Rear tire size 295/35 vs 305/30

[blueline]

@CarBot

For road course racing/track days with a 2021 718 GT4 running 19" Apex forged wheels and assuming all other factors are equal, which tire size is preferred for the rear - the wider but shorter 305/30 or the narrower but taller 295/35?

[CarBot]

For road course racing/track days with a 2021 718 GT4 running 19" Apex forged wheels and assuming all other factors are equal, which tire size is preferred for the rear - the wider but shorter 305/30 or the narrower but taller 295/35?

On a 718 GT4 for road course/track days, assuming the wheel widths are appropriate for each size and you’re not constrained by class rules, the 305/30-19 is usually the preferred rear.

The main reasons are that the 305/30 typically gives you a wider contact patch and a stiffer, shorter sidewall, which tends to sharpen response, reduce sidewall “wallow” in fast transitions, and tolerate higher lateral load better. It also keeps overall diameter closer to many common GT4 track setups, which helps avoid gearing/ABS/PSM oddities.

A 295/35-19 is noticeably taller. That extra sidewall can add compliance (sometimes helpful on bumpy tracks), but it more often feels a bit slower to respond and can add heat/movement in the carcass on a heavier, high-grip car like the GT4. The taller diameter also effectively lengthens gearing a touch and can change your rake slightly, which may or may not be what you want.

The big caveat is fitment: the 305/30 needs the right rear wheel width and enough inner/outer clearance at full compression. If you share your exact Apex wheel widths/offsets and what tire model you’re considering (Cup 2, RE-71RS, A052, etc.), I can sanity-check which size tends to measure “true” and what usually clears on the GT4.

[blueline]

For road course racing/track days with a 2021 718 GT4 running 19" Apex forged wheels and assuming all other factors are equal, which tire size is preferred for the rear - the wider but shorter 305/30 or the narrower but taller 295/35?

On a 718 GT4 for road course/track days, assuming the wheel widths are appropriate for each size and you’re not constrained by class rules, the 305/30-19 is usually the preferred rear.

The main reasons are that the 305/30 typically gives you a wider contact patch and a stiffer, shorter sidewall, which tends to sharpen response, reduce sidewall “wallow” in fast transitions, and tolerate higher lateral load better. It also keeps overall diameter closer to many common GT4 track setups, which helps avoid gearing/ABS/PSM oddities.

A 295/35-19 is noticeably taller. That extra sidewall can add compliance (sometimes helpful on bumpy tracks), but it more often feels a bit slower to respond and can add heat/movement in the carcass on a heavier, high-grip car like the GT4. The taller diameter also effectively lengthens gearing a touch and can change your rake slightly, which may or may not be what you want.

The big caveat is fitment: the 305/30 needs the right rear wheel width and enough inner/outer clearance at full compression. If you share your exact Apex wheel widths/offsets and what tire model you’re considering (Cup 2, RE-71RS, A052, etc.), I can sanity-check which size tends to measure “true” and what usually clears on the GT4.

Thanks CarBot!

Your thought that the 305/30 tires are better has also been my impression having run both the 295/35 and the 305/30 tires on the Apex 19" wheels.

The rear SM10RS Apex wheels are 11" width. I don't have the offset on hand at the moment but they were 718 GT4 specific. I've been running both the 295/35 and the 305/30 with no issues due to the car's alignment setup.

[CarBot]

Thanks CarBot!

Your thought that the 305/30 tires are better has also been my impression having run both the 295/35 and the 305/30 tires on the Apex 19" wheels.)

The rear SM10RS Apex wheels are 11" width. I don't have the offset at hand at the moment but they were 718 GT4 specific. I've been running both the 295/35 and the 305/30 with no issues due to the car's alignment setup.

Good data point, and with an 11" rear SM10RS that’s exactly where the 305/30-19 tends to make the most sense for track use on the GT4.

If both sizes clear for you, I’d stick with the 305/30 as the default. On an 11" wheel it usually supports the tread better and feels more precise on turn-in and mid-corner, and it generally manages heat a bit more predictably when you’re leaning on the rear hard.

I’d only lean back toward the 295/35 if you specifically want the extra overall diameter for a gearing change, or you’re on a rough track surface where the extra sidewall compliance is giving you better drive off and less wheelspin. Otherwise, your seat-of-the-pants impression matches what most folks end up with once they’ve tried both.

If you can grab the exact tire model you’re running, that can matter too since some 295s run “wide” and some 305s run “narrow,” which changes how meaningful the size difference is in practice.

[blueline]

Thanks CarBot!

Your thought that the 305/30 tires are better has also been my impression having run both the 295/35 and the 305/30 tires on the Apex 19" wheels.)

The rear SM10RS Apex wheels are 11" width. I don't have the offset at hand at the moment but they were 718 GT4 specific. I've been running both the 295/35 and the 305/30 with no issues due to the car's alignment setup.

Good data point, and with an 11" rear SM10RS that’s exactly where the 305/30-19 tends to make the most sense for track use on the GT4.

If both sizes clear for you, I’d stick with the 305/30 as the default. On an 11" wheel it usually supports the tread better and feels more precise on turn-in and mid-corner, and it generally manages heat a bit more predictably when you’re leaning on the rear hard.

I’d only lean back toward the 295/35 if you specifically want the extra overall diameter for a gearing change, or you’re on a rough track surface where the extra sidewall compliance is giving you better drive off and less wheelspin. Otherwise, your seat-of-the-pants impression matches what most folks end up with once they’ve tried both.

If you can grab the exact tire model you’re running, that can matter too since some 295s run “wide” and some 305s run “narrow,” which changes how meaningful the size difference is in practice.

Absolutely!

For the 305/30 rear tires I'm running Hoosier Track Attack Pro. For the 295/35 rears I've run Michelin Pilot Sport Cup 2 tires in the past.

As a side note, the Hoosier Track Attack Pros are apparently now available in the 295/35 size which was not the case last year. Also as I just now found out, The Michelin PSC2 are available in 305/30, something I did realize until today.

I think I'll stick to the 305/30 no matter which of the two I use.

[CarBot]

Absolutely!

For the 305/30 rear tires I'm running Hoosier Track Attack Pro. For the 295/35 rears I've run Michelin Pilot Sport Cup 2 tires in the past.

As a side note, the Hoosier Track Attack Pros are apparently now available in the 295/35 size which was not the case last year. Also as I just now found out, The Michelin PSC2 are available in 305/30, something I did realize until today.

I think I'll stick to the 305/30 no matter which of the two I use.

That makes sense, and with those two specific tires your conclusion to stay 305/30 is even easier to justify.

The Hoosier Track Attack Pro generally has a stiffer, more track-focused carcass than a PSC2, so in 305/30 on an 11" wheel you’re getting a very well-supported rear that tends to feel locked-in and consistent once up to temp. Going to a 295/35 in the same Hoosier line would add diameter and sidewall, but you’d likely give up some of that crispness you’re already liking, and you may also change the car’s effective rake a bit.

On the Michelin side, a PSC2 in 305/30 is usually the better match to an 11" rear than a 295/35 if you’re chasing response and rear support on track. The 295/35 PSC2 can work fine, but it’s more likely to feel a touch “rounder” and less immediate, especially as temps climb.

If you do swap between Hoosier and PSC2 in the same 305/30 size, just keep an eye on your hot pressures and balance. The car can feel like it gained or lost rear spring rate just from the tire construction change, so sometimes a small pressure tweak (or minor alignment tweak if you’re picky) is all it takes to get the same feel back.

[blueline]

Absolutely!

For the 305/30 rear tires I'm running Hoosier Track Attack Pro. For the 295/35 rears I've run Michelin Pilot Sport Cup 2 tires in the past.

As a side note, the Hoosier Track Attack Pros are apparently now available in the 295/35 size which was not the case last year. Also as I just now found out, The Michelin PSC2 are available in 305/30, something I did realize until today.

I think I'll stick to the 305/30 no matter which of the two I use.

That makes sense, and with those two specific tires your conclusion to stay 305/30 is even easier to justify.

The Hoosier Track Attack Pro generally has a stiffer, more track-focused carcass than a PSC2, so in 305/30 on an 11" wheel you’re getting a very well-supported rear that tends to feel locked-in and consistent once up to temp. Going to a 295/35 in the same Hoosier line would add diameter and sidewall, but you’d likely give up some of that crispness you’re already liking, and you may also change the car’s effective rake a bit.

On the Michelin side, a PSC2 in 305/30 is usually the better match to an 11" rear than a 295/35 if you’re chasing response and rear support on track. The 295/35 PSC2 can work fine, but it’s more likely to feel a touch “rounder” and less immediate, especially as temps climb.

If you do swap between Hoosier and PSC2 in the same 305/30 size, just keep an eye on your hot pressures and balance. The car can feel like it gained or lost rear spring rate just from the tire construction change, so sometimes a small pressure tweak (or minor alignment tweak if you’re picky) is all it takes to get the same feel back.

I monitor pressures religiously as well as how the car feels, so great advice. Thanks CarBot!

[CarBot]

I monitor pressures religiously as well as how the car feels, so great advice. Thanks CarBot!

Sounds like you’re doing it exactly right. With the Hoosier Track Attack Pro versus PSC2, the pressure window and the way the tire “talks” can feel pretty different even in the same 305/30 size, so staying on top of hot pressures and correlating that to balance is the fastest way to keep the car consistent.

If you ever notice the rear getting vague late-session on the Hoosiers, it’s often just a small hot-pressure creep or heat management issue rather than anything mechanical. And if you swap back to PSC2s and the car suddenly feels a bit more forgiving but less sharp, that’s usually just the carcass construction difference showing up.

Glad to help, and nice to see another GT4 getting used the way it was meant to be.

[blueline]

I monitor pressures religiously as well as how the car feels, so great advice. Thanks CarBot!

Sounds like you’re doing it exactly right. With the Hoosier Track Attack Pro versus PSC2, the pressure window and the way the tire “talks” can feel pretty different even in the same 305/30 size, so staying on top of hot pressures and correlating that to balance is the fastest way to keep the car consistent.

If you ever notice the rear getting vague late-session on the Hoosiers, it’s often just a small hot-pressure creep or heat management issue rather than anything mechanical. And if you swap back to PSC2s and the car suddenly feels a bit more forgiving but less sharp, that’s usually just the carcass construction difference showing up.

Glad to help, and nice to see another GT4 getting used the way it was meant to be.

Indeed!

[CarBot]

Indeed!

Anytime. If you want to really tighten the comparison between the Hoosier Track Attack Pro and PSC2 in 305/30, the most useful thing is to jot down cold pressures, hot pressures immediately off track, and a quick note on balance (entry/mid/exit) for each session. Patterns show up fast, especially as ambient temps change.

Also worth keeping an eye on rear shoulder wear. If the 305/30 starts to look like it’s working the outer shoulders harder than expected, that’s usually a hint to revisit hot pressure targets or rear camber rather than changing sizes.

If you post your typical hot pressure targets and your alignment numbers, I can sanity-check whether they’re in the usual GT4 track-day range for those tires.