tyres/rims - any thoughts?

[Ed Levin]

Sorry if I didn't explain it well, but by "heavy" steering I mean heavy steering effort. And this isn't a function of the weight of the wheels and tires, but rather a function of the friction of tire contact patch. A large tire contact patch (wider tire) generates greater resistance when the steering wheel is turned, and thus requires more physical effort and results in slower response to steering input.

IMHO, for street use it's best to keep the overall tire diameter as close to original as possible; otherwise teh tire diameter will change the effective gear ratios. Too small, and it's more tiring for both you and the engine on motorways; too large, and it will kill acceleration.

So, in my oipinion, for street use, you're better off staying very close to the original tire size, and compensating for teh small contact patch by buying the best tires you can afford.

[ZanettiZA]

Interesting thoughts...

The problem that I am having is that of finding the correct size.

I'm able to get a 175/70/14 Michelin Energy Saver tyre, is this recommended? Can't seem to find the XAS though...

[gamma a.i.]

a reply: my Mich Energy 185x14 are fine, look good, are not loud & meet/exceed my expectations, if I remember correctly they were fairly priced as well ! I'd assume it would be the same for 175s:)

[Huib]

The Michelin XAS 165HR14 is available through the Michelin Oldtimer sales organisation which is totally seperate from the regular Mcihelin organisation.

Others are:
165/80R14
GT Radial Champiro
Barum Brillantis
Falken SN-80Z
Toyo 330

165R14
Uniroyal Rallye 380
Vredestein Sprint Classic

[Huib]

In reaction to your first paragraph, Ed, I must confess I have never understood this.

If my simple mind applies the physics formula's which for some reason still linger in my left little toe, I get the following.

Contact patch

Pressure * area = force.
Written differently:
contact patch = area = force divided by pressure.

The force in this case is the weight of the car for the particular wheel. Does not really change.
The pressure is around 2 bar which everybody puts in his tires irrespective of the size.
The contact patch is thus the same whether you have a wide or a narrow tire

Friction

Total friction = friction coefficient * pressure * area.
Pressure * area = weight
Thus total friction = friction coefficient * weight
The area or contact patch drops out of the equation

[gamma a.i.]

I think this reply to a Fulvia question, which was answered by "Fulvia Kay Borck"; has something to do with the above topic "tyres & rims"; it is from Viva Lancia - German, where recently a Fulvista named Berndt asked why his rear ride height is now 'so high', after doing some rear-end work on his Coupe.
I'll try to translate accurately:

Kay wrote:
Hallo Bernd,
die Daten sind (a) aus dem "kleinen" deutschen Rep.Handbuch und diese wiederum (b) aus dem originalen, mehrsprachigen technischen Unterlagen von Lancia. the data you have received (in a previous reply in the small Repair-Book are from the original, multi-language, technical-specs from Lancia

Wichtig ist der Belastungs-Zustand der Fahrzeuges (der Achse) beim Einbau. Important is the weight on the axles at time of installation
Probleme gibt es aber auch, wenn Du die Federn der HA bearbeitet hast (z.B. aufschmieden, die Lagen auseinandergenommen, den Herzbolzen entfernen, die vorderen und hinteren Buchsen neu machen lassen, o. ä.). (oh my, this will not be so easy (to translate), so I will not translate it all : problems arise when you have done something with the springs on rear axle,,,goes on to list possible tasks done that require removal of springs

Dann "kommt" sie zwangsläufig höher. Then the springa are automatically higher

Das gleiche gilt auch für vorn. the same in the front
Die Probleme hatte ich vor 17 Jahren auch...I had this problem 17 years ago ...als "meine " Federschmiede es damals zu gut meinte.... when my tech-expert was trying to hard to do a good job ... und die Fulvia dann vorn und hinten etwas höher Stand after which the Fulvia was too high, front & rear) .

Das hatte hinten aber auch einen "Vorteil". this actually was advantageous in the rear

Die 6x14 mit 185ern haben bei einfedern dann nicht sofort bei einer größeren Bodenwelle beim einfedern an den nicht umgebördelten Radläufen angesägt...the 6x14 with 185 did not, when rolling over uneven surfaces, smash into the not-trimmed fender.lips

Bei weiteren Fragen kannst Du mich auch gern anrufen. call me if you have further questions end of message.

if the translation sounds a bit simple; Kay's text was not written in engineering language (thank hvns) & easily lends itself easily to a simple easy translation. Is that unclear now ? ha ha ha

Today he posted a photo of his "High Fulvia". Very very nice & required in flood-prone areas; which I understand, is happening (again) in East Europe :S.

Kay, if you read this & wish to make corrections....be my guest:P.
Same goes for any others who may not like my "Ami-Deutsch"

[Ed Levin]

Sorry, Huib, but I can’t say I agree with those equations and assumptions.

I’m afraid you’re simply wrong in thinking that wider tires don’t have greater contact patches; in fact, the increased contact patch is the only reason any racer uses wider rubber. You would be correct in thinking that, on the same car with the equivalent tire pressures per sq cm of area, that the a narrower tire and a wider tire will have contact patches of essentially the same length. Where they will differ is the width of the patch.

Leaving aside the issue of slip angles, the wider patch will create greater friction in the lateral direction–generally perpendicular to the direction of travel. That’s why wider tires will allow greater lateral acceleration, and therefore higher cornering speeds. And although it would be more efficient is the patch were turned 90 degrees, the greater contact area will also help straight-line braking.

Steering effort–the force required to turn the steering wheel–is a function of the distance from the center of the contact patch (the theoretical turning axis of the tire) to either extreme end of the contact patch. Those two points describe a moment arm, and the force required to rotate the tire around the turning axis will increase on the square of the length of that moment arm. Therefore, the wider the tire, the wider the contact patch, the longer the moment arm about the axis of rotation, and the greater the force to rotate the tire around that axis.

[ZanettiZA]

Ok the final decision: Either Michelin Energy Savers (73 euros each) OR Firestone Multihawk (63 euros each)

Any thoughts on the Multihawks - I'm not too familiar with them.

So 175 x 14 will be the size BUT what should be the profile?

Attached is a comparison between 3 different size - so what is the safest bet?

[Huib]

I think racers use wider tires for several reasons:

- cooling

- mileage. F1 tires are sort of inverted rolls of self adhesive tape. They wear extremely fast. High friction coefficient means high wear. You need more kgs of rubber to start with to have the same mileage.

- spoilers increase down force thus load on the tire

- on cornering weight shifts to one side of the car. Under sporting conditions it is a good idea to increase the load rating of the tire, thus a larger tire.

- on extreme cornering the load also goes to the outer edge of the tire. Wider tires act like increasing track width.

There is of course a difference in slip angle. If this is important for a Fulvia the owner better makes sure he has a factory service team following him.

If you lift a car with wheels off the ground, the tire is perfectly round. When you lower the car, the tire deforms till it has enough contact patch to carry the weight. No more, no less. I fail to see how this surface area could be anything other than weight divided by pressure. And pressure is of course the air pressure in the tire. Narrow tires have a long narrow patch. Wide tires have a short wide patch.

The suspension was designed late 50's for the Flavia. Large narrow wheels was the way of thinking then.

The center of the contact patch does not coincide with the axis going through top and bottom ball joint, the axis around which the wheels pivot when steering. The distance between the point where the steering axis goes through the road and the center of the contact patch is called scrub radius. It contributes highly to how the forces are transmitted from tire / road contact to the hands of the driver.

Look at the heavy aluminum towers, wishbones, cross member for the spring etc. Lancia spent a fortune of making sure the geometry is as desired under all conditions. Changing tire size and even more changing rim width ruins all that. Lancia may not even have gone bankrupt if they realized in the 60's people were going to put on wide wheels and tires anyway.

[gamma a.i.]

both are rated high----I have just read a few tire-tests, including a 2009 ADAC rating...
ADAC is a "neutral-tester"; so I think they are not fibbing !
,,,but the Mich is at least 30% higher priced & may not really give 'more tire' !

F'stone Internet price in Germany, incl shipping & 19% VAT is in the € 35.oo range, which seems to be a bargain.
Firestone is now the bargain branch of Bridgestone, so it is a "good-name"

Michelin Internet price in Germany is €55....Yikes !! .

I'd go for the funny-named Firestone & save the difference....for something else nice (for a Fulvia , of course)