Interesting article on bigger alloys...

[edo]

Want to make your car slower?



http://www.caranddriver.com/features/10q1/effects_...

[TheRoadWarrior]

Would be interested to see a comparison of the extremes of the test, i.e. a 15" wheel and a 19" wheel but using wheels of the same weight as I suspect this is the main factor affecting acceleration and MPG.

Edited by TheRoadWarrior on Thursday 15th April 09:31

[raceboy]

edo said:

Want to make your car slower?

Or looking at the other side of the coin......want to make your car go round corners faster, and stop quicker.

It's all about balance, I'll take 0.3s of my 0-60 to gain a few mph through the corners any day.

[kambites]

Bigger alloys tend to make cars corner slower on anything but perfectly smooth roads though, because the lack of compliancy in the side wall makes breakaway more sudden and removes the very fast springing you get from having almost zero unsprung mass between the flexing side wall and the road. Plus the ruin the ride, cost more to buy tyres for, get damaged more easily,...

The extra lateral grip on the skip pan in the article comes from the extra width of the tyres, not the larger diameter wheels.

Edited by kambites on Thursday 15th April 09:43

[Targarama]

My Stepdad ran a MK2 Escort 1.1 for a while. It was dog slow. He needed rear tyres and I had some old spare wheels/tyres (in good nick) from my MK1 Escort. Trouble was that they were only 12" and the mk2 ran 13" wheels. Well they fitted and saved him some money on tyres. A side effect was that they made the car much nippier (OK, less slow).

[Curry Burns]

kambites said:

Bigger alloys tend to make cars corner slower on anything but perfectly smooth roads though, because the lack of compliancy in the side wall makes breakaway more sudden and removes the very fast springing you get from having almost zero unsprung mass between the flexing side wall and the road. Plus the ruin the ride, cost more to buy tyres for, get damaged more easily,...

I'm assuming you talk with adenoids....

[kambites]

Curry Burns said:

kambites said:

Bigger alloys tend to make cars corner slower on anything but perfectly smooth roads though, because the lack of compliancy in the side wall makes breakaway more sudden and removes the very fast springing you get from having almost zero unsprung mass between the flexing side wall and the road. Plus the ruin the ride, cost more to buy tyres for, get damaged more easily,...

I'm assuming you talk with adenoids....

Not that I'm aware of.

[k-ink]

The roads in the SE are so bad I'd never consider lower profile than standard anyway. The fact your paying more money for supposedly better looks and measured worse performance is also incredibly shallow.

[pilchardthecat]

The more important question is - why do so many modern cars need low profile tyres in order to look good, when plenty of older cars (cobra, etc) look great with tiny hubs and masses of rubber?

[Garlick]

On my MINI Cooper S JCW I binned the 17'' wheels for 16'' ones and it was such a sweet car as a result.

Most JCW owners go up to 18'' so I was certainly in the minority.

[anonymous-user]

If bigger wheels are changing performance statistics then they have incorrectly sized tyres on them, if the correct size of tyres are used the rolling radius should remain the same and performance should remain the same also.

[Gad-Westy]

kambites said:

Bigger alloys tend to make cars corner slower on anything but perfectly smooth roads though, because the lack of compliancy in the side wall makes breakaway more sudden and removes the very fast springing you get from having almost zero unsprung mass between the flexing side wall and the road. Plus the ruin the ride, cost more to buy tyres for, get damaged more easily,...

The extra lateral grip on the skip pan in the article comes from the extra width of the tyres, not the larger diameter wheels.

Edited by kambites on Thursday 15th April 09:43

When I had my second Westfield, I bought it with 15" wheels but more or less immediately changed to 13" wheels. I had a few reasons. Partly it was availabilty (and cost) of decent tyres, partly to lower unsprung mass (the combined weight of wheel and tyre being less on the 13s) and partly because I thought they looked better. The side effect (and the reason why most people who race these things run small wheels) was that the the ride and grip were hugely improved. And that was using the same tyre type and same width on both sets of wheels.

[madbadger]

yellowbentines said:

If bigger wheels are changing performance statistics then they have incorrectly sized tyres on them, if the correct size of tyres are used the rolling radius should remain the same and performance should remain the same also.

So the extra weight of the wheels in the article probably plays a big part.

As has been said it would be interesting to see a comparison done with same or lower weight but wider / bigger tyres to see what that does.

I have gone lighter and wider while keeping the wheel size the same and the outer circumference the same.

Extrapolating the above data somewhat it looks like that is a good way to go.

[k-ink]

yellowbentines said:

If bigger wheels are changing performance statistics then they have incorrectly sized tyres on them, if the correct size of tyres are used the rolling radius should remain the same and performance should remain the same also.

Try accelerating on a bike with lead wheels.

[kambites]

yellowbentines said:

If bigger wheels are changing performance statistics then they have incorrectly sized tyres on them, if the correct size of tyres are used the rolling radius should remain the same and performance should remain the same also.

If you look at the picture of the Golf wheel arches at the bottom of that artical, that is clearly not the case with the Golf. The rolling radius is increasing as the wheel size rises.

Interestingly, the pictures show that they don't even bother to change the ride height to match the greater tyre diameter, so the ride height is actually increasing noticeably with larger wheels (this is clear if you go to the pictures than flick through the pictures of the arches).

Edited by kambites on Thursday 15th April 10:58

[DrTre]

k-ink said:

yellowbentines said:

If bigger wheels are changing performance statistics then they have incorrectly sized tyres on them, if the correct size of tyres are used the rolling radius should remain the same and performance should remain the same also.

Try accelerating on a bike with lead wheels.

Try steering too.

[jbi]

i would be more concerned about the risk of pothole damage these days

I have just replaced all 4 of my wheels and tyres with 235/60 r16 after bending on of my 245/45 R18 alloys into an egg.

Edited by jbi on Thursday 15th April 11:07

[CrisW]

The weight and corner issues are a little unfair.

Given a 15x6 wheel and a 19x8.5 wheel you are increasing the diameter by 4" AND the width. I wonder if the width increase is more sigificant that the diameter (pretty much all of the extra width comes at the largest section of the wheel - the perimeter thus the difference is even greater.

Perhaps not surprising that a wider tyre can generate more grip.

Obviously this represents the real choice people tend to make but it would have been more interesting to pick a suitable tyre width and just vary the wheel diameter.

The 17 vs 18 sample is intersting...

[k-ink]

But on the road a shallow sidewall created LESS grip! Big wheels will always be worse on the road. More weight, less grip, less acceleration, worse steering. But more chav factor which is all that matters with some.

[Mermaid]

wider tyres, more wind resistance?