The speedo is off but I compensated for it. Running 64mph indicated on
the speedo = 60mph, double checked with the lovely automated radar-speed
signs they scatter around Spokane, WA. Someone has dinked around with
this thing since if you assume a stock tire size of 235/75R15 and
compare it to a 31x10.5R15 tire, it SHOULD read 56mph when I'm actually
doing 60mph rather than what it does now, which is read 64mph when I'm
doing 60. Which is why I'm wondering what the heck a previous owner did
to the gearing on this truck, and exactly what speedo gear is riding
below the speed distance sensor to give it it's current reading.
When I first bought it I drove it home on the freeway in a 70mph zone
doing an indicated 66 figuring that was the proper speed -- and was
being blown past by traffic that usually does 5 under in that same area
and I couldn't figure out why considering I calculated it before I drove
home so I'd not get a speeding ticket! ;)
MattB
Brian wrote:
> Unless you have adjusted your PCM for the taller tires, it doesn't know what
> size tire you have on there, so while the speedo might have been reading
> 60mph, you weren't going 60mph.
>
> brian cropp
> -----Original Message-----
> From: owner-dakota-truck@bent.twistedbits.net
> [mailto:owner-dakota-truck@bent.twistedbits.net] On Behalf Of
> teseract@moparhowto.com
> Sent: Thursday, May 07, 2009 2:57 PM
> To: dakota-truck-moderator@bent.twistedbits.net
> Subject: DML: Gears
>
>
>
> Was a 4.11 rear end available in '95 from the factory? I was on the freeway
> last night and noticed that with 31" tires at 60mph, the truck is pulling
> about
> 2000rpm. I've read in the archives that trucks with the 3.90 rear end with
> the
> stock tires (which are a good 3" shorter in diameter than my 31" tires) pull
> about 2000rpm at 60mph. This seems odd to me as the underhood sticker
> doesn't
> indicate anything about the different gear ratio - but if I had the standard
> 3.22 gears I don't think I'd be pulling the RPM I'm pulling at 60mph with
> the
> size of tires I have.
>
> I guess I'll be doing the string trick next time I'm under the truck...
>
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>
>
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