20" Rear Tire Thread - 295/35R20, 305/35R20, etc...
#41
10-04-2016 | 07:39 PM
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From: Detroit, MI
No argument here; but i was just talking about preventing wheel spin. Its the single most popular misconception that a wider rear tire will reduce wheel spin, and that's just not true. Now I would argue that once a vehicle starts to understeer, a wider rear tire would just hurt times at the track; especially if you're already traction limited at the rear in a straight line.
#43
10-04-2016 | 09:11 PM
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From: Detroit, MI
Since the tire is squished to create a contact patch, that contact patch is affected by the weight of the car. Since the weight of the car hasn't changed, and the pressure in the tire hasn't changed, the contact patch will be the same size because it is squishing the same amount due to the weight. The only way to increase contact patch size is to decrease tire pressure. And here is a handy-dandy calculator to help you maximize contact patch area/direction based on your needs:
BND TechSource - Tire Data Calculator
And also an article that maybe explains it better than I did:
When you install wider tires without changing anything else, the size of the tire's contact patch (i.e., the rubber touching asphalt) stays relatively constant. That size is based on a tire's overall diameter, inflation pressure, and the weight acting on it. Installing fatter tires widens the patch, but it also shortens it front-to-back. Because of this, cornering gains can be offset by diminished straight-line traction, including braking and hydroplaning resistance. The increased mass and friction can also translate to slower lap times and a drop in fuel economy.
If you want to improve cornering grip, you're better off switching to a higher-performance tire of the same size. Buy right, and you'll get a stiffer sidewall for crisper turn-in and steering feel, as well as a stickier rubber compound and a tread pattern focused on dry grip.
Width won't do it. Merely increasing the width of a tire doesn't increase the area touching the pavement. It just makes it a wider, shorter patch.
A bigger donut. If other vehicular factors remain constant, increasing a tire's overall circumference is the only way to enlarge the contact patch. Of course, your car's body and suspension were designed around a specific tire circumference. Changing it might cause more problems than it solves.
Pressure and weight. Reducing air pressure or increasing the weight on a tire increases the size of the contact patch. But again, there are drawbacks. Some poor engineer has already fought this battle: Keep the stock size and just buy a more aggressive tire.
Source: Road and Track
http://www.roadandtrack.com/car-cult...-tire-patches/
If you want to improve cornering grip, you're better off switching to a higher-performance tire of the same size. Buy right, and you'll get a stiffer sidewall for crisper turn-in and steering feel, as well as a stickier rubber compound and a tread pattern focused on dry grip.
Width won't do it. Merely increasing the width of a tire doesn't increase the area touching the pavement. It just makes it a wider, shorter patch.
A bigger donut. If other vehicular factors remain constant, increasing a tire's overall circumference is the only way to enlarge the contact patch. Of course, your car's body and suspension were designed around a specific tire circumference. Changing it might cause more problems than it solves.
Pressure and weight. Reducing air pressure or increasing the weight on a tire increases the size of the contact patch. But again, there are drawbacks. Some poor engineer has already fought this battle: Keep the stock size and just buy a more aggressive tire.
Source: Road and Track
http://www.roadandtrack.com/car-cult...-tire-patches/
P.S. I'm the poor engineer fighting these battles.
#46
10-04-2016 | 10:33 PM
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From: Detroit, MI
#47
10-05-2016 | 04:20 PM
Agreed, but that's where proper throttle modulation (read: light foot) comes in.
#48
10-05-2016 | 08:52 PM
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Joined: Jun 2014
Posts: 682
Likes: 243
From: Southern Cal
Haven't mounted my spacers yet... Do you see any potential issues with rub or appearance if 17mm spacers are used in conjunction with PSS 305's and Velocity AP Springs at .8" drop?
#49
10-05-2016 | 09:25 PM
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Joined: Jun 2014
Posts: 682
Likes: 243
From: Southern Cal
Well, you're not increasing the contact patch. You're just changing its shape. That's the misconception. Most people assume that when you add tire width wise, the tire touching the road length wise stays the same, but it actually decreases.
Since the tire is squished to create a contact patch, that contact patch is affected by the weight of the car. Since the weight of the car hasn't changed, and the pressure in the tire hasn't changed, the contact patch will be the same size because it is squishing the same amount due to the weight. The only way to increase contact patch size is to decrease tire pressure. And here is a handy-dandy calculator to help you maximize contact patch area/direction based on your needs:
BND TechSource - Tire Data Calculator
And also an article that maybe explains it better than I did:
The summary of all this is: Wider tires generally help lateral grip. Taller tires generally help reduce wheel spin (with lower air pressure to boot). And stickier tires help everything.
P.S. I'm the poor engineer fighting these battles.
Since the tire is squished to create a contact patch, that contact patch is affected by the weight of the car. Since the weight of the car hasn't changed, and the pressure in the tire hasn't changed, the contact patch will be the same size because it is squishing the same amount due to the weight. The only way to increase contact patch size is to decrease tire pressure. And here is a handy-dandy calculator to help you maximize contact patch area/direction based on your needs:
BND TechSource - Tire Data Calculator
And also an article that maybe explains it better than I did:
The summary of all this is: Wider tires generally help lateral grip. Taller tires generally help reduce wheel spin (with lower air pressure to boot). And stickier tires help everything.
P.S. I'm the poor engineer fighting these battles.
Prior to the change over at 8K miles with lots of tread left on the Pirellis, my RWD 2015 "R" spun the rear tires like there was no tomorrow. Straight line, rounding corners, 1st, 2nd, 3rd, even 4th gear... didn't matter. the ability to break the rear-end free at will was certainly entertaining, to the point of being irresponsibly dangerous.
The change at all four corners to PSS 305's on the rear and stock PSS on the front (with no other simultaneous change to the vehicle set-up) created a profound change in the handling and spinning of the rear tires.
Even with 9K now on the PSS rubber, I have to work hard to break the rear tires free. The tail-happy drift and correction of the rear end accelerating out of a corner is reduced to no less than half the excessive drift that existed before. and hooking up the tires in a straight line acceleration is remarkably easier. Still need to modulate the throttle some, but the finite line to good traction is far more forgiving.
I would be surprised if this difference is 100% due to the different rubber compound of the two tires.
#50
10-05-2016 | 09:28 PM
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Joined: May 2016
Posts: 34
Likes: 3
From: Northern Virginia
Regardless of all this engineering babble, I can assure you that the PSS 305's provide substantially less wheel spin than the OEM 295 Pirellis.
Prior to the change over at 8K miles with lots of tread left on the Pirellis, my RWD 2015 "R" spun the rear tires like there was no tomorrow. Straight line, rounding corners, 1st, 2nd, 3rd, even 4th gear... didn't matter. the ability to break the rear-end free at will was certainly entertaining, to the point of being irresponsibly dangerous.
The change at all four corners to PSS 305's on the rear and stock PSS on the front (with no other simultaneous change to the vehicle set-up) created a profound change in the handling and spinning of the rear tires.
Even with 9K now on the PSS rubber, I have to work hard to break the rear tires free. The tail-happy drift and correction of the rear end accelerating out of a corner is reduced to no less than half the excessive drift that existed before. and hooking up the tires in a straight line acceleration is remarkably easier. Still need to modulate the throttle some, but the finite line to good traction is far more forgiving.
I would be surprised if this difference is 100% due to the different rubber compound of the two tires.
Prior to the change over at 8K miles with lots of tread left on the Pirellis, my RWD 2015 "R" spun the rear tires like there was no tomorrow. Straight line, rounding corners, 1st, 2nd, 3rd, even 4th gear... didn't matter. the ability to break the rear-end free at will was certainly entertaining, to the point of being irresponsibly dangerous.
The change at all four corners to PSS 305's on the rear and stock PSS on the front (with no other simultaneous change to the vehicle set-up) created a profound change in the handling and spinning of the rear tires.
Even with 9K now on the PSS rubber, I have to work hard to break the rear tires free. The tail-happy drift and correction of the rear end accelerating out of a corner is reduced to no less than half the excessive drift that existed before. and hooking up the tires in a straight line acceleration is remarkably easier. Still need to modulate the throttle some, but the finite line to good traction is far more forgiving.
I would be surprised if this difference is 100% due to the different rubber compound of the two tires.
#51
10-05-2016 | 10:27 PM
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From: Detroit, MI
#52
10-05-2016 | 10:28 PM
That should be no trouble at all. Might be getting just a bit too close with an H&R spring set, but no issue with the VAPs.
#53
10-06-2016 | 12:05 AM
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Joined: May 2012
Posts: 323
Likes: 100
From: S NJ
Just like you could throw on a 275 drag radial have no wheel spin from a more narrow tire...
#54
10-06-2016 | 03:31 PM
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Joined: May 2014
Posts: 150
Likes: 180
From: Virginia
Can you give more details on your spacers in term of brand/vendor? thanks!
#56
10-06-2016 | 05:23 PM
775-351-1000
Wheel Adapters, Wheel Spacers, Hub Rings, and much more! | Motorsport Tech
#58
01-10-2017 | 04:53 PM
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Joined: Jun 2016
Posts: 376
Likes: 56
From: LA
Pics of 305s
to the guys running 305s on the stock 10.5 inch wheels, do any of you have close up pics of side and rear profiles?
I want to see how the sidewalls sits with 305 on 10.5. I usually don't do 305 on anything smaller than 11 inch, but am thinking about it as I'm due for tires...
Thanks
I want to see how the sidewalls sits with 305 on 10.5. I usually don't do 305 on anything smaller than 11 inch, but am thinking about it as I'm due for tires...
Thanks
#59
01-10-2017 | 07:41 PM
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Joined: Dec 2016
Posts: 240
Likes: 51
From: Houston, Texas
I'm sold on PSS since I've run them on other vehicles over the last few years and have seen the improvement they provide. I'm also sold on increasing the rear size to 305/30. Where I'm not certain how to proceed is on the front. Why do most of you that increase the tire size on the rear then leave it stock on the front? Why not go 265? Thanks.
#60
01-10-2017 | 07:48 PM
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Joined: Jun 2016
Posts: 376
Likes: 56
From: LA
Mods: not sure why you merged my thread with this one as I wasn't undecided on the size, I specifically was asking for close up pictures of 305/30/20 in the factory 10.5 inch wheel.
So now that its buried in the end of this thread, most probably its gonna be glossed over and ignored with no answer...
Thanks
So now that its buried in the end of this thread, most probably its gonna be glossed over and ignored with no answer...
Thanks