Two 19x11 Square Setup Installs

[BmacIL]

What a crazy useful thread, much love to those that contributed. It's hard to tell from the pics - do the front wheels poke a bit more than the rear wheels? If so, anyone running extended studs and spacers in the rear?

A little bit more in the front. No need for spacers/extended studs in the rear.

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[3er]

A little bit more in the front. No need for spacers/extended studs in the rear.

Gotcha, but wondering from an aesthetic standpoint so they’re equally flush front to back.

 

[BmacIL]

Gotcha, but wondering from an aesthetic standpoint so they’re equally flush front to back.

You can do a 5 mm spacer on stock studs w/o issue, but it'll poke a little then.

 

[SgdriskillGT]

I just upgraded my wheels tires to this same setup as well (305/30/19 square from the stock 275 rear and 255 front). A friend suggested going to a shorter tire like this is bad for the differential. He also suggested the car is setup for staggered so I should keep that to decrease front wheel rolling resistance/increase cooling to brakes.

The PP2 S550 has 305/30/19 square setup, but I don't know if they tune the car differently. I've also read a square setup is better for the track, even though my car came staggered. I feel like gaining front grip at the expense of rolling resistance would be favorable.

I guess my main question is will this 305/30/19 setup create issues with the differential? What do others think?

 

[3er]

I just upgraded my wheels tires to this same setup as well (305/30/19 square from the stock 275 rear and 255 front). A friend suggested going to a shorter tire like this is bad for the differential. He also suggested the car is setup for staggered so I should keep that to decrease front wheel rolling resistance/increase cooling to brakes.

The PP2 S550 has 305/30/19 square setup, but I don't know if they tune the car differently. I've also read a square setup is better for the track, even though my car came staggered. I feel like gaining front grip at the expense of rolling resistance would be favorable.

I guess my main question is will this 305/30/19 setup create issues with the differential? What do others think?

Maybe the question should be, "Why would changing the diameter of wheels/tires impact the differential?" I'd challenge that since the story your friend told you sounds incorrect unless further detail was provided. I can't imagine how this would cause issues since your tire diameters are evenly matched (not like your running one 305/30 and one 305/35 in the rear). The main sensitivity that I've heard around tire diameters comes from AWD vehicles in that you want to ensure all four are the same diameter to prevent issues. Given that everything is evenly matched, whether 305/30 or 305/35, is the part that matters.

 

[SgdriskillGT]

Maybe the question should be, "Why would changing the diameter of wheels/tires impact the differential?" I'd challenge that since the story your friend told you sounds incorrect unless further detail was provided. I can't imagine how this would cause issues since your tire diameters are evenly matched (not like your running one 305/30 and one 305/35 in the rear). The main sensitivity that I've heard around tire diameters comes from AWD vehicles in that you want to ensure all four are the same diameter to prevent issues. Given that everything is evenly matched, whether 305/30 or 305/35, is the part that matters.

Right, that’s what I thought. I think he was thinking I should stay staggered but I don’t think that is necessary.

I guess flat out acceleration will decrease bc the same engine RPM equals lower mph.

In general, is it better to give this up in favor of higher overall grip? I guess gain speed in the corners but lose it in the straights?

 

[3er]

Right, that’s what I thought. I think he was thinking I should stay staggered but I don’t think that is necessary.

I guess flat out acceleration will decrease bc the same engine RPM equals lower mph.

In general, is it better to give this up in favor of higher overall grip? I guess gain speed in the corners but lose it in the straights?

The opposite is true. Running a 305/30 versus say a 275/40 or 305/35 results in a smaller diameter tire. So acceleration would be greater in this instance and your car will think it's traveling faster than it actually is (the same occurs if changing your diff ratio from 3.55 to 3.73). And to be honest, the differences between a 305/30, 275/40, and 305/35 in terms of acceleration are likely imperceptible. My criteria for choosing between the two tends to come down to what 1) looks best on the car, 2) maintains good ride quality, and 3) closely matches OEM diameters so that the speedo reads correctly. #2 & #3 would be the reasons to go with a 305/35, but both options are solid.

 

[SgdriskillGT]

The opposite is true. Running a 305/30 versus say a 275/40 or 305/35 results in a smaller diameter tire. So acceleration would be greater in this instance and your car will think it's traveling faster than it actually is (the same occurs if changing your diff ratio from 3.55 to 3.73). And to be honest, the differences between a 305/30, 275/40, and 305/35 in terms of acceleration are likely imperceptible. My criteria for choosing between the two tends to come down to what 1) looks best on the car, 2) maintains good ride quality, and 3) closely matches OEM diameters so that the speedo reads correctly. #2 & #3 would be the reasons to go with a 305/35, but both options are solid.

Won’t it take the same amount of time to get to 7400 RPM in say 2nd gear, but you’ll be going slower at the end of 2nd gear with a smaller diameter tire. So your acceleration will be slower.

Unless the smaller diameter tire is easier for the engine to increase in RPM. Maybe I’m thinking about this too simplistically.

 

[3er]

Won’t it take the same amount of time to get to 7400 RPM in say 2nd gear, but you’ll be going slower at the end of 2nd gear with a smaller diameter tire. So your acceleration will be slower.

Unless the smaller diameter tire is easier for the engine to increase in RPM. Maybe I’m thinking about this too simplistically.

This will help: Link.

 

[SgdriskillGT]

This will help: Link.

Got ya, thanks. FYI here's the warning in the '18 manual about using different size tires than OE on the rear axel with torsen diff. Doesn't sound like it's a big deal, but it is there:

"Extended use of tire sizes other than the manufacturer’s specified tire size on these axles could result in a permanent reduction in effectiveness. This loss does not affect your normal driving and should not be noticeable."

 

[3er]

Got ya, thanks. FYI here's the warning in the '18 manual about using different size tires than OE on the rear axel with torsen diff. Doesn't sound like it's a big deal, but it is there:

"Extended use of tire sizes other than the manufacturer’s specified tire size on these axles could result in a permanent reduction in effectiveness. This loss does not affect your normal driving and should not be noticeable."

Good find. I wonder what the technical explanation of this would be. Maybe they've programmed the Torsen slip conditions to work with OEM sizes, so running wider tires may not allow the diff to maximize the added grip and optimize slip characteristics.

 

[Norm Peterson]

Gotcha, but wondering from an aesthetic standpoint so they’re equally flush front to back.

11" wide wheels up front on a Mustang is probably far enough outside the preferences of the average owner or Cars & Coffee attendee that it wouldn't be worth the effort to space the rear wheels out for an equal amount of sidewall 'poke'. They're still not going to understand it, probably wouldn't even like it with or without rear spacers.


Norm

 

[Norm Peterson]

Good find. I wonder what the technical explanation of this would be. Maybe they've programmed the Torsen slip conditions to work with OEM sizes, so running wider tires may not allow the diff to maximize the added grip and optimize slip characteristics.

That note is not specific to just Torsen differentials. The Traction-Lok is mentioned as well. What we do know about the T-lok is that it doesn't like having to transmit power when the wheel rpms are different side to side (why autocrossing is particularly abusive on them). Whether the Torsen would ultimately wear itself out under the same conditions of use is for somebody else to answer.

At any rate, there has to be some tolerance built in with respect to making both rear tires x% shorter than OE. Like at least the 3% or so that gets mentioned from time to time for ABS purposes. Use of a spare tire might have been considered as well, where if you had to do this at all you'd want to keep it to as short a duration/few miles/mildest driving possible.


Norm

 

[dharts9]

Maybe the question should be, "Why would changing the diameter of wheels/tires impact the differential?" I'd challenge that since the story your friend told you sounds incorrect unless further detail was provided. I can't imagine how this would cause issues since your tire diameters are evenly matched (not like your running one 305/30 and one 305/35 in the rear). The main sensitivity that I've heard around tire diameters comes from AWD vehicles in that you want to ensure all four are the same diameter to prevent issues. Given that everything is evenly matched, whether 305/30 or 305/35, is the part that matters.

I agree. I have the setup with 305/35’s and it handles perfectly especially with my suspension upgrade.

 

[dharts9]

I just upgraded my wheels tires to this same setup as well (305/30/19 square from the stock 275 rear and 255 front). A friend suggested going to a shorter tire like this is bad for the differential. He also suggested the car is setup for staggered so I should keep that to decrease front wheel rolling resistance/increase cooling to brakes.

The PP2 S550 has 305/30/19 square setup, but I don't know if they tune the car differently. I've also read a square setup is better for the track, even though my car came staggered. I feel like gaining front grip at the expense of rolling resistance would be favorable.

I guess my main question is will this 305/30/19 setup create issues with the differential? What do others think?

I am not sure that information is right because numerous track mustangs run square setups. Some even come from the factory square. These cars are made to be pushed to the limit, the differential hasn’t been an issue.

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