Wheels/tires
 

Summer cometh... slowly. Last day of finals here in Iowa, but we were hit with a small blizzard and 4 or so inches of snow... Just a few days ago, it was 80F. Go figure.

Anywho, my 1987 LeSabre is in need of some new tires (the old Cooper Trendsetters are shot), and I'm trying to decide whether to keep the stock alloy wheels (15" and fairly bulky) or buy some 16" lightweight alloy wheels.

Michelin Defenders look like a good set of tires...

Suggestions?

I am in a similar boat, well actually it's a Versa, and am in need of two new tires. I am also currently considering going up in wheel as well as rim diameter to bring my revs down a bit on the highway.

I don't have a lot of time on them but the car has relatively new Michelin Defenders on the front of the car and they are a nice quiet tire with decent grip and are supposed to wear very well.

I have worn out coopers on the back, not sure what model.

If I stick with the same size I think I will put another couple Michelin Defenders on the back so they are all the same and am considering some Michelin Energy™ Saver A/S tires if I go up in size.

Car tires are pretty new to me so take that all with a grain of salt. I am getting used to the idea of considering sizes that aren't preceded with "LT"

First, changing to a larger diameter wheel doesn't do much for the steady state rolling resistance. The change in tire size has very little affect. So unless the change makes a different set of tires available to you, I wouldn't go there.

But what about the non-steady state - the acceleration and braking? It depends on the weight. Some wheels may be lighter - that would be advantageous. But what's important is the inertia - and the polar moment of inertia at that - something you can't measure without specialized equipment.

Other should chime in, but I am of the opinion that this is NOT an avenue that is advantageous.

- BUT -

If you can increase the diameter of the tire, that might be advantageous - and you might not need to change wheels to get there.

One point often made is that larger-diameter wheels, even of the same weight, effectively weigh more, because the weight is further from the center.

Several guys have tried this, and tested it. So use the search function seeking "tall tire test" and such. The best test I saw was from Sentra SE_R ... search for it and others. Consider more factors: LRR capability, tire weight, and tire width. Remember to calibrate your distance and speed readings to accommodate what is essentially a change in gear ratios, the wheel/tire being in essence another gear. If you don't calibrate, before and after the swap, it will be tough to know if you got a benefit because of the distance undercount on the odometer.

I plan to switch to michelin defenders eventually. Running down my current tires first.

Assuming you have a scangauge (see link in sig) to test results.....

There are generally 4 common issues on tire/wheel:

A.) increase air pressure to 40+ psi. (see threads) It's free to do and most all see an improvement in mpg. Some go as high as 50psi. The trade-off is a harder ride. But since you are driving 'easier' it's not so noticeablr

B.) search 'taller tires':
First, decide if a 5-8% decrease in rpm at cruising speed will cause your engine to get better mpg. Drive 65, then slow down to 59 (use scangauge to test 10 mile run) Second, check for clearance issues before purchasing a taller diameter tire. Check at the strut tower and check at hard left and hard right. Next go to a site like TIRERACK.COM and see the tire measurements.
There are several members who have done great tests. here are my results:
1. Infiniti Q45: 245/45/18 stock rims went to 245/50/18
2. Kia Sportage 235/60/16 stock rims went to 235/70/16
both showed improved mpgs

C.) Reseach Low Rolling Resistance Tires LRR several members have positive results here. Capri Racer (posted above is tops on this issue)
(I did not concider LRR tires but could have)

D) Increasing WHEEL (not to be confused w/ TIRE) size.
Going to a 16 from a 15 will move the weight out 1 inch (even if it is a lighter rim). a spinning weight is 4 times the static weight. So if you havent increased the diameter of the tire over stock, you wont see a gain.
Do not increase wheel size unless you are also increasing the overall diameter of th tire. I wouldn't change rims uless they were free or you have $$$$$ to burn.

My current size (P215/65R15) is pretty limited for tire choices, especially LRR - there are like three LRR tires available, and one of them is a snow tire (Michelin X-Ice2 or 3). Bumping it up to 16" would give me hundreds more tires to choose from.

Calibration might not be so simple on a car with a spring driven speedometer... ;-) I'm not sure what system the odometer uses... :confused:

You could almost think of a wheel as a radial lever working against you, the longer the lever (ie the bigger the diameter) the more the force is multiplied.

I've heard good things about Michelin Defenders. A tire's only job is traction, so that's the first thing I look at when shopping for tires, tread wear, noise, comfort and LRR come second. I'd rather avoid an accident than squeeze a few more miles out of a tank.