4.3 to 4.1 diff speedo correction

spikes · Postby **spikes** » Fri Oct 12, 2012 4:27 pm

Does anybody know roughly how much the speedo will be out going from a 4.3 to a 4.1 with 195/50R15 tyres? I know it was something around the 4% the speedo overreads with stock wheels but with larger tyres and the new diff ratio?

Apu · Postby **Apu** » Fri Oct 12, 2012 4:32 pm

That's tricky...when I went from a 3.63 to a 4.1, the speed variation was not constant - that is, the faster I went, the bigger the gap.

Dave (from Mania) drove the car whilst I noted the speed differences on the GPS - it was something like (from memory) 5-10km/h difference up to about 60-70km/h speed, but once we got up to 100km/h if was off about 20km/h.

However, going from a 195/50/15 to 205/50/15, the difference in speed was minimal - less than 5km/h off.

sailaholic · Postby **sailaholic** » Fri Oct 12, 2012 6:56 pm

What car? Jdm na6? Will probably read right for once.

Also speedo will always be out by a percentage not a fixed number.

Change on same tires will be 4.3÷4.1* What ever speed your checking it at. But na6 jdm 4.3 speedo and gearbox sensors read well over the correct speed (ie doing 130 on the speedo at 110 road speed.)

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spikes · Postby **spikes** » Fri Oct 12, 2012 8:55 pm

Yep na6 jdm import. I'm going to check with a GPS now

Tedsmx5 · Postby **Tedsmx5** » Fri Oct 12, 2012 10:39 pm

Apu wrote:That's tricky...when I went from a 3.63 to a 4.1, the speed variation was not constant - that is, the faster I went, the bigger the gap.

Dave (from Mania) drove the car whilst I noted the speed differences on the GPS - it was something like (from memory) 5-10km/h difference up to about 60-70km/h speed, but once we got up to 100km/h if was off about 20km/h.

However, going from a 195/50/15 to 205/50/15, the difference in speed was minimal - less than 5km/h off.

Please prove me wrong if I am! :roll:

But the error is a % there fore the difference (in kph) will increase as the speed increases.
At 10kph (GPS) a +20% error read 12kph on the speedo (2 kph difference) and at 100 kph (GPS) reads 120 kph (20kph difference).
Ted

spikes · Postby **spikes** » Fri Oct 12, 2012 11:34 pm

Okay so I used a speedo app on the iphone and got pretty much spot.

60kph speedo = 59kph gps
70kph speedo = 79kph gps
100kph speedo = 98kph gps

I have 15" wheels, 195/50R15 tyres and went from a 4.3 to a 4.1. Have a 5 speed box.

sh*t yeah no need for new speedo drive, unless the GPS ain't that accurate.

sailaholic · Postby **sailaholic** » Fri Oct 12, 2012 11:55 pm

Gps isn't super accurate, but it's close enough! Maybe a couple of km/h each way. Thought it would end up about right. I swear Mazda stuffed up and never actually made a 4.3 sensor. (there is a part number for it though)

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Apu · Postby **Apu** » Sat Oct 13, 2012 5:06 am

Tedsmx5 wrote:
Apu wrote:That's tricky...when I went from a 3.63 to a 4.1, the speed variation was not constant - that is, the faster I went, the bigger the gap.

Dave (from Mania) drove the car whilst I noted the speed differences on the GPS - it was something like (from memory) 5-10km/h difference up to about 60-70km/h speed, but once we got up to 100km/h if was off about 20km/h.

However, going from a 195/50/15 to 205/50/15, the difference in speed was minimal - less than 5km/h off.

Please prove me wrong if I am!
But the error is a % there fore the difference (in kph) will increase as the speed increases.
At 10kph (GPS) a +20% error read 12kph on the speedo (2 kph difference) and at 100 kph (GPS) reads 120 kph (20kph difference).

Ted

Well yes, that's what we found. I then changed the spend sender and it was spot on (by GP) interestingly enough. Then I went to 205 tyres and it was out again but by a small margin.

Apu · Postby **Apu** » Sat Oct 13, 2012 5:10 am

spikes wrote:Okay so I used a speedo app on the iphone and got pretty much spot.

60kph speedo = 59kph gps
70kph speedo = 79kph gps
100kph speedo = 98kph gps

I have 15" wheels, 195/50R15 tyres and went from a 4.3 to a 4.1. Have a 5 speed box.

sh*t yeah no need for new speedo drive, unless the GPS ain't that accurate.

Is there a typo there? You were 1kmh slower, then 9kmh faster, then 2kmh slower?

spikes · Postby **spikes** » Sat Oct 13, 2012 9:54 am

Apu wrote:
spikes wrote:Okay so I used a speedo app on the iphone and got pretty much spot.

60kph speedo = 59kph gps
70kph speedo = 69kph gps
100kph speedo = 98kph gps

I have 15" wheels, 195/50R15 tyres and went from a 4.3 to a 4.1. Have a 5 speed box.

sh*t yeah no need for new speedo drive, unless the GPS ain't that accurate.

Is there a typo there? You were 1kmh slower, then 9kmh faster, then 2kmh slower?

Whoops corrected

Apu · Postby **Apu** » Sat Oct 13, 2012 12:42 pm

So it looks like you're spot on! That's pretty much what I was on when I changed to the 4.1 sender.

spikes · Postby **spikes** » Sat Oct 13, 2012 6:14 pm

Apu wrote:So it looks like you're spot on! That's pretty much what I was on when I changed to the 4.1 sender.

I think it was in my head, cruising down the F3 at a 110kph felt alot faster than normal. I'll double check it later this evening on the freeway to see how what its like at 100-120kph. Anyways, hope this is good future reference for those swapping from a 4.3 to a 4.1!