I have a 93 jeep grand cherokee,It calls for tire size 215/75R15
I got a great deal on new 235/75R15S,My question is how much did this throw the speedometer off? And how do i calculate the speed while driving, Like if i'm showing 70mph, how fast do you think i'm going? 60-65,and does it change at like 30?
I really appreciate all the help i get from everyone
Thank You
2007-07-10 07:31:28 · 6 answers · asked by want to smile 2 in Cars & Transportation ➔ Maintenance & Repairs
The height of the tires are NOT the same, the "75" means that the sidewall is 75% of the width.
The 215 has an OD of 27.7 and 772 revs per mile
The 235 has an od of 28.9 and 721 revs per mile.
Your new tires will turn 51 revs less per mile.
If my math is correct,
50 mph = 51.2
60 mph = 61.44
70 mph = 71.68
Maybe someone will check my math, good luck
2007-07-10 07:37:43 · answer #1 · answered by jon_mac_usa_007 7 · 1⤊ 1⤋
215 is the width of the tire. 75 is the percentage of how high the height of the tire is in relation to the width. So the height is 75% of the width of the tire.
If you change to a 235, the width will increase and therefore, even tho it is still a 75R tire, the height will increase also.
This will have the effect that you will traveling faster than your speeometer says you are.
I know of no calculation to get this difference, but here is what I would do. Get a friend, that has the recommended tires on his car, to follow you and see what the difference is between yours and his speedometers. Should be very much maybe a mile or two.
Also you can find miliage markers along the highway. They are one mile apart. Check your milage at one and then check it at the next one. Whatever the variance is on your speedometer is how much faster you are going.
Another way is to time yourself. Check your watch and then run 60 mph for one mile. Did you speedometer register less than a mile? If so that is the difference. If you do the same thing but decrease your speed to 55 and check you odometer after one minute.....does it read a mile. If it does than your speedometer is 5 mph slow. Good luck. Pops
2007-07-10 14:45:08 · answer #2 · answered by Pops 6 · 1⤊ 0⤋
With the larger 235/75 tire, you would actually be travelling 62.55mph when your speedo says 60. The 235/75 tire has a diameter of 28.88 inches and is about .8 inches wider, the old 215/75 has a diameter of 26.7 inches. The good thing is that your odometer will also spin slower, so you'll rack up miles slower. For some basic speeds, here's what your speedo will read:
40mph = 41.7 mph
50mph = 52 mph
60mph = 62.5 mph
70mph = 73 mph
80mph = 83.5 mph
90mph = 94 mph
100mph = 104.2 mph
Another great way to get an actual reading is to use one of the GPS navigators, Magellan, Tom Tom, etc. since they will give you a very accurate speed indication.
2007-07-10 14:47:14 · answer #3 · answered by StaticTrap 3 · 1⤊ 1⤋
Best test is to measure with a tape the tread circumference around the tire on each one, old and new, subtract to get difference and compare difference to old tire size you measured.
These are so close as to be insignificant compared to how much tire changed from full new tread to old bald tire..
2007-07-10 14:40:10 · answer #4 · answered by Dennis in Central Florida 3 · 0⤊ 0⤋
It should stay the same , because the heighth of the tire is the same.
2007-07-10 14:34:46 · answer #5 · answered by nvrrong 5 · 0⤊ 3⤋
just drive in the middle lane
then relax, however fast you are going
the people in the left lane get the tickets
2007-07-10 14:34:30 · answer #6 · answered by Anonymous · 0⤊ 4⤋