Did a little searching around, but didn't come up with anything conclusive...

I've been running the "requisite" wheel/tire combo for sp Hondas. 13" x 9" wheels with 225/45/13 Hoosiers. Now that the car is in SM, reasons for going with the small wheel size due to gearing and power are moot.

So what is the advantage to larger wheels in autox? Does the contact patch change shape? I know turn-in can be affected, but that's not such a big deal since my sidewalls are pretty short to begin with. Speeds aren't really high enough for stability to be an issue, but autoxer's who know a great deal more than I are going with larger diameter wheels, so what am I missing?

 

You'd have to move up to a 16" to get a wider tire, so I personally don't see much point.

 

In a nutshell theory, an equal width, taller tire will provide a contact patch shape better suited for putting power down coming outta corners. So in that sense, a 225-45-15 would be better than a 225-45-13. Gearing is a non-issue in SM. Slightly heavier weight is no biggy either with the power you should be putting down in SM.

Kinda like with highpower drag cars. A taller tire provides an elongated contact patch better suited for straight line traction. And you'd figure dragsters would be just as concerned with low wheel/tire weight and gearing as autocrossers...But the traction benefits outweigh the added weight and rotational inertia...

 

with each inch up from 13, you do increase contact patch, even all with a 225 hoosier.

 

The most scientific information I've seen about this topic is some testing that Mark Daddio did with his SM Neon. He was testing the difference between 225/45R15s and 245-45R16s. Using a G-analyst to measure acceleration forces, he found that the larger tires did not allow the car to maintain any higher level of acceleration. The car would pull up to the same peak 'g' level, then it would break traction. It seems the weight transfer of a FWD car has the largest effect.

One benefit you do get is that the larger OD tire has more time to cool, and has more mass, so it should keep from overheating as quickly as the 13s do. The downside is that to maintain the same ride height, you have to lower the suspension more to run the 15's, and for some of us (3rd gen Civic), it simply isn't possible to lower the suspension any farther (axle already hits the frame). For me to run 15's, my ride height would have to go up an inch or more, which is enough to think about. I'd still like to give it a try sometime, maybe at a test and tune somwhere.

-Chris (7th place in SM @ Nationals this year)

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by fsp31 &raquo;</TD></TR><TR><TD CLASS="quote">So what is the advantage to larger wheels in autox?</TD></TR></TABLE>


well, i run 15" wheels on a naturally aspirated civic (basically stock integra motor) in SM, and i think it is damn competitive. due to a earlier brake choice (4 years ago, before i even knew what autox was...) i am forced to run 15's. i had an arguement with hoosier tom about this. (i ended up walking away from him vowing to never buy anything from that dick.. ) he said i don't have a chance in hell with 15's on a civic. i should change to 13's "trust me, i have been around this sport longer than you have been alive". well, i got 4th out of 34 entrants. *****. as you can see, i am still bitter about it . anywho, i think the larger/taller tire works better with more hp, basically allowing me to put all that i have to the ground. for next year, i will have more practice under my belt and with any luck, my head out of my *** and hopefully bump it up a notch.

 

I've always thought that any FWD Honda over 2100lbs needed 14" or 15" hoosiers on them (15" ideal) or any SM Honda running a ton of power. This is why I disagree with the tire choice that the DSP Integras run, regardless of their gearing issues. BMWs have the same problem but put as big of a tire as they possibly can under the car and it seems to work pretty well.

If you think about it, the 1600lb CRXs run the same size tire a 2400lb GSR does. There's no way the GSR is even going to come close to the times of the 1600lb CSP car, and the top DSP guys were running CSP CRX times this year.

As for Hoosier Tom-- he's all about himself and I don't think the guy has driven a car in years. Times change, but he doesn't seem to. What may have worked in 1993 doesn't mean it is still the best thing to have today.

If the R ever got put into DSP, you can bet that I'd show up on 15's or 16's because we all know cornering speed is much more important that straight-line speed on any autox course.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by rodney &raquo;</TD></TR><TR><TD CLASS="quote">i had an arguement with hoosier tom about this. (i ended up walking away from him vowing to never buy anything from that dick.. )</TD></TR></TABLE>

I laughed out loud at this.

And to Todd00000, yeah, ultimately cornering speed is the #1 priority.
But, with all those ground pounding ponies my little motor makes,
I need to get back up to full speed and the tiny 13s are what makes that happen.

And they look cool, too.

 

eeeppppp, the argument differs for you since you weigh what, 900 lbs now? also, with the larger tire on the heavier car means that you have more rubber to heat up, hopefully not overheating the tires as quickly......i think....i dunno....i run 15s, and have contemplated 16s since it's hard for me to find relatively inexpensive 7.5 in 15s.

 

Well, what's better?

Not as wide HOT sticky rubber, or wider COLD rubber?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Eee Pee &raquo;</TD></TR><TR><TD CLASS="quote">Well, what's better?

Not as wide HOT sticky rubber, or wider COLD rubber?</TD></TR></TABLE>

On your car, you want 13's due to car weight and those 'unique' Prep. rules. Plus, pure slicks are a different ballgame.

On something like a 2400lb GSR or 2200lb hatch, you'll get plenty of heat into a 15" tire and you won't have the odd camber wear.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Eee Pee &raquo;</TD></TR><TR><TD CLASS="quote">And to Todd00000, yeah, ultimately cornering speed is the #1 priority.
But, with all those ground pounding ponies my little motor makes,
I need to get back up to full speed and the tiny 13s are what makes that happen.

And they look cool, too.</TD></TR></TABLE>

how can you compare your slick shod 100hp, 1700lb car to chris' DOT shod 180hp 2300lb car? very different animals. and what are you talking about getting _back_ up to speed???? what are you braking for!

nate

 

Ever take tire temps?

My front slicks get up to about 120-125 degrees. Those were the "too soft" compound.
Not even close to warmed up...

What about those R compounds? Any hotter?

Gotta lightly brake on asphault. And those st0opid 180* hairpins.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Todd00 &raquo;</TD></TR><TR><TD CLASS="quote">This is why I disagree with the tire choice that the DSP Integras run, regardless of their gearing issues.

If the R ever got put into DSP, you can bet that I'd show up on 15's or 16's because we all know cornering speed is much more important that straight-line speed on any autox course.</TD></TR></TABLE>

Todd00, have you ever driven a GSR at an autocross on both 13's and 15's? Having much experience driving both setups I can tell you without a doubt that the 13's are faster in every case except for corvette style courses (nothing but straights).

To keep on topic running a SM civic I would never run anything less then 15's. I drove a LS/Vtec SM civic putting out 200whp with an ITR tanny and I can say the gears were just to short for that much HP and gear ratio. If it were my car I would go about trying to fit some 245/45/16 hoosiers on it. But then again what do I know, I but 13's on a GSR

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Geratol &raquo;</TD></TR><TR><TD CLASS="quote">

If it were my car I would go about trying to fit some 245/45/16 hoosiers on it. But then again what do I know, I but 13's on a GSR </TD></TR></TABLE>

lol... i wish. if i could find a 5.2 final drive, or a 245/40 or 245/35-16 i would be all over it. a 245/45-16 would ruin my car.... would look cool though

 

&gt;&gt;running a SM civic I would never run anything less then 15's. I drove a LS/Vtec SM civic putting out 200whp with an ITR tanny and I can say the gears were just to short for that much HP and gear ratio.&lt;&lt;

In SM, it's legal to swap FD ratios, gears, etc. to get the ideal ratio. So, assuming my gear ratios would be "ideal" either way, what are the benefits of a larger wheel?

I guess the shape of the contact patch is the most concrete advantage so far. But I wonder if it offsets the additional unsprung, rotating weight. And what about the higher COG as a result? Other than additional sidewall flex, how about a 15" wheel compared to a 13" wheel with a taller tire (like the 225/50)?