265/65/17 to 265/70/17 how much difference?

[SWR Banned Find all posts View Profile Close SWR]

Yep!.. If you are running factory stock tyre size then your speedo is generally running approx 4% faster than true speed hence the acceptable fuel consumption. (I believe higher or lower tyre pressures impact on speedo accuracy also)

Go the bigger tyres and your speedo slows 4% then you think your fuel consumption has died but it is actually your speedo distance that has been reduced.

Hence the GPS always gives a shorter distance to destination compared to your odometer until bigger tyres are fitted.

Cheers

[D4Dforme Senior Member Find all posts View Profile Close D4Dforme]

Gday timmo23

I am basically repeating what was said above and as "Steve M" said it could cause insurance technicality's if in a prang!

If you change your Tyres from 265/65/17 to 265/70/17 then your speedo will slow down approx 4km (4%).....

By going a taller Tyre your speedo then reads true speed/distance (excluding Tyre wear) and by achieving this you will notice your fuel consumption drop (According to odometer) due to you now loosing 40km per 1,000km (4%).... this is purely because your odometer is now giving you true distance which is now a shorter distance (That has to put a damper on your "True" fuel consumption).

By going the bigger height in your Tyre this will also slightly increase gear ratio so gearing is also higher. (Maybe be noticeable if carrying or pulling heavy loads)... You may also notice your brake pedal slightly harder when pulling-up.

Here is the link below for the holy grail on Tyres in NSW

http://www.rta.nsw.gov.au/registrati...vsi09_rev4.pdf

Minor changes to wheels (pg2)

Wheels up to 26mm wider than the largest optional wheel recommended by the vehicle manufacturer for the
vehicle can be fitted without the need to notify the RTA.

The outside diameter of the wheel and Tyre combination must be no more than 15mm over the largest diameter
wheel and Tyre combination specified for the vehicle.

EG: Approx

265/65-17 - Circumference 30.6 inch = 777.24mm

265/70-17 - Circumference 31.6 inch = 802.64mm

Total Circumference increased by 25.4mm.... That's put me 10mm outside total Circumference legal limit!!

Cheers

Mate circumfrance and diameter are two very different measurements.....................Diameter is accross the tyre's center point at the two most furtherest points.....................Circumfrance is measured around the outmost perimiter of the tyre.


Dan

[timmo23 Lurker Find all posts View Profile Close timmo23]

My thought on the fuel consumption was that a larger tyre effectivly raising the gear ratio will be harder to turn thus the engine working harder to push the vehicle along leading to increaced fuel consumption and decrease in power. Has anyone had a noticable loss of power when going to the larger diameter tyres. It seems to be that some people have no increase in fuel consumption and some have a big increase?

[SWR Banned Find all posts View Profile Close SWR]

Gday D4Dforme

Eeeeek!!!

Quote: Mate circumfrance and diameter are two very different measurements

Answer: You are 100% correct and now i am also 100% embarrest...... Especially when i got G.S.E Grade 2 Tech-Drawing. My teacher would kill me and now i have to hang my head in shame! (silent chuckle with red face).

Ok!!... I will start again but keep in mind this time that "diameter" is from outer to outer across the center line of total circumference.

#1 If you change your Tyres from 265/65/17 to 265/70/17 then your speedo will slow down approx 4km (4%).....

#2 By going a taller Tyre your speedo then reads true speed/distance (excluding Tyre wear) and by achieving this you will notice your fuel consumption drop (According to odometer) due to you now loosing 40km per 1,000km (4%).... this is purely because your odometer is now giving you true distance which is now a shorter distance (That has to put a damper on your "True" fuel consumption).

#3 By going the bigger height in your Tyre this will also slightly increase gear ratio so gearing is also higher. (Maybe be noticeable if carrying or pulling heavy loads)... You may also notice your brake pedal slightly harder when pulling-up.

#4 Here is the link below for the holy grail on Tyres in NSW
http://www.rta.nsw.gov.au/registrati...vsi09_rev4.pdf

Minor changes to wheels (pg2)

# Wheels up to 26mm wider than the largest optional wheel recommended by the vehicle manufacturer for the
vehicle can be fitted without the need to notify the RTA.

# The outside diameter of the wheel and Tyre combination must be no more than 15mm over the largest diameter
wheel and Tyre combination specified for the vehicle.

EG: Approx

265/65-17 - Diameter 30.6 inch = 777.24mm

265/70-17 - Diameter 31.6 inch = 802.64mm

Total Diameter is increased by 25.4mm.... That's put me 10mm outside total Diameter legal limit!!

With all the above put into consideration one would have to agree that the RTA's regulation's on tyre Diameter are really vaige as tyre pressures (Including when the tyre heats up) will instantly change the total diameter of the the tyre and the speedo calibration will follow.

EG: inflate your tyres from 38psi to 48psi and take note on how much the car has risen!... Your total diameter has just widened.

Thanks "D4Dforme" for the observation. This is why a healthy debate is very productive at getting the correct facts.

Quote: "timmo23" My thought on the fuel consumption was that a larger tyre effectively raising the gear ratio will be harder to turn thus the engine working harder to push the vehicle along leading to increased fuel consumption and decrease in power

Answer: "yes" this is absolutely correct but if you have "torque" in your favor (Diesels have torque) you can take advantage of the higher gearing (Within reason) when cruising long journeys, But a higher gearing will always load any engine. That is where overdrive comes into play on cruise.

Cheers

[Troy1 Member Find all posts View Profile Close Troy1]

Ok so what your saying basically is if i change my tyres from 265 65 17 too 265 70 17, the tyres will actually be illegal according to RTA? Unless I get it engineered?

[wooley Avid PP Poster! Find all posts View Profile Close wooley]

Ok so what your saying basically is if i change my tyres from 265 65 17 too 265 70 17, the tyres will actually be illegal according to RTA? Unless I get it engineered?

I think the main thing to worry about is that: what we're basically saying is if you change from 265 65 17 to 265 70 17 you will be much happier. LoL.

[Steve M Addicted PP Member Find all posts View Profile Close Steve M]

Yep. no other answer, unless different rules for different states but as mentioned before. Here in NSW it would definately be illegal unless its engineered then you may still have issues with insurance ??. Now you and I know that 65 profile to a 70 is jack shit, same as these clowns that say lifting a 4wd even 50ml will make it unstable, some of these wankers have no idea. While I havnt lifted the 120 yet I had the two 90 series prior both lifted with OME and the things handled like another vehicle, less body roll, minimal nose diving under brakes, even with just passengers on board, and the later 90 grande I had stability control and there was no issues what so ever. Just some numnuts talking out there arse trying to justify their jobs..............Cheers Steve

[Steve M Addicted PP Member Find all posts View Profile Close Steve M]

Yep I agree with Wooley, its suprising just how much more clearance you get. I looked into getting an engineers certificate for my 120 and have done all the chasing and crap, I would be required to get a controler that I can flick between running the 70's over the 65's due to speedo inaccuracy, I think this for memory was $800 ?? cant remember now and this involved splicing into my speedo sensor on gearbox (not happening) brake testing (now is done at Eastern creek so Im led to believer 3k as they need to hire the circuit for a minimum time, 3 hours or some crap) has to be done in a controlled enviroment !!.So needless to say Im not paying over 4 k just to go one profile higher then standard. Again it comes down to if your willing to take the risk with insurance. Some have and have made claims for whatever reason and all has been ok. My main concern would be if you cleaned some one up and killed them, could see the headlines """man killed by monster 4wd running ilegal size tyres which contributed to killing""" then you would be screwed.........Not trying to scare you but anyone is willing to sue some one these days..........Cheers Steve

[SWR Banned Find all posts View Profile Close SWR]

Gday Troy1

Quote: Ok so what your saying basically is if i change my tyres from 265 65 17 too 265 70 17, the tyres will actually be illegal according to RTA? Unless I get it engineered?

Answer: ....... Yes!!

There is no yes-but, no-but or because-but... its.... yes! Lol (Jump in on the humor).

MY THEORY: If there is a set law on total wheel diameter (Ignore all the other wheel stuff) percentage based on factory compliance tyre size then if your tyres are pumped-up rock solid then the total diameter of the tyre will never make your speedo run slower than "true" speed because this was put into the equation of the manufactures of approx 4%.... By achieving this you can never be going faster than actual speed according to your speedo (Unless bigger diameter tyres are fitted).

Bigger tyres slow the speedo down and even more on high tyre pressures which increase more un-witting speeding drivers by de-fault!

As the RTA speeding campaigns go, "Therese is no such thing as safe speeding"...... How fast are you going? ..... Eer? not sure co's got bigger tyres Lol

The story goes that the government put laws in place to protect us from us.

After all that i like many others am 10mm outside of legal limit Eeeeek!

Cheers

PS, hope this doesn't trigger another Modification rant! Lol

[SWR Banned Find all posts View Profile Close SWR]

After re-reading what i have just written i think i will be going back to 265/65/17's when worn-out but the lift kit will stay as the car handles 100% with it and is legal but the tyres are not!

Cheers

[Guest Close Guest]

I had my lift and 70 series tyres approved and now run two compliance plates. Cost was about $300 bucks.

[wooley Avid PP Poster! Find all posts View Profile Close wooley]

I had my lift and 70 series tyres approved and now run two compliance plates. Cost was about $300 bucks.

Who did that for you, Piggy?

Might see if they can do wheels and a bigger tyre: say a 305/65/17

[Davros Advanced Member Find all posts View Profile Close Davros]

I had my lift and 70 series tyres approved and now run two compliance plates. Cost was about $300 bucks.

Yep, That is around what I paid for the lift/tyres and upgraded brakes on my last vehicle. The engineer required a replacment tyre placard, and another compliance plate. I had to get the plates made up at an extra cost though.

[Guest Close Guest]

My Plate is simply laminated paper and lives in behind the tool board in the rear door.

There is a thread on engineer reports on PP with all the details. I used a guy at Goodwood

[Guest Close Guest]

Here is the link
http://www.pradopoint.com/showthread...tive-Engineers

Other engineers
http://www.toymods.org.au/forums/tec...ineers-sa.html