technical questions - GT350R CF Rims

[AgSurfer]

I posted this the other day in "Wheels & Tires" and did not get much traction. Figured I would re-post in this group.

I have received a lot of info on the GT350R CF rims and also read a lot of posts from others members. Some great intel on these forums from members. I am struggling to understand the following. Would appreciate some technical wisdom.

1. If the CF rims are say 30-50 stronger than a metal (AL) rim, then why are owners so concerned about potential road damage from say pot holes? Would the risk be the same if you were driving on a AL rim? Or, is the concern that if you do incur road damage to a CF rim, it is very expensive to repair / replace? Why would the CF rims be more susceptible to road damage if they are supposed to be 30-50% stronger than an AL rim?

2. Explain to me the specs of the ceramic coating on the inside of the barrel. I understand this it to defer / deflect potential heat build up from significant braking while racing. But what potential damage could be done to the front CF rims if the inside ceramic coating was to fail? What would happen to the inside of the CF rim - especially considering that CF is supposed to be 30-50 stronger than an AL rim?

Thanks for the input.

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[Demonic]

The real experts on the CF wheels on the forum seem to be those who have never owned or driven an R, so I'll wait for those to chime in shortly. It's important to distinguish between worrying about functional damage vs cosmetic damage. Those of us who drive around on the street with them aren't really worried about functional damage as much as cosmetic damage. Coming from other cars, you have a couple factors working against you. First the tire sidewalls are very low profile and stretched slightly in the rears. So not only do the rear wheels protrude slightly, but the widest part of the car is from rear wheel rim edge to rear wheel rim edge, and these edges are very close to the ground. So while you might not 'curb' the wheel in a parking lot, a large pot hole can cause enough tire deflection to scrape the wheel rim. There are other things on the street you can't always account for. Say you're driving but have to pull aside for an ambulance - if you have to pull off the side of the road, the edge between the road and grass or gravel could be enough to scrape the wheel. Or you're going down a street and enter a road construction zone. The torn up road could contact and scratch the wheel somewhere.

That being said - that's cosmetic damage, and can typically be repaired. When I spoke with one of the employees at Carbon Revolution back in 2017 he had said the outer rim layers of carbon aren't really structural - they couldn't produce a street legal wheel in which curb contact would render it structurally weakened. Frank at Spyder Composites in CA, the official service and repair spot for the wheels, confirmed, and said that he can even lay in a new layer of weave if the rim gets scraped up. Grant it, you're then looking at an expensive repair or refresh.

When I spoke to the person at CR, if I recall correctly (again this was several years ago), he said the ceramic coating was something they were applying to the wheels even before the GT350R. It wasn't necessarily that the GT350R 'required' the coating, but more that they and Ford spec'd it given the proximity to the calipers. So I don't know if anyone can honestly tell you what the risks of a failed coating would be. You quoted the increase strength there too, but remember the ceramic coating isn't related to the strength of the wheel as much as the melting point of the epoxy.

Actual "functional" failures of the wheels are relatively rare. I can only recall having seen a couple on the forum in the past couple years. So all that being said, you can drive the car on the road without living in constant fear of something that couldn't later be touched up or refinished by Spyder. Now, driving thousands of miles on the road without ever seeing a scratch? That might be harder.

 

[svttim]

The CF is a stiffer wheel. A Significant impact will break the rim. The same impact may bend the metal (may break too) The CF rim can be repaired. The metal rim is probably not worth repairing. I use my CF wheels for track and Shelby CS21s on street (cant afford two sets of CF wheels) because I want two sets of wheels so I can eventually run race rubber. And you cannot beat the CF wheel on track due to weight and stiffness. Like Demonic stated, let the non owners pipe in and tell us all the technical reason why CF is a bad wheel

 

[AgSurfer]

Great input. Thank you. My CF rims are currently off the car and at the Ford Dealer for inspection and warranty claim submission. The dealer (body shop manager) has been awesome with this process. I sent them so many pics of the damaged ceramic coating, but Ford wanted even more pics of the ceramic coating damage while the rims were off the car. Picking it back up later today.

And holy lord - the brake dust on the front rims. I wiped them down shiny clean two days ago. I drove maybe 10 miles the other day and then 7 miles today and the brake dust accumulation is crazy. I put Hawk ceramic pads on my 2018 front rims and this cut back on brake dust big time. Do the 2020 GT350Rs come with ceramic pads from the factory?

 

[oldbmwfan]

They are very strong and survived all the standard Ford wheel torture tests, which includes fairly high-speed strikes into a curb.

People are worried mostly about cosmetic damage and the expense of repairs.

In extreme cases, if there is a failure, it is likely to render the car undriveable (as noted above, a big hit can bend an Al window but will crack a CF wheel - but that is a VERY big hit).

Your 2nd question is what happens when the ceramic coating fails? Here is one failure mode, that is unique to my knowledge. What you are seeing is a bubble in the resin layer under the ceramic coating. (You can see red paint from where the 'bubble' scraped the caliper). The bubble happened while the car was parked ... no issue while rolling off the track, then I parked the car, then 10 minutes later jumped back in to move it and the wheel welt was hitting the caliper.

Also note that the rash on the inside of the barrel lip is from dropping the wheel off the inside of a curb at Mid Ohio in a 100-mph corner, 2+ years and many track events before the ceramic/ resin failure. Doing that lap after lap did no damage to the wheel structurally. Ford replaced this wheel under warranty.

 

[oldbmwfan]

And holy lord - the brake dust on the front rims. I wiped them down shiny clean two days ago. I drove maybe 10 miles the other day and then 7 miles today and the brake dust accumulation is crazy. I put Hawk ceramic pads on my 2018 front rims and this cut back on brake dust big time. Do the 2020 GT350Rs come with ceramic pads from the factory?

No, they come with pads that work. Dust is a byproduct. (Sorry, I f'n HATE ceramic pads and their mushy pedal feel)

 

[AgSurfer]

They are very strong and survived all the standard Ford wheel torture tests, which includes fairly high-speed strikes into a curb.

People are worried mostly about cosmetic damage and the expense of repairs.

In extreme cases, if there is a failure, it is likely to render the car undriveable (as noted above, a big hit can bend an Al window but will crack a CF wheel - but that is a VERY big hit).

Your 2nd question is what happens when the ceramic coating fails? Here is one failure mode, that is unique to my knowledge. What you are seeing is a bubble in the resin layer under the ceramic coating. (You can see red paint from where the 'bubble' scraped the caliper). The bubble happened while the car was parked ... no issue while rolling off the track, then I parked the car, then 10 minutes later jumped back in to move it and the wheel welt was hitting the caliper.

Also note that the rash on the inside of the barrel lip is from dropping the wheel off the inside of a curb at Mid Ohio in a 100-mph corner, 2+ years and many track events before the ceramic/ resin failure. Doing that lap after lap did no damage to the wheel structurally. Ford replaced this wheel under warranty.

Great info sir.

 

[luc]

The real experts on the CF wheels on the forum seem to be those who have never owned or driven an R, so I'll wait for those to chime in shortly. It's important to distinguish between worrying about functional damage vs cosmetic damage. Those of us who drive around on the street with them aren't really worried about functional damage as much as cosmetic damage. Coming from other cars, you have a couple factors working against you. First the tire sidewalls are very low profile and stretched slightly in the rears. So not only do the rear wheels protrude slightly, but the widest part of the car is from rear wheel rim edge to rear wheel rim edge, and these edges are very close to the ground. So while you might not 'curb' the wheel in a parking lot, a large pot hole can cause enough tire deflection to scrape the wheel rim. There are other things on the street you can't always account for. Say you're driving but have to pull aside for an ambulance - if you have to pull off the side of the road, the edge between the road and grass or gravel could be enough to scrape the wheel. Or you're going down a street and enter a road construction zone. The torn up road could contact and scratch the wheel somewhere.

That being said - that's cosmetic damage, and can typically be repaired. When I spoke with one of the employees at Carbon Revolution back in 2017 he had said the outer rim layers of carbon aren't really structural - they couldn't produce a street legal wheel in which curb contact would render it structurally weakened. Frank at Spyder Composites in CA, the official service and repair spot for the wheels, confirmed, and said that he can even lay in a new layer of weave if the rim gets scraped up. Grant it, you're then looking at an expensive repair or refresh.

When I spoke to the person at CR, if I recall correctly (again this was several years ago), he said the ceramic coating was something they were applying to the wheels even before the GT350R. It wasn't necessarily that the GT350R 'required' the coating, but more that they and Ford spec'd it given the proximity to the calipers. So I don't know if anyone can honestly tell you what the risks of a failed coating would be. You quoted the increase strength there too, but remember the ceramic coating isn't related to the strength of the wheel as much as the melting point of the epoxy.

Actual "functional" failures of the wheels are relatively rare. I can only recall having seen a couple on the forum in the past couple years. So all that being said, you can drive the car on the road without living in constant fear of something that couldn't later be touched up or refinished by Spyder. Now, driving thousands of miles on the road without ever seeing a scratch? That might be harder.

What Is the weight difference between a light, good quality aluminum wheel and CF ?

 

[ChipG]

What Is the weight difference between a light, good quality aluminum wheel and CF ?

From what I've seen, I think the CF wheels are 17/18# and a good lightweight forged wheel could be found in 21# - 25# range.

 

[Demonic]

What Is the weight difference between a light, good quality aluminum wheel and CF ?

There are high quality aluminum rims that come close to the CF rims in weight alone, like Forgelines on the GT350C, say in the range of 21-22 lb if I recall. But you also have to consider where the mass is. For the sake of angular momentum you want to avoid weight around the edge/rim. The advantage of the CF is a light barrel, and the strength decreases barrel deflection in hard corners. In a high G corner, the barrel of the wheel can deflect enough to change the tire camber.

 

[460Fred]

They are very strong and survived all the standard Ford wheel torture tests, which includes fairly high-speed strikes into a curb.

I’ve always been curious about the OEM standards and testing for wheels sold in the US market.
Please provide further information or a link.
I know wheels sold in the German market must pass rigorous testing set by the German Govt. This includes aftermarket or OE wheels.
Here in the US, not so much.
I’m thinking standards the OEM’s follow are set internally for liability reasons first, performance second for Cars sold in the USA.

 

[Scoobs]

The ceramic coating on the front CF wheels was designed to handle the heat caused by a complete failure of the brakes due to excessive heat from braking, exceeding 900 degrees C.

https://www.motortrend.com/news/ford-spills-details-on-shelby-gt350r-mustangs-carbon-fiber-wheels/

https://sam.abuelsamid.com/2015/05/06/2015-ford-shelby-gt350-built-from-the-wheels-up/


Tom mentions testing the brakes to failure in the first post of his thread

https://www.mustang6g.com/forums/threads/gt350r-carbon-fiber-wheel-repair.120081/

 

[Demonic]

I’ve always been curious about the OEM standards and testing for wheels sold in the US market.
Please provide further information or a link.
I know wheels sold in the German market must pass rigorous testing set by the German Govt. This includes aftermarket or OE wheels.
Here in the US, not so much.
I’m thinking standards the OEM’s follow are set internally for liability reasons first, performance second for Cars sold in the USA.

Since these are OEM wheels for a car, they are also required to go through very specific and rigorous govt testing. The inside label on this pic shows the DOT-T rating. (pic lifted from elsewhere on the forum).

https://www.govinfo.gov/content/pkg/CFR-2002-title49-vol5/pdf/CFR-2002-title49-vol5-sec571-120.pdf

 

[honeybadger]

Count me in the camp not recommending the CF wheels for heavy track use...but my objection is purely practical and not performance oriented.

This happened this weekend to my forged wheel when my upper control arm broke. I’ve also bent a few and scraped all the rest. The nice thing about forged wheels is they can be bent back to round for about $75 if they didn’t fully break. And, you can buy an entire forged set of wheels for the cost of 1 to 1 1/4 of a CF replacement (or replace a broken forged wheel for the cost of repair to a CF wheel).

The carbons are badass. And superior in performance. But from a practical standpoint, they just don’t make sense to me. Spend enough time on track, you’re going to break stuff. I’d rather break stuff that’s more repairable and cheaper to fix. Wheels are a consumable regardless of material.

 

[WildHorse]

People are worried mostly about cosmetic damage and the expense of repairs.

If you chip or take a chunk out of a aluminum rim, which we all know happens IE curb rash, it's usually not a big deal. Try the same with a CF wheel. You don't need own CF wheels to realize the outcome as one poster alluded to.

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