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Hi all. I'm the new kid here. Strictly speaking, I am not building a locost car. I am building a low cost high performance sidecar rig. The rig will have equal length A arm suspension hung off the sidecar frame. The tug is a 1985 BMW K100 RS. I am using locost techniques to build the front and sidecar suspension. The front spindle is based on a wheel/hub assy from a 2000 Chevy Cavalier. The brake disc will be inboard of the spindle. Otherwise, the ball joints will have to be directly over the brake disc. My spindle differs from an automotive spindle in that the ball joints will be in the same vertical plane, in the center of the wheel. The wheels I'm using are 16 x 6 Pontiac Grand Am/Sunfire ABS wheels. The ABS wheels get me 47mm of offset as opposed to the non ABS 35mm offset wheels. The spindle will have 5 degrees of caster. The reason for the ball joints to be vertically in the same plane is to have no scrub radius, and easy steering, as the handlebars only move about +/- 30 degrees from straight ahead. I will only have 60 degrees total movement of the handlebars to go lock to lock on the wheel. You automotive guys get about two and a half turns of the steering wheel to go lock to lock. So, to my problem. I am trying to work out ball joints and a spring/shock for the front suspension. After reading the suspension posts here, it seems that you folks like the Moog/TRW ES2074R (I think) tie rod end from the 72-80 Ford Courier/Mazda B series pickups for the upper ball joint. So what do I use for the lower ball joint? A part number or application would be helpful here. The same goes for a spring/shock unit. Anything that works for a locost application will be a good starting point for me. Also, a note of caution. I read in the suspension thread that some of you are also using bolt on wheel/hubs from fwd cars. Please be aware that you must have an axle end or large bolt in the hub to preload the bearings, otherwise you will not make it out of the driveway. Well, I hope the first post wasn't too long. Looking forward to hearing your advice. Thanks for listening,

Mike Lydon

Welcome! Does the upper ball joint have to differ from the lower?

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-Scratch building 7; Multi-link Mazda IRS & Renesis rotary

CJ

The reason a lot of us use that ball joint it because it fits the Miata spindle's upper taper, and has a convenient thread (14mm, I think?) for a Kinetic upper control arm (and other designs). You'll need to get a ball joint that has the correct taper and length for your uprights.

I'm not real clear on what you are doing. Is this a traditional motorcycle sidecar? And you're using the front spindle from a Cavalier? This spindle won't be steering on the sidecar, will it? If so, I gotta see that!

If this wheel is not articulated for steering (I'm assuming that's the case), I'm having a hard time seeing how caster would affect the bike's steering. Would you mind teaching me a little?

Is the sidecar fixed to the bike, or do they lean?

-dave

_________________
...nowadays people are so intellectually lazy and lethargic that they can't build ANYTHING with their hands. They'll spend hours watching whiny people marooned on an island, but won't spend a second adding anything to the world. -weconway
Visit my [Locost 7 build log]

It sounds like a trailing uca and lca with a bell crank on the steering head of the k100 for connection to a lever on the diy upright.

I’d look at a legend car shock from speedway motors and a 1-5/8” spring. It can be hard to find rates less than 100#/”. For oem, try a miata front shock with a miata rear spring.

Are you planning to use an automotive tire or a bike tire on the 6” rim?

Since your fabricating the upright, just use spherical bearings with rubber sealing washers. OEM joints are heavy. A tapered fit would be better, but it isn’t necessary if the fasteners stay tight and the weights are low.


The bolt hubs use modified outer cv joints with the cup machined away.

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Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12

Agreed, but be careful about range of motion; a regular rod-end may not work.

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Kimini book: Designing mid-engine cars using FWD drivetrains
Both available from https://www.lulu.com/

For tires, I am planning on using 195/50 R16's. The sidecar wheel will not steer. Camber affects steering as the wide (compared to motorcycle front wheels), flat profile tire tries to roll up on the edge of the tire when turned. The more camber, the more pronounced the rolling up on the edge becomes. I could use the Corvette way and have the ball joints vertically in line (zero caster), and place the centerline of the hub behind the vertical centerline of the ball joints. But that makes steering difficult in that you are now trying to rotate the contact patch of the tire around the vertical axis of the ball joints.

Thanks,

Mike Lydon

That is still positive caster. If the balljoints and the centerline of the axle fell on the same vertical line perpendicular to the ground, that would zero caster.

_________________
Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12

So I'm probably completely missing something here, but if the wheel isn't going to steer, why not use a rear suspension design where the hub is at a fixed angle.

I'd also wonder how well it will turn, considering a bike tire has very little contact patch with the road and will have to try to overpower the much wider side car wheel. Unless your building some kind of a trike where its 2 weels up front and one out back, but in that case I would think you'd want to use a more of a rack & pinnon style steering...

dilbert, they'll be automotive wheels all around. I just discovered, today, that Miata front suspension can be used as is. 90-93 Miata's have zero scrub radius geometry (how about later years?). The driver's side front suspension will be the the rigs front suspension, the passenger's side will be the sidecar's suspension (placed 16" ahead of the rear wheel). A turnbuckle on the steering knuckle will allow easy toe in changes on the car. Since the BMW uses a bolt on wheel on a single sided swingarm, an adapter for an automotive is quite simple.

Mike

If your using the control arm geometry, the tire will move back and forth laterally relative to the chassis, following the arc created by the lca. Thats why I assumed in the previous post that you are using a trailing arm system on the front.

I think all the first gen/na miatas have zero scrub with the standard wheels. Some had optional wheels with a different offset.

_________________
Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12

Okay, now I'm confused. (It doesn't take much!) Are we talking about taking a BMW motorcycle and attaching a sidecar to it? Or using the BMW as a donor for a new creation?

Any chance you could post a sketch or a photo of a bike similar to what you're shooting for? I'm having a hard time envisioning exactly what you're building, and would sure hate to offer any advice that contradicts what you're doing.

-dave

_________________
...nowadays people are so intellectually lazy and lethargic that they can't build ANYTHING with their hands. They'll spend hours watching whiny people marooned on an island, but won't spend a second adding anything to the world. -weconway
Visit my [Locost 7 build log]

Dave, surf on over to www.hpsidecar.com for photos of similar rigs. My rig will not have one of those fancy high buck fiberglass bodies. What I will use for a body is still open for discussion.

Mike

The suspension on the bikes in the link is exactly what I'm talking about versus using the uca/lca pivots to the right of the spindle. Your suspension will be similar, yes?

_________________
Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12

Well, not exactly. I will be using the mobec layout, which is uca, lca to the right of the spindle. You can see this at www.mobec.de, look for the easydrive. My chassis will be flat, and connected to the BMW via a subframe, since the K100 has no frame below the engine.

Mike

You being happy with it is all that matters. I look forward to seeing build pics.

_________________
Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12