Hey guys,

just a quick question.
looking at new tyres for my TJ VRX Series 2.
i have stock VRX rims on there with Grid2 225/50r17s.

i have been offered so cheap tyres that are 225/45r17's.

is it legal/possible to have this size tyre??
what could happen to handling/speedo if i get them?

Cheers,

Liam.

The rolling diameter will be out. Dunno about handling. Best to stick with the 225/50/17 to be honest.

Hey guys,

just a quick question.
looking at new tyres for my TJ VRX Series 2.
i have stock VRX rims on there with Grid2 225/50r17s.

i have been offered so cheap tyres that are 225/45r17's.

is it legal/possible to have this size tyre??
what could happen to handling/speedo if i get them?

Cheers,

Liam.
Yes, rolling diameter will be out. I think up to 10% change is legal.
The sidewall height will be reduced from 112.5mm to 101.25mm. So it will drop the car by 10mm in height as well as increasing the gap between tyre and wheel arch. Your speedo will be out eg.. Showing 100 really doing 90, etc..
IMO, get the correct size tyres.

thx guys, i'll just have too look harder!!

Yes, rolling diameter will be out. I think up to 10% change is legal.
The sidewall height will be reduced from 112.5mm to 101.25mm. So it will drop the car by 10mm in height as well as increasing the gap between tyre and wheel arch. Your speedo will be out eg.. Showing 100 really doing 90, etc..
IMO, get the correct size tyres.
Actually, the ruling in most states is +/- 15mm of the rolling distance.

so your 225/50r17 rolling distance is 1674 mm (or 1.674m)
and the 225/45r17 rolling distance is 1709 mm (or 1.709m)
which is an illegal change in most states (without recalibrating your speedo and getting an engineers cert.)

cheers,
.wook

Actually, the ruling in most states is +/- 15mm of the rolling distance.

so your 225/50r17 rolling distance is 1674 mm (or 1.674m)
and the 225/45r17 rolling distance is 1709 mm (or 1.709m)
which is an illegal change in most states (without recalibrating your speedo and getting an engineers cert.)

cheers,
.wook

Don't know where you got those numbers from.. how can a tyre with a smaller profile (and therefore smaller sidewall) have a larger circumference?

Numbers taken from: http://www.miata.net/garage/tirecalc.html

Specification Sidewall Radius Diameter Circumference Revs/km Difference
225/50-16 112mm 316mm 631mm 1984mm 504 0.0%
225/45-16 101mm 304mm 609mm 1913mm 523 -3.6%

Actually, the ruling in most states is +/- 15mm of the rolling distance.

and I think ull find its the diameter and NOT the circumference :doubt:

going by ur profile and cthulhus calculations perfectly legal in victoria.

Don't know where you got those numbers from.. how can a tyre with a smaller profile (and therefore smaller sidewall) have a larger circumference?

Numbers taken from: http://www.miata.net/garage/tirecalc.html

Specification Sidewall Radius Diameter Circumference Revs/km Difference
225/50-16 112mm 316mm 631mm 1984mm 504 0.0%
225/45-16 101mm 304mm 609mm 1913mm 523 -3.6%
17" rims dude, not 16.

17" rims dude, not 16.

Good call. Easy fixed.

Specification Sidewall Radius Diameter Circumference Revs/km Difference
225/50-17 112mm 328mm 657mm 2063mm 485 0.0%
225/45-17 101mm 317mm 634mm 1993mm 502 -3.4%

The 225/45 will have a lower load rating (<= 91) which makes it illegal. It is 3.5% smaller
or 23mm smaller in diameter. You'll be doing 96.57km/hr when it says you are doing
100km/hr. Also, for every 100000 km, your odo will add an extra 3425.7kms. It is not
recommended to go beyond +/- 2.5%.

just get the tires you wont get pinned with 17s on your car at all trust me

just get the tires you wont get pinned with 17s on your car at all trust me

Can you guarantee that in writing so that when he does get pinned, he can come running
to you. :nuts: Those tyres are designed for your medium sized cars like the liberty, wrx etc. Trust me, your insurance company won't like it a single bit.

Diameter can't change by more than 15mm, diameter will change by 22mm, so they are illegal tyres. The chance of anyone picking up such a small difference is pretty slim though.

Diameter can't change by more than 15mm, diameter will change by 22mm, so they are illegal tyres. The chance of anyone picking up such a small difference is pretty slim though.

until he/she has an accident or when the tyres blow out during high speed braking etc.

You do know of course that a load bearing of 91 gives you 610 kg at each wheel. Therefore 2440 kg overall. Which means that you would need 5 x 140 kg passengers + 1 car full of petrol (est. 1600 kg) + 140 kg of luggage before you came anywhere near being dangerous on those sorta tyres. And then you'd have to be doing some pretty insane break testing (using something more substantial than the stock calipers and pads) to come close to breaking something

until he/she has an accident or when the tyres blow out during high speed braking etc.
Only if it were proven that the tyres were at fault.

You do know of course that a load bearing of 91 gives you 610 kg at each wheel. Therefore 2440 kg overall. Which means that you would need 5 x 140 kg passengers + 1 car full of petrol (est. 1600 kg) + 140 kg of luggage before you came anywhere near being dangerous on those sorta tyres. And then you'd have to be doing some pretty insane break testing (using something more substantial than the stock calipers and pads) to come close to breaking something
It doesn't matter, they're still illegal. In some cases an insurance company may investigate the tyres and if they are infact illegal your insurance will be void, regardless of if they were the cause or not. (within reason, use your brain)

my insurance company knows what size rims are on my car and they dont mind and im running 20s

if we are all worried if its legal or not legal then buy a standed car and do nothing to it
all mods can be defected any thing that is non standed on a car from a gear know to what ever the case may be if the cop is having a bad day he will pin you for it but its not likely

legal or not legal if you want it get it if you get pinned get it fixed and get the defect cleared and then put it back the way it was :badgrin:

we all run the risk of getting defected but ahh well what can ya doo if you dont want to get defected stay stock

or get what you want on your car make it what you want it to be and run the risk like most of us doo

running 20s are fine as long as the load rating, etc are fine. Also, you can use the static
weight of a car when talking about load rating. When you brake heavily, more weight gets
transfered onto the front wheels/tyres and if doing a right turn at the same time, then the
front left wheel/tyre takes the majority of the load. Think about it.