phineas

I just bought a '91 RS TBI/Auto, and I'm seeing the wierdest speedometer problem (and a forum search didn't turn up anything relevant). My speedo reads pretty much dead on (plus or minus a couple MPH compared to my other car) until about 65-70mph, where it seems to read faster and faster than actual speed. When it reads 70, it's actually going about 65mph, and it reads around 90mph when actual speed is more like 75-80mph. Has anyone seen anything like this before ?

deadbird

What size are the tires (e.g. 245/60-16)?

Some people don't go with OEM sized tires because the next "closest" size (usually smaller) is cheaper. A smaller tire will usually cause small increment (faster reading)changes that amplify as speed picks up. Mine is 3mph slow@50 on my camaro because the back tires are 255/50's instead of 245's (they are taller, just under ½" height difference)

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phineas

The tires are something like 245/55-16. I'm not positive about the width, but that shouldn't matter much.

deadbird

Yes,, width does matter. The sidewalls are in direct proportion height-wise to the witdh of the tread. 245/55's are taller that OEM tires,, your speedo should be slower than when it rolled off the dealer parking lot unless the gears have been changed as well.

phineas

Actually, it has 235/55-16's, which is the stock size according to my owners manual. I guess we can rule out tire size causing the problem.

deadbird

stock size is 245/50-16,, that is a tire 25.65" in height

235/55-16 is 26.18" in height,,, your speedo should still be slow

if you want to prove this to yourself,,, chech this site out,,,

http://elvis.rowan.edu/~kristovi/java/Tire.html

the 1st box is width 235/55-16
2nd box is sidewall ratio 235/55-16
Last is wheel size 235/55-16

I've got a formula firebird that came 245/50-16 that I upgraded the wheels to GTA wheels,,,, same tire 245's,,, I've got the 91-92 wheels on my camaro,, same tire size,,,245's. Trust me,, 235/55 is not OEM size for 16 inch wheels.


[This message has been edited by deadbird (edited October 25, 2001).]

SlowCamaro88SC

actually.........

the 91-92 v8 RS's had an option for 16" wheels rather than 15" wheels like the v6 models. they were offered with 235/55-R16's rather than the 245/50-ZR16's that the z/28's had. good luck finding somebody with 235/55's on them though, most people I know have upgraded to 245/50's.

and look @ the 4th gens.

the tire size was 235/55-R16 on them
245/50-R16 was standard on the Z/28, but was likely optional on the v6 models.

225/60-R16
235/55-R16
245/50-R16

I've seem these on f-bodies and grand prix (w/ the 16x8 crosslace wheels) gallore.

they 245/50's look best but the others will work just fine with minimal effects on the speedometer.

my IROC wheels had 235/55-R16's on them when I got them. That's because the kid that had them before me went to the local goodyear store for new tires, and when they looked up 16" wheels for his car, they told him 235/55-R16 and 245/50VR(and ZR)16 was a factory size. and of course he got the 235's because they were cheaper (no speed rating)

but to what I said up top (about factory sizes), check it out, it's for real.

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Dan Briones
1988 Camaro Sport Coupe
2.8 V6, TCI 3200 Stall TC, B&M Transkit, Flowmaster & Catback
1983 Z/28 CFI Hood, 1989 IROC Foglamps, Custom Painted Tails, 1987 IROC Wheels
Z/28 Grille, "Heritage" Style Stripes, White Face Gauges/Gear Indicator, Homemade DRL's

phineas

Yeah, according to the "Tech Data" section on thirdgen.org, under Camaro - 1991:

"RS was available for the first time with 16 inch wheels. Tires for the 16 inch wheels on the RS and RS convertible were P235/55R-16. RS also got an optional grid taillight to match Z28. The CHMSL was moved from the spoiler to the inside leading edge of the hatchback glass. The slightly smaller non-CHMSL spoiler from 1982-1986 replaced the CHMSL spoiler on the RS."

The paperwork for the car (orig. window sticker, dealer order) shows that it was shipped with this size tire as well.

On a separate note, I spoke to a few area mechanics and they all seem to aggree that in some cases if the speed sensor is going bad, it will "amplify" the error as the speed of the sensor's gear increases. At $45 for a new VSS, I'm going to have it replaced and see how it goes.

deadbird

Interesting.. I've never seen anything that the 245's on a 16" oem wheel.

Thanks for the corrective info

SlowCamaro88SC

your welcome, I'm glad you didn't think I was being a jerk.