tire question (will 175/70/13 hurt mpg? 165/70/13 is stock)
 

I have a 84 crx with the 1.3 and high gear ratio. they came stock with 165 70 13 tires. I just bought this car, and it has 175 70 13 tires on it. I am having a hard time finding stock tires, will the 175 tires hurt my mpg much?

That depends. They must be a little heavier, a couple pounds each, probably, doubled as "rotational mass" you have 8-16 lbs more for the whole car. That's not a lot of weight. In the city it'll affect mpg marginally--maybe insignificantly--but on the freeway it's virtually nothing. And on the freeway slightly larger tires such as these will reduce you cruising RPM, probably benefiting MPG. It's as if you gave yourself taller gearing. I hope that helps.

The added width will also negatively affect aerodynamic drag slightly. The slightly raised ride height may too.

But in combination with the slightly reduced cruising RPM it's probably all a wash, or pretty close to it.

I live in the mountains, and the crx is really high geared any way. I can only use 5th on flat ground, and if I am gouing down an incline , I am coasting. most grades of any significance I have to drop to 3rd gear, and sometimes I am tempted to go to 2nd. I could definitely use the extra power, but it might coast better with the larger tire.

155/80 R13 would be a narrower, lighter weight tire that is about the same height as the 175/70 R13 and the CRX is well within the weight range of the 155mm wide tires.
Another option is going up to 14" rims (off a older civic hybrid, civic hx, Honda insight, or any number of other vehicles) and getting 165/60 R14 tires and getting low rolling resistance tires as well, at least that is what my plan is as the Civic VX calls for the same 165/70 R13 tires as the CRX and they are getting hard to find.

I don't think it will hurt you enough to talk about. As you mentioned, you might be able to coast a bit further.

You certainly have freeway gearing! Hmmmmm!!!!

Maybe we should just trade cars!

In my Civic VX I notice the difference when I switched from 175/70 R13 to 165/70 R13 tires, the biggest chance I noticed was that the car handled better and felt lighter, less sluggish, nothing huge but the kind of change you notice by having an extra passenger in the car, in my current VX I have 175/70 R13 tires again and I can't wait to switch to stock height.

thanks for the info, I will try to find some 165 70 13 tires

Tire Search Results

is the only tire that tirerack lists in the stock size, that tire used to be listed as a low rolling resistance tire too, not sure how it compares to others but it's not in that category any more.

I have a 94 Civic hb. I recently change the 175/70-13 for 185/70-14 for two reasons. 1 Theyare getting harder to find. 2 I wanted to lower the revs on the highway a bit. I put Kumho solus lrr's on it and am still waiting for the results. It apears to have given me about 2 mpg on the highway but it is too soon to tell. My car is used 99% highway.