I have a 89 camaro 305TBI, I bought some new rims and tires. I thought it would look cool with some 275/60/15 on the rear and some 235/60/15 on the front with the rear bumped up about a inch. Sure it looks good and pissed off but I think its slowin me down. Do you think the 275/60/15 are too much for my slightly modified 305? You think it is just boggin' me down to much? I think I noticed a difference. Am I crazy? Or do they really slow me down enough to notice??? If so what would be a good size on my 15x8 in. rims?

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'89 RS camaro: 305 TBI, 700R4. Upgrades: Edelebrock proflow air filter open element, Dynomax Superflow cat, Stage 2 Jet performance chip. 160 thermostat. New paint job.

 

My thought is if you eventually ran 255/50/R15s on all 4, you would have slightly better acceleration and increased handling capabilities. These tires have a shorter sidewall which would lower your car's profile a bit too (lower center of gravity). Just a thought. BTW, they'd fit very nicely on 15x8" rims.

[This message has been edited by nFORM91 (edited April 30, 2001).]

 

pgriffith, welcome to the world of "effective gear ratios".

Here's a page for you to check out: http://www.tolan-hoechst.com/cars/tirecalc.htm You'll need your stock tire size, which should be on the inside edge of the driver's side door, or in your owner's manual. (My stock size was P215/60r15). You also need to know your rear gear ratio... according to https://www.thirdgen.org/newdesign/tech/techdb.shtml , your car had the 2.73 rear gear.

Fill out the "initial information" spot of that web page. (Leave offset alone, I always do.) Then, roll down to the "effective gearing results" spot, and put in "65 MPH" to the first box. Make the fourth line say "Engine rpms with 2.73 differential gear and 1.00 transmission gear ratio". Then, press the "TAB" key. Read the second line (your speedometer is now reading "too slow"), and the fifth line (your "new" rear gear ratio).

A tire that's taller than stock will make the car faster (higher top speed). A shorter than stock tire will make the car quicker (higher 0-60 and 1/4 mile). The calculation for the effective gear ratio is as follows: (rear gear) times (original tire height) divided by (new tire height).

For instance, I have the same rear tire size and rim size as you do now. My original 3.42 rear gear became an effective 3.18! I swapped in a 3.73/posi/disc brake axle last year- now my effective ratio is at a 3.46.

Here's some hope for you- the 85-89 2.8 V6's (with automatic trannies) usually had a 3.42/open/drum brake rear axle. You can switch axles between a junkyard 2.8 car and your car... everything will bolt up. There are NO structural differences between V6 and V8 rear axles. There was an axle design change in '89, all axles (both V6 and V8) received 28-spline (stronger) axleshafts instead of 26-spline. You can search the transmission/drivetrain message base for info on that. You can probably find a 3.42 rear axle for what you'd pay for new rear tires- AND, you'll have boosted your performance over what your car was "stock". Keep in mind though that your speedometer will still be inaccurate... watch out for cops.


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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 May 01, 2001).]

 

the 255/50/15 are an odd size. Im having some trouble finding them. Where could i get these

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'89 RS camaro: 305 TBI, 700R4. Upgrades: Edelebrock proflow air filter open element, Dynomax Superflow cat, Stage 2 Jet performance chip. 160 thermostat. New paint job.

 

235/60R15 or 245/60R15 will work well and are easy to find. And alot cheaper. You killed your probably already poor gear ratio going with the tall tires. If you like the 275's, install 3.73 gears.

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82 camaro--original steering wheel, brake/gas pedals, seats--everything else modified
82camaro