I don't think anyone has stated it was not because of a mismatched tire, the issue is the original poster keeps saying it is due to the tread pattern, which would not have any effect on the computer system in the car, the circumference however would have a major effect on how the computer system reacts to the data it is receiving.

Also as to front or rear I doubt it will make a difference as I would think the ABS system is where the computer is reading its information from and that would be from all four tires. If the replacement tire is rotating at a different RPM then the other three tires that is going to be a flag to the computer system that something is wrong. The manufacture could program the computer to ignore the space saver spare by programming the spares circumference into the program so it does not start acting up, this would more then likely disable certain features that are Dependant upon the rotating RPM data of the tires, i.e. engine management, ABS brakes ect.

It is very clear that this problem is due to the tires, it is just erroneous to blame it on the tread pattern.

 

Not only will circumfernce cause a problem but weight could also attribute to the problem.

 

Well, thanks to the OP for bringing to our attention that a mismatched tire will cause erroneuos CVT operation.

 

My replacment tire was in the rear when the crazy RPM issue occured.

 

This is VERY interesting.
Despite taking a lot of heat for it, thanks to the original poster for bringing this issue to our attention.
I too, think that the circumference was likely the problem here, not merely the tread pattern.
IF you have the exact model numbers of the two tires, we could probably look them up (TireRack.com, I think), and see what the difference was (width, diameter, circumference, revolutions per mile. While this won't tell you exactly everything about your scenario (like tire pressure for each tire, and circumference under load), it would be helpful information. I'd personally like to know, as I've NEVER experienced such a severe issue with (ever-so-slightly) mismatched tires on any car. The Civic (is it JUST the Hybrid, I wonder?) seems overly sensitive in this regard.
Again, thanks for the original post - it got the juices flowing from several members here .

BTW, welcome to GreenHybrid. Stick around. We learn a lot from each other! There's TONS of information on this site specifically about our vehicles.

 

Don't forget that all tires that are spec'd on the sidewall for example 195/70/R15 will be listed as an example 24.2, however there are differences between manufactures, one of the biggest things that causes tires to be different circumferences are the tires mold, the older and well used the mold is the more out of spec it becomes that is where you start getting the larger differences in circumference between tire manufacturers.

Michelin, Goodyear, Bridgestone and other major names switch out their molds to try and control the circumference problems, the no name brands use those old molds for far longer and the circumference problem only grows with time for them.

I bet the original poster bought a second tier brand i.e. milemaster, or road king, ect and not a tire from Bridgestone, Michelin or Goodyear ect.

As to why the HCH II is so sensitive it may well be the CVT transmission and the way the computer processes the signals it gets from each wheel sensor for the RPM of each tire, this may be cured in the future with a software up date to make the computer less sensitive to a certain range of RPM difference between the tires. I would think that the computer gets its RPM readings from each of the ABS sensors on each wheel of the car.

 

Got this from TCH side http://www.paspeedo.com/calculator.htm this will give you a good idea how a different circumference can effect your cars MPH which is what your engine computer is also reading from sensors on the car.

 

While that may contribute to the issue, that's not why all tires circumferences differ from manufacturer to manufacturer. Take 2 different named brand tires (1st tires off the mold) with identical tire sizes on the side wall, these 2 tires can have different circumferences. How? The construction of the tire will allow a certain flex in the tire, it controls how a tire feels, comfort level, etc. This flex when it comes in contact with the road can alter the circumference. It's a minor difference but over a length of a mile, it adds up. So it has more to do with how the tire is constructed than when in time it came out of the mold.

 

You are correct in stating that there are many factors that alter a tires circumference, I posted the link from the TCH side just to show how much the MPH can be altered by a minor circumference change.

Toss in one tire that is reading a different MPH then the other three tires and the computer can go nuts.

I only hope that people are not going to make an issue of the tread pattern which is what was alleged in the start of this thread, I would hate to be a tire sales person who now has to over come a false issue of tread pattern causes the cars computer to go wacky.

 

I agree tread pattern had little to do with this issue unless you can show me the data.

If all else being equal, tread pattern should not cause this issue.