Im about to throw tires on my rims,and i know Stock is P215/65R-15 and i wanna put P275/60R-15 on my rims for the rear tires since i got a deal on them and already bought them.Does anyone know if they might not fit on the rim for some reason?Thanks a lot..Al in NJ

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86 Trans Am 305 TPI,Bored 30 over,Blower Cam,Fordged Racing Pistons,High Volume Oil Pump,3" Flowmaster Exhaust,Hypetech Coil,Acell 300+ Race Wires,Bosch Platinum +4 Plugs.Best Et was 12.5 with a Paxton.

 

[Edited because ws6formula is a dumbass at 6 o'clock in the morning...my god have mercy on his soul.]

[This message has been edited by ws6formula89 (edited June 22, 2001).]

 

I run P275/60r15's on 15x8 rims in the back.. I didn't want to chance 'em on 15x7 rims... it's a wide tire. Also, the P275's are taller than the P215's, not the other way around.

P215/65r15 height: 215 / 25 = 8.6 inches wide
8.6 * 0.65 = 5.59 sidewall height
(5.59 * 2) + 15 = 26.18 tire height (two sidewalls with 15" rim)

P275/60r15 height: 275 / 25 = 11 inches wide
11 * 0.60 = 6.6 sidewall height
(6.6 * 2) + 15 = 28.2" inches tall

This is going to lower your effective rear gear ratio. This will raise your top speed, but make you're 0-60 and 1/4 mile time a bit slower. Effective rear gear ratio equation: ((rear gear) * (old tire)) / (new tire)

So if I had 3.42 gears..

(3.42) * (26.18) = 89.5356 ; 89.5356 / 28.2 = 3.175 ; my effective rear gear ratio would be a 3.18. So with the new larger rear tires, your car will feel exactly the same as if you changed the rear gears from 3.42's to 3.18's. This is one of the reasons I put a 3.73 axle into my car... that makes my effective gear ratio into a 3.46. My original axle held 3.42 rear gears. I also see wheelspin decreasing, since a tire's footprint on the track is judged both by tire width AND tire height.

Oh and with this combo, it's the other way; speedometer will be running "slower" than you're going. Ex- you "think" you're doing 55 mph, but you're really doing 59. Keep that in mind when you see a cop. If you want to play with these numbers, visit http://www.tolan-hoechst.com/cars/tirecalc.htm for a calculator. Make sure that in the
"Engine rpms with ??? differential gear and ??? transmission gear ratio" you change that .7 for whatever gear you want... like, in 3rd gear for an automatic, it's 1.0.

[edit] Oh, almost forgot- your wheel well lip will most likely scrape the sidewalls. I run air shocks to correct this problem. I had the air shocks lowered this winter in the snow, and forgot- I backed out of a driveway quickly, and my tire ripped into the wheelwell- it bent the wheelwell, and the wheelwell took a nice bite out of my tire.

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-Tom P (Hot rodded 1986 Firebird 2.8l) from http://www.f-body.net/mailbag/3rd/3rd_mailbag.html message boards
---Think your car could be pic of the week? Visit http://www.f-body.net for details!

[This message has been edited by TomP (edited June 22, 2001).]

 

JEEZ! I guess I didn't read his question good enough, maybe I'm dyslexic? I got the 2 tire sizes confused. I was thinking he wanted a shorter/wider tire instead of his tall/skinny tire. But in fact...his original tire is shorter than the one he's getting! Gosh, now I feel dumb.

Yes, the speedometer function will be reading lower than you are actually going. But with me being mixed up, it put all my answers backwards. The final ratio will be higher if you get a taller tire, (not contradicting you tom....i.e., 3.42 -> 3.18, that's what I'm saying too.). It was like 6 in the morning here, what can I say, I'm a 'tard in the mornings. Sorry for any confusion. I know this stuff...but I can't comprehend it at 6:17. Thanks guys.

-ws6formula-

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1989 Pontiac Formula WS6
69,000 miles.
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305 TBI, 4.10 gears, SLP Zexel/Torsen Limited Slip Differential, 700r4 B&M TransPak, LT4 Hot Cam/Valvesprings, GM Aluminum Driveshaft, 2700 RPM Stall, Edelbrock Performer RPM intake manifold, Turbocity TB. Ran on 6-19-2001 again: UPDATED: 14.1 @ 97.68 mph. Dyno'd Bone Stock @ 172.6 rwhp, 266 ft-lbs. of rw-torque.

[This message has been edited by ws6formula89 (edited June 22, 2001).]

 

A 275/60R15 on a 7 inch wheel will look funny, deform the tire causing odd tire wear and bad cornering, and might rub when you hit dips and bumps(depending on your suspension)

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350 with stealth intake, holley carb, 470 lift cam. 700r4 with .5 boost valve, vette servo, tci lock-up kit, B&M megashifter. Richmond 3.73 gears, powertrax locker, timkin bearings, synthetic lube. Custom 3 inch single into 2 2.5 pipes. 1 1/2 drop springs, 1 5/16 solid front sway bar, 1 inch rear bar, custom subframe connectors, custom LCA relocation brackets. Kobel ground FX, current red metallic paint. Lots of other stuff...
82camaro

 

Thanks for the help guys.What size tires do you guys recomend running? Keep in mind i wanna make up for not having the paxton on my car anymore and i have a 2.77 stock rear,I think thats what i was told,i know its that, or a ratio close to it according to the differential case atleast,and i dont think im upgrading the rear anytime soon.

Now im really thinking twice about putting these tires on only cause then im gona loose out on my initial take off.I just figured i might throw them on cause i got both for $100 and their Eagle GTII tires.

Thanks,Al in NJ

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86 Trans Am 305 TPI,Bored 30 over,Blower Cam,Fordged Racing Pistons,High Volume Oil Pump,3" Flowmaster Exhaust,Hypetech Coil,Acell 300+ Race Wires,Bosch Platinum +4 Plugs.Best Et was 12.5 with a Paxton.

 

The stock 7" rims can hold a 265 50R15. Not that much different in width from what you had but about 2" shorter. 275 60's fit funny for sure, its too tall to work well on a small car anyways.

 

Never go more than a 255/60/15 or 245/50/15 on a 15 x 7 rim, otherwise it'll just look like an overly fat tire on a small wheel

 

That's alright, you caught me in a goof-up too! You're right, higher gear ratio, "numerically" lower. I just figured if I threw out a ton of formulas, 86TransAmTPI could pick out his own tire size.

86TransAmTPI, take all those calculations, and work out info for each tire. Grab a Summit catalog (or similar), pick all the tire sizes that sound good to you, and run down the #'s. That's how I settled on mine.


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-Tom P (Hot rodded 1986 Firebird 2.8l) from http://www.f-body.net/mailbag/3rd/3rd_mailbag.html message boards
---Think your car could be pic of the week? Visit http://www.f-body.net for details!

 

I had 245/60's back when I had 88 Iroc 15x7's on my 82. I thought they even looked a bit wide on the wheel, but still looked OK. For a common, good priced tire, I like the look of 235/60R15's on stock 7 inch wheels.


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350 with stealth intake, holley carb, 470 lift cam. 700r4 with .5 boost valve, vette servo, tci lock-up kit, B&M megashifter. Richmond 3.73 gears, powertrax locker, timkin bearings, synthetic lube. Custom 3 inch single into 2 2.5 pipes. 1 1/2 drop springs, 1 5/16 solid front sway bar, 1 inch rear bar, custom subframe connectors, custom LCA relocation brackets. Kobel ground FX, current red metallic paint. Lots of other stuff...
82camaro

 

i lke the way my 245/50's look on my 16X8 rim not to thick in the sidewalls and still good enough up front not to squeal through the turns............i used to have 235/55's stock but since i have the z28 rim on my rs i went ahead and upped the tire size when we switched them out......i thought you couldnt put 275s on a 7 inch rim? that would look way goofy.......ive heard of 275's on 9 inch rims and very rarely 8.5 inch rims but never 7 inch rims......sheesh.......actually the way that you guys are talking i guess i could put 335's on my 8 inch rim? can i?

 

So basically my 2.77 rear is gona be more like a 2.40 something or basically something to those lines now if i use these tires????

Sorry guys im not good at all at understanding this stuff with rears and tire sizes and all that.All i know is anythings better than my stock rear i have and its sounding like if i use these tires now my cars gona basically perform even worse.

 

I have 295's on the rear of my 83 Z28.
And 265's on the front.

No problems yet..

 

Larz - Whats size wheels do you have?

 

Stock 15 x 7 Z28 rims.

The tyres are BFGoodrich T/A's