5th Gen running 285's and speedo/mileage question

[BigEyeDuck]

Quick question. I purchased a used 5th gen back in March that have 285/70/17 tires.

My question on the 285's. How do the plus size tires affect the speedo and mileage??

If am doing 60 mph on the freeway per the speedo, what is my actual speed??

Same scenario on mileage, if the speedo shows I traveled 1000 miles, what is the offset??

Thanks in advance.

 

[97BlackAckCL]

Best way to determine actual MPH is to use a GPS app on a cellphone that will tell you your speed, then compare it to your speedometer and MPH digital readings

 

[md-lucky]

Quick question. I purchased a used 5th gen back in March that have 285/70/17 tires.

My question on the 285's. How do the plus size tires affect the speedo and mileage??

If am doing 60 mph on the freeway per the speedo, what is my actual speed??

Same scenario on mileage, if the speedo shows I traveled 1000 miles, what is the offset??

Thanks in advance.

I have noticed very little difference. If you do the actual math, you are looking at roughly at +/- 2mph difference at 60mph.

So at 60mph you are likely doing closer to +/- 62mph.

The challenge with your question about 1000 miles is that it is the difference is a % of the speed. So the +/- 2mph at 60mph is going to be different if you are traveling 65, or 70, or 20.

So unless you traveled at exactly "60mph for 1000 miles" you wouldn't really be able to calculate it.

I noticed very little difference with my 285s. I don't drive "below the speed limit" or anything like that to compensate, and have never had an issue.

 

[r6morrison]

I would recommend getting a gps app that shows speed. When I made the switch to 285’s, it actually corrected my vehicle as it showed I was going faster than I really was with the stock size. As for MPG, that’s gonna be dependent on your foot really. I will say that past 70mph, my mpg goes way down. But, at 60-65, I’ll average close to 20. Otherwise, it’s close to 16-17

 

[A10MileHusker]

I'm about 1 MPH off my actual speed. But I pull up Waze on my phone and it will give you your true speed. So I keep it at 59 if I want to go 60.

I've never thought of the mileage difference but if you really wanted to, a 285 tire is approximately 33" and stock would be 31" if I'm not mistaken.

So 33/31=1.0645.... basically you would multiply your mileage by that 1.06 and it should give you an estimated mileage.

This is all very hypothetical...I personally wouldn't (or have I ever) worried about it but thats the basic math.

 

[bnorton00]

It depends. I had 285 BFG KO2s mounted in 7.5” width wheels, and I was showing accurate both on radar and GPS. I now have 285 Toyo R/Ts mounted on 7” width wheels, and I’m between 1-2 MPH faster than the speedo. There’s a few variables that influence the delta. Best thing to do is monitor it with a GPS and pay attention to courtesy radars, and learn your rig.

As far as mileage goes, legally, whatever your odometer says is gospel. I wouldn’t get too worried about it.

 

[DesertCanyons]

Speed with 285/17R70

One way to test speed is to time your vehicle over a known distance. If you know where one of these highway mile marker signs are, showing mile 0, mile 1, mile 2, mile 3, etc, you can drive at what the speedometer says is 60 mph and record the travel time. Then do the math knowing that 60 mph would be one mile per minute.

Mileage has too many variables. Tire and wheel weight, wind speed and direction, rates of acceleration, stop and go traffic, inclined grades, driving habits and so forth. But if you drive over a known distance you can do the math for gas consumption versus distance. This will work better over several tanks of gas.

 

[4runr4eva]

Quick question. I purchased a used 5th gen back in March that have 285/70/17 tires.

My question on the 285's. How do the plus size tires affect the speedo and mileage??

If am doing 60 mph on the freeway per the speedo, what is my actual speed??

Same scenario on mileage, if the speedo shows I traveled 1000 miles, what is the offset??

Thanks in advance.

Not sure if you saw this thread but its super helpful. Good luck OP.

http://www.toyota-4runner.org/5th-g...r-5th-gen-tire-fitment-guide.html#post1550444

 

[Ol'Baditude]

Not that they're the end all be all of speed sensors, but when I pass any radar that displays how fast you're going and then displays it on a flashy sign at the side of the road, it's always what it says on my speedo give or take 1-2km/hr(0.6-1.25mph). It's a negligible difference in speedo compared to stock size in my experience.

There are three noticeable differences when going from stock to 285's:
1. Highway Mileage: 11-12L/100km(20-22mpg) stock vs. 14-16L/100km(15-17mpg) with my 285's and current 295's. A lot of that has to do with the extra 1000lbs I've added to the truck as well, but the massive amount of extra un-sprung weight when going from a P265 to an LT285 will make you sit up and take notice regardless.
2. Acceleration: Sluggish is the word. You'll have a tenancy (or a requirement due to stock gearing and hilly terrain) to put your foot down more, so see point 1 again.
3. Braking: The runner just flat out won't brake as quickly with the aforementioned extra un-sprung mass of the larger tires.

Bottom line - if you don't drive it like you stole it, you can still get 550+ km(350'ish miles) out of a tank, which is pretty damned good(at least for a vehicle that is as heavily modified as mine anyway). Got as high as 700km(435 miles) out of a tank with the wind when it was stock, but the fill up was 83.3L(22galons) so I was pretty much on fumes.