Handling after changing Rims on my Bora

[EdwinConan]

Hi Volks

I finally saved enough to change the stock wheels on my Bora to the Audi RS6 wheels that I always wanted.
However, it feels to me that the handling is not as sharp as before, i mean the response is a little slower now, the moment between me turning the steering wheel to the front of the car changing direction has become a tiny bit longer.

My stock wheels are 205/55 R16, the new wheels that I got now are 225/45 R18.
When I first drove the car with new wheels, the steering feels very light, then I found out the tyre shop pumped the tyres to a higher pressure then what's said on the fuel cap, so I let out some air. Should the tyre pressure be different with different tyre size? or should it remain the same? (very rarely do i carry any passengers or luggage)

Is this handling change normal? or is it just me thinking it's gone worse, while in fact it's the same? I thought changing to wider tyres makes the car handles better. Or is it just me expecting too much?

[leighaus]

it should ride a little more rough, but it shouldnt really change handling much. Looking at your ride (looks great btw) though, id consider lowering it to remove a lot of the slop youd be experiancing at that height.

[governor22]

I remember once going a bit anal with the required tyre pressure and filling it up to what it said on the fuel lid every 2 weeks or so. Then when i took the Golf to get serviced, the mechanics said I had 50PSI in there!!! (even though the pump i'd been using at the servo said i had 40). guess it doesn't hurt to let air out now and then

it could just be that you need to get used to the new tyres and wheels... as leighaus says though, lowering it a bit could tighten up the ride

(great pics mate)

[Ironman]

Nice rims. The label on the fuel tank is for the "Stock" rubber. Check out the pressure marking on the new rubber for correct inflation pressure. You will also find that with low profiles on you'll slip into the "tram tracks" (grooves in road where downward pressure has created parallel impressions in the ashpalt) and that can also be a reason for the steering issues. I found this out when I got new rubber and rims for my Mk3. Ride will also be a little bit more vibrating too. Probably doesn't help that my coilovers are would down real low and stiffened lol.
Your bora looks great btw. I might just have to stick my head in this MK4 forum more often lol.

[mikinoz]

Best thing you can do is fit a rear sway bar that will increase turn in.

But in the mean time you should be running the tyres (my personal view here) at about 34-36 PSI.

Anything less and you will get a bit of sidewall deflection on turn in.

The tyre placard is for comfort, not performance in all reality.

[noone]

As a rough guide, I'd be shooting for around 37 in the front, 34 in the rear. All depends on the tyre rating, etc, some like lower, some like higher pressures. Is it FWD or Quattro? If FWD, I personally think more pressure in the front (up to a point) for sharper turn in.

You've likely added a chunk of unsprung weight, meaning more effort for the power steering and more weight for the springs to work with.

Nice setup.

[wai]

Wide tyres will not necessarily make the car handle any better.

What is important is how the tyre sits in relation to the rest of the suspension of the vehicle.

You have gone for a wider tyre. Now if the outside of they tyre sits no further out than the previous narrower tyre did, then you have changed the suspension geometry. The centre of the contact patch has effectively moved closer to the centreline of the vehicle.

The other aspect is the axis about which the tyre will turn (rather than rotate). This is a line from the upper mounting point of the strut through the lower ball joint and then projected to the road surface.

If the car originally had negative offset geometry (where the axis point on the road was further outward than the centre of the contact patch) moving the contact patch closer to the centreline of the vehicle increases the negative offset, whereas if the car originally positive offset geometry, then you would now have a smaller positive offset. Depending on the change, you can go from positive offset to negative offset, or the other way, or even end up with zero offset.

This change in offset will change the feel as it will change the amount of steering force required to turn the wheels.

The amount of friction a tyre has with the road depends on the rubber compound and the road surface and not the width of the tyre. The wider the tyre, the lower the contact pressure, and the narrower the tyre, the higher the contact pressure. A wider tyre allows the manufacturer to use a softer, more grippy rubber, however this is rarely done for standard road tyres.

I have had to do drawbar tests where you have a wide tyre locked at one end of the bar and a narrow tyre locked at the other end. The bar is then dragged from its mid-point and you see that both wheels lose grip at the same point.

What a wide tyre can do is make it more difficult for the tyre to disperse water because of the lower contact pressure and so you can end up with much less grip in wet road conditions. A wide tyre can make it more difficult to turn the steering wheel because the effective resistance of the tyre patch is increased because you are trying to rotate the contact patch around the steering axis, and that has a higher mean radius so a greater resistance.

When you change wheels and tyres, you need to ensure that the wheel has the same offset, and that the tyre has the same rolling radius. This will not change the geometry.

Oh yes, alloy wheels are not necessarily lighter than steel wheels. When you see that most alloy wheels will have wider tyres than comparable steel ones, and the tyres are wider, you end up with more weight. This changes the unsprung mass of the suspension, but even here, you will only notice this if you are driving on washboard surfaces and going around corners.

Low tyre pressures will make the steering feel a bit mushy, but even here, the pressures would have to be really low.

So, it is much more likely to be a steering geometry issue. No point in making a whole lot of other changes until you get the geometry right first.

[dylan8]

Wheels are reps and bigger, so probably weigh a extra 5kg more a corner.
I hope you made a mistake in your typing and actually have 225/40/18s, because a 225/45 is way to big.
I know my 18x8.5/9s feel completely different to my stock 16x6.5s. I find my 16s feel sloppy compared to the 18s, and all i fee is the huge side wall stretching and flexing when cornering

[Diesel_vert]

I finally saved enough to change the stock wheels on my Bora to the Audi RS6 wheels that I always wanted.
However, it feels to me that the handling is not as sharp as before, i mean the response is a little slower now, the moment between me turning the steering wheel to the front of the car changing direction has become a tiny bit longer.

Is this handling change normal? or is it just me thinking it's gone worse, while in fact it's the same? I thought changing to wider tyres makes the car handles better. Or is it just me expecting too much?

New tyres will not provide full grip until they are run-in for the first 500 km. Also, since new tyres have full tread depth, compared to your old tyres it won't feel as responsive, since a worn tread surface produces less block movement.

What tyres did you get?

When I first drove the car with new wheels, the steering feels very light, then I found out the tyre shop pumped the tyres to a higher pressure then what's said on the fuel cap, so I let out some air. Should the tyre pressure be different with different tyre size? or should it remain the same? (very rarely do i carry any passengers or luggage)

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.

Having said that, try 2.3 (33 psi) or 2.5 bar (36 psi) cold all round, and stick with whatever feels best.

My stock wheels are 205/55 R16, the new wheels that I got now are 225/45 R18.

Can you double check? They should have fitted 225/40 R18 tyres.

[EdwinConan]

Hi Dylan and Diesel Vert

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