Best tires and rim size for racing

[bbbart]

Greetings everyone,

There are significantly more choices available for 20 in. rims that would vastly improve the skidpad performance of the ST (i.e. Toyo R888R, Nitto NT01, Falken Azenis RT660 only go up to 20 in.). A few sizes of the aforementioned tires are on the borderline of the load rating, however, they are not too far off from the OEM tires on the Cayenne Turbo GT which are as follows:

Front Tires (rim size 22 x 10.5") Pirelli P Zero Corsa

• Size: 285/35ZR22
• Load Index: 106
• Max Load: 2,094 lbs per tire

Rear Tires (22 x 11.5") Pirelli P Zero Corsa

• Size: 315/30ZR22
• Load Index: 107
• Max Load: 2,149 lbs per tire

The curb weight of the Cayenne Turbo GT is roughly 5050 lbs, whereas the ST's is 4700. Weight distribution is 55:45 F:R in the Turbo GT, 51.3:48.7 in the ST.

When looking at the weight distribution of the GT, it is 55% front-loaded and the front tires are rated at 2,094 pounds each. Under maximum braking, the front tires will be loaded at about 72.6% (3,664.5 lbs for the Turbo GT front wheels) according to ChatGPT. The number for the ST is slightly less at 68.9% front-load shift, making the total "front tire load" 3,238 lbs.

There is likely some suspension wizardry affecting this number, such as the active anti-roll bars in the Turbo GT mitigating load on outer wheels during "at-the-limit" cornering, but it shouldn't be too far off.

If Porsche is leaving an allowance of 523 pounds in the GT, it would be reasonable to assume that the minimum load rating for a tire on a track-focused Explorer ST would be 1,880 lbs.

Now, if 20 inch tires are inherently disadvantaged to 22 inch tires for track performance, all of these are moot points and we might as well apply the same wheels and tires from the Turbo GT or RSQ8 to the Explorer ST and call it a day. Based off all the research, it is tough to determine whether Porsche and Audi put 22 inch rims on the SUV's they sent to the Nurburgring specifically to break records, or to break records in "production guise." It wouldn't be a stretch to assume that very few people would opt for 20 inch rims (if they were offered) for aesthetic reasons.

What tire and rim combo would theoretically provide the best value for handling, with emphasis on cornering ability?

The use case scenario is 1-2 passengers max, weekend usage, dry to damp conditions, 50-100 F temps, and 100-200 pound weight reduction (prioritizing unsprung weight). Since there are limited options for 21 inch tires, it'd be ideal to focus on 20 inch tires vs 22 in. imho.

What are your thoughts?

Once the built engines from ZFG are up and running, it seems likely that we can achieve something worthy of comparison, or dare I say even more capable, for a fraction of the price.

 

[2020FordRaptor]

Interesting perspective. Purely from a weight reduction perspective, 20s are you’re best option. I’d have to do a little research to see what would be my recommended “maximum performance” (odd to say on a SUV) wheel and tire setup would be. That could be pretty expensive, what are you looking to spend?

 

[Cruising68]

When I was road racing my CTSV, I was running a 19” square wheel setup and predominately ran either R888’s or NT01’s. The R888’s were pretty sticky but usually cycled out before end of tread. The NT01 was slightly less traction but I could get a couple more track days out of a set. Money no option, R888 imo.


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[bbbart]

Interesting perspective. Purely from a weight reduction perspective, 20s are you’re best option. I’d have to do a little research to see what would be my recommended “maximum performance” (odd to say on a SUV) wheel and tire setup would be. That could be pretty expensive, what are you looking to spend?

When I was road racing my CTSV, I was running a 19” square wheel setup and predominately ran either R888’s or NT01’s. The R888’s were pretty sticky but usually cycled out before end of tread. The NT01 was slightly less traction but I could get a couple more track days out of a set. Money no option, R888 imo.

$2,000 every 5000 miles would be ideal for weekend usage. This would be cut short to 250-500 miles on the track, so a compromise between those two numbers. For wheels, forged magnesium monoblock seem like the best value, carbon fiber seemed like they would be the best, but it was surprising to learn that the load rating isn't much higher than aluminum forged wheels. Coupled with the fact that CF is more likely to crack than bend, it is nerve-wracking to think of cracking a CF rim at high speed. Magnesium and aluminum is more likely to bend, so I'm leaning towards those two options.


Definitely planning on using the R888R's first, specifically 305/35/zr20 on 20x11 rims. It's the main reason we're considering a 20 inch rim above the 22 inch option. Hopefully the heat cycles aren't too bad. The load rating is 1,984 per tire so it seems more than adequate for the ST.

 

[UNBROKEN]

11’s won’t fit under the front with that tire. You’ll have strut clearance issues. 10.5’s clear fine. That’s also an extremely short tire for this car.

 

[bbbart]

11’s won’t fit under the front with that tire. You’ll have strut clearance issues. 10.5’s clear fine.

Really appreciate that info . I was having a hard time finding that information in the forum. The 305/35/zr20 R888R should work fine on a 20x10.5.

 

[UNBROKEN]

Really appreciate that info . I was having a hard time finding that information in the forum. The 305/35/zr20 R888R should work fine on a 20x10.5.

I edited that post…didn’t notice your tire size. I would consider something in the 30-30.5” tall range. That tire is going to affect a lot of stuff being as short as it is.

 

[bbbart]

I edited that post…didn’t notice your tire size. I would consider something in the 30-30.5” tall range. That tire is going to affect a lot of stuff being as short as it is.

Very much agree, the 295/40/r20 I have on my ST's 20x10's +35mm saved my rims more than once. Driving with the R888R's will be significantly more stressful but the feeling of yeeting into a corner will be priceless. I have had a few year's of experience running 245/40ZR20 on 20x9 up front and 275/35ZR20 on 20x10 Rohana RF1's in back and have learned the hard way daily driving that setup in Chicago (on a 5,100 pound Lexus LS600hL). The front took significantly more damage every time, the back is still in good shape (structurally).

What would you recommend for the front offset to be on a 20x10.5 with a 305/35/zr20?

 

[UNBROKEN]

10.5 +30 is flush fitment with plenty of strut clearance up to a 315.

 

[2020FordRaptor]

Very much agree, the 295/40/r20 I have on my ST's 20x10's +35mm saved my rims more than once. Driving with the R888R's will be significantly more stressful but the feeling of yeeting into a corner will be priceless. I have had a few year's of experience running 245/40ZR20 on 20x9 up front and 275/35ZR20 on 20x10 Rohana RF1's in back and have learned the hard way daily driving that setup in Chicago (on a 5,100 pound Lexus LS600hL). The front took significantly more damage every time, the back is still in good shape (structurally).

What would you recommend for the front offset to be on a 20x10.5 with a 305/35/zr20?

Should be at +30 all around.

 

[bbbart]

I edited that post…didn’t notice your tire size. I would consider something in the 30-30.5” tall range. That tire is going to affect a lot of stuff being as short as it is.

Definitely a concern, I asked ZFG for advice and will report back. Seems like updating the wheel size through Forscan or SCT will help. Mainly concerned about the ABS performance assuming that ZFG tuning can solve the engine RPM issue even if updating the wheel size via Forscan doesn't help.

The stock ST wheel diameter is 30.7 inches

Current setup is 29.3 inches.

The setup I am planning to switch over to is 28.4 inches.

 

[2020FordRaptor]

Definitely a concern, I asked ZFG for advice and will report back. Seems like updating the wheel size through Forscan or SCT will help. Mainly concerned about the ABS performance assuming that ZFG tuning can solve the engine RPM issue even if updating the wheel size via Forscan doesn't help.

The stock ST wheel diameter is 30.7 inches

Current setup is 29.3 inches.

The setup I am planning to switch over to is 28.4 inches.

That’s not the concern. Not a big deal, easy to change with Forscan. It’s aesthetics, looks weird.

 

[bbbart]

That’s not the concern. Not a big deal, easy to change with Forscan. It’s aesthetics, looks weird.

What do you think about high speed stability (i.e. taking corners at 150mph+)?

Top speed is aerodynamically limited to 170mph until I can get a functional front splitter installed so I was thinking it would be beneficial to have slightly smaller wheels.

It can definitely hit 180mph+, but the car starts shaking uncomfortably at 170mph.

HSF said he would be willing to take on the front splitter project down the line but even then it will be extremely rare to hit those speeds.

 

[2020FordRaptor]

What do you think about high speed stability (i.e. taking corners at 150mph+)?

Top speed is aerodynamically limited to 170mph until I can get a functional front splitter installed so I was thinking it would be beneficial to have slightly smaller wheels.

It can definitely hit 180mph+, but the car starts shaking uncomfortably at 170mph.

HSF said he would be willing to take on the front splitter project down the line but even then it will be extremely rare to hit those speeds.

I think you’re starting to think a little crazy here. 150 MPH around a corner in these cars is not safe nor most likely possible ever. I don’t think these cars could hit 180s, the S550 GT500s top out at around 186 so I don’t think these cars are going to ever get close to that.

 

[bbbart]

I think you’re starting to think a little crazy here. 150 MPH around a corner in these cars is not safe nor most likely possible ever. I don’t think these cars could hit 180s, the S550 GT500s top out at around 186 so I don’t think these cars are going to ever get close to that.

That's were things get interesting. I hit 170mph on a 93 tune with the stock block and it took about 5 seconds to go from 165mph to 170mph. But, doing that without a total suspension overhaul was a terrible idea in retrospect, more on that...

ZFG is building blocks that have forged rods, pistons, ARP studs, KelFord springs, more aggressive cams, and beefier main caps. The aforementioned parts, mainly the rods and main caps, were the weakest links on the stock block which topped out on a dyno at 839whp/827 lb ft. torque. 200mph will be no problem for the built block.

It was a terrible idea to hit 170mph because after driving 30 easy-going, cruising miles following the top speed run, my rear toe link snapped which could've been a lethal and catastrophic failure if it happened while I was doing the run.

It was on a private road, but at 170 with the rear, driver's side tire dragging, I don't want to imagine what could've happened...

Granted, the rear toe link was stock but I mistakenly though it was a stronger, aftermarket part because it was powder-coated blue. If I had known it was stock, I would've swapped it long before the run.

If all of the following suspension upgrades are made, what would prevent the ST from taking corners at 150mph?

Fenfab rear toe links
Fenfab rear vertical links
Fenfab subframe support bushings
aFe Front / rear sway bars
Billet control arms
BC Racing coilovers (hopefully Bilstein/JRZ soon)
Weight reduction (nothing crazy; spare tire, forged wheels, low-profile tires, lightweight car battery).

One key question that needs to be answered is how to stop the car from shaking at 170mph+. I believe that the car was shaking for a couple reasons:

1. The air ride was set fairly low at about 90psi in the bags all around (about 2 inches lower than stock) which resulted in a soft feeling suspension. Coilovers should eliminate that but hopefully the air suspension can be tuned to be stiffer while lowered.

2. Aerdoynamics. With the HSF underbody panel, a functional rear diffuser, and a functional front splitter like the one in the Ford Performance ST (white with blue pinstripes), the turbulence should be significantly reduced.

 

[GearHead_1]

I'd like to be there the day one of these "bricks" ring the 200 mph bell. If that is a goal, start with a more aerodynamic vehicle.

 

[2020FordRaptor]

That's were things get interesting. I hit 170mph on a 93 tune with the stock block and it took about 5 seconds to go from 165mph to 170mph. But, doing that without a total suspension overhaul was a terrible idea in retrospect, more on that...

ZFG is building blocks that have forged rods, pistons, ARP studs, KelFord springs, more aggressive cams, and beefier main caps. The aforementioned parts, mainly the rods and main caps, were the weakest links on the stock block which topped out on a dyno at 839whp/827 lb ft. torque. 200mph will be no problem for the built block.

It was a terrible idea to hit 170mph because after driving 30 easy-going, cruising miles following the top speed run, my rear toe link snapped which could've been a lethal and catastrophic failure if it happened while I was doing the run.

It was on a private road, but at 170 with the rear, driver's side tire dragging, I don't want to imagine what could've happened...

Granted, the rear toe link was stock but I mistakenly though it was a stronger, aftermarket part because it was powder-coated blue. If I had known it was stock, I would've swapped it long before the run.

If all of the following suspension upgrades are made, what would prevent the ST from taking corners at 150mph?

Fenfab rear toe links
Fenfab rear vertical links
Fenfab subframe support bushings
aFe Front / rear sway bars
Billet control arms
BC Racing coilovers (hopefully Bilstein/JRZ soon)
Weight reduction (nothing crazy; spare tire, forged wheels, low-profile tires, lightweight car battery).

One key question that needs to be answered is how to stop the car from shaking at 170mph+. I believe that the car was shaking for a couple reasons:

1. The air ride was set fairly low at about 90psi in the bags all around (about 2 inches lower than stock) which resulted in a soft feeling suspension. Coilovers should eliminate that but hopefully the air suspension can be tuned to be stiffer while lowered.

2. Aerdoynamics. With the HSF underbody panel, a functional rear diffuser, and a functional front splitter like the one in the Ford Performance ST (white with blue pinstripes), the turbulence should be significantly reduced.

So many things to unpack here. 200 MPH would be impossible in these cars. It’s not power that’s the problem, it’s aerodynamics. What would prevent the ST from taking corners at 150 MPH? It’s weight. A purpose built Mustang would struggle to take most corners at 150 MPH. Thes cars are a somewhat blocky SUV and still weigh a lot.

Your mod list, good but not abnormal. BC coilovers are not meant for aggressive driving, they say it themselves. The Ford Performance car is just their show car and I’ve never seen it actually do an hard track run. You can’t get past this is a blocky heavy SUV.

200 MPH is a problem. Can’t beat the fact these aren’t aerodynamic car. The changes you mentioned wouldn’t help that much. My grandfathers good friend, Boris Murray (legendary motorbike racer) would always say:

“Aerodynamics is everything. There’s a point where you start meeting resistance, let’s say it’s like driving through milk. You start hitting a milk, it turns into cream, it then turns into butter, and then it it turns into a solid wall. You can have all the power you can get, at some point you’re going to hit a wall.”

 

[Cruising68]

Gonna be difficult getting those speeds imo. Wind resistance squares as speed doubles. My CTSV had 700hp at the rear wheels, had much better aero, weighed about 4400lbs, and would hit 180mph. It was factory limited there due to the automatic but you can feel it fighting the wind. Wild guess would be you need 800hp at the wheels at least to overcome aerodynamics of the ST. Who knows how the drivetrain would hold up. I had a massive diff in my CTSV and the components making up the suspension were much beefier than my ST. I don’t think ford was thinking 180mph road racing when they designed the components in the ST. The suspension and steering components look like toys compared to a vehicle designed for those conditions.

Having said that, I’m all for those trying to find the limits of any vehicle.


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[bbbart]

So many things to unpack here. 200 MPH would be impossible in these cars. It’s not power that’s the problem, it’s aerodynamics. What would prevent the ST from taking corners at 150 MPH? It’s weight. A purpose built Mustang would struggle to take most corners at 150 MPH. Thes cars are a somewhat blocky SUV and still weigh a lot.

Your mod list, good but not abnormal. BC coilovers are not meant for aggressive driving, they say it themselves. The Ford Performance car is just their show car and I’ve never seen it actually do an hard track run. You can’t get past this is a blocky heavy SUV.

200 MPH is a problem. Can’t beat the fact these aren’t aerodynamic car. The changes you mentioned wouldn’t help that much. My grandfathers good friend, Boris Murray (legendary motorbike racer) would always say:

“Aerodynamics is everything. There’s a point where you start meeting resistance, let’s say it’s like driving through milk. You start hitting a milk, it turns into cream, it then turns into butter, and then it it turns into a solid wall. You can have all the power you can get, at some point you’re going to hit a wall.”

Definitely agree with the aerodynamics being suboptimal. One thing I have to point out is that the coefficient of drag is surprisingly low on the ST (0.35)

The following cars have worse aerodynamics than the Explorer ST and are getting very close to 200mph.

Lamborghini Urus SE c/d 0.39 (top speed 194mph)
Porsche Cayenne GT c/d 0.37 (186mph)

I believe the upgrades I listed will allow the ST to beat these numbers. In regards to the front splitter on the FP ST show car; a front splitter that is designed for reducing lift instead of creating maximum downforce will make a significant difference when approaching top speed along with flat underbody paneling.

I'm mostly concerned with making sure the car doesn't fall apart or behave erratically when it's making a relatively sharp turn at 150mph.

 

[bbbart]

Gonna be difficult getting those speeds imo. Wind resistance squares as speed doubles. My CTSV had 700hp at the rear wheels, had much better aero, weighed about 4400lbs, and would hit 180mph. It was factory limited there due to the automatic but you can feel it fighting the wind. Wild guess would be you need 800hp at the wheels at least to overcome aerodynamics of the ST. Who knows how the drivetrain would hold up. I had a massive diff in my CTSV and the components making up the suspension were much beefier than my ST. I don’t think ford was thinking 180mph road racing when they designed the components in the ST. The suspension and steering components look like toys compared to a vehicle designed for those conditions.

Having said that, I’m all for those trying to find the limits of any vehicle.

100% agree with all of your points. I'm not trying to be the first one to hit 200mph unless there's a tempting financial incentive. All the data points to it being a reasonable expectation with all the new parts. I just want to make sure I'm overbuilding it for my goal which is a reliable 800whp. We believe 800whp is a very safe number for the new block and have the fueling and turbos to push it up well above 1000whp. 800whp for several months will likely expose some more weak links, whether that's the differential, crankshaft, driveshaft, or something else, remains to be seen.