Vectra handling after Wheel Upgrade

[McTwistie]

I have upgraded from the Stock 17" vectra wheels with 215/50/17 tyres to 19" Snowflakes with Kumho KU31 225/40/19 tyres.

I did a quick run around nebo today, and noticed the handling felt different to what I had previously. On sharper corners, I could really feel the mass of the car shifting across and then "Locking at limit". It still cornered very well, but it felt disconcerting, and at first I fought it a little (Which did not help much).

Once I got used to it, it was ok, but I don't remember feeling this previously. Is this now a matter of better springs ? (am planning on it). Why do I feel this now, when I did not feel this before?

The car is actually lower to the ground now as 17" with 50mm is HIGHER then 19" with 40mm. I was expecting a tighter ride.

Cheers :cool:

[rjastra]

I

The car is actually lower to the ground now as 17" with 50mm is HIGHER then 19" with 40mm. I was expecting a tighter ride.

Cheers :cool:

The 50 and 40 refer to aspect ratio, not mm height

[tomtom]

I have upgraded from the Stock 17" vectra wheels with 215/50/17 tyres to 19" Snowflakes with Kumho KU31 225/40/19 tyres.

I did a quick run around nebo today, and noticed the handling felt different to what I had previously. On sharper corners, I could really feel the mass of the car shifting across and then "Locking at limit". It still cornered very well, but it felt disconcerting, and at first I fought it a little (Which did not help much).

Once I got used to it, it was ok, but I don't remember feeling this previously. Is this now a matter of better springs ? (am planning on it). Why do I feel this now, when I did not feel this before?

The car is actually lower to the ground now as 17" with 50mm is HIGHER then 19" with 40mm. I was expecting a tighter ride.

Cheers :cool:

Not sure what youre describing here but you should know that apart from the increased tyre width, going from the 17's to the 19s is a slight performance DOWNGRADE as the 19s are heavier than the 17s by ~2.XXkgs each corner (on the H's anyway).

The increased weight at the wheels (however negligible) would affect turning, acceleration and braking so that may be the cause.

[AfterBurner]

Also just to clear another miscernoma, the 'ride height' should not change at all otherwise ur speedo will be way outtttttt.. The rolling diameter must stay the same, the difference is that ur rims look closer to the guards, giving it a 'lower look'...

AzzA

[McTwistie]

The tyres on the car now are definately of a lower profile then the last set. Their distance from the edge of the rim to the outside edge of the tire is about 3cm less. 2 inches difference makes it about 5cm thicker on the rim. The overall difference cannot be more then 2 or 3 cm.

I have seen other threads that calculate this kind of difference and show it to be about 2km/hr at 100km/hr. Can anyone verify that ?

Next stop is eibach spring set, lowering the car 3cm :)

CHeeers

[AH08]

Your speedo will be 2.4klm slow
check here.... http://www.miata.net/garage/tirecalc.html

[McTwistie]

Great site, thanks for that.

I will test my speedo vs the GPS over a nice long trip. GPS can be out a bit, but once you drive evenly (cruise control) over a few k's the average reading will be correct within a few meters and .km/hr

If it's to far out, I will have to take it to holden for a remap/update ?

[McTwistie]

Ok, tested the speedo today, using Cruise Control over serveral kilometers the car speedo was reporting exactly 101 km/h. The GPS reported 99/100 - It's bang on.

I have noticed in other cars they are set to 2-3km/hr at 100 km/hr on purpose....

Anyone else notice that ?

[Wraith]

I'm not exactly sure what's happened there either McTwistie, but having an educated guess I'd say that because you now have lower profile tyres with lower height sidewalls, when cornering the flex of the tyrewall is alot less than before, therefore the cars weight shifting will be more pronounced or 'felt' whereas before it was more taken up by the compliance of the tyres or absorbed and cushioned - if that makes sense...

On all my cars running larger dia. rims and lower profile tyres, the effect has been as you've thought it should be, ie. given a tighter firmer ride and better cornering characteristics, but at the limit it isn't necessarily better though...:)

[McTwistie]

Thanks wraith.

After reading this and another post, I think this is "Bump Steering" - Check out this thread...

http://www.opelaus.com/forums/showthread.php?t=24715

[nuggz]

The tyres on the car now are definately of a lower profile then the last set. Their distance from the edge of the rim to the outside edge of the tire is about 3cm less. 2 inches difference makes it about 5cm thicker on the rim. The overall difference cannot be more then 2 or 3 cm.

I have seen other threads that calculate this kind of difference and show it to be about 2km/hr at 100km/hr. Can anyone verify that ?

Next stop is eibach spring set, lowering the car 3cm :)

CHeeers


are you still using the tyres that came with the wheels?

rubbish brand
low load rating
could be your problem right there

[McTwistie]

NO mate, I replaced the tyres with Kumho KU31's.

They are 93y

Cheers

[HoldenAstra]

actually the ground clearance of your car changed by 0.311 inch. it's higher than before.

check this site
http://www.euroshina.com.ua/calc.php?lng=en

[Danboy_LMF]

I'd also add that the tyre size your using isn't what Vauxhall/Opel use over here in the UK, as my car has 19 inch Snowflakes and it running 235/35/19's.