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Author Topic: Tire MPH question  (Read 6606 times)

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Offline Shimy87

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Tire MPH question
« on: September 21 2018, 12:59:51 PM »
I got my new rears installed and they are 28 inches tall. stock tranny and rear end, is there a way to calculate how far off my speedo is now. Reading 60 on the speedometer seems like Im going closer to 70.

Thanks!
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Offline daveismissing

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Re: Tire MPH question
« Reply #1 on: September 21 2018, 01:47:40 PM »
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Offline Shimy87

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Re: Tire MPH question
« Reply #2 on: September 21 2018, 01:55:46 PM »
perfect...than ks...chart says old tires 60 mph/ new one 67.5
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Offline Steve Wood

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Re: Tire MPH question
« Reply #3 on: September 21 2018, 01:58:03 PM »
It's about 8% off.  Go to a 27 tooth speedometer gear and it will read right.

That is a black gear if that helps.  Takes about three minutes to change and one more minute to clean up the fluid that leaks out of the tranny which you pull the original out
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Offline earlbrown

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Re: Tire MPH question
« Reply #4 on: September 21 2018, 03:52:07 PM »
Set your GPS to show your speed. Click the left scanmaster button 6 times and make it read 100.

Whatever your GPS says is your actual real world error. :)
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Offline Shimy87

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Re: Tire MPH question
« Reply #5 on: September 21 2018, 06:13:07 PM »
my car wont go 100 :icon_eyes: :cheers:
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87 GN, K&N cold air, gutted cat, TT 5.7 chip, AFPR, 340 Walbro w/ hotwire, 60 LBS injectors, 981 valve springs, 206/206 Cam, RJC Powerplate, LS1 MAF & translator, Vacuum brakes, Hellwig rear sway bar, Energy suspension poly bushings, Razors Alky, Pypes exhaust, 5931 turbo, CK9.5 converter

Offline Steve Wood

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Re: Tire MPH question
« Reply #6 on: September 22 2018, 04:58:59 PM »
Although the correct speedometer gear for 28" tires is the 27 tooth black gear, I'm going to post this link as it has all the gears listed at the end. Remember we want the ones for the 200-r4

https://www.hotrod.com/articles/calibrate-gm-mechanical-speedometers/amp/
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Offline TexasT

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Re: Tire MPH question
« Reply #7 on: September 22 2018, 05:32:54 PM »
Those are some nice charts
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Offline larrym

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Tire MPH question
« Reply #8 on: September 23 2018, 01:05:18 AM »
Funny this topic has come up. I been trying to figure out a speed sensor on the Vega
Our computer needs a 2000 ppm signal and a lot of aftermarket VSS or between 4000 and 16000.
I found a GPS that is programable and I spoke to the manufacturer and they will set it up for me so it has the correct signal for my computer. The nice thing is a won’t have to worry about tire size or gear ratio and I can use the low gear timing and fueling adjustments in my old chip and my poor mans edash will have a work speedo again


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Offline daveismissing

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Re: Tire MPH question
« Reply #9 on: September 23 2018, 11:16:32 AM »
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Offline larrym

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Tire MPH question
« Reply #10 on: September 23 2018, 11:42:49 AM »
Thanks Dave that is a handy little unit. Cost effective too still need a speed sensor they are pretty inexpensive also.
My thought with the GPS is it’s once and done it will automatically compensate for any changes I make to the car down the road


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86 white T type with t tops and blackout trim. 60lb injectors Gen 2 with Extender Chip TR6 ignition 212/206 roller cam Turbonetics BB CPT 61 CAS V4 Intercooler Cobbled together Alky Injection 4 inch MAF pipe with integral sensor
2800 stall lots of fun with a little 6 banger!
Best ET 11.36

Offline Steve Wood

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Re: Tire MPH question
« Reply #11 on: September 23 2018, 11:46:33 AM »
Will gps update fast enough to work?
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Offline larrym

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Tire MPH question
« Reply #12 on: September 23 2018, 07:01:14 PM »
We will soon find out


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86 white T type with t tops and blackout trim. 60lb injectors Gen 2 with Extender Chip TR6 ignition 212/206 roller cam Turbonetics BB CPT 61 CAS V4 Intercooler Cobbled together Alky Injection 4 inch MAF pipe with integral sensor
2800 stall lots of fun with a little 6 banger!
Best ET 11.36

Offline larrym

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Tire MPH question
« Reply #13 on: September 23 2018, 10:51:43 PM »
What do you think 10hz update rate.
https://c-a-i.net/skydrive



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86 white T type with t tops and blackout trim. 60lb injectors Gen 2 with Extender Chip TR6 ignition 212/206 roller cam Turbonetics BB CPT 61 CAS V4 Intercooler Cobbled together Alky Injection 4 inch MAF pipe with integral sensor
2800 stall lots of fun with a little 6 banger!
Best ET 11.36

Offline Steve Wood

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Re: Tire MPH question
« Reply #14 on: September 23 2018, 10:56:41 PM »
I would like to think ten times a second will keep up with acceleration.  I guess proof will be in the pudd'n.

that is probably as fast, or faster, than a vss samples
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Steve Wood

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A lot of broken parts does not make you a racer; it makes you a slow learner.
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