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[arisonford]

what are the benefits/changes between the two? Thanks, if this has been beaten to death, i apologize but i couldn't find it so just send me the right way!

[SLO]

Originally Posted by arisonford

what are the benefits/changes between the two? Thanks, if this has been beaten to death, i apologize but i couldn't find it so just send me the right way!

I was going to ask a similar question. I know that it's generally preferred to get the widest tires on the front and back as possible (within reason) and usually there is more clearance in the rear since there is the variable in the front with an important factor called steering. Also, a wider tire in the rear gives more traction for acceleration. However, what is best for handling? I imagine it depends on the car and how it is set up with suspension, weight disti, ect., right?

Is the only benefit of going the same size all around to be able to rotate tires?

[PC Valkyrie]

Here is my simplistic way of looking at this.

The grip of a car depends heavily on that contact patch between the tire and the road. The stickier the rubber, the more grip a car has. The larger the contact patch (ie wider tires), the more grip a car has......the only exception to this rule is in unshovelled snow, when a thinner tire car better slice through snow and slippery conditions when a thinner tire with higher pressure per square area at the contact patch results in more traction when driving.

The only other downside of wider tires is higher aerodynamic resistance and higher unsprung weight.

So the question is the following: do you want more relative grip up front or in the rear? The answer depends what performance parameters you value. If all you care about are straight line drag races, a wider rear tire will offer better grip for acceleration because it is RWD. If you track or autocross your car, you want wider front tires to improve turn in grip and help reduce understeer.

[SLO]

Originally Posted by PC Valkyrie

Here is my simplistic way of looking at this.

The grip of a car depends heavily on that contact patch between the tire and the road. The stickier the rubber, the more grip a car has. The larger the contact patch (ie wider tires), the more grip a car has......the only exception to this rule is in unshovelled snow, when a thinner tire car better slice through snow and slippery conditions when a thinner tire with higher pressure per square area at the contact patch results in more traction when driving.

The only other downside of wider tires is higher aerodynamic resistance and higher unsprung weight.

So the question is the following: do you want more relative grip up front or in the rear? The answer depends what performance parameters you value. If all you care about are straight line drag races, a wider rear tire will offer better grip for acceleration because it is RWD. If you track or autocross your car, you want wider front tires to improve turn in grip and help reduce understeer.

Great answer, thanks! Are you the same Valkyrie from E46Fanatics back in the day?

[fourtailpipes]

to be perfectly accurate, wider tires to not change the area of contact patch between the tires and the road. this is constant, given the same tire pressure. lowering your tire pressure will increase your contact patch. wider tires change the SHAPE of the contact patch, which is advantageous.

[JME]

Originally Posted by fourtailpipes

to be perfectly accurate, wider tires to not change the area of contact patch between the tires and the road. this is constant, given the same tire pressure. lowering your tire pressure will increase your contact patch. wider tires change the SHAPE of the contact patch, which is advantageous.

Are you sure? For a consistent material I would agree (because it is true,) but--because the sidewall adds an extra stiffness--a wider tire increases the contact patch width laterally, narrowing the length of sidewall providing a resistance, and allowing the contact patch to increase in area since the air pressure provides a larger portion of the force overall. Assuming, of course, the force provided by the sidewall is proportional to the length of sidewall touching the ground.

I think I explained that right.

[akak1997]

Originally Posted by JME

Are you sure? For a consistent material I would agree (because it is true,) but--because the sidewall adds an extra stiffness--a wider tire increases the contact patch width laterally, narrowing the length of sidewall providing a resistance, and allowing the contact patch to increase in area since the air pressure provides a larger portion of the force overall. Assuming, of course, the force provided by the sidewall is proportional to the length of sidewall touching the ground.

I think I explained that right.

nah, he's right. the contact patch total area is determined by the weight of the car and tire pressure. If you don't change tire pressure or weight of the car and just change the width of the tires, the contact patch total area stays the same where the shape of the patch is changed, and it'll be wider but also narrower.

[WhiteOne]

You can rotate your tires if they are all the same size.

[riguy]

I can speak to one issue with having all the wheels the same size. I have snows on mine @ 225/40/18 all around. The rear rims are VERY exposed to damage with that narrower tire on there. As an example, I just went thru the car wash a few days ago and got damage on one of my rear wheels due to the rim being scraped against the wheel guards of the car wash. DOH! Not too bad and I will get repaired come spring when I put summer's on, but still....what a painful sight that was on a 3 day old car! I hate car washes....

[JME]

Originally Posted by akak1997

nah, he's right. the contact patch total area is determined by the weight of the car and tire pressure. If you don't change tire pressure or weight of the car and just change the width of the tires, the contact patch total area stays the same where the shape of the patch is changed, and it'll be wider but also narrower.

He seems to disagree.

http://www.performancesimulations.co...on-tires-1.htm

I agree that the theoretical formula states that, and is correct, but that formula does not take into account the stiffness of the sidewall.

[crzy4135i]

Originally Posted by arisonford

what are the benefits/changes between the two? Thanks, if this has been beaten to death, i apologize but i couldn't find it so just send me the right way!

The safe way to explain it is you run the risk of the rear end coming around in a turn if running wider than stock tires up front. Of course, that would only apply with DTC in full defeat mode.

[SpeedballTrix]

The smaller the difference in front and rear tire width the more understeer turns into oversteer.

Large difference = slow and easy to drive.
Small difference = fast and hard to drive.

Watch the berk videos.
That's what I mean by fast and hard to drive.

[jotapeh]

Originally Posted by SpeedballTrix

The smaller the difference in front and rear tire width the more understeer turns into oversteer.

Large difference = slow and easy to drive.
Small difference = fast and hard to drive.

Watch the berk videos.
That's what I mean by fast and hard to drive.

Sorry, can I ask what exactly are the 'berk videos'? Are they available online? I googled it but I got some fitness trainer videos, I doubt that is what you meant..

[Blacky]

It depends on if you like understeer (wide rear tyres) or oversteer same front and rear.
Not that I am any expert, but I understand one of the reason BMW put wider tyres on rear (other than cosmetic) is they believe understeer is a much safer trait than oversteer.
Please correct me if I am wrong.

[snkeyez95]

Spot on to what I've always heard. A lot of folks at track events will square up the tires to reduce understeer.

Originally Posted by Blacky

It depends on if you like understeer (wide rear tyres) or oversteer same front and rear.
Not that I am any expert, but I understand one of the reason BMW put wider tyres on rear (other than cosmetic) is they believe understeer is a much safer trait than oversteer.
Please correct me if I am wrong.