Simplicity Broadmoor 728 XC

Welp, time for a new design. The year 2019 saw the "stock" Simplicity Adventure Edition finish near the back of the pack in the Top tractor challenge. It wasn't a surprise as the adventure edition was designed for....adventures, not for racing. So shortly after the 2019 TTC, designers at Simplicity racing HQ started drawing up a plan for a machine that would be a top finisher for the 2020 TTC, the Broadmoor R/S. It was to have full suspension, front IFS, extremely low center of gravity, and a crap ton of HP. Unfortunately, this design was somewhat overly complicated and progress on the build was slow. The team ran into issues trying to figure out the steering geometry, and as the 2020 TTC was rapidly approaching, a decision needed to be made...

Adventure edition in stock form, 8hp and 500lbs


The Adventure edition would be temporarily modified with a larger engine, light weight hood, and all non essential parts such as the winch, lights, and even the battery would be removed. Some 60+ lbs were shaved off the original 500lb weight. Also the front shocks were exchanged with ones that lowered the front end a few inches. While still not as hot of a setup as it could be, it was a major improvement and was good enough for a 4th place finish in 2020.

The 2020 TTC setup with 10hp engine and CARDBOARD hood!


The 2020 TTC saw a bit rougher course than 2019 and the full suspension broadmoor R/S design would have been cutting it extremely close already with ground clearance in 2019. After seeing the changes for 2020, the Simplicity team felt it was a better option to come up with some sort of hybrid design somewhere between the Adventure edition and the full suspension R/S. Basically, the idea is to take the temporary mods done to the Adventure edition one step further without going overboard. Sticking to a mostly traditional off road tractor layout without going crazy.

What that will mean is, light weight body parts like hood, grill, and fenders. Front suspension only to cut down on weight and simplify the design and contraction. More power from an opposed twin. And a light weight frame which has a low center of gravity. While the R/S design with independent front suspension and all the high tech weirdo angles in the frame necessary for the planned rear suspension might have worked ok for trail running, we now think a more contemporary design will be the answer for 2021.

Toying with the idea of mounting the alloy wheels from the R/S project directly on the 633a axles.


I'll be posting more soon as our design team sorts out the details of the new Simplicity Broadmoor 728 Cross Country

Great writeup, those fellas at Simplicity Racing don't mess around.

Definitely looking forward to seeing this!

Looks good, can’t wait to see how it turns out 

Oh man Im so excited! I think this is a excellent build plan and will be a dangerous competitor!

Thanks people. Yeah I just wasn’t feeling trying to get the steering and rear suspension figured out on the RS, besides the fact I think this will be better for the TTC. So we’ll see how it goes. I would like to get ag tread tires for the rear wheels though.

I've been trying to decide how to do the front suspension before I start laying out the frame. I have two sets of golf cart leaf springs and I was thinking that they might be a simpler way to hook the front axle on vs making another wishbone setup like on the adventure edition. I think they would be close on weight, you have a bit heavier spring but you don't have to have the wishbone or joint in the back and you don't need the panhard bar to keep the front axle in line either since the springs hold everything in place by themselves. I worry that they may be too springy and "sloppy" when really being hard on them though. I would add shocks of course and I think that should take care of things...Not 100% sure. The front suspension on the adventure edition works about perfect. Not sure if there is any big advantage in either direction.


Here's a golf cart front axle with a lot of extra gingerbread on it. Mounts for the shocks, a 1" box steel brace across the bottom which is super un-nessesary, and leaf spring mounts which are not usable because they are set on an angle. The golf cart had half springs in front and full springs in back. I'd be using the golf carts rear springs for the front of the tractor. I really only need the knuckles from this axle and I can remake the center. I believe it's too wide anyway. They drop the front axle a couple inches lower over a tractor setup because the spindle is at the center of the axle instead of the bottom. Lawn tractors usually have the axle higher than the spindle. This is not only better for center of gravity but the golf cart stuff is much heavier duty and the front hubs have good quality bearings.


Here's a good video showing redlinemotorsports leaf springs that he used on his MTD. In this video, he didn't have any shocks and he wasn't going ultra fast, but it shows about how they would go in.


Leaf springs:
-Easier to build?
-Lower center of gravity?
-Cheaper since I already have parts available

Mono link with coil overs:
-Softer more responsive suspension?
-Front end doesn't have to stick out quite as far, more compact
-Possibly lighter, hard to say...

thats a tough call, I like the linked suspension better personally but I get the argument for leaf springs, and leafs just plain work, alot of fast desert stuff still on leaf springs, plus its simpler and tougher, less to go wrong. also theres the easyer quicker to build argument, less time building more time getting to know the tractor, practicing and tuning etc instead of building right up to the wire or loosing alot of sleep building and only a week or two to get used to the tractor.

Yeahhhh I don’t know. I did some rough checking and I think the golf cart leaf springs are way too stiff. I’m leaning towards the mono link setup again. It’s really not all that bad to set one up I suppose because you’ve got one attachment point at the back and the panhard bar. The leaf springs do have the brackets already made but I would still have to make the springs fit the axle. The plates that are on it aren’t in the right spot for me to use them. Here’s a couple pics of the adventure edition wishbone/mono link setup. If I went that route, it would be very similar to that but I would try to save weight where I could.

I have kept with the monolink myself as well.  I used your version as my basis for Kal and later Red.

Depending on the arc in the leaf springs, they can require a panhard bar as well. Are the golf cart springs a single leaf or are there a few in the pack? If it’s a pack I’d remove a leaf at a time till you’re happy with the spring rate. What about a single transverse leaf spring above the axle with a mono link? That way you wouldn’t have to work around shock towers

I actually copied it from redlinemotorsports after he switched from his leaf springs to the mono link. That's actually not a bad idea going with a transverse spring craftsmanquad, that would be kinda different. I think I'd have to modify the ends of the spring to do that though to give it something to ride on and I think the spring is too wide for that also. Yeah it's a pack of 3 leaves. The main one, a mid one, and a small one. I was thinking of taking the middle one out but I think it's probably gonna be too soft then. I could try it and see. I think maybe the mono link with some more ebay coil overs would work decent tho. Not sure if I should but new shocks or use the ones for the broadmoor rs which are kinda stiff. I could mount them on an angle though.

I ordered keyed 1" collars to fix up the rear hubs so they will fit on the 633 axles. I also think I can move the engine over enough to get rid of the pain in the neck jack shaft from the adventure edition. So the plan is coming along.

Started working on the frame a little bit tonight. Starting at the transmission end and using part of a sears suburban frame. Since this is the high tech cross country racing model, we don’t need the hitch, or all the extra weight.


Cut off a pretty good chunk of the frame. The section I removed weighs about 7.5 lbs, more than an opposed starter. In my opinion, it’s not really going to effect the strength. As of now I’m not sure how I’m going to continue the frame forward. I have a couple ideas.


I took the front spindles back off the broadmoor rs front suspension. I weighed the IFS after removing the spindles and it weighed around 45 lbs! Way too heavy. Also the 5” or so of ground clearance was at the top of the suspension travel. Right now we’re looking at about 5” clearance under the 633 with the golf cart wheels, but the wheels are fairly narrow, so I think it’ll be alright.

You still planning on using the RS suspension on something? Would be a shame to let that go to waste

Unfortunately at the moment no. It is kind of a cool idea but I don’t really like how it turned out. Not that there’s anything terribly wrong with it but For some reason it’s just not what I had in mind when I started with it. I’ll save the joints and stuff of course. I might end up using part of it for something but who knows.

Maybe build another four zero with that as the front end. That would be really cool. Build a matching suspension for the rear and drive it with an ATV diff and a peerless 700 turned sideways to use a driveshaft from the trans to the diff....dang it now you got my mind working

It's pretty beefy that's for sure. Looks like I'm gonna end up with about 35 or so inch width with this build. The actual stock broadmoor 728 is about 32" wide at the rear wheels. I think the adventure edition is around 36". So it'll be a pretty small machine compared with most of the builds out there. I think it should end up under 500lbs for sure. Gonna be interesting.

Under 500 lbs with the power you’ll have will be Rowdy!

I hope so, should be pretty hot I'm thinking. I was looking on ebay and I can get some ag tread tires for the rear, same size as what came on those wheels, but I don't know if they're as good for gripping rocks as the knobs that are on there now. Plus it's another $120 worth of tires if I get new ones. Might leave em for now. Another random build note, I'm leaning towards using a stock cam in the opposed with the EC racing springs or whatever they are. I figure I want torque more than top end for the TTC, and also, my theory is with the ARC rods, the stock cam will limit rpm a bit and be much easier on the valve train, while the heavier springs will still give me another 1500ish? rpm or who knows. But I think it would be pretty indestructible that way. Just hold the throttle flat out and don't worry about it. I do have some various cams to play with too if I so choose. I'll probably end up building a second engine eventually. This thing is gonna be compact too, so it'll be pretty interesting.

Both of these tires are the same size, 18 x 8.50 x 8, which is what golf carts use and actually pretty close to the stock rears on the old 70's simplicitys too. I'd like to use those AG treads on the rear (mainly for looks) but also I think they'd do better in mud. Worried about how they would do on hard surfaces like rocks though. The TTC has a lot of rock ledges and things where I don't know if the AG's are gonna flex enough to grip over stuff.

Ag treads from ebay


These knob treads are what I currently have for all 4 tires.

I think the AG's in back would definitely look more like a tractor and less like a go kart. I don't wanna go for the go cart look.

you've got it right when talking about ags not having much flex, i can run the ones on my yt16 nearly flat and still not get much in the way of flex, mine are 23x9.50 -12 deestones but i don't think the size difference really matters when it comes to tire flex

I really like those knobbies. I’d stick with those and see what happens

These are kinda low profile and I think that prevents some flex too. I actually tried finding some bigger tires to fit those rims but there doesn’t seem to be much available in 8”. It was kinda my original plan to keep it low anyway so it’s alright. I think larger diameter tires roll up over stuff better for sure, but the low center of gravity gained by lowering both the transaxle and seating position might be worth the trade off. Not only that but the smaller wheels and tires weigh a lot less. Since the machine is going to be so narrow compared with most built tractors, it’s pretty much necessary to keep the weight low to keep the same handling.

Cutting the spindles off the golf cart axle. The XC axle is going to be much narrower.


Golf cart spindles/brackets removed from the old axle and any remaining weld ground smooth. Turned out nice and clean. Next step is to measure out the front wheel spacing and weld in a new axle. After that I can better see how to build the frame.

Lining up the axle before welding.


The main part of the front axle is 1” square tubing. It will also have gussets on each side. The middle 1” square tubing is only about 13” long and the whole axle is around 19”.

I’m pretty sure Johnathon ram ags the first year and the actually did really good for what they were. What about these?

https://www.amazon.com/Kenda-K472-Bias-Tire-22x11-00-10/dp/B00D6OIGYO

I run a similar tire on the AMF and was really impressed, slightly shorter lugs but very flexible and gripped logs and such well, unlike the bar tires I used in the past, shorter bars might be good for getting the rear to slide around turns also

Ps they have those for about 125 a pair on eBay