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Discussion Starter · #1 ·
What difference (if any) can I expect from the way my 2013 SRT handles or rides with a change from 245/45ZR20 to 255/40ZR20 in the front?

I recently decided to replace my venerable Firehawk Indy 500 Wide ovals (rear) with some Michelin Pilot Sport 4S. Have always ran 275/40ZR20s on the rear wheels, but my fronts always had 245/45ZR20s. Although my current BFG Sport Comp 3 tires on the front still have usable, safe tread, I decided to swap them out as well so I'll have matching tires with the same tread life all around. Opted to take a chance on a slightly wider and shorter tire on the front this time, though and am curious what I should expect.

I actually got a follow-up email from the TireRack sales rep regarding the front tires, asking me to verify that these were what I wanted, which gave my pause, but I checked numerous tire fitment guides and they seem to fit ok on my front rims. Apparently most tire fitment applications seem to default to the 45mm tire height as the standard tire profile for the 2013 SRT, but that doesn't mean that a slightly wider and lower-profile tire won't be as safe, right?
 

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The Bacon Hauler (‘12 Cop Charger)
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What difference (if any) can I expect from the way my 2013 SRT handles or rides with a change from 245/45ZR20 to 255/40ZR20 in the front?

I recently decided to replace my venerable Firehawk Indy 500 Wide ovals (rear) with some Michelin Pilot Sport 4S. Have always ran 275/40ZR20s on the rear wheels, but my fronts always had 245/45ZR20s. Although my current BFG Sport Comp 3 tires on the front still have usable, safe tread, I decided to swap them out as well so I'll have matching tires with the same tread life all around. Opted to take a chance on a slightly wider and shorter tire on the front this time, though and am curious what I should expect.

I actually got a follow-up email from the TireRack sales rep regarding the front tires, asking me to verify that these were what I wanted, which gave my pause, but I checked numerous tire fitment guides and they seem to fit ok on my front rims. Apparently most tire fitment applications seem to default to the 45mm tire height as the standard tire profile for the 2013 SRT, but that doesn't mean that a slightly wider and lower-profile tire won't be as safe, right?
The 245s will be 10mm narrower and have a sidewall about 8mm shorter according to the raw math.

In reality you won’t notice any difference in the handling or riding of the car in daily driving and occasional spirited operation from that small of a difference in tire size.

If you do notice a difference between the tires, it would be because one tire is made differently or constructed differently, and the same difference would have been noticed with a switch to the tire in the new brand/model but same size as old tires.
 

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It will work just fine, but why not go to 275/40/20 in the front? That way it will handle better and you'll also be able to rotate them.
 

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The 245s will be 10mm narrower and have a sidewalk about 8mm shorter according to the raw math.
In reality you won’t notice any difference in the handling or riding of the car in daily driving and occasional spirited operation from that small of a difference in tire size.If you do notice a difference between the tires, it would be because one tire is made differently or constructed differently, and the same difference would have been noticed with a switch to the tire in the new brand/model but same size as old tires.
I agree that you will not notice any difference in handling between a 245/45-20 and a 255/40-20 on the front of your car. 275/40-20s, however, on the rear, will provide greater traction and will look great. I have Cooper Zeon RS3-G1s 275/40-20 tires on the rear of my SRT and 245/45-20s on the front for that "old school" staggered look.

If you decide to go with 255 tires, get the 45 profile to more closely match the height of the 275/40-20 rear tires.

Check out this tire size calculator. Here are the dimensions of the four tires:

245/45-20- 28.7" diameter and 9.6" width
255/45-20- 29" diameter and 10" width
255/40-20- 27.7" diameter and 10" width (NOT RECOMMENDED)
275/40-20- 28.7" diameter and 10.8" width

 

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Discussion Starter · #5 ·
It will work just fine, but why not go to 275/40/20 in the front? That way it will handle better and you'll also be able to rotate them.
I considered going with the same width all around for that specific reason, but truth is, I like the slightly staggered look and have found that my car tends to wear tires very evenly, even without tire rotations. I got over 30k on my (current) Firehawk Indy 500 Wide Ovals which were on the car when I bought it (used) in 2015. The fronts had to be swapped out for the current BFGs, but even those seem to wear pretty good. I'm confident that if I wasn't going to swap them now, that I could get another 15k-18k on them.

My new tires, which just arrived yesterday are the Michelin Pilot Sport 4S which, based upon my initial inspection, do not APPEAR to by unidirectional...they only indicate an exterior or "outside" side, which leads to me to think that I should at least be able to swap the tires from side to side periodically. I know that isn't a true tire rotation, but it's better than nothing.

I agree that you will not notice any difference in handling between a 245/45-20 and a 255/40-20 on the front of your car. 275/40-20s, however, on the rear, will provide greater traction and will look great. I have Cooper Zeon RS3-G1s 275/40-20 tires on the rear of my SRT and 245/45-20s on the front for that "old school" staggered look.

If you decide to go with 255 tires, get the 45 profile to more closely match the height of the 275/40-20 rear tires.

Check out this tire size calculator. Here are the dimensions of the four tires:

245/45-20- 28.7" diameter and 9.6" width
255/45-20- 29" diameter and 10" width
255/40-20- 27.7" diameter and 10" width (NOT RECOMMENDED)
275/40-20- 28.7" diameter and 10.8" width

Thanks for the figures. I figured the prescribed 45mm sidewall height/aspect ratio on the front tires was designed to ensure a mostly level ride height for the car. I honestly don't think I'll mind a slightly "raked" appearance that might result from the reduced height on the new front tires, though.
 

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Discussion Starter · #6 ·
Just returned from a 1500 mile vacation over the last week. Drove the car up to Nashville, then southern Illinois, then through the Smokey Mountains to Asheville, NC. Lots of interstate driving. Also spent a full do on the Blue Ridge Parkway carving up the scenic route with my wife. The car handled superbly. Seriously, this was the first time ever taking the car into the mountains. Couldn't believe how well it handled and responded. Those new Michelins stuck the road marvelously. NOW I see what all the hype is about...

In any case, the lower front tire profile didn't seem to make any difference in how the car drives or handles.
 
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