[yzf1999]

My 2019 Scat M6 came from the factory with lightweight forged wheels with 245 tires…that should have been illegal. First gear pulls were scary..tires could not hold the power and the rear was dancing all over the place. Upgraded to 275’s in all four corners and problem solved…highly recommend going 275.

 

[Stay Thirsty My Friends]

Here is a photo of two new 245/45-20 and 274/40-20 tires. Even unmounted, there is a significant contact patch difference.

View attachment 1114489

It would be nice to take a yard stick to those and tell us the width of the tread, the overall width and the overall height. The DOT should be disbanded for many reasons, one of them being their inability to assure every xxx/yy-zz tire matches every other xxx/yy-zz tire in size.

 

[Xylander]

Here is a photo of two new 245/45-20 and 274/40-20 tires. Even unmounted, there is a significant contact patch difference.

View attachment 1114489

Who cares about an unmounted tire? Mounting is what ruins a good tire if you put it on a wheel that's the wrong size.

I'll use a gross example to kinda drive this point home. Assume for a moment you could physically mount a 275 on a bicycle rim. To get it to fit, you'd have to pinch the tire flat and it would cause the tire to balloon outwards. Your contact patch would then be a sliver of its original width. It would basically look like a wobbly wagon wheel. All that tread that should be on the contact patch rolls up into the sidewall. In this example, it wouldn't hold the car's weight due to there being no rigid sidewall to help the tire maintain form.

This same effect occurs when mounting a 275 to a 9" wide or smaller wheel. Tread rolls up to match the wheel width and a portion of the rolled up tread is taken up into the sidewall, compromising the tire's strength. While it will still safely mount and be a safe tire to drive on, it no longer has a 275 expected contact patch. It's a 235-245. That soft tread you're not using is rolled up into the sidewall and making it less rigid. This causes a degree of lateral skating at launch, more wheel hop, and reduced lateral grip load rating.

Folks can either accept this as fact, or they can try and come here and explain why their car is the only magic fantasy car on the planet that is blessed with the uncanny ability to ignore the laws of physics.

 

[Metalchewy]

Who cares about an unmounted tire? Mounting is what ruins a good tire if you put it on a wheel that's the wrong size.

I'll use a gross example to kinda drive this point home. Assume for a moment you could physically mount a 275 on a bicycle rim. To get it to fit, you'd have to pinch the tire flat and it would cause the tire to balloon outwards. Your contact patch would then be a sliver of its original width. It would basically look like a wobbly wagon wheel. All that tread that should be on the contact patch rolls up into the sidewall. In this example, it wouldn't hold the car's weight due to there being no rigid sidewall to help the tire maintain form.

This same effect occurs when mounting a 275 to a 9" wide or smaller wheel. Tread rolls up to match the wheel width and a portion of the rolled up tread is taken up into the sidewall, compromising the tire's strength. While it will still safely mount and be a safe tire to drive on, it no longer has a 275 expected contact patch. It's a 235-245. That soft tread you're not using is rolled up into the sidewall and making it less rigid. This causes a degree of lateral skating at launch, more wheel hop, and reduced lateral grip load rating.

Folks can either accept this as fact, or they can try and come here and explain why their car is the only magic fantasy car on the planet that is blessed with the uncanny ability to ignore the laws of physics.

Since you asked...

I believe your theory is off a bit, definitely not fact.. I have LT285/70s on my trucks stock 17x7s wheels and have over 11 inches of contact proven by the chalk test that I did when working out the best pressure to run at. Based on what you say, physics says I cannot have more than 7" contact.

Pressure dictates the contact in combination with the wheel and tire width and other variables.

Sidewall rigidness is based on not only pressure and width, but how many layers, rubber compound and the speed rating of the tire. It's not just one variable that is at play here.

 

[HowLong?]

Who cares about an unmounted tire? Mounting is what ruins a good tire if you put it on a wheel that's the wrong size.

I'll use a gross example to kinda drive this point home. Assume for a moment you could physically mount a 275 on a bicycle rim. To get it to fit, you'd have to pinch the tire flat and it would cause the tire to balloon outwards. Your contact patch would then be a sliver of its original width. It would basically look like a wobbly wagon wheel. All that tread that should be on the contact patch rolls up into the sidewall. In this example, it wouldn't hold the car's weight due to there being no rigid sidewall to help the tire maintain form.

This same effect occurs when mounting a 275 to a 9" wide or smaller wheel. Tread rolls up to match the wheel width and a portion of the rolled up tread is taken up into the sidewall, compromising the tire's strength. While it will still safely mount and be a safe tire to drive on, it no longer has a 275 expected contact patch. It's a 235-245. That soft tread you're not using is rolled up into the sidewall and making it less rigid. This causes a degree of lateral skating at launch, more wheel hop, and reduced lateral grip load rating.

Folks can either accept this as fact, or they can try and come here and explain why their car is the only magic fantasy car on the planet that is blessed with the uncanny ability to ignore the laws of physics.

I have 275/40/20s on a 9.5" rim. I can guineapig, if we can find someone willing to do a 275/40/20 on 9" rim to do the same

Since you asked...

I believe your theory is off a bit, definitely not fact.. I have LT285/70s on my trucks stock 17x7s wheels and have over 11 inches of contact proven by the chalk test that I did when working out the best pressure to run at. Based on what you say, physics says I cannot have more than 7" contact.

Pressure dictates the contact in combination with the wheel and tire width and other variables.

Sidewall rigidness is based on not only pressure and width, but how many layers, rubber compound and the speed rating of the tire. It's not just one variable that is at play here.

I think mud tires/all terrain are a bit different... My buddy has 305 mud tires on his 8" rim (or something like that, I dont remember the exact size)

 

[Metalchewy]

I think mud tires/all terrain are a bit different... My buddy has 305 mud tires on his 8" rim (or something like that, I dont remember the exact size)

Different constants in the calculations, but the concept is similar, just less sidewall height to play with to flatten out the tread.

I posted the truck tires as an extreme example. But still maintain tire width and wheel width arent the only factors at play here.

Many,any Other historical posts even in this forum contradict...

https://www.challengertalk.com/threads/275-40-20-on-8-5-wide-rim.78797/#post-1078259

https://www.challengertalk.com/threads/275-40-20-on-scatpack-with-20x9-wheels.691638

There are a lot more contradictions, too many to list.

https://www.challengertalk.com/search/924408/?q=275%2F40+on+20x9&o=relevance

 

[HowLong?]

Different constants in the calculations, but the concept is similar, just less sidewall height to play with to flatten out the tread.

I posted the truck tires as an extreme example. But still maintain tire width and wheel width arent the only factors at play here.

Many,any Other historical posts even in this forum contradict...

https://www.challengertalk.com/threads/275-40-20-on-8-5-wide-rim.78797/#post-1078259

https://www.challengertalk.com/threads/275-40-20-on-scatpack-with-20x9-wheels.691638

There are a lot more contradictions, too many to list.

https://www.challengertalk.com/search/924408/?q=275%2F40+on+20x9&o=relevance

Just because you can, doesnt mean you should... Minimum means exactly that, minimum. Its like paying someone a wage of $7.50 (minimum wage in my state). It is the absolute lowest amount required to obtain the desired outcome...

If you want to run 275 tires on 8" rims, by all means go ahead. I have consulted with multiple rim shops and tire manufactures about the best rim size to run a 275/40/20, they all say 9.5" rim.
I have even been told some tire shops (such as firestone, good year, ect) they will not install a 275 on anything smaller than a 9" rim, meaning 9" is the absolute smallest rim size to use with a 275/40/20 tire.

 

[Metalchewy]

Just because you can, doesnt mean you should... Minimum means exactly that, minimum. Its like paying someone a wage of $7.50 (minimum wage in my state). It is the absolute lowest amount required to obtain the desired outcome...

If you want to run 275 tires on 8" rims, by all means go ahead. I have consulted with multiple rim shops and tire manufactures about the best rim size to run a 275/40/20, they all say 9.5" rim.
I have even been told some tire shops (such as firestone, good year, ect) they will not install a 275 on anything smaller than a 9" rim, meaning 9" is the absolute smallest rim size to use with a 275/40/20 tire.

I would never put them on 8s either. Which is why they aren't on my 2014 R/T.

The 'fact' stated above was that if you put them on 9s, that there would only be 9" of contact on the ground, which is totally opinion stated as fact.

 

[HowLong?]

🤷‍♂️Not sure about all that. What I know is that 9.5" rim is ideal for 275/40/20. Why argue about cooking a frozen pizza in a toaster, just do it right the first time and put it in the oven 🤣.

It read to me like you are advocating for running 275/40/20 on a smaller rim. Granted I didnt read everything, a couple of the links you provided suggests that it is acceptable to run a 275/40/20 on 8", 8.5" and 9" rims. I will agree that 9" is the absolute smallest rim for a 275/40/20, but for ideal contact patch and proper rim-to-tire fitment, I suggest a 9.5" rim.

 

[Richs 66]

Wow, lol............didnt think i would get this much info.........im gonna go with the 275 later this summer........but im not having too many traction problems with the 245"s..........i can take off pretty good without spinning them to death. You boys must have a heavier foot than me........lol

Once thanks for the great info

Rich

 

[GSBrockman]

Good move all around. I had 275 P-Zero Summer tires on my 19 R/T Challenger and I have 275 P-Zero Nero all seasons on my 23 Scat, and the summer tires are definitely more sticky. As for the size, I haven’t driven on the 245s, but I certainly like the look of the wider tire, especially on a scat.

And….the SCORE is recorded in the record books.

These came off of a 2023 Dodge Challenger R/T with the Performance Plus Package.
187 miles, $500 cash (didn’t EVEN try to negotiate any cheaper) and $359.93 each on Tire Rack.

The owner also went with the identical same Continentals that @19johned53 has.

 

[Rob446]

I'm more a student of science.

Where have we heard that before?

 

[2020GoMango]

Wow, lol............didnt think i would get this much info.........im gonna go with the 275 later this summer........but im not having too many traction problems with the 245"s..........i can take off pretty good without spinning them to death. You boys must have a heavier foot than me........lol

Once thanks for the great info

Rich

Just another vote for the 275, on the rear especially. I kept the 245 upfront so now have the staggered set-up. I also experienced way too much tire spin with the Goodyears that came on the car. I definitely feel the difference but you need to get a quality brand as well. With tires, you get what you pay for. I went with the Goodyear Exhilarate which is amazing on both my '14 Mustang GT and now my R/T. Just as pricey as the Michelin Pilot Sports but it's about as good as it gets. 'Top of the line' and Made in USA. They look great on the R/T as well.

 

[grandpa-srt4]

Since you asked...

I believe your theory is off a bit, definitely not fact.. I have LT285/70s on my trucks stock 17x7s wheels and have over 11 inches of contact proven by the chalk test that I did when working out the best pressure to run at. Based on what you say, physics says I cannot have more than 7" contact.

Pressure dictates the contact in combination with the wheel and tire width and other variables.

Sidewall rigidness is based on not only pressure and width, but how many layers, rubber compound and the speed rating of the tire. It's not just one variable that is at play here.

The chalk test is an old racers trick.
On my 73 Challenger I ran a 10 wide tire on a 8" wide rim. Did this by using the chalk test to adjust the tire pressure to get a even thread pattern across the width of the tire.
The best pressure was 21 pounds during the summer.

 

[Rocket Man]

21 pounds? I'm sorry, but I can't see how that would safely handle the weight, speed and cornering forces put on those tires. Maybe if you drove it like a grandpa

 

[Cabdriver]

The 275s fill the fender width better and the 9.5 rims are the way to go. Tire brand affects traction immensely. My 275 Firehawks grip better than my friend's 315 Pirellis.

 

[HowLong?]

The 275s fill the fender width better and the 9.5 rims are the way to go. Tire brand affects traction immensely. My 275 Firehawks grip better than my friend's 315 Pirellis.

If you can afford it, I had good experience with Michelin Pilot Sport 4S

 

[Cuda340]

It would be nice to take a yard stick to those and tell us the width of the tread, the overall width and the overall height. The DOT should be disbanded for many reasons, one of them being their inability to assure every xxx/yy-zz tire matches every other xxx/yy-zz tire in size.

I measured it. Mounted, the 245/45-20 leaves an 8-inch tread patch and the 275/40-20 leaves a 9-inch patch.

 

[HowLong?]

Inches matter 😂

 

[Stay Thirsty My Friends]

If the DOT would step up to the plate:

245 tire should be 9.6".
275 tire should be 10.82".