Yamaha Truly Unlimited UTV - Rustfish Racing 2921

Rynomx785

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Thanks for the nod. Bad Ass seems to be the theme here. :)

We have been talking about the preload a lot on our 1992 car and we have it fully sorted. It flies, but not without a lot of tuning. A lot. If anyone has seen this car move over whoops, it is impressive. Now, that being said, preload adjustment can cause a lot of weird side effects. One of the guys we are partnering up with has a new Can Am X3. This thing is awesome. We took it out and realized that they had remove some preload from the car when it was delivered. Davey had used a Cam Am tester while he waited for his car and it was spot on. But his newly delivered car was not working as well.

As it turns out, Can Am had removed some of the pre-load to lower the front end. We don't know why, but once we brought the car back up, added back preload, we came back into the sweet spot for the valving and spring rate. When you move around the preload, you do a couple of things, you move the timing for the secondary spring engagement which can have impacts on the valve to spring interactions. From the factory, cars are usually tuned pretty well. They know how this works. Then guys go and add preload and the cars jump all over the place.

I would say that if you have a stock vehicle, do not mess with the preload unless you really know what you are doing. You will coil bind and mess up valve and spring interaction. This will kill the ride. If you are going to buy a kit, talk to the builder about your vehicle weight and driving style and have them set it up. Or have a shop that specializes in the tuning do the work.

Reid will probably have a lot more to say, like diagrams and math, but this is the jist. :0)
I would never set my crossovers until after I have my ride height set. I am not running stock springs and I have tested a few different rates on my RZR. With the rates I have tried, I have had to run between 0.75" and 1.5" of preload to get to ride height so I am no where near coil bind. I don't want to hijack your thread too much more so I will wait for Reid to respond and not drift if any further off course.
 

kornfed

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I think we all want to hear from Reid on this one. We should create an ask Reid forum. Actually not a bad idea. We should have an experts corner with the build nerds fighting it out. Not sure everyone is as open as Reid on the details of their math, but it would be cool... Maybe hit up Joey and see if a few builder/shop boss' types would be into it.
 

Rynomx785

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I think we all want to hear from Reid on this one. We should create an ask Reid forum. Actually not a bad idea. We should have an experts corner with the build nerds fighting it out. Not sure everyone is as open as Reid on the details of their math, but it would be cool... Maybe hit up Joey and see if a few builder/shop boss' types would be into it.
I actually started a thread on Race-Dezert a year ago about this same topic thinking there may be some truck or buggy guys that would be willing to share some info but I got nothing. I never thought to ask Reid for some reason.
 

zambo

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Nov 13, 2016
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Thanks for the nod. Bad Ass seems to be the theme here. :)

We have been talking about the preload a lot on our 1992 car and we have it fully sorted. It flies, but not without a lot of tuning. A lot. If anyone has seen this car move over whoops, it is impressive. Now, that being said, preload adjustment can cause a lot of weird side effects. One of the guys we are partnering up with has a new Can Am X3. This thing is awesome. We took it out and realized that they had remove some preload from the car when it was delivered. Davey had used a Cam Am tester while he waited for his car and it was spot on. But his newly delivered car was not working as well.

As it turns out, Can Am had removed some of the pre-load to lower the front end. We don't know why, but once we brought the car back up, added back preload, we came back into the sweet spot for the valving and spring rate. When you move around the preload, you do a couple of things, you move the timing for the secondary spring engagement which can have impacts on the valve to spring interactions. From the factory, cars are usually tuned pretty well. They know how this works. Then guys go and add preload and the cars jump all over the place.

I would say that if you have a stock vehicle, do not mess with the preload unless you really know what you are doing. You will coil bind and mess up valve and spring interaction. This will kill the ride. If you are going to buy a kit, talk to the builder about your vehicle weight and driving style and have them set it up. Or have a shop that specializes in the tuning do the work.

Reid will probably have a lot more to say, like diagrams and math, but this is the jist. :0)
I know I'm continuing the hijack, but the reason CanAm lowered the ride height after everything was already designed and speced out was to make it pass some DOT rollover test. With all that travel the car can get a little sloppy if not driven correctly and lowering it made it stick to the ground well enough to pass that test with your average schlep behind the wheel. I understand that test isn't a requirement to pass, especially for a UTV and most UTVS in fact don't pass that test. Oh well, its something can am wanted.

In any event, as you mentioned, lowering the ride height by removing preload from the shock takes the piston out of the zone it was designed to be in when it was built. As delivered, the piston is right at the bleed hole for the IBP tube and its harsh as hell in the small stuff. Raising the ride height puts the piston in a happier spot and smooths out the stutter bumps quite a bit. And if you raise the ride height you can remove the third tender spring because now you'll have enough preload to keep the dual rate springs in place at full droop without a limit strap.

The real key is modifying the internal bypass tube. Requires a ton of effort to take the shocks all the way apart, weld and re-drill holes in the bypass tube, reshim and revalve, etc. But guys have already figured out some good formulas and are selling them. My x3 is insane after having the shocks reworked and revalved and mating it up with a set of springs from Eibach.
 
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NIKAL

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Zambo, Are you racing the Lord Humongous at the Norra 1000 this year? Or are you having to much fun and spending to much money on the X3? It's pretty amazing what these UTV's can do and ride like when tuned right. What are you enjoying more the X3 or the truck right now?
 

zambo

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LOL I'm having a blast with the x3 but its not ready to race by any stretch yet. This year will be the swan song for the Humungus at NORRA. I'll be racing with a for sale sign on it.
 

NIKAL

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Cool your racing it again this year, but bummer your selling it! Not using the truck enough or have other plans for something else?
 

badassmav

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Look guys, I appreciate your patronage and all, but this is not why I dove into this thread. I don't want to distract from what Dave has started here, because if it is anything like the Monstermav chronicles ended up being, I would like to enjoy it from the other side of the isle this time. This thread is in worthy hands.

Regarding shock set up, Zambo said it pretty well. It's all about the "zone". What area of travel the wheel is in relative to where the internal shock shaft piston travels through the bypass section(s) of the inner tube of the shock. Through how many holes and of what diameter that oil it passes, and the rigidity of the "trap doors" that help regulate the flow of oil through said holes. Controlling the hydraulic activity inside the shock is a far more effective tool in regulating how quickly a corner of your car passes through a given section of wheel travel. Its kinda like horse shoes and hand grenades. Just get close with the spring set up, then just nail it in the valving.

Although I was involved in the process of dialing in our shocks, we always had one of Fox's top technicians there to lead the way. Marc is well tied in to Fox, and has been since his truck racing days. When building the Monstermav, UTV shock technology was in its infancy. The longest stroking shock available at that time, from any top manufacturer, was a mere 12.2", and that just wasn't going to work for our application. Marc had his buddies in Fox's truck racing division make up a set of internal bypass shocks to suit our dimensional needs. These "bohemoths" were not UTV shocks at all, but instead modified versions of the 2.5" with 7/8" shaft truck racing shocks. Extended length on the rear 16" stroke shocks was a lengthy 42", and used a 300# 16" over a 150# 14" set of springs to support each rear corner. The 4 sprung shocks counted for just under 9% of the cars total GVW! After the first test drive, I thought to myself, "My god, I just built a truck with a 1 liter, 2 cylinder engine barely producing 100 hp, and a rubber band for a transmission"! Lucky for us, there werent many efforts like Dave's back then. That car (The Monstermav) wouldn't have a snowballs chance in hell of winning a championship against today's more polished teams and their equipment.

Ahh, shocks-smocks. Lets get on with the build. Haha!
 
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sconym

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Great thread. Can't wait for more updates. Also some info on the double cab in the background of one of the pics....
 

kornfed

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Ha, the double cab is in the background again? ooops. :) Jerry always has race cars and a few one off cars in the shop. Last month there were 2 class 1 cars, an historic race truck, a VW thing and a Rat Rod. Pretty cool place to work...
 

NIKAL

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I'm still surprised and not sure why they are sticking with a rear steer setup? Not one class 1, 10, TT or any a-arm car runs rear steer. Penhall has never built a rear steer a-arm race car before. Just wondering why they are wanting too now? Is it a packaging issue due to the front dif location? May I asked what rack & pinion you will be running?

Overall very impressed and glad to see someone take the big leap and build a true Unlimited UTV.
 

kornfed

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Again, over my skis, but getting details from Will, Kent and the CAD guy.

The CAD designed front end allowed us to align the suspension, shocks and arms to the stock layout and geometry for steering. The designer was able to create and model the suspension into the rear steer configuration, use the stock spindles and allowed for testing in the computer. It works in the computer according to the designer. In the desert, we will see. Will is cautiously optimistic. If it works, we will have a much easier way to do spares and keep the cost down. If it does not work in real life, we will have to look at the spindles, move the rack and potentially move the diff. Not ideal. Really hope this works. According to the designer, it will work.

Great thing about these theories is that they are easily tested. Do well at the World Championships... Simple proof. :)

The Rack and Pinion is from Weller...
 

Glamisfan

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The rear steer configuration will work fine. But......a front steer is better. All of us stock utv's have rear steer except for the wildcat . It's not the end of the world!
 
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tatum

Hans Solo - 2009 UTV Baja 500 & 1000 Winner - UTVU
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The rear steer configuration will work fine. But......a front steer is better. All of us stock utv's have rear steer except for the wildcat . It's not the end of the world!
Definitely not the end of the world but they have gone all out on everything else. Car is still super bad ass .
 
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badassmav

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At what point does a desert car stop being a UTV and start being something else entirely?
Man, do I read too deep into everything, or what? Let me stab at this again:
A UTV continues being a UTV as long as the engine and drive train configuration remains UN-butchered. Period.
Aside from 4WD and 4 wheel independent suspension, It is what gives the cars their unique sound and performance abilities. Keep the OEM engine block, transmission, transfer case, and differential housings, and you still have a UTE in my opinion. What Dave is doing is exploiting what he believes to be the best drive train package out there. I'm sure when asked what kind of car he races, he will proudly say its a highly modified, Penhall-built Yamaha UTV. I doubt he would say, "It's a class 1 inspired custom buggy running a UTV drive train". I dont know of anyone out there who could mix/match components and build a 1 liter car as fast and reliable as today's UTE's, on a realistic budget.
 
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zambo

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Well it's an interesting topic. These turbo motors with injectors and a good tune are making as much power as the ecotecs pushing class 10 cars around and we know those cars are fast. So without some limits I think you run the danger of someone just building basically a class 10 with a UTV engine and running wild. Keeping the diff, axles etc makes sense.

I just think the car counts are so high because basically anybody can buy one from a dealer (financing baby!), and with some reasonable garage skills and race parts put a decent car on the track. I think the number of people who are gonna spend class 10 (or more) type money on a UTV is much much smaller. I love the fact that UTV racing has exploded, hell I bought my first UTV just a couple months ago after seeing what they can do....it would be a shame to turn it into a class where you can't win a race if your car isn't $100k plus.

Anyway a friend got a few of these yamahas into the shop a few weeks ago and they are undergoing desert race surgery. It will be interesting to see what they come up with. Are there many yamahas racing desert and if so how are they doing? At first blush I'd wonder how stock size axles and cv joints would hold up with the geared trans.
 

badassmav

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Again, over my skis, but getting details from Will, Kent and the CAD guy.

The CAD designed front end allowed us to align the suspension, shocks and arms to the stock layout and geometry for steering. The designer was able to create and model the suspension into the rear steer configuration, use the stock spindles and allowed for testing in the computer. It works in the computer according to the designer. In the desert, we will see. Will is cautiously optimistic. If it works, we will have a much easier way to do spares and keep the cost down. If it does not work in real life, we will have to look at the spindles, move the rack and potentially move the diff. Not ideal. Really hope this works. According to the designer, it will work.

Great thing about these theories is that they are easily tested. Do well at the World Championships... Simple proof. :)

The Rack and Pinion is from Weller...

A few thoughts on steering geometry:

(this will take a few paragraphs, so bear with me. I promise it will be worth it in the end)

Your CAD guy was smart in designing around the OEM components. This is how building a car in a timely fashion is achieved. If you mandated a completely different and opposite steering layout, what would he have used as input for spindle geometry? Without successful past experience remodeling front spindles for front steer applications, he would be spending countless hours, and probably days using approximate figures for non existing hypothetical spindles. It surely would have stagnated the forward momentum of the design progress at that point. Like I said earlier, the decision to front steer our Maverick added 2-3 weeks extra build time.

As an eager young fabricator in the late 80's preparing to build my first race truck, I dove head over heels into reading everything I could get my hands on about race car engineering and suspension dynamics. No internet back then boys and girls. I'm talking libraries and mail order books. Big, fat boring books. When build time came, I carried over everything I could from what works in a road racing environment, and religiously applied those fundamentals into the truck I was building. I took rear steer F-250 camper special I beams and spindles, and forced them into complying to the front steer conversion I was performing, and still maintain proper steering characteristics. Enter Ackermann steering.

Lay-mans alert:
So, Ackermann steering was discovered in the 17th century for the purpose of helping horse drawn carriages corner with less resistance, and therefore, less fatigue to the horse (I told you, it's nothing that hasn't been done before!). Ackermann steering, quite simply is the ability of the inside tire during a cornering maneuver to steer at a sharper angle than does the outside tire. This is desirable because it is following a tighter circle than the outside tire is, therefore must turn at a sharper angle to avoid the friction caused by tire "scrubbing".

Anyhow, I remember watching the truck I built as it was being pushed through contingency at its first big SCORE event. Just a few trucks ahead of him was another new class 8 "hi-tech" build that used the same I-beam/spindle combination that I did (copycat!), except when converting his spindles to front steer (by converting, I mean just switching assignments for each spindle, The driver side spindle is rotated 180 degrees and used on the passenger side of the vehicle, and vice-versa. Then, wala! Instant front steer), he left the steering knuckles in the stock location, essentially introducing the reverse effect of Ackermann into his steering geometry. Suffice it to say that while we were able to push our truck around the corner, they could not do the same. They had to start it up and drive it around the corner. Between their front tires scrubbing, and the rear tires squealing due running a solid rear axle (spool), the resistance to turning was ferocious.
Then, the next day while watching both trucks entering into Osbornes Wash, it all became crystal clear to me why I spent the time to do it right. As our trucks front tires grabbed hold, and as though on rails, guided the vehicle effortlessly around the corner, while when the other truck negotiated the same corner, the front end immediately "pushed" hard to the outside of the turn, slowing the truck down considerably while the rear tires shot rooster tails high into the air as they struggles to push the lazy front end through the corner.

Fast forward 25 years, and I'm watching RG negotiating a kink in an otherwise endless straight pole line road in Baja. Now, these last 3 paragraphs are not narcissistic-ally added in an effort to toot my own horn, but rather to share a very poignant revelation that occurred to me at that very moment, which was this:
Perhaps pure Ackermann steering geometry in today's race cars is not the best or smartest design criteria. What I saw was a truck pivoting around the outside front tire as it crisply changed direction at over 90MPH. I thought maybe that due to weight transfer, and the higher slip angles the outside tire sees over the inside tire during a high speed turn, just maybe modern race vehicles, because of their vastly increased average speeds would be better off with "anti-Ackermann" steering. The modern off road racer is light and fast, and rarely is seen at low speeds "plowing" through a turn. Conversely, they are usually observed powering through lower speed corners at opposite lock, hard on the gas.

So, to Ackermann, or not to Ackermann. That is the question I ask. How say you Todd and Haans?
It's certainly a hard point to argue against, because when you think about it, the outside tire has more influence during a high speed turn as it is more heavily weighted than the inside one. It will consequently will see higher slip angles, so could benefit from turning a bit sharper by design, than the inside tire.

So Dave, for the sake of your thread, and input to it, possibly phase 1 will benefit from true Ackermann, while phase 2 with its more wide open motor and resultant higher speeds, will not.
 
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tatum

Hans Solo - 2009 UTV Baja 500 & 1000 Winner - UTVU
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Thats an interesting thought Reid that is way above my pay grade, it sure got me thing though.
 
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