Re: Tires and speedometer
 

I think your speedo will read SLOW now. When it reads 60, yoiur actual speed
will be 65, for example. (You'll need to take measurements to arrive at the
actual error.)

Your original tires were about 26.5 inches in diameter, the new tires will
be closer to 29.5. This gives a diameter increase of about 3 inches, which
will give a circumference increase of around 9 inches.

You will need to calibrate the speedo as a result. It ought to be as easy as
swapping a gear on the speed sensor in the transmission, or wherever they
mounted the sensor on your truck.



"tk" <thomas_kessler@comcast.net> wrote in message
news:1169848358.200219.234310@j27g2000cwj.googlegr oups.com...
>I upgraded to alum canyon wheels and 30" tires from 195/75R15 steel
> wheels and tires. Does my speedometer need to be adjusted?
>
> Has anyone done this?
>
> Tom
>

Re: Tires and speedometer
 

I think your speedo will read SLOW now. When it reads 60, yoiur actual speed
will be 65, for example. (You'll need to take measurements to arrive at the
actual error.)

Your original tires were about 26.5 inches in diameter, the new tires will
be closer to 29.5. This gives a diameter increase of about 3 inches, which
will give a circumference increase of around 9 inches.

You will need to calibrate the speedo as a result. It ought to be as easy as
swapping a gear on the speed sensor in the transmission, or wherever they
mounted the sensor on your truck.



"tk" <thomas_kessler@comcast.net> wrote in message
news:1169848358.200219.234310@j27g2000cwj.googlegr oups.com...
>I upgraded to alum canyon wheels and 30" tires from 195/75R15 steel
> wheels and tires. Does my speedometer need to be adjusted?
>
> Has anyone done this?
>
> Tom
>

Re: Tires and speedometer
 

I think your speedo will read SLOW now. When it reads 60, yoiur actual speed
will be 65, for example. (You'll need to take measurements to arrive at the
actual error.)

Your original tires were about 26.5 inches in diameter, the new tires will
be closer to 29.5. This gives a diameter increase of about 3 inches, which
will give a circumference increase of around 9 inches.

You will need to calibrate the speedo as a result. It ought to be as easy as
swapping a gear on the speed sensor in the transmission, or wherever they
mounted the sensor on your truck.



"tk" <thomas_kessler@comcast.net> wrote in message
news:1169848358.200219.234310@j27g2000cwj.googlegr oups.com...
>I upgraded to alum canyon wheels and 30" tires from 195/75R15 steel
> wheels and tires. Does my speedometer need to be adjusted?
>
> Has anyone done this?
>
> Tom
>

Re: Tires and speedometer
 

Larger tires will make the speedo even slower than it was before.

The truth is, most speedos read fast from the factory. The idea is that if
the speedo says 60, and the speed limit is 60, then you do not want to be
exceeding 60, therefore the actual speed is more like 57. The speedo reads
fast. New tires will make the speedo read slow, therefore the ground speed
of 57 will be displayed closer to 57 than before, the speedo will read
slower.

I am of the opinion that the change he made will be greater than the factory
error, and the new 60 will really be something like 63. The speedo will read
too slow because the actual ground speed will be greater than the indicated
speed. The potential problems with this should be obvious.




"billy ray" <billy_ray@SPAMfuse.net> wrote in message
news:6d2d2$45ba7968$422afc51$21394@FUSE.NET...
> Jeep speedometers generally read slow stock, you are probably closer to
> the correct reading now than before. (but still slow)
>
>
> "tk" <thomas_kessler@comcast.net> wrote in message
> news:1169848358.200219.234310@j27g2000cwj.googlegr oups.com...
>>I upgraded to alum canyon wheels and 30" tires from 195/75R15 steel
>> wheels and tires. Does my speedometer need to be adjusted?
>>
>> Has anyone done this?
>>
>> Tom
>>
>
>

Re: Tires and speedometer
 

Larger tires will make the speedo even slower than it was before.

The truth is, most speedos read fast from the factory. The idea is that if
the speedo says 60, and the speed limit is 60, then you do not want to be
exceeding 60, therefore the actual speed is more like 57. The speedo reads
fast. New tires will make the speedo read slow, therefore the ground speed
of 57 will be displayed closer to 57 than before, the speedo will read
slower.

I am of the opinion that the change he made will be greater than the factory
error, and the new 60 will really be something like 63. The speedo will read
too slow because the actual ground speed will be greater than the indicated
speed. The potential problems with this should be obvious.




"billy ray" <billy_ray@SPAMfuse.net> wrote in message
news:6d2d2$45ba7968$422afc51$21394@FUSE.NET...
> Jeep speedometers generally read slow stock, you are probably closer to
> the correct reading now than before. (but still slow)
>
>
> "tk" <thomas_kessler@comcast.net> wrote in message
> news:1169848358.200219.234310@j27g2000cwj.googlegr oups.com...
>>I upgraded to alum canyon wheels and 30" tires from 195/75R15 steel
>> wheels and tires. Does my speedometer need to be adjusted?
>>
>> Has anyone done this?
>>
>> Tom
>>
>
>

Re: Tires and speedometer
 

Larger tires will make the speedo even slower than it was before.

The truth is, most speedos read fast from the factory. The idea is that if
the speedo says 60, and the speed limit is 60, then you do not want to be
exceeding 60, therefore the actual speed is more like 57. The speedo reads
fast. New tires will make the speedo read slow, therefore the ground speed
of 57 will be displayed closer to 57 than before, the speedo will read
slower.

I am of the opinion that the change he made will be greater than the factory
error, and the new 60 will really be something like 63. The speedo will read
too slow because the actual ground speed will be greater than the indicated
speed. The potential problems with this should be obvious.




"billy ray" <billy_ray@SPAMfuse.net> wrote in message
news:6d2d2$45ba7968$422afc51$21394@FUSE.NET...
> Jeep speedometers generally read slow stock, you are probably closer to
> the correct reading now than before. (but still slow)
>
>
> "tk" <thomas_kessler@comcast.net> wrote in message
> news:1169848358.200219.234310@j27g2000cwj.googlegr oups.com...
>>I upgraded to alum canyon wheels and 30" tires from 195/75R15 steel
>> wheels and tires. Does my speedometer need to be adjusted?
>>
>> Has anyone done this?
>>
>> Tom
>>
>
>

Re: Tires and speedometer
 

Larger tires will make the speedo even slower than it was before.

The truth is, most speedos read fast from the factory. The idea is that if
the speedo says 60, and the speed limit is 60, then you do not want to be
exceeding 60, therefore the actual speed is more like 57. The speedo reads
fast. New tires will make the speedo read slow, therefore the ground speed
of 57 will be displayed closer to 57 than before, the speedo will read
slower.

I am of the opinion that the change he made will be greater than the factory
error, and the new 60 will really be something like 63. The speedo will read
too slow because the actual ground speed will be greater than the indicated
speed. The potential problems with this should be obvious.




"billy ray" <billy_ray@SPAMfuse.net> wrote in message
news:6d2d2$45ba7968$422afc51$21394@FUSE.NET...
> Jeep speedometers generally read slow stock, you are probably closer to
> the correct reading now than before. (but still slow)
>
>
> "tk" <thomas_kessler@comcast.net> wrote in message
> news:1169848358.200219.234310@j27g2000cwj.googlegr oups.com...
>>I upgraded to alum canyon wheels and 30" tires from 195/75R15 steel
>> wheels and tires. Does my speedometer need to be adjusted?
>>
>> Has anyone done this?
>>
>> Tom
>>
>
>

Re: Tires and speedometer
 

I agree. Sorta.

If the factory fitment of speedo gear was to accomodate the largest factory
tire, then with the small tires on the stock models, the speedo should be
fast, they should read considerably higher than the actual speed.

If the speedo gear for the stock base-models is selected properly for the
tires, then changing the tires should result in an error where the speedo
reads slow with the new tires.

Your experience with the XJ was such that you swapped a tire that was nearly
30 with one that was 30, and the error that caused dialed the speedometer's
accuracy in almost perfectly. (I had a similar experience with my BMW, by
the way.) But, the OP is making a drastic change from a 26.5" tire to a 30.
This is 3" different in diameter, and 9" in circumference. That's a large
difference, and the speedo should logically not be able to display the
actual speed anymore.




"Mike Romain" <romainm@sympatico.ca> wrote in message
news:45ba8063$0$6662$9a6e19ea@unlimited.newshostin g.com...
> You need to find a measured mile or use a GPS to see what it is now. I
> have found that Jeep speedometers are calibrated for the largest stock
> tire size so yours might be right on now.
>
> Our XJ's became right on with 235's which are almost 30" tall.
>
> Mike
> 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
> 88 Cherokee 235 BFG AT's
> 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)
>
> tk wrote:
>> I upgraded to alum canyon wheels and 30" tires from 195/75R15 steel
>> wheels and tires. Does my speedometer need to be adjusted?
>>
>> Has anyone done this?
>>
>> Tom
>>

Re: Tires and speedometer
 

I agree. Sorta.

If the factory fitment of speedo gear was to accomodate the largest factory
tire, then with the small tires on the stock models, the speedo should be
fast, they should read considerably higher than the actual speed.

If the speedo gear for the stock base-models is selected properly for the
tires, then changing the tires should result in an error where the speedo
reads slow with the new tires.

Your experience with the XJ was such that you swapped a tire that was nearly
30 with one that was 30, and the error that caused dialed the speedometer's
accuracy in almost perfectly. (I had a similar experience with my BMW, by
the way.) But, the OP is making a drastic change from a 26.5" tire to a 30.
This is 3" different in diameter, and 9" in circumference. That's a large
difference, and the speedo should logically not be able to display the
actual speed anymore.




"Mike Romain" <romainm@sympatico.ca> wrote in message
news:45ba8063$0$6662$9a6e19ea@unlimited.newshostin g.com...
> You need to find a measured mile or use a GPS to see what it is now. I
> have found that Jeep speedometers are calibrated for the largest stock
> tire size so yours might be right on now.
>
> Our XJ's became right on with 235's which are almost 30" tall.
>
> Mike
> 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
> 88 Cherokee 235 BFG AT's
> 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)
>
> tk wrote:
>> I upgraded to alum canyon wheels and 30" tires from 195/75R15 steel
>> wheels and tires. Does my speedometer need to be adjusted?
>>
>> Has anyone done this?
>>
>> Tom
>>

Re: Tires and speedometer
 

I agree. Sorta.

If the factory fitment of speedo gear was to accomodate the largest factory
tire, then with the small tires on the stock models, the speedo should be
fast, they should read considerably higher than the actual speed.

If the speedo gear for the stock base-models is selected properly for the
tires, then changing the tires should result in an error where the speedo
reads slow with the new tires.

Your experience with the XJ was such that you swapped a tire that was nearly
30 with one that was 30, and the error that caused dialed the speedometer's
accuracy in almost perfectly. (I had a similar experience with my BMW, by
the way.) But, the OP is making a drastic change from a 26.5" tire to a 30.
This is 3" different in diameter, and 9" in circumference. That's a large
difference, and the speedo should logically not be able to display the
actual speed anymore.




"Mike Romain" <romainm@sympatico.ca> wrote in message
news:45ba8063$0$6662$9a6e19ea@unlimited.newshostin g.com...
> You need to find a measured mile or use a GPS to see what it is now. I
> have found that Jeep speedometers are calibrated for the largest stock
> tire size so yours might be right on now.
>
> Our XJ's became right on with 235's which are almost 30" tall.
>
> Mike
> 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
> 88 Cherokee 235 BFG AT's
> 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)
>
> tk wrote:
>> I upgraded to alum canyon wheels and 30" tires from 195/75R15 steel
>> wheels and tires. Does my speedometer need to be adjusted?
>>
>> Has anyone done this?
>>
>> Tom
>>