Rep Power: 339

So I realized awhile ago, that more than performance tires, going with a SMALLER tire dimater overall could help me with performance. I reasoned that for each rotation I would increase the amount of power going to the ground, despite actually travelling a smaller distance. I consulted another honda enthusiast online, autocross racer James Brett Howell, about possible tire sizes and to interpret the codes, to determine really the best size ot go with. I will start with his reply to me:

"Hey Rabbit,

I believe you are thinking about this with the right perspective. Most people make the mistake of trying to add larger diameter rims thinking that will make their car work better, but more often than not that actually hurts performance.

The one thing you want to be mindful of is ending up with a sidewall that is too short and therefore too stiff to allow the tire to bite into the asphalt. Think of a dragster's rear tires (or a Champ car, or an Indy car, or a F1 car, etc.) - they do not use super short sidewalls because they require some sidewall flex (and the resulting distortion of the contact patch) to get all the power they produce to the ground.

The tires I run on my Civic are 225/45-13 Hoosier A3S03s (DOT radials), and although the aspect ratio (45) is relatively low, the sidewall height is a product of tread width (225) and the aspect ratio. Since the tires are very wide then the sidewall is still reasonable despite the low aspect ratio (basically ~45% of 225 = ~101.25). The result is a large, wide contact patch with enough "crinkle" in the sidewall to get the tires to bite.

The other part of my setup is the wheels - 13" x 9" 3-pc. aluminum rims. They are very lightweight (about 7.5 lbs apiece) which reduces not only unsprung weight (the amount of mass the suspension is trying to manage), but also reduces rotating mass which helps accelleration and braking. The most important characteristic though is the 9" width. I believe your stock rims are 6" wide...maybe 5"...which limits how wide a tire you can put on them before you begin to compromise the geometry of the sidewall relative to the tread surface.

In my case the 9" rims are actually a little bit wider than the tread surface which results in the sidewalls being spread out a little bit (other rim widths frequently used with these tires are 8" and most recently the recommended width is 8.5", although I know of at least on National Champion who runs 225/50-13 Hoosiers on 5" wide rims...its a pretty tight fit).

A rule of thumb is that the lateral stability of the tire is compromised as your rim width shrinks to more than one inch (25.4mm) below your tread width. For instance, an 8" rim is 203.2mm wide...203.2 + 25.4 = 228.6, which is greater than 225mm, the approximate width of a 225/45-13 tire's tread, so this would be a desirable rim width for that tire. On the other hand, a 6" wide rim is is 152.4mm wide...152.3 + 25.4 = 177.7, which indicates that a 175mm wide tire is probably the widest tire you could run on this rim before compromising lateral stability.

So, after all that we have concluded that 185 is just about the widest tire you want on your rims (whew... ).

Now let's think about the sidewall height...on your tires it is ~185 x .7 = 129.5. I could see reducing that a little bit to something around 100 mm...maybe as low as 95 mm. So to figure out what that aspect ratio would be close to you take 95 / 185 = .514...or somewhere between a 50 and a 55 ratio tire. A 50 would give you a sidewall that was approximately 92.5 mm high which is on the border of being too short, while a 55 would give you a 101.75 which is a pretty good height in terms of rip and reduced deflection.

So with a little figuring I would suggest a tire sized 185/55-14 for your car. The question is, does such an animal exist? A quick check of Tirerack.com shows that they sell three very good performance tires in that size: Michelin Pilot SX GT @ $111 (not cheap, but a very good all around tire), Pirelli P7000 @ $66 (great performers and a bargain price), and Kumho Ecsta V700 @ $95 (an R-compound DOT race tire that would provide nearly ultimate grip in the dry and decent grip in the wet, but will wear relatively quickly).

You could also try a slightly taller sidewall in the same width, 185/60-14 and still greatly enhance the performance potential of the tire over the current setup. The Pirelli P7000 is available in this size for the wopping low price of $47 per tire (Wow!). Another tire of interest in that size is the Yokohama AVS Intermediate @ $60 (old school, but tenacious grip for the price).

Another option would be to go with a slightly wider tire (not optimal with your current rims, but would give you the option of upgrading to wider rims in the future to make better use of the tires). Probably anything wider than a 195 on that rim is going to be an issue though, so I did a little checking for 195mm wide tires in 14" sizes and found little if anything below a 55 series tire. So if you were to go with a 195/55-14 series tire then you would have a 107.25mm high sidewall (much shorter than your current tires with plenty capable of delivering excellent bite). There are a slew of excellent tires available in that size ranging from the Dunlop SP Sport 8000 @ $74 to the Hoosier R3S03 @ $138 (though I would strongly recommend against the R3S03 for use on the street).

Just as an FYI - I used to run Yokohama A008RSII's (a DOT competition tire) sized 185/60-13 on a 13x7 rim. They were stretched out pretty far on those rims, but they worked great. The reason I am mentioning this is to point out that you can probably go as wide as a 7" wide rim and still make good use of the 185 wide tires...but if you have thoughts of going to a really wide rim (7.5" or wider) then the 195's will probably be the narrowest tire you could fit on those.

All things being equal, for a daily driver the 185/60-14 P7000 seems to be the bargain. I can't think of a better tire anywhere near that price, and the combination of the tire's design combined with the lower sidewall will really enhance the handling of your Civic. Next choice IMHO would be the Yokohama AVS-i in the same size, followed by the 185/55-14 P7000. These are very reasonably priced tires built with performance in mind, and all of them are available in sizes that will really make the most of your current rims.

I know you basically asked me what time it was and I told you how to build a watch, but I hope that helps.

Good luck.

Brett"

 
Rep Power: 339

So, with this understood, it was time to buy new tires! it turns out the pirelli's which i had set my sights so dearly on were discontinued! bummer! I redid some calculations for myself, and decided Id have liked a slightly larger contact patch. so 195 it was, the math told me a 50 mm sidewall was ideal. did THEY exist? well, according to some SCCA racers, they did, as on teh scca website, i found multiple racers running kumho tires, 195/50/14. a search on kumho's site was a dead end, however.

so after finally gicing up, i decided to go with a 195/55/14, of which there were plenty of tires! my final decision went to the dunlops.

http://www.tirerack.com/tires/tires.jsp?tireMake=Dunlop&tireModel=SP+Sport+8000& vehicleSearch=false&partnum=955ZR48000&fromCompare 1=yes

a call to Tirerack, I discovered they were rated to run for 15,000 miles. But since they were designed for a Miata, they would wear out faster on my car. They didnt even know abotu the stereo. So armed with hte understanding that they would basically last to the end of summer (they are a summer tire, right? =D) and $325 in my pocket, I decided to give these tires a try.

but wait!! theres a HUGE problem! the tire calculator here was quick to inform me that my speedometer will read TOO fast if i put these tires on! 7.5% may not seem like a very large number, but after I travel 10,000, do i really want my speedometer to read 10,750? if im gonna have 750 extra mile son there, i wanna be the one putting them on there!

now back to the internet! after a bit of research, i found these:

http://www.blackrobotics.com/index.htm

but there were so many changes to the new hondas, will they even work? An email to black robotics assured me that it would work, as many of the newer hondas run off the 3 wire design. so on a whim, and nothing to lose, i ordered one. I had no idea they were based in Australia! regardless, less than 7 days later, I had my recalibrator at my door. perfect!

Do i know how to install tires? hell no. shop cna do that, my local honda performance specialist reccommendd a great shop, they put them on right quick. but what abotu the recalibrator? do i REALLY need to pay someone to install that? pfft, 4 wires, no problem!

needed the tech info tho, and thats what brings me here today, for anyone else wanting to have an accurate speedometer!

 
Rep Power: 339

So! here is my yellowbox, all tuned and ready to be installed:


so where is that speedo sensor? on teh transmission, naturally! so out comes the resonator:


Here is where there was a discrepancy. the tech info tol dme it was a white/green wire. the tech at the honda speciallist then pointed out to me a plug, you see on teh bottom. said the green wire with the yellow stripe was it. I was confused. didnt black robotics say it was a 3 wire design? i guess it could be the 2 wire design, afterall...

didnt the tech info say it was a WHITE wire? might have gotten it backwards, i guess....


so naturally, when it didnt work, i scratched my head for 20 minutes, before hunting all over the tranny for the REAL sensor. found it! its below the cables you see at the top of the transmission, where the arrow is. tucked up under there! easy for a honda tech to miss, its understandable!.

so we pull the plug, and yes its a 3 wire design! black robotics, yoru on the ball!


so peeling back teh case, i see... yes! a white wire with a green stripe, a black wire, and a black wire with a white stripe. ever look at yrou ignition harness? you bet it matches! black with a white stripe is ignition, black is ground, and the tech info was right afterall! yes!

so I put a T-tap on power. my failed attempts previously found me a different location for the white wire, and also a different ground location. at this point, starting afresh, I would have cut the sensor wire here and put butt connectors on it. and also a t-tap on the ground.


as is tho, a tap for power is good enough for me now. you can see in teh next couple pics where the ground wire comes out, i could have easily tapped ground where power was as well, however. but since ground is ground is ground, im all set! my butt connectors innterrupt teh signal of the sending wire, and now my cluster of wires looks liek this:


zip tie the molex plug to a convenient location, and free from harm caused by water, set and installed! and the tests work out well! setting the thing for 28% innaccuracy REALLY messed up the speedo reading! so now that we know it works, i can set it back to 7.5% fast, and go get my tires installed!


tiem fir cleanup. gotta electrical tape up all those wires, make it look clean, and make sure they arent in the way of anything. then jsut put the resonator back in!


results? well, I'm no expert, but my car actually FEELS liek its pulling me in 2nd gear now! cornering is INFINITELY better now than with stock tires. they ride great, and even if they only last to teh end of the summer, these tires were WELL worth my money. I look forward to a fun filled driving summer!

but a smaller tire? how will that LOOK, you say? well, the smaller tire drops my car nearly an inch, and the stereo nicely matches that. so with my own "custom" lowering kit, you tell ME how it looks!





I must say this project has been well worth every penny of the net $500 i spent for new tires, install, yellow box, tires, absolutley everything.

and when i change tires again, a few switches flicked, and my speedometer will be accurate!

 
Rep Power: 433

aww smart man!!
nice job