A friend of mine was just telling me that when you get bigger tires on your vehicle that your speed could be off by 5-10 MPH depending. This is my first vehicle with big tires and I had no clue. My wife called the place that put the tires on they said it was true and they do not fix the gauge because it would be to expensive. They never told her about it until she called and asked. So my question to you all is how expensive is this to fix and would you at all? Thanks..

 

Yeah, but it really depends on how much bigger you go on how much off the speedo is

if you went to 33" tires from a 265 70 17 your speedo won't be off much

here's a link, plug in the numbers to see how much off it is

I'm putting new wheels/tires on my truck this week and my speedo will be off 1% so I'm not gonna bother changing it

when my speedo says 69.4 mph I'll really be travelling 70 mph
Tire Size/Speedo/RPM/Gear Ratio Calc

 

my truck had 235/85r16 and I found some 245/65r16's for a good deal. They're about 1inch smaller in overall height and when my speedo says 70, the GPS is sayin 60ish. So yea, different size tires make a difference in speed compared to speedo.

 

You can have the computer reset at the dealership. You will need to know the Revolutions Per Mile for the new tires. Cost? Some dealerships do it at no cost; others charge up to $80. Go figure. I would have the computer reset.

 

Polarisgeek, those tires are 3 inches shorter, and when your speedo says 60 you should be doing about 66 mph

and yeah, forgot to mention the resetting of the computer, my dealership's gonna charge me 60$ if I do it, but my speedo will be off less than 1mph at 70 so it doesn't matter to me

 

i dunno i got 35's now but my truck came stock w/ 245x75x16....my speedo isn't that far off... i dont think, either that or everyone around here is speeding....

 

probably speeding :P

70 mph (112.63 kph) 64.44 mph (103.69 kph
If your speedometer has been calibrated for 245/75 R 16 (30 x 9.65 x 16) tires, replacing them with 343/67 R 15's (35 x 13.50 x 15's) would result in the speedometer reading low by 7.94%.

 

hrmmm, news to me..
i couldn't firgure out how to use that formula website,
plus i dont know my gear ratio...
i'll firgure it out soon...

 

you don't need your gear ratio/rpms to calculate tires

your tires, 33x13.50x15 is a 343 67 15

just scroll down, and use the righthand side, type in
245 75 16 in tire a and 34367 15 in tire b

click the option "Compare tire a and tire b" and then click submit and it'll come up with a graph for speedometer error up to 200mph and odometer error up to 100,000 miles

also the overall height/width/sidewall height/circumference as well

pretty good site once you get the hang of it

 

Thanks for all the info guys. My wife is going to call the dealership today.

Oh and by the way Chauncy, that is a great looking Ram you have there.