V35 Tyre Question, My Speedo Is Out

[Murry33]

Hey all,

Just got a V35 Coupe recently and loving it so far! One thing i have noticed with the wheels that came on the car, is that the speedo is out by 3-4km/h.

The wheels in question are:

19x10" front (245/35/19 tyres)

19x11 rear (275/30/19 tyres)

One of the rear tyres need replacing soon anyway, was just wondering what size rear tyres you would recommend to get my speedo back to normal?

Any help is much appreciated! Thanks

[Commsman]

There's been plenty of talk on this very subject recently.

Nissan designed these cars to have optomistic speedos. With 'correct' sized wheels & tyres, the speedo will be out ~10km/h @ 100km/h (will read 110 when doing 100). If yours is out 3-4km/h then you have a larger diameter wheel/tyre combo.

It's worth noting (as previously discussed) that the ECU knows how fast you are going (with correctly sized wheels & tyres) but chooses to display the incorrect speed. This can be confirmed by an OBDII reader whilst driving.

[Murry33]

i wish it would show the right speed then lol, it's very noticeable driving next to other cars doing the speed limit. I've confirmed it was out by using a GPS to compare the speed.

I'm thinking a larger profile on the rear may fix it? (suggestions?)

Edited February 4, 2013 by Murry33

[Nightcrawler]

Using this: http://www.exploroz....s/SizeCalc.aspx

Tyre Size Difference Comparison

Select Wheel/Tyre 1 / 240/45 R18 ** for some reason it thinks 245/45 tyres don't exist and changes it to 240/45

Select Wheel/Tyre 2 / 275/30 R19

Results for your selected Wheel/Tyre 1

Rolling Radius 338.85mm

Circumference 2129.06mm

Diameter 677.7mm

Wheel Cover Size Size 003

Results for your selected Wheel/Tyre 2

Rolling Radius 323.8mm

Circumference 2034.5mm

Diameter 647.6mm

Wheel Cover Size Size 001

Differences between Wheel/Tyre 1 & 2

Rolling Radius -15.05mm

Circumference -94.56mm

Diameter -30.1mm

When your speedo reads 100km/hr you're actually at 95.35 km/hr

[Nightcrawler]

Were you at the BSM cruise Murry? What colour is your new V35? I saw a heap of silver ones (and Triggs on SAU cruised with me) but couldn't find the owners of any of them (not surprising given there were over 1,000 cars!)

[t5iv]

Isn't it illegal to change your rolling diameter by more than 1 inch either way?

[Nightcrawler]

Yeah, but it is illegal to modify pretty much anything on a car technically ..... obviously the rim track is the big one where basically any set of rims with any sort of reasonable offset is completely illegal by the letter of the law. In SA you are allowed to increase your wheel track by like 26mm per axle legally, where my rear is 86mm wider than stock

Wheels

The wheel track must not be increased by more than 26 mm beyond the maximum specified by the vehicle manufacturer. Maximum allowable track measurements for individual vehicle models can be obtained from the Department of Planning, Transport and Infrastructure.

Tyres

The overall diameter of a wheel and tyre fitted to a vehicle must not be more than 15 mm greater than the largest tyre size listed on the tyre placard and not more than 15 mm less than the smallest tyre size listed on the placard.

[t5iv]

That's what I thought. 86 mm?!?1 What are you running on the rear?

[Nightcrawler]

18" x 10" +12 with 275s :) and they fit under the guards easily with only a few degrees of camber.

[t5iv]

Yeah. Ok. Since they're 18s they wouldn't attract too much attention. If they were 20s, different story.

[scotty nm35]

As Leon said, the obd2 port outputs the correct speed. Just get an informeter and use that as a speedo.

[sonicii]

Has anyone ever managed to re-calibrate the speedo? I was able to do this on my old J30 maxima.. but not sure if it is possible on the V35?

[GeeDog]

Murry,

With the stock 18" rears (245/45R18) my speedo is almost spot-on. Your rear tyres are about 5% smaller than stock, and that's the main reason your speedo is so far out. If you went to 275/40R19 you'd still be slightly smaller (but much closer), while 275/45R19 would be slightly larger (so the speedo would probably read 1-2kph less than actual). I use the calculator at http://www.miata.net...e/tirecalc.html - you can directly compare 2 different tyre sizes.

Your fronts are also smaller than OEM, but this won't affect the speedo.

Edited February 5, 2013 by GeeDod

[sonicii]

Your fronts are also smaller than OEM, but this won't affect the speedo.

I think it will. Speed is determined by wheel speed sensors. Not transmission output like the old days.

You can change diff ratio without affecting the speedo.

[Daleo]

I think it will. Speed is determined by wheel speed sensors. Not transmission output like the old days.

You can change diff ratio without affecting the speedo.

I'm pretty sure you'll find the speed is determined by the REAR wheel sensors, so smaller fronts won't affect the reading.

This is also why a diff ratio change doesn't affect speedo reading.

[GED59]

This is a really good tyre calculator, actually states what speedo error you will have http://www.alloywheels.com/Tyre_Calculator

[Murry33]

Nightcrawler, yep i was at the cruise in a silver v35 your tyre comparison is pretty much spot on really

Thanks for your input guys, what other tyres could i use on the rear instead? (keeping in mind it's 11" wide lol)

Edited February 5, 2013 by Murry33

[Murry33]

I'll probably try to just go 275/35/19 on the back now, should just about do the trick i reckon!

[sonicii]

I'm pretty sure you'll find the speed is determined by the REAR wheel sensors, so smaller fronts won't affect the reading.

This is also why a diff ratio change doesn't affect speedo reading.

Maybe it is.. but I though the reason the staggered wheel setup on the coupe didn't impact the speedo accuracy is because the front tyre sizes are reduced by the same amount the rear tyre size is incresed, when compared to a non-staggered setup? so the average speed from all 4 wheel speed sensors is the same?

Also, the speedo doesn't 'shoot up' when you break traction on the dirt with VLSD as much as it did in my old R31.

[Murry33]

ended up putting 275/35/19s on the rear, she's all sweet now

bit worried about lowering it though, may need the guards rolled