13 inch

[yutz]

just installed 13 inch tires.how does that affect my gas mileage?what about the speedometer? any body have an answer ? thanks

[ejp2fast]

what size are the tires??
see this link for info

[69shelby]

if the tire diameter is the same, shouldnt affet anything.

[Safety Guy]

While tire diameter is one large factor, other factors would be:

-tire weight
-wheel weight
-tire width: adds to rolling friction and somewhat to CX
-tire rubber compound
-larger negative offsets that put the wheel/tire outer edge out of the fenders and into the windstream, adding to the CX

There are so many variables here that you simply have to try each combo and observe real world results for your answer, though accurate measuring of those results may be difficult.

For best mileage, I'd:

-get the lightest wheel you can with a width from 4.5 to 5.0 inches
-get the lightest tire you can
-get tires designed for lower rolling resistance
-stick with tires from 145 to 165mm wide
-stick with positive offsets from 40 to 45mm
-stick with tire diameters as close as possible to the 145/80-12 stock tire sizing, with slightly larger probably being a bit better than slightly smaller

Example:

Honda VX 13 X 5" aluminum wheels (9 pounds each) with 155/70-13 tires

or 165/65-13 tires

or 145/80-13 tires (probably best due to skinniness, but your handling will suffer, if this matters to you)

Stock Aspire alloys are 13 X 4.5" size, but they weigh 13 pounds each!

With the commonly available 13" tires, 155/80s should give superior mpgs over the wider and heavier 175/70s. (They are effectively the same diameter.)

Just some thoughts.

Karl

[TominMO]

Good upgrade. It's about the diameter, the width, the weight, and the inherent rolling resistance of that particular model tire; but mainly the diameter. In general, taller tires give you better hwy mileage; but city mileage will suffer if the tire is heavier than the stock one, because there is more inertia to overcome from a stop to get it rolling again. Also, heavier tires/rims will make for longer stopping distances, a big reason for the Aspire brake upgrade.

As to the speedo (and odometer), it will read slower for a taller tire, faster for a shorter one. Since speedos tend to be a little optimistic anyway, a small increase in diameter might actually make it read more accurately. See if you can test it over a known distance. If you drive at 60 MPH for one minute, that should be exactly 1 mile. if you go one measured mile in 54 seconds at an indicated 60 MPH, for example, you know the speedometer is reading 10% slow, and you are actually going 66 MPH.

To check the odometer, I use hwy mileage markers on a course that measures distance every .2 miles, over a distance of 10 miles. Ten miles is 100 tenths. If the odo reads .5 slow, I know that it is 5% off.

[TominMO]

Good writeup Safety Guy! You just beat me as I was writing mine.

[Safety Guy]

Well Tom, I didn't mention inertia effects like you did!

Also, worth mentioning (I suppose) is that putting on the Aspire running gear increases your weight, and will not contribute to better mileage. I doubt it will prove that noticeable though. The larger rotors and rear drum are close to the center and won't be creating that much of a "flywheel" effect, while providing much better wheel choices and better braking and handling. The most weight difference is probably in the rear stabilizer bar.

FYI, auto Aspire rotors weigh 3 pounds more than the manual rotors. (I weighed pairs of PG Plus rotors a while back because I was curious to see the difference.)

Karl

[Team Lightning]

According to 1010tires.com tire size calculator, 155-80-12 are 21.76" in diameter
155-80-13 are 22.76", 175-60-13 are 21.26". I am running 155-80-13 on my Festy and getting 40 mile per gallon. The speedometer is correct for the first time in it's life. It's always been 10% fast with the 155-80-12's. With the 12" wheels and 155-80-12 tires I got around 44 MPG. I always kept a running total of mileage since I bought the car. Hope this helps.
This is the link to the tire size calculator I used

http://www.1010tires.com/tiresizecalculator.asp

[TominMO]

Also, worth mentioning (I suppose) is that putting on the Aspire running gear increases your weight, and will not contribute to better mileage. I doubt it will prove that noticeable though. The larger rotors and rear drum are close to the center and won't be creating that much of a "flywheel" effect, while providing much better wheel choices and better braking and handling. The most weight difference is probably in the rear stabilizer bar.

FYI, auto Aspire rotors weigh 3 pounds more than the manual rotors. (I weighed pairs of PG Plus rotors a while back because I was curious to see the difference.)

Right; what little flywheel effect comes from the heavier Aspire rotors is way more than compensated for by the better braking, and I suspect larger bearings, which should tolerate larger wheels/tires better than Festy bearings.

[Safety Guy]

Tom, you might want to check an online parts catalog, but I'm pretty sure Festiva and Aspire front bearings are the same. Check for part numbers. I would, but I gotta go.

Karl

[TominMO]

Tom, you might want to check an online parts catalog, but I'm pretty sure Festiva and Aspire front bearings are the same. Check for part numbers. I would, but I gotta go.

Karl

FMS lists them as different part #s, and their normal practice seems to be to use one part # if it applies to both Festys and Aspires.

EDIT: Correction: comparing specs on Rock Auto for Festy and Aspire wheel bearings shows them to be the same.

[GenevaDirt]

According to 1010tires.com tire size calculator, 155-80-12 are 21.76" in diameter
155-80-13 are 22.76", 175-60-13 are 21.26". I am running 155-80-13 on my Festy and getting 40 mile per gallon. The speedometer is correct for the first time in it's life. It's always been 10% fast with the 155-80-12's. With the 12" wheels and 155-80-12 tires I got around 44 MPG. I always kept a running total of mileage since I bought the car. Hope this helps.
This is the link to the tire size calculator I used
http://www.1010tires.com/tiresizecalculator.asp

well not to argue with you.(but I guess I am...lol)...I ran both of the setups you had. on 2 different cars. With the 155/80/12's, using a GPS and measuring with mile markers....both speedo's were right on. I switched to the 155/80/13's and on both cars the speedo's are about 3-4 mphs off. When doing 60 I am actually between 63 and 64 mphs. Just my observation with 2 different cars and also if you look at the tire size calculator it says the 155/80/13's would run about 3 mph's faster.

http://www.miata.net/garage/tirecalc.html

[yutz]

13 inch

they are 155/80 /13 sorry took so long. they handle very nicely.