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I have a 1998 Civic HX MT and have been toying around with the car to increase my MPG . 2008 adjusted EPA ratings for my car are 35city/40hwy.

So far, I've lowered my car 1.5" to cut down on drag, picked up Low Rolling Resistance Tires (Sumitomo HTR200 this is a top ranked LRR tire - http://greenseal.org/resources/repor...resistance.pdf), taken out the spare tire and jack, installed a lightweight flywheel (Fidanza 7lbs), and bumped up my air pressure from 30lbs to 41lbs all around.

The next thing I'm looking at is to change my tire size. As some of you may know HX cars have really lightweight wheels (11.75LBS). I’d like to keep up with this lightweight emphasis too. I'm thinking about changing from 185/65/14 to 175/70/14.

The stock 185/65/14 tire’s weight is 16lbs and the OD 23.5”

185/65/14 HTR200 weighs 17lbs and the OD is 23.3"
http://www.tirerack.com/tires/Spec.jsp?make=Sumitomo&model=HTR+200&partnum=77HR4HTR200&vehicleSearch=false&fromCompare1=yes&place=1

175/70/14 HTR200 weighs 17lbs and the OD is 23.7”

The alternative tire is

175/70/14 General Altimax RT. It weighs 14lbs and its OD is 23.6"
http://www.tirerack.com/tires/Spec.jsp?make=General&model=Altimax+RT&partnum=77TR4AMAXRT&vehicleSearch=false&fromCompare1=yes&place=2

Using 1010tires's wheel size calculator, difference is within the recommended 3% in the favor of higher gearing.

For reference here is the calculator link.
http://www.1010tires.com/TireSizeCal...?action=submit

Going with 175s

Pros: lower rotational mass (lower overall weight and the weight is closer to the middle of the tire). A more narrow contact patch (better straight line performance - both acceleration and braking) would be more efficient and would probably lead to better mpgs. The gearing (slightly higher) will yield lower cruising rpms.

Cons: the car loses some aerodynamic gains from lowering the car. The slightly taller gearing will hurt acceleration. The more narrow tire wouldn’t be as stable or competent when cornering hard (emergency situations).

HTR200
Even though it is a top LRR tire it still sticks to the road pretty good. Braking/Cornering will be better. The downside is its weight.

General Altimax RT
It will probably be a better LRR tire and its weight is very low. Acceleration will be better. Braking will be helped because of its lighter weight but probably not as much as the HTR’s grip.

Right now, I'm looking at going with the Altimax RT.

Any opinions or better yet anyone actually do this and care to share his/her experience?


For reference here are some links.

Unsprung weight
http://hondaswap.com/general-tech-ar...art-2-a-29058/

Wheel weights
http://www.superhonda.com/tech/wheel_weights.html

Contact Patch
http://www.toyojapan.com/tires/pdf/TTT_08.pdf

Aerodynamics
http://www.recumbents.com/car_aerodynamics/
http://forum.ecomodder.com/showthread.php/list-aero-mods-you-can-do-your-vehicle-83.html

FYI, the oem size on my DX is 175/70/13.

Rolling Resistance will make a bigger difference than size, I believe.

Don't forget that you'll need to correct your MPG calculations because your speedo and thus odo will be off.

Rolling Resistance will make a bigger difference than size, I believe.

Absolutely.

FYI, the oem size on my DX is 175/70/13.

Rolling Resistance will make a bigger difference than size, I believe.

Interesting that your wheels are 13" and mine are 14". HX's came with 14" wheels for sure. I also checked and found that your car does come with 13" wheels.

http://www.edmunds.com/used/1996/honda/civic/4259/standard.html

http://www.edmunds.com/used/1996/honda/civic/4248/standard.html

The OD of your wheels is 22.6" and mine is 23.5" That is a huge difference (over 3%). I wonder now if the odometer has been alterted to compensate for the differences between these two versions of civics. I too considered 13" Civic VX wheels (only 9.5lbs each vs. steel 13" wheels at probably 17lbs each ...14" steel wheels are 18lbs) myself but the gearing would go down and my rpms would go up and my mpgs would suffer. You have a couple possible options. Get Civic VX wheels ($200) and stay the same tire size (your acceleration would improve .... less gas used to get the car moving) or get HX wheels and stick to the same width (175 like what I want to do).

Wider tires = more rolling resistance, so me going more narrow would actually mean that my rolling resistance would go down. Couple this with harder rubber All Season vs Summer Performance and rolling resistance should also be improved from that angle.

The fact that your DX has tires 175 wide makes me feel better about this planned switch.

Don't forget that you'll need to correct your MPG calculations because your speedo and thus odo will be off.

I'll will adjust for the difference though it won't be much. 23.5" vs 23.6".

unfortunately speedometers/odometers aren't very accurate to start with.

some are a few percent high and some a few percent low.