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Why 13 inch Wheels?

 
Old 04-23-2019, 06:32 PM
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Dirty Howie
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Default Why 13 inch Wheels?

Why do I see most guys going with 13 inch rears instead of 12 inch. The 335 tire most are using specs out at 12.5 inches anyways


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Old 04-23-2019, 07:00 PM
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When comparing a single tire size against two different wheel widths, it's better to go with the wider wheel (assuming it's within reason) as that will end up putting more of the tire on the ground. Additionally, there is better sidewall support which reduces deflection and improves not only grip, but feedback and driver confidence. In this particular case, running a 335 on a 13" wheel provides more performance than a 12" wheel would. A good rule of thumb is to have the tread width and wheel width the same value, or the wheel width slightly greater than the tread width.

- Cory
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Old 04-23-2019, 10:38 PM
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Originally Posted by APEXRaceParts View Post
When comparing a single tire size against two different wheel widths, it's better to go with the wider wheel (assuming it's within reason) as that will end up putting more of the tire on the ground. Additionally, there is better sidewall support which reduces deflection and improves not only grip, but feedback and driver confidence. In this particular case, running a 335 on a 13" wheel provides more performance than a 12" wheel would. A good rule of thumb is to have the tread width and wheel width the same value, or the wheel width slightly greater than the tread width.

- Cory
Thanks for the input. Wonder why BF doesn't extend the wheel size recommendation to 13 inches.


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Old 04-24-2019, 02:11 AM
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Originally Posted by APEXRaceParts View Post
When comparing a single tire size against two different wheel widths, it's better to go with the wider wheel (assuming it's within reason) as that will end up putting more of the tire on the ground. Additionally, there is better sidewall support which reduces deflection and improves not only grip, but feedback and driver confidence. In this particular case, running a 335 on a 13" wheel provides more performance than a 12" wheel would. A good rule of thumb is to have the tread width and wheel width the same value, or the wheel width slightly greater than the tread width.

- Cory
Are you finally making Vette sized EC7's?
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Old 04-24-2019, 10:22 AM
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Few people having issues with fitting 13" on C7 wide body. I'd go 12.5" when I am ready.
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Old 04-24-2019, 04:07 PM
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Originally Posted by GoatHead View Post
Few people having issues with fitting 13" on C7 wide body. I'd go 12.5" when I am ready.
I was told by Forgestar that they do not make 12.5 in F14


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Old 04-24-2019, 10:15 PM
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I have used several sets of 18x13 wheels on a c7 gs with no issues.
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Old 04-25-2019, 12:41 AM
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Originally Posted by c5racr1 View Post
I have used several sets of 18x13 wheels on a c7 gs with no issues.
Do you remember the offset or back space?
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Old 04-26-2019, 10:50 AM
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Originally Posted by Dirty Howie View Post
Why do I see most guys going with 13 inch rears instead of 12 inch. The 335 tire most are using specs out at 12.5 inches anyways


DH
It has to do with contact patch shape. There is only so much area of a tire touching the ground. Say your tire has to support 1500 lbs and you are running a tire pressure of 30 psi. That means the tire is putting 50 square inches on the ground (50x30=1500). Since the contact patch is equal to width x length the wider you make the 50 square inches the shorter the patch. The shorter the patch the faster the tire reacts to changes in direction.

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Old 04-26-2019, 03:09 PM
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Originally Posted by Bill Dearborn View Post
It has to do with contact patch shape. There is only so much area of a tire touching the ground. Say your tire has to support 1500 lbs and you are running a tire pressure of 30 psi. That means the tire is putting 50 square inches on the ground (50x30=1500). Since the contact patch is equal to width x length the wider you make the 50 square inches the shorter the patch. The shorter the patch the faster the tire reacts to changes in direction.

Bill
Bill
Thanks for the science lesson and I get it

Just wondering why the manufacturer wouldn't include this size wheel in their specs ???


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Old 04-27-2019, 01:00 PM
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Wider contact patch = less grip to accelerate forward.
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Old 04-27-2019, 01:38 PM
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Originally Posted by Apocolipse View Post
Wider contact patch = less grip to accelerate forward.
??????


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Old 04-27-2019, 01:44 PM
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Same reason wider gives you more lateral grip. Wider side to side means narrower front to back.
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Old 04-27-2019, 11:44 PM
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Originally Posted by Apocolipse View Post
Same reason wider gives you more lateral grip. Wider side to side means narrower front to back.
Likely I will notice the increased lateral grip and not notice lack of acceleration.......I will be going from 325x30x19 to 335x30x18. Wonder if the smaller diameter rear wheel will make a noticeable difference in acceleration.


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Old 04-29-2019, 11:36 PM
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Originally Posted by Apocolipse View Post
Same reason wider gives you more lateral grip. Wider side to side means narrower front to back.
Except you would just run less tire pressure if the wider wheel were really widening the useful contact patch. By running lower air pressure, you'd have a wider contact patch with the same length compared to the narrower wheel. This is what people always fail to take into account with any wider wheel/tire combo.

That said, I'm not sure it's a given that a 13" wheel with the 335 actually puts more tread width on the ground. Or at least I'm not sure it does so without reducing the pressure in the center of the contact patch. It seems to me that a useful way to approach is by dividing the millimeters of section width by the wheel width. The common 315 fitment is to use them on 11" wheels. That gives 28.64mm of section width per inch of wheel. A 335 tire on a 12" wheel only has 27.92mm of section width per inch of wheel width - it's already more stretched than the 315mm/11" fitment! That makes sense when we realize that the 335 is less than an inch wider than the 315 in section width, and it's only 0.4" wider in tread width. On a 13" wheel, it would be down to only 25.77mm per inch of wheel width - a lot more stretched than the 315/11 fitment. That is outside BFG's recommended wheel widths for the 335, and for obvious reasons.
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Old 04-30-2019, 12:13 AM
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Originally Posted by MatthewMiller View Post
Except you would just run less tire pressure if the wider wheel were really widening the useful contact patch. By running lower air pressure, you'd have a wider contact patch with the same length compared to the narrower wheel. This is what people always fail to take into account with any wider wheel/tire combo.

That said, I'm not sure it's a given that a 13" wheel with the 335 actually puts more tread width on the ground. Or at least I'm not sure it does so without reducing the pressure in the center of the contact patch. It seems to me that a useful way to approach is by dividing the millimeters of section width by the wheel width. The common 315 fitment is to use them on 11" wheels. That gives 28.64mm of section width per inch of wheel. A 335 tire on a 12" wheel only has 27.92mm of section width per inch of wheel width - it's already more stretched than the 315mm/11" fitment! That makes sense when we realize that the 335 is less than an inch wider than the 315 in section width, and it's only 0.4" wider in tread width. On a 13" wheel, it would be down to only 25.77mm per inch of wheel width - a lot more stretched than the 315/11 fitment. That is outside BFG's recommended wheel widths for the 335, and for obvious reasons.
This addresses my question ........ why is everyone exceeding the 12inch recommendation by the manufacturer ??


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Old 05-08-2019, 08:23 PM
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Simply put a "very sticky" IE hot slick or super 200 tire will feel better on track with the wider wheel.

A 13" wheel will have less sidewall deflection than a 12".

Sharper feel will make you faster.

People have been mounting 18x13's with no problem since a week after the C7Z came out.

Note this is for track use where you are at the limit. For the street a 12" actually is more pleasant to drive.
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Old 05-09-2019, 01:40 AM
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Originally Posted by blkbrd69 View Post
Simply put a "very sticky" IE hot slick or super 200 tire will feel better on track with the wider wheel.

A 13" wheel will have less sidewall deflection than a 12".

Sharper feel will make you faster.

People have been mounting 18x13's with no problem since a week after the C7Z came out.

Note this is for track use where you are at the limit. For the street a 12" actually is more pleasant to drive.
Good explanation. I ran 345 MPSS on track and they gave me plenty of feedback. I see two sides to this issue.


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Old 05-09-2019, 02:08 AM
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You guy's running 13 inch lowrider wire wheels??
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Old 05-18-2019, 07:05 PM
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18x13s because 345/35/18 hoosiers out back.
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