Help with theory: Improved cornering with wider wheels, lower offset. Same tyre

[noone]

I have a Polo GTI, since buying it a year ago, I'm on my 3rd set of rims (I like to play).

I noticed going from the OEM 16's with Conti' CCS2's to the VW Siata 17's with Kumho KU31's that the traction was improved. It was difficult to say much about the change as the unsprung weight, rims and tyres all changed.

Recently I changed from the Siata rims to some Audi TT rims. I had the existing tyres put on the new rims.

Since using my new rims, I've noticed a definite improvement in the cornering. I'm trying to understand why.

Here is a little data:

Siata rims (Old):
Size: 17"
Width: 7"
Offset: 38
Weight: Around 8kgs

Audi TT rims (New):
Size: 17"
Width: 7.5"
Offset: 32
Weight: Around 12kgs

So the obvious differences are:
- Wider Rims (but same rubber)
- Heavier Rims
- Lower offset (Wider stance)

The distance from wheel center to center has only increased by 12mm total. This is not a lot, not even a 1% change in the overall track width. The wheel being further from the suspension will have an effect on the way the spring / shock is worked and for lack of a better way to put it, the load on one side of the fulcrum has changed.

The weight of the rims adding to the unsprung weight can make the car handle worse, but feels like it works more compliantly with my stiff suspension setup. I'm running coilovers, sways and whiteline bushes.

The rubber being stretched a little more across the rim could change the way the tread meets the road. Someone said the tread could have opened up a little more, but I'm not sure.

The tyres are 205/40/17 and are suitable for both rim widths.


All these small changes affect the way the car handles. Does anyone have some understanding or experience as to which of these changes is making the bulk of the difference in improving the handling, or is it something I've missed?

[JoshFair]

basically the broader your wheel base is, the stronger contact you will make with the ground, thus creating better performance around corners if you want awesome conering.. get your self as low and as wide as possible.. the decrease the body roll as well with strut braces (front and rear) and get your hands on some thick sway bars! the thicker the better IMO

Hope this helps

[gareth_oau]

i cant offer you any advice, but good to read a comparison, and youve managed to minimise too many variables so a direct comparison is more realistic.

i'm surprised at the weight difference between the two rims and that the heavier rim feels better.

[99gti]

Ive just gone from 19x10 and 19x8.5 to 17x7.5's

The difference is EPIC! Kinda feels like a family car again lol.

[VWindahouse]

Hey Noone, anything with a lower offset and wider stance will be better for cornering no doubt about that.

As for acceleration, 4kg difference per rim heavier is massive and you are not doing a light car like the polo any justice. They say you times a kg or unsprung weight by 5 - 8 (can't really remember sorry).

As for the tyres, if you are running a 205 on the 7 - 7.5" rim you are going to get a bit of stretch which will give you a better contact patch and more grip. If you go to a 8" rim a 215 tyre might be a good option.

Then there is tyre pressure, believe it or not this can play a massive part in handeling.

Just read up on a few MX5 forums for more insight into your questions! And google a youtube clip of the current MX5 in the Mazdaspeed 1 G project.

[noone]

Thanks for the feedback. I was expecting a difference, but I was not expecting much improvement in cornering due to the added weight. The wheels are much heavier, which is more to say the Siatas were light (sometimes referred to as Siata - Light Alloys), to pick up each bare rim on its own you certainly can feel it.

I think there is a lot to be said for the steering feel and feedback, I definitely have more confidence going into a corner at speed now.

I would not be surprised to find my car is a little slower in a straight line, but the trade off has been well worth it. Maybe one day I'll get myself something lightweight, but this combo is far more fun than the stock or 2nd set of rims (plus I think it looks good and I've had plenty of complements and random people staring).

For those who don't come into the Polo section, here are the new wheels on:

[madglf3]

Wow those look great, I've never seen that style of wheel. Centres cap design is pretty cool too. It's a polo I'd consider driving, tough looking.

I have recently gone from a 205/55 on a 6.5" STD rim of 42 offest, to a 215/45 on a 8" with 32 offset and I have the same tyre (Falken Ziex ZE912) on both sets and I can notice a much nicer and noticably firmer ride in the new wider and lower-offset rims. I could have gone for 205 though to get a little better clearance for the front guard but I'm pretty happy nevertheless. Next set maybe I'll get skinnier.