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      04-24-2012, 10:30 AM   #1
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Please educate me on tire width and grip

I have always been one to think that wider tires equate to more grip and indeed you see some very powerful cars with very wide tires.

I have also heard, however, that grip isn't related to the width of the tires, but rather, to the inflation pressure. By this, I mean that at the same inflation pressure on a given car, a narrower tire will have a narrower but longer contact patch, while the wider tire will have a wider but shorter contact patch. In the end, however, the actual area of rubber contacting the pavement is the same. If this is true, going wider shouldn't make a difference in terms of better grip.

The downside to wider tires is that they are heavier, so I want to know if they actually do give you more grip or not?

Thanks.
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      04-24-2012, 10:32 AM   #2
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If that were true, we'd all have 185 tires on our cars. Width plays a huge role in grip.
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      04-24-2012, 10:38 AM   #3
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A narrower tire would have to have low pressure to equal the contact patch of a wider tire. If you every go to a quarter mile track, you see guys dropping pressure like crazy to increase their contact patch. Your thought could hold some validity on a 245 to 255 ratio. But let's say you go from a 255 to a 295.....the pressure you would have to drop to equal the patch would be unsafe in most cases.....................Phil
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      04-24-2012, 10:41 AM   #4
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Quote:
Originally Posted by THE TECH View Post
If that were true, we'd all have 185 tires on our cars. Width plays a huge role in grip.
In theory, you could do this, but you would really have to decrease the inflation pressure significantly......like to almost being flat!!! This will affect safety, fuel economy as well as handling from the standpoint of the sidewall being very bowed.

However, within a reasonable range, of say 265 to 295 tires, does it really matter? If it does, can you make up for the 265 tire by just dropping the inflation pressure like 2 psi compared to the 295 tire?
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      04-24-2012, 10:43 AM   #5
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Quote:
Originally Posted by VVG View Post
In theory, you could do this, but you would really have to decrease the inflation pressure significantly. This will affect safety, fuel economy as well as handling from the standpoint of the sidewall being very bowed.

However, with a reasonable range, of say 265 to 295 tires, does it really matter? If it does, can you make up for the 265 tire by just dropping the inflation pressure like 2 psi compared to the 295 tire?
You can do a lot of things in theory but in life would never do.

The difference in width on a 265 to a 295 tire is 1.182" so you'd have to drop the pressure quite low I would think to make the narrower tire match the wider one. Doesn't make sense to me. Sounds like a penny pinching tactic to be honest.
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      04-24-2012, 10:54 AM   #6
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Quote:
Originally Posted by ///M Ryder View Post
A narrower tire would have to have low pressure to equal the contact patch of a wider tire. If you every go to a quarter mile track, you see guys dropping pressure like crazy to increase their contact patch. Your thought could hold some validity on a 245 to 255 ratio. But let's say you go from a 255 to a 295.....the pressure you would have to drop to equal the patch would be unsafe in most cases.....................Phil
Conventional thinking would lead you (and me) to think this way. However I still don't fully see why a narrower tire at the same inflation pressure wouldn't just give you a longer contact patch. Hence, the overall contact area will be the same as a wider tire.

I am probably missing something obvious. It has been a long time since high school physics !!
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      04-24-2012, 10:56 AM   #7
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I guess the real question is, does 1" to 1 1/2 inches make a difference? I would say for daily driving you can feel a difference but you don't really need it. For track purpose I would say it could make all the difference in your set up...............Phil
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      04-24-2012, 10:58 AM   #8
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Quote:
Originally Posted by THE TECH View Post
You can do a lot of things in theory but in life would never do.

The difference in width on a 265 to a 295 tire is 1.182" so you'd have to drop the pressure quite low I would think to make the narrower tire match the wider one. Doesn't make sense to me. Sounds like a penny pinching tactic to be honest.
Not a penny pinching tactic, but as I said, wider tires are also heavier, and that weight is in a location that matters more than even the weight of the wheels.
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      04-24-2012, 11:02 AM   #9
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Quote:
Originally Posted by VVG View Post
Not a penny pinching tactic, but as I said, wider tires are also heavier, and that weight is in a location that matters more than even the weight of the wheels.
After a week of driving on my new set up my MPG hasn't change at all. So from that stand point the weight is minimal at best. From a track standpoint, most find a smaller lite weight wheel to offset the wider tire weight.......Phil
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      04-24-2012, 11:32 AM   #10
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Quote:
Originally Posted by ///M Ryder View Post
A narrower tire would have to have low pressure to equal the contact patch of a wider tire. If you every go to a quarter mile track, you see guys dropping pressure like crazy to increase their contact patch. Your thought could hold some validity on a 245 to 255 ratio. But let's say you go from a 255 to a 295.....the pressure you would have to drop to equal the patch would be unsafe in most cases.....................Phil
They also lower tire pressure to have a softer sidewall. The softer sidewall allows more movement before tire breakaway. Ever see a drag slick and the sidewall is all creased. Also, they increase front tire pressure to cut rolling resistance from the front tires.

Dave
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      04-24-2012, 11:34 AM   #11
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Quote:
Originally Posted by VVG View Post
Not a penny pinching tactic, but as I said, wider tires are also heavier, and that weight is in a location that matters more than even the weight of the wheels.
This depends on brand, also most of us would give up a little weight to get more grip. On launch your tires may be heavier but now you can leave at a higher rpm therefore reducing your 60ft. time meaning lower 1/4 mile times. Also goes for handling..if the wider contact patch means you can get on the throttle earlier after the apex than you will be faster coming out of the corner.

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      04-24-2012, 11:35 AM   #12
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Quote:
Originally Posted by THE TECH View Post
You can do a lot of things in theory but in life would never do.

The difference in width on a 265 to a 295 tire is 1.182" so you'd have to drop the pressure quite low I would think to make the narrower tire match the wider one. Doesn't make sense to me. Sounds like a penny pinching tactic to be honest.
Not top mention that 1.182" is per tire..you will have over 2.36" of more width per axle. Thats a lot more tire..

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      04-24-2012, 11:38 AM   #13
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Quote:
Originally Posted by THE TECH View Post
If that were true, we'd all have 185 tires on our cars. Width plays a huge role in grip.
Agree but extreme plus sizing of tires is also not called for..the stagger and profile differences as well as over all tire diameter should not deviate greatly from OEM spec
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      04-24-2012, 11:45 AM   #14
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Quote:
Originally Posted by tibra1 View Post
Agree but extreme plus sizing of tires is also not called for..the stagger and profile differences as well as over all tire diameter should not deviate greatly from OEM spec
Where did you get this from? The M3 out of the box is undertired. Thats why the GTS has 255/285 setup and even then its still undertired. The M3 is a heavy car with short gearing. Can you go to far, yes you can. I know several people who track their cars and everytime they went with a +1 sizing their lap times dropped. Many track guys run 275/35/18 and 295/35/18s with great results.

4sevens dropped his lap times at Road America I believe by 4 seconds going to a 275/295 setup on his OEM ZCP car.

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      04-24-2012, 11:59 AM   #15
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Quote:
Originally Posted by Dave07997S View Post
Where did you get this from? The M3 out of the box is undertired. Thats why the GTS has 255/285 setup and even then its still undertired. The M3 is a heavy car with short gearing. Can you go to far, yes you can. I know several people who track their cars and everytime they went with a +1 sizing their lap times dropped. Many track guys run 275/35/18 and 295/35/18s with great results.

4sevens dropped his lap times at Road America I believe by 4 seconds going to a 275/295 setup on his OEM ZCP car.

Dave
The M3 is NOT the M3 GTS

There are known reports of extreme plus sizing upsetting the balance of the car..its common sense that if you dont keep the same F-R stagger and F-R overall tire diameter similar to OEM...you may have issues..

FYI ..http://www.m3post.com/forums/showthr...ease+emissions
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      04-24-2012, 12:00 PM   #16
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Quote:
Originally Posted by tibra1 View Post
Agree but extreme plus sizing of tires is also not called for..the stagger and profile differences as well as over all tire diameter should not deviate greatly from OEM spec
extreme plus sizing meaning what, and according to who? I disagree. 265/245 is about the bare minimum for a heavy powerful car like the E92 M3. I plan on going 275 all round or 295/275 in the near future for extra grip on the track. If you only drive street and don't go fast in corners or auto-x it then yeah, maybe it doesn't matter, but it is a false statement to say plus sizing is uncalled for.

Also, to stay on OP's question, wider tires work better until they either rub or become too wide to overcome their drag with the better cornering. On a 420+ hp car that weighs 3700 ish, a 245/265 setup is not appropriate. On a 2500 lb racecar with 240 hp, a 245/245 combo is ideal, because the lower power car can't pull 285's around that well and the light weight chassis doesn't need very wide tires to get grip in corners.

Edit: I agree with keeping the diamaters/rake similar, but that can be accomplished by changing profile.
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      04-24-2012, 12:22 PM   #17
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This is an interesting question since if I remember correctly from college physics class, the weight applied to each tire divided by the pounds per square inch of pressure within each tire equals the contact patch. Therefore the contact patch of two tires with equal weight one them and air pressure be the same regardless of width, but that is assuming the tires themselves are completely flexible, which they are not, but I'm not sure that would be a huge factor.

The consensous does seem a wider tire has greater traction, so I'm guessing there must be more too it than just purely the size of the contact patch. Maybe a wider contact patch has more traction for some reason due to the way the weight is applied during corning than a narrow one of the same size?
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      04-24-2012, 01:29 PM   #18
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extreme plus sizing meaning what, and according to who? I disagree. 265/245 is about the bare minimum for a heavy powerful car like the E92 M3.
So you know more than BMW engineers?..hmm doubt it

To each their own..but there are 2 sides to the coin
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      04-24-2012, 01:38 PM   #19
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Quote:
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So you know more than BMW engineers?..hmm doubt it

To each their own..but there are 2 sides to the coin
That's comical. Every production car is built with constraints, and one of the reasons the tires and alignment are the way they are is to build in understeer so less skilled/experienced drivers don't get in over their heads. I agree that rake and diameter should remain similar to stock, but the width is less than ideal for track/handling and that is not an issue up for debate. No offense, but if you follow your logic you could never change a single thing about your car without downgrading it from the holy grail of perfection that left the factory.

Every quick guy at the track runs wider than stock front/rear unless budget keeps them from it.

If you're pleased with stock sizes then that is perfectly fine, but don't spread misinformation that running wider tires somehow causes ill-handling etc. when in fact the opposite is true.
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      04-24-2012, 01:44 PM   #20
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Quote:
Originally Posted by Porschefile View Post
That's comical. Every production car is built with constraints, and one of the reasons the tires and alignment are the way they are is to build in understeer so less skilled/experienced drivers don't get in over their heads. I agree that rake and diameter should remain similar to stock, but the width is less than ideal for track/handling and that is not an issue up for debate. No offense, but if you follow your logic you could never change a single thing about your car without downgrading it from the holy grail of perfection that left the factory.

Every quick guy at the track runs wider than stock front/rear unless budget keeps them from it.

If you're pleased with stock sizes then that is perfectly fine, but don't spread misinformation that running wider tires somehow causes ill-handling etc. when in fact the opposite is true.
Im just trying to give people an accurate idea of whats going on here..a small fraction of people's cars live on the track and unless your's does or you are putting down MUCH more power than stock..(i.e, supercharged) then the 245/265 setup is fine...I have had no issues to date and I drive very aggresively..

Im not averse to modding cars at all..in fact my last car (335) was heavily modified..

Whats comical is people always wanting to go bigger..newsflash..bigger is NOT always better.
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      04-24-2012, 01:51 PM   #21
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Quote:
Originally Posted by Porschefile View Post
That's comical. Every production car is built with constraints, and one of the reasons the tires and alignment are the way they are is to build in understeer so less skilled/experienced drivers don't get in over their heads. I agree that rake and diameter should remain similar to stock, but the width is less than ideal for track/handling and that is not an issue up for debate. No offense, but if you follow your logic you could never change a single thing about your car without downgrading it from the holy grail of perfection that left the factory.

Every quick guy at the track runs wider than stock front/rear unless budget keeps them from it.

If you're pleased with stock sizes then that is perfectly fine, but don't spread misinformation that running wider tires somehow causes ill-handling etc. when in fact the opposite is true.
Agree...

You know the old addage, "you can lead a horse to water but you will never make him drink".
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      04-24-2012, 01:52 PM   #22
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Quote:
Originally Posted by tibra1 View Post
Im just trying to give people an accurate idea of whats going on here..a small fraction of people's cars live on the track and unless your's does or you are putting down MUCH more power than stock..(i.e, supercharged) then the 245/265 setup is fine...I have had no issues to date and I drive very aggresively..

Im not averse to modding cars at all..in fact my last car (335) was heavily modified..

Whats comical is people always wanting to go bigger..newsflash..bigger is NOT always better.
Fair enough, on the street it really isn't going to matter unless you're supercharged or cornering really aggressively anyway. I personally dislike the stock sizes, but I know it works for many.
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