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Post by noahkatz on May 14, 2016 12:50:17 GMT -5
Right, I still don't understand what ride quality has to do with roll center.
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Post by captainamerica on May 14, 2016 19:41:57 GMT -5
Alright so I read Joker's question awhile back and didn't really have a good grasp on it, not sure if I do now but it seems to have generated some controversy. My comment would be that while you could make the roll "zero" by putting the roll center on top of the CG, you could also just reduce roll by using an anti-roll bar, want no roll, use a really stiff one. The bar at the front of the Spartan is way to strong but I can tell you that there is almost no roll in that vehicle. I really don't see the benefit to trying to design out the roll of the vehicle completely by moving the roll center, your camber curves would go to Poop I expect among other things. All of that said, ride quality is quite a subjective idea, someone might drive an indy car down a normal road and think that its way to stiff any time it hits a pot hole or bump, yet that same car on a speedway might handle like a dream yet they are the same car. So handling is more important relative to the roads you will be driving, I realize that roll in a trike causes loss of rear wheel contact patch if your using a car tire, but tires especially at lower pressures can handle "camber" and still keep a reasonable contact patch. So I think if you just limit your roll using an anti-roll bar you will find what you are looking for without compromising your suspension design all for one parameter.
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Post by DaveJ98092 on May 14, 2016 21:51:15 GMT -5
A roll (SWAY) bar of the correct size will work like Andrew said. It makes suspension design a bit easier. The (slight) problem with roll bars is it also limits a independent suspensions independence some what, but do you really need true 100% independent suspension?
I had a Chevy 3500HD dually truck with a SOLID I beam front axle and Kingpins, not ball joints. It would corner with almost any non sports cars in corners. My son had a 85 Toyota SR5 4X4 pickup that had a solid differential axle up front. One day his his Autocross car broke at the track and he asked if he could take the pickup out and give it a run JUST to see. It was in the middle of the slow class of CARs as far as time.
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Post by endeavor on May 15, 2016 6:25:20 GMT -5
You are correct in the assumption an anti-roll bar of sufficient heft would zero out the roll nicely. It would also limit the independance in the suspension. However there are substantial differences between a 4 wheel vehicle and these tadpole designs as far as suspension and cornering dynamics. On a 4 wheel vehicle you can tune your handling and ride characteristics both front and rear. You would be running anti-roll on both ends and 4 wheeler tends to run down the road fairly flat while the individual wheels move quite independently. On a trike things are slightly different as there is not sway stability on the rear as the rear wheel acts as a hinge allowing movement without resistance. All the tuning, anti sway roll center etc is totally up to the front end geometry. Trikes also do something which I call waddle. where the trike body tends to rotate as the wheels encounter bumps as there is not any resistance in the rear to offset this action. Even with soft roll bar and soft suspension this waddle will occur. One does acclimate to this however quite quickly but a newbie tends to feel the trike is moving laterally or dodging sideways when in fact it is just the waddle that offers the illusion of lateral movement. So in general I believe a stiff anti-sway is a good idea as it solves some problems and only slightly exaggerates others.
I am open to other opinions I have done 180's on ideas many times.
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Post by Liteway on May 15, 2016 8:36:27 GMT -5
You make some good points I have not seen expressed here before, pointing out there are trade-offs with a thick anti-roll bar, that simply making it super thick may not give the best overall result, there are always compromises to be made.
I would point out the "waddle" will be less apparent the lower the driver is located in the chassis, so its more of a problem with a sit astride trike.
4 wheel road testers sometimes refer to it as "head toss" which tends to be more apparent in high sitting suvs and pickup trucks, particularly if they are stiffly sprung.
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Post by endeavor on May 15, 2016 8:50:50 GMT -5
Yes I tend to forget most of the builds here are low slung and mine tend to focus more on the higher riding position. Good point. Yet the theory is the same just the perception differs.
One other aspect I have run accross which may or maynot be of interest. Because I don't run idlers on the tie rods the rods are a one piece unit. obviously this poses a small problem as the tie rod arc and A-arm arcs do not coincide. During body roll if the center mount on the steering shaft is higher than the balljoint to tie rod mount on the wheel the trike will tend to overcompensate for lean and drift by toeing in so you end up with an oscillation due to this aspect and the rider also trying to overcompensate. I found that in lowing the center mount position I can effectively slow down this oscillation to a controllable almost unnoticeable amount. For instance my tie rod to ball joint measure is 5" and my steering mount is 1" less so when there is roll the wheels actually toe out just a degree or so softening the drift to a very gradual amount. Raising the mount would cause the old Burt Munro 190mph head shake.
The theory is much the same as cargo ships vs passenger cruise liners. A cargo ship rides low in the water so it is very stable and will resist tip over in heavy seas however the rocking motion will be fierce and quick. A cruise ship rides high so these oscillations are gradual and soft, the purpose is to lessen the likelihood for motion sickness.
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Post by endeavor on May 16, 2016 22:51:33 GMT -5
OK I finished the latest build tonight. The top A-arm hinge was dropped 1-1/2" in hopes of altering the roll center. While I am sure it worked (the math would support this) I am unable to honestly comment. If all I did was make this change then I could voice an honest opinion however I also changed the A-arm design, shock mounts and even the shock length and the swaybar. With all these changes I can't commit to a report. All I will say is things are good and didn't get worse. The bike handled great before and does now. You can see the A-arm stance here along with the anti-sway setup - the sway bar was also changed with this build. Camber is set to zero, Caster 8 degrees positive and toe 1/4" positive. Tire pressure is 17psi.  Sideview just for reference. Also a good view of the powercoated items  |
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Post by mtntech on May 17, 2016 9:02:26 GMT -5
Your tire pressure is interesting. I have been experimenting with lower pressures as well.
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Post by endeavor on May 17, 2016 9:09:09 GMT -5
BRP recommends 12.5 to 17psi on all the Spyders, of course most people (curbside engineers) are running 25 to 32psi as they can't seem to live with such low air pressure. The end result is a poor handling machine and tire mileage in the 8-9k range. The unit pictured has 22k on the tires and I fully expect 50k min.
A slightly higher pressure may be good for all out racing if you can control the bounce however in general tire patch is a result of air pressure vs applied weight.
At least this has been my findings regarding the matter.
One thing you may notice is the grill is pretty open so what air doesn't go around can pass through this reduces the forward pressure area and aids in high speed control and efficiency.
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Post by Liteway on May 17, 2016 17:19:45 GMT -5
I am struck by how much mass appears near, over the top or even behind the rear tire. Thats even before accounting for the mass of the driver, the high perched passenger and luggage seeming everywhere but where it might help balance. Track is not very wide. This will slide before it tips?
I will concede looks can be deceiving, but it looks unstable.
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Post by endeavor on May 17, 2016 21:00:02 GMT -5
It is surprisingly stable and you are right looks are deceiving but the mass is all plastic the heavy materials are at axle height so even with a passenger it will slide before lifting a wheel. Keep in mind each front wheel also weights about 65lbs due to the heavy rotors and calipers (Chevy II) That really keeps the wheels planted.
I had some handling issues today and realize I was in a hurry and forgot to tighten the steering shaft lower bearing mounts so I had substantial play in the bars. Snugged her up tonight and it really handles well. Can't commit for sure but it appears there is slightly less lean so maybe the A-arm change did work OK.
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Post by mtntech on May 18, 2016 8:05:10 GMT -5
What is the weight of your completed trikes?
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Post by endeavor on May 18, 2016 8:59:48 GMT -5
The kit adds 140lbs to the base machine most of that is in the wheels which does sort of defy standard suspension ideals however it also greatly aids in stability as the wheels act as ballast weights. This was something unplanned and just happened due to product choice. This is also the reason my trikes are rated higher than CanAm in cornering tests as the CA will tip without VSS where mine stay planted. It has little affect on actual suspension dynamics mainly due to the low inflation rates. Tires being the primary suspension component.
Weight seems to be a concern mainly due to auto advertisers promising better fuel economy with less weight however this mostly applies to stop an d go as you well know the main fuel robber is not weight but air resistance. This is why autocycles like Elio can claim 80+ mpg. It is something I see here and on other RT forums is the desire to build in a streamlined body shell - it's a good plan.
The GL1800 which is the heaviest bike around comes in at +- 1100lbs complete after the build
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Post by Liteway on May 22, 2016 13:32:34 GMT -5
The kit adds 140lbs to the base machine most of that is in the wheels which does sort of defy standard suspension ideals however it also greatly aids in stability as the wheels act as ballast weights. This was something unplanned and just happened due to product choice. This is also the reason my trikes are rated higher than CanAm in cornering tests as the CA will tip without VSS where mine stay planted. It has little affect on actual suspension dynamics mainly due to the low inflation rates. Tires being the primary suspension component. Weight seems to be a concern mainly due to auto advertisers promising better fuel economy with less weight however this mostly applies to stop an d go as you well know the main fuel robber is not weight but air resistance. This is why autocycles like Elio can claim 80+ mpg. It is something I see here and on other RT forums is the desire to build in a streamlined body shell - it's a good plan. The GL1800 which is the heaviest bike around comes in at +- 1100lbs complete after the build Your take on the effects of low tire inflation are certainly unconventional, and it's an interesting topic that I do not recall having been taken up elsewhere in the forum, despite it having a big influence on chassis behavior. Thanks for bringing it up for discussion. I had mostly assumed, based on what I thought I knew, that the best inflation for dry tarmac was largely just a compromise with the ride harshness to be endured vs all other aspects of performance, that the flexible sidewalls that resulted from low inflation gave a cushier ride at the expense of greater rolling resistance and tread stability which in turn resulted in soggy handling, rapid uneven tread wear and increased fuel consumption. Based on that and the low tire loads imposed on my very lightweight trike I rather arbitrarily selected 27/32 psi as my normal inflation. Not very scientific of me, but those inflation pressures left me little to complain about the trikes handling, though it does ride a bit harsh, and the rear is a little loose under heavy throttle in tighter corners. I put tire pressures out of my mind and concentrated on other suspension tuning methods. So now I read your take, and I was finally inspired to do serious testing of juggling pressures while every thing else remains the same. Thanks for a fun afternoon, as I repeatedly returned to my favorite series of local tight turns to check the effects of the incremental changes. 16/28 psi. (as compared to my normal 27/32) Handling slightly more sluggish, with slower turn-in and much higher effort required, particularly noticeable at parking lot speeds. In really pushing it through the turns, more body roll was apparent with a tendency to run wide through the corner (understeer) and slip at lesser speeds. The ride did improve by not so much as I expected. I would attribute that the trikes very low unsprung weight which allows the wheels to follow the bumps without asking for so much compliance from the tires. The tire/ wheel assembly weighs 14 lbs as opposed to your typical aluminum wheeled compact which is about 3 times that. I also have aluminum hubs and calipers along with small discs. 32/38 Not much change from 27/32 with ride and front end behavior about the same but with a bit better responsiveness. The biggest difference came at the rear where it stays better planted coming out of the corners with noticeably less wheel spin. As for wear at the front with 10K of aggressive driving, I Don't have enough to project their ultimate life, but they already show a bit of weather cracking after 10yrs so that will be the reason they will ultimately have to be replaced. I am hoping the discovery that the back tire spins less in tight corners with higher pressures will extend its life a bit as it is wearing pretty fast. |
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Post by endeavor on May 22, 2016 14:37:13 GMT -5
I can only speak of my own discoveries related to my specific configuration so you are right to assume the best fit will be one you devise. Part of the difference may be in rim type as I am running 6.5 inch wide rims with a narrow 165x60x15 tire so they are overstretched. This offers more lateral control. I am currently running into some mishandling issues with bikes that have the narrow 3" wide rear rim as I have to run a 175x70 tire which is just the opposite. That configuration causes a lost of side to side movement so the trike tends to jiggle from side to side especially in windy condition. Unless I can find a stiff wall tire like a run flat in the correct size I may have to go to a MC tire on the rear on those bikes. Most of the large asian tour bikes run a 5.5 inch rim on the rear so a standard 205 tire works very well with minimal side drift.
What I found on front tires is anything over 20psi causes tire bounce and center wear so lower works for my setup pretty well.
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Post by Liteway on May 22, 2016 18:13:06 GMT -5
Right. The trikes built here are so different in specification, that it would be highly unlikely that any 2 would work best with the same pressures. Even then , the qualities the builder is looking for will be different. Just as for example, one might be wanting a good ride and interstate stability, while another wants responsiveness and grip.
Not sure what you mean by bouncing; the wheel following sharp bumps up and down or overshooting them with the tire actually leaving the surface? The former would define proper suspension action, the latter needs better shock control. Or maybe you are referring to oscillations occurring after the bump. Again an indicator of under damping.
What kind of tires wear the center first with 20lbs in them? Most are designed the run near twice that. As I said, I have a very light trike and run 27 in the front and 32 in the rear. Both are wearing evenly across the surface. I should think running with 20 would wear the edges more quickly, especially as that would allow the edge to roll under when cornering.
I suspect that BRP recommends such low pressures and has Kendra deliver tires specifically designed to run at low pressures in order to limit cornering grip and promote under steer to discourage riders from approaching tipping speeds as a backup for the electronic nannies. OK, just my opinion. No facts there.
Most testers complain of slow handling and quick intervention of the nannies when testing the Spyders and I cannot help but think the under inflated tires are a factor in that.
Photos removed 11/12/16 to save data limits.
This is after 10k of hard use. Sorry for the repetition to those who have looked at my build posts.
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Post by noahkatz on May 24, 2016 13:24:28 GMT -5
I really don't see the benefit to trying to design out the roll of the vehicle completely by moving the roll center, your camber curves would go to Poop I expect among other things. The biggest conundrum is suspension design is the ride/handling compromise. The crux of this is that the suspension compliance needed for good ride compromises handling, because the resulting roll in cornering causes camber changes, uses up suspension travel, and the dynamic instability of the sprung mass sloshing around. The reason for this roll is low roll center. So IF there were a suspension that had high roll center (at the CG) without issues like the camber change and lateral scrub that wishbones give, the ride/handling compromise would be eliminated. I've come up with a couple but the geometry is klutzy - lots of links, some very long that make packaging difficult. All of that said, ride quality is quite a subjective idea, someone might drive an indy car down a normal road and think that its way to stiff any time it hits a pot hole or bump, yet that same car on a speedway might handle like a dream yet they are the same car. That just says that a car that handles really well rides poorly. Ride quality is not really subjective, in the sense that it's been established that a suspension frequency of 1 - 1.5 Hz is considered comfortable by the vast majority of people, whereas sports cars are in the range of 2 - 2.5 Hz; note that double the frequency corresponds to 4X stiffer. |
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Post by noahkatz on May 24, 2016 13:29:07 GMT -5
I had a Chevy 3500HD dually truck with a SOLID I beam front axle and Kingpins, not ball joints. It would corner with almost any non sports cars in corners. The only reason for having suspension is to deal with bumps; on smooth roads suspension type hardly matters. I bet the track was smooth and your story would change on a bumpy surface. |
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Post by noahkatz on May 24, 2016 13:39:37 GMT -5
Not sure what you mean by bouncing... My guess is all that unsprung mass oscillating on the tire spring. What kind of tires wear the center first with 20lbs in them? Most are designed the run near twice that. Other things being equal, half the weight (trike vs. car) means half the inflation pressure for the same size contact patch. |
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Post by Liteway on May 24, 2016 16:33:06 GMT -5
Not sure what you mean by bouncing... My guess is all that unsprung mass oscillating on the tire spring. What kind of tires wear the center first with 20lbs in them? Most are designed the run near twice that. Other things being equal, half the weight (trike vs. car) means half the inflation pressure for the same size contact patch. Yep;a large unsprung weight has to be controlled with stiffer shock valving and this only adds to the ride deterioration caused by the heavy unsprung mass's inability to accelerate upward rapidly in response to a bump which in turn moves sprung mass along with it . Result: you and the chassis become part of the suspension or tied more closely to it. In response that a trike that only weighs half of what a car weighs (at a given corner) needs only half the tire pressure to maintain contact patch sounds ok in theory. There are a lot of variables with respect to the tire's construction and tread profile. In my case, it's hard to find data on a 165/70r10 as not many cars use or have used it. But going to the BMC Mini Cooper forums, the consensus seems to be 26 or 27 lbs up front is good for the street with considerably more for competition. I am only ball parking figures here, as trying to be precise would be delusional. Mini with driver aboard weighs about 1650 with 60 percent up front or 495 on each front corner. My trike with driver loads each front with 193 . So the best pressure for maintaining the same contact patch as the mini drivers have would be 193/495=.39 .39x26lbs = 10.4 lbs. Interesting. |
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