Does offset/wheel size affect handling?

[IanHindley]

I am looking at changing the wheels on my sierra based YKC roadster, currently on 195/60/14 sierra pepperpots (offset ET38), to get bigger wheels to fill the arches more, and also to maybe move the wheels further out, particularly at the rear.
I am going to stick with 195 tyres as I don't have power steering and don't want any more steering effort than I already have, and also am keeping to 60 or even 65 aspect ratio as it is quite a firm ride already, so don't want to go lower.

So I am thinking of 16" wheels,. Do the larger wheels/tyres impact on handing/comfort at all? And also does anyone have experience of using wheels with a lower offset all round, perhaps as much as ET15, and whether this is too big a jump in offset - would it cause poor handling or tramlining etc? Similarly, would such an offset put undue stress on the steering/ axle components ?

Another option is to go for different size wheels at the back - perhaps even 17" at the back and15" at the front? Has anyone tried this, and any comfort/handling/drivability comments would be useful

[Stewart Vickers]

Re: Does offset/wheel size affect handling?

My YKC Julietta (Sierra origin) had ET22 rims fitted by the factory as standard. This offset and wheel nut spacing is also common on Puegeot/Citroen cars so is useful when trying to source replacement wheels. There is a spreadsheet on the locost site that may also be of use when calculating the effect on gearing, you can play around with different combinations of tyre size and final drive ratios to give new mph figures. I found it useful when changing the wheels from 14" to 15". I have tried adding to this post but it will not attach as it is an excel file or maybe I'm doing something wrong. If you want a copy I can email it direct.

[stevejgreen]

Re: Does offset/wheel size affect handling?

I think there are several factors at work here. In general the handling of a vehicle is a compromise between many different and conflicting factors.
Deviating in any way from the 'standard' can have minor, or significant effects.
From the point of offset change I think there are two main factors that revolve around the centre of the tyre/road contact point.
If the contact point is offset further out from the norm it will add additional load on the wheel bearings, that may lead to premature failure.
In the same way the pivot point of the steering is generally as close to the centre contact point, so tyre scrub is more likely, which will equally impact on self centering of the steering.

Moving to different tyre profiles can also change handling characteristics. Radial tyres move a lot more than you might suspect, and running with low profile tyres that do not deflect as much as high profile can make the car feel more sensitive, but road vibration will increase as the tyre no longer has the flexibility to absorb the first impact, before the suspension starts moving, for example the extreme of hitting a curb, when the load is initially far from vertical.

I think the subject is complex one, and changes to handling will be unpredictable and could go either way.

[IanHindley]

Re: Does offset/wheel size affect handling?

Thanks for your replies. I may well give the lower offset a try (ET20 or so) as that is the main (visual) issue I am trying to resolve - getting the wheels to sit slightly further out to match up with the wings. I guess that is the beauty of these cars - give it a try and see how it works. Ebay here I come. Like you say, it is complex and I am no engineer. I have quite a firm ride, and certaintly don't want to make it any firmer, so I am going to treat myself to a new set of tyres at the same time to see if that helps a bit.

[Mike]

Re: Does offset/wheel size affect handling?

Hi Ian

I researched this via the internet for my Cabrio, and came across a Youtube of a young US student who explained wheel geometry/suspension very well. It was very informative, and presented in a manner a layman can follow.
Have a look and see what you think?


Steering Axis - this is one of the items you will affect by changing the offset.

https://www.youtube.com/watch?v=IUcZ63unEyU

Camber

https://www.youtube.com/watch?v=jSFmUmVWBp0

Castor

https://www.youtube.com/watch?v=Gh7gWJAvOvs

Toe

https://www.youtube.com/watch?v=83_GTZeuF6M

Mike

[danny_nelson]

Re: Does offset/wheel size affect handling?

Hi Guys, Have a look on ebay. The YKC that was at Sheffield auction is now advertised at £7295. I find thia very sad for the family.
Danny.