cooper tires and crappy gas milage

[mac308]

I just changed from 255/60R18 to 285/60R18 tires. After the change I noticed that my suspension wouldn't lower or raise. I haven't tried to do other in a couple of months so I am not sure if it is related to changing the tires or just a coincidence. Did anyone else have any issues when they made the change?

 

[duckdive]

Don't see how one would have anything to do with the other.

 

[CMGRover]

Coincidence. Any faults? Unless while doing an alignment the shop messed something up, like damaging a sensor. Maybe they didn't put the computer into the aligning mode.

 

[mac308]

No Faults. They did do an alignment after installing tires. I bought the tires on-line and had them mounted, balanced, and an alignment done at NTB instead of dealer. Probably a big mistake.

 

[di_LR3_co]

so.. despite all the debate about the trip computer being off.. i'm not convinced that is true. when i go past the big brother "slow down" signs that tell you your speed, the speedometer and the "gun" display the exact speed.

i have yet to validate this with a GPS as i have a 2G iphone.. but will keep you updated

 

[jimbiram]

On my various trips, I've compared my speed with my Magellan GPS vs the Onboard NAV and speedometer. With the Coopers, when my speedo shows 65, I am really traveling 67-68, so I am sure the onboard computer is being fooled by distance vs mileage. I really have to watch myself on the open highway to avoid getting picked up by radar, even though speedo says its right, but the GPS tells me otherwise..

One thing that will affect your Coopers is the tire pressure. I run the fronts at 37, instead of factory 32, and the rears at 43, and increase to 45 when running with a full load. The soft sidewall will mush too much with a full load on a trip. I have noticed that even a couple of pounds difference will have a dramatic impact on ride comfort as well as mileage.

 

[krizza91]

i'm sure this has probably already been asked somewhere, but since nearly the entire vehicle is computerized, can you "recalibrate" something or input a new tire size somewhere and have the speedometer or something make the adjustments to give a modified speed and MPG?

 

[jimbiram]

There is a place in the NAV SYSTEM to "calibrate" after a tire change, but I have no idea how or whether is actually works.

 

[Bad Bonez BJ]

My biggest concern after up-sizing the tires was with this warning:

- When changing tire sizes, we recommend staying within 3% of the diameter/height of the original tire. Any more than this and you face the risk of brake failure.

I've got the V6 version LR3 and it has 2" smaller rotors than the V8 version. So the 4.63% diameter difference in the tires equates to a lot more pressure on these smaller brake rotors.

I've not had any problems yet, but I am planning to upgrade the brakes (rotors and caliper cradles) to the V8 version as soon as I need to work on the brakes. I stop almost the same as I did before changing tires.

BJ

 

[jimbiram]

NWOODS had a V6 coil suspension LR3, first with a set of Nitto's and then a set of the Cooper Zeon LTZ's. Not aware that he had any brake issues as a result. Nathan, want to comment further?