235's BFGs affecting actual speed???

Well after getting pulled over 3 times in the last 2 months, and having the cops tell me im going faster than i think i am...im really starting to think that BFG 235's are NOT the same size as whatever crap came stock on the explorer. Last night i checked it out and unless the milemakers on the highways are off... my spedo is off.

I have about 35000 miles on the tires and there is still TONS of tread left.

My guess is that when my spedo reads 75MPH actual speed is about 80 mph.
If i could somehow figure a way to set the cruise at 60 and go that slow i could time it and do the math and figure out the actual speed but im not too sure i can go that slow. And well the faster you go the farther off the spedo reads...

So does anyone else have a prob with BFG's and actual speed?

-Gigantor
{Nick}
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[jimbo74]

stocks are 235...there shouldnt be any problems at all...unless you run them at like 40 psi all the time or something... my speedo is that far off at the same speed but i also have 31s..... maybe just happy cops :smoke:

 

[Gigantor]

I run 35 in the front and 37 in the rear, I do a lot of interstate driving and havnt hit the trails in a few years, so the wear at that pressure is ALMOST PERFECT. Ok so a little wear on the inside of the fronts but a front to back rotation will solve that problem. What do you expect at almost 35,000 miles??

As far as the happy cop syndrome... they can be as happy as they want but well... my uncle is the fire chief, fire inspector, and part time police dispatcher AND a very close family friend is Lut. AND Im friends with the old chief, AND i did an internship with the police dept so i guess knowing people does help )> I have been lucky and got nabbed in my hometown 2 of the last 3 times, but that other time the cop and i talked and it was all cool.

I might just literally ask to get 'trapped', and compair the spedo with the Radar reading...

who knows...
-Nick
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[jimbo74]

remember that their radar isnt always accurate too....i am not saying it isnt accurate, a few innocent get pegged as a guilty....

 

[RFR2212]

Yer tires wont affect yer speedo much if any...
Pete

 

[MSTNGGUY88]

Just because it is a 235 doesn't mean it is the same height as the stock tires. The 235 just means it's width and is involved in the calculation for the height. S o your height can be different than stock.

 

[Yomie]

Just FYI my stock tires were a 225/70 R15 check your door jam to see what that sticker says!

 

[kvo]

You could always check your odometer by the mile marker on the highway.

 

[Robert]

First, check the sticker in your door jamb. If your stock tires were 5% shorter than your current tires, your speedometer will be off by 5%. I've seen tires as small as 215 70R15 on early '90s Explorers. Once you've determined the percentage you are off, you can get a new speedometer gear for $8 from Ford that has fewer teeth than the stock gear by the same percentage. The amount you posted would be the equivalent of one tooth. If your numbers are correct and you are off by 5 MPH at 80 MPH, get a new speedometer gear with one less tooth than your stock one. It will put you closer, but probably not exact though.

 

[Damn Yankee]

Yer tires wont affect yer speedo much if any...

Tires sizes WILL actually have a VERY significant effect on your speedometer/odmeter/MPG readings!

-->>>Click Here For Tire Size Comparison Calculators<<<--]

 

[BislamJoe]

Gigantor - I have EXACTLY the same problem. I run my 235/75R15s at the same pressures as you (actually 35psi all around, but you get the idea) and have the same trouble.

 

[southtxexplorer]

I may be off, but I believe the 235 BFG's are slightly shorter than the 235 Firestones Wilderness AT's that came stock on mine. But that would have the opposite impact on speedo indication. Nonetheless, I would think that any variance between actual speed and registered speed would be very small.

 

[graybaer]

If you want to find out exactly how much error there is in your speedo, I would use a GPS. Have a friend keep an eye on the GPS at different speeds,and that will give you the most accurate comparison. You can't beat a GPS for speed,distance, and direction calculations. :exp: