Wheel advice

[DUBGTI]

Hey guys I am looking to get some new wheels and tyres for the RS wagon, has anyone had experience with larger than OEM size of 225 40 R18 x 7.5 with 51ET I'm trying to figure out what is the fattest tyre I can fit under the guard, I plan to lower the car at least 25mm maybe double that if possible.

Is it possible to run a 19"x 8.5" with a 235 35 or 245 30? what fits best? It seems a 225 35 R19 is the closest to stock rolling diameter being -0.45% out and doing 59.73mph at a speedo reading of 60mph (tyre size calc worked in mph).

What are you guys running on ya Octy's? would love to see some pics of different wheel combos

cheers guys,

[zei20t]

I have 19x8.5" with a 235x40x19 tyre. I don't notice any rubbing except on hard turns on the outside wheel when the suspension compresses. harder spring/shock will help that.

[donweather]

Zei do you have stock or lowered suspension. And what ET are you running?

[DUBGTI]

Hey can I ask how accurate your speedo is? the tyre calculator shows your setup to be almost 5% larger than stock and would result in a roughly 5km/h difference from stock. At an indicated 100km/h on your speedo your actual speed would be roughly 95km/h, but how accurate are they at that speed to start with, most cars would read less than 100km/h at an indicated 100km/h to start with, is this increased with your size tyres?

I am trying to stay as close as possible to the stock rolling diameter to avoid and potential issues be it with the car or the law
I'm just cautious off speeding fines......haha, I'd be thinking I'm going at the speed indicated on the speedo, but actually doing another.

cheers

[brad]

Hey can I ask how accurate your speedo is? the tyre calculator shows your setup to be almost 5% larger than stock and would result in a roughly 5km/h difference from stock. At an indicated 100km/h on your speedo your actual speed would be roughly 95km/h, but how accurate are they at that speed to start with, most cars would read less than 100km/h at an indicated 100km/h to start with, is this increased with your size tyres?

I am trying to stay as close as possible to the stock rolling diameter to avoid and potential issues be it with the car or the law
I'm just cautious off speeding fines......haha, I'd be thinking I'm going at the speed indicated on the speedo, but actually doing another.

cheers

As all these vehicles seem to differ, best to check with reasonably modern GPS. As an indication, I've gone up 4% (+20mm diameter) and am still 2kmh under at 100kph. From the factory my speedo was 10kph out at 100kph

I get the feeling that zei20t has made a typo & has 235/40r18 but maybe I'm wrong.

Keep in mind that you also have to consider maintaining the correct load rating & this gets difficult when you get into 19"s.

[harlie]

Mine was in for an alignment to sort the rear geometry during the week. Local tyre shop recommended I go to 235/40R18 next time - cheaper tyres ect ect - they are 8mm larger in diameter. are they wrong?

Now I'm shopping for wheels - 18x8 et45. during balancing they noticed one of my badly scratched neptunes has what he calls a flat spot, (I call it buckled) on the inner rim - that will be the vibration at 100kmh.

[Dutch77]

Mine was in for an alignment to sort the rear geometry during the week. Local tyre shop recommended I go to 235/40R18 next time - cheaper tyres ect ect - they are 8mm larger in diameter. are they wrong?

Now I'm shopping for wheels - 18x8 et45. during balancing they noticed one of my badly scratched neptunes has what he calls a flat spot, (I call it buckled) on the inner rim - that will be the vibration at 100kmh.

Tyre shop is correct on both counts (but I agree with Brad's advice, check it out before playing is preferable).

8mm larger diameter, which means you will be going a fraction slower than indicated. 235/40/18s are often cheaper than 225s as the 235s are a common Falcodore 18 inch fitment and thus bought in large quantities.

Loads of wheel options, check out the Mk7 thread if you like as plenty of 18x8 ET45 or similar wheels in there.

[Guest001]

Hey can I ask how accurate your speedo is? the tyre calculator shows your setup to be almost 5% larger than stock and would result in a roughly 5km/h difference from stock. At an indicated 100km/h on your speedo your actual speed would be roughly 95km/h, but how accurate are they at that speed to start with, most cars would read less than 100km/h at an indicated 100km/h to start with, is this increased with your size tyres?

I am trying to stay as close as possible to the stock rolling diameter to avoid and potential issues be it with the car or the law
I'm just cautious off speeding fines......haha, I'd be thinking I'm going at the speed indicated on the speedo, but actually doing another.

cheers

In fact ALL car speedos must read over the speed you are actually doing and legally cannot read less.
The ADR rule states that they may be up to 10k over at 100kph <> 4 so they could be up to 14k fast but are not allowed to read under.
Putting larger tyres on makes it read slower but in my case in the Polo it is 7k over and to get it right would take tyres 40mm larger which are illegal

See here for accurate alterations Custom rims, wheel tire packages for your ride - RIMSnTIRES.com

[brad]

In fact ALL car speedos must read over the speed you are actually doing and legally cannot read less.
The ADR rule states that they may be up to 10k over at 100kph <> 4 so they could be up to 14k fast but are not allowed to read under.
Putting larger tyres on makes it read slower but in my case in the Polo it is 7k over and to get it right would take tyres 40mm larger which are illegal

See here for accurate alterations Custom rims, wheel tire packages for your ride - RIMSnTIRES.com

Hillbilly, if I can move mine 8kph by going up 20mm in diameter (which is still illegal) then why do you need 40mm to move the same approximate error? What am I missing?

[Guest001]

Hillbilly, if I can move mine 8kph by going up 20mm in diameter (which is still illegal) then why do you need 40mm to move the same approximate error? What am I missing?

Well according to the comparator I posted a 195/55/15 has a diameter of 595mm on a 5.5in rim

To get a 6.7% difference I would have to go to a 195/65/15 which has a diameter of 635mm. Diff is 40mm

Remembering the diameter is right across widest point and not the radius which is from the centre to one edge. In QLD 26mm is largest legal diameter difference
Put the figures in the comparator with the larger size on the left and you will see.