Tuning tips: Alloy wheels

obi_waynne

Administrator
Staff member
Moderator
Points
1,157
Location
Deal, Kent UK
Car
A3 1.4 TFSI 150 COD
Whilst many people view the wheels as a purely cosmetic addition to a car they actually have a profound impact of the handling. We shall look at the pros and cons of fitting alloy wheels to a car. Steel wheels that come with cars tend to be quite heavy and are usually solid, save for [...]
More...

What do you think of this tip then, read the article and post your comments in here.
 
I don't entirely agree about the unsprung mass thing. Let's face it, how many cars had 245/50/Z18 fitments in the 1980s?

Cars have got heavier overall, and this includes ever larger wheels and tyres.

Also, brake cooling. It's less to do with airflow through the wheel and more to do with the fact that you've bolted a bloody great chunk of aluminium alloy directly to the hub. Aluminium is a very good heat conductor. Steel isn't.
 
Unsprung weight makes a difference to the handling as each corner will be working to different levels and different frequencies. If a heavier corner is in place of an original lighter set up the suspension will be working harder and the rebound more aggressive. General rule of changing wheel diameters is to keep the rolling circumference within 2.5% of the OE fitment. I did this on my own MG when changing from 17s to 18s and chose the correct tyre profile and this kept it to around 1.2%.
 
Unsprung mass does make a difference to handling and roadholding. But modern cars still have much heavier wheels than older ones due to the fad for ever larger rims and tyres.

One of the best cars I've used in snow was our ancient (15 yrs old) FWD Seat Ibiza 1.9D With its little 13" rims and skinny 175 width tyres there was so much digging in through the snow that I could wander (even cruise, perhaps, at low speed) up and down steep hills with total equanimity in early Jan this year. Countless 4wds had been abandoned by their drivers.

Bigger isn't always better.
 
Very true Hdi. My Focus hates the snow because it has wide tyres. Whereas the C2 I borrowed as the start of the year went everywhere it was great in the snow.
 
I'm slightly concerned about this forthcoming winter. 225/55 on a RWD car, DSC or otherwise, is going to be more of a handful in the getting off the line stakes than the Seat was on it's skinny jims.
 
BMW on snow ! yup thats going to be a fun one


i also thought most alloys were aluminium alloy, magnesium ones are the super dooper expensive ones that cannont be easily repaired
 
BMW on snow ! yup thats going to be a fun one


i also thought most alloys were aluminium alloy, magnesium ones are the super dooper expensive ones that cannont be easily repaired

I'm not desperately bothered as the 5 series does have pretty even, if not perfect, f/r weight distribution. In normal driving, even on wet and greasy roads it simply understeers, albeit far more gently than some FWD cars.

I'm more wary of the 3 series models which are quite nose heavy in comparison.

It'll still be intersting though, especially with the funding cuts for gritting and salting but this applies equally to anyone in any car really.
 
gritting cuts where ? i drove up to edinburgh on sat, car was clean when it left here and by the time i got there it was covered in salt. then again snows only 15miles north of us
 
Don't have any specifics but the local roads authority here (Bucks County Council) were trimming the spend in late 2009 so there's goona be more to come.

I'll manage though. I'd rather drive at 10mph if necessary in lethal conditions - it's still quicker and more comfortable than walking.
 
yeah we got alot of cuts last year and then had the worst winter in a long time, didnt help that our salt had to be sent down south so we ran out on more than one occasion, not that it really was doing much at -13
 
"Wider wheels will improve grip and cornering ability as you have a greater contact areas"

WRONG, WRONG, WRONG, WRONG, WRONG!!!!!!!
 
"Wider wheels will improve grip and cornering ability as you have a greater contact areas"

WRONG, WRONG, WRONG, WRONG, WRONG!!!!!!!

Different shaped contact patches but not necessarily better for lateral grip.

Wheel and tyre mods have to be seen as part of an overall package of suspension mods. In isolation there is generally little, if any, benefit at all.

Even with stiffer damping (I'm not a fan of hard springs and uprated AR bars) this is not generally ideal for mixed road use.
 
Contact patch area is, for all practical purposes, the same size irrespective of the tyre width or diameter. The size of the patch is governed by the pressure exerted on the tyre by the car and the gas pressure inside the tyre.
 
"Wider wheels will improve grip and cornering ability as you have a greater contact areas"

WRONG, WRONG, WRONG, WRONG, WRONG!!!!!!!

couldn't agree more, i remember when I had my Alfasud Sprint with 165 x 70 x 13 tyres, I replaced them with 185 x 60 x 13, and absolutely ruined the handling.
 
Thanks for the comments chaps, these have all been passed on.

But playing devils advocate here then.

If a wider wheel changes the contact patch then theoretically this contact patch is shorter (front to back) and wider (side to side). Will this really not improve or at least alter the cornering grip where lateral forces are trying to slide the tyre to the side?

Racing cars and F1 cars have very wide wheels? So shouldn't this mean that wider wheels on a road car improve things? ;)
 
Thanks for the comments chaps, these have all been passed on.

But playing devils advocate here then.

If a wider wheel changes the contact patch then theoretically this contact patch is shorter (front to back) and wider (side to side). Will this really not improve or at least alter the cornering grip where lateral forces are trying to slide the tyre to the side?

Racing cars and F1 cars have very wide wheels? So shouldn't this mean that wider wheels on a road car improve things? ;)

Right.........

By widening the tyre you reduce the length (around the tyre) of the patch. When the tyre is in contact with the road heat is generated. This has to be dissipated by the time the same area of tyre is back in contact with the road surface. By reducing the length a smaller percentage of the tyre's circumpherence is heated at any one time so there is more time for it to cool.

This allows a tyre with a shorter patch length to be driven harder before it overheats or for softer compounds to be used (these heat up quicker).

It's the area of rubber in contact with the road, not its shape, that governs cornering performance. With a wider tyre there is more chance, especially with today's low profile road tyres, of the tyre tread tipping when cornering hard thereby reducing tyre contact with the road surface.
F1 cars don't roll in corners and have a lot of downforce so the wide tyre stays in contact at all times.

Well, that's my take on the subject :)
 
So heat in the tyre has a large bearing on grip, I guess that makes sense then.

Taking the arguement further then, what would be the difference if one fitted narrower tyres to their car? Would this potentially increase the grip in certain conditions?
 
So heat in the tyre has a large bearing on grip, I guess that makes sense then.

Taking the arguement further then, what would be the difference if one fitted narrower tyres to their car? Would this potentially increase the grip in certain conditions?
yep on ice/snow;)
 
What OG is saying really, you pick your tyres for the right conditions and you need to change your suspension accordingly so do so,

if you use gripper tyres, you need to stiffen you suspension because you will find that the car will roll more before it starts to break it's lateral grip but also on the other had, softer suspension in certain conditions will help to increase cornering grip also,

it is rather a big mind field really, like paul said you have to upgrade all the drive train accordingly to maximise your cars grip.

Also wider tyres are more likely to aquaplan in comparison,

To further explain things, I found this clip on youtube which AutoCar magazine recorded which I think you will find rather informative that what we are saying it "horses for courses"

http://www.youtube.com/watch?v=s_abW86x9Fc

I think you will be plesently supprised....
 

Similar threads


Please watch this on my YouTube channel & Subscribe.


Back
Top