I know this is vague, but Tire Rack's data isn't organized to show what's common and what isn't.

What I'm doing is designing Kimini's successor. This time I'll be using 15, 16, or 17 inch wheels, due to availability issues with anything smaller. The big question is, what's a very common tire diameter? I have a feeling it's about 23", but you guys know and use tires in this size and I don't.

I'm hoping people come on and say, "I needed tires of this size, 'X', and found that there's ton's of them out there", or, "This size is hard to find." Right now I'm only concerned about tire diameter, not width or aspect ratio.

Any ideas? I'm looking into this myself but thought I'd ask here first. The last thing I want to hear when it's done is, "Duuuude, you should have used this size tire, instead, yours are hard to find."


Modified by kb58 at 5:58 PM 12/17/2007

 

I don't think there is a single diameter that's most popular. If anything, it's changing over time, as wheels and tires tend to get larger in diameter. For example, look at the Honda Civic, one of the most popular cars on the road for many years. Prior to 1996, most Civics came with 175/70-13 tires, which have a calculated outer diameter of 22.65 inches. For '97-00, most came with 185/65-14 tires, 23.47" diameter. For '01-05, most came with 185/70-14 tires, 24.20" diameter. For '06-present, most came with 205/55-16 tires, 24.88" diameter, or 215/45-17, 24.62" diameter.

You can do the same analysis on any model you like. The Tire Rack website lets you look up the stock tire size for a given year/model/version, and you can find out its diameter using a tire calculator like this one.

One way to measure a particular tire size's popularity is how many tires are available in that size. You can look that up on the Tire Rack website, too; for example, 76 tires are listed in 215/45-17, which means it's one of the most common sizes.

I've noticed that more and more top-of-the-line tires are no longer available in very many, sometimes any, 15" or smaller sizes.

 

Yeah I know I'm aiming at a moving target; today's hot tires are tomorrow's dogs. Still, I have a hard time believing that in 10 years we'll all be riding on 37" wheels. God, I hope not.

I guess I have to aim toward the larger size, 17" maybe, much as I hate the cost, weight, and PMOI.

 

You would almost think that 15s are more or less going to be phased out by 16s b/c cars aren't really getting much lighter these days and in fact heavier b/c they have more parts/safety and require larger diameter brakes.. . Not to mention more style!

16s are slowly gaining more options but I'd say most new cars are 17s as NSXtasy pointed out the number of options one has in the 215/45/17

How wide of a tire do you think you need?

 

25" diameter, plus or minus 1/2". 17" wheels seem to have the highest number of options with 18's a close second.

 

I spend some of my employer's time this morning running through TireRace's tire data screens, and I agree that 25" appears to be very common.

Kinda stucks, though, as they weigh more, cost more, and the wheels are heavier and expensive, but so it goes.

Thanks for the input, guys.

 

Any hints as to what your next project will be? Will it be Honda powered?

 

Tire Stagger ftw

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by ekim952522000 &raquo;</TD></TR><TR><TD CLASS="quote">Any hints as to what your next project will be? Will it be Honda powered?</TD></TR></TABLE>
At the moment, a Honda product is at the top of the list of possible donor drivetrains

 

Can we get a clue as to the power, downforce and weight of this project? If you do something light enough, it might just make sense to stay smaller.

As a point of reference, going from 225/45 R15 to 235/40 R17 on my Prelude gave me some advantage (about a second at a couple tracks) and definitely improved consistancy across a 35 minute race.

You might also consider brake options.

-Chris, presumptuous enough to ignore your original question... but mostly because I don't have a solid answer.

 

200-250whp, no downforce, very, very light. I agree a big-*** wide tire isn't needed, but if smaller (diameter) ones are hard to get, it doesn't really matter. I can go a little narrower to help weight and PMOI, but the current thinking is that I'm pretty much stuck with 17s simply for future availability. If this was for track only, hell, I could stick with 13s, but as it'll be street-legal, too, needing both means going up in size. 15" seems to be on the way out already. For what I'm planning, it's important that the tires be around for years, in both track and street compounds.

The Ariel Atom uses 185s in a 14" size. Great for low weight, but it sucks for any sort of selection. Very surprising they didn't at least go with 15s.

Thanks for the data point about the lap time improvement; it helps me adjust to the fact that larger wheels/tires don't always slow down a car. While 17s are almost always heavier than smaller sizes, the larger OD gives a larger contact patch for improved traction.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by kb58 &raquo;</TD></TR><TR><TD CLASS="quote">the larger OD gives a larger contact patch for improved traction.</TD></TR></TABLE>

Nope. It gives a wider contact patch, but the size (area) of the contact patch remains the same. The size of the contact patch is determined by the weight of the car and the air pressure in the tires. If you have a 2640-pound Integra Type R and you inflate the tires to 33 pounds per square inch, the size of the four contact patches will total 80 square inches - and that number will be the same regardless of whether you have skinny 185 treadwidth donuts or 235 treadwidth steamrollers, and regardless of whether your outer diameter is 22" low rider style or 25" cram everything you can in the wheel wells style.

You can read more about it in this article.

 

I tend to figure things out by taking them to an extreme. So if I put, say, 120" (10-foot) diameter tires on my car, I have a hard time believing that the large radius isn't going to cause a larger portion of the circumference to touch the ground. No?

Even if the above is somehow wrong, with larger tires I'm certainly going to run lower air pressure, which will increase the contact area. AFAIK, no one runs the same tire pressure when increasing tire size, so while, in theory, what was said might be true, I don't think it's reality.

The example given sounds a lot like something from high school physics, where no one has to worry about proper tire temperatures...

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by kb58 &raquo;</TD></TR><TR><TD CLASS="quote">
The example given sounds a lot like something from high school physics, where no one has to worry about proper tire temperatures...</TD></TR></TABLE>

yeah, no crap right! A toyo RA1 205/50/15 still needs to be around 200deg the same as a 275/35/15 to operate optimally.

I did like that read on tires though. That website has a ton of good articles. Thanks for sharing nsxtasy

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by kb58 &raquo;</TD></TR><TR><TD CLASS="quote">I tend to figure things out by taking them to an extreme.</TD></TR></TABLE>

Taking things to an extreme won't work. Lower the air pressure in your tires to zero and theoretically your contact patch should be infinite. Obviously, it isn't.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by kb58 &raquo;</TD></TR><TR><TD CLASS="quote">I have a hard time believing that the large radius isn't going to cause a larger portion of the circumference to touch the ground. No?</TD></TR></TABLE>

With realistic numbers, no. As the tread width increases, the contact patch gets wider (side to side) but narrower (front to rear), leaving the area the same (if the air pressure is the same):



The wider shape can be an advantage in cornering and in tire cooling, as explained in the article.

The nice folks at the Tire Rack have actually measured the size of the contact patch with various width tires on the same car with the same pressure in the tires. They have found that the differences in size are smaller than their measurement error, which is about 2 percent.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by kb58 &raquo;</TD></TR><TR><TD CLASS="quote">with larger tires I'm certainly going to run lower air pressure, which will increase the contact area. AFAIK, no one runs the same tire pressure when increasing tire size, so while, in theory, what was said might be true, I don't think it's reality.</TD></TR></TABLE>

I've never heard anyone recommend lower air pressures with larger tires. In fact, if anything pressures are sometimes higher with larger tires. For example, Hoosier's recommendations are for higher pressures with heavier vehicles, which typically use larger tires.

If you want to play around with pressures and see what works best, get a pyrometer (Harbor Freight has some inexpensive laser thermometers, basically the same thing) and check the temperatures across the tread after a hot session. You're looking for roughly equal temperatures in the middle vs the edges.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by nsxtasy &raquo;</TD></TR><TR><TD CLASS="quote">
Lower the air pressure in your tires to zero and theoretically your contact patch should be infinite. Obviously, it isn't.
</TD></TR></TABLE>
Correct, but it does increase due to being deformed into a D-shape by the weight of the car.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by nsxtasy &raquo;</TD></TR><TR><TD CLASS="quote">
I've never heard anyone recommend lower air pressures with larger tires. In fact, if anything pressures are sometimes higher with larger tires. For example, Hoosier's recommendations are for higher pressures with heavier vehicles, which typically use larger tires.
</TD></TR></TABLE>

And logically, lower pressure for lighter vehicles. A wider tire's going to have a longer transverse distance to bulge the tire outward for a given tire pressure. I would expect for the same pressure, a wider tire will run hotter in the center due to this, hence lowering the pressure to even it out.

I'm currently running 18lbs in 215/50-13 tires. If I installed 275/30-13 (if there were such a thing) I'd expect to have to lower the pressure. As said above, another reason to lower pressure is to get the larger tire up to the same operating temperature as the narrower one.

Or, maybe I'm completely wrong.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by kb58 &raquo;</TD></TR><TR><TD CLASS="quote">I'm currently running 18lbs in 215/50-13 tires. If I installed 275/30-13 (if there were such a thing) I'd expect to have to lower the pressure. As said above, another reason to lower pressure is to get the larger tire up to the same operating temperature as the narrower one.

Or, maybe I'm completely wrong.</TD></TR></TABLE>

Maybe.

Are you running these tires on the dragstrip, or on the racetrack? I assume the latter (since we're in the road racing forum, not the dragstrip forum). 18 psi is a really, really low pressure for track use, even if you're talking about measuring it cold. Granted, different tires and different cars require different pressures. But most people I know are trying to achieve hot pressures anywhere from 35 to 45 psi, and set their cold pressures typically 25-35 psi. I've never heard of anyone using 18 psi. Have you used a pyrometer with those pressures? What were your temperatures from one side to the other?

 

Road-racing, or as much as a trackday can be considered "racing."

The car weighs 1600lbs, with 40/60 f/r weight distribution. I'm running Kumho V710s, 215/50-13s. Locosts (Lotus Super-7 type cars) typically weigh about 1100-1400lbs, and they run pressures of 15-20psi, so I don't think I'm out of line.

I ran across an excellent article by Mark Ortiz, discussing tire width, but much of it applies to this situation here.
http://www.2kgt.com/MarkOrtiz/2004_9_10_11.pdf The pertinent info starts about 25% into the newsletter. The key part is:

"for a given static deflection or tire spring rate, a wide tire needs a lower inflation pressure. Consequently, if we compare wide and narrow tires at similar static deflection or tire spring rate, rather than similar pressure, they will have similar-length contact patches and the wider one really will have more rubber on the road, just as we would intuitively suppose from looking at them."

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by kb58 &raquo;</TD></TR><TR><TD CLASS="quote">"for a given static deflection or tire spring rate, a wide tire needs a lower inflation pressure. Consequently, if we compare wide and narrow tires at similar static deflection or tire spring rate, rather than similar pressure, they will have similar-length contact patches and the wider one really will have more rubber on the road, just as we would intuitively suppose from looking at them."
</TD></TR></TABLE>

If you use a lower pressure, yes, the contact patch will be larger. But it's larger because of the lower pressure, not because of the fact that it's wider.

Incidentally, the increase in size of the contact patch is why drag racers use extremely low tire pressures.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by nsxtasy &raquo;</TD></TR><TR><TD CLASS="quote">
If you use a lower pressure, yes, the contact patch will be larger. But it's larger because of the lower pressure, not because of the fact that it's wider.
</TD></TR></TABLE>

Yes, but Ken, if you doubled the width of your tires (yeah, a 410/25 R15), wouldn't you, couldn't you, halve the air pressure to get about the same sidewall deflection and same "spring rate" of the tire/road interaction? Yes, another extreeeem example...

Taller tires give me more rubber surface area to absorb and dissipate heat.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Chris F &raquo;</TD></TR><TR><TD CLASS="quote">Yes, but Ken, if you doubled the width of your tires (yeah, a 410/25 R15), wouldn't you, couldn't you, halve the air pressure to get about the same sidewall deflection and same "spring rate" of the tire/road interaction? Yes, another extreeeem example...</TD></TR></TABLE>

If you create extreme examples, you can find the limits of the rule. If you can fit 410/25-15 tires on your car, I wanna see it. They might rub off the flame stickers.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Chris F &raquo;</TD></TR><TR><TD CLASS="quote">Taller tires give me more rubber surface area to absorb and dissipate heat.</TD></TR></TABLE>

Sounds like someone read the article. (NOT the same thing as a larger contact patch though.)

So, when are we gonna do lunch with all the guys?

 

Here's another good article:
http://www.2kgt.com/MarkOrtiz/...7.doc

The tire discussion starts about 30% down.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Chris F &raquo;</TD></TR><TR><TD CLASS="quote">
As a point of reference, going from 225/45 R15 to 235/40 R17 on my Prelude gave me some advantage (about a second at a couple tracks) and definitely improved consistancy across a 35 minute race.
</TD></TR></TABLE>

Sorry to hijack a little here, but Chris, what did you do with your tire pressures when you moved from the 225's to the 235's? When I went from 205/50-15s to 225/45-15 RA-1s, I noticed that the "fast" hot pressures went from about 38-ish for the 205's to about 34-ish for the 225's. Did you see a similar drop going to the 235's?

 

You should run the lightest tire/wheel combination possible that will put the power down you have available. 17" wheels and tires weigh a ton more than 15" tires and wheels. But if you're driving a 2009 Corvette 620 HP ZR-1, 15" tires are just not going to cut it. A 225/45/15 is a nice size and weight tire.

Now who has the best explanation as to why wider tires have more grip given the same contact patch area?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by descartesfool &raquo;</TD></TR><TR><TD CLASS="quote">if you're driving a 2009 Corvette 620 HP ZR-1</TD></TR></TABLE>

Sounds like I'm not the only one who read the Autoweek which arrived today.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by descartesfool &raquo;</TD></TR><TR><TD CLASS="quote">Now who has the best explanation as to why wider tires have more grip given the same contact patch area?</TD></TR></TABLE>

I think the one in the article to which I posted the link is pretty good.