BMW 1 Series Coupe Forum / 1 Series Convertible Forum (1M / tii / 135i / 128i / Coupe / Cabrio / Hatchback) (BMW E82 E88 128i 130i 135i)
 





 

Post Reply
 
Thread Tools Search this Thread
      01-20-2017, 01:05 PM   #23
bNks334
Major
bNks334's Avatar
427
Rep
957
Posts

Drives: '11 135i (N55)
Join Date: May 2014
Location: New York

iTrader: (1)

Quote:
Originally Posted by MightyMouseTech View Post
Same laws of physics.
What you're saying is that the contact patch would just be longer, and more narrow, due to the same load just being distributed differently?

Here is a more technical rebuttle I found, but now were just above my head:
Quote:
It's inaccurate to assume that as the section width or tread width increases that the contact patch area also increases. Nor does it remain constant as [Vertical Force] / [Constant Inflation Pressure] suggests. Conceivably, it could decrease depending on the relative vertical stiffnesses. But what will change is the shape of the contact patch, becoming shorter in the longitudinal direction as it is made wider (assuming a constant load), and this may be partly responsible for more uniform unit loading over the area of the contact patch. All else equal, integrating a more uniform unit load and associated grip coefficient function over the entire contact patch should give more total lateral grip. The wider tire probably also has higher vertical and lateral spring rates, meaning less camber loss and lateral distortion in actual driving respectively.
The above supports that, yes, mechanical grip can be improved with varying tire constructions and section widths.

Last edited by bNks334; 01-20-2017 at 01:13 PM..
Appreciate 0
      02-10-2017, 04:26 PM   #24
dbronnik
Lieutenant
dbronnik's Avatar
223
Rep
542
Posts

Drives: N54 E88
Join Date: Mar 2012
Location: California

iTrader: (4)

Garage List
Quote:
Originally Posted by MightyMouseTech View Post
It is simple physics. The size of the tire does not change the size of the contact patch. The only thing that determines contact patch size is the tire pressure and the weight on that tire. That's it. Different tire sizes just change the SHAPE of the contact patch.

You can actually fairly accurately figure out the weight of a vehicle by using just the size of the contact patches and the tire pressure. We actually did this in first year Engineering.
TIL, interesting stuff! This certainly makes sense for a tire that is at rest (static). Though I don't believe the physics is that simple for tires in motion, which is more relevant to this thread..


__________________
Appreciate 2
      02-10-2017, 07:10 PM   #25
2008135i
Private
11
Rep
58
Posts

Drives: 2008 135i
Join Date: Nov 2016
Location: Milwaukee, WI

iTrader: (0)

Quote:
Originally Posted by MightyMouseTech View Post
Nope, serious.

Does not matter the size of the tire, the contact patch size will be the same, as long as tire pressure is the same. Skinnier tires will have a long, narrow contact patch better for acceleration, a wider tire will basically turn that patch sideways, better for cornering, worse for accel.
So... Why do drag cars run such wide tires? They aren't cornering (hopefully).

Not saying your lying, cause I've heard this before, but I definitely notice a difference with acceleration between my summer and winter tires.
Appreciate 0
      02-11-2017, 10:45 AM   #26
WDE82
Major
United_States
815
Rep
1,199
Posts

Drives: 2018 440iGC F36
Join Date: Aug 2015
Location: Torrance, CA

iTrader: (0)

Quote:
Originally Posted by 2008135i View Post
So... Why do drag cars run such wide tires? They aren't cornering (hopefully).

Not saying your lying, cause I've heard this before, but I definitely notice a difference with acceleration between my summer and winter tires.
Tires have adhesion properties as well, not just traditional frictional. They're very complex. Soft race and drag tires have more of this adhesion effect than street tires (by a lot).

Wider tires do provide more grip but not to the degree and not via the mechanisms that most people think. He's correct on his principles of contact patch size. If pressure is equal between two sets of tires of different widths, the static patch will be the same size. But that's just static. Tires become extremely complex in a dynamic state almost to a point where you can't say anything too general without experimental data from the tires in question.
Appreciate 0
      02-11-2017, 06:15 PM   #27
Dyno Junkie
12.92 @ 173.0km/h - 1.84 60'
Australia
2
Rep
36
Posts

Drives: 135i
Join Date: Jul 2015
Location: Perth

iTrader: (0)

There is a lot of theory in this thread.
Let me give you my own real word experience.

As I mentioned earlier our 135i is my work car and the car I am using for this comparison is a 2001 Holden Monaro, similar to pontiac GTO.

The car is lowered on coilovers and set up more for circuit rather than drag racing. The rear shock absorbers are double adjustable for compression and rebound.

On Mickey Thompson 245/40/18 drag radials full power can not be applied off the line.
With Mickey Thompson 265/40/18 drag radials full power launches have resulted in several 1.52 second 60' times.
Reducing the compression on the rear shocks I have launched gently on Kumho 275/30/19 street tyres and so far run a best of 1.67 second 60' times which is quicker than I have been able to launch the much stickier 245/40/18 drag radials.

There is no substitute for taking it to the track and experimenting.
By the way 135i suspension is a lot better than the car I run down the strip.
Attached Images
 
Appreciate 0
      02-15-2017, 09:56 PM   #28
xQx
General
Australia
903
Rep
1,003
Posts

Drives: 2008 BMW 135i (E88 N54 6AT)
Join Date: Aug 2016
Location: Sunshine Coast QLD Australia

iTrader: (0)

Wow, I was following this thread actively for the first week but I just checked back and it's still going! Thanks everyone for all the answers - esp to WDE82, Vigilante375, kirill1221 & Ginger_Extract which were all along the lines of 'stop relying on the computer and learn to drive you bloody idiot.'

I'm loving WDE82's response, I think it sums the answer up perfectly:
Quote:
Originally Posted by WDE82 View Post
I like how OP never considers not using WOT all the time. Dumbest thing I've seen posted in a minute.
... on reflection, I wholeheartedly agree. It comes from years and years of driving AWD's where after the launch you just mash the pedal to get the best straight-line acceleration - that said, I've always had a steep turbo-driven power-band around corners and naturally work with it by 'calibrating the throttle' where grip is limited - I don't know why I'm struggling with the same thing in a straight line. I guess it's just experience.

Now, this conversation has veered towards tires, I’ll weigh in with some science that lays very strong credence to WDE82’s claim that “Tires have adhesion properties as well, not just traditional frictional. They're very complex.”

Not only is the contact area between the tire and the road dependant only on the weight of the car and the pressure of the tire, not the width of the tire (ie. A wider tire will just have a wider, shorter contact patch and a narrower tire will have a longer, narrower contact area); but the amount of friction you have between your car and the road doesn’t change depending on your contact area.

Theoretically, it doesn’t matter if you have 145/45R18’s at 42PSI or 285/30R18’s at 18PSI – your friction is determined by the ‘stickiness’ of the rubber, not by the size or shape of the contact patch. The two laws of friction are 1) The friction between two surfaces is proportional to the force pressing one to the other. And 2) The friction is independent of the contact area.
Furthermore, (on wet roads) you can sometimes get more grip with a smaller contact area because it’s easier to get the water out of the way and thus less likely to aquaplane.

The standard friction equation Ff = μN says the only way you can get more grip is to get sticker tires (or a heavier car).

Now, you might be saying “That’s BS”. But if you google “does contact patch affect friction”, you’ll find plenty of articles saying it’s not. The science checks out. The reason performance tires are bigger and wider (so they say) is because they wear quicker, so it’s helpful to have more rubber to wear away.

But, it is BS - to an extent - and it's easy to test: if you let your tires down to 18 psi then do a few timed laps, or measure your breaking distances, then repeat for 30 psi and 45 psi, you’ll find it does make a big difference. Why? Well, in the real world, your grip and handling is affected by much more than just the amount of friction between your tires and the road beneath them.

As WDE82 said: "They're very complex.”
Appreciate 0
      02-16-2017, 08:49 AM   #29
bNks334
Major
bNks334's Avatar
427
Rep
957
Posts

Drives: '11 135i (N55)
Join Date: May 2014
Location: New York

iTrader: (1)

Quote:
Originally Posted by xQx View Post
Wow, I was following this thread actively for the first week but I just checked back and it's still going! Thanks everyone for all the answers - esp to WDE82, Vigilante375, kirill1221 & Ginger_Extract which were all along the lines of 'stop relying on the computer and learn to drive you bloody idiot.'

I'm loving WDE82's response, I think it sums the answer up perfectly:

... on reflection, I wholeheartedly agree. It comes from years and years of driving AWD's where after the launch you just mash the pedal to get the best straight-line acceleration - that said, I've always had a steep turbo-driven power-band around corners and naturally work with it by 'calibrating the throttle' where grip is limited - I don't know why I'm struggling with the same thing in a straight line. I guess it's just experience.

Now, this conversation has veered towards tires, I’ll weigh in with some science that lays very strong credence to WDE82’s claim that “Tires have adhesion properties as well, not just traditional frictional. They're very complex.”

Not only is the contact area between the tire and the road dependant only on the weight of the car and the pressure of the tire, not the width of the tire (ie. A wider tire will just have a wider, shorter contact patch and a narrower tire will have a longer, narrower contact area); but the amount of friction you have between your car and the road doesn’t change depending on your contact area.

Theoretically, it doesn’t matter if you have 145/45R18’s at 42PSI or 285/30R18’s at 18PSI – your friction is determined by the ‘stickiness’ of the rubber, not by the size or shape of the contact patch. The two laws of friction are 1) The friction between two surfaces is proportional to the force pressing one to the other. And 2) The friction is independent of the contact area.
Furthermore, (on wet roads) you can sometimes get more grip with a smaller contact area because it’s easier to get the water out of the way and thus less likely to aquaplane.

The standard friction equation Ff = μN says the only way you can get more grip is to get sticker tires (or a heavier car).

Now, you might be saying “That’s BS”. But if you google “does contact patch affect friction”, you’ll find plenty of articles saying it’s not. The science checks out. The reason performance tires are bigger and wider (so they say) is because they wear quicker, so it’s helpful to have more rubber to wear away.

But, it is BS - to an extent - and it's easy to test: if you let your tires down to 18 psi then do a few timed laps, or measure your breaking distances, then repeat for 30 psi and 45 psi, you’ll find it does make a big difference. Why? Well, in the real world, your grip and handling is affected by much more than just the amount of friction between your tires and the road beneath them.

As WDE82 said: "They're very complex.”
This is all great, and it makes sense, but you're also ignoring sidewall stiffness. Tires act as part of the effective dynamic spring rate under load. Stiffening the sidewall (higher psi) will result in a higher effective spring rate and less traction. I don't have the technical knowledge though to tell you whether this is a function of friction or suspension... or whatever, but I can definitely agree with you that tires and suspension are a very technical field to navigate.

Question: Will lowering psi, therefore, softening the sidewall, increase the effective contact patch area?

I would say, yes. It is so counter-intuitive to think that the resulting increased surface area, and compliance under load, wouldn't lead to increased friction... At the very least, the tire would heat up faster; therefore, improving the amount of chemical adhesion to the pavement.

As I posted earlier, wouldn't distributing the applied "force," or load, differently have an effect on the friction coefficient?

Quote:
All else equal, integrating a more uniform unit load and associated grip coefficient function over the entire contact patch should give more total lateral grip. The wider tire probably also has higher vertical and lateral spring rates, meaning less camber loss and lateral distortion in actual driving respectively.
You say "2) The friction is independent of the contact area. " However, this does NOT mean that friction cannot correlate to changes to the contact area depending on what changes are made...

This thread is geared toward people drag racing. Traditionally, people drag racing run very soft, sticky, and fat tires coupled with very a very soft and compliant suspension (to absorb the initial load of launching). I take my car to road courses, so I am personally ok with running wider tires with stiff sidewalls to gain cornering ability and agility at the loss of a bit of traction under dynamic loading situations.

Last edited by bNks334; 02-16-2017 at 09:09 AM..
Appreciate 0
      02-16-2017, 09:02 PM   #30
WDE82
Major
United_States
815
Rep
1,199
Posts

Drives: 2018 440iGC F36
Join Date: Aug 2015
Location: Torrance, CA

iTrader: (0)

Quote:
Originally Posted by xQx View Post
Wow, I was following this thread actively for the first week but I just checked back and it's still going! Thanks everyone for all the answers - esp to WDE82, Vigilante375, kirill1221 & Ginger_Extract which were all along the lines of 'stop relying on the computer and learn to drive you bloody idiot.'

I'm loving WDE82's response, I think it sums the answer up perfectly:
Quote:
Originally Posted by WDE82 View Post
I like how OP never considers not using WOT all the time. Dumbest thing I've seen posted in a minute.
... on reflection, I wholeheartedly agree. It comes from years and years of driving AWD's where after the launch you just mash the pedal to get the best straight-line acceleration - that said, I've always had a steep turbo-driven power-band around corners and naturally work with it by 'calibrating the throttle' where grip is limited - I don't know why I'm struggling with the same thing in a straight line. I guess it's just experience.

Now, this conversation has veered towards tires, I’ll weigh in with some science that lays very strong credence to WDE82’s claim that “Tires have adhesion properties as well, not just traditional frictional. They're very complex.”

Not only is the contact area between the tire and the road dependant only on the weight of the car and the pressure of the tire, not the width of the tire (ie. A wider tire will just have a wider, shorter contact patch and a narrower tire will have a longer, narrower contact area); but the amount of friction you have between your car and the road doesn’t change depending on your contact area.

Theoretically, it doesn’t matter if you have 145/45R18’s at 42PSI or 285/30R18’s at 18PSI – your friction is determined by the ‘stickiness’ of the rubber, not by the size or shape of the contact patch. The two laws of friction are 1) The friction between two surfaces is proportional to the force pressing one to the other. And 2) The friction is independent of the contact area.
Furthermore, (on wet roads) you can sometimes get more grip with a smaller contact area because it’s easier to get the water out of the way and thus less likely to aquaplane.

The standard friction equation Ff = μN says the only way you can get more grip is to get sticker tires (or a heavier car).

Now, you might be saying “That’s BS”. But if you google “does contact patch affect friction”, you’ll find plenty of articles saying it’s not. The science checks out. The reason performance tires are bigger and wider (so they say) is because they wear quicker, so it’s helpful to have more rubber to wear away.

But, it is BS - to an extent - and it's easy to test: if you let your tires down to 18 psi then do a few timed laps, or measure your breaking distances, then repeat for 30 psi and 45 psi, you’ll find it does make a big difference. Why? Well, in the real world, your grip and handling is affected by much more than just the amount of friction between your tires and the road beneath them.

As WDE82 said: "They're very complex.”
You've got most of it. However tires are hard to summarize with just a coefficient of friction. That coefficient changes dynamically with load. Also the coefficients don't account for the fact that tires must slip to grip.
__________________
Appreciate 0
Post Reply

Bookmarks

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off



All times are GMT -5. The time now is 09:04 PM.




1addicts
Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.
1Addicts.com, BIMMERPOST.com, E90Post.com, F30Post.com, M3Post.com, ZPost.com, 5Post.com, 6Post.com, 7Post.com, XBimmers.com logo and trademark are properties of BIMMERPOST