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Post by raklor on Aug 18, 2020 13:34:44 GMT -5
Just picked up a 2011 triumph sprint gt with the intent of making a 2-seater ride-in reverse trike. Starting the process of brainstorming and design and trying to come up with best couple options for front suspension.
I'm a bit nervous at the idea of fabricating from scratch a double A-arm setup or anything more exotic. Easiest option seems to be front beam out of the old 60s vw bugs. Are there any other reasonably priced and/or easy to source all in one suspension options that are recommended? Going the vw route makes spindles, steering boxes and modifications on the surface seem comparatively easy vs going from scratch. Any major drawbacks that I am not seeing or good alternatives?
A-arm would be cool but getting the geometry perfect to function well enough at high speeds seems like it could be the biggest challenge in a build.
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Post by davej98002 on Aug 18, 2020 20:07:57 GMT -5
It all comes down to function over form. 90% of people will say that a VW Beam is junk and quote many wifes tales of how bad they are. The same ones will say you must have a full 'Formula 1' front double A arm.
I will be using a VW beam.
How fast top speed are you talking? How many G's are you going to be pulling? I bet I could take a Ford Model A drop axle with King Pins and keep up with a lot of full A Arm Formula 1 type trikes.
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Post by fatherchuck53 on Aug 18, 2020 22:20:51 GMT -5
I'll agree with Dave, not necessarily on the ford, but the VW front system is well proven. And parts are readily available and affordable. My own preference on the VW would be a later ball joint version. Lots of good imfo out there on setting them up. Just be careful , as Dave said you have alot of nasayers
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Post by raklor on Aug 18, 2020 23:39:00 GMT -5
I have no intentions of racing my trike but id like to be able to push it on a fun weekend drive and not end up in a ditch with a wrecked toy. Obviously that could happen with any suspension but I just wanted to make sure I wasnt drastically handcuffing myself by going the tried and true "safe" route of a VW beam since so many seem to point to A-arm. I need to look into cost difference as I am trying to keep my build cost as down. Seems that if I can do the fabrication work A-arm could be cheaper.
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Post by davej98002 on Aug 19, 2020 1:06:11 GMT -5
VW beams in the 1966 and up are out there. But they are not cheap like back in the 1970's. I bought a 1966 drum brake ball joint Karmann Giha beam 4 years ago for $45 but it needs all ball joints and bushings.
Deals can be found. But average will run $150 to $1200 depending on what you want. I do not see the absolute need for disc brakes up front with the light weight of a trike, drums with real good shoes are fine. I have a set of Simi-metalic shoes for mine. I have some mods that I can share if you go VW. One of the easy mods is to remove the center height adjusters and cut the top tube inboard of the swingarms bushing, then mounting two inboard Coil over shocks. Then the bottom leaf spring can be made into the anti-sway bar. And setting one up to work well is on the 'Formula Vee' forums. These race cars are very fast.
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Post by noahkatz on Sept 5, 2020 17:25:59 GMT -5
IMO the biggest downside to VW front suspension is the weight.
Based on my memory of my brother's '74 bug that I used while he was on vacation, they work quite well; firm but compliant, pretty direct feeling steering, and precise handling.
Dave, in the first picture above, is that huge angle of the steering arms stock?
Looks like it would have awful bump steer.
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Post by davej98002 on Sept 5, 2020 21:25:23 GMT -5
The VW stock tie rod angles are steeper. On the US left steering wheel the steering box is way left with a short shaft to the left wheel and a longer to the right wheel.
The control arms on a VW swing differently than a double A Arm angle. That is why the tie rod angle is sharper.
Once you remove all the stuff not needed on a VW beam they can be lighter somewhat.
The 50's thru 1965 are King Pin and are OK but a lot of work. The 1966 up is Ball Joint and easier to adjust.
Stay away from the aluminum ones as they are prone to flex cracking from what I'v read.
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Post by noahkatz on Sept 7, 2020 22:53:25 GMT -5
> The control arms on a VW swing differently than a double A Arm angle.
Yes, the move vertically because of the pure trailing arms.
Therefore any lateral movement of the steering arm ends will give bump steer, and the steeper their angle, the worse it will be.
I just googled and apparently it is an issue, at least for stock.
This shows how to get zero bump steer
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Post by liteway on Sept 8, 2020 14:43:38 GMT -5
So that's how those work. Always wondered.
Still don't see how it could camber properly in a turn to keep the patch flat on the road. No advantage for a wider tire. I would guess the formula V types are so stiff that travel is limited anyway. A humongous anti-roll bar might be a good idea.
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Post by fatherchuck53 on Sept 8, 2020 22:20:15 GMT -5
It almost sounds like you are trying to talk yourself out of the VW front end. Sure they don't have the cool factor, and they are a very old design. Yes, they do suffer from bump steer on beetles and dune buggies. You're more then likely not going to be hitting big bumps frequently. A-arm setups can be had fairly cheap as used on the locost style cars. I would look spend some time checking out a couple of their forums. very helpful people and lots of experience with high speed light weight road race cars. And most are hand build by normal people.
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Post by fatherchuck53 on Sept 8, 2020 22:27:16 GMT -5
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Post by noahkatz on Sept 10, 2020 13:52:09 GMT -5
Further enlightening comments on Bug bump steer from www.eng-tips.com/viewthread.cfm?qid=378451 : "Understand the steering geometry, too. Note that the steering box is off-center in the car. You might think this gives unequal geometry and bump steer - but it doesn't. The steering box is ahead of the tie-rod connection to the steering knuckles in the same relationship as the trailing arms. In side view, the arc is the same. No bump steer even though the left and right tie-rods aren't the same length." The rest of the thread is very interesting too. |
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Post by davej98002 on Sept 10, 2020 15:34:52 GMT -5
Noah, where folks get into trouble is when they change the position of the steering box/rack. They can not dial out the added bump steer so "VW Beam steering is CRAP" comes out.
Are they perfect? NO!!!!
They are simple and work well for a simi sport vehicle.
You should NEVER use one on a race trike. But of all the members on here, how many are driving their trikes at 1.2G all day? Even 0.85G?
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Post by noahkatz on Sept 11, 2020 1:12:06 GMT -5
> Noah, where folks get into trouble is when they change the position of the steering box/rack. They can not dial out the added bump steer so "VW Beam steering is CRAP" comes out. Ah. > You should NEVER use one on a race trike. You mean not if you want to win, right? Seems like it's not a safety issue, as no camber control just means more understeer. |
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Post by liteway on Sept 11, 2020 7:30:23 GMT -5
> Noah, where folks get into trouble is when they change the position of the steering box/rack. They can not dial out the added bump steer so "VW Beam steering is CRAP" comes out. Ah. > You should NEVER use one on a race trike. You mean not if you want to win, right? Seems like it's not a safety issue, as no camber control just means more understeer. Guess it matched up ok with the old bugs rear, which also had unusual camber characteristics. The ends competed to be the first to come unglued. The rear usually won because that was where the weight was. If it didn't tip over first. Of course I could be wrong and often am, but I think it's not a good choice for R.Ts as they are already prone to plenty of understeer because of all the roll stiffness much of the mass being up front. I do not think it would take particularly spirited driving for the understeer to show itself to be a damper on handling satisfaction. Just my opinion. |
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Post by noahkatz on Sept 11, 2020 14:27:33 GMT -5
For sure, RT's don't need more understeer.
I probably misconstrued your statement as implying that it would be dangerous.
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Post by davej98002 on Sept 11, 2020 16:20:37 GMT -5
A VW can be adjusted. You use caster shims, curved plates of different thickness.
Then Camber is adjusted by eccentric buckets on the top ball joint or using off set king pins.
Here is the layout of a stock beam
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Post by davej98002 on Sept 11, 2020 16:31:31 GMT -5
Again, if you are going to just jump in the trike and go for a day ride up in the mountains and there are some nice twisty curves, a VW beam will work just fine. I'd even do the "Tail of the Dragon" with a trike on a VW Beam front. If you are going to AUTOCROSS it then NO. If you are going to do TRACK DAYS then NO again.
Set your designed use limits and build accordingly.
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Post by todde13 on Dec 20, 2020 15:54:09 GMT -5
Dave: This mod is very intriguing to me. Would you be able to provide more detailed instructions on how to do it? VW beams in the 1966 and up are out there. But they are not cheap like back in the 1970's. I bought a 1966 drum brake ball joint Karmann Giha beam 4 years ago for $45 but it needs all ball joints and bushings.
Deals can be found. But average will run $150 to $1200 depending on what you want. I do not see the absolute need for disc brakes up front with the light weight of a trike, drums with real good shoes are fine. I have a set of Simi-metalic shoes for mine. I have some mods that I can share if you go VW. One of the easy mods is to remove the center height adjusters and cut the top tube inboard of the swingarms bushing, then mounting two inboard Coil over shocks. Then the bottom leaf spring can be made into the anti-sway bar. And setting one up to work well is on the 'Formula Vee' forums. These race cars are very fast.
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