enjoyable read about tires

[kevin derhouson]

what do you think about it?

http://www.autospeed.com/cms/A_108915/article.html?popularArticle

[CamWeiss]

I read the first section and stopped.

Not really relevant to us, I'm sure most DSM'ers run 50 series or less tires, which have (as they put it) 'extremely stiff sidewalls'.

Their arguements aren't really valid either. With most performance tires that do have shorter and stiffer sidewalls, contact patch comes down to tire size followed by pressure. But the handling characteristics of a tire at 10psi are pretty shitty, unless you're a drag racer. There's a reason why I pump my Azenis up to 40psi at the start of my autocross day. The contact patch does in fact shrink slightly, but the sidewalls are supported correctly and the tire responds faster.

Tires are designed with a specific operating range in terms of pressure/sidewall deflection. It's the very reason why running an underinflated or overinflated tire for long periods will give you a bad wear pattern.

My gist: Run the widest tires you can fit. Match them appropriately to your wheel width (a 225/50-16" tire won't work very well with a 6" wide wheel, as it tucks the sidewalls in and they fold over easily) - Match the section width of the tire to the width of the wheel within reason.

Softer compounds always work better than harder compounds when it's warm and dry. A quick look at the traction and temperature grades on the sidewall of the tire, in conjunction with the treadwear rating, will give you lots of information about the grip characteristics of the tire.

[Robert Vorley]

I was distracted by the authors' artificial emphasis on the order of variables that affect grip.  For example, "The size of the contact patch has no bearing on the amount of grip generated at all".  How can grip be achieved without a contact patch??? Magic, levitation, super conductors or perhaps magnets??  The area necessarily imposes one condition on the maximum available grip that will be dependent on the constant of all other variables.  IOW, variables that affect the area of the contact patch (which the author discusses), such as width, pressure, or weight are merely being assigned a new hierarchy of importance, according to the authors opinion. 

He also arbitrarily dismisses what he refers too as "secondary factors" in order to strengthen his argument.  "Tyre width has no direct relation to the amount of grip generated; it is a secondary factor".  Since he also states that width affects the rate of cooling he seems to be contradicting himself because heat is related to friction which is directly related with grip.  Secondary or primary, they are both factors when calculating grip.  These type of comments weakened his overall argument.

Considering how many changing variables affect our tires in the real world such as; surface cf, humidity, heat, vegetation, oil, sand, downforce, drag, suspension, tire wear, alignment, tire temp, corner balance, etc., maybe it would have been more helpful if he just spent the same time explaining why (or why not) performance tires are usually wide, low, and soft compound slicks. His arguments are too abstract and artificial which is evident when he says, "we are only discussing tyres here".  No sir, we are discussing, "Tyres, Grip and All That..." which is the title of his article!

I would give him a 2/5 although it would have been higher if he could spell tire correctly. 
     

[Richard Steger]

I think "tyre" is a British spelling, but this guy doesn't make much sense.  Maybe he kinda knows his subject, but has a lousy way of making his point?  I don't like his page at all.

This page much better explains the benefits/limitations on tread width.

http://www.f1technical.net/features/10862
"""The  traction demands of a Formula One car with their high power engines mean a wider rear tyre is desirable and in Formula One’s past we have even seen far wider rear tyres because of traction and cornering requirements."

So, for more grip you need a wider tyre? To an extent yes, but you can go too wide. "Obviously we are constrained by the regulations, but even if we had free reign on the size of a tyre, we would not see cars with massively wide tyres because the current generation of Formula One cars are not designed for them," says Hamashima.

"A wider tyre means a bigger contact patch and more aerodynamic drag and rolling resistance, which can slow the car in a straight line, although a slightly wider tyre could enable higher speeds in the corners."

A tyre works best when it is in its correct operating temperature. Heat generation in the tyres relies on a certain amount of work going through the tyres, making a tyre wider, and its contact patch greater, means that not so much heat is generated for any given compound. ""


I think the above proves that Mr. Jensen's "myths" are true after all.

[John Hartman]

F1 and street cars have less in common than you might think.  We have no downforce. We have tires that last longer than 30 kilometers.  We have braking systems that might pull 1g, they pull 6.

As for the first article, and Cams critique, plus 1 for Cam, as usual.

I will add tho, that you can easily over tire a car for its suspension.  If the tire itself can generate more grip than the chassis is capable of putting down, the tire can make the car roll over too far, upsetting the balance.  I have experienced this first hand in my Mazdaspeed.  With fully stock suspension and stock tires, the car is very balanced, precise and grippy.  Once I put on the Star Spec Dunlops(in wider size too) I found that while the limits were higher, it would just roll over and get out of balance and loose precision, whereas with the stock tires, it would slowly and predictably loose grip allowing me to drive it at the limit.

After I put in camber adjustment up front and was able to dial in the alignment, I was definately able to take it further than both stock and just the tire upgrade.  I would say it still needs more rear swaybar and better dampers to fully take advantage of the tires.  At that point the stock tires would be a big weak link however.

As well, I would like to add that tire pressures do not have to be symmetrical side to side or front to back.

I drive the car and read the wear marks and adjust pressures accordingly.  I have as much as 10-12 psi difference between tires, and thats just for daily driving/canyon carving/on ramps.

[Richard Steger]

Nice posts, John and Cam.  You guys obviously have a good deal of experience with suspension, tire sizes and pressures in the real world and performance driving.  I just thought I'd go to the pinnacle of car performance and engineering to refute Mr. Jensen's article.  As you pointed out John, changing one thing (like tire width) upsets the factory balance and other parts have to be upgraded/calibrated to compensate/take full advantage of the change.  Maybe Jensen just had a lousy way of saying that.

What info/stats/feedback from your Mazdaspeed led you to run pressures varying by 10-12 psi?  I would never have thought it a good idea to do that    Are you making those decisions based on differing corner weights of your car?

[John Hartman]

Based on reading the tread.  IE, if the "heat" line or obvious wear line is down the sidewall, up the air pressure.  If you are not getting full contact on the whole flat surface of the tread, lower the pressure.

You can chalk/grease pen your tires and drive it but if you have fairly soft tires, its quite obvious.  there will be a darker black line that is clearly visible.

[kevin derhouson]

mission start tire discussion was a success, just wanted more info :p

[Robert Vorley]

I am surprised  too,  re: pressure variance.  10 psi, wow.  On the one hand I can appreciate trying to get your contact patch even, but at some point I would expect the mechanical properties of the tire to become less predictable due to the difference, wouldn't that indicate that the suspension needs some tweaking?

Richard, I liked the f1 info although it doesn't always translate easily into daily driving performance.  . 

John, I just had my alignment set up at PDM. What camber do you typically recommend for 2gs? 

 

[John Hartman]

rear about 1 deg negative would be a good start.  Any more and when you launch and it goes even more negative you end up having less tire on the road.  Also you add more rear grip in hard corners, which we don't want as the car is already an understeering car by design.  Same with 1g cars.

front as much as you can get within reason.  Daily driver, about negative 1 deg.  Serious daily driver/occasional autox, about neg 1.5 deg. Weekend warrior up to negative 2 or 2.5, depending on other things at this point.

Each car will be differnt, depending on other suspension things, tires, driving style, weights etc.

Also zero toe out in the rear, or maybe just a wee bit toe out.  With 1g cars, some toe out( 1/16th or so total) is good to counter act the factory stupid active toe bs.  If you have eliminated that, you can go 0 or just a really small amount.  Too much and its twitchy, especially under braking, but too little or toe in and it understeers and feels numb.

A small amount of toe out is good in the front as it helps turn in feel and promotes quickness in the steering response.  Again too much and its twitchy.  I like maybe 1/8th total toe out in the front on a weekend warrior and 1/16th total(both sides combined) for a daily/aggressive street car.

Also, too much toe WILL wear your tires.  You have been warned!!

If you have the means(money and fully adjustable coil overs and somewhere to have it done) corner weighting a car with you in it and the appropriate amout of gas can be great.  And aligning the car with your weight in the car is a good idea too for a performance alignment.

[John Hartman]

sorry I didn't see the part about the tire pressures.

I run up to 48 psi so even if its a full 10 psi difference from the lowest to the highest the lowest tire still has a full 38 psi in it.

I suspect my lowest and my highest are actually off by about 7 or so, not the full 10 right now.  Even wear, even load distribution and predictability are more important to me on that car than all out 10/10ths performance.

As for suspension tweaking, well, when I need dampers I will, and I would like to do a bigger rear bar, but for now it has camber ball joints and a good alignment along with good tires(Dunlop Star Specs in 225/45/18) on Konig 18x8 wheels.  That along with what Mazdaspeed(not just Mazda) did with the suspension is fine by me.  There are no worn parts, car has low kilometers and its maintained well.

[CamWeiss]

I typically run 40psi front, 35 rear when I'm at the track. I'm also lazy and don't DD the car very often, so I just leave it around there and check/top up before each event.

I've screwed with the camber a bit since the last alignment, but it's roughly 2.3 deg neg camber front, and about 3 deg neg camber rear. I run zero toe, f/r, and maximum available positive caster in the front. The tires have worn more evenly than one would expect, but keep in mind they're abused autocross tires. There is some camber wear.

[John Hartman]

you run that much negative in the rear?  Is it just because you can't ajust it due to MOAR LOW or is it by design? 

I run the same camber as you up front on the Talon tho, its nice 

[Robert Vorley]

John, that sounds pretty close to my current set up.  I currently have -2 camber on the front and -1.2 rear,  slight toe out on the front and some toe in on the rear.  I usually run the same psi all around or a few more in the front for higher speeds, and I dial the rear dampers a little softer than the front which seems to work well in the bends. I was never really happy with the handling until the sway bars were installed though.  The factory roll is horrible for fast transitions at high speeds but with lowering and coil overs it was significantly improved.

Even though I rolled my fenders I am only running 225/40R18 (Star Spec) so once they wear I may try 245's.   
                 
re: 10/10ths - I hear you, some compromise is necessary to keep it a livable dd. 

Cam, how much castor can you get?  I have 5 deg.  I usually run about 40 too. 

Any feedback on corner balancing?  It is something I have been thinking of doing once the interior is redone.

[CamWeiss]

My rear camber is due to moar lows and no adjustability. However: It works fairly well. Tire temps at the track are even across the back tires. It lightens up the rear and and helps the car rotate a bit. It's not ideal for launches, but I only spin tires if I'm doing a HARD launch from 4500+. Not something it typically sees when the first corner is 50 feet ahead.

I dug out my last alignment. I've added a tiny bit more front camber since then:
Front Caster: +3.6
Front Camber: -2.5
Front Toe: 0.0
Rear Camber: -3.1
Rear Toe: 0.35 Total (.1/.25)


Haven't corner weighted the car as there's usually glaring, more pressing issues to be taken care of that hinder performance.