Tire UP-sizing (Honda CRX HF)....did the unthinkable yesterday

[Brian D.]

So I had a trip planned from NJ to the D.C. area yesterday. I knew I had an old set of '91 CRX Si wheels in my garage. They had HUGE tires on them. My '89 CRX HF's current setup still had the 175/70/13's on it, but I figured if I was going to experiment, this longer trip would be just the ticket!

My '91 Si wheels (14") had the following tires on them: 195/70/14's and 185/70/14's. So I pulled the small tire/wheel setup off my car and swapped it with these Si wheels. I even put the 195/70's up at the front wheels (yikes!). This was going to be an interesting trip.

Google called my drive from NJ to my D.C. destination to be 221 actual miles. From the time I reset my trip odometer while exiting my driveway in NJ to reaching my desination, my odometer called this same 221 mile trip "198.6" miles. WOW, that's a huge difference...but I knew it would be with such large tires up front. (BTW, the "miata tire size calculator" on the internet is a fantastic resource for plugging in different tire sizes for this type of experimentation).

After some more driving on this same wheel/tire combination today I then went to fill up. With my ACTUAL trip mileage at 232, my car's odometer called this mileage to be 216.6. After filling up (pumped it myself, because this ain't New Jersey anymore)...I made sure it was topped off. My by-the-trip-odometer-FE was 50.8MPG -- but my EFFECTIVE FE (because it truly makes sense to figure how far I have actually gone, not just how far the CAR thinks that I've gone) was 54.04MPG. All in all, I'm impressed.

If anyone else considers doing this (and I know many already have), I definitely wouldn't suggest going with such a large diameter tire (per your particular vehicle's setup), as the drive was not very pleasant. These large tires were a struggle for the car in 5th gear. I found myself having to downshift to 4th gear several times - just for slight upgrades on the I-95 Interstate....just because the small 60 Horsepower 8-valve HF motor couldn't handle this stress in 5th gear. If this whee/tire combination was placed on an Si....or any other car that made significantly more horsepower, this wouldn't have been such an issue.

I know this post is long, but I thought it would be good info for the other FE geeks out there. This is not a practical everyday setup for my car and I WILL be putting my 175/70/13's back on the car as soon as I return home. However, I am happy with the results of my experiment.

[theholycow]

[pgfpro]

Thanks for sharing your finding's. Nice write up!!!

[kamesama980]

Do it myself in all my cars. the Cressida has almost double the engine though... 3l, 200 hp. I run 215/65r16 instead of 195/65r15 (16" equivelant from the supra is 205/55r16) BIG improvement since it's definitely not geared for economy: 5th @ 30 mph @ 1k rpm is fine and 2600rpm @ 65 mph sucks gas down. It's almost 15% adjustment on the odometer IIRC and I can still pass people without downshifting.

[imzjustplayin]

Not really sure what the OP is adding when we have nothing to compare it with. Right now, it's just some random data point... 54mpg seems kinda low in a CRX HF, what do you normally get? How come you don't have a fuel log?

[Mayhim]

I put 14" rims and tires on my 89 CRX DX. I don't remember what size the tires are at the moment, but my correction factor is 1.06046.

The larger rims/tires help a lot over speed bumps, potholes, and trash in the roadway, but make it handle funny. Extreme caution is required in rain/snow/dew, and overinflation could easily become fatal on a fast highway curve in rainy or icy conditions. One has to be on one's toes to drive this car/tire combo. I think it looks better with the larger tire/wheel combination.

I couldn't say what the increase in mileage may have been. It was well within background noise for me and my driving style.

[Jonathan40]

I'm glad to have found this thread. Just a few hours ago I purchased a complete set of '91 14" Si rims, and have been wondering if it will be practical to install them on my '91 CRX HF. One thing that concerns me is whether the additional 20mm of width will actually affect the gas mileage in a negative way. I am not really concerned with performance, so it's OK if acceleration suffers from the larger tire diameter. I'm thinking the biggest benefit of this conversion will be on long-haul highway driving. However, having to downshift to 4th on slight inclines may defeat the purpose. There is much to think about here, especially since I will need to invest on a new set of tires before any experimentation can begin.

[FrugalFloyd]

This is ridiculous. We have three posters in this thread who have experimented with larger tires, and none of them have done ABA testing, nor told us if their mpg improved or got worse with the larger tires.

[theholycow]

A-B-A testing tires is impractical and impracticable unless you have extra wheels or free tire mounting/balancing.

I may eventually be able to do some due to having extra wheels but mine won't apply to fuel-injected cars.

[kamesama980]

Originally Posted by SentraSE-R

This is ridiculous. We have three posters in this thread who have experimented with larger tires, and none of them have done ABA testing, nor told us if their mpg improved or got worse with the larger tires.

Sorry, I didn't specifically say that I've changed tires/wheels more than once. I've got 3 or 4 sets of rims/tires. After adjusting for odometer error the Fe records look like ____----____--- like clockwork. My cressidas got so much torque and geared so low (3L L6 doing 3k@70!) I can't fit a tire big enough to hurt FE.