Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com - View Single Post - Largest Tire Diameter on a 6th Gen Civic (for lower RPM)

UnCivic · 10-27-2009, 04:53 PM

I find it strange that more people haven't posted anything more about this. Surely there are others out there who have tried the oversize tire thing.

Anyway, after many months I managed to pick up a set of 195/60/15's and an old school set of 15" Integra at 5 wheels that I found on Craigslist.

So, here's the comparison...

Before
185/65/14 OD=23.5" % OD Diff = 0 MPG = ~34 to ~36

After
195/60/15 OD=24.2" % OD Diff = +2.9% MPG = ~32 to ~33

So even with the MPG correction for the diameter difference, I'm actually seeing a slight decrease in mpg.

Now, there are a few hundred disclaimers here.
1. A lot of my driving is in Pittsburgh PA on relatively steep hills.
2. Driving style is 'approximately' the same. However, I am not using any of the more exotic or serious hypermileing techniques. Actually, with my car, I can drive it really hard by shifting near the redline or really soft by shifting at 2,300 rpm, and MPG doesn't vary much.
3. The car has 10,000 more miles on it now than it did a few months ago.
4. I'm making no account for temperature / humidity difference.
5. I'm using 87 octane gas from different sources.
6. Tire air pressure is "about" the same, and neither set was overly inflated.
7. The weight of the 195's on Fat 5's is about 3 or 4 pounds heaver than the 185's on stock steelies.

And if you were wondering....
1. The effect of the larger OD tires is interesting. It seems to make the car roll better. Though this could be the result of a better wheel alignment than before.
2. The 195/60/15's don't rub during normal driving. However, if a heavy person is sitting in the passenger seat, the front tires do rub the inside of the wheel well when the wheel is fully locked left or right.
3. The difference in 5th gear cruising RPMs is minimal (ie, 2.9%)
4. The difference in reduced acceleration feel is less than minimal. (ie, more than 2.9%)
5. From a handling perspective, the 195/60/15's feel much more solid than the 185/65/14's.

I still want to try 185/65/15's... However, apparently this is not a common tire size (excepting snow tires) and I'm having problems finding a cheap or used set to experiment with.

10-27-2009, 04:53 PM	#20 (permalink)
UnCivic EcoModding Lurker Join Date: Sep 2008 Location: Pittsburgh, PA Posts: 17 Thanks: 0 Thanked 2 Times in 2 Posts	Update I find it strange that more people haven't posted anything more about this. Surely there are others out there who have tried the oversize tire thing. Anyway, after many months I managed to pick up a set of 195/60/15's and an old school set of 15" Integra at 5 wheels that I found on Craigslist. So, here's the comparison... Before 185/65/14 OD=23.5" % OD Diff = 0 MPG = ~34 to ~36 After 195/60/15 OD=24.2" % OD Diff = +2.9% MPG = ~32 to ~33 So even with the MPG correction for the diameter difference, I'm actually seeing a slight decrease in mpg. Now, there are a few hundred disclaimers here. 1. A lot of my driving is in Pittsburgh PA on relatively steep hills. 2. Driving style is 'approximately' the same. However, I am not using any of the more exotic or serious hypermileing techniques. Actually, with my car, I can drive it really hard by shifting near the redline or really soft by shifting at 2,300 rpm, and MPG doesn't vary much. 3. The car has 10,000 more miles on it now than it did a few months ago. 4. I'm making no account for temperature / humidity difference. 5. I'm using 87 octane gas from different sources. 6. Tire air pressure is "about" the same, and neither set was overly inflated. 7. The weight of the 195's on Fat 5's is about 3 or 4 pounds heaver than the 185's on stock steelies. And if you were wondering.... 1. The effect of the larger OD tires is interesting. It seems to make the car roll better. Though this could be the result of a better wheel alignment than before. 2. The 195/60/15's don't rub during normal driving. However, if a heavy person is sitting in the passenger seat, the front tires do rub the inside of the wheel well when the wheel is fully locked left or right. 3. The difference in 5th gear cruising RPMs is minimal (ie, 2.9%) 4. The difference in reduced acceleration feel is less than minimal. (ie, more than 2.9%) 5. From a handling perspective, the 195/60/15's feel much more solid than the 185/65/14's. I still want to try 185/65/15's... However, apparently this is not a common tire size (excepting snow tires) and I'm having problems finding a cheap or used set to experiment with.