Hi everyone, 

Newbie here. 

From the July of 2019 to July 2022  I ran a Mk 4 St-Line with the 150hp engine.  I loved it.

When it was time to give it back - contract hire - I decided to buy a second hand 2018 68 plate ST-Line X with the 182hp engine, and some of the extra trimmings such as climate control. 

The X came with 18" wheels on 235-40 profile tyres. 

The ST-Line came with 17" wheels on 215-50.

The X is unsurprisingly a less compliant, harsher ride, but it also tramlines more and feels a bit twitchy and less secure. A hoot to drive, but doesn't provide the same level of confidence as you approach the limit. The ST-Line was pretty faultless by comparison. As a result, I'm considering dropping down to the ST-Line 17" wheels for the X and am curious whether anyone has done something similar, or has any experience that might be useful.

Both cars were run on Conti SportContact 5s or 6s, so I don't think the tyres are responsible for the difference.

Thanks.

14 hours ago, ModernDayEscort said:

Hi everyone, 

Newbie here. 

From the July of 2019 to July 2022  I ran a Mk 4 St-Line with the 150hp engine.  I loved it.

When it was time to give it back - contract hire - I decided to buy a second hand 2018 68 plate ST-Line X with the 182hp engine, and some of the extra trimmings such as climate control. 

The X came with 18" wheels on 235-40 profile tyres. 

The ST-Line came with 17" wheels on 215-50.

The X is unsurprisingly a less compliant, harsher ride, but it also tramlines more and feels a bit twitchy and less secure. A hoot to drive, but doesn't provide the same level of confidence as you approach the limit. The ST-Line was pretty faultless by comparison. As a result, I'm considering dropping down to the ST-Line 17" wheels for the X and am curious whether anyone has done something similar, or has any experience that might be useful.

Both cars were run on Conti SportContact 5s or 6s, so I don't think the tyres are responsible for the difference.

Thanks.

Part of the reason I went for the ST-Line 1.5 150hp, like the look of the 18" wasn't sure how the diamond cut would last on UK roads, also too low profile on for me, mine still thumps on bumps from the rear.

Thanks Mark. I had the same concern, but then the car I bought came with the wheels in black. Not seen them on another ST-Line X.

Ultimately, I curious as to whether there will be any downside to the change I'm considering. 

I haven't seen the black wheels, might be a new colour? hopefully someone who has the 18" wheels will let you know what they ride like.

For general info, the black wheels are on a 68 plate ST-Line X, and I'm assuming they were original equipment when it was new.

And to be clear on my question here:

I know what the 18" ride like in an ST-Line X and I know what the 17" ride like in a ST-Line.

I'm wondering about whether there are likely to be any issues putting the 17" on an ST-Line X. 

47 minutes ago, ModernDayEscort said:

Thanks Mark. I had the same concern, but then the car I bought came with the wheels in black. Not seen them on another ST-Line X.

Ultimately, I curious as to whether there will be any downside to the change I'm considering. 

That'll just be a cheap refurb job.  The wheels were originally diamond cut on the face.  Much cheaper just to spray paint the whole thing when refurbishing. 

38 minutes ago, ModernDayEscort said:

I'm wondering about whether there are likely to be any issues putting the 17" on an ST-Line X. 

No.  

I'm no expert by any means but is the suspension set up the same on a st line to a st line X ?

It may not just be as simple as swapping out the 18s for 17s 🤔

14 minutes ago, Wino said:

I'm no expert by any means but is the suspension set up the same on a st line to a st line X ?

Yes.  Both 'sports' suspension.  Lower and stiffer than Titanium/TX.  1.5EB on a 68 plate should still have IRS as well.

No issues downgrading to 17" on your ST-Line X just make sure they have the correct size tyres fitted that a Standard ST-Line would have

You'll need to update the car's config so that it can calibrate the speedo and record mileage accurately.

EDIT: It will also count as a modification on your insurance.

1 hour ago, alexp999 said:

You'll need to update the car's config so that it can calibrate the speedo and record mileage accurately.

EDIT: It will also count as a modification on your insurance.

I'm not an expert, but the overall diameter of tyre would stay the same, wouldn't it?

3 minutes ago, Nimrodmk8 said:

I'm not an expert, but the overall diameter of tyre would stay the same, wouldn't it?

No, the circumference of the 17" is 2032mm, the 18" is 2027mm.

It's not a lot, but it will change the indicated speed and recorded mileage from being as accurate.

That's why the car has the option to specify the wheel size. Also one reason why you shouldn't deviate from the manufacturer recommended tyre size.

3 minutes ago, Nimrodmk8 said:

overall diameter of tyre would stay the same, wouldn't it?

No.

Depending on what wheel / tyre combination you choose the overall diameter will change

This link will help you see the difference in sizes as you change the tyre sizes:

https://tiresize.com/tyre-size-calculator/

In the real world, it won't make any difference.  It's literally 0.3mph difference at 70mph...  

Didn’t the mk4 have 2 different rear suspension set ups depending on engine?

multi Link and twist beam.

worth checking if both were multi link.

22 minutes ago, RL123 said:

worth checking if both were multi link.

Multi link is now only available on the Estate version as far as I know.

18 minutes ago, unofix said:

Multi link is now only available on the Estate version as far as I know.

ST is still multi-link

My guess is his 2019 had the twist beam and the 2018 the multi link hence the difference in ride quality. Tyres do make some difference but not as much as suspension layout. Multi link better for track  use, twist beam more compliant imo.

Twist beam isn't compliant.  The second wheel is dragged in the same direction as the first.  Fine on a perfectly smooth road, useless on anything rough.

I've had to avoid anything non-IRS since my health conditions worsened.

2 hours ago, alexp999 said:

No, the circumference of the 17" is 2032mm, the 18" is 2027mm.

It's not a lot, but it will change the indicated speed and recorded mileage from being as accurate.

That's why the car has the option to specify the wheel size. Also one reason why you shouldn't deviate from the manufacturer recommended tyre size.

Thanks for the info.

1 hour ago, TomsFocus said:

Twist beam isn't compliant.  The second wheel is dragged in the same direction as the first.  Fine on a perfectly smooth road, useless on anything rough.

I've had to avoid anything non-IRS since my health conditions worsened.

Having had both set ups, my personal preference would be the twist beam for a more comfortable ride and the fully independent for faster handling ond off road driving. It also depends how well designed and set up they are.

On 11/15/2022 at 9:36 AM, TomsFocus said:

That'll just be a cheap refurb job.  The wheels were originally diamond cut on the face.  Much cheaper just to spray paint the whole thing when refurbishing. 

And there was me thinking I has some sort of rare combination of black wheels and red brake callipers!  *🙄Sigh*

On 11/15/2022 at 10:47 AM, alexp999 said:

You'll need to update the car's config so that it can calibrate the speedo and record mileage accurately.

EDIT: It will also count as a modification on your insurance.

Thanks Alex, I wouldn't have thought of the insurance point.  

On 11/15/2022 at 12:51 PM, unofix said:

No.

Depending on what wheel / tyre combination you choose the overall diameter will change

This link will help you see the difference in sizes as you change the tyre sizes:

https://tiresize.com/tyre-size-calculator/

That's really helpful Unofix!