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gustave
09-28-2004, 10:57 PM
OK, it's sort of trick question, because I think that I know the answer(s). Well mostly anyways 8^)

But I am curious what others think.

It is a seemingly simple issue, in fact few people really even question it. Wider tires are always assumed to be better on a performance car (well except for Shep ;-), who claims that too wide a front tire prevents proper heat build up, and there is merit to that line of thinking, it's certainly part of the overall picture).

I am prepared because I know from experience that this issue can be somewhat "controversial", sort of like big brakes. Some folks have very fixed ideas about how tires work. But it would still be cool to have a discussion about it.

I have things to learn about the subject myself, which is why I am curious.

Gustave



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gpj
09-28-2004, 11:22 PM
are better I assumed it was because larger surface area allowed better traction on a suitable surface. Since this is a trick Q, I guess I was wrong.

jsirota
09-28-2004, 11:40 PM
Contrary to popular belief, going wider does not increase the size (area) of the contact patch -- it merely changes its shape.

Generally, a wider contact patch will increase cornering grip, at the expense of braking/acceleration grip. Since most cars have plenty of "headroom" under braking/acceleration (especially acceleration in taller gears), there is little penalty to going wider (provided that you also have a suitably wide wheel that can maintain the contact patch size).

StMedina
09-28-2004, 11:45 PM
265 front 285 rear in street tire form....and the same dimensions in slicks are what seem to be favored right now...


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gustave
09-28-2004, 11:47 PM
been more specific about the question being for dry conditions.

You bring up one of the primary points.

Does a wider tire really have a larger contact patch?

In other words, is a tire like a "balloon" in that any change in tire pressure has a directly proportional change in contact patch size?

Or is a tire some other type of beast, in that its contact patch size (and shape) is more a function of the construction of the tire, and only indirectly linked to tire pressure?

I've seen folks offer convincing arguements for both points of view. I would have to say that from what I have read on the subject, that the balloon theory is more the correct answer, but it does lie a little bit in-between.

Gustave

<img src="http://gsperformance.com/temp/signature.jpg" height=200 width=350>

StMedina
09-28-2004, 11:52 PM
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gustave
09-28-2004, 11:56 PM
important.

What you are saying, that a wider tire is better for cornering since it lines up the contact patch with the direction of force, does seem to be the commonly accepted modern theory. This makes the contact patch into a lot of short segments, each of which assumes a slip angle and produces lateral force, and all the little forces add up to a much bigger force (slip angle is an important part of this discussion btw).

The part about longitudinal traction is not so clear to me. For sure drag cars use wide tires to promote traction. At least it seems that way based on what I have seen. If what we are saying is true, then they should really be using really big diameter tires. I suppose to some extent they do, certainly in Top Fuel the tires expand due to centrifugal force and are not really all that wide when it counts, though they become quite large in diameter.

I also read once about Super Touring cars wanting to use larger OD tires, since width was regulated, and it gave them better braking. This is another data point in my mind that links contact patch shape and the ability of the patch to support forces in certain directions.

Good points.

Gustave

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CBsaksiri
09-28-2004, 11:59 PM
my thoughts (not scientifically grounded in any way)

I. Along the lines of what Josh was saying... if a wider tire gives you a differently-shaped contact patch, I would assume that the contact patch is wider and less long rather than long and narrow. Under braking and acceleration, I imagine this is advantageous because you want to be able to stretch the tread of the tire to make the most of the traction and there is more length of tire to stretch if a smaller arclength of the tire is in contact with the road. If we're talking about cornering force, I would guess tires are generally constructed to be more effective at holding side loads across a wide section of tire stuck to the ground rather than over a long, narrow contact patch. Also if you bring slip angles into the picture, in a corner the tire should be stretching diagonally across the tread... with the vector of the ground force acting on the tire pulling diagonally back along the wheel + toward the inside of the turn, so I imagine again that the wide, less long patch stretches better.

- Shep's thing about keeping tire temps within a range: I think this applies to race tires which need to be kept in a certain range (high enough) to be effective, but for a street tire it seems that generally heat is bad &mdash; and the tire is designed to have grip at cold temps &mdash; so following that thinking a street tire can't be wide enough.

- I don't consider this subject simple at all and I think about it all the time... tire temps, construction and setup (e.g., how tire construction can affect how much static camber is required in a suspension and driving style, etc.), optimum slip angles, etc.
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gustave
09-29-2004, 12:04 AM
traction due to temperature vs. traction due to wider contact patch.

I understand the arguement, it makes a lot of sense. The front tires are not subject to forces from engine power, so it seems reasonable that they will not slip as much, not get as hot, and therefore might not get to the sweet spot of the friction vs. temperature curve.

So, if the front tires are too wide, then they don't heat up enough, the mue is lower and overall traction decreases.

The only thing one needs to know to determine if a wider front tire will produce more grip in practice, is whether the loss of mue due to a cooler tire will outweigh the increase in traction due to a wider contact patch.

I don't think that is easy to answer on paper. You, Shep and others are finding that for them the front width limit is at about 265 no?

I'll be honest, my gut feeling is that the wider contact patch over-rides the temperature consideration. But that is only my intuition. You guys should do what works best for you. If you can get softer front slick compounds, then you might try a wider front tire.

Gustave

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gustave
09-29-2004, 12:09 AM
I beleive that a wider tire is better for cornering due to the shape of the contact patch. I also feel that this then logically implies that a wider tire is not as good for lateral acceleration.

But what I cannot get my head around is that all of the "traction circles" that I have seen (real ones based on data, not theoretical circles) show that race cars will pull as many (or more) G's under braking than they do while cornering.

I currently have no way of explaining that.

Gustave

<img src="http://gsperformance.com/temp/signature.jpg" height=200 width=350>

gustave
09-29-2004, 12:13 AM
You've come to the conclusion that tires are incredibly complicated.

There are no single right answers I suspect, though some answers may be more correct than others.

Gustave

<img src="http://gsperformance.com/temp/signature.jpg" height=200 width=350>

jsirota
09-29-2004, 12:15 AM
I'm only regurgitating things I've learned spending the last 15 years hanging out with people attempting to set up race cars. I don't actually understand all of the physics behind it!

hayaku
09-29-2004, 12:20 AM
wheel rim also affects grip and slip angle...

too tired to regurgitate it now, but thoroughly explained in fred puhn's book about handling... also from talking with glenn yee. btw, my explanation will do neither of them any justice... most of it went over my head...<div align="left">
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gustave
09-29-2004, 12:22 AM
the assumption is that the rears can be heated better due to the accelerative forces from engine torque. I agree.

But what about braking? That develops large longitudinal forces right? Why should this not heat the crap out of the front tires, regardless of their width? This is not a rhetorical question, I honestly wonder about this...

I'll take it a bit further. If the balloon theory is right (which modern experts seem to lean towards) then a 265 will have the same contact patch SIZE as a 285 (if at the same pressure). The only thing is that the 285 is wider, thus better able to support cornering loads, though possibly not as good at supporting longitudinal loads.

This seems to hold, the rear tires are not as good under accelration (forward) and thus get hot and therefore presumably get closer to their temp vs. friction sweet spot (though possibly past the sweet spot too, you don't know for sure).

Gustave




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CBsaksiri
09-29-2004, 12:22 AM
The brakes will be able to deliver a greater download on the tires (especially immediate). This would have a multiplicative effect on how much friction can be generated, since more friction -> more braking force -> more friction, and so on...

I think the tread-stretching thing has something to do with it as well... an instructor told me once that a wheel can be turning 30% slower than the tread, due to the stretching of the tread/sidewalls and this stretching generates a lot of force.
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StMedina
09-29-2004, 12:22 AM
sprint or main, and i believe that's what shep is thinking of also...

if we look at what ptg is running (iknow, iknow...big leap) but it tells alot...


on a 10x18 front, they're running a 280-650/18
on a 10x18 rear, they're running a 285-680/18

so tread width on front is 280mm, tread width rear is 285mm.....

last time out....i ran 285-645/18 pirelli slicks D4 compound on the 9.5 inch SSR comps, so basically I have more "fold over" than ptg would on their wider wheels....after basically 10 laps at speed, 20 miles.....tire temps were in the 140-150 range....where optimal temp is 170-180 ish...perhaps i could have gotten up to those temps if i had run longer, or if it had been a 30 minute main or sprint...who knows....

it was a hot day as well, in the low 90's....with the sun beating down on the concrete...so imagine my surprise after runnning the dickens out of them....to find that heck, they were in the 140ish range....



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StMedina
09-29-2004, 12:24 AM
hint of understeer, that allows for "get on the pedal like all getout before apex"....rear end sticks like glue....

i've yet to run a smaller front, i may try it next time...




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StMedina
09-29-2004, 12:27 AM
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gustave
09-29-2004, 12:30 AM
outdated on the tire thing though (no offense). So much has been learned in the last 20 years.

This is a better, more recent book, though it too has its limitations.

The best source for info in my opinion is the many ariticles found in "Racecar Engineering" and "Race Tech" over the last few years.

Gustave

mike_m3
09-29-2004, 12:34 AM
also, doesn't a wider tire running at the same pressure deform less while providing the same contact patch? less heat, less rolling resistance<br><br><br><a href="http://m3.madrussian.net"><img src="http://osbdesign.com/webpics/m3v5.jpg" border=0 alt="Go To BMWM3.org!"></a><br><br>

gustave
09-29-2004, 12:41 AM
achieving it.

Get bigger front tires, assuming they provide better cornering capability.

Then put on a big front sway bar to control body roll and keep cambers aligned to pavement.

Then soften or delete the rear sway bar.

Now you also have a car that tends towards understeer. But the soft rear end provides killer longitudinal acceleration so you can really get on the throttle early, and if you left foot trail brake, then the car still rotates well at the apex.

Sounds familiar doesn't it? 8^)

It's like my "Party Line" or something...

Anyone watch the Chinese GP? See the rear of those cars leaning in the corners? See the inside front tires lift in the tight corners? Wonder how soft they are running the rear? Wonder why, even though the drivers always complain about understeer? Maybe the engineers know better? Ok, ok... I'm kidding. Mostly 8^)

Gustave

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meem
09-29-2004, 12:46 AM
i know that's not the angle you're approaching this question from, but i really think that's the reason why many people like them (though that itself is perhaps due to conditioning from watching too many races ;-)
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gustave
09-29-2004, 12:48 AM
What I mean to say is that it is very difficult to measure the temperature of the contact patch WHEN IT IS AT MAX LOAD. That only occurs during part of the corner, and by the time to get half way down the next straight the contact patch has cooled off quite a bit already (as much as 50 def. F or more from data I have seen).

But, if those optimum temps were measured in the pits, and you are measuring them under the same conditions (after the same type of last corner, straight, pit entry scenario) then it is reasonable to use those numbers as a guide.

Tire temperature is very critical, but subject to large variations when measured, and as such subject to a great deal of misuse.

Gustave

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gustave
09-29-2004, 12:50 AM
Deform less when corning? Yes, due to smaller attained slip angle as mentioned earlier.

Gustave

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StMedina
09-29-2004, 12:51 AM
on...

and the pit entrance was right at the end of a chicane...using probe pyrometer.....should have seen me duck into the pits....and get on the binders....looked like i thought i was kimi

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mike_m3
09-29-2004, 01:02 AM
we've beaten this subject to death with cycling and especially when it comes to time trialing tires - the virtues of 23mm vs 21mm vs 19mm width, etc - when run at the same pressures even though the patch is the same the amount the casing has to "deform" to accommodate the patch varies with width - the wider the tire the less it has to deform and the less mechanical change (for lack of a technical term) occurs. In test after test (real world with bicycle tires) a wider tire will roll faster at the same pressure as a narrower version though in real terms in the cycling world narrower tires (21 or 19mm vs 23 or 25) are run at higher pressures to offset the difference in patch size though most seem to agree their main advantage is aerodynamic rather than in rolling resistance (plus the ability to run at higher pressures)<br><br><br><a href="http://m3.madrussian.net"><img src="http://osbdesign.com/webpics/m3v5.jpg" border=0 alt="Go To BMWM3.org!"></a><br><br>

gustave
09-29-2004, 01:06 AM
8^)

At least you should have the tire temps up right?

Gustave

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StMedina
09-29-2004, 01:07 AM
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gustave
09-29-2004, 01:12 AM
my knees abandoned me (used to love Mountaineering too).

I was just thinking about bicycles and rolling resistance today.

I saw some funky recumbant on the side of the road with like a 10" diameter front wheel. I though, boy, that wheel must really catch all the potholes and slow down forward progress.

Then I thought, hmm, perhaps a racing bike should have really large O.D. tires, so that holes and dips in the pavement would produce a smaller component of force in the rearward direction.

I mean, if you redesign the frame using modern concepts you could fit wheels in there that are say 20-30% larger no? And it should roll along like a banshee.

Who knows what we'll see in the 2010 Tour de France time trials?

Gustave

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///Mous3
09-29-2004, 01:29 AM
My final year project was to calculate the stresses in a fly-wheel that spins at 1 million RPM. It was a steel disc at the center with concentric rings of single thread carbon fiber composite.

So you can only go wider, not larger in diameter.

I think we have to look at tire as static friction which is directly proportional to area of contact and the normal force.

edhchoe
09-29-2004, 01:34 AM
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ChuckD
09-29-2004, 03:05 AM
once set up for a particular road course will use temps and pressure to do most of their tuning and are able to dial the car in this way and be highly competative without much adjustemnt to the suspension.

Sorry I can not elaborate further or give you the team. Maybe shep can get into it further... I am not sure ou realize.. but alot of what he shares at times is trickling down from some of best people in the business.

shep01
09-29-2004, 05:58 AM
which is why the street car has the widest tires i can put on, within reason, with the downside being performance in the rain. in the wet - narrow is king of course but....

on the track - i loose grip when i cannot get the heat into the front tires - it is just that simple. when too narrow, i burn them up and out-run them. to date, we have continued to add rubber to the rear end, since we rely almost exclusively on mechanical grip anyway, and if i could fit anything larger on there - i would do so. up front, with the addition of a very well built splitter, we found aerodynamic grip in cornering the car and have found the tire size that seems to maximize grip while still getting up to enough heat to 'work'. race rubber does not work well below a threshold low temp, each tire being different of course but most seeming to gain grip from 150F-220F. below 150, they are not nearly as sticky; above 220 they are too greasy as well. air pressures play a major role in the equation as well. ultimately, the clock is what determines the ideal set up for us. also, be reminded of weight distribution on the car! with a 50/50 (or close) car it is far different than say, a F1 or champ car with everything that matters lying behind the driver!

shep01
09-29-2004, 06:07 AM
as with all our tuning and quest for performance, we started out running 245 x4 on the track. well, needless to say, the weight of the car alone was enough to have us looking for more rubber in the rear. ironically, if only running an all out sprint at say 30-45 minutes, an ideal set-up may well mean a 245 up front and a 275 in the rear. the time ptg got from that set up in speed wc year before were incredible! yes, they ran out of tire near the end but the cars were blazing fast. obviously, they have major suspension mods. and the luxury to tune out any bad handling habits with all their customized sway bars, control arms, etc. just the redesigned location and track of their suspension - their caster range and the extreeme camber make up for a lot. for us, it is cost prohibitive and we can't afford to burn through tires quite that fast either.

ah, theory vs the real world - always makes for a great contrast

Alameda Mountie
09-29-2004, 07:30 AM
It seems to be a foregone conclusion that wider = better for rears on a RWD car for dry grip. OEM wheels on performance cars seem to bear this out, i.e. M3s, Vettes, 911s etc. Since I doubt it's difficult to keep your rears warm on the track, no matter how wide they are or what compound you're using, I would guess then that you should work out your fronts first, depending on your driving style, the track and weather conditions (and of course your wallet), and then choose your rears accordingly to give you as much contact as you can handle without understeering you into oblivion. Does this sound like the right way to go?

I only do the occasional lapping day right now but I'd be interested in tracking the car next summer, so I'm looking into some of the same issues right now.

gustave
09-29-2004, 08:53 AM
These days it is much closer to 50/50 then one might think. On the order of 47/53 (dependent on ballast).

It's also interesting that they are trying to go to a wider and wider front tire (as possible within the rules), moving the weight balance further forward to compensate.

Gustave
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gustave
09-29-2004, 09:02 AM
be remembered that are not ever measuring the temp of the tire when it is in the condition of max cornering. It is just not physically possible to do this, the tires cool off too fast.

But as long as one is consistent about how tire temps are measured then they can be used for tuning.

I.e. if you know that the last time you were at a particular track that the car was really good then the tire temps were such and such, then you might strive to tune the car again to arrive at those temps the next time you're at the same track. That tells you the car is close to where it was the time before.

See the distinction? You're still using temps as a tuning tool, but you're not fooling yourself that the temps measured represent the tire in its condition of max cornering.

Sure tire performance is dependent on pressure. Yet using pressure to tune the car is more an American concept. The Europeans seem to leave the pressure where it is optimum and tune the suspension for handling. This is just the general flavor of things from reading trade rags.

Gustave



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gustave
09-29-2004, 09:04 AM
and I don't think we really arrived at any conclusion on why racecars always strive to fit wide tires.

I've presented what I know about it. But I still have some big holes in my understanding. Things that are not addressed in any of the available books on the subject.

Gustave

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txse46m3
09-29-2004, 09:06 AM
285/30 R3S03 fronts on a somewhat tight, off camber track. I conciously try to use the front end to scrub speed into turns, however.<p align="center"><a href="http://www.doubledracing.net">
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txse46m3
09-29-2004, 09:20 AM
Under pure cornering, ie turn in to apex, the 2 outside tires are providing the vast majority of the traction due to weight transfer. The inside front is all but worthless as it's pretty much unloaded and the inside rear is in a similar if less extreme state. Similarly, under braking the fronts are providing the vast majority of the traction, again due to weight transfer.

So in both cases, you have a pair of tires doing most of the work...heck...a well setup car might have more overall traction under braking.<p align="center"><a href="http://www.doubledracing.net">
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hayaku
09-29-2004, 09:34 AM
actually, glenn told me the same exact thing about fred's book and recommended that book too.. hehehe

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hayaku
09-29-2004, 09:36 AM
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hayaku
09-29-2004, 10:04 AM
with that elasticity changing as the slip angle changes, no? and heat (on the tread and the air pressure) changes the grip of the tire dynamically... lots of things to factor in i think<div align="left">
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shep01
09-29-2004, 10:33 AM
no question they have moved toward a more balanced weight distribution - still, no getting around 900hp (or whatever it is) delivered to the rear wheels. i also suspect they would like to have more rubber up front at this point

shep01
09-29-2004, 10:44 AM
since so much of the is subjective (within the confines of the law of physics, obviously) i often consider the real-world experience at play. i have consistantly seen 9-11k miles on the rear tires while i certainly can get 15-18k on the fronts. i do not drive overly agressively, i never 'patch-out' (intentionally) and my alignment specs provide me with perfectly even tread wear patterns. still, i cannopt keep rear tires under me.

this must speak to the way i have the car set-up - very soft rear suspension with alignment for maximum mechanical grip. do i assume since i maximize for rear grip i would also get more heat in the rears and consequently more wear?

this seems to hold true on the track and on the street -
also, as you mentioned tire reaction and slip angle under braking and turn in - driving styles do come into play. as the track car evoles, our driving style adapts to the changes. we are fast in fast out right now (finally). we can late brake to create a maximum contact patch and need very little throttle steer to turn in. obviously, we cannot set the car up perfectly for every corner on a track like sebring - close to 4 miles long - so we do trail brake and throttle steer to avoid push at a few corners.

also, the foward attitude of the set-up, as we diminish the rake and overall lower the center of gravity, plays to tire selection as well. we consider this subject a moving target anyway - great to discuss as there is no correct answer - just the stop watch i suppose.

mike_m3
09-29-2004, 11:43 AM
that a given shape is more efficient than another (less structural deformation to achieve it thus less resistance and heat) - with cycling obviously the goal is somewhat different from a race car but the physics are still the same. The other thing is that (I believe you ride?) we are looking to lower rolling resistance first and foremost so the point is to run on the bead of the tire and since a smaller casing is easier to run at higher pressures that usually ends up dictating tire width used – now once you get into the effects of lowering or raising pressure in mountain bike tires it becomes a REALLY interesting conversation – I really don’t have the patience to type all of the stuff out (and you most likely know this as well as I do) on that subject but there a wider tire provides more volume allowing you to run safely (snake bites, etc.) at lower pressures creating a bigger patch and better traction…. Fun fun fun<br><br><br><a href="http://m3.madrussian.net"><img src="http://osbdesign.com/webpics/m3v5.jpg" border=0 alt="Go To BMWM3.org!"></a><br><br>

gustave
09-29-2004, 12:06 PM
There really is no other explanation that works.

Wheelbase is larger than track width, so forward weight transfer under braking is less than sideways weight transfer when cornering.

Thus all four tires can be use when braking, only 2-3 tires really effective when cornering.

So even though contact patch "shape" is optimized for cornering, the sum total of factors still makes braking pretty effective.

I am still stumped why braking can't be used to heat the crap out of the front tires?

Brakes can provide much more torque than any engine, even in first gear (I did the math to convince myself once). And even though the rear tires help out, fully 70-80% of braking forces can be carried by the front tires (perhaps less when the car is low). Why would modulating the throttle heat the rears so much, while modulating the brake pedal would not so the same to the fronts?

Gustave


<img src="http://gsperformance.com/temp/signature.jpg" height=200 width=350>

gustave
09-29-2004, 12:23 PM
torque. I was wondering about this one day some time ago and did a simple calculation with mue, rotor diamter, assumed brake line pressure etc...

F1 cars will brake at 4-5 G's but only accelerate (forwards) at about 1.5 - 1.8 G's (in first gear), however this is a function of aero load.

An F1 car at say 180 mph will decelerate at over 1G simply from the driver letting off the throttle! Fascinating...

But I digress 8^)

Gustave


<img src="http://gsperformance.com/temp/signature.jpg" height=200 width=350>

W///MD
09-29-2004, 12:24 PM

M3 Cab Guy
09-29-2004, 12:41 PM
Is there a limit to how wide you can get rears in an E46 M3? I have the OEM 19's and was thinking of trying something wider, just curious as to the upper limit available. I don't track the car so I'm not worried about understeering the front, just putting down as much contact as I can in back!

StMedina
09-29-2004, 12:55 PM
oem 19"s the upgrade size to run is 275/35/19
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more lateral G JayDee
09-29-2004, 01:23 PM

JayDee
09-29-2004, 01:28 PM

JRX5
09-29-2004, 01:36 PM
So you can achieve a higher centripetal acceleration before it overcomes the force of friction, at which point your car would skid.

This is useful in a corner when the angle affects the inward centripetal force, which is why they are sometimes banked.

Remember that the centripetal acceleration is proportional to the centripetal force, a product of Newton's Second Law.

That screech you hear coming from your tires on a fast corner is the centripetal force becomming greater than the force of friction.

M3 Cab Guy
09-29-2004, 02:05 PM
Is there some physical limit to how wide you can get the rear wheels, and is there a commonly known "widest rear wheel" available for the E46 M3? I'm just curious so don't feel the need to flame me if this is a stupid question. :)

StMedina
09-29-2004, 02:37 PM
could get a 10.5 under there....tire size would still be limited, unless u rolled the fender, but there isn't really that much to roll...

offset would be the key...

10 inch rear is plenty wide....
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(Issac Newton died a virgin) JM
09-29-2004, 02:46 PM
Tires are big (or should be big) to last a stint. The softer the tire, the bigger it needs to be. Hopefully there will be a net gain.

example: The more hp, the more grip needed. the more grip needed, the softer the compound. the softer the compound, the sooner the wear. The sooner the wear, the wider the tire needs to be.

My thoughts on greater G-force under braking than cornering is that in cornering the outside tires reach their limit before the front tires reach their limit under braking. Another way to think of it is that the tire loads are more evenly dispersed between all four tires under braking than in cornering.

I was told that Isaac Newton died "unfulfilled" by Dr. Otto Berzerjian. I have no firsthand knowledge if it is true or not.

jay

gustave
09-29-2004, 03:23 PM
<img src="http://gsperformance.com/temp/signature.jpg" height=200 width=350>

txse46m3
09-29-2004, 03:32 PM
rolling. Ideally, the tires aren't slipping much under braking, right? <p align="center"><a href="http://www.doubledracing.net">
<img border="0" src="http://members.roadfly.com/txse46m3/hotsauce_scornedwoman.jpg"></a></p>

DoubleD Racing (http://www.doubledracing.net)
Mod List: Buncha stuff that makes it sound like a barrel of washers rolling down the street.

gustave
09-29-2004, 04:40 PM
That's the whole idea. It is referred to as slip ratio, not slip angle, but the same principles apply.

Note, it is not sliding (as in a skid). It is slip. A tire will produce maximum longitudinal acceleration at some slip ratio (often on the order of 7-10%), and will produce less grip when operating above or below that ideal ratio.

This is the slip ratio that is programmed into the "Electronic Brakeforce Distribution" routine in the DSC software. The computer compares the rotational speed of the rear wheels via the ABS sensors, and compares that to the calculated vehicle speed to determine the instantaneous rear slip ratio and adjust the rear brake pressure in real time to keep the rear tires near their peak.

Of course race tires produce peak longitudinal grip at higher slip ratio than the factory street tires, which is why the EBD program is no longer optimum when you swap tires.

Gustave


<img src="http://gsperformance.com/temp/signature.jpg" height=200 width=350>

shep01
09-29-2004, 05:49 PM

JRX5
09-29-2004, 07:00 PM

txse46m3
09-29-2004, 07:27 PM
seconds of abs inducing braking sure doesn't heat up my tires as much as 3 seconds of somebody-turned-in-like-a-fool understeer. I suspect that there is significantly less slip under braking.<p align="center"><a href="http://www.doubledracing.net">
<img border="0" src="http://members.roadfly.com/txse46m3/hotsauce_scornedwoman.jpg"></a></p>

DoubleD Racing (http://www.doubledracing.net)
Mod List: Buncha stuff that makes it sound like a barrel of washers rolling down the street.

sayemthree
09-30-2004, 12:24 AM
there are so many variables.....but bigger is not always better.

StMedina
09-30-2004, 12:58 AM
20lbs of spring rate more or less...
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StMedina
09-30-2004, 01:15 AM
even the softest race compound is harder than any street compound...more or less.
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Corvette77
09-30-2004, 01:16 AM
Your logic makes no sense meem...sorry. In that case you would have bought a 325i?

mike_m3
09-30-2004, 01:30 AM
BUT UCF (world governing body of pro cycling) has set somewhat draconian standards on the "professional" bicycle - things like the diamond frame, 700c wheels, minimum weight requirements, etc are truly anachronisms but due to the way the UCF rule book is written many cutting edge things will stay in the experimental world or limited to the multi-sport (triathletes, etc) ranks. A recumbent is almost always faster than a "bent" (traditional bicycle) if simply because of the aerodynamic forces and position the rider uses to pedal which is typically more efficient. Tri bikes have more comfortable and far more aerodynamic frames than road racing bikes - they also experiment with wheel size quite a bit.
If you look at the time trial bikes used in the tour a bit over a decade ago you will see the use of innovative technology and go fast goodies but UCF stamped much of that out. Since what the pros ride is what Joe weekend "racer" like me buys things will stay the way they have been for the last 100 years for the foreseeable future - quite unfortunately.
The recumbent guys are really on the edge of the development of efficient human powered vehicles - I love looking at the stuff but I'm too ingrained in the tradition of it all to get off my road bike.
Bikes are sort of ultimate machines - its incredible how fast one can go on 1/3hp (if you're Lance) or far less.
<br><br><br><a href="http://m3.madrussian.net"><img src="http://osbdesign.com/webpics/m3v5.jpg" border=0 alt="Go To BMWM3.org!"></a><br><br>

gustave
09-30-2004, 01:05 PM
We built a full carbon fiber unibody recumbant with full front and rear suspension. The fairing and the frame were one unit (hence unibody, my idea, first time anyone ever did it).

One of our riders hit 55 mph on an early morning tryout near the beach! On flat ground! Maybe a slight tail wind...

Gustave

<img src="http://gsperformance.com/temp/signature.jpg" height=200 width=350>

gustave
09-30-2004, 01:09 PM
acceleration - under engine power.

Why is it that we feel (or have shown?) that a lot of heat can be put in the tires with the throttle, yet not as much heat can be put in the front tires with the brake pedal?

Same torque, same mass to accelerate/decelerate. Only difference is some contribution from opposite side tires when braking (the rears) while when accelerating it is all done by one pair of tires (rwd).

Turning is different I agree.

Gustave

<img src="http://gsperformance.com/temp/signature.jpg" height=200 width=350>


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