About those old MPC plastic eating BFG Radial T/As tires ???

[Can-Con]

As everyone knows, they always eat the plastic they come in contact with. Well, maybe not always , ,

I built this MPC annual '81 Z-28 Camaro over 35 years ago. Didn't like the tires that came in the annual kit so just used some from another then current kit. The infamous BFG Radial T/As that "ALWAYS" eat the plastic.

So, remember, this kit has been wearing these tires for over 35 years, probably closer to 40.
Pulled one apart and this is what I found , , ,

No damage whatsoever.

So, Why?

I didn't do anything to protect the plastic from the tires, didn't even paint the surfaces where they meet.

Was it the blue plastic? Were the tires made in a different plant? Different country? Dumb luck???

Don't know but this has been my experiences with these tires for the most part.

But, seriously, were the ones in the Canadian boxes, sold in Canada made in a different plant with a different eormula for the vinyl then the ones from the U.S. ???

[Bugatti Fan]

Who knows ?   Best to err on the side of caution and put some sort of barrier between the vinyl tyres and the plastic of the wheel.   Paint or foil. 

Not sure whether necessary or not on wheels that are vacuum posted though. I expect someone will know.

 

[Mark]

Pure luck.  Earlier this year, I spotted damage on the wheels of a '72 GTO I had built in the early Eighties using those tires.  The kit inner wheels, and the outers ("honeycomb" wheels from a mid-Seventies MPC Chevy Monza) were all painted on their outer surfaces (outers were stripped of plating).  Still got the gumball effect.  Took it apart, edges of outers and inners were softened.  Sanded all of that off, repainted the wheel edges, and reassembled.  Tires used this time were AMT hollow Goodyear Polyglas with molded-in lettering, same as I used on a '71 Trans-Am rebuild I did around the same time as the Goat.  No problems noted with the Trans-Am.

[Can-Con]

17 minutes ago, Mark said:

Pure luck.  Earlier this year, I spotted damage on the wheels of a '72 GTO I had built in the early Eighties using those tires.  The kit inner wheels, and the outers ("honeycomb" wheels from a mid-Seventies MPC Chevy Monza) were all painted on their outer surfaces (outers were stripped of plating).  Still got the gumball effect.  Took it apart, edges of outers and inners were softened.  Sanded all of that off, repainted the wheel edges, and reassembled.  Tires used this time were AMT hollow Goodyear Polyglas with molded-in lettering, same as I used on a '71 Trans-Am rebuild I did around the same time as the Goat.  No problems noted with the Trans-Am.

I'll have to pull out some more old builds to check on them. There definitly is some melt as you discribe on some but I don't remember all of them doing it. 🤔

Edited Saturday at 09:22 PM by Can-Con

[Mark]

Another solution would be to use resin wheel halves, inside and outside.  

[oldcarfan]

I still have a few models I built in the 90s and the only one that has tire melt is the Revell Acura NSX. The Monogram and MPC kits seem to have fared well. 

[peteski]

It is the luck of the draw. Tire melt is a real thing.  The vinyl mixture used to mold the tires can vary in composition. The melt is caused by the plasticizer leaching out of the PVC material.  Virgin vinyl (PVC) is a hard plastic (most modern sewage plumbing is made of PVC).   To make the PVC soft, a chemical called plasticizer is added to the PVC, making it soft.  That stuff can leach out of the the tire PVC material, and when it comes in contact with polystyrene or ABS (both are hard plastics used for molding model kit parts) the plasticizer will try to make those hard plastics soft, thus the infamous "melt" happens.

Why some vinyl tires leach plasticizers while others don't is anybody's guess.  There might be different formulations of PVC and or plasticizer being used at the time by the model company. Some might leach the plasticizer while others don't   Over the years model kit tires were also made from materials other then PVC.  Those usually do not cause any adverse reactions. Most Japanese kits have tires made from rubber. Those do not cause any problems but they can get brittle in time.  Best solution would seem to make the tires from the same hard plastic as other parts of the kit, then just paint them "rubber" color.  Since models are mostly static, model tires do not have to be soft to look realistic. Not even sure how that trend started.

Edited 15 hours ago by peteski

[Can-Con]

3 minutes ago, peteski said:

It is the luck of the draw. Tire melt is a real thing.  The vinyl mixture used to mold the tires can vary in composition. The melt is caused by the plasticizer leaching out of the PVC material.  Virgin vinyl (PVC) is a hard plastic (most modern sewage plumbing is made of PVC).   To make the PVC soft, a chemical called plasticizer is added to the PVC, making it soft.  That stuff can leach out of the the tire PVC material, and when it comes in contact with polystyrene or ABS (both are hard plastics used for molding model kit parts) the plasticizer will try to make those hard plastics soft, thus the infamous "melt" happens.

Why some vinyl tires leach plasticizers while others don't is anybody's guess.  There might be different formulations of PVC and or plasticizer being used at the time by the model company. Some might leach the plasticizer while others don't   Over the years model kit tires were also made from materials other then PVC.  Those usually do not cause any adverse reactions. Most Japanese kits have tires made from rubber. Those do not cause any problems but they can get brittle in time.  Best solution would seem to make the tires from the same hard plastic as other parts of the kit, then just paint them "rubber" color.  Since models are mostly static, model tires do not have to be soft to look realistic. Not even sure how that trend started.

I've known all that for a long time Peter but thanks for adding it so those who are not familiar with the problem will know.

To be clear, I never said it dosen't happen, just that it dosen't happen in every case.

I dug out some stuff I built back in the late '80s with these tires last night to see how they have been holding up.

First issue MPC Dodge Daytona molded in dark metallic grey, slight melt, edges of rims slightly soft in places. 

First issue MPC Pontiac Fiero molded in red, moderat melt, soft rims edges, I wouldn't re-use those wheels.

First issue AMT A-Team van molded in black, MPC tires used instead of kit tires. Minimum melt. slight markings on inside lip of rims. Wheels definitly re-useable.

So, wht didn't the Camaro wheels melt too? That's the point of the post, not what could have been done to prevent it or whatever ,, just why this particular set of tires and wheels? 

I didn't do anything to clean them up before use or anything like that, just painted the letters, [with Tesors flat white bottle enamel BTW,] and threw then on the car. 

Also, have anyone had the MPC Desert Dog truck tires do this? seems they should have been made from the same vinyl .

[peteski]

17 minutes ago, Can-Con said:

So, wht didn't the Camaro wheels melt too? That's the point of the post, not what could have been done to prevent it or whatever ,, just why this particular set of tires and wheels?

Well as I mentioned, there are several factors at play and we will likely never know for sure why.  I doubt it was just a single set. It was likely whole batch of of models (not just your single Camaro). Whatever material they used at the time must have been more stable.

I posted all that info because this seems to be a reoccurring subject, so I thought I would dive more into the details as to why that happens, and why it seems random.

[Mark]

I'm thinking this particular tire is molded from a softer material.  Using the same material as other tires may have made the molded tire tough to remove from the mold during production.  

I don't believe Round 2 has used this tire in any of their kits.  That could be due to not having BF Goodrich licensing, but could be for other reasons.

[1972coronet]

3 hours ago, peteski said:

Best solution would seem to make the tires from the same hard plastic as other parts of the kit, then just paint them "rubber" color.  Since models are mostly static, model tires do not have to be soft to look realistic.

I admit that for a long time I was opposed to styrene tyres... then I discovered a way to make them look like rubber :

1.) Primer and then paint the tyres with Tamiya ( my choice here ) Black Rubber ( I use the aerosol delivery type ).

2.) Sand the tread / contact surface , followed by dark grey or black panel line accent 

Your mileage may vary - paint preferences and whatnot. 

No dreaded "tyre melt" , either ! 

[Can-Con]

6 hours ago, Mark said:

I'm thinking this particular tire is molded from a softer material.  Using the same material as other tires may have made the molded tire tough to remove from the mold during production.  

I don't believe Round 2 has used this tire in any of their kits.  That could be due to not having BF Goodrich licensing, but could be for other reasons.

Oddly enough I had remembered seeing a set in a kit I recently got as a door prize at a show a couple months ago. 

Checked earlier today , theres a set in this kit along with the newer white letter tires.

[Big Messer]

As soon as I learned about this (long time ago) I put the tires of all the unbuilt kits in separate bags, just in case. Had an ancient Hawk sports car glue bomb that got a bad case of the melts, I ended putting it in a diorama as a car being repainted with the wheels covered with tarps.