Use the tire and wheel calculator to calculate the differences between 2
tires at
http://www.dakota-truck.net/TIRECALC/tirecalc.html
The 245 has a circumference of 80.79 inches.
The 235 has a circumference of 90.72 inches.
The 255 has a circumference of 88.13 inches.
I don't recall the tires that your Dak was delivered with. If it had the
15x7 wheels then it was the 235's. If it was the 15x8 wheels then it was
the 255's. If it was the 255's then most likely you will not be able to
reprogram to a smaller circumference. Unless the RT tires are smaller.
You went to a smaller circumference tire from stock. This would cause your
speedo to give you a reading that is faster than your actual speed.
changing from the 255's, if your speedo is now giving you a reading of 71
mph, you are actually only going 65 mph.
-----Original Message-----
From: Eric Jerman [mailto:ejerman69@hotmail.com]
Sent: Thursday, June 13, 2002 3:39 PM
To: dakota-truck@dakota-truck.net
Subject: DML: Re: RE: PCM question
So what would I go with if I have 245/40ZR18s? Would I go with 235 or 255?
Seems like I'd be better off going lower right because it would make my
speedo read a little fast instead of being a little slow? Thanks for the
help.
----- Original Message -----
From: "Kenneth Eng" <keng@novadigm.com>
To: <dakota-truck@dakota-truck.net>
Sent: Thursday, June 13, 2002 3:17 PM
Subject: DML: RE: PCM question
>
> Eric,
>
> The only factor that will affect your speedo reading is the circumference
of
> your tires. The size of the rim has no affect if you manage to maintain
the
> circumference of the factory supplied tire. The PCM is programmed at the
> factory for the specific tire that is delivered with the vehicle. The PCM
> is also configured to accept other tire sizes. However, these tire sizes
> will only be the ones that are available for the Dak from the factory.
> These will include the P215, P235, P255, RT tires, and the 31" ones on the
> 4x4. If you upgraded to a tire whose size is not one of those listed in
the
> PCM, you will then need to select one that is closest in circumference to
> the ones you installed. The PCM will need to be reprogrammed by your
> dealer.
>
> HTH,
> Ken
>
> -----Original Message-----
> From: Eric Jerman [mailto:ejerman69@hotmail.com]
> Sent: Thursday, June 13, 2002 2:50 PM
> To: dakota-truck@dakota-truck.net
> Subject: DML: PCM question
>
>
>
> Ok,
> I keep seeing posts on here about a 3.91 gear upgrade...and from what I
> understand going from 15" to 18" rims will cause a change in gear
ratio...do
> I also need to reset my PCM and if so, how do I do this? Will that
correct
> the difference in my speedo?
> Eric Jerman
>
> ----- Original Message -----
> From: <SEMIHEMI01@aol.com>
> To: <dakota-truck@dakota-truck.net>
> Sent: Thursday, June 13, 2002 11:30 AM
> Subject: DML: Rice for Breakfast.
>
>
> >
> > Hey Guys,
> > Can you believe a kid in a low rider Toyota Camry wanted to try on
the
> > Dak this morning from a light. I let him have the first run by 2 car
> lengths
> > just to make him feel good. Never even made positive manifold pressure.
> Then
> > at the next light, I showed him what the SEMIHEMI could really do. He
was
> 2nd
> > gear history. Damn, I LUV IT. Bill
> >
> > SEMIHEMI01@AOL.COM> KB SuperCharged, 4.7L, 2001, QC,
> > <A HREF="http://hometown.aol.com/semihemi01">the "DAK",</A> <A
> > HREF="http://southernmopar.org">SouthernMopar</A>
> >
>
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