Tyre size change much speedo difference?

[pradopommie Lurker Find all posts View Profile Close pradopommie]

Hi,
I'm changing my tyres from some dodgy Maxis tyres to Micky Thompson STZ but the MT's are bigger.
Will it make much difference to the speedo reading? If so can you get the speedo recalibrated as the speed limits are slow enough in Oz without going under the speed limit as well !!
Also am I going to notice any other differences?
Old tyres are 265/65 17
new ones are 275/70 17

[Guest Close Guest]

That's a big size jump and you will get rubbing of the tyres. There will also be a big difference to the speedo. Depending on the year of the Prado, it could be an issue. Whichever the case, the speedo must not under-read.

Stick with 265/70R17 or 275/65R17.

[discoveraus Member Find all posts View Profile Close discoveraus]

Hello Pradopommie,

The 275/70-17 tyres are 816 mm in diameter whilst the 265/65-17 are 776 mm. This will change your true speed by 5.25% for the same indicated speed and engine revs so you will technically be unroadworthy as your speedo will read low by upto 5.25%. It will probably be about 3% low in reality because the standard tyres give a reading about 2% high as standard. ie when your speedo says 100kph you will be doing some 103.5 plus and will be booked and maybe even given an unroadworthy sticker for your trouble.

The tyres will also probably rub the bodywork or suspension somewhere under some conditions and give you some grief. This also makes the car unroadworthy. 265/70-17 seems to be ok in some states whilst all states accept 275/65-17. Until the rules change you are limited by law to these sizes.

regards

Ross

[pradopommie Lurker Find all posts View Profile Close pradopommie]

Thanks for the info guys..

The car is a 2003.
it's got a 40mm lift so i'm hoping they are not going to rub too much.
Is there anyway to get the speedo recalibrated for new tyre size?
also i forgot to ask.. will it affect the changing of gears at the correct time on the auto box? It's just a guy at work said his Jeep now changes at the wrong time after fitting bigger tyres but i would have thought it wouldn't make a difference.

[Guest Close Guest]

I think with a 40mm lift you will be fine. I have MTZ's on that are only 8mm smaller than the STZ in diameter. But the MTZ has a chunky sidebiter and the 265 is actually wider than the 275 STZ!! They "should" only touch the sway bar at very full lock, and it is not a sharp item, they will merely leave a patch of wear on it as my MTZ's do. Chances are having no sidebiter they will possibly not even touch.

I am also going to this size tyre next. I have an engineering certificate already making the larger tyres compliant.

You CANNOT adjust the speedo. It will read out. EG Speedo shows 100 on mine when my true speed moving is 104.5 in reality.

Be interested on feedback on how they fit up and if any issues. I know a lot of the members are looking at this very same tyre fit currently.