2006 ZD30 Ratios and Highway Driving

[davejenadelaide]

Hi guys,

Brand new here so I apologise in advance I'm this isn't the right place or this has been discussed.

As the title says: 2006 ZD30 Manual, D22 STR
Tyres: 255/70/16 (slightly smaller than stock)
At 110km/hr my rev's are at 3100 RPM = 51.66 rev/sec
This is ridiculous for a diesel...
The plate under the bonnet = CA43 so I'm assuming a 4.375 ratio diff.
I have checked the speedo using GPS.
110km/hr = 30.55m/s
circumference of my tire = 2.397m
30.55/2.397 = 12.745 rev/sec (of the tyre)
12.745x4.375 = 55.75 rev (gearbox output shaft)
51.66 (engine rev/s) / 55.75 (gearbox output rev/s) = 0.926 (5th gear ratio)
Can someone please confirm that a 2006 d22 ZD30 has this 5th gear ratio and that my calcs are correct?
I struggle to believe that in 2006 Nissan were unable to get the gearing correct on a brand new car, such that driving long distance is practically unbearable? What am I missing???

Keep in mind that if the factory wheel size of 265/70/16, this equates to a circumference of 2.440. This produces only a 1.8% difference, ie, my RPM with factory wheels would be 3055 RPM. This can't be right???? Are other people with this model car experiencing this RPM when doing 110km/hr?

Cheers guys

 

[Stelianos]

yes 4.375 ratio diff.
but 5th gear ratio is 0.760 not 0.926.
according to manual factory tyre on the zd30 is 255/70R16 but i cant confirm this.
at least thats what we got in europe, 255/70R16

 

[Dion]

I've sat in similar era ZD30 D22s on the freeway and not noticed any specific issue. Do you consider the engine noise to be easily noticeable over the road noise? Whilst 3100RPM is 'high' for a diesel, these are small capacity engines in vehicles with a GCVM pushing 5T - don't be surprised when they rev their ring off at 110.

From the service manual, your OD gear ratio is 0.760:1. In the petrol models there was a 0.821:1.

Even if your differential had been replaced with the highest available ratio (4.8:1), you wouldn't be able to get those numbers to work out.

One possible factor that usually makes these calculations fail to work out is that the effective rolling radius of the tyre is not the same as the marketed tyre size, this is down to a combination of load, tyre pressure, tread wear and how far from the 'size' the manufacturer has deviated (put two same sized tyres from different brands side by side to see what I mean). You can attempt to measure the radius at a stand still to get closer.

I'd imagine you've accounted for this but surely with smaller tyres and an existing over-reading speedometer, you must now have significant speedometer error? What was the error when cross referenced against the GPS?

 

[davejenadelaide]

Thanks guys.
I will measure circumference tonight using a tape measure. Maybe tyre wear has attributed, or the manufacturer of that specific tyre is faily out of spec. Good thinking.

Speedo was spot on compared to GPS.

Any other thoughts on how these calculations are wrong?
Something just isn't right here...

 

[Old.Tony]

The Australian ZD30 is supposed to have a FS5R30A gearbox (same as the earlier QD32 and the later YD25 D22). Gearbox ratios are 3.580, 2.077, 1.360, 1.000, 0.811 (1st - 5th) with 3.636 for reverse. With a 4.375:1 diff (that's what the manual specifies for the ZD30) the final drive ratio should be 3.548:1 in top gear.

255/70R16 tyres should have ( (255*0.7)*2+(16*25.4) )*3.141592 = 2398.29mm circumference.

At 3,000rpm you should be getting 3000/3.548=845.5 RPM on the rear axle or 50,732 revolutions per hour. At 2.398m per revolution that should be getting you around 121.65km/h actual speed.

So the question becomes - where have things gone wrong in the calcs or with your car, or are MY calcs out of whack?

 

[Stelianos]

hey tony but manual says 5yh gear is 0.760:1

 

[tweak'e]

tony has the spec for the earlier QD32 gearbox.

 

[Rumpig]

Ecutalk has two rpm readings, one from the crank sensor and one from the fuel pump, they both say the tacho over reads by 10%. 3000 rpm on the tacho shows 2700 rpm on ecutalk.

 

[Old.Tony]

Ok, I've found the wrong box! Let's re-do the math.

With a 4.375:1 diff the final drive ratio should be 3.325:1 in top gear.

255/70R16 tyres should have ( (255*0.7)*2+(16*25.4) )*3.141592 = 2398.29mm circumference.

At 3,000rpm you should be getting 3000/3.325=902.25 RPM on the rear axle or 54,135 revolutions per hour. At 2.398m per revolution that should be getting you around 129.81km/h actual speed.

The problem is even worse!

 

[bods]

If you speedo is spot on with the gps speed, then your tacho has to be over reading. I'd suggest as above, a 10% error. Most d22s rev around the 2700rpm at 100km/h. The only way to verify that is with ecutalk or a nissan consult scanner on the zd30

 

[davejenadelaide]

Good replies guys.

Old.Tony i believe your maths is correct in those examples.

Tonight I measured the circumference with some thin rope and got 2.37 (compared to 2.398m if the tyre was 'exactly' to spec)
As you can see this is not the source of my problem, they are very comparable.

Next proposed answer by Rumpig is the RPM is overestimated by 10%.
I need to account for a 17% discrepancy using the 0.76 5th gear ratio.

However... if I use the 0.811 ratio that Old.Tony said it might be... then I'm only 11.5% out. If you then combine the fact that the RPM is over-stated by 10% then I'm only 1% out.

Next step..how to confirm which gearbox I have so I can be sure this is the case.

Thanks for the knowledgeable replies.

 

[davejenadelaide]

Okay so I ran a test in 4th gear as this removes the ambiguity of which gearbox as they are all 1:1 in 4th gear.

I rang a few mates and compared. My car is the last column.
I think if you combine this with the 10% over-stated RPM on the dash... then these are within measurement error and it all checks out.

 

[Old.Tony]

The 2006 D22 doesn't talk OBD2 either so using a generic BT adapter and a phone tool like Torque won't work. You'd need a mechanic to stick his widget in the OBD port to get the engine RPM from the ECU (and that will be accurate - it has to be!).

 

[davejenadelaide]

So Old.Tony do you know how to determine which gearbox I have?

 

[Jased22]

I have a 2006 d22 at 110km/h think its at about 2750rpm. I have 265/75/tyres

 

[Old.Tony]

I looked it up in the manual, discovered that it was a FS5R30A then looked up the ratios for the older FS5R30A from the QD32 - but that is the gearbox you should have.

 

[Stelianos]

are you the first owner of the truck? if yes there absolutely no way that you have the older gearbox ratios and you definately have the 0.760 5th gear, if you got the d22 second hand then you have no idea whats been tempered with, might be a replacement gearbox from a scrap yard previous owner replaced for some reason or different diff gears in the stock casing.