I installed new 255/55/18 tires with wheel spacers on my rx 330 and the gas mileage got crappier than ever may be 15 miles per gallon or less,what do you think

 

What do we think about what? It is already a done deal and now you have to live with it I would think..

 

First, measure the gas mileage; don't just do it by feel. Why did you need spacers and what was your original tire size?

 

Just a thought.
Can the wheel spacers alter the wheel alignment? Also the brand/type of tire can have an effect.

 

They sure do.... You need to get an alignment with out a doubt. He must have bought new rims also with a different offset if he needed spacers unless he just wanted spacers. We need more info.

 

I just used the oem 18 wheels,yokohama geolanders and spacers 5mm because only one front wheel was rubbing on full steering.tires look nice and even tread wear.

 

By going to the oversize tires, you have changed your speedometer calibration and thus your odometer reading. You are now going farther per revolution of the wheels than before so it looks like worse mileage. What will get worse from your tire size change are:
1. Ride due to heavier unsprung weight
2. Acceleration due to heavy tires
3. Handling due to larger tires and spacers to fit
4. Loads on wheel bearings which could lead to early failure

I'm glad they look nice.

Steve

 

Don't forget braking, for the same reason.

 

Your stock rims came with 55 series tires so your odometer will not change at all for one. 2, With the wider tires your handling should improve.3, I can't believe you or anyone would ever notice worse acceleration due to HEAVIER tires. 4, When putting on spacers and installed correctly you will not put any more tension on your wheel bearings. I still don't understand why you needed spacers going with a 7" rim. I have 255/50/19x8" on my vehicle and there is no rubbing on the front at all.

 

[QUOTE=ZIN;3636961]Your stock rims came with 55 series tires so your odometer will not change at all for one.

I'm not sure where you got the idea that staying with 55 series tires keep the same OD when you go to larger tires. The stock MXV4 at 235X55 turn 763 revolutions per mile. The 255X18 that he installed turn only 718 revs per mile so the odometer will be off by that percentage that revs per mile change. As far as the other "stuff", wider tires do not always mean better handling. Tire design has much more impact. The tires are 6 pounds per wheel heavier than stock which is not insignificant.

If you don't think putting spacers behind the wheels don't increase bearing side loads, draw your own force diagrams.

Steve

 

5mm wider barely makes a difference on bearing load. it just a very small increase in wear, nothing to worry about.

are you really getting 15mpg or does your car just THINK that.

 

The gas mileage is calculated using the odometer and this is now showing fewer than the actual miles. Each rotation of the wheel travels a greater distance and therefore to get the actual mileage, you will have to take that measurement into consideration. If 10% futther then the distance between fill ups will have to corrected. If you drive 300 miles and it actaully 10% further than use 330 miles.

 

Hi,acceleration is the same,breking is like before,handling improved,look is great,i have air suspension so may be that is the reson for rubbing on full stearing and if the ballbrings will fail in few years it will be time to replace the car anyhow

 

[QUOTE=oldcajun;3637074]
Good stats there! But that does not explain 15 MPG. Assuming 21 MPG before the change, his readout should now show 21*718/763 = 19.8 MPG

 

[QUOTE=biff44;3639219]Your calculations are correct. I assumed from his comment that the mileage got "crappier than ever" that the mileage was poor before the tire change. Getting 21 mpg average on an RX330 would seem pretty good to me if that included much city driving.

The new tires probably have a bit more rolling resistance than the originals, but that is probably a second order effect.
Steve