Speed is decieving

1QuikV6

Registered User
I was racing a CTS on 295 and I have no earthly idea how fast i was going... All i know is I was in 4th and the speedo had just pegged out... any idea what a stock 5 speed SC is good for? Guess I need a 145mph speedo now...


Felt good to hang it out tho... didnt feel like 120+ at all. Speed is so decieving in an SC
 
1QuikV6 said:
I was racing a CTS on 295 and I have no earthly idea how fast i was going... All i know is I was in 4th and the speedo had just pegged out... any idea what a stock 5 speed SC is good for? Guess I need a 145mph speedo now...


Felt good to hang it out tho... didnt feel like 120+ at all. Speed is so decieving in an SC

If you know your tire size, rear gear ratio and rpm, it's easy to figure out.
 
1QuikV6 said:
I was racing a CTS on 295 and I have no earthly idea how fast i was going... All i know is I was in 4th and the speedo had just pegged out... any idea what a stock 5 speed SC is good for? Guess I need a 145mph speedo now...


Felt good to hang it out tho... didnt feel like 120+ at all. Speed is so decieving in an SC

She'll do between 145-150 stock.

Speed is deceiving in well built cars period. If it was for you, how do you think the CTS felt? :)
 
If you know your tire size, rear gear ratio and rpm, it's easy to figure out.

I have P225 65 R16s on it, i believe 5 speed SCs have 2.73 ratios, and I was hovering around 4000 rpm.

Yeah, I imagine that CTS was quite comfortable too... Just glad i was FAR ahead of him when i we let off. :D
 
If I figure that your 225/65/16s have normal wear on them, they will be about 27" in diameter. That's 84.8" of travel everytime the wheel goes around once. If you are in 4th gear, that's 1:1 ratio so you can apply the 4000 rpm directly to the differential and divide it by the 2.73 gear. That gives you your wheel rpm of 1465.2. So you mulitply the wheel rpm by the 84.8", divide by 12 to get feet, divide that by 5280 to get miles, then multiply that number by 60 to turn your miles per minute into miles per hour and you get 117.66 mph. Maybe that's why it didn't feel like 120 mph. It was 117 mph. :D
 
1QuikV6 said:
well, still better than my LX 3.8 that couldnt even get that far up, lol

I'm looking at 77.29 mph in 5th gear at 2000 rpms with stock 26.6 inch tires.

He's even slower at 115.93 (116) if you use 26.6 inches as the tire diameter.

Something in my head is sticking that a speedo only has to be within 6 mph to be considered gov't accurate? I have no proof, but it feels like I read it years ago. Time to research.

Either way, I'd rather be 3 mph lower than speedo than over. :)

Edit: Is this viable court defense?

http://tipmra.com/trial_transcript-2.htm

By asking for the speedo and radar calibrations of the officer issuing a citation, if they don't have it, they can't support their claim of your offending mph?

Edit #2: Called a speedo shop. No federal regulation, just that manufacturers have their own. 2-3% is the norm. Also, he mentioned that as you go faster, your tire gets larger a tad so basing it on tire hieght x RPMs can be off. Also, how accurate is your tach? :)
 
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My speedo was calibrated after takin the 18" rims off of it. so its accurate. theyre 70 series to btw
 
OEM rated

I bought my '89 5-spd XR-7 new. With the OEM 225/60/16's it was good for 146 mph in 5th.

68COUGAR
 
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