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Post by liteway on Mar 11, 2019 10:02:23 GMT -5
I am wondering what front caster angles the other builders on this forum are using and if they are getting the steering characteristics they wanted or expected by using them.
In researching before construction, not directly quoted here but generalizing:
Bigger caster angles result in better tracking (less wondering) better self centering and higher steering efforts.
One source said higher angles are used with power steered cars because steering effort is not an issue and the other results are mostly good.
In some cases, in racing and in particular formula 1, angles up to 10 degrees are used to promote suspension camber gain in corners.
Production cars generally use 1 to 5 percent.
With this info in mind, I made my front end adjustable for angles between 5 and 9 degrees
I chose about 7.5 degrees to start.
The results are wonder free tracking whether in straight lines or sweeping curves, good self centering with zero corrections needed on good roads such as interstates and acceptable steering effort even at lowest speeds. But: unsatisfactory bump compliance even with springing set soft and with not much penalty for stiffer springing. Poor tracking over roads that feature dips and potholes, especially dips that are not even across the lane.
I did some more research and found that overdoing caster angle can result in ride harshness and a tendency to follow road contour (dips). My shortcomings exactly.
So I'm gonna reduce caster to the minimum I designed in without cutting and welding, 5 degrees, and test as the weather allows. I'll try more toe settings (currently about 3 degrees in) to go along with it.
Of course caster is not the only factor here, other things like scrub radius kingpen axes and trail play their part, but those are locked in with my Can Am spyder geometry, so no reason to fret over that which cannot be changed.
A good starting point might be just use Can Am Spyder spec caster, but that appears to be top secret.
I tried 9 degrees some time ago and did not notice any differences.
I assume the science is the same for reverse trikes as 4 wheeled cars and that may be assuming too much.
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Post by davej98002 on Mar 11, 2019 12:49:55 GMT -5
When some kit car builders that use Mustang II front suspension, they raise the rear mount of the top A arm for Anti Dive during braking. I was told this also helps some with pot hole wander. But I do not have any link to data on this. I think it deals with Kingpin Inclination Angle (KIA) and such. No matter if you use King Pin or Ball joint, they all work off of KIA. Caster is part of KIA. CanAm Spyder's have been well known to have wander issues, the Ryker blogs seem to say the same. I had a 1985 Dodge Omni 2.2 econo box. The car had been in a front end crash and I got it for $250 in 1987. After I peeled the front apart and fixed the frame and body damages it drove and everything fine except it had a bit of bump wander. In diligent testing of the front end alignment, the front end had a split SAI & Included Angle difference left to right by a couple degrees. I had to take the K-member down and slot the holes on the left side and reweld the hole offset so the K-member could slide forward only 3/32 (0.094") inch on the left. Not a lot but was enough.
The original owner said the car always had swerved around on real bumpy roads so the SAI miss-match was from when the car was new.
So I had the front of my Shelby Charger tested and it had a split SAI too and the caster's were real uneven too. So I fixed that K-member too. So in building a front suspension for our trikes we must understand Caster, Camber, KIA, SAI and Toe angles. Get the left A Armes off set from the right by just a bit can cause unwanted effect. This is not a place to be "Horseshoes and Hand Grenades" close, you must be exact in this area or have someone else do it for you.
Above comments are NOT pointed at any one person, these comment are for the whole forum. Get it right or please don't do it. |
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Post by liteway on Mar 11, 2019 14:14:51 GMT -5
Thanks Dave
Indeed my ability to be as precise as necessary given my crude methods is suspect.
But if I have an asymmetric alignment problem, wouldn't that give a tendency to pull to one side or the other, or is that not necessarily the case?
Weather is improving. I'll be going out a little later to see if a slight reduction in caster has made any difference.
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Post by davej98002 on Mar 11, 2019 15:29:27 GMT -5
I posted your question over on Facebooks Reverse Trike forum and this is one answer:
Kurt Betton said "For starters, the assumption of 3 wheel 'science' being the same as 4 wheel, is definitely a bad assumption.
Let's do a simplified force model, assuming an infinitely stiff chassis, and racecar-stiff suspension.
When the right front wheel hits a bump, a rev trike will be inclined to rotate around the other 2 wheels; A 4 wheeler 'resists' this rotation by trying to compress the left rear suspension.
There are many other effects involved (mainly mass inertia & compliance effects), but this is a start in comparing the 2.
That said, many of the steering geometry effects do translate between 3 & 4 wheelers (with the obvious difference that the rear of a trike has zero roll resistance; But in many ways, it's similar to a car with front-heavy weight distribution).
======================
Regarding your specific problem, I have more questions than answers (probably more than you'd be willing to measure/answer at this point. I have no idea if your trike is the 3 wheel equivalent to the Batmobile tumbler, or a 750lbs formula car).
Note: I think you're hoping to solve a compliance issue using geometry. While the two are often related, I think you'll need to separate the two issues (compliance & tracking).
My recommendation: Continue your plan and set yours to 5 deg; See if that is satisfactory enough for you. I expect it will help your tracking issues somewhat, but I doubt your bump compliance will change noticeably. (You may however find bump compliance tolerable if your tracking issues become moot...).
If you still decide to tackle the bump compliance issues later on, make another post and I'll try to help. (A pic of the trike will be a good starting point)."
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Post by liteway on Mar 11, 2019 15:57:41 GMT -5
I think there is some useful info there. Mine is the only trike I have ridden under lots of conditions , or any conditions. There may be things inherent to the configuration, not present with 4 wheels. Anyway, just back from a 30 min test over a mix of roads. There is no change in behavior, maybe the slimmest bit of a step backward. I think there was better self centering on the steering before so I am inclined to go back to the previous setting. The trike seems relatively insensitive to caster changes within its the range of adjustment (5 to 9 degrees). Next step is figure out how to take more accurate measurements of all the suspension parameters or get professional help. Wife says the latter. i.pinimg.com/originals/b5/ae/03/b5ae03829a3a8c356412b482343cecb5.jpgi.pinimg.com/originals/ef/c4/8f/efc48f0cc786d7e8566b9f265d1b31db.jpg |
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Post by davej98002 on Mar 11, 2019 18:03:25 GMT -5
My wife's been saying I need professional help for years now. I may be crazy but I'm not insane. With Insane you get room and board.  What size tires are you running now? I thought 205/60 17's but I'm not sure. |
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Post by liteway on Mar 11, 2019 18:53:41 GMT -5
165/55 14 front 175/55 17 rear
I paid over 300 dollars for the odd sized 17 to be shipped from England and now its near worn out. 195 won't fit.
Dave, I don't know that you will remember but you gave me a much cheaper domestic source for that some time ago.
Ben searching the old forum, but can't find the thread. Ring a bell?
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Post by davej98002 on Mar 11, 2019 23:22:15 GMT -5
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Post by davej98002 on Mar 11, 2019 23:40:00 GMT -5
Another reply from Kurt Betton. I did not understand *wheel* rates. Kurt Betton said "What *wheel* rates have been tried on the front?"David J said "Kurt Betton, He first was running ATV front wheels. But the change to the Spyder front end he is now running 165/55 HR 14 front and 175/55 VR 17 rear."Kurt Betton said "By wheel rate, I mean the *effective* spring rate (factoring in the motion ratio & pushrod angle).
Here's a worksheet containing the formula:eibach.com/us/p-101-suspension-worksheet.html " |
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Post by liteway on Mar 12, 2019 8:19:20 GMT -5
Much thanks for tip on the tires. And free shipping Too. I ordered one immediately.
On the spring rates:
A little history is necessary.
The ATV type shocks/springs were ordered when the trike still had a directly sprung (no bell cranks) atv front end.
They are progressively wound and the rate was determined by the seller after I gave him the loading at each corner. They arrived a bit soft and bottomed a bit too easily, so I requested they exchange for the next incrementally stiffer one available. They did that, no hassle. I felt those springs were perfect as they allowed nearly all the trikes full 5.5 inches of travel to be used (with a bit of preload) without bottoming. Ride quality was not terrific but not bad. I did have to use a lot of preload to try to keep body roll under control.
When I switched to the bell cranks, I experimented with different pushrod mounting points on the cranks to give me the same characteristics, and largely succeeded, preserving the ride qualities but getting far better handling with the addition of the anti-roll bar.
It was when the heavier Spyder related components were substituted that the ride suffered. Its not terrible, just harsher and bouncier than it was. Again I have experimented with different pushrod mounting points on the bell cranks to give me optimal travel without bottoming with minimum preload. I have also tried various effective spring rates (via the bell cranks) with different preloads looking for the best compromises.
I do not believe there is anything to be gained with a change in spring rates.
I believe the doubling of unsprung weight is the culprit. It would be unrealistic to not expect some ride deterioration to go along with that, so I should stop with the complaining. The Spyder parts are heavy vs ATV stuff, but are featherweights compared to what you find on small automobiles. Having said that, my trike is a 200 lbs lighter at the curb than a Spyder, so the ratio of sprung vs unsprung weight for my trike compares unfavorably with a Spyder. I could get a better ride by adding sprung weight, but for me the tradeoff in other performance factors isn't worth it.
Another reason to believe this; I have more travel available, 3.25 " compression, 2.75 rebound than I did with the ATV front end and the bell crank tuning allows taking maximum advantage of that.
I might add that I ran about 27 or 28 lbs of pressure in the 10 inch tires and have wound up with 15 as a suitable compromise for ride/ handling in the 14s.
Another relevant factor. The 10 in wheels were shod with 70 aspect tires and the 14's 55, giving a lot more sidewall to flex, though they were both so lightly loaded this probably doesn't play a big role.
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Post by davej98002 on Mar 12, 2019 14:09:19 GMT -5
I'd have ordered 2 as Potenza's are a soft tread. Plus in 1 year will they still be available? This is always an issue working with a basterdized rim size and a narrow swingarm. There are not a lot of sub 205/35 17 out there. They are mostly Temp Spare tires. They do a good burn out smoke show but suck for street use.
Take my scooter as an example. It came from the factory with a 160/60HR14 in the rear. I run a car tire in the rear between a 155/65 HR 14 to a 165/65 HR 14. But if I wanted to lower my overall gear ratio for drag racing I may just run a tire at 155/55 14 as it is 1.73 inch shorter and my RPM will go up. Fine for the drag strip but not for street cruse's |
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Post by liteway on Mar 12, 2019 15:02:31 GMT -5
My Bridgestone has gone a paltry 6500 miles. Still beats the 4000 miles on the prior 200 dollar motorcycle tire.
Later;
Sorry,
I posted a lot of off topic rambling earlier with some number errors so came back to edit down this latest post to the first sentence.
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Post by firstrike001 on Oct 2, 2020 13:16:14 GMT -5
My Bridgestone has gone a paltry 6500 miles. Still beats the 4000 miles on the prior 200 dollar motorcycle tire. Later; Sorry, I posted a lot of off topic rambling earlier with some number errors so came back to edit down this latest post to the first sentence. Hi Liteway!! Firstof all great trike, awesome implementation. Love your trike. Did you do any further testing to fix the issues you are having? The issues you having with swerving when you hit a bump, is it also called Bumpsteer? |
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Post by liteway on Oct 2, 2020 13:37:07 GMT -5
A short time after my last entry here, I converted the trike to conventional steering and in the process pretty much eliminated stability problems though now there is less self entering and kickback remains an annoyance. In hindsight, I wish I had continued to refine the side stick steering. It's more fun and unusual. I think the stability problems could have solved through stiffer componentry had I not lost patience. reversetrikes.freeforums.net/thread/176/selling-out |
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