speedometer not working after tire install

Thorazine_IM · 08-13-2012, 09:14 PM

All warning lights came on speedometer not working car just seems confused after install of nitto 305 45 18 drag radials on stock 18 x 9 on rear only. Im going for wide look on the rear without changing stock wheels. How do I fix this? Any input guys?

BGTV8 · 08-13-2012, 11:02 PM

The ECU is confused because you've altered the overall rolling diameter of rear tyres with respect to the O/D of fronts.

OD of OEM on 18" wheels is 225/50R18 and rear is 245/45R18 which is OD on front and rear of ~680mm. The OD of 305/45R18 is going to be 730mm and because the ECU is monitoring the relative numbers of turns of front and rear wheels (expecting them to be very close) but your car is not, it has thrown a hissy-fit because it does not know which end of the car is correct and has been taken out-of-bounds for all sorts of electronic aids - stability control, traction control, electronic brake assist etc.

I'll leave it to others with more (drag) experience to suggest a way aroundyour problem - my simple answer would be to find a tall front tyre with 370mm OD but that might be easier said than done and it would jack the frnt of the car up by at least an inch as well.

Thorazine_IM · 08-14-2012, 01:35 AM

Can't just plug it to a scanner and fix it? I'm gonna be taking the car back to the shop tom. I tol d them what happened they said they're gonna plug it to scanner to see what's up.

NitrousZ34 · 08-14-2012, 06:47 AM

wow you fit a 305 on a stock 18x9?? Pics of how that looks please. I thought i was pushing it with a 315-30-18 on a 18x10. With my setup you can see that the tire sticks out of the rim a little bit more than its suppose to, idk if that makes sense or not.

Like BGTV8 said, your ecu is thrown off. Your best bet is to get your front and rear tires in proportion to what it is from the factory.

Thorazine_IM · 08-15-2012, 05:31 AM

yeah i ended up getting a falkens in 275 40 18. i calculated the O/D and it was 677.2 which was pretty much the same as stock. the car is back to normal. i only drove it a few feet and all the lights turned off and speedometer was back online. ecu picked it up real quick. i thought i was gonna have to drive a few miles before ecu learns it. i had to have the shop reset my CEL though. it came on after the fact. i think it said speedometer failure or something on the scanner. sorry i didnt have a chance to snap pics before i had it swapped out.

08-13-2012, 09:14 PM	#1 (permalink)
Thorazine_IM Base Member Join Date: Aug 2012 Location: CA Posts: 158 Drives: 13 Nissan 370Z PW M6 Rep Power: 13	speedometer not working after tire install All warning lights came on speedometer not working car just seems confused after install of nitto 305 45 18 drag radials on stock 18 x 9 on rear only. Im going for wide look on the rear without changing stock wheels. How do I fix this? Any input guys?

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08-13-2012, 11:02 PM	#2 (permalink)
BGTV8 A True Z Fanatic Join Date: Dec 2009 Location: 03350 Australia Posts: 1,514 Drives: 09 Nissan 370Z M6 Rep Power: 39973	The ECU is confused because you've altered the overall rolling diameter of rear tyres with respect to the O/D of fronts. OD of OEM on 18" wheels is 225/50R18 and rear is 245/45R18 which is OD on front and rear of ~680mm. The OD of 305/45R18 is going to be 730mm and because the ECU is monitoring the relative numbers of turns of front and rear wheels (expecting them to be very close) but your car is not, it has thrown a hissy-fit because it does not know which end of the car is correct and has been taken out-of-bounds for all sorts of electronic aids - stability control, traction control, electronic brake assist etc. I'll leave it to others with more (drag) experience to suggest a way aroundyour problem - my simple answer would be to find a tall front tyre with 370mm OD but that might be easier said than done and it would jack the frnt of the car up by at least an inch as well.

08-14-2012, 01:35 AM	#3 (permalink)
Thorazine_IM Base Member Join Date: Aug 2012 Location: CA Posts: 158 Drives: 13 Nissan 370Z PW M6 Rep Power: 13	Can't just plug it to a scanner and fix it? I'm gonna be taking the car back to the shop tom. I tol d them what happened they said they're gonna plug it to scanner to see what's up.

08-14-2012, 06:47 AM	#4 (permalink)
NitrousZ34 Banned Join Date: Apr 2012 Location: Canoga Posts: 505 Drives: Myself crazy Rep Power: 0	wow you fit a 305 on a stock 18x9?? Pics of how that looks please. I thought i was pushing it with a 315-30-18 on a 18x10. With my setup you can see that the tire sticks out of the rim a little bit more than its suppose to, idk if that makes sense or not. Like BGTV8 said, your ecu is thrown off. Your best bet is to get your front and rear tires in proportion to what it is from the factory.

08-15-2012, 05:31 AM	#5 (permalink)
Thorazine_IM Base Member Join Date: Aug 2012 Location: CA Posts: 158 Drives: 13 Nissan 370Z PW M6 Rep Power: 13	yeah i ended up getting a falkens in 275 40 18. i calculated the O/D and it was 677.2 which was pretty much the same as stock. the car is back to normal. i only drove it a few feet and all the lights turned off and speedometer was back online. ecu picked it up real quick. i thought i was gonna have to drive a few miles before ecu learns it. i had to have the shop reset my CEL though. it came on after the fact. i think it said speedometer failure or something on the scanner. sorry i didnt have a chance to snap pics before i had it swapped out.