Wheel/tire combo addressing fitment and heat issues

[RedAutobotMX3]

I'm looking at some Enkei RPF-1's in black for my GS and the bottom line issue I keep coming back to is the size. Undoubtedly, I would prefer them in 15" as their about 5lbs lighter at each corner than my stock enkei's that came with the car, but 16" would allow for more show, bigger tires (215/50/16), and most likely help relieve all the built up heat. The down side being heavier (although still lighter than the stock rims) and with my car recently being lowered about 1.5" all around(and confirmed that a 205/65/15 wont even fit on the vehicle, wrong winter tires) I have a lingering fitment issue i'd rather not have to face that certainly wouldnt be an issue if i end up with the 15's.
I will be doing mostly autocross(3-4 times a month), a few trips to the drag strip, and possibly a track day or two this coming season at our local places, but the autoX has me worried. I've done enough crossing (not in my mazda) to know that things get real Effin hot when you're able to do more than one run within a few minutes of each other and my paranoia is growing that perhaps 15" would not help that situation. I understand the wheels i have on their now are very closed and the RPF1's are alot more open, I just don't want the wheels being affected by an overabundance of heat cycling, as i don't know how the GS will handle a full summers afternoon of conekilling.
I'm not planning a BBK, atleast not for a WHILE, but do plan on replacing my rotors and pads w/ slotted ones and tougher pads when those currently on the car start to go. Certainly the slotted rotors will help expel the hot gases produced by the heavy and hard braking, but will all the heat have an adverse affect on the wheels themselves? Enkei's are reputable, but its such a huge investment, i wanna get it right the first time.

Long story short, convince me that 15" is fine for my applications, and that im worrying about nothing. I'm fairly certain there are other Autox'ers on here that run a 15" wheel; I'd love to hear some first person experiences. Also, what tire size do the masses on here prefer? My choice for the poll is option 3 If i have my way; i dont think 215 is too fat to fit.

[solo_ryder]

For the race-type person 15-16" is usually used on a MX3. You have to realize though that if you get 15's, yes they are lighter rim wise, but you will be adding more sidewall which = more weight on the tire then a 16" tire. You can run a 204 45 on a 16" rim as well, that is more common then a 205 50 (at least for mx guys) but I prefer my 205/50's

But for someone that doesn't race or auto-x I cannot really comment on what performs better, but from what I have read 15" is a good option with plenty tire sizes available to use (you can get some sticky 205 50's). However, IMO, 15s look kinda of out of place just because of the size of the wheel wells and the stock tire size is pretty large...

[RedAutobotMX3]

yes they are lighter rim wise, but you will be adding more sidewall which = more weight on the tire then a 16" tire.

I'm not too worried about tire weight, as all the ones im looking at are right around 20lbs regardless of size. Also, i dont think the drivetrain is really affected by whats gripping for said acceleration. Sure you're spinning that weight, but its negligible since its applying the force of friction onto the pavement.
Im worried 16's wont fit since my 15's with a 205/65 wouldnt even get on the wheel hub.

[Ryan]

Man, the tire weight is MORE important concerning rotational inertia... its further from the axis of rotation. A 1 lb difference in rim may have the same inertia as a 0.2 lb difference in tire.

Not saying this should affect your choices too much, just don't say the tire weight is negligible.

[solo_ryder]

Your worried about 16" fitment? Man 205 65 is two profiles larger then stock no wonder your having issues. I am running 205 50 16 and I have the lowest car on the site and I don't have rubbing issues.. Even under extreme conering

[RedAutobotMX3]

I really feel the tire weight isnt the important issue here. Tires will wear, potentially decreasing their weight, so that's neither here nor there. Tirerack lists tire weights, but i dont think the info is based on size, rather a base unit for each brand/tread.

The 205/65's were on my 15's. now thats a total diameter, with tire on the rim, at just about 515mm. 25.4mm x 15" +(205x.65)
16's with a 215/45/ would equal 503mm

515-503 = 12mm, or roughly a half inch less than a combo that would not fit on my car AT ALL. I do not think 16's will fit after having seen the snowies hit the bottom of my strut with the car off the ground.

Please correct me if im not doing my math right.

[Inodoro Pereyra]

I'm not too worried about tire weight, as all the ones im looking at are right around 20lbs regardless of size. Also, i dont think the drivetrain is really affected by whats gripping for said acceleration.

Sorry, but you're dead wrong. Tire and rim weight affect grip in 2 different ways: Rotational inertia, and vertical inertia, as part of the car's unsprung weight.
As Ryan accurately said, when it comes to rotational inertia, the TIRE is the most important part of the equation, as it has the highest momentum in the whole assembly.
When it comes to vertical inertia, the tire weight is just as important as any other unsprung part in the car, as it contributes, with the rest of the car's unsprung parts, to make the wheels bounce off the floor.

[Ryan]

For your physics learning:

http://www.youtube.com/watch?v=7PRZ5IIT5Tg
http://www.youtube.com/watch?v=fHDB7PMUdZE


And you can find many many websites that will find overall diameters for you, calculate how far your speedometer will be off... etc..

[RedAutobotMX3]

If i had enough information from each tire manufacturer for weight on each specific size and tread i was looking at, sure id try and find the lightest combo. BUT I DONT, can we stop harping on the tire weight now? I'm more interested in fitment and heat issues, regardless of whether my initial thoughts on the subject were wrong, which they were and im man enough to admit that. I just dont care as much seeing as how that variable is out of my control atm.

[Ryan]

Bottom line is unless you're a hardcore autox guy, it comes down to only a few things to consider:

-what profile looks best
-what is affordable (some sizes are just cheap, others are expensive)
-ride comfort (sidewall thickness plays a big roll)
-if an accurate speedometer is important to you or not.

[solo_ryder]

I really feel the tire weight isnt the important issue here. Tires will wear, potentially decreasing their weight, so that's neither here nor there. Tirerack lists tire weights, but i dont think the info is based on size, rather a base unit for each brand/tread.

The 205/65's were on my 15's. now thats a total diameter, with tire on the rim, at just about 515mm. 25.4mm x 15" +(205x.65)
16's with a 215/45/ would equal 503mm

515-503 = 12mm, or roughly a half inch less than a combo that would not fit on my car AT ALL. I do not think 16's will fit after having seen the snowies hit the bottom of my strut with the car off the ground.

Please correct me if im not doing my math right.

Just to put into perspective:

Stock 205 55 15:
Sidewall 4.4"

Yours 205 65 15:
Sidewall 5.2"

That is nearly 1" more tire on the car, no wonder it was rubbing.. If you got a 215 45 you would be at:

3.8" sidewall, but the circumference is 74.2 which is close to the 75" of the stock tire. 205 65 15 is 80.1"

[RedAutobotMX3]

ust to put into perspective:

Stock 205 55 15:
Sidewall 4.4"

Yours 205 65 15:
Sidewall 5.2"

That is nearly 1" more tire on the car, no wonder it was rubbing.. If you got a 215 45 you would be at:

3.8" sidewall, but the circumference is 74.2 which is close to the 75" of the stock tire. 205 65 15 is 80.1"

stock sidewall w/ wheel would be 19.4"
215/45/16 would be 19.8, just .3 inches smaller than the 205/65's in overall diameter. Also, they didnt RUB, they wouldn't even get on the wheel hub because the tire was literally up against the side of the bottom spring seat (or bottom of the strut)

unless you're a hardcore autox guy, it comes down to only a few things to consider:

-what profile looks best
-what is affordable (some sizes are just cheap, others are expensive)
-ride comfort (sidewall thickness plays a big roll)
-if an accurate speedometer is important to you or not.

3-4 times a month is pretty serious, no? Other than the visual appeal of the 16", im not concerned with any of the aforementioned issues such as the speedo being off, ride comfort, or price. Im worried about getting the biggest tire that will fit, and making sure i dont have tons of brake fade going around the course a few times cause its all stuck in the wheel.

[solo_ryder]

If 215 45 won't fit then why can I fit a larger 205 50 16 on my car?

Just because the rim is larger doesn't mean the profile of a tire stays the same. A 50 series 15 is gonna have a larger sidewall then a 50 series 16" tire. 215 45 Will fit.

Your balloon 65 series was the issue.

[Inodoro Pereyra]

stock sidewall w/ wheel would be 19.4"
215/45/16 would be 19.8, just .3 inches smaller than the 205/65's in overall diameter. Also, they didnt RUB, they wouldn't even get on the wheel hub because the tire was literally up against the side of the bottom spring seat (or bottom of the strut)

Nope.
RS's stock wheel (185/65R14) is 23.5" diameter.
GS's stock wheel (205/55R15 is 23.9" diameter.

Your 205/65R15 is 25.5" diameter. That is, as Solo said, a full 2 inches bigger diameter (1" radius) than the stock RS's tire, or 1.6" bigger diameter than the GS's tire.

[Sleeper6]

wow lots of talk about size and inertia.. ever think about sidewall strength when your considering auto-x and jumping sizes from 15 to 16s with obvious sidewall differences? Thats going to have a big role in your overall handling but thats just my 2 cents and Ill let you think on what you want to do...