Morning folk',

 

I bought a set of 18" Gemini's to replace the 17" on my 1.8TSI prefacelift.

 

I was wondering if any coding is required, the wheel size should be very similar but I read somewhere that vcds had a correction feature for it.

 

With the current set of 17" OEM, my Speedo is off about 2.5mph

 

Many thanks!

 

Does anyone have picture or Gemini's fitted on normal octy's?

Thanks

 

 

Are you putting tyres on the 18" rims that are going to keep the Total Circumference / Diameter much the same or just a little more?

 

If a little more then it will likely just have the speedo more accurate rather than over reading as much as it is. 

It should be the same ish, yeah!

 

My 17's 225 45 17

The Gemini's: 225 40 18

 

It shows a minor size difference.

+0.4%

 

Probably not worth the bother indeed.

 

 

One problem with 18" Gemini rims is that they are 7.5J wide which makes them more prone to kerbing damage when fitted with 225/40R18 compared to 7Jx17 rims fitted with 225/45R17.

 

To get around this problem you could use the slightly wider 235/40R18 tyre size to give the 7.5Jx18 rims almost as muich kerbing protection as 225/45R17 fitted to 7Jx17 rims.

 

As you can see in the chart below, the sidewalls of 235/40R18 will bulge out by 2.5mm more each side compared to 225/40R18 when both are fitted to a 7.5J rim width. 

 

Actual inflated width of tyre when fitted to 7.5J rim

225/40R18 224mm

235/40R18 229mm

 

Actual inflated width of tyre when fitted to 7J rim

225/45R17 219mm

 

Compared to the hard riding 225/35R19 fitted to a 7.5J rim, the below tyre fitted to a 7.5J rim will be in a different league when it comes to ride comfort. This MIchelin Primacy 4+ is a summer touring tyre and not an UHP (Ultra High Performance) tyre so has softer and more flexible sidewalls for a better ride. It's also not overspecified when it comes to the load rating and speed incex, ie. SL and not XL, and W speed rating and not the higher Y speed rating.

 

Michelin Primacy 4+ 235/40R18 91W (Euro label C A 69dB) (summer touring tyre)

https://www.camskill.co.uk/m61b0s322p213489/Michelin_Tyres_Car_Michelin_Primacy_4%2B_235_40_R18_91W_RG_TL_Fuel_Eff_%3A_C_Wet_Grip%3A_A_NoiseClass%3A_B_Noise%3A_69dB

 

By comparison with the above 235/40R18 91W, the below 225/40R18 92Y XL will give a noticeably harder ride when both are fitted to a 7.5J rim width. It's 72dB noise rating is also far worse.

 

Michelin Pilot Sport 5 225/40R18 92Y XL (Euro label C A 72dB) (UHP Ultra High Performance tyre)

https://www.camskill.co.uk/m61b0s134p209254/Michelin_Tyres_Car_Michelin_Pilot_Sport_5_PS5_225_40_R18_(92Y)_XL_TL_Fuel_Eff_%3A_C_Wet_Grip%3A_A_NoiseClass%3A_B_Noise%3A_72dB

 

Edited 7 November, 20232 yr by Carlston

Oh thank you kindly mate! I was a bit worried about kerbing them. Especially with the World war 2 type of roads here in Belgium.

 

I'll definitely go for the wider tires!

The Goodyear Eagle Asymmetric 5 offers decent rim protection, shown here on 19" rim.