new 35" tyres dont know correct rpms. help!

[nipper]

gday! im hoping someone can answer my question for me
today i swapped my 275/65/r16 tyres for 35 inch tyres. and i have realized that my speedo is now fairly off but what i was wondering is about is my rpms...
im not sure what gear i should b in ( i know it sounds dumb) but with my old tyres at 60kmph my rpms were at around 2100 - 2300 in 4th gear now with the 35's doing the same speed and same gear my rpms are arounds 1700 - 1900rpms. should i still b in 3rd gear and have my rpms at 2500 - 2700 or is 1700 - 1900 rpms normal for 4th with 35's.
if anyone could let me know what the correct rpms for gears with 35's on that would b much appricated. cheers

[BigRAWesty]

If you have the foot to the floor and still loosing speed then drop back a gear.

[threedogs]

Just drive as you normally do and use your GPS to Check speed.
You'll be doing lower revs for the same speed, not a bad thing IMO
Or you can buy speedo correction gears for the gearbox, I think
most speed shop should sell them

[Clunk]

go by feel and sound............ gps helps with getting the speed right

[megatexture]

If your paranoid and want to fix it marks sell digital correction kits to suit and at the flick of a switch you can swap between your offroad tyres and highways http://www.marks4wd.com/catalogsearch/result/?q=speedo+correction+boxes

[lhurley]

You have essentially changed gears by putting bigger tyres on. The gear box is set so that the ratios for the box and tyres match that of the speedo/tacho. Larger tyres are like changing up. I think with 35s 1st becomes pretty much 3rd.

[nipper]

thanks for explaining it simply to me. besides the inconvenience of the speedo being wrong will having 35's on cause any damage to the car or engine?

[the evil twin]

thanks for explaining it simply to me. besides the inconvenience of the speedo being wrong will having 35's on cause any damage to the car or engine?

For a given speed in a given gear lets say 110 KPH in 5th your engine RPM's will now be lower so your engine will be under more load to maintain the speed and your EGT's will be higher (by how much is wildy variable between vehicles).

That is why, ideally, for every 2 inches in tyre size you should change one factory diff ratio.
IE if you go from 31's to 33's and had 3.9 diffs you should change to 4.1 or if you go to 35's you should go to 4.3 diffs
and that is why the 4.6'' diffs out of the 2.8 litre patrols are so popular with the guys running big tyres

[nipper]

Thanks the evil twin. That all makes perfect sence. Is it a costly exercise puttingin a 4.3 diffs?
Also thanks everyone for commenting, its helping heaps

[the evil twin]

Thanks the evil twin. That all makes perfect sence. Is it a costly exercise puttingin a 4.3 diffs?
Also thanks everyone for commenting, its helping heaps

For 3.9 to 4.1 or 4.3... or... 4.1 to 4.3 then not really.
If you want to go to 4.6 it gets interesting as they aren't nearly as common a diff ratio.
When I changed diff ratios about 3 Patrols ago I also put in a front locker so that made it heaps worth it.

If you only need to go up one ratio to max 4.3 then most people just suck it up UNLESS you do a lot of crawling then it is worth it

If you put 35's on and don't have 4.3's stock (which most won't) then the difference the 4.6's make is definitely an advantage on and offroad IMHO

Just my opinion tho and others are welcome to disagree

[nipper]

can anyone recommend any joints to get 4.6 diff installed in melbourne at a good price?

[GU CAMPER]

X2. I need to change my diff gears to 4.6 or 4.3 at minimum

[@GUte]

4.3's will get your ratios's back to standard with 35". If you decide to go back down to 33", the 33" ratio will still be fine.

I bought a brand new GQ rear in the original Nissan box for $450 and the front centre with an air locker off Ebay for $935. Fitted to my GU.