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Old 05-14-2019, 12:10 PM
jgmick jgmick is offline
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Default Need some advice on tires/wheels

Started a project to build a 1/12 wheeled excavator (Gradall). Got the cab/boom/bucket part done, now looking at the chassis. Have most of that worked out but...

I am stuck on wheels/tires. Basically I don't know what I am doing. I have tried in the past to make solid tires out of molded urethane. That worked, sort of, but they don't work well in soft stuff. Plenty of traction, but no flotation. I think I need something with some give to it. I can get the appearance about right, they just don't function well.

Give me some advice on where to look for tires/rims and a general education on how they work and go together. Are they air inflated, thick rubber to get some load carrying capability, foam filled, other?

Dual tires on the back, what kind of hubs?

I'm not too concerned about exact scale, just something that looks about "right".

I plan on doing the drive train from scratch to suit me. Not (at least right now) trying to get too authentic on the rear axle/differential/transfer case. That may change as this thing evolves. (It's all easier when it is just on paper.)

All suggestions welcome, I'm plowing new ground here.
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Old 05-15-2019, 03:25 PM
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Default Re: Need some advice on tires/wheels

My only help on tires I can give you may already know, but here goes: A lot of folks fill their tires with BBs or lead shot to increase overall weight and traction. Otherwise tires usually have foam insert. I image there are different densities of foam available.

Not exactly sure what size you would need but how about the 2.2 Mil spec tires from RC4WD. Would they work? Hope that helps at least a little...

BTW, did you post your Gradall build so far, I couldn't find it? I'd love to see it and I'm sure others would too.
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Old 05-15-2019, 05:20 PM
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Default Re: Need some advice on tires/wheels

I don't know specifics about what would be suitable for 1/12 construction equipment, but page 20 here shows how Tamiya does dual rear wheels.
https://www.tamiya.com/english/rc/rcmanual/56318.pdf
RC wheels are often listed as 1.55, 1.7, 1.9 or 2.2. This is the diameter of the rim in inches. 1.9 is the standard size for 1/10 touring and trail cars. 1.7 is the size used for Tamiya 1/14 trucks. 2.2 is often used for larger or more capable crawlers. The tires are hollow rubber tires. Technically filled with air, but not sealed. They can be used with soft or firm foam inserts, but the tires themselves can also be anywhere on a spectrum from very soft to very firm. The stock Tamiya 1/14 kits have pretty firm rubber and no foam inserts.
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Old 05-16-2019, 12:32 AM
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Default Re: Need some advice on tires/wheels

Its nice to see someone else modeling a Gradall
What model of Gradall are you making? If its a modern one like the xl4100v or the xl5100v the spec sheets have the tire sizes for the 6x6 and 6x4 undercarriages, the 6x4 uses a 385/65R22.5 and the 6x6 uses a 425/65R22.5 so the rim is 22.5" at 1/12 scale that is 1.88" (47.63mm) so a 1.9 tire is close to scale.

Here are the tire dimensions in 1/12 scale just in case you need them.

385/65R22.5
Diameter: 3.52" (89.32mm)
Width: 1.27" (32.17mm)

425/65R22.5
Diameter: 3.69" (93.77mm)
Width: 1.39" (35.35mm)

The "MIL-SPEC ZXL 1.9" tire from rc4wd will be a little over sized even for the 425/65R22.5.

Hope this helps.



Shawn
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Old 05-19-2019, 11:34 AM
jgmick jgmick is offline
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Default Re: Need some advice on tires/wheels

No specific model, more of a generic. I got intrigued by the telescoping boom structure and decided to see if I could make one. After some fooling around I got one built and working. It was sized as much by having to fit an actuator into the end of the inner boom to run the bucket dig/dump. (So much for scale). That is all done and working, so I'm moving on to the truck part.

I found some tires on eBay (China) that are 3.35" (80 mm dia.) x 0.78" (20mm) wide. Ordered those and am laying out the hub and drive structure. Need to get them in hand before I go too much farther.

I am going to need about 1-2 LB/tire load carrying capacity. That is where I bog down in trying to figure out what to do next. From what I can see here and elsewhere it looks like cutting donuts out of foam rubber as tire inserts gets the load carrying capacity up. I think I'm going to have to play with that some. (Yet another science project.)

As I said in my first post I do know that solid tires won't work. They just don't carry loads well in soft stuff. (sandbox). That is mostly where I need some coaching. I want to be able to drive around in beach sand to dig. (My kids love watching that action. Also a great way to get a crowd of adults around. ) Tracked vehicles work pretty good there, now I want to do it with tires.

Suggestions for tire to rim retention? Do they tend to spin the hubs in the tire when loaded and trying to drive? Also what types of foam to use as a fill donut?
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Old 05-19-2019, 04:40 PM
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Default Re: Need some advice on tires/wheels

I tried this once before and it tanked but lets try again. Some pictures of the Gradall as far as I have gotten in the build.





More work needed on some covers for the electronics but this is all functional.
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Old 05-19-2019, 07:12 PM
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Default Re: Need some advice on tires/wheels

If it needs pickup truck size wheels instead of semi truck wheels, Lego has some that are like 64.5x20 (mm). Thick sidewall hollow tires, street tread.

You'd need to make your own rims, but that doesn't look like a problem for you. Small Hauls tonkas usually have these

If you find you're spinning the rim in the tire, get some Rubberized CA. Couple dots in the bead area for testing. If racing they do full inner/outer beads, you're not likely to load tires like them.
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Last edited by frizzen; 05-19-2019 at 07:22 PM.
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Old 05-19-2019, 07:41 PM
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Default Re: Need some advice on tires/wheels

That looks very good!
For reference, I'm using these in both 22mm and 30mm wide versions on my fire truck, with the included foams and Tamiya 1/14 truck rims. They have no problem carrying about 12 pounds on 6 wheels, but I don't know how they would handle beach sand. They're 85mm in outer diameter. https://www.stellamodels.com.hk/trac...u-pr-8495.html
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Old 05-31-2019, 01:25 PM
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Default Re: Need some advice on tires/wheels

Wombii

I looked at those tires. Like the tread pattern. The ones I got have a pretty simple road tread pattern. Might be good enough for the front tires. You said you are using both 22mm wide and 30mm wide. Those you referenced look to be the 22mm version. Is that correct? What diameter is the rim? (I have rims made for a 43mm I.D. so I have some interest in not re-doing a lot. (OTOH, now is the time to make changes.) Do you have a reference for the 30mm wide tires?
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Old 05-31-2019, 10:16 PM
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Default Re: Need some advice on tires/wheels

https://www.stellamodels.com.hk/trac...su-p-8494.html Here are the 30mm version.

https://www.stellamodels.com.hk/alum...u-p-10503.html Here's a good profile view of a typical rim for this type of tire. When I measure the stock Tamiya rims I get 47mm outer diameter and 44mm in the valleys on both sides where the tire rests. Maybe it would be a good idea to buy a set of cheap Tamiya rims for measurements. https://www.stellamodels.com.hk/5654...a-p-10104.html and https://www.stellamodels.com.hk/5654...a-p-10106.html
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Old 06-02-2019, 03:57 PM
jgmick jgmick is offline
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Default Re: Need some advice on tires/wheels

I cut a couple of rims at 44.5mm where the tire sets. That seemed to work pretty good on the tires I got.

I'm going to order some of those 22mm wide ones you are using. They look really nice from a tread standpoint. I think I'll wait until I get them to final cut the rims. I like the idea of the 30mm wide tires to get more footprint, but the drawings make it look kid of fat. Fall back position for now if the 22mm tires don't work out.

I had cut the rim OD at 48mm just based on what looked good with the time, so I was pretty close to what you have.

Thanks for the info. Pressing on ....
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