Fat Tire Trail Bike Questions

[wardog]

Well it has been a few months since I completed the 3x3 mini bike so it's about time to start a new project. This is going to be my go-to trail bike, so light, simple,and reliable are key.

This is the plan so far:
-1978 ATC90 engine, 4 speed with hi/lo range
-single tube frame like the original 3 wheeler with engine hanging underneath
-single sided frame and forks with 4 on 4" trailer hubs
-custom widened 8" wheels with 22x10-8 Kenda Snow Mad tires
-no suspension, shock under seat

I am leaning towards no front brake for simplicity, but both of my other bikes have front brakes, and I use them a lot, so Im worried about missing them. Do you guys think I need front brakes? If I go rear only, I am considering a small brake on the jackshaft similar to my big 2x2 bike, but then if I lose the chain I lose the brakes..... and no downshifting to slow down either.

 

[KingCobra]

My gokart has no front brakes and it stops just fine and I know it's on 4 wheels and a bit heavier. BUT a rear brake is safer than a front brake! Front brakes can get you into trouble unless its on 4 wheels and can't fall over and hurt someone badly. IN GENERAL with a safety back-up plan<> REAR BRAKE ONLY for my vote!!! I've also had many a car with only rear brakes and I could control them better. Same as a trail bike with rear only brakes. Then have an EMERGENCY brake as a back-up plane. I disagree with a JACK-SHAFT mounted brake though. Like you said, lose the chain, lose control. And remember, when the JACK-SHAFT chain comes off and you are doing 30 or 40 mph heading towards a tight curve of stop sign (if you happen to be on the street at the time) and you have no choice to use that front brake..... You're going down hard. I can't wait to see progress here!!! 'T-Man's Garage' (youtube) has nothing on you!!! And what's wrong with an 8" X 8" aluminum wheel? Be careful because I bent a rim mounting a Carlisle AT 101. After I repaired the rim, they now stay hung up on my peg board now as I have a fear of mounting heavy duty tires in .192 gauge aluminum wheels. I'm looking for a set of slicks for them. My mistake was buying 'NO-COIN' racing wheels. I should have bought the 'Douglass Wheel' 8 X 8 4 on 4" golf kart version. Heck, your tires might weigh more than your trail bike. Anyway, enough rambling...

 

[wardog]

Ok, so I need a brake on the rear wheel, not the jackshaft. Since the frame is single sided I cant put a brake rotor on the other side of the wheel as the sprocket which leaves using the sprocket as the rotor. I like that idea.... light and simple, but there are a couple potential issues. One is the actual thickness of a #40 sprocket which is .284".... I haven't been able to find a mechanical caliper wide enough to accept a rotor that thick. The second issue is the diameter of the sprocket vs the tire. A 9" diameter sprocket/rotor wont have much leverage on a 22" tire and I'm worried it wont have enough braking force.

 

[Hellion]

I think I've seen what you're attempting before, on the interwebz. Basically a conversion of an old Honda ATC 3-wheeler to 2 wheels, but using a majority of the factory frame and parts.

Those big fat bouncy tires on a narrow-track certainly creates an agile machine.

 

[wardog]

I think I've seen what you're attempting before, on the interwebz. Basically a conversion of an old Honda ATC 3-wheeler to 2 wheels, but using a majority of the factory frame and parts.

Those big fat bouncy tires on a narrow-track certainly creates an agile machine.

I am only using the engine, much wider wheels, totally custom frame.
Similar to my big 2x2 bike only smaller, MUCH lighter, and only rear wheel drive.




I really liked the way my big bike looked during construction when it was a stripped frame.




---------- Post added at 08:21 PM ---------- Previous post was at 07:26 PM ----------

These are the 9" wheels I cut and widened for 25x13-9 tires. I plan on doing the same for the 8" wheels with 22x10-8 tires.

First pic is how I trued them.

 

[KingCobra]

IF it is feasible, you can always weld up a 'swivel brake plate' ( and you have the room AS an emergency braking system on the rear tire)that swings at the tire with pressure to slow it down like on some go karts but I feel they could wear down a tire but I think you have a few good options!! The real question is if mud get's cake in between the swivel plate and the tire. And I know that metal against wet tires don't do so well. You could also buy some of that black FLOOR GRIP stuff that looks like rough sand paper for no slip footing, and cut and stick a piece against the painted metal part. Remember, it is only for an emergency need IF your jack shaft chain comes off(but what are the chances of that with routine maintenance)You are good at creating creations. You'll come through ok!! I like it!

BTW, how do you like those tires? I was thinking of getting a pair for my go kart. AND, I have been looking for NEW 4 on 4" by 9" wheels because they are usually 9" to 10" wide. Have you found a source for new 9" wheels? I find rusty over priced ones every day on Ebay, like someone thinks thinks GATOR or John Deere is worth it's weight in gold... LOL...Would you pay $55 PLUS $90 in shipping for one????.....Thanks, Scott

 

[vpd66]

I too am interested in your fat tire trail bike. I've always thought these were cool and would be get for going through the woods where there isn't any trails. Back when I was growing up a buddy of mine had a Carl Herald Super Bronc and I road it many times and thought it was the greatest. I've seen the Honda atc 3 wheelers converted to two wheels and thought they were cool. I could never find a good enough deal on one to convert. I think a single back brake would work if its on the tire or axle that the rear tire is connected to, but if your brake is on a jackshaft then you should have a front brake. What is the advantage or what is your reason for a single sided frame?

 

[wardog]

Scott,
I'm not sure a scrub brake would be very effective on a 2 ply "balloon" tire with extremely low pressure and wide spaced ribs. With no suspension, I'll be running these tires at wildly different pressures depending on the terrain, all the way down to less than 1 psi... if my big bike is any indication.

Speaking of tires, check out the Kenda Snow Mad. Do yall think it is a good choice? I'm looking for traction, but without tearing up the trails too much.

As to the 9" wheels, I can't find them anywhere either in 4 on 4"! They are fairly common and affordable in 4 on 110, which is why I bought 110s and recentered them to 4 on 4" for the 2x2 bike. It was a pain, and I would rather have just bought some like that. You can find them on Amazon..... 9x9 ITP steel wheels for $50 each with free shipping.



vpd66,
Getting through the woods is exactly why I want to build this bike..... I love trail riding, it brings together mini biking and the outdoors in an awesome, challenging way. I just need a light, quiet, and reliable bike to do it.

I have pretty much settled on a disc brake caliper on the wheel sprocket, I just need to decide on mechanical or hydraulic, and find one that can fit a .284" thick sprocket in it. Maybe I can find a 2 piece caliper that I can make a spacer for to widen the space between the pads. I think the Airheart mechanical calipers are like that.

The single sided frame/forks has advantages and disadvantages, I like the simplicity, compactness, and ease of fabrication, and of course I like that it is different. Also using trailer hubs cuts down on expense and the total number of parts, and allows the tires to be quickly changed like a car. Realistically, it will probably weigh a little more to be equal strength, but I'm willing to sacrifice a few pounds for all the advantages. This frame will be MUCH lighter than my 2x2 bike and the frame/fork offset will be opposite sides.

 

[mckutzy]

Airheart's can be spaced for offset of a thicker rotor... Honestly I think those will be fine with out shims.... I use a sprocket for a rotor on my both of my mini-choppers...

 

[KingCobra]

Airheart's can be spaced for offset of a thicker rotor... Honestly I think those will be fine with out shims.... I use a sprocket for a rotor on my both of my mini-choppers...

Is there a photo of such set-up?

 

[mckutzy]

Here's my bike the "jimmy rig"
An example...

http://www.diygokarts.com/vb/showpost.php?p=425458&postcount=177

Of my thread...

http://www.diygokarts.com/vb/showthread.php?t=5461

 

[wardog]

I guess the next question is will a mechanical caliper have enough clamping force for a 22" dia tire on a 8" dia rotor?

 

[mckutzy]

It will... I would also get a large levered hand brake(a small motorcycle or scooter) , as that will increase leverage, moreso than a bicycle version.

 

[Hellion]

Judging from your prior creation shown in post #5, I am really liking this. It’s artful and also sort of Mad Max’ian, without looking cobbled together.
It’s like, FACTORY looking...

It has similarities to the Rokon, but better executed. Egad, those Rokons are ugly.

 

[wardog]

Thanks Mckutzy, Ive got a nice long brake lever to use.

Wow Hellion, nobody ever called it factory looking before..... thanks. I really just cobbled it together as a proof of concept and it just turned out this way. I too think Rokons are ugly..... especially the new ones. I have to give the Rokons some credit though, because they are light. Sometimes I feel like the front wheel drive on mine is necessary to pull around the extra weight of the front wheel drive system if you know what I mean. There are definitely places where awd helps, but at least as many where it is a hindrance..... That said, having the front pulling on my little 3x3 makes a huge difference because I kept the weight down, and probably because of the much smaller tires.

 

[Hellion]

I looked into the tires, the Kenda Snow Mad and they seem to be lightweight, high floatation tires.

Good reviews but this statement caught my eye; “The lightweight carcass takes advantage of centripetal force to grow the tire at high speed like a top-fuel dragster...”

If your bike(s) have that ability, it could present a fit problem as your tires are more ‘captive’ by the frame and fenders than the tires would be if mounted on open ATV axles—meaning there’s more room for that kind of tire formation.

However, I get the impression that this bike is going to be more of a low speed trail bike/trundler and not one for creating rooster tails. So, basically a non-issue.

https://www.atvrider.com/products/thrashed-kenda-snow-mad-tire-product-review

 

[wardog]

If I ever get this bike going that fast, I will welcome automatic frame to tire scrub braking.... ha!

 

[Hellion]

If I ever get this bike going that fast, I will welcome automatic frame to tire scrub braking.... ha!

I'm sure it'll make a lovely sound and reverberate through the frame like crazy when it does.

How's the bike coming?

 

[wardog]

Not much progress yet. I have replaced the pull start rope on the old atc90 engine, and made a few drawings. The wheels should be here Monday, and I will start the widening process. Once that is done, I can go about fabricating the frame.

Now I need to figure out how wide I want the wheels. They are 8" wheels that are 7" wide with 0 backspacing. I'm thinking I should add 4 ro 6 inches in width, but I have to keep in mind the difficulty of mounting tires on ridiculously wide wheels. Opinions? Suggestions?

 

[vpd66]

Whats the reason for super widening the rims? Seems like a lot of work.