Handling

[10594087]

Hi,

Maybe just a newb question but i would like to ask why when we change our rims and tyres to a slightly larger say from a 17x7 to a 18x9. The handling of the car feels stiff and not so responsive. I thought the wider base would of made a better handling car. I understand that the manufacturer have made the settings of the suspension to accomodate the stock wheel sizes say 17x7. If this is the case how do modify the car to suit the new rims and tyres. This has been the case with a few cars that i've owned and other people i know as well. Also even after a complete wheel allignment it dosen't make it better.

Thanks,
Ken

[1200Datto27]

As a quick answer, and due to there not being any real specific data in your post, I'd say that the main reason for the "handling" of the car changing is due to an increase in the unsprung weight of the rims and tyres, possibly an increase in the rotational mass and changes to the track width and suspension geometries from the use of the wider rims.

As you haven't stated the type of car in question, then the fixes are hard to quantify for you.

[10594087]

i'll take my friends car as an example, its a nissan skyline r33 gtst road car. He has changed the stock rims to Rays engineering TE37's 18x8 in the front and 18x9 in the rears. Im not sure which information you would require.

[tristancliffe]

The trouble is that the spring rates and damping rates on the cars are chosen to compliment the standard wheels. Changing them will probably make the suspension settings 'wrong'. Plus, if you change the dampers and/or springs for uprated or lower/shorter ones, then you'll be even further from ideal (probably - there is a small chance you luck onto a brilliant combination, but manufacturers don't spend LOTS of money tuning these things because it's easy).

The larger wheels might also upset the geometry of the suspension, although if the overall diameter and the offset remains correct this should be minimal.

More rubber on the road will make the steering heavier and less precise.

Handling, grip and responsiveness are all different things, and it's VERY hard to improve one without ruining one or more of the others. Bigger wheels and tyres might increase outright grip (but only a tiny, tiny, tiny amount really), and might improve response (stiffer sidewalls) but will almost certainly ruin the ride and the handling unless other changes are made to correct that.......

Most cars are, in my opinion, better to drive as standard, and quite probably quicker and more fun from A-B as well. But I'm dull like that, and get my thrills from F3 cars instead.

Determine what you want - looks, ride comfort, handing (the stuff that puts a smile on your face), grip or response, and work towards that. I do appreciate that looks are the major aspect of car mods, and that it doesn't matter to the owner if the car is technically better because of it - cite: big exhausts or bodykits etc.

[Chris Wilson]

Originally Posted by 10594087

i'll take my friends car as an example, its a nissan skyline r33 gtst road car. He has changed the stock rims to Rays engineering TE37's 18x8 in the front and 18x9 in the rears. Im not sure which information you would require.

I have done a lot of development work on GTS-t's as I like them for their low initial purchase cost, their tail happy, fun handling, and their much lighter weight than the portly GTR. His problem may well be that in order to accommodate wider rims and tyres within the stock wheel arches he has changed wheel offset a lot. This alters the kinematics of the suspension and can result in tram lining and wooden steering feed back. The stock rubber suspension bushes are now probably too compliant to cope with increased loadings and are failing to constrain the geo under some loads. Quite often people lower road cars with no real understanding of what it will do to bump steer, camber curves and roll centre heights. A lower car is often a slower car. The R33 in particular has terrible rear bump steer changes when lowered much at all, and the front roll centres move to where the car tries to roll more when lowered. Stock or near stock ride height is best, short of buying or fabricating a lot of custom stuff to accommodate lowering whilst maintaining good roll centre control and minimising bump steer. Finally, the budget is often strained with buying nice light rims, and corners are cut on the tyre mounted upon them, which is plain daft. Bear in mind both race and road car designers often start with a wheel and tyre size as their first defined object, and a vast amount of stuff is based on their characteristics, fiddle with them only of you are sure you know what you are doing. I see disastrous wheel and tyre combinations on all manner of road cars as my everyday job, much more rarely do I see well thought out modifications that actually make a car quicker or nicer to drive. Modern cars that run ultra wide and low profile tyres as standard wear have, or should have suitable geo to keep a stiff sidewalled wide tyre flat on the road, add such tyres to a car not designed for them and their discomfort shows in odd tyre wear and none linear handling as the tyre tread partly lifts off the road in cornering or braking due to unsuitable camber control. I am convinced there are many modern cars with ultra low profile rubber that would be far nicer to drive on a taller sidewall, but the buying public mainly associate rubber band tyres on huge diameter rims with having good looks and performance. It's a bit like platform shoes, the media made us all of a certain age believe they were a must have, whilst we broke ankles and stumbled around trying to look "cool"

[Richy_Rich]

Originally Posted by Chris Wilson

It's a bit like platform shoes, the media made us all of a certain age believe they were a must have, whilst we broke ankles and stumbled around trying to look "cool"

Lulz. I agree though, I see a lot of road cars that have been 'modded' and can't help thinking 'surely you've just made it 10x worse'