Tyres balooning

[Karlbar2k]

OK I have changed my wheels and tyres but am curious what effect ballooning of the tyre wall has on aerodynamics.

original size was 205/55/16 on 6.5J rims (Skoda Ride) so sidewalls were nice and straight, wheel/tyre combo weighed 40lbs

new size is 195/65/15 on 6J rims (Audi Pepperpots) and sidewalls are ballooning, wheel/tyre combo weighs 30bls

I know the weight advantage is good but I am not sure there has been a reduction in the front on profile width of the tyre due to the ballooning of the sidewalls?

[mcrews]

maybe i;m missing something.
the old tire tread was 7.5 inches wide.
the new tire tread is 6.1 inches wide.
Even IF it was 'ballooning 1 inch (which it not) you would still have a lower profile.
But besides that, the aerodynamic effecy would be, just a guess, .00001.
My only concern is that the new tire is actually a little smaller, 25 inches in diameter as opposed to 25.1 inches. So you will see a slightly higher rpm when cruising. (slightly)

But u have reduced the weight by 9lbs a tire and reduced the width by 1 inch. Surely you cant think that a slight 'ballooning' overcomes the other two very LARGE advantages?

[Daox]

Darin posted some research BMW did a while back... aha, found it. The effect is more than you would think.

http://ecomodder.com/forum/showthrea...g-cd-7475.html

[mcrews]

ok, in a 'larger' tire.
But the poster is DOWNSIZING. By more than 1" in tread width. And dropping at least 9 lbs (tires only....dont know about the rim)
Given the 2 dramatic decreases, a slight ballooning is not going to be of any significance.Size........205/55R16........195/65/15
Weight.................. 28 lbs...........20lbs
section Width...............8.4 ..........8.1
Tread Width................ 7.5................6.1
overall Diam..................25.1..............25
Revs Per......................837.................832

My point was that IF he got lower mpg, he would wrongly assume it was from 'ballooning".


or have i missed something...

[ChazInMT]

It is interesting to note that the Section Width went down by .3 inches, but the Tread went down by 1.4 inches. That'll make it look different. 4 Schwarz Luftballons indeed.

[Karlbar2k]

Where did you guys get that info regarding the tread width?

figures taken from willtheyfit.com shows the following:
205/5516 195/65/15
Diameter 631.9mm 634.5mm
Circumference 1985.2mm 1993.3mm
Poke 44.6mm 38.2mm
Inset 120.6mm 114.2mm
Speedo error 0% -0.41%
Reading at 30mph 30mph 29.88mph
Reading at 60mph 60mph 59.75mph
Ride height gain 0mm 1.3mm
Arch gap loss 0mm 1.3mm

this means a decrease in revolutions of 0.41%

the profile width is reduced by 10mm or 0.393700787 inches which is fairly accurate but why would the tread width drop by 1.4 inches?

also
old diameter of 631.9 millimetres = 24.8779528 inches
new diameter of 634.5 millimetres = 24.980315 inches

I am a bit confused? please help..

But the main question remains, are narrower tyres that balloon better than wider tyres that do not in terms of aerodynamics? I know the weight loss has great advantages for lower speed savings but I am looking at high speed improvements as I spend most of my time at 70MPH on UK motorways (30k+ miles PA)

[mcrews]

the profile width is reduced by 10mm or 0.393700787 inches which is fairly accurate but why would the tread width drop by 1.4 inches?

The 55 and 65 numbers are a ratio of a tire. you now have a taller ratio and a narrower tread.

I pulled my information from tirerack.com

Look, the tires are almost the same in diameter so that doesnt really matter.
The new tire is narrower than the old tire. End of discusion.
the balloning would only matter IF it made the new tire bigger than the old one.
It doesnt. So your trying to worry about something you cant change.
A 65 tire WILL absolutely curve more than a 55. It is inherent in the taller sidewall design.
I dont understant your fixation on it.
It would be like worrying about the weight of a spare tire. You have to have a spare. Now you can take it out but is it worth it?

[YeahPete]

Mr Crews is right.
195/65/15:

195 = width of tire in millimeters
65 = ratio of height to width in %
15 = rim size inches

His new tires are narrower.

[Karlbar2k]

OK Thanks

I am not fixating, I am just curious

My thought process is that looking at the wifes A2 (15" pepperpots with 185/60/15's) the wheel and tyre have a fairly straight profile, kind of like when people use pizza trays to improve the aero.. Mine seems to look a bit more like a donut so was curious if I would be better off with a wider rim to straighten up the sidewall a bit. Swapping wheels is relatively cheap as they never fail to sell on Ebay

[mcrews]

Ok....that is new information.
BUT on the 205 standard rim size is 6.5" wide 5.5 to 7.5 will work
on the 195 standard rim size is 6.0" wide 5.5-7 will work

So no you shouldn't go wider to 'remove' the curve. The curve is a natural byprodut of the size.
Going wider, with a narrower tread is counter-productive to the characteristics of the tire.

On tire reack, when you get to a specific tire, look for the 'spec' tab in the description or body. it's where I go for ALLLLLL my tire info.