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Discussion Starter #1
I need to purchase a new set of tire for the 85. Currently I have 15 inch rims with 205/65/15. (I have no idea why they were this size to begin with.) I would like to keep the 15 inch rims but am curious as to what other size option I might have (with the 15 inch rims). Also, I would like to keep all four tires the same size. I am still running the original open rear with a TH400. I am planning on upgrading to a posi in the near future, but I really need tires soon. I hope this falls under Trans and Drive line topics. Any advise would be greatly appreciated.
 

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I'm running 215/65/15s all the way around on my '87 with 15x8 Corvette wheels. That's about the tallest tire you can run on a 5th gen without changing some suspension setups in the front. My ChooChoo SS fascia would catch anything larger than this size.
 

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My 1983 had 235-60-15 tires on it when I got it from previous owner. They were too large and hit the frame whenever I tried turning the wheel fully to get into a tight space. Also made a bad clunking noise whenever I took a hard turn at an intersection. After I put on a Camaro-style front end with fascia and spoiler, the tread actually touched the end of that assembly and made more great noises. I replaced these tires with 205-60-15's to avoid even the hint of further interferences or noises. Good luck. Better to be one size smaller than maximum than being one size too big! Stay conservative.
 

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I'm not exactly sure but I think 1983 was the first year that the Elkys were actually "G-Body" until then they were A-Bodies. Just like my 76 and 72 although there are differences none the less.

My 80SS has Billet Specialties GT 93, true directional wheels 16x9.5". BFGoodrich g-Force T/A KD P255-50ZR16 all the way around with a 4" back spacing. They come very close to rubbing the frame but don't. The difference between just getting a set of Rims and planning the wheels and tires is "No rubbing and or weird Noises"

I have heard of owners putting on 17" Rims also but I think from what I found while looking, is that 9.5" is as wide as you can do. Actually 9 or 8" would be perfect, with the correct backspacing.

Changine the diameter of the overall base circle will throw off the speedometer.

Good luck and have fun with it.

This is just what I ran into while doing my projects.
 

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Discussion Starter #6
Elky Pete,

The tire calc website was informative but I forgot one thing. I am running a TH400 in the 85 now and do not know what the original trans was. When I enter the original tire size of 195/75/14 (is this even correct?) and my current size, the difference in the spedo reading and the actual speed is really close but I know at 40MPH (spedo) I am going what seems alot faster. I guess my questions are 1. What was the original trans for the 1985 Elky w/ 305 and 2. How can I recalibrate the spedo to the TH400 gearing and different tire size. (still using original non-posi rear and gear)I believe the TH400 is geared 2.48, 1.48 and 1.0. I think I am going to stay with the 205/65/15's. I guess there is always following my buddy at different speeds and making a note of it. Thanks for all the tire advise from everyone else.
 

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What I did was go to the local highway, where they have "mile markers" and read what my speedo said I travelled between one of the mile markers, in my case .8 of a mile. Then I went to an old speedo calibration shop in Chattanooga and told the guy what the reading was. He sold me a compensator that screwed in between the speedo cable and the tranny box (I'm running a TH350), for about $40 bucks. It brought the speedo to within 2mph at 55mph of what the spouses car reads when she drives alongside me for a test. The compensator, probably not the right name, measures about 2'' x 3". I think he said it was a 20% "thingy", which makes sense if I travelled .8 in the mile marker test.
 

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Discussion Starter #9
Thanks for the info ElkySS. I will try your idea if I can get on the highway this weekend and find some open road. I just read in the June issue of Hot Rod about a GPS speedo that works off satellities. It is supposed to function regardless of gearing or tire size. Sound like an easy way out though.
 

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GPS based speedo, wow, very interesting.
 

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You don't really have to have a GPS or a buddy to figure out what your speed is. Check this out;

Final drive X Rear End Ratio X 168 (Constant Number) X Forward Speed/Tire Diameter = RPM

But wait! :cry: I said you could figure speed. Well you can...

If you have a Tech then plug in 60 MPH. That is still a legal speed that is used. So plug in 60. As an example my Rear end in the 76 is a 2.73:1 the final drive ratio of the transmission is 1:1 or 1.0, the tire radius is 13"

So for a speed of 60

1.0 (Final drive Ratio) X 2.73 (Rear End Ratio) X 168 (A Constant) X 60 (Forward Speed) / 13 (Tire Radius) = 2100.64**

So at 60 Miles per hour I should be turning ~ 2100 RPM. I verified this on the speedo. At 2100 RPM I am going 70 according to the Speedo. So my speedometer is 10 Mph off (Slow).

It works for any speed and as long as the numbers are true so are the figures.

Try it! It works really well.

Hope that this helped. It took me a while to dig this formula up I had thought that I had lost it. :oops:

Have fun and good luck.
 

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Discussion Starter #12
Elky Pete,
Thanks for the formula. I am going to try it this weekend.
 

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I just got my new 225 45 17s on 7inch wide tork thrusts 2s front & 255 40 17s on 8inch wide rear tork thrust 2s i just hope they fit on the front with my choo choo nose when i get the whole front clip put back on.
 

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Chris85 said:
I need to purchase a new set of tire for the 85. Currently I have 15 inch rims with 205/65/15. (I have no idea why they were this size to begin with.) I would like to keep the 15 inch rims but am curious as to what other size option I might have (with the 15 inch rims). Also, I would like to keep all four tires the same size. I am still running the original open rear with a TH400. I am planning on upgrading to a posi in the near future, but I really need tires soon. I hope this falls under Trans and Drive line topics. Any advise would be greatly appreciated.
23560Rx15's fit fine on most any fifth gen Elky with stock wheels or any other wheels with 4" or less backspacing. I have 4.25" BS on my 15x7 Vette wheels and they do rub a tiny bit, but you never hear it.

I've had two Elkys...the 78 we have now and an 83...both had 235's with no problems.
 
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