Newb 91 CRX HF
 

Hello, been lurking for a few weeks. I just purchased a 91 CRX HF (unmolested) and from California for the first 17 years of its life. I have only been through 1 tank of gas so far, got 40.8 mpg BUT! the car does have larger wheels, 195/60/14 and i found out 1 day into my current tank that my right front tire only had 16PSI in it!!! So i am hoping for better results on this tank, i will find out tomorrow. I have also just purchased a federal ECU to put in and i have also purchased 4 used factory wheels, just need to blast and paint them and find some good tires. Every tire store around here only sells the 175/70/13 should i do this, buy the 165/70/13 on the internet, or the 155/80/13. Hoping to get some insight from others on here, if it helps the rims i found were 13x5 not the original 13x4.5 I am hoping also that the federal ECU gives me a slight boost in mpg also. I have been doing alot of engine off coasting and engine on neutral coasting and trying to maintain 55-60mph on the highway. I am typically a 90% hwy driver averaging 65-75 miles a day. I bought the CRX because im sick and tired of my v6 ranger getting 15.5 -18 mpg. The way i see it the CRX will have paid for itself in 10 months. I did have to pay a premium for the car 2,000 mostly because they are extremely rare, and its unmolested, new exhaust freshly rebuilt engine and VERY little rust only in the typically quarters none anywhere else. Well i plan on inputting as much to this forum as i can, enjoying reading everyones stories, and everyones help!!

Thanks!

CRX HF envy. I has it. Post a pic or 2!

As for tires, I'd say: keep the 14 inch rims and get some gen. 1 Insight tires - 165/65/14 Bridgestone Potenza RE92's. Ben (SVOboy) put them on his CRX and was amazed at how nicely they roll.

Did you account for the larger tire size (if they actually are.. just guessing here) throwing off your odometer reading? It would have caused it to under-report, making your calculated MPG lower than actual.

And - welcome to the forum.

ArinCRX -

Welcome to EM! What MetroMPG said. I use sites like this to correct my MPG calculations in my fuel log :

Tire size calculator

I cross-reference the odometer against a portable GPS to verify what the tire size calculator says.

CarloSW2

yes...
 

Yes I did account for the tire difference, I don't have my sheet with me to get an exact # but its between 2 & 3 MPG (too low) difference. So you would keep the 14's?? I would love some vx wheels but wow they are hard to find

I think you will find that LRR tires > wheel weight. The RE92's are hard to beat for LRR.

todays fill-up
 

Well with the increased PSI in my tires and even more eoc, and trying to keep it at 55-58 MPH I got 45.39 MPG I'm pretty happy with that. Also this was in cold weather, I will be installing the federal ecu Saturday, we shall hope that helps another 3-4 MPG.

yes, go with the 14 inch rims.

I bought a 91 CRX HF a few weeks ago also. The brakes are locked and the engine has a miss and it needs exhaust work. Nice car, no time yet to fix it.

welcome to em

The civic HX, 4 bolt civic hybrid (first generation) and Honda Insight rims are all pretty decent 14" rims, the civic HF rims are not only narrower but lighter weight compared to other steel rims, the VX rims I think are the only common alloy rims that will be a direct fit, 155/80R13 tires are not avalible as low rolling resistance tires, 175/70R13 are and there is debate but it seems like it is worth going with a wider LRR tire over an unknown narrower tire, of course some of that can be made up if you can get a higher max side wall pressure, of course if you go over that side wall pressure you are doing so at your own risk.

Sorry to open an old thread. But, I have a 90 CRX HF. I have 185/60/14 tires on mine and I am getting mid to upper 40's. I am running Yokohama Avid TRZ tires. They are NOT LRR tires. I get my correct miles traveled by dividing the indicated by .9715. I had a bunch of issues initially. The PO had a SI ECU in the car. The EGR ports in the intake were very clogged and the EGR valve was sticking. It is running great now and my mileage has finally kind of become consistent. I think I would go to the 13" wheels and the proper size tires if I had to do it over again. I want to put rear wheel skirts on the car but the 14 inch wheels stick out a bit too much. I will have to curve the skirts out a little.

I would keep the 14 inch rims and use 175/70R14 tires. I am going to see how 165/80R15 tires fit.

Everyone seems to lean towards 14" Wheels for some reason. I guess there are better LRR tire options available in 14".

IMO I figure the taller 175/70R13 tires would give a taller ratio on the final drive and keep engine RPMs down. That should improve fuel economy right?

I am a california resident, so after seeing the Federal ECU (3-4mpg gain) comment from the Original Poster, I was wondering, why does the Federal ECU improve fuel economy on the CRX HF? Is that true for all years of CRX HF and Honda Civics?

Thanks
Dave

I'm going to revive a dead thread instead of creating a new one!:)

I just bought a 1990 honda crx hf which has 155/80-13 and My current '98 civic has 175/70-14. The 1998's tires were bought by me and I know the history of them compared to this crx where I have NO idea. I want to switch the 14's to the crx but I have no idea what that is going to do to the speedometer reading, how the bigger wheel and tire is going to affect the MPG's, or what problems I'm going to run into.

Measure the height of the tires, multiply it by 3.1416. take that number in inches and divide by 12 to get feet.

Divide the number of feet into 5280 and get the number of revolutions per mile. Do the same for the other tires.

The difference in revs per mile will give you the speedo correction percentage. On my Ranger it was 2.6%. I multiply the odometer reading by 1.026 to get actual mileage travelled.

regards
Mech

Ok, I think I'm going to switch them over to have practically new rubber on the car rather than nervously waiting for a blowout

For the lazy people who no like mathz: 155/80-R13 vs 175/70-R14 Tire Comparison - Tire Size Calculator

Bumping the Question ( FEDERAL ECU MPG GAINS ON CALIF. CRX HF???)
 

HERE'S my .02 cents on the tire size question. Take the difference in tire height divide by tire diameter, then multiply by 65mph or whatever highway speed you cruise at to get the difference in speed from your odometer reading after tire change.

EXAMPLE: old tire 21" tall, new tire 21.5" tall
Difference in height is 0.5"
Divide by old tire height 0.5" / 21" = .0238
Multiply by hwy cruise speed 0.0238 * 65 mph = 1.55 mph change in speedo

Changing to a Taller tire will cause speedo to read less than actual
Changing to a Shorter tire will cause speedo to read more than actual

in this example if your speed were reading 65mph after switching to the taller tire(21.5" diameter) your actual (true speed) would be 1.55 mph less than the speedo reading 65 - 1.55 = 63.45 mph (actual speed)

The effect also reduces your engine RPM's which could reduce fuel consumption assuming your engine has sufficient torque at the given speed and throttle setting. Your power/torque curve of your engine is not constant and generally as RPM decreases so does power and torque. So too tall of a tire could require more throttle to maintain the same speed thus offsetting any potential gains. A small change such as .5" in tire height is not bad though.

Changing to a taller tire also affects the final ratio in all your gears, so when you are accelerating your engine will have a little less mechanical advantage meaning your acceleration might be noticeably reduced. If you are tempted to push the throttle further down to accelerate as you are accustomed to, this may increase fuel consumption. Keep this in mind, as good/bad driving technique often nets the biggest change in fuel economy.

I noticed that California models tend to have lower gear ratios in the tranny, and some owners will swap to a federal tranny to gain the taller ratios for more fuel economy. I often wondered why Honda provided the lower ratios for California cars, and I think it may be due to California having more hills and or California drivers preferring better acceleration. I have noticed after switching to taller tires that my car requires more downshifting on tall and steep hills. The car is less capable of maintaining a good cruising speed going up long hills. If the engine RPM's drop below 2500 the power/torque drops off significantly provoking a downshift or more throttle (wasting more fuel)

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NOW TO BUMP MY QUESTION In hopes somebody might chime in their .02cents about it. (read below) I would like to know if swapping to a federal ECU on the 1988 CRX HF will improve my fuel economy on a California model? Would the tranny gear ratios have any impact on any potential benefit of a federal ECU? Perhaps the Federal ECU is also tuned to work better with the taller ratios on the Federal model HF Tranny?

Thanks
Dave