All this talk of tires and my purchase today of a spanky new set of 305/70 Nitto's has me thinking about a speedo correction gear. When I had my 80 I bought a speedo gear from Slee..is there such a beast for the 100 to correct for 33's?
Speedo correction for 33's (1 Viewer)
- Thread starter dieselbigot
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Christo has the Superlift Tru-Speed Calibrator for $195.
http://www.sleeoffroad.com/products/products_interior_main.htm
http://www.sleeoffroad.com/products/products_interior_main.htm
80and100cruisers
SILVER Star
I forget what the stock tire size was for my 99 cruiser. I just assume it was 30 inches, and that my 305s are 33 inches, meaning there was a 10% increase. So, I assume that the speedo is 10% off, meaning 30mph is really 33mph, 70mph is really 77mph, etc. My reasoning is that the 33 inch tire covers 10% more ground each rotation than the 30 inch stock tire. That seems like a huge difference, can anyone correct me if my logic is flawed.
Anyways, if Im' right the 10% rule is a cheap/easy method to judge your true speed.
-Matt
Anyways, if Im' right the 10% rule is a cheap/easy method to judge your true speed.
-Matt
good excuse to buy that GPS 
Kaderabek
GOLD Star
I have a Tru-Speed in my 80. Works great.
TJK
TJK
80and100cruisers said:
OE tires are 31.2" and the difference to 33" is 5.4%, your logic is good but the difference not as big as you stated.
80and100cruisers said:
Close. Actually, your stock tire size is 31 inches, so it's really more of a 6% rule. Which, of course, is more of a pain to do in your head.
80and100cruisers
SILVER Star
Thanks, that was just the info I was looking for.
-Matt
-Matt
hoser
SILVER Star
I find that most OEM speedometers read low anyway. Yeah, get a GPS and see what your actual speed is.
Circumference difference
Actually if you compare the circumference of both sizes (275-75/16 & 305/70-16) you arrive at a net difference of 1.7%
275-75/16
D= (.75 x 275/25.4) x 2 + 16" = 32.24"
C= Py x D
C= 101.29"
305-70/16
D= (.70 x 305/25.4) x 2 + 16" = 32.81"
C=Py x D
C= 103.08"
The difference in percentage between the above two circumferences is only 1.7%. We all know the actual measurements of each brand of tire will probably be different than the theoretical diameter.
Actually if you compare the circumference of both sizes (275-75/16 & 305/70-16) you arrive at a net difference of 1.7%
275-75/16
D= (.75 x 275/25.4) x 2 + 16" = 32.24"
C= Py x D
C= 101.29"
305-70/16
D= (.70 x 305/25.4) x 2 + 16" = 32.81"
C=Py x D
C= 103.08"
The difference in percentage between the above two circumferences is only 1.7%. We all know the actual measurements of each brand of tire will probably be different than the theoretical diameter.
That is a 5.4% difference for 285/75R16 vs the 275/70R16 stock tires.
Last edited:
spressomon said:
Correct me if I'm wrong, but I think the stock tires are 275-65/16's, which are 31.65" in diameter, which equals a 3.54% difference.
Comparing the %delta in diameter is the same as comparing the %delta circumfrence, but is just easier since you are leaving out the pi calculations that you would do on both sides of the equation.
/nerd
Bahh... percentage this; percentage that.
I checked my speedo on 285/75R16's and at an indicated 65 I was doing 68 via GPS monitoring. That was without changing speedo calibration at all. To me that didn't warrant speedo correction.
If you can just get a buddy to ride with you and check the speedo with a handheld GPS unit.
Tad
I checked my speedo on 285/75R16's and at an indicated 65 I was doing 68 via GPS monitoring. That was without changing speedo calibration at all. To me that didn't warrant speedo correction.
If you can just get a buddy to ride with you and check the speedo with a handheld GPS unit.
Tad
Stockers
1999 100 series stock tire size: 275/R7516.
1999 100 series stock tire size: 275/R7516.
hoser
SILVER Star
You sure it's not 275/70R16?
Corrected
Yes you are correct...the stockers are 275/70R16....
hoser said:
Yes you are correct...the stockers are 275/70R16....
