Benefits of different A Arm options...

[Metal_man_Rob]

I bought american star A Arms and don't have an issue with them other than having to disassemble the front end to make any castor adjustments. 

What are the benefits of other A Arms? Mine are standard travel +2+1 and have no real reason to go with long travel. Roll Design and Lone Star make better looking arms but are there other benefits other than build quality?

[tfaith08]

I bought american star A Arms and don't have an issue with them other than having to disassemble the front end to make any castor adjustments. 
What are the benefits of other A Arms? Mine are standard travel +2+1 and have no real reason to go with long travel. Roll Design and Lone Star make better looking arms but are there other benefits other than build quality?

Build quality and hardware quality.

I’d personally figure out what your caster should be and just leave it. When it’s time to replace the hardware, order FK rod ends.

Give me your ride height and swingarm length and I’ll tell you what it should be.


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[Metal_man_Rob]

Build quality and hardware quality.

I’d personally figure out what your caster should be and just leave it. When it’s time to replace the hardware, order FK rod ends.

Give me your ride height and swingarm length and I’ll tell you what it should be.


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My ride height is 10 1/4 and swing arm is stock length. +2+1 A arms. I have the caster set at 4.5 now and like it in tight trails but it is horrible on anything more open.
Have gone back and forth with caster and just went back to 4.5 for now.
Been working on the kids’ LT80s lately and haven’t had a chance to get back to the banshee.
I have a higher ride height but with some of the trails I ride it works awesome.

I think I need a better method of measuring caster angle. Hard to get any angle finders and straight edges in there to go off of.

Everything else in the suspension write up was easy enough to understand and execute.


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[tfaith08]

My ride height is 10 1/4 and swing arm is stock length. +2+1 A arms. I have the caster set at 4.5 now and like it in tight trails but it is horrible on anything more open.
Have gone back and forth with caster and just went back to 4.5 for now.
Been working on the kids’ LT80s lately and haven’t had a chance to get back to the banshee.
I have a higher ride height but with some of the trails I ride it works awesome.

I think I need a better method of measuring caster angle. Hard to get any angle finders and straight edges in there to go off of.

Everything else in the suspension write up was easy enough to understand and execute.


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10-1/4” with you on it?

The bump steer you’ll run into is going to make that rough.

Generally, you want to set your ride height for the terrain and then bias it toward the center of the bump steer curve. That takes a ton of work to sort out in some cases but isn’t a total nightmare.

I’d personally never run 10-1/4” unless I was in the 15” vertical travel range or more.

You get into something called full dynamic load, which is where you’re under the most extreme dive you’ll experience under braking. At that point, you want a no shit minimum of 1 degree of caster. Once you have that set, you let your caster be whatever it is at ride height.

The trick with caster is basically a matter of two things:

A. How it plays with KPI on the outside tire and affects camber

B. Trail (what we’ll talk about here)

To find trail, look at the quad from the side. Then draw a line through your ball joints and extend it to the ground. The distance from that point to the center of your contact patch is trail. The more trail, the more the quad wants to track straight ahead. This does play with toe to a significant extent but how toe pertains to trail and scrub radius is immensely complicated without diving into the math.

Now that you can see trail, you may also be able to visualize how trail reduces on dive and increases on droop, as well as how trail drops when you hit a bump and increases off the face of the bump.

Back to full dynamic load, you can see that caster approaches the vertical plane as you hit a full dive. One of your few hard rules in suspension geometry is that caster should never go past vertical.

So the correct way to set caster is to work from full dynamic load.

I’ll help more when I’m not fighting sleep and can contribute more, but you’ll be giving up more than you gain with a ride height that high for the width you’re at.


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[Metal_man_Rob]

10-1/4” with you on it?

The bump steer you’ll run into is going to make that rough.

Generally, you want to set your ride height for the terrain and then bias it toward the center of the bump steer curve. That takes a ton of work to sort out in some cases but isn’t a total nightmare.

I’d personally never run 10-1/4” unless I was in the 15” vertical travel range or more.

You get into something called full dynamic load, which is where you’re under the most extreme dive you’ll experience under braking. At that point, you want a no shit minimum of 1 degree of caster. Once you have that set, you let your caster be whatever it is at ride height.

The trick with caster is basically a matter of two things:

A. How it plays with KPI on the outside tire and affects camber

B. Trail (what we’ll talk about here)

To find trail, look at the quad from the side. Then draw a line through your ball joints and extend it to the ground. The distance from that point to the center of your contact patch is trail. The more trail, the more the quad wants to track straight ahead. This does play with toe to a significant extent but how toe pertains to trail and scrub radius is immensely complicated without diving into the math.

Now that you can see trail, you may also be able to visualize how trail reduces on dive and increases on droop, as well as how trail drops when you hit a bump and increases off the face of the bump.

Back to full dynamic load, you can see that caster approaches the vertical plane as you hit a full dive. One of your few hard rules in suspension geometry is that caster should never go past vertical.

So the correct way to set caster is to work from full dynamic load.

I’ll help more when I’m not fighting sleep and can contribute more, but you’ll be giving up more than you gain with a ride height that high for the width you’re at.


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When I measured my ride height I wasn’t on the quad. So I will have to remeasure it. I have Elka stage 2 in the front made for the a arms, tire size and my weight. I actually did do the leverage ratio calculations you described in your suspension thread and sent that with the order.
The ride is actually way more smooth than stock and maybe even a little smoother than the YFZ450 but that is a 10 year old quad.

I will remeasure my ride height and go back through all of my measurements and post that again.


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[tfaith08]

When I measured my ride height I wasn’t on the quad. So I will have to remeasure it. I have Elka stage 2 in the front made for the a arms, tire size and my weight. I actually did do the leverage ratio calculations you described in your suspension thread and sent that with the order.
The ride is actually way more smooth than stock and maybe even a little smoother than the YFZ450 but that is a 10 year old quad.

I will remeasure my ride height and go back through all of my measurements and post that again.


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Get that back to me if you will.

To find target caster, see below:

C = caster in degrees
RH = ride height
MC = minimum ground clearance (usually 1.75”
UT = up travel (RH-MC)
WB = wheelbase
R = rake in degrees

SinC = UT/(WB-{UT x sinR})

For smooth terrain, subtract 2 degrees
For normal terrain, subtract a degree
For lower tire pressures, add a degree

Stock wheelbase and 7.25” ride height gives a caster target of 6.92

Stock WB and 7” RH gives 6.63

+1 WB and 7.25” RH gives 6.78

+1 WB and 7” RH gives 6.49

I also don’t know what swingarm you’re running but a +4 is common. Paired with +1 forward arms and a 7” ride height, you get 6 degrees of caster.

Ride height, rough terrain, and softer tires dictate caster requirement.


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[Metal_man_Rob]

Get that back to me if you will.

To find target caster, see below:

C = caster in degrees
RH = ride height
MC = minimum ground clearance (usually 1.75”
UT = up travel (RH-MC)
WB = wheelbase
R = rake in degrees

SinC = UT/(WB-{UT x sinR})

For smooth terrain, subtract 2 degrees
For normal terrain, subtract a degree
For lower tire pressures, add a degree

Stock wheelbase and 7.25” ride height gives a caster target of 6.92

Stock WB and 7” RH gives 6.63

+1 WB and 7.25” RH gives 6.78

+1 WB and 7” RH gives 6.49

I also don’t know what swingarm you’re running but a +4 is common. Paired with +1 forward arms and a 7” ride height, you get 6 degrees of caster.

Ride height, rough terrain, and softer tires dictate caster requirement.


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Ok my ride height is pretty much exactly 9 inches.
My swing arm is stock length and I have a +1 wheelbase.

I have 23” Front tires and 22” rear. I do ride through moderate to rough trails almost exclusively. It handles way better than it did stock and is a smoother ride. But I know it can be better.

The handling has been great for the woods. Predictable, sharp and no where near as demanding. The open portions of trail or class 6 roads are where the quad wants to wander at speeds above 30mph.

So I am not sure what my MC is with the larger tires or how I would measure that.
And what does Rake refer to. I can find the sine of any of the angle but need to know how rake is measured. My Google search results in attachments used for raking lawns. But considering the rake on a motorcycle would I be correct in assuming it is the angle of the steering stem from perpendicularly to the ground?

One more question on measuring: What method do you use for measuring caster? I have just used an angle finding spirit level (really shitty for any accuracy beyond 2 degrees) and a straight edge against the outside of the ball joints. With that it’s nothing more of an eyeball job not to measure some degree of a compound angle. So I say my caster is set to 4.5 when in actuality I don’t know what it really is.

Anyway, I appreciate all of this.


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[kawa110]

Attempting to align some fireball arms soon. I have two sets one bike for dune/play. The other for desert race/district37-38 ama.
To many adjustments


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[tfaith08]

Ok my ride height is pretty much exactly 9 inches.
My swing arm is stock length and I have a +1 wheelbase.

I have 23” Front tires and 22” rear. I do ride through moderate to rough trails almost exclusively. It handles way better than it did stock and is a smoother ride. But I know it can be better.

The handling has been great for the woods. Predictable, sharp and no where near as demanding. The open portions of trail or class 6 roads are where the quad wants to wander at speeds above 30mph.

So I am not sure what my MC is with the larger tires or how I would measure that.
And what does Rake refer to. I can find the sine of any of the angle but need to know how rake is measured. My Google search results in attachments used for raking lawns. But considering the rake on a motorcycle would I be correct in assuming it is the angle of the steering stem from perpendicularly to the ground?

One more question on measuring: What method do you use for measuring caster? I have just used an angle finding spirit level (really shitty for any accuracy beyond 2 degrees) and a straight edge against the outside of the ball joints. With that it’s nothing more of an eyeball job not to measure some degree of a compound angle. So I say my caster is set to 4.5 when in actuality I don’t know what it really is.

Anyway, I appreciate all of this.


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9” ride height is kind of pushing it imo.

Rake is the angle that the lower arms mount to the frame at when viewed from the side.

It farting side to side suggests either a camber or toe issue. I’m personally leaning toward toe die to bump steer.

Are you setting toe at ride height?

With an arm angle that’s too steep, any side forces on the tire can compress or extend the suspension. This is compounded by taller tires but the effect is more sluggish.

I’d personally bump it down to around 8 but that’s just me. A lot of the pro XC guys are 7.5-8.25 in the front.

Also, where are you measuring the ride height?

Minimum clearance is usually a result of tire compressibility and terrain. Smooth MX and TT/FT can get away with 1.25-1.5” minimum ground clearance and most others require around 1.75”. For desert racing, 2” is a good number.

As for measuring caster, there are a few details. As long as you’re at ride height or the lower frame rails are parallel to where they are at ride height, you can set the caster accurately.

Make sure the tire is dead straight ahead. You don’t want to factor toe in for this, so set the tire straight and not the bars. If you mistakenly factor toe in, you’ll be measuring KPI as well.

After that, line the lug nuts up with the ball joints and measure there. Throw a zip tie around the brake lever to help hold it. Then just an angle finder or a ruler and spirit level with some trig.

Be wary of anything that isn’t a dedicated angle finder. I’ve got a solid dozen spirit levels with a rotating bubble for angles and every one of them read differently. One is as much as 3 degrees off. Empire is usually the closest if you must use it.


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[tfaith08]

Attempting to align some fireball arms soon. I have two sets one bike for dune/play. The other for desert race/district37-38 ama.
To many adjustments


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Use some blocks and hold off on installing the shocks and youl save a lot of time with alignment.


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[Metal_man_Rob]

9” ride height is kind of pushing it imo.

Rake is the angle that the lower arms mount to the frame at when viewed from the side.

It farting side to side suggests either a camber or toe issue. I’m personally leaning toward toe die to bump steer.

Are you setting toe at ride height?

With an arm angle that’s too steep, any side forces on the tire can compress or extend the suspension. This is compounded by taller tires but the effect is more sluggish.

I’d personally bump it down to around 8 but that’s just me. A lot of the pro XC guys are 7.5-8.25 in the front.

Also, where are you measuring the ride height?

Minimum clearance is usually a result of tire compressibility and terrain. Smooth MX and TT/FT can get away with 1.25-1.5” minimum ground clearance and most others require around 1.75”. For desert racing, 2” is a good number.

As for measuring caster, there are a few details. As long as you’re at ride height or the lower frame rails are parallel to where they are at ride height, you can set the caster accurately.

Make sure the tire is dead straight ahead. You don’t want to factor toe in for this, so set the tire straight and not the bars. If you mistakenly factor toe in, you’ll be measuring KPI as well.

After that, line the lug nuts up with the ball joints and measure there. Throw a zip tie around the brake lever to help hold it. Then just an angle finder or a ruler and spirit level with some trig.

Be wary of anything that isn’t a dedicated angle finder. I’ve got a solid dozen spirit levels with a rotating bubble for angles and every one of them read differently. One is as much as 3 degrees off. Empire is usually the closest if you must use it.


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You are awesome! Thanks!

Elka made the front shocks for me based on the tire size, my weight, primary terrain and riding style and a arms. I could drop the tire size back down to 21 front and 20 rear but the riding I do makes having that added clearance an ass saver at times.

I cross a lot of streams, lots of rock gardens, really rough terrain, etc that even the 4x4 guys don’t do. I have never stuck the Banshee.

I opted for the wider stance for the stability at a higher ride height. Well, at the time I wasn’t thinking ride height but ground clearance.

Many people have mentioned that where I ride was not what the banshee was intended for but I have a lot of fun with it and love 2 strokes. And then on mellower trails it fun to wind it out.

I did not set the toe at ride height. Now that I discovered that my oldest boy weighs as much as me, everything can be done at ride height. Haha.

I do have real angle finders at work. I’ll just bring one home. Those are accurate within a few minutes. I like your idea of lining the lugs up with the ball joints and doing it that way.

When I measured my KPI a couple of months ago (I’ve been trying to use your set up guide to wrap my head around the suspension) the KPI was pretty much dead nuts centered. But I could be measuring that wrong too. It seems like, if the A Arms are manufactured with the intended KPI to remain the same as stock using the OEM tire size, my KPI would fall outside of center with the larger tires.

Either way, I appreciate your help!


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[Metal_man_Rob]

Oh yeah, I measure the ride height from right in front of the pegs. And right behind the A Arms before the slight upward bend in the frame.


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[tfaith08]

You are awesome! Thanks!

Elka made the front shocks for me based on the tire size, my weight, primary terrain and riding style and a arms. I could drop the tire size back down to 21 front and 20 rear but the riding I do makes having that added clearance an ass saver at times.

I cross a lot of streams, lots of rock gardens, really rough terrain, etc that even the 4x4 guys don’t do. I have never stuck the Banshee.

I opted for the wider stance for the stability at a higher ride height. Well, at the time I wasn’t thinking ride height but ground clearance.

Many people have mentioned that where I ride was not what the banshee was intended for but I have a lot of fun with it and love 2 strokes. And then on mellower trails it fun to wind it out.

I did not set the toe at ride height. Now that I discovered that my oldest boy weighs as much as me, everything can be done at ride height. Haha.

I do have real angle finders at work. I’ll just bring one home. Those are accurate within a few minutes. I like your idea of lining the lugs up with the ball joints and doing it that way.

When I measured my KPI a couple of months ago (I’ve been trying to use your set up guide to wrap my head around the suspension) the KPI was pretty much dead nuts centered. But I could be measuring that wrong too. It seems like, if the A Arms are manufactured with the intended KPI to remain the same as stock using the OEM tire size, my KPI would fall outside of center with the larger tires.

Either way, I appreciate your help!


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If the tires you have now are working, I say stick with them. Any suspension setup should be done starting with the tire anyway. I just personally don’t like the ride height that high because of how it rides in more technical high speed settings.

The KPI is typically geared around getting the scrub radius to the target with the stock tire size. However, adding caster will increase scrub radius as well. This is where it gets extremely hard to visualize, especially without drawings of some sort.

I don’t know the math off the top of my head for it, let me see if I can figure it out really quick and get back to you.


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[tfaith08]

The formula is essentially how to find the distance from the center of the tire to the steering pivot (KPI, Caster, and camber) AT WHEEL VERTICAL CENTER. It’s only real utility

It’s pretty useless outside of comparing numbers unless you take the time to measure effective offsets vs. tire heights.

Either way, it’s as follows:

IA = KPI + camber in degrees
C = Caster
TRH = tire center rolling height

TRH x sec C x sin IA

Tire center rolling height is rollout while loaded on the quad divided by 2pi. This eliminates any effects due to tires compressing under load. Since we haven’t measured that, we’ll just call it half the tire diameter.

I don’t know the KPI of a stock banshee off the top of my head but a YFZR is 15.3. Add in 2 degrees of camber and 6 degrees of caster with a 21” tire and you get this:

10.5 x sec 6 x sin 17.3 = 3.141”

Compare that to a 23” tire and 3 degrees of camber and 7 degrees of caster:

11.5 x sec 7 x sin 18.3 = 3.638”

This means that when switching those setups around and using the same offset rim, your scrub radius has moved by .497”

You still have to plot it out and take accurate measurements, but it just goes to show that not everything is as simple as face value. This is why it is often the case that another PSI in the front tires and another degree of camber can sometimes amount to nothing and sometimes completely wake a front end up.

Getting your scrub radius as close to zero as possible is easily the biggest bang for your buck improvement on a front end.


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[Metal_man_Rob]

The formula is essentially how to find the distance from the center of the tire to the steering pivot (KPI, Caster, and camber) AT WHEEL VERTICAL CENTER. It’s only real utility

It’s pretty useless outside of comparing numbers unless you take the time to measure effective offsets vs. tire heights.

Either way, it’s as follows:

IA = KPI + camber in degrees
C = Caster
TRH = tire center rolling height

TRH x sec C x sin IA

Tire center rolling height is rollout while loaded on the quad divided by 2pi. This eliminates any effects due to tires compressing under load. Since we haven’t measured that, we’ll just call it half the tire diameter.

I don’t know the KPI of a stock banshee off the top of my head but a YFZR is 15.3. Add in 2 degrees of camber and 6 degrees of caster with a 21” tire and you get this:

10.5 x sec 6 x sin 17.3 = 3.141”

Compare that to a 23” tire and 3 degrees of camber and 7 degrees of caster:

11.5 x sec 7 x sin 18.3 = 3.638”

This means that when switching those setups around and using the same offset rim, your scrub radius has moved by .497”

You still have to plot it out and take accurate measurements, but it just goes to show that not everything is as simple as face value. This is why it is often the case that another PSI in the front tires and another degree of camber can sometimes amount to nothing and sometimes completely wake a front end up.

Getting your scrub radius as close to zero as possible is easily the biggest bang for your buck improvement on a front end.


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I just checked the scrub radius again and it really does seem the KPI is dead center. It totally makes sense, the different points of adjustment. I haven’t trigged everything out yet but with your write up and this thread, I am pretty confident I can make a decent project out of it.

A lot of people seem to give up and convert their entire quad back to OEM or retrofit front ends from other quads. I’d rather set it up with what I have for a couple of reasons. Main reason: I already spent the money. But I’d like to know I can do it.

I’m a tool and die maker so the math makes sense to me as well as picturing the results of certain adjustments.

I appreciate all your help and time!


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