Vodnik's M939 Wheels Sets Review

Big Foot boxart

RESIN WHEEL SETS FOR
ITALERI M923A1 BIG FOOT
Updated 2003.05.23

Originally I planned to build the Italeri's Big Foot out of the box, but after seeing some pictures of the original trucks I decided that I must at least change one element to make it look good: wheels.

Below are two pictures - one of my model with original wheels from the kit and the picture of the real truck.

Unfinished model with original wheels on the left and the real truck (M923A2) on the right.
The model just doesn't look right...

After quick search on the web I've found two wheels sets: one from CAM (Custom Aeronautical Miniatures) - these are wheels for M939A1 series of trucks, originally offered by TAC Scale. The other set was from CMK (Czech Master's Kits) and was for M939A2 trucks (with CTIS - Central Tire Inflation System). I decided to order both - the former from Brookhurst Hobbies, and the latter from Hannant's. They arrived to me almost at the same time. I expected to find almost the same wheels in both sets just with different rims - with CTIS in CMK set. But what I've found after opening both boxes surprised me so much that I decided to write this little review.

To be able to evaluate the accuracy of resin wheels I first needed basic information about the original Michelin XL 14.00R20 tires, that are used on M939A1 & A2 series of trucks. On http://truckus.webmichelin.com/ you can find a lot of specification details for those tires, but I decided to use the set of tires/wheel dimensions provided to me by Major Rob Gronovius (Thanks a lot Rob!) in this review. Rob took some measurements of the wheel of the US Army M939 truck for me, so his measurements show the dimensions of used, correctly inflated tires, not brand new ones like on the Michelin web site. Those dimensions are:
- tire is 48 inches (1219 mm) in diameter - measured from side to side, not top to bottom,
- tire is 15 inches (381 mm) wide,
- the rim is 24 inches (609 mm) in diameter.
In 1/35 scale those dimensions translate to :
- tire diameter: 34.82 mm,
- tire width: 10.88 mm,
- rim diameter: 17.4 mm.

Picture below shows the Michelin XL 14.00R20 tire on the M939A2 truck (photo from Major Rob Gronovius' motor pool gallery on http://www.armorama.com/motorpool).

The front wheel of M939A2 series truck (M931A2 in this case).
Click on the picture to enlarge.

The wheels that Italeri included in their Big Foot kit measure: 33.5 mm in diameter and tires are 10.5 mm wide. They are significantly too small in diameter (1.32 mm - in full scale it would be 4.62 cm) and also a bit too narrow (0,38 mm or 1.3 cm in full scale). The rim is 16.5 mm so it is too small. Also the tread pattern is nothing like the real one - actually it hardly resembles any tire tread pattern at all...

CAM R35-002: 1/35 M923A1 Big Foot Tire Set (for Italeri kit)

CAM tire set.
Click on the picture to enlarge.

CAM tire set comes in a small box that contains seven resin wheels plus a small one page instructions. You get two front wheels, four rear ones plus a spare.

Installation manual.
Click on the picture to enlarge.

The resin CAM used for those wheels is a bit brittle and my wheels arrived with small parts of rims broken (see the picture below). It should be relatively easy to fix by replacing those parts with curved strips of plastic. The silicon molds must have been used for many molds before my set was molded and were a bit damaged. As a result the tread pattern will require some work with a knife in several places, as it is not fully molded.

The rims are correctly reproduced with all the screws etc. and is correct for A1 version of M939 trucks (no CTIS).

Rear and front wheels. Note the missing bits of resin on the rims.
Click on the picture to enlarge.

The tread pattern looks quite well, although I think the tire is a little bit too "square" in cross-section. Also the tread pattern blocks should be molded slightly closer to each other as they are now spread a bit too much.

Tread pattern resembles the real thing. The tire
cross-section is a little bit too "square".
Click on the picture to enlarge.

Dimensions of CAM wheels are:
- tire diameter: 34.5 mm,
- tire width: 11.7 mm,
- rim diameter: 16.8 mm.

The most important dimension (that will make the wheel look right on the model) is the outer diameter and here the CAM wheels are almost right on spot. They are a 0.38 mm too small, but it translates to just 1.12 cm in full scale. I expect that in the real world the diameter of tires can change more than that just because of the temperature change and the change of air pressure. The tire measures 0.82 mm more in width than it should (or 2.87 cm in full scale). Although the width of the tire can also change with pressure and temperature, I think that CAM wheels are a bit too wide. The diameter of the rim is too small (0.6 mm), but it will not be noticeable on the model.

See Update for additional information!

CMK 3005: 1/35 M939 series trucks - wheel set (for Italeri kit)

CMK tire set. First problem is obvious - three front wheels
and three rear wheels in my set, instead of two front and four rear.
Click on the picture to enlarge.

CMK tire set comes in slightly smaller small box than CAM set, and also contains seven resin wheels plus a small instruction sheet. Additionally there are six resin parts for the brake chambers. Unfortunately my set of wheels came completely useless - I got three front wheels and three rear wheels plus a spare one. Of course it should be two front and four rear ones. I'll try to contact CMK to get a fourth rear wheel and will update this review as soon as I hear anything from them. (UPDATE: I have received a small package from Prague two days ago with the missing rear wheel in it. Very good service - the part arrived just five days after I e-mailed CMK. UPDATE2: After a few weeks I received another replacement resin wheel from CMK. Looks that their service is great but their call logging system is not ;-) Now I have nine wheels: three front, five rear and one spare, and no idea what to do with them...). The addition of brake chambers is a nice thing, but it is a pity that there is just six of them - each of the rear wheels of the truck should have two such chambers attached, one large and one small, so total of ten chambers should be in the set: eight for rear wheels and two for front ones.

Installation manual.
Click on the picture to enlarge.

CMK wheels in my set were fully molded and without any missing pieces. Six wheels are molded flattened. The rims have elements of CTIS reproduced, so are supposed to be used to build replica of M939A2 series truck. If you look at the picture below and compare it to the picture of the real wheel you may notice that CTIS parts are simplified and not quite correct.

Rear and front wheels. CMK added parts of CTIS.
Click on the picture to enlarge.

The tread pattern blocks are molded closer to each other, what could make it look better than CAM wheels, but unfortunately the worse problem of CMK wheels is that outer blocks are completely rounded and smoothly disappear on the side of the tire. CMK tires do not have the square edge, that gives the original tires the "sharp" look.

Tire is nicely flattened - possibly even too much.
Contrary to CAM wheels, these are much too rounded in cross-section...
Click on the picture to enlarge.

Dimensions of CMK wheels are:
- tire diameter: 33 mm (measured from side to side),
- tire width: 9.8 mm,
- rim diameter: 16.2 mm.

CMK wheels are too small in all dimensions. Actually they are smaller even than the Italeri's ones. They are a 1.82 mm too small in diameter, what translates to 6.37 cm in full scale, and also are 1.08 mm to narrow (3.78 cm in full scale). The diameter of the rim is also significantly too small (1.2 mm, or 4.2 cm in full scale).

Brake valves are a nice addition to the CMK set, but do not compensate for its problems.

Direct comparison

Below are two pictures that show direct comparison of CAM wheels, CMK wheels and original Italeri ones.

CMK wheel on the left, CAM on the right and painted Italeri wheel
in the middle. You can notice the difference in size and tread patterns.
Click on the picture to enlarge.

This time CAM wheel is on the left, and CMK one on the right.
The difference in size is again clearly visible.
Click on the picture to enlarge.

Conclusion

If you consider that CMK wheels are significantly underscale, have poorly reproduced tread pattern and CTIS that is not quite correct, than you know that you must look somewhere else for a replacement of the Italeri's wheels. CAM wheels are a good choice if you want to build M939A1 series truck replica, but you will have to scratch build CTIS parts if you need M939A2. Actually it should be quite an easy task - at least it is easy to do it the same way CMK did. And with little effort you can do it better than they did.

Just recently I discovered several other sets of resin wheels for M939 trucks available on the market. Tank Workshop offer three sets of wheels for M939 trucks - original low profile tires, Michelin "Big Foot" tires and also big "Goodyear" tires. Real Models also sell two sets of wheels for M939 trucks. MR Models and Hobby Fan also have sets of M939 wheels in their offer. I have not seen any of those sets yet, so at the moment I can't comment on their accuracy and quality. One day I may order some of those sets and then I will update this review, but don't expect it any time soon.

Update - some observations from the actual model build

I decided to build my model as M939A1 series truck, so I used CAM set without adding CTIS. I used a file and sandpaper to round wheels profile a bit and it worked nice - they are not longer so "square" in cross-section. However I must say that the quality of mold is quite poor - the resin pour blocks are too big and they ruin significant part of thread pattern. Also there is A LOT of air bubbles on these wheels, some in places where it is almost impossible to fill them.