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02-10-2013
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#1 |
 
Join Date: Sep 2012
Location: Rockwall, Tx
Posts: 1,510
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Speedo correction
I'm getting ready to replace my factory 17" A molds with Series One's which are 18's with 335/35 PS2's. Any idea how far off my speedo is going to be and the most efficient way to correct it?
I did a search and the following thread is a couple of years old so I thought I would check and see if it's still relevant. http://www.zr1.net/forum/showthread....ter+correction
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_________________ 1994 AB/Grey #141 430 RWHP/392 RWTQ FBI Lyposuction / Secondaries relieved of duty / SW Long Tube Headers / Corsa Exhaust / FIC SS Injectors / MSD Coils / Lightweight Pulleys / Corey tuned B & M Shifter / Aluminum Flywheel / Samco Hoses / Shelby Series One's / C4 No Flex Frame Stiffener BBC - Bling By Carter: Custom ZR-1 Center Caps / Custom Plenum Plate / Air Box Knobs / TB Cover / Oil Filter Cover |
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02-11-2013
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#2 |
 Join Date: Sep 2005
Posts: 90
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Re: Speedo correction
Are you sure the tires aren't 335/30/18?
When I changed to 335/30/18, I checked the diameters of the original tires and the 335/30/18 on the Tire Rack website. The diameters were very close. That was a long time ago so you should probably check again with the specific tires that you are getting. |
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02-11-2013
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#3 |
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Join Date: Sep 2012
Location: Rockwall, Tx
Posts: 1,510
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Re: Speedo correction
You are correct. They are 335/30/18. Not sure where I got 335/35/18. I don't even think they make a tire in that size. Anyway, the overall diameter shows to be 25.9 so I'll compare that to what I have on there currently.
If there is a difference or when I go to 410's is the preferred method of speedo correction with these correction boxes or is it with a Haibeck speedo gear swap?
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_________________ 1994 AB/Grey #141 430 RWHP/392 RWTQ FBI Lyposuction / Secondaries relieved of duty / SW Long Tube Headers / Corsa Exhaust / FIC SS Injectors / MSD Coils / Lightweight Pulleys / Corey tuned B & M Shifter / Aluminum Flywheel / Samco Hoses / Shelby Series One's / C4 No Flex Frame Stiffener BBC - Bling By Carter: Custom ZR-1 Center Caps / Custom Plenum Plate / Air Box Knobs / TB Cover / Oil Filter Cover Last edited by Fully Vetted; 02-11-2013 at 05:10 PM. |
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02-11-2013
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#4 | |
  
Join Date: Nov 2007
Location: Squires (near Ava MO in the Mark Twain N'tl Forest) - Missouri
Posts: 6,493
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Re: Speedo correction
Quote:
Yep! Handy tool for tire diameter comparison (C-Link). Variance % (speedo error) = 100D1/D2 where D1, D2 = respective tire diameters. In the case of the 315/35/17 vs. 335/30/18, the difference is approx 1%; not enough to get me to change anything. But, CCmano's digital speedo correction would interest me, should I ever need to calibrate the speedo. P.
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Good carz, good food, good friendz = the best of timez! 90 #1202 "FBI" top end ported & relieved Cam timing by "Pete the Greek" Sans secondaries Chip & dyno tuning by Haibeck Automotive SW headers, X-pipe, MF muffs Former Secretary, ZR-1 Net Registry |
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02-11-2013
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#5 | |
  
Join Date: May 2007
Location: Peoria, AZ
Posts: 9,153
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Re: Speedo correction
Quote:
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GOLDCYLON - 91 ZR-1 #2014 GOLDCYLON - 90 ZR-1 #2794, 4L60e (Formerly Schrade's) GOLDCYLON - 11 CTS-V Arizona State Director  91 WHITE/BLACK #2014. 380 P&P&PCed,Ported Heads, Jeal Long tubes, Corsa Exhaust/FIKSE FM-5s /LED TLs, LED Headlights, Front Wilwood 6 piston narrowlite calipers and rear Wilwood caliper street shop mod,CNCed Coolant Pipes,TPI Cvr,Filter cover,Stainless Bolts, DRM/DOM PROM /ZFDOC mod build #102,DRLs,BMAD with stainless Debris Screen,Coplan Air Blaster, Pioneer APP Radio 4,Brey-Krause HB,Sub Bar,Fire extinguisher seat mount,DRM Coilovers,LEDs everywhere,Compass mirror (orange),V1 DIC hidden display, Homelink sun visor, Carbon Fiber top x3 and APSIS Carbon Fiber interior, APSIS CF Steering Wheel/NAPA Leather, Banski trailing arms, Guldstrand front suspension,urethane bushings from Prothane (total suspension) ZFDoc drive shaft safety loop, raptor shift light (orange),AO engineering louver front plate, Console seat cushion, 96CE seats with black custom Sheepskins, ss billet catch can,Viper remote entry/alarm,Cragar Rear Louvers,LED side louver lights, Dewitts Radiator with SPAL fans and a Woods 160 T-Stat 90 RED/BLACK #2794. 4L60e Automatic Stage V by RPM Transmission, TCI Dedicated TCM, OBX Stainless Headers, Corsa Exhaust, SAN Secondaries and Haibeck PROM, Exotic Muscle Coil overs, LED Interior Lights, LED Tail Lights, LED Headlights, 94 Sport seats with black custom Sheepskins , Cragar rear louvers, GS Front calipers, Banski Trailing arms, APSIS Carbon Fiber steering wheel, Front and Rear Baer Eradispeeds, DRLs, Guldstrand front suspension,urethane bushings from Prothane (total suspension), Dewitt's Raditor with Dual SPAL fans and a Haibeck 170 T-Stat 11 RED/GREY CTS-V |
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02-11-2013
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#6 |
Join Date: Apr 2007
Location: Northern VA
Posts: 2,644
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Re: Speedo correction
Check this link
http://www.rimsntires.com/specs.jsp
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Phil Wasinger 1994 Torch Red ZR-1 WAZOO Member George Braml Intake |
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02-11-2013
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#7 | |
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Join Date: Aug 2006
Location: McLean, VA
Posts: 3,704
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Re: Speedo correction
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Funny you should ask. I just had Michelin 275 35 18s (front) and 335 30 18s (rear) mounted last Saturday. Prior to this I was running Michelin Pilot Sport 335 30 18s in the rear. Speedo reading at 60 mph was reading 61 (actual) on my Garmin - error is negligible in my opinion. BTW you will love these PS2s. 
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02-11-2013
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#8 |
Join Date: Jan 2009
Location: Mandeville, LA
Posts: 340
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Re: Speedo correction
Speedo error can be corrected with the PROM programming. The only issue is that the FX3 curves will be shifted by the amount of the VSS signal error. This will illustrate it:
VSS signal(4000 pulses per mile) is output directly to FX3 module and ECM in parallel. ECM measures frequency of incoming signal and converts to MPH using the road speed constant variable. ECM outputs speed info digitally on the 8192 baud serial line to the CCM. CCM takes the speed info and displays it on the LCD. ECM also generates a signal (2000 pulses per mile) to the Cruise Control module. This is not a 2:1 pulse divider circuit in the ECM. The ECM actually generates the 2k pulse/mile signal based on the measured MPH. Therefore, adjusting the road speed constant variable will correct any speed errors due to tire/wheel or rear ratio changes. Speedo will read correctly and cruise will operate properly. The FX3 damping adjustments will be affected by the amount of the VSS error. When I swap in my 4.10 gears, I intend to adjust via the ECM and my FX3 damping adjustment points(in MPH) will shift approximately 19% in a stiffer, more aggressive direction, which is a good thing as far as I am concerned. Jep |
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Linear Mode
