Handling after changing Rims on my Bora

[kaanage]

wai's comments are pretty much spot on - I disagree about the increase in unsprung weight only having an effect on very bumpy corners and the aquaplane issue is more about the contact patch becoming shorter as it gets wider so the tread has less distance to disperse the water (contact pressure stays pretty much the same unless going a LOT wider) but that's all.

Most people get wider rims with enough increase in offset to maintain the same backspacing (or at least to minimise any reduction in backspacing) which leads to the contact centerline moving outwards - this almost always has the effects that you have noticed (borked up steering) since no macpherson strut car has negative offset steering.

Higher tyre pressure will improve steering response.

[Diesel_vert]

Hi Dylan and Diesel Vert

Thank you for pointing out my mistake, yes, the tyres are 225/40 R18.

Thanks, at least the tyre size is proper.

I can see that you've bought a set of Kumho Ecsta tyres, but which Ecsta model are they?

[EdwinConan]

I just went out and had a look the tyres, it says Kumho Ecsta Seven. If this makes sense.

[PeanutButterWolf]

Hey bud, your car looks great. I love those wheels, so much so that I received a set last month I haven't fitted them yet though. A little off topic here but did u find the rears look ok without the need for spacers?

Cheers, Don

[Diesel_vert]

I just went out and had a look the tyres, it says Kumho Ecsta Seven. If this makes sense.

Thanks for that.

To expand on my earlier post - when the steering wheel goes light, it's an indication of reduced grip. Fitting brand new tyres will often induce this condition due to their slipperiness, but as the tyre is run-in and the tread roughens up, grip and steering weight should gradually increase.


Tyre choice also affects grip, handling and response. The Ecsta Seven (KU23), although positioned as an ultra high performance tyre by Kumho, appears to be optimised for ride comfort and low noise rather than more sporting attributes, which may contribute to the mushy feel depending on the stiffness of its sidewalls.

Not exactly the sportiest tyre in the world then, but hopefully you'll at least enjoy a calmer and quieter ride than is usual with big wheels & low profile tyres - though if the road surfaces you regularly drive on resemble goat tracks, you might be better off without fitting super stiff tyres that would just bounce you & the car around and end up providing less grip anyway.

I think one aspect of handling where you'll see an improvement, is that lower profile tyres will generally allow you to corner faster before they start to let go.

BTW, the wheels really suit your car - they just look the business.

[EdwinConan]

Hi Don,

Good to hear that you choose this rim as well. Yeh, I know the rear wheels are not flush to the wheel arch, but it's a lot better than the stock wheels. I'm ok with the look at the rear, but it's just me.

Cheers, Edwin

[EdwinConan]

Yes, you are right, the first thing i felt after the wheel change is the ride is a lot quieter. And I can hear the engine noise a bit more clearly. Thanks for giving me these information about my tyre, I didn't know any of these, the tyre shop just told me that they've got Kumho tyres that fits the rim. And, thanks for your complement on my wheel choice.

[Manaz]

In short, yes, changing your wheel/tyre combination can have an effect on steering.

Bigger wheels necessitate lower profile tyres to maintain the same rolling diameter, and lower profile tyres require higher pressures.

Wider tyres will also have a greater resistance to changing direction as the contact patch is wider but shorter (when considered in relation to the axis of the vehicle). This is why wider tyres often grant better cornering capability, as the direction of slip due to momentum as you turn is along the width of the tyre, which is the same direction in which the contact patch is longest.

Letting air out (and reducing pressure) would certainly have an impact on handling, particularly turn-in, as it allows the tyre to flex in the sidewalls more. You get a softer ride, but duller handling.

As already noted, your new wheels are almost certainly heavier than stock ones as well. This means you have a larger unsprung mass (weight that isn't sitting on your suspension), and heavier wheels, particularly once you're moving, have more momentum and rotational inertia to overcome to make them turn (this is how a gyro works, and indeed how motorbikes and even pushbikes maintain stability and remain upright - a spinning object has a natural resistance to change in the rotational axis).

For what it's worth, putting R32 brakes (15kgs per front rotor is my understanding, not sure on the absolute stock weights, but they're significantly lighter) on my Bora V6 4Motion also had an impact on steering - it's much heavier now than it was with the stock brakes.

Though VW recommend different pressures for each model in the Mk4 Golf/Bora range, they recommend the same pressures for each vehicle irrespective of tyre fitment - with the exception of the R32.

Funny that - the R32 was the only Mk4 released with 18" wheels from the factory.

[Manaz]

I think one aspect of handling where you'll see an improvement, is that lower profile tyres will generally allow you to corner faster before they start to let go.

Umm, no. The tyre profile does not (and indeed cannot) influence the coefficient of grip of a tyre (which is largely dictacted by compound, road surface, tread pattern and the size of the contact patch).

What lower profile tyres do actually achieve in terms of handling is to let you feel more accurately what's going on at the road surface - lower profile is generally related to sidewall stiffness, and what this in turn means is that the feeling the driver gets is that grip becomes slide in a short period of time. Higher profiles/softer sidewalls tend to obscure the feeling of this moment (and thus feel to have a smoother transition from grip to slip) because the sidewalls flex and allow the car to shift laterally even though the tyre surface has not begun to slip significantly - so you feel the chassis of the car start to move outwards in the corner before the tyre actually lets go, meaning the transitional period "feels" longer.

What may, for some people, confuse the matter and lead to an association between lower profile tyres and better lateral grip is that, in general, lower profile tyres tend to be aimed more at performance than comfort/quietness, and thus provide more grip due to the difference in the compound, rather than geometrical aspects of the tyre design.

[Diesel_vert]

Funny that - the R32 was the only Mk4 released with 18" wheels from the factory.

Tyre pressures for factory-fitted standard tyres

1J1 Golf, 3.2 l 177 kW
225/45 R17 - F : 2.7 bar / R : 2.5 bar
225/40 R18 - F : 2.5 bar / R : 2.3 bar

Although I only realised it while typing this, the 17" wheels are probably meant to be fitted winter tyres, as one normally adds 0.2 bar due to colder ambient temps, which would explain the pressure difference above.

Just to clarify (as I'm not sure I made sense before), but as for the rest of the range, whatever the specified pressures are, they don't change with different tyre fitments. For example...

1J1 Golf, 1.6 l 74 kW
175/80 R14, 195/65 R15, 205/60 R15, 205/55 R16, 225/45 R17 - F : 1.9 bar / R : 1.9 bar

1J2 Bora, 2.3 l 110 kW
195/65 R15, 205/55 R16, 225/45 R17 - F : 2.1 bar / R : 1.9 bar

1J2 Bora, 2.3 l 125 kW
205/55 R16, 225/45 R17 - F : 2.3 bar / R : 2.1 bar

Of course these are just factory figures, one doesn't have to stick to them religiously, just don't go under them. Use whatever works for you.

I think one aspect of handling where you'll see an improvement, is that lower profile tyres will generally allow you to corner faster before they start to let go.

Umm, no. The tyre profile does not (and indeed cannot) influence the coefficient of grip of a tyre.

I don't recall saying that the tyre profile influences the coefficient of grip.

Wider tyres will also have a greater resistance to changing direction as the contact patch is wider but shorter (when considered in relation to the axis of the vehicle). This is why wider tyres often grant better cornering capability, as the direction of slip due to momentum as you turn is along the width of the tyre, which is the same direction in which the contact patch is longest.

What lower profile tyres do actually achieve in terms of handling is to let you feel more accurately what's going on at the road surface - lower profile is generally related to sidewall stiffness, and what this in turn means is that the feeling the driver gets is that grip becomes slide in a short period of time. Higher profiles/softer sidewalls tend to obscure the feeling of this moment (and thus feel to have a smoother transition from grip to slip) because the sidewalls flex and allow the car to shift laterally even though the tyre surface has not begun to slip significantly - so you feel the chassis of the car start to move outwards in the corner before the tyre actually lets go, meaning the transitional period "feels" longer.

What may, for some people, confuse the matter and lead to an association between lower profile tyres and better lateral grip is that, in general, lower profile tyres tend to be aimed more at performance than comfort/quietness, and thus provide more grip due to the difference in the compound, rather than geometrical aspects of the tyre design.

... which at the end of the day, allows you to corner faster like I said - does it not?