2004-2007 Cadillac CTS-V General Discussion Discussion, I found a set of used tires-will they fit? in Cadillac CTS-V Series Forum - 2004 - 2007; They are 255/35/zr18 90w will they fit my V1? They are only 500.00 for four with wheels...

- 04-06-13 01:44 AM #1Cadillac Owners Member
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## I found a set of used tires-will they fit?

They are 255/35/zr18 90w will they fit my V1? They are only 500.00 for four with wheels

- 04-06-13 02:57 AM #2
## Re: I found a set of used tires-will they fit?

nope, not at all.

where can i find this sale, though :-D

just kidding, I'll bite: that sounds like the right size. are you saying they are already mounted on wheels, and it's all $500? (what wheels are they?)

they're lower profile than stock (I'm using 245/45/18), but they'll fit. meaning the total height of the wheel and tire as it's mounted, will be shorter. affects your speedometer reading, and torque, and top speed.

first number 255 is the width, second is the height of the sidewall (as a percentage of the width, I think), and last is... the diameter of the wheel it's supposed to fit on.

might be the same height sidewall, since the width is bigger than what I've got (245)

if i'm wrong, people will log in to slay me on the forums. just stay tuned. - 04-06-13 04:08 AM #3
Slayed.

Will they fit? Yes.

Will they look ridiculous? Yes.

That is a full 2 steps down in aspect ratio. My V with slicks that were 1 down looked noticeably smaller... - 04-06-13 04:29 AM #4
## Re: I found a set of used tires-will they fit?

GUAHH!

(though I think you mean slain)

maybe it has a tread pattern he likes - 04-06-13 09:18 AM #5
## Re: I found a set of used tires-will they fit?

Will they physically fit on your car? Yes. Are they the right size? No, not even close.

http://www.rimsntires.com/specs.jsp

Not to mention the load rating is very low compared to stock.'05 Stealth Grey CTS-V, 19x8.5/10" CCW T140s with Toyo Proxes T1 Sports (summer), black Team Dynamics ProRace 1.2 wheels with 275/35-18 R-compounds (track), Hyperblack Rota Torques (winter), KW Variant3s, V2 front brakes, Hotchkis rear sway bar, EPS cam, TEA-ported 243 heads, FAST92 intake w/LS2 TB, JBA Camaro/G8 1-3/4" shorty headers w/JBA cat pipes, Corsa exhaust, UUC motor and tranny mounts, UUC shifter, MAPerformance trailing arms, Specter cradle bushings, etc... - 04-06-13 11:47 AM #6Cadillac Owners Enthusiast
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- 04-06-13 05:05 PM #7
## Re: I found a set of used tires-will they fit?

will do this:

(in no particular order)

lower your car,

your shift points will arrive faster

speedometer reading will be inaccurate

lower your top speed

increase torque-iness

increase gap with top of wheel well

make ride harsher

brakes will feel grabbier (closer to outside of tire radius = more mechanical leverage)

car is lowered .825 inches

1/2 x (stock tire height->26.68in - 25.03in<-new tire height)

final gear ratios (speedo, speeds, torque-iness) will be affected by 6.18%

(stock tire circumference->83.77in - 78.59in<-new tire circumference) ÷ 83.77in = 6.18%

will feel like +24 ft/lbs of torque at motor

...readout will be higher than actual speed by 3mph every 50mph...

25mph = 23.5mph,

50mph = 47mph,

100mph = 94mph

correction: brake grabiness increases by 6.199% <-I'm not sure if the braking benefit is the percentage difference between stock and smaller radius, I have a feeling it might not be. but if it IS:

braking characteristics of the car goes from 1.06g -> 1.125g

which is equivalent to WRX-STI

and good for 10 to 12 feet better 100-0 stopping distance - 04-06-13 07:53 PM #8Cadillac Owners Connoisseur
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## Re: I found a set of used tires-will they fit?

wow that's an amazingly complete answer post!

- 04-06-13 08:14 PM #9
## Re: I found a set of used tires-will they fit?

I'm glad you like it! I'm taking physics right now, and I love it~! (pre-engineering)

I would love to be proven wrong by an automotive engineer (any engineer, or physicist)... their advice tends to come with a mathematical explanation and I love that shit.

I don't think I want to work in the automotive industry, but I love me sum physics

at some point the motor loses the mechanical leverage benefit to the higher speed the drive train and shorter wheel/tire needs to rotate compared to the stock wheel/tire, and kinetic energy isn't linear; it's proportional to the square of its speed... (and it's the same wheel--it didn't lose 6% of mass to compensate for the 6% reduced circumference, and if it did, the whole rotating assembly(the system) would need to shrink proportionally (and it hasn't, it's the same wheel/disc/lugs/hub))

(similar mass/linear energy, but higher rotational energy of the smaller wheels.. to the order of +6%*squared*x 1/2...*x 4 wheels*... and now the motor has to push that~)

convert it all into newtons, and you see why the engine tops out after succumbing to air friction and rotating mass...

physics is ****ing beautiful. it's divine

according to the CIA world factbook, America is one of three remaining countries in the WORLD that hasn't adopted the metric/international standard (SI) system. Burma, Liberia, and us. That should bother you. the Brits moved to SI after we rebelled, but we never made the change (Sir Isaac Newton lived 1642 – 1727, which is telling)...

I think we're gimping ourselves by using inches and pounds, rather than the measurement system of Physics (SI)... no doubt in my mind America is denying its school-going youth, the experience of discovering Physics (and the units they're accustomed to using, "clicking" together so beautifully).

International System of Units

I might've taken an interest in school as a teen and not run off into the military at 18, and then spent my 20s there. Not that I'd do anything differently if I had the choice, but at the time I had no idea Physics could explain the world around me better than any answers I found in the last decade.

the reason why not switch to SI includes the cost of road signs etc. and all the infrastructure that uses pounds and inches... but I think TX as a state can handle the cost locally, I think we should secede*and*switch to SI.

//the important thing isn't whether I'm right, it's that I'm open to being wrong and interested in knowing what's right. - 04-07-13 12:02 AM #10
- 04-07-13 07:54 AM #11
## Re: I found a set of used tires-will they fit?

I've got it.

*assuming*the wheel is 22 lbs and the weight is evenly distributed, the shorter height wheel and tire combo requires 3*additional horsepower per wheel*at 60mph, and that's pretty close to 6%...

I'm going to bet that had my estimations been more accurate, it would more strongly support the 6% figure, and show the net hp to "feel like -24 hp at the motor"

since the wheels are about the same weight but shorter, they require more horsepower to turn at a given speed compared to stock height, due to the increase in radians per second (radians = how many times does the wheel roll the distance of its radius. at 62 mph or 100 km/h, it's 82 times a second for the stock wheel, and 87.5 times a second for the shorter wheel... and those figures are later squared, and that's where the seemingly slight 6% difference becomes significant ...the difference of 5.5 radians is 6.28% of 87.5 radians)

stock wheel has 5563 Joules @100km/h (3864 Joules kinetic + 1699 Joules rotational)

short wheel has 5805 Joules @100km/h (3864 Joules kinetic + 1941 Joules rotational)

this is an increase in 242 Joules, or 242 kg x meters squared x seconds squared @62 mph or 100 kmh

which is equal to 178 lb/ft, (trust me)

and 1 horsepower is 550 lb/ft per second, so

550 foot pounds / 178 foot pounds = 3.08 hp. per wheel. required @62 mph or 100 kmh

so. it will feel like +24 ft/lbs of torque, and*a loss*of 24 hp at the motor.

stock top speed of 163 mph is reduced to 153 mph.

because the shorter wheel/tire combo needs to spin faster,

and the energy required to do that compared to stock is increased by 1/2 of +6% ...*squared*.

...yes if you note the time of the post it's 4:30 AM... this wheel problem has been killing me all day (it took me all day because rotational energy is next week's chapter or the week after that, and new concepts are accompanied by a 3-hour practical lab). Lucky for me, all I have going on this weekend is studying for an algebra exam Monday and a Physics exam Tuesday.

//tbjs, I'm going to bet you know what your "top-out" speed on your slicks is, compared to your stock tires, and that it's 3-4% lower with those 40 series slicks... possibly 5% since the rubber is heavier. (am I right ) - 04-07-13 09:07 AM #12Cadillac Owners Fanatic
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It's awesome to see someone who enjoys what they are doing! Glad you like physics... And are here to give us the math & science behind our car questions!!

It's also refreshing for someone to be open to the possibility of being wrong !!!

Great thread so far - 04-07-13 11:33 AM #13Banned
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## Re: I found a set of used tires-will they fit?

245/45 is 110.25mm sidewall height.

255/35 is 89.25mm sidewall height.

So yeah, they'll work. Your speedometer will be off, and you'll have wheel gap, but if you're in a pinch and need tires, I'd probably go ahead and check craigslist before I did anything, tbh. People sell solid used tires for 30-50 bucks each constantly. - 04-07-13 01:15 PM #14Cadillac Owners Enthusiast
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Way too much math/physics in this thread... I just trust the ol butt dyno, my ass never lies. And gauges of course. I love me gauges to see what the car is doing.

- 04-07-13 11:54 PM #15
## Re: I found a set of used tires-will they fit?

math city

math math city

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