Lets talk Shocks

[FOMOGO]

I am looking for information on Minibike/Motorcycle rear shocks.

On a car/truck there are good amounts of angle and bad or excessive amounts of angle. Automotive I have all the real world information I need or want. But I have ZERO real world experience with what is used on a mini bike/motorcycle. I have never owned or even ridden a street bike. Owned 1 Honda XR600 dirt bike. It was worn out and I probably rode it 500 feet and sold it to my BIL. Him being an old motocross racer rebuilt it and promptly broke his ankle when it kicked back the 3rd or 4th time he started it.

I ask this question>>>>> What is to much angle and what is considered the best angle range (between X and X) for proper function.

I see custom bikes with the shocks straight up. I know this is not an issue as it allows the shock and spring to work at the full rated function. The more you add angle the more that number changes. I have seen few custom street bikes with the shocks laid down at least to 45 degrees or maybe a little lower. That much angle changes the function drastically.

I would think that there are some folks on here that have enough real world experience with Motorcycles to have a very educated answer for this. I know all of it is "rule of thumb" but there are also pretty hard numbers that are the preferred range I would think.

I even saw a drawing of a swingarm and the shock was laid down and served as the top link of the swing arm. It must have been laid down to 30 degrees forming a cute triangle. It looked good and looked simple BUT does it really work that way???

Thanks to everyone that contributes to this as I think it will be good information to share.

Doug

 

[Raskin]

..if shock is mounted straight vertical then when compresses it will lean back some due to chain..I'd say a little in on top best..how much depends on shock length of compression....seem logical

 

[mrpat]

Hey Doug, the absolute perfect situation for a shock is to have both shock mounting holes equal distance from the pivot.
This allows the shock to move smoothly and not bind

 

[ole4]

Before the mono shocks dirt bikes were looking for more travel and rear shocks were travel limited so they started laying them down at larger and larger angles to get more rear wheel travel. Not sure if that helps with your question.

 

[FOMOGO]

Hey Doug, the absolute perfect situation for a shock is to have both shock mounting holes equal distance from the pivot.
This allows the shock to move smoothly and not bind

Pat this is the first time I have heard this statement and I have talked to a few automotive engineers about shock placement. The common train of thought is the shock is most effective the further from the pivot of the link it is attached to. You have the most control and can use a better spring rate because of the reduced fulcrum effect beyond the shock/spring mount. Shocks get layed over for packaging more than any other reason in the automotive world.

Pat I can see the function of what you are saying and It makes sense to me. I will keep this in mind when I am trying to figure out shock placement. Thanks for the input as this is what I was looking for. :thumbsup:

Before the mono shocks dirt bikes were looking for more travel and rear shocks were travel limited so they started laying them down at larger and larger angles to get more rear wheel travel. Not sure if that helps with your question.

Ole that helps too. Like I said I have no motorcycle experience and every little bit helps with my decisions. I have considered a mono shock arrangement as well but I think that 2 shocks would be easier to make work than the leverage and the length and the mounts that a mono shock entails....

Thanks for the input ole! :thumbsup:

I hope to hear a lot more from more members. I will take all the help I can get.... Not only will it help me but hopefully it will help someone else in the future.

Doug

 

[PAP]

One thing to consider is where the shock is mounted in relationship to the load. If the shock was mounted vertical right above the axle, it would take the rated load. If it is mounted ahead of the axle and tipped, the travel of the axle is more than the travel of the shock. What ever is between the shock mounting point and the axle is more leverage, so it would take less force to compress the shock. As Mrpat said, equal distance from the pivot point, and the closer to the pivot point the less effort it takes to compress.
If you are not sure, give your self some options. Make your shock mounting tabs with several holes just to see what works best.

 

[FOMOGO]

[MENTION=55688]PAP[/MENTION], thanks for the input. I am trying to decide what length shock I will need and how much angle they need to be equal distance from the pivot. Due to packaging I may not have the luxury of being exactly on that number. We will see.

I have been researching different street bike specs and find it interesting how little shock travel some big bikes have on the rear. I also have been comparing wheelbase verses swing arm length and it looks like the rule of thumb is roughly 1/3 the wheel base for swing arm length, pivot to axle.

Anybody have any thoughts on the swingarm length verses wheelbase?

Thanks,

Doug

 

[PAP]

That sounds about right, mine has a 14" swing arm on a 44.5" wb. Of course this was figured on a huge freezer box blue print.:001_rolleyes:
Who knows....once I actually test ride it, it may not be worth a shit!:shrug:

 

[FOMOGO]

That sounds about right, mine has a 14" swing arm on a 44.5" wb. Of course this was figured on a huge freezer box blue print.:001_rolleyes:
Who knows....once I actually test ride it, it may not be worth a shit!:shrug:

I doubt that.....

A Honda Rebel has a 57.5'' WB and a 21'' SA. So that is close enough to 1/3 to me.

The stretched Warrior has a 49'' wheelbase and I am thinking that 18 inches should be about right.

That is my plan of attach. I will start there at least. It may end up at 16 or 17. Its all about packaging 5 pounds of stuff in a 2 pound container....

Doug

 

[Dr. Shop Teacher]

You're going to have limited choices in mini-bike shocks. Most are 12" OC. I put Honda 13.3" shocks on my Trail Bike in the stock locations (top directly above the axle and canted 1.25" to the rear of the axle on the swing arm). My f/r (+1 / +1.3) ride height is higher than normal but I wanted more front spring travel and a bit more in the rear. I'm 6'5" so it's a good fit for me.

Weight, in your case, is going to play into what shock you do use. That 420cc engine and the added TAV may cause the bike to squat more than you'd like. I'd think the weight would also be biased to the rear of the bike. The suggestion to do a set of mounting holes to try it out first is a great idea.

 

[FOMOGO]

You're going to have limited choices in mini-bike shocks. Most are 12" OC. I put Honda 13.3" shocks on my Trail Bike in the stock locations (top directly above the axle and canted 1.25" to the rear of the axle on the swing arm). My f/r (+1 / +1.3) ride height is higher than normal but I wanted more front spring travel and a bit more in the rear. I'm 6'5" so it's a good fit for me.

Weight, in your case, is going to play into what shock you do use. That 420cc engine and the added TAV may cause the bike to squat more than you'd like. I'd think the weight would also be biased to the rear of the bike. The suggestion to do a set of mounting holes to try it out first is a great idea.

Yeah I know we are fighting weight. I don't know what the front to rear ratio will end up being. I am looking at shocks with a spring rates of anywhere from 350 to 750 pounds per inch. They just seem way to stiff. We usually run somewhere in the 200's on the rear coilovers on most cars. And 500 to 600 in the front. It just seems that it is to much for what we need. Been thinking about the 350 set just to try and see. I know that the further from the pivot the lower the effective spring rate but also the more control the setup will have and that translates into ride quality... Shock placement translates to travel too. The shocks I am looking at are 2 to 2 1/2 inch of travel, seems way to short until you look around and see that a Honda Rebel only has 3 inches of travel in the rear....

Thanks,

Doug

 

[Dr. Shop Teacher]

^^^^You might be overthinking just a bit^^^^ Try to do a calculation of the total weight of the bike w/o rider and w/rider. Remember you only have two wheels doing the work of the four on a car, so a spring rate would be proportionally lower at each corner of the car (with weight distribution and the assist of suspension components).

Take a look at this thread: http://www.oldminibikes.com/forum/projects-and-rides/129743-modified-gilson-fat-tire.html
The builder is one sharp guy, and might give you some guidance.

 

[VintageMoneyPit]

To add to this with some personal experience the farther towards the wheel and further from the pivot point the less of a spring rate you need. building the rear swing arm on my doodle bug with an atv shock with a large spring moving the spring an inch would make the suspension able to be compressed by hand or too stiff for compression. its more of a keep trying to get it to work situation. the shocks for minibikes that are 220 spring rate are pretty much worthless unless there at the very back of the bike even with 2 of them.

 

[FOMOGO]

To add to this with some personal experience the farther towards the wheel and further from the pivot point the less of a spring rate you need. building the rear swing arm on my doodle bug with an atv shock with a large spring moving the spring an inch would make the suspension able to be compressed by hand or too stiff for compression. its more of a keep trying to get it to work situation. the shocks for minibikes that are 220 spring rate are pretty much worthless unless there at the very back of the bike even with 2 of them.

These will be at the end of the swingarm very close to directly above the axle to not more than 2 inches ahead of the axle. Its been 3 weeks plus since I even looked at the Warrior swing arm and I don't remember exactly but I think I was working on building a 16 to 18 inch arm. And it looks like about a 30 degree angle forward to mount the top of the shock. I haven't done all the measurements yet but I intend to finish the Super Bronc this week and get hot and heavy on the Warrior next week. Finishing the swing arm jig and building it is the first priority.

Thanks for the input. Every little bit helps.

Doug

 

[Raskin]

Glad you're on it again..sounds like a good plan...once your done you'll be happy :thumbsup: