Would I be able to change my 215/50 18 tyres on my SEL 18" Braga alloys to 225/50 18 tyres?  

In theory yes but it's right on recommended limits. Best advice is check with your insurer.

Our 190 TDI SE L was supplied from the factory on 225/50x18 tyres on 8J Braga alloys. It will raise the gearing a bit and your speedo should be a bit more accurate than it is now.  However, best to check it against a GPS speed reading when you have then fitted.

7 hours ago, Schtum said:

Our 190 TDI SE L was supplied from the factory on 225/50x18 tyres on 8J Braga alloys. It will raise the gearing a bit and your speedo should be a bit more accurate than it is now.  However, best to check it against a GPS speed reading when you have then fitted.

 

All 18" rims on the Karoq are 7J, and that includes the 7Jx18 ET45 Braga alloys.

 

Karoq alloy rims

https://eshop.skoda-auto.cz/en_CZ/alloy-wheels/c/alloyWheels

 

Changing 215/50R18 to 225/50R18 raises the gearing by about 1.5%. As the standard speedometer will over-read by about 5% your speedometer will over-read by about 3.5% once the tyre size change has been made. However, google maps now has a GPS option so it's always worth checking.

 

The Karoq does have a 225/40R19 tyre size option for 2WD cars and 225/45R19 for 4WD cars (as you can see on wheel-size.com), so fitting the 225/50R18 tyre size won't increase the car's performance compared to those tyre sizes.

 

However, if you want a cheap and comfortable tyre size, 215/60R17 might be worth a look. You could fit this size to steel or alloy 6.5Jx17 ET38 Kodiaq rims. Compared to 215/50R18, 215/60R17 will raise the gearing by about 2.6%.

 

6.5Jx17 ET38 5/112 57.1 steel rims from the Kodiaq

https://www.mytyres.co.uk/rims/rim-selector

 

ETRTO lists a 6J to 8J rim size range for the 225/50R18 tyre size, with 7J highlighted because that's the normal rim width for this size tyre.

 

ETRTO approved rim widths
225/50 6.0-7.0-8.0

 

wheel-size.com

https://www.wheel-size.com/size/skoda/karoq/2019/#trim-15tsi-eudm-148

 

Edited 1 December, 20223 yr by Carlston

Changing the width of the tyre will not affect the speedometer reading as the circumference is the same, or am I missing something?

The circumference is not the same, because 215/50 has a lower sidewall than 225/50.

 

Sidewall   215*50% = 107.5mm
Sidewall   225*50% = 112.5mm

The 50 in a 215/50 size indicates that the sidewall height is 50% of the 215 width, therefore 107.5 mm. Similarly for a 235/50 tyre the sidewall is 50% of 235mm = 117.5mm, so the tyre will have a rolling diameter not far off an extra inch.

There is a useful  tool that indicates the change in speed when tyres other than those specified by the manufacturer are fitted:

 

Speedo error calculator – speedometer error as a result of tyre size change – Speedometer calibration (tyresizecalculator.com)

1 hour ago, Karock said:

There is a useful  tool that indicates the change in speed when tyres other than those specified by the manufacturer are fitted:

 

Speedo error calculator – speedometer error as a result of tyre size change – Speedometer calibration (tyresizecalculator.com)

 

That tool incorrectly assumes that the speedometer is correct when on standard tyre sizes.

 

This isn't the case, because car speedometers tend to over-read by about 5% when on standard tyre sizes.

 

So by fitting slightly oversize tyres, you make the speedometer more accurate not less accurate.

 

Edited 2 December, 20223 yr by Carlston

However even though the speedo is optimistic, the trip meter is near enough spot on over a 100 mile trip on the supplied tyres when new to the distance calculated by the navigation. So it could be nearly exact if they wanted!

17 minutes ago, Carlston said:

This isn't the case, because car speedometers tend to over-read by about 5% when on standard tyre sizes

 

 

I think every VAG vehicle I've driven in recent years has indicated 80 mph when my GPS has shown 76 mph.   

 

On the other hand two rental Nissans, a Murano in USA and a Note on Fuerteventura have agreed exactly with my GPS. 

 

I'm currently running 215/60x17 Dunlop D5 Winter Sport on Audi Q3 alloys, on the Karoq.  The handling is a fair bit more "pointy" on these than it is on the 18" Bridgestones. 

Edited 2 December, 20223 yr by Schtum

I’m know that 73mph on my speedo is an exact 70mph with a speed app. With my current 16” winter wheels on I have to get 75 on speedo for exact 70.

Carlston, you are splitting hairs!

 

The tool is a useful guide to anyone not sure what effect changing tyre size and or profile would have on the speedometer reading, the fact that most speedos are designed by the manufacturer to read slightly high is neither here nor there.

 

www.bertram-hill.com

 

16 hours ago, kenfowler3966 said:

I’m know that 73mph on my speedo is an exact 70mph with a speed app. With my current 16” winter wheels on I have to get 75 on speedo for exact 70.

For those who want to be pedantic, it will depend on tread depth.

 

As tread wears, tread will go down about 4-5mm, so the diameter decreases by 8-10mm.   If you take a diameter of about 690mm, then 10mm is about 1.4%

 

1.4% of 73mph is 1mph, so your calcs will be wrong by 1mph when tyres wear.

 

So personally I wouldn’t worry about few mm diameter difference 

 

 

1 hour ago, SurreyJohn said:

For those who want to be pedantic, it will depend on tread depth.

 

As tread wears, tread will go down about 4-5mm, so the diameter decreases by 8-10mm.   If you take a diameter of about 690mm, then 10mm is about 1.4%

 

1.4% of 73mph is 1mph, so your calcs will be wrong by 1mph when tyres wear.

 

So personally I wouldn’t worry about few mm diameter difference 

 

 

It’s safe though because as tread wears the speedo is even more optimistic