LocostUSA.com

Hello guys, first I'd like to introduce myself since this is my first post. My name is Kevin, I'm a 25 year old Mechanical Engineering student studying at Harrisburg Area Community College in the Central PA area. I've been surfing this site and reading as much as I possibly can about the suspension set ups for all your Locost's and have been trying to wrap my head around some of it. I've been building a 2003 Ford Focus SVT to participate in the local Pennsylvania Hillclimb Association races but after discussing things with a professor of mine have decided to possibly sell the car in favor of starting from scratch. After kicking the idea around for awhile I decided to continue work on my Focus and start the design process of the replacement car and sell the Focus if things get serious with the design.

Now, I'm not looking to design and build a Locost, but instead I'm looking to build my version of a Diasio as I really enjoy the look of the car and all other LMP styled cars. The goal is to keep with the two seater design of the Diasio and power it with a motorcycle engine and keep with the Daisio 72" track width. From there I've been having issues designing and fully understanding what exactly I'm doing to successfully build a front set up that works in as efficient of a manner as I can. So far I've decided to use Hankook Ventus Z214 tires for race applications in a 225/45R15 size (Street tires would be same size). From there I gathered that the actual width of the tires to be 8.9" with a total diameter of 22.8". These tires are mostly selected to keep small and cheaper rubber in supply, and because I enjoy using these tires in a 16" size on my Focus when I take it to the autocrosses around here. From there I stumbled into the treasure trove of Spindle measurements posted on this thread viewtopic.php?f=5&t=1292)

From that I've decided to start designing my front suspension with the Chevette/Fiero spindles. Now the issue(s) I'm finding now are understanding the importance of the roll centers vertical location. I'm also having issues with deciding how long to make my a-arms, I'd like to go with a SLA design and I can only assume once you locate your roll center you follow the lines from the spindle with your a-arms to locate the mounting points on the frame itself, but how do you know when your arm is to long?

I've been trying to follow along with all the threads I can find here and any information I can find for Formula Ford vehicles since its pretty hard to find LMP style cars being built by people. I have AutoCAD 2012 and have drawn out the wheels at the track width and drawn in the mounting points for the Chevette/Fiero spindles. This is with the wheel mounting surface being dead center of the tires and the spindle being offset back 5.75" to center of the top BJ as shown in a link from that thread I linked earlier.

I know my car isn't a Locost but from what I have found on numerous occasions is that this site pops up as one of the top Google results with my searches, and it seems like there are a great number of users that know what they are doing. Any help would be greatly appreciated, I'm hoping that this design comes to life!

Tracks are a measurement to the center of the tyre, not the width of the car.

My suggestion would be to read up about some of the successful but home built DSR racers.
http://sports.racer.net/index1.html < chassis section on left
http://dsrforum.yuku.com/
http://sportsracernet.smugmug.com/

Plan around using Formula 3 wheel sizes to use F3 tyres, good selection of the very best of the latest compounds, widely avaliable and reasonable in price. I worked with one Sports racer in Oz (similar to DSR in concept) who did very well and 80% of that was directly due to being able to use F3 rubber.

I doubt you will find many production uprights with a low enough KPI suitable for what you want to do (depending on how serious you want to get with it, just a semi-serious fun track day car Chevette uprights will be ok), more likely you will have to build some low KPI uprights - maybe some speedway ones would work.

Instead of chevette, you might consider a small, low power, fwd vehicle. The spindles are usually rear steer with high mount arms, which should get the steering system above the drivers lower legs and feet with a lower than oem floor relative to the spindle's height from the ground. Reuse the outer cv spindle but remove the axle, balls, and cage. You'll need a tool to hold the hub by the lug bolts for installation and removal of the nut. A .250"x 4" x 2' steel plate, drilled to accept two or three of the wheel studs and matching the curvature of the concentric ring works well.

You'll probably need to use a centered pinion rack for a buggy application given the short intermediate shaft compared to front steer (less weight). It doesn't matter if the buggy rack is front or rear steer since you can flip it upside down if necessary, but don't order one until you've determined the correct width between the rack's inner pivots based on the spindles arc of travel.

For the rear, use the same spindles and brakes but tie the tie rods into the frame.

If you wish to have a hand brake, a small mechanical caliper can be added to one of the rear wheels and actuated with a standard ebrake lever assy.

Not sure what track you want, but pick a donor with a sufficiently long axle on one side that will place the inner cv at the correct position for a narrow chain diff. Leave room for larger driven wheels since I'm sure you want the cheap adjustability and lower parasitic loss of a chain final drive rather than a bevel drive diff.

Horizon, a member of this board, has a Formula Ford. I'm build a formula vee style front half for a tandem reverse trike using a kubota diesel with a polaris cvt.

I also reccomend you get a copy of Tony Pashley's book on motorcycle engined cars.

Cheap thanks for the links to all the info, I'll have to read through as much of that stuff as I can when I get the chance. I kind of figured something was up with my original geometry plot when in order to get a RC 1" above ground level both the a-arms on the Chevette spindles angled down by about 358* and 352* respectively. As far as track width many places I've read have listed it as being the distance between the outside most edges of the wheels not the centers of them.

As far as the spindles go I seem to be having some issues with finding ones to use, would I have to be looking into building my own spindle and using a well known hub? Miatav8 I understand what your saying but by using a small FWD car's FW assembly but do you have particular suggestions. The over all ride height I'm looking for is right around 2" with travel to be figured from there. So I'm mostly looking for a spindle/hub combo that will fill most of the void behind the wheels and keep the car low without having to mount the LCA in the middle of the frame.

I've read part of motorcycle powered cars book you suggested mostly, about the rear drive train assembly and construction to try and figure out what was going on back there. I figure since PHA loosely uses SCCA rules and following with their classing the lowest Sports Racer class allows for a up to a 1300c.i. engine in an NA application if I can remember correctly. I figured I'd shoot for a Hyabusa engine with an open chain diff using a Ford Fiesta diff like the book suggests. But thats all for the rear which is a totally different animal at this point.

Right now I'm trying to get the front of the car plotted out and then work back to main hoop and which point the rear of the car becomes the next issue. So now I guess the question is what spindles should I be looking for since it seems to be a huge pain to find some and then my original question still remains about RC locations.

Thanks again guys this is really helpful!

Use fwd spindles from a vehicle where the base model comes with a 16" rim for larger rotors and a lower ball joint further from the spindle. The lca pivot should determine where the lowest outside node of the chassis should be. If it doesn't, it's just secondary structure.

MiataV8 could you possibly list a few examples of cars with their lower ball joint further from the spindle center line than the top? Also couldn't I just find any front spindles like that and rob the same donor car of its steering rack and use that as well? Unfortunately classes have started again so my time is limited when it comes to scouring junkyards for cars without any idea of a few models too keep an eye out for. Messing around a little bit in AutoCAD I've been playing with A-arm angles and seeing the relations to the instance centers and the roll centers of the car so I think I'm getting the geometry down slowly, just finding the right spindles to use next. Thanks again for the help!

EDIT: After a tiny bit of googling I'm looking at drop spindles to keep it lower, now where you suggesting finding spindles from a 16" OEM set up just for the brakes and to continue with the wheels I have selected?

What is the purpose of this cars and what are your goals for it? Obviously you want to hillclimb with it...But you apparently want to drive it on the street as well. How much are you willing to compromise competitiveness for streetability, and how much are you willing to compromise streetability for competitiveness? Are you building within a specific rule set that will place limitations on any aspects of your build like car? What are your capabilities and limitations regarding fabrication, basic machining? How much of a factor is budget in your build, and what compromises are you willing to make in order to meet it? I think these are important questions for you to have realistic answers for before going too far with detailed component selection.

I think your design envelope is too large. Justin has good questions for you to think about. Your project as stated will likely require thousands of hours of time. Your looking at one of the fastest and prettiest cars made and thinking you will just build one at home and compete in the most dangerous form of racing.

So no one is chasing you away from here and by all means keep thinking! You have to make choices though to get to the end of this project. We do have one member of our forum that is currently winning hillclimb races, another member building a hillclimb car and I'm designing one that will be suitable ( they no longer allow formula cars at my local hillclimbs because they don't have sufficient cages ).

You should drive your Contour at local events. You need to get wheel time somehow and an extremely fast car is probably not the way to do it. A slower car can encourage you to learn how to thrash the last few seconds out of it - that will give you the driving skills you'll need for the faster car. Don't try to become fast by building/buying faster, do it by learning how to drive faster. Otherwise you just land up being over your head.

Don't invest a lot in your Contour, it will never be a sports car like what you want to build. Either is any other street car your likely to see.

I would suggest that at this early stage, it is not the right time to be thinking from scratch. We have FEA frame models posted on our forum for 3 designs. Cheapracer is posting pictures of another. So grab those designs and download the free software and start there. You can modify them and see how they work. We are having some discussion now on several threads on suspension design using Vsusp. That tool will educate you much more quickly then the CAD package you are using now. Mind you, it's worth learning that too!

I currently do not have tooling to build the frame itself let alone the space. The original idea for this was just to design the car something like a FSAE but wider that can accommodate two people, while I do want to win races I know that it is almost impossible to get a carrier of being a racing driver. As such I just want to build a fun car that will have a good competitive edge, I'm not looking to build a insanely fast car that breaks all kinds of records, but I've always figured if your going to build something build it to the max and then tune it down and progressive tune it faster as your skills start to exceed the capabilities of the car. I don't want to build a car and then through some off chance miracle be stuck wishing the car was quicker in this aspect or wishing it had a different engine or something else, there are ways to knock the speed off of an engine. I will admit I haven't really read into the class ruling all that much since I've been mostly concerned with learning more about the front suspension geometry. Which is what I'm mostly on this forum for. This hasn't moved passed pencil and paper/CAD drawing yet and since I do wish to build a car I kind of want to learn about all the different aspects that are go into building a car like this, I'm hoping that once I finish my schooling I can get a job working on these types of cars or other automotive engineering areas and work my way to race engineering.

The idea here isn't to just hurry up and pound out a drawing and sell my Focus and start throwing materials and parts together to see what comes out, its to learn about the design process, design the car, get a price listing together and have fun with it. I don't see myself building the actual car for a few years. All the while I will be getting more seat time in my Focus on the hills. I do appreciate all the questions you have asked about what I'm really looking to build, and the truth is a competitive car that isn't comfortable to drive as a street legal car, (and street legality as stated in my first post isn't even a primary concern its a secondary) I want a race car first and a street car second. From different sources I have read you start designing a car from the outside in starting with the front suspension geometry, while I'm working on that portion of the project I will be researching through the PHA rules to find out about classing regulations, safety regulations and car regulations. And cost is never an issue, its just time, and since I'm not looking into spitting out a full car tomorrow I'm not worried about cost saving money is the name of the game and spending it on quality parts once the design is finalized and I have access to tools and space to build it the consideration of even building it starts.

Again I've decided to go with a 15" wheel and a 225/45R15 tire since they seem to be cheaper and easier to find and the the Rota Slipstreams I have on my Focus at 16" respond well with the Hankook Ventus 225/45ZR16 C71 compound tires I have on them, They grip substantially well. To pair with those 225/45R15 tires I would like to know what for hubs I could use, Miata V8 suggested finding a FWD donor car and using those spindle assembles with the axles removed. I'm still curious as to why you suggest a FWD Spindle assembly as I'm still looking at popular cars with a rwd assembly and trying to narrow those down to the cars with double wishbone front setups and rear steer spindles. I stumbled into another website of a guy building a "cheaper" DSR/CSR style car where he used Miata hubs, Now my issue again is that when I try to get the roll center to be around an inch or two above or below the ground level at the center of the car my a-arms just don't look right to me. See this picture here of my attempt of locating the roll center at an inch above ground level using the measurements of the Fiero/Chevette spindles on the 225/45R15 tires.

I know I have to be doing something wrong with figuring out the geometry, I see a lot pictures of DSR/CSR cars and it looks like quite a few people are making their own spindle assemblies to fit what they want. All I'm really looking for is about 2 inches of ground clearance on the bottom of the car to road surface, now its going to make for some pretty stiff suspension and alot of scraping the ground I know but I want to keep a low profile with the car I don't know the first thing about making a body for this type of car so I will have to assume that the aero characteristics of my car would not be greatly beneficial. Also the wish to set the RC one inch above the ground is solely based upon another thread I read where it appeared people where suggested to keep the RC 1 to 2 inches above or below ground level, again please correct me if this is ill thinking.

Thank you all again for the help and I'm sorry I did not clarify that this is more of a learning project then actual going out and building it in a few months with a solid plan from scratch. I did not intend for everyone to assume that I was building the car asap like I said earlier I want to learn the process behind designing and engineering a DSR/CSR car, and obviously if you want to race a car you design to win.

If you are considering license plates you'll want to pay close attention to the sidewall height.
Most if not all (honestly I don"t know if this rule is universal) licensing agencies require the lowest point on the body to be above the bottom of the rim.
Multiple mounting points is always an option though it would require some additional engineering investment.

When you consider brake balance, track width, matching wheels and tires, similar geometries front and rear, it makes sense to use the front of two identical fwd cars. That is basically an Ar-i-el At-om. You want to go a step further and use a bike engine, which may make it impossible to get registration once it is titled due to emission testing but then you won't have enough ground clearance to go over any parking lot speed bumps, so maybe that's not an issue. You also want to go yet another step further by having special spindles with a lower than normal lbj. Since you don't have the equipment, space, or time to build it anyway, just draw your ideal spindle using a commonly available fwd donor with a bolt-on bearing hub and plan on a custom upright. You could use focus uprights.

I don't understand the usage of a focus upright the shock mounts directly to the top of the hub assembly and has one ball joint on the bottom. Also I'd like to design to build eventually so as far as the spindle option right now I'm looking for something that is corporeal and not just a "Pull it out of thin air" kind of thing. And please everyone just forget about the street legal thing I don't care about it it was just a pleasant thought I should never had mentioned it. I have a minimum ride height allowance of 2" so I'm shooting for a two inch ride height. Since it can't be figured out as far as what spindles to use I guess my only question that remains for this thread is the importance of roll center position. What I read before about keeping it 2"+/- ground level does that ring true? Also the CAD drawing I posted, is that the appropriate method for finding roll center? TBH I just made a mark dead center of the car at 1" and extended lines from the centerline of the tires out at the angles needed for both to cross at 1" above the dead center of car. From those lines I had reference lines for the for left and right instance centers. and then I picked locations on those two reference lines for the LCA and UCA to meet at their extended lines.

Is that the proper method?

It looks like your doing the roll center the right way.

You need to run 13" rims and real slicks for a small fast car. The slicks on my Formula Ford weigh like 10-12 pounds. You can't even afford the weight of street tires and their rotational inertia. The tires should have a diameter of 20"-22". Try this link for some common race tires size and applications: http://www.philstireservice.com/ Click on Hoosier and Goodyear slicks.

You need front uprights with the axle pin higher up on the upright, often called "dropped spindles". The hot rod parts are too big and heavy for you though. The economical choice is Spitfire spindles that are modified to remove the trunion and then weld stubs to the bottom to accept a rod end joint. If you look thru oval track catalogs you will see many fabricated spindles that general consist of a vertical piece of square tube with a steering arm and axle pin or snout welded to it. You can start with the Spitfire part in your design and when you acquire the skills you can design the spindle from scratch. They sell the axle stubs and tapered steel bungs for this.

When you have spindles that mount the lower wishbone closer to the ground, it's easier to get a low roll center. It also produces less tire scrub as the chassis moves in ride and dive.

A ride height of 2" is common for a race car. That doesn't mean it hits the ground, or at least it has rub strips to prevent damage to the frame.

Thank you for that information I was stuck using Tirerack and couldn't find another tire source for the car itself. With that info I can restart with the geometry and go from there. I found some DSR/CSR "DIY" spindles that where just a spindle that you could weld your ball joint mounts to, but I think I'll start with the spitfire spindles and work from there. Is it possible to find Spitfire drop spindles or are the modifications the only thing that can be done? Thank you again for the info it defenently sets my design off in the right direction. I think once the a-arm angles are set the next step is the design of the a-arms themselves and then suspension placement. I'm debating weather or not to use push rod actuation or direct mount or just fiddle around with some stuff I haven't seen on cars yet just to see what the rates do during tests. Is there a good program that can simulate suspension travel with customizable spring rates and what not or would Working Model 2D work well enough to get a general idea of the rates of the spring through travel?

EDIT: Horizon, you said that some cars use a spindle welded to some square stock with its needed bracing and everything else. What is the importance of the KPI if I were to design my own spindle with just a snout, is keeping it with 4-12* advisable? something like this quick drawing with an 8* KPI is what people are making though? obviously with a steering arm attached to make it rear steer, if so I think it is wholly possible to design and build my own spindle for the front.

F3 wheels/tyres are 13" x 7" or 8" and 13" x 10".



It also allows the upper arm to effect more finite control as more of the load is put into the lower arm. Most racing cars were like this before aero took over design. A little scrub is not a bad thing, saturates the slip angle faster for better steering response.


Sauce, go read this ..

viewtopic.php?f=5&t=3517&start=30

There's also other custom made uprights around the net, I know DPCars website has some plans - it's not a hard task.

I would be looking at around 3 degrees KPI and when you add camber you will have 3 to 5 degrees (people always forget to add the camber). You will need about 8 to 10 degrees caster, front RC above ground about 1" and rear 2" to get some response from roll bar adjustment but try to design adjustability into everything.