Red Lands Racing/Motive Engineering BITD build
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motive
Active Member
I'd say you are ahead of the curve on avoiding flats! I'm thinking ITP is the tire to run. I would have no issues running Method wheels. Talked to the rep some at V2R. Real cool guy.
Years ago I remember reading about some time trial team in Japan that ran cast wheels because they were getting too much flex with forged wheels. The casting process makes it easier to forms ribs and such on the backside of the wheel where no one ever looks. While cast wheels are typically heavier than a forged one, the extra freedom in design without having to do secondary machining to produce details like strengthening ribs, makes one wonder if a good designed cast wheel can't out perform other options. I have never looked at the backside of an OMF but if it is flat, they are sacrificing strength by not increasing the center thickness then machining lightening pockets. Reid, I would be interested in what is happening to your centers?
badassmav
Well-Known Member
If you PM me your email address, I'll send over some pics. I'd rather not do it here.
A lot of us guys thay rum tire balls run them with no air in the tire, just in the balls so a bead lock is a most. I really like the OMF, it's one of the best if not the best for sure but I run the Methods and I'm really happen with them. The Avid Mav that I race BITD with runs them and during V2R I shredded a tire and the rim was fine. They're 15" rims with 30" mongrels. I personally wouldn't run an LT tire.
Interesting to see a tube used in a cast beadlock wheel. Not sure how you are using tire blocks or balls with a tube, or did I miss understand your comments about V2R?
BiggJim
I Hate Rules - UTVUnderground Approved
Says the full disclosure king!! Bwahaha....Just Rib'n ya reid!
badassmav
Well-Known Member
Yeah, I'm learning to take it! Just didn't want the ugly images going out over the airwaves. I'm trying to consider our sponsors when sharing info publicly, which I dislike doing. I am morphing into a "kinder, gentler" version of the Badassmav
, if there ever could be such a thing.
badassmav
Well-Known Member
That's what it looks like when the Cognito boys build a chassis, except for the fact that it is not a time lapse! Those dudes whip out a rolling chassis like its a front bumper. Start, whoosh,.......... done!
So, what does the bare bones platform weigh in at?
Yeah its not my car. I come out to help/drive in BITD. I'm in NC, my car out here has them.
sand shark
Well-Known Member
So when do we get to see the chassis on whats left of the frame?
badassmav
Well-Known Member
Well,what do you know. Perhaps Nikal may have a "fighting dog" after all
!
motive
Active Member
Ok fellow students of suspension dynamics, everyone decide what tire size and wheel offset you are going to use? Good. Lets move on. (What happened to Jake? I thought he was going to chime in. Probably just too busy with Camp RZR. Hope you are all having fun at the dunes, I'm just over here trying to build a race car.)
Now that you know the critical dimensions of your wheel and tire you can start designing from there. Now would be a good time to choose your track width. This will determine the points in space where your outer pivot points will be if you are using the factory spindle. If changing the inner pivot points were an option, I would say that you can design a suspension to do what ever you want while keeping the factory spindle. Designing a desired camber curve or roll center is very easy to do given any outer pivot points, and lower control arm with its inner pivot. In this case, the lower control arm defines and controls the track width. The upper inner pivot point is found by intersecting circles drawn from the upper outer pivot point with the wheel positioned in various points along its desired path.
This is a photo I stole from hdt28 on instagram. He has some cool stuff on his feed. Go give him a follow.
Now that I have told you how to do it if you could change the inner pivot points, I need to remind you that it is not allowed in BITD or SCORE. It is allowed to change the pivot points on the spindle but do we need to? Most likely, as a desert racer, the track is going to be widened. This is both for stability reasons and it makes it possible to get more travel, especially with the factory length shock. So how does that affect the dynamics of the suspension above just creating more travel? Anytime the A arms are lengthened, it is going to narrow the ratio of upper to lower lengths as well as the angle between the a-arms. This has the effect of slowing the camber gains, softening the suspension, and more body roll. While some of that is easy to deal with, you will probably be changing shocks and springs anyway, it should at least be understood. Other things like ackerman are also effected by widening the track.
There is a lot of things to think about besides just getting the most travel possible.
Now that you know the critical dimensions of your wheel and tire you can start designing from there. Now would be a good time to choose your track width. This will determine the points in space where your outer pivot points will be if you are using the factory spindle. If changing the inner pivot points were an option, I would say that you can design a suspension to do what ever you want while keeping the factory spindle. Designing a desired camber curve or roll center is very easy to do given any outer pivot points, and lower control arm with its inner pivot. In this case, the lower control arm defines and controls the track width. The upper inner pivot point is found by intersecting circles drawn from the upper outer pivot point with the wheel positioned in various points along its desired path.
This is a photo I stole from hdt28 on instagram. He has some cool stuff on his feed. Go give him a follow.
Now that I have told you how to do it if you could change the inner pivot points, I need to remind you that it is not allowed in BITD or SCORE. It is allowed to change the pivot points on the spindle but do we need to? Most likely, as a desert racer, the track is going to be widened. This is both for stability reasons and it makes it possible to get more travel, especially with the factory length shock. So how does that affect the dynamics of the suspension above just creating more travel? Anytime the A arms are lengthened, it is going to narrow the ratio of upper to lower lengths as well as the angle between the a-arms. This has the effect of slowing the camber gains, softening the suspension, and more body roll. While some of that is easy to deal with, you will probably be changing shocks and springs anyway, it should at least be understood. Other things like ackerman are also effected by widening the track.
There is a lot of things to think about besides just getting the most travel possible.
motive
Active Member
Scrub radius would be modified just by the nature of changing wheels and using a 30" tire. I would consider the factory scrub radius to be very satisfactory, either stock or with a 30" tire and the right wheel offset. The closer to zero the better but not the end of the world if it is within say 10% of the tire.
Reid, does yours have an excessive amount? Just wondering why you need steering stabilizers on you car. I would also be interested in someones argument why a larger moment of polar inertia would be desired. Care to make a case for it? I can think of a few arguments but it would all be playing devils advocate.
Anti-dive: two thumbs way up for polaris. For the high center of gravity and the long travel these things have its a good thing. I have never put in any anti dive in the stiffly sprung road based cars I have worked on. they were extremely low with very little camber gain in bump so the front tires were still upright if the front dove the little travel it had.
Reid, does yours have an excessive amount? Just wondering why you need steering stabilizers on you car. I would also be interested in someones argument why a larger moment of polar inertia would be desired. Care to make a case for it? I can think of a few arguments but it would all be playing devils advocate.
Anti-dive: two thumbs way up for polaris. For the high center of gravity and the long travel these things have its a good thing. I have never put in any anti dive in the stiffly sprung road based cars I have worked on. they were extremely low with very little camber gain in bump so the front tires were still upright if the front dove the little travel it had.
I believe the steering stabalizers are to save the rack. The electric P/S doesn't give and is hard on them.
Hey Reid, are the front a arm pick up points on the po po not parallel to each other?
badassmav
Well-Known Member
They are not. At a glance, the top arm pivot axis will intersect the bottom one just past the rear of the car, increasing the caster as the suspension bumps.
The stabilizers on the Monster Mav were an afterthought, and were added right after the first shakedown race we ran last year (The Rosarito 200). The rack handled the loads o.k., at least for 180 miles when the gearbox for the electric power steering went south. Broke the internal gears. It was a shame because we were running 2nd overall when it happened, and were honing in on the 1st place car, a 1-2/1600 I believe.. Then, on the way back to the pits, the primary clutch let go.
badassmav
Well-Known Member
When I modified our spindles, I adjusted the lower ball joint position to add a bit more scrub radius than stock. I want to say that it is about 1 1/2" - 2" in its current configuration. I am a fan of the scrub radius because it gives the driver more feedback through the steering wheel. I designed the second truck I ever built with 0 scrub radius, and only 1-2 degrees positive caster. The result was that the steering gave very little feedback, and made it more difficult to drive hard in the corners. It wasn't too good at returning to center neither.
About the PMOI, I would like to build a vehicle without restrictions so I could play with it a bit. I think that drivers with limited experience would adjust to a car much faster if the moment of inertia was high. The car will not be as responsive as it would if it had a low PMOI. I remember watching Ivans truck, and how nimble that thing was. It responded so quickly, and with minimum diving or body roll. When we built Mc Millins class 8, we had no choice but to build with the PMOI off the scales due to an 80 gallon cell at the rear, flanked by 2 quarter eliptic springs packs mounted all the waY to the rear. Add to that, the rules mandated stock firewall location, so the motor was mounted only a bit lower than stock, and crammed tight against the firewall. I recall 5,250 lbs. being the dry weight, and 50 % of that weight was located no less than 3 to 4 feet from the CG. It rolled quite a bit in the corners, but with Scott driving, it was competitive.
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motive
Active Member
Not only are the a-arm pickups not parallel to each other, they are also canted up in the front.
I have to wonder if the monster mav had the failure on the power steering unit due to the added scub. I don't know what kind of unit you had but a quick google search finds several units that appear to utilize a worm gear arrangement. Worm gear sets only like power being applied to the worm side. A sudden sharp load on the steering due to your additional scrub could have induced torque on the gear. If the electronics couldn't compensate by spinning the worm fast enough to match, it would strip teeth off. Of course this is all speculation.
I totally agree with the need for the driver to have some feel back though the steering wheel. There are several ways though that feedback can be designed into a suspension/steering. They all have their shortcomings but they all share the same effect of inducing a load into the steering that wouldn't be present if their respective measurements were zero. The major things that can be altered to increase or decrease feedback are the following:
1: Caster. It induces feedback because of its jacking effect when the wheels are turned. Every time the driver turns the steering wheel he is lifting the front outer corner of the car. It also applies unwanted positive camber on the outer wheel. The plus side of increasing castor is that self centering is also increased.
2: Steering axis inclination/king pin inclination. It also induces positive camber and a jacking effect. It does have some self centering effect but not as effective as caster. In a a-arm layout it is often dictated by packaging the upper and lower pivot points to be far apart as possible while avoiding the tire and wheel. Adjusting in more negative camber has the side effect of increasing the SAI unless you have some fancy Porsche 962 style uprights.
3: Scrub radius. Closely tied to SAI but variable with wheel offset changes. This makes the tires turn in an arch instead of rotating at the center of its contact patch. It does not cause any changes in geometry but does increase "wheel jerk" which in violent cases will reduce driver confidence, over load steering component or even break thumbs.
Of the 3, I would take Caster. As long as one of the a arms has rod ends instead of bushing, it is easily adjustable to give the desired feed back. By changing your lower pivot to increase scrub, you reduced you SAI. While the net result could very well be increased feel, the positives have to outweigh the negatives. That is something that can only be quantified by the driver and lap times. I can't argue with your results, Reid, but I can bench race your methods. What say you?
I have to wonder if the monster mav had the failure on the power steering unit due to the added scub. I don't know what kind of unit you had but a quick google search finds several units that appear to utilize a worm gear arrangement. Worm gear sets only like power being applied to the worm side. A sudden sharp load on the steering due to your additional scrub could have induced torque on the gear. If the electronics couldn't compensate by spinning the worm fast enough to match, it would strip teeth off. Of course this is all speculation.
I totally agree with the need for the driver to have some feel back though the steering wheel. There are several ways though that feedback can be designed into a suspension/steering. They all have their shortcomings but they all share the same effect of inducing a load into the steering that wouldn't be present if their respective measurements were zero. The major things that can be altered to increase or decrease feedback are the following:
1: Caster. It induces feedback because of its jacking effect when the wheels are turned. Every time the driver turns the steering wheel he is lifting the front outer corner of the car. It also applies unwanted positive camber on the outer wheel. The plus side of increasing castor is that self centering is also increased.
2: Steering axis inclination/king pin inclination. It also induces positive camber and a jacking effect. It does have some self centering effect but not as effective as caster. In a a-arm layout it is often dictated by packaging the upper and lower pivot points to be far apart as possible while avoiding the tire and wheel. Adjusting in more negative camber has the side effect of increasing the SAI unless you have some fancy Porsche 962 style uprights.
3: Scrub radius. Closely tied to SAI but variable with wheel offset changes. This makes the tires turn in an arch instead of rotating at the center of its contact patch. It does not cause any changes in geometry but does increase "wheel jerk" which in violent cases will reduce driver confidence, over load steering component or even break thumbs.
Of the 3, I would take Caster. As long as one of the a arms has rod ends instead of bushing, it is easily adjustable to give the desired feed back. By changing your lower pivot to increase scrub, you reduced you SAI. While the net result could very well be increased feel, the positives have to outweigh the negatives. That is something that can only be quantified by the driver and lap times. I can't argue with your results, Reid, but I can bench race your methods.
What say you?
motive
Active Member
I think we are on the same page as far a PMOI although I looked at it as far as vehicle dynamics and you looked at it from the drivers perspective. I totally agree with the drivers ability to adjust but it is relative to how a vehicle is to be driven. Even though I have heard people say a UTV is like a trophy truck that anyone can buy, they do not drive like a trophy truck.
A heavy, large, high horsepower, over built truck can survive pounding bumps and rocks at high speed and sideways. A utv on the other hand needs to be driven with precision. It needs to avoid obstacles that a truck wouldn't blink an eye at. They also use 4 wheel drive to get though tough spots where a larger vehicle uses raw power.
It does need to be considered though even for an underpowered utv. When we first began visualizing a plan to build a car we took our families on a trip to Moab. Ryan had his 4 seat wildcat we had raced in a couple local races. He also rented an XP1000 2 seater. I rented the XP4 1000. At the time Ryan was set on the 2 set but after driving both back to back, we both agreed the 4 was the way to go. That was largely due to the fact that the 2 seater would come around too fast when the throttle was dropped. Yes something that a skilled driver could handle but at a certain fatigue factor.
With that said, most LT kits lengthen the wheelbase which would slow the tenancy to rotate. Since I had complete freedom on my suspension design I did not lengthen the wheelbase since we are building on a 4 seat chassis. Its already LOOOONNNNG enough and I didn't need the extra trailing arm length to get the desired travel since we are using a longer shock.
motive
Active Member
The current state of my upright design. About time to start machining but Reid got me thinking about ackerman vs. anti-ackerman. While I fall under the pro-ackerman philosophy, I thought it would be fun to be able to test different set ups. A few changes later and now I can easily modify ackerman, steering ratio, and bump steer by changing a simple weldment.
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