfriend with you down the drag strip will cost you a tenth of a
> > second. As far as sprung and unsprung weight, all I know is it makes a
> > great deal of difference in their ride and cornering ability, like road
> > racers need independent suspension to win.
> > God Bless America, ßill O|||||||O
> > http://www.billhughes.com/
> >
> > Dave Milne wrote:
> >
> >>I read somewhere that every lb of unsprung weight is worth 10 lb of sprung
> >>weight ; don't know if that's true or not.
> >>
> >>Dave Milne, Scotland
> >>'91 Grand Wagoneer, '99 TJ

When I tossed the stock tires on my 2.5l, I was surprised at just how fast I
could move.

Once I get these 4.88s in, I'm hoping to get back to that point. Not that I
need to be darting everywhere lifted this high... :-)

Eric
99 TJ SE
"L.W. ("ßill") Hughes III" > wrote in message
...
> Before the 31"s my Brother-in-law's '94 YJ four banger could go any
> speed he wanted on the straight and level, and got a ticket for ninety,
> after the extra weight limited that to seventy miles per hour and that's
> with a tailwind: http://home.att.net/~taschers/beach03.jpg
> God Bless America, ßill O|||||||O
> http://www.billhughes.com/
>
> Coasty wrote:
>>
>> Yep another one,
>> A friend has a 2.5L TJ X, 5 speed tranny,with standard OEM tires
>> 215/75R-15,
>> he wants to put 31s on it. His question to me how bad will his mileage
>> suffer? He averages about 17-18 MPG now with gas the way it is he uses
>> the
>> TJ as the daily driver and drives 120 miles round trip to work each day.
>>
>> --
>> Coasty
>> SEMPAR PARATUS
>> (ALWAYS READY)
>>
>> Remove The SPOOGE To Reply

Daughter's 95 YJ with 2.5 sucked on gas stock, sucked on gas with 31"s,
and still sucks on gas with 33"s and 4.88s.

"Eric" > wrote in message
...
> When I tossed the stock tires on my 2.5l, I was surprised at just how fast
> I could move.
>
> Once I get these 4.88s in, I'm hoping to get back to that point. Not that
> I need to be darting everywhere lifted this high... :-)
>
> Eric
> 99 TJ SE
> "L.W. ("ßill") Hughes III" > wrote in message
> ...
>> Before the 31"s my Brother-in-law's '94 YJ four banger could go any
>> speed he wanted on the straight and level, and got a ticket for ninety,
>> after the extra weight limited that to seventy miles per hour and that's
>> with a tailwind: http://home.att.net/~taschers/beach03.jpg
>> God Bless America, ßill O|||||||O
>> http://www.billhughes.com/
>>
>> Coasty wrote:
>>>
>>> Yep another one,
>>> A friend has a 2.5L TJ X, 5 speed tranny,with standard OEM tires
>>> 215/75R-15,
>>> he wants to put 31s on it. His question to me how bad will his mileage
>>> suffer? He averages about 17-18 MPG now with gas the way it is he uses
>>> the
>>> TJ as the daily driver and drives 120 miles round trip to work each day.
>>>
>>> --
>>> Coasty
>>> SEMPAR PARATUS
>>> (ALWAYS READY)
>>>
>>> Remove The SPOOGE To Reply
>
>