97accordbuildlx

found a calculator so just double checking if this is right. if there is any loose ends then let me know. as far as ive read and understood, the tire size can affect your mph correct?

a site told me the stock 93 civic dx tire size is P175/70R13.

i now have 15" rims with p195/60r15 snow tires on. the online converter took the diameter size of 13" rims to 15" rims and when my spedometer now reads 80mph, it should really be reading 92mph.......??? if this were true that would mean i have the longest gearing in all of honda history. my 1st gear goes to 50ish, my second gear goes to 80ish, if it actually goes all the way to 92 then im baffled. or is the calculator backwards saying that when my speedo is showing 80 im really going 70..

heres the links to the sources:

http://www.dragtimes.com/Honda-Civic...-m18-n214.html

http://www.onlineconversion.com/bigger_tires.htm

97accordbuildlx

by the way i have a d16z6 bolted to a S20 A000 tranny(cx/vx i believe) if that helps anyone

apexi_rsx

that calculator must be off. i have 18" wheels with 215/45/r18 and im only a few mph off from stock. ride next to a friend on a 2 lane highway and have them hold a steady speed at 50mph and try to steady your car next to theirs. if anything u may be 5mph off not 12mph. if u put a stock tire next to your rims im sure the overall diameter is damn near the same. maybe if u were running the same profile tire from your 13" wheel on your 15" wheel it would be a few inches bigger and yes it would prob be 12mph off. when you run 15's you have a lower profile tire then stock.

hyperblu

Size of the wheels doesn't matter. It's the size of the tires.

hyperblu

Your speedo says you're doing 80 when you're actually doing 89.14285. However, if you notice every guage cluster will be 3-4mph faster than actual speed due to DOT regulations. You can also buy a speedohealer to calibrate your speedo.

97accordbuildlx

yes well the new tires are 15r's they have somewhat thick tread as well. yea i was planning on doing the friend test tomorrow but was just curious tonight, and can u rent a speedohealer? i see theyre a good chunk of change. ididnt know if auto zone had one i could just rent out.

and that means that my gearing is actually even alittlbe bit longer than i tohught.......if i ever did a 1/4 mile id probably be finishing in high 2nd low 3rd gear LOL

Dakota D16z6

hyperblu

The speedohealer is something you have to hardwire into the crank sensor wires and intercepts the tach signal and changes it accordingly. It's not something you can rent.

hyperblu

15 r means the inner diameter, meaning it's a 15inch wheel, 16r means 16" wheel. The "sizing" you're looking for is the first number. p195 or p175 That is the size of the tire in millimeters.

motegicivic

Yes, it does affect speedo, I have 16's orig was 14's and I am plus 2 (what is recommend) but still about 4 mph under what the speedo says.

grumblemarc

iTrader: (4)

The unsprung weight of the larger wheel will also have a negative impact on mileage and a lot of impact on acceleration AND affects the speedo.

97accordbuildlx

so youre saying that even thought the spedo was calibrated for a 13 inch wheel and that now i have a 15 inch wheel
that doesnt matter, its only the difference of p195 and p175? and through your calculations my spedo should be reading 89ish when its reading 80mph correct?

o alright and sorry, i thought the speedohealer was just something you could rent and it would just like recalibrate the spedo i didnt know it was a permanent addition.

JDM-Punk

this^

ccbb34

The P195 is the width of the tire in millimeters. The 60 is the aspect ratio which is essentially, the height of the sidewall in proportion to the width. A P195/60r15 will be taller than a P195/50r15 and therefore have a larger rolling circumference. The calculator you posted the link to does not factor that into their formula. That calculator is assuming the sidewalls are the same height which they are not. Your snow tires are def bigger than your originals, which is going to affect your speedo. This link i posted is a more accurate calculator an will answer your questions.

http://www.miata.net/garage/tirecalc.html