hello guys, i just bought the hypertech power programmer and while i was installing it asked what was my tire height , my tires are the stock 245/50/16's, what is my tire height? is it 26" or higher, thanks.

 

I used 26.5 in my HPP for 245/ 50/ 16's. I think my actual number is like 26.6. Hope this helps.

 

25.6" tall
do a search on google for "miata tire size calculator"
the first one on top, is the link you wanna go to
it has a neat java program to compare sizes

 

Doh, go the numbers backwards.

 

245/50/16

What the above means is...

The tire is 245mm wide.

The 50 means the side walls are 50% of the width so 50% of 245mm is 122.5mm. Since there is a sidewall below the wheel and above the wheel, you would double this number so your total sidewall height is 122.5 x 2 = 245mm. There is 25.4mm per inch. So, 245mm / 25.4mm per inch = 9.6 total inches of sidewall.

The 16 is the wheel diameter in inches.

The two sidewalls at 9.6 inches and the wheel at 16 inches gives you 25.6 inches for the total tire height.

Of course, it is sometimes easier to just take a tape measure to the garage and measure the damn thing

 

Tire diameter = 2 x ((245)(50)/2540) + 16

Tire Diameter = 25.6456

 

when i programmed it i put 26" , do you think i should go back and change it or you think im not gonna notice a whole big difference in my speedo.

 

The best thing to do is not change it from the factory setting, which is 25.65" in the stock PCM tables. HPP doesn't offer that choice.

If you set the value at 26.0" your speedo and odometer will be off by 1.36%. The speedo will read about 0.8MPH high at 60mph, and the odometer will rack up 1014 miles when you actually travelled only 1,000.

 

I *think* (but there is a 95% chance I'm wrong if you've considered this LOL!) that when certain options are selected on the HPP+ it forces you to input a tire height? No? Probably wrong but I thought I heard that before... or maybe had a dream about it

 

I honestly don't remember.... its been 5 years since I used mine. But I know when I did a file dump from the PCM, AFTER using the HPP, the PCM file still had the 25.65" diameter in it. It also had a 3.73 gear ratio... so I know I changed some things but not others... but it was too long ago to be certain.

Old age is a bitch

 

Tell me about it! I'm starting to feel the affects already!!!

With your data, sounds like I must have had a dream. Sigh... you're just old.... I'm old and delirious

 

I used a tape measure and my stock 245/50/16 tires came out at 24.75 so that's what I used and my speedo is dead on 3000 rpm at 80 mph with the 3.73s.
The tires sit into the rim so that may be the difference between a calculation and the tape measure

 

thats true, i tried keeping a stock option for my tires but it won't let me change my gear ratio ( i have currently switched from 2.73 to 3.23's) so the minute i put 3.23 option than it won't except my stock tire option, i have to put in something so i think ill change it and put in 25.6 if it lets me, if not than ill just keep it 26", it seems that there isnt really too much noticeable difference for me to be too much concerened with, i want to thank all of you guys for your input, greatly appreciated.

 

and by-the-way, if anyone looking to purchase a hypertech i strongly recommend it, i changed my shift firmness in it ( everything else i kept stock) and i instantly noticed a huge difference, my car shifts really hard now, my second gear chirps my tires very easily if i step on it ( i think it did that at times even before i bought the HPP) but you can really tell the difference, the tranny feels more tight or something.