Wheel & Tyre Size Change - Cupra 300

NotSoSimple

Simple
Mar 3, 2017
243
17
Suffolk
I am thinking about moving from 19" to 18" alloys in order to replace the wheel size reduction with tyre sidewall.

So my thinking is to maintain the existing overall size of the wheels by reducing the allow size by 1in and increasing the sidewall height of the tyres by .5. Is this even possible? Does it do what i think it should do?

Existing - 235/35R19 - 19" alloy
Proposed - 235/40/R18 - 18" alloy

Does this maintain my overall "wheel" size as i have now?

The aim is to facilitate better winter tyres choice thats available in 18 than in 19"
 

JackB

Active Member
Jan 18, 2020
100
60
I'm in the process of making the same change from 19in to 18in.

235/40/18 is indeed the closest possible match to 235/35/19. That's what I have gone for.

Technically speaking it is about 0.3% smaller than the OE setup.

Differences in wear (brand new tyres vs used) are more than that... it's really negligeable and not something so worry about.

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JackB

Active Member
Jan 18, 2020
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60
I went down from 19in to 18in because I wanted to reduce weight (the car sees some track use) and also increase sidewall for compliance on the road.

A side benefit is that both the wheels and accompanying tires are cheaper.

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Carbonara

Active Member
Aug 19, 2018
81
21
Just mind out if you have the Performance Pack larger brakes as only certain 18" wheels will fit. Search the thread referring to winter wheels/tyres.

Also you might find a saving between 225 and 235 section width. This was the case when I got my 18" Conti AllSeason Contacts, where I defaulted to 235. An image of a door sticker from a standard car showed the 225 option which, when checked, was a fair bit cheaper than the 235 and arguably with a slight snow/standing water advantage.
 

NotSoSimple

Simple
Mar 3, 2017
243
17
Suffolk
Yes, thanks for the heads up - i have the standard Cupra brakes so shouldn't have as much of an issue.

I'll check out the 225 for winters, i am running 235 winters at the moment to match my summers and they have worked well but do miss my skinnier winters on the old Polo as that thing was unstoppable in the snow on steel wheels and skinny rubber!
 

JackB

Active Member
Jan 18, 2020
100
60
Just a heads up - If you go to 225 as well it will have a more significant impact on your speedo/mileage readings, which will be slightly higher than reality.
  • 235/35/19 - Stock
  • 235/40/18 - 0.3% smaller (mph reading change not applicable until crazy high speeds, odometer will go up by 1003 miles for every 1000 travelled)
  • 225/40/18 - 1.5% smaller (where your stock car would read 69mph, the same speed will now read 70mph, odometer will go up by 1015 miles for every 1000 travelled)
I believe you can actually correct for this using VCDS / OBD Eleven but this is not something I have researched.

Tool for checking measurement changes: https://www.wheel-size.com/calc/
 
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Mikertroid

Active Member
May 31, 2019
142
39
Could you post your rim choices here? I'll be doing the same as there are too many potholes on my commute for 19" wheels....
 

NotSoSimple

Simple
Mar 3, 2017
243
17
Suffolk
Could you post your rim choices here? I'll be doing the same as there are too many potholes on my commute for 19" wheels....

I like multi spoke black rims - so something like the following:

Sparco Assetto Gara (matt black) (£768)
OZ Racing Ultraleggera (matt black) (£1300)
Revo RV018 (anthracite - gloss black is yuck) (£1200)

Probably based on price and the fact that Sparco alloys are made by OZ, i'll probably go Sparco.

I fear this post might spark some serious trolling

:banghead2:drive2:

ozw_ultra-blk.jpg
ozw_assetto-blk.jpg
rev_rv018-matte-anth_nov19.jpg
 

JackB

Active Member
Jan 18, 2020
100
60
I looked at a few wheels (pretty much those suggested above and Team Dynamics Pro Race 1.3's) and ended up with Bola FLC's in matt gunmetal, 18in x 8.5 ET45 (£755).

As mentioned above, I was looking for lightweight - these were advertised at 8.2kg and I have weighed them myself at 8.1kg. This is really impressive for the size.

I then got them fitted them with Michelin Pilot Sport 4 S tyres (my scales claim 10kg for these, 18.1kg total) in 235/35/18.

Cupra 11.png

I am really happy with them so far, they look great. Not gone on the car yet but will be soon :).
 
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BigJase88

Jase
Apr 20, 2008
3,767
1,069
The standard leon 18’s run 225/40/18 tyres, 235’s are a waste of money.

the speedo difference is negligible and i highly doubt they have different calibrations depending on wheel size fitted to the cars. Smaller alloys = bigger tyres so rolling radius across the range is similar

my FR is on 18’s with 225/40/18 tyres
 

jt20vt

Active Member
Sep 17, 2010
185
41
If the width of the wheel is 7.5 you can fit the 235 size tyre as it is a size allowed, it might give a bit more side ways roll under hard conering but not really noticable on the road and will give you more kerb protection. I have 235/45/17 wheels on my mk3 cupra st.
 

NotSoSimple

Simple
Mar 3, 2017
243
17
Suffolk
So i did it.

Bola B14 18in Alloys wrapped with PS4

I think they look great and have made a vast difference in comfort over bumps, cracks and small pot holes.

Got some all black metal bola centre caps coming too to make it more stealth....

IMG_20200529_105522.jpg
IMG_20200530_210430.jpg
IMG_20200605_084347.jpg
 
Jun 14, 2020
4
1
I'm looking to fit some 18" rims with 225/40 tyres.
What is the lowest offset I can go to that will just fit inside the wheel arches safely? (I'm thinking somewhere around ET40)
 

JackB

Active Member
Jan 18, 2020
100
60
I'm looking to fit some 18" rims with 225/40 tyres.
What is the lowest offset I can go to that will just fit inside the wheel arches safely? (I'm thinking somewhere around ET40)

225 will give a little more clearance from rubbing than 235.

I can tell you that on my car with 235/40/18s with 8.5j rim width and ET45 offset I haven't had any issues at standard ride height.

All these variables make a difference to clearance:
Tire width
Tire profile
Rim diamater
Rim width
Rim offset
Camber
Ride height
 
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