18 replies to this topic

[NeilR]

What sort of G forces would be encountered in speedway cars on unsealed tracks?
It is proposed on another forum that some speedway parts could be used in a road car, specifically these: http://www.speedwaym...Inch,29430.html
Now I quite like speedway for the spectacle, but I profess that I don't like these wishbones.
So any numbers for loads in speedway

[GSpeedR]

What sort of G forces would be encountered in speedway cars on unsealed tracks?
It is proposed on another forum that some speedway parts could be used in a road car, specifically these: http://www.speedwaym...Inch,29430.html
Now I quite like speedway for the spectacle, but I profess that I don't like these wishbones.
So any numbers for loads in speedway

At first glance, that arm does NOT appear to be acceptable for road-car use. Threaded bolts used in single-shear and rod-end used in a member that experiences bending (the rod axis on the LS member is not parallel to the axis between the UBJ and the rod-end spherical). It might be usable in the IMCA series since the loads will be reduced significantly from a larger US stock car...in fact it is likely a bad design mandated in the rules. US stock cars will typically see roughly 1.5G's laterally (body-fixed coordinates) at the "super-speedway" tracks (Daytona, Talladega), where they are restricted to roughly 190-195mph. Unrestricted, they could obviously reach much higher corner speeds and thus higher G's, but that has not been the case for many years.

Edited by GSpeedR, 20 November 2012 - 17:15.

[kikiturbo2]

parts like this one are used in some homebuilt vehicles, mostly locosts of some sort.... I think they do OK because such builds are usually really light, but I would not use such a design, ever..

[Greg Locock]

Road cars need to cope with much higher impact loads than race cars, by a factor of 2 or 3, and need to run for thousands of hours between rebuilds, not 5-20. That design could be made to work, but it would end up a lot beefier. it isn't a very pretty design in itself, I can't think of a good reason to use it as the basis for a new one. I'm a bit over the bolts and rod ends in bending objection, if you know what your loads are you can design accordingly.

[Lee Nicolle]

I too do not like that style of wishbone and feel it would fail in normal competition. AND I have never seen that style in use on a car!! If you look further on that site you will see the normal A arms, both offset and straight. With and without alloy cross shafts [which are not very durable] The chrome moly A arms are extremely tough and never bend in competition unlike a production style one do with monotonous regularity.. They do bend ofcourse when hit hard, as they should.
I used that style on my Sports Sedan for some time with no problems. [the factory ones used to bend all the time] I have seen them on hotrods and classic rally cars too. Though as Greg says they will not be as durable in the bushings etc as a production one. And sometimes throw load back into the pick up points which then fail. Just like eurathane bushes do, with those be warned, theyt are junk on a road car, and sometimes on a race car too as they bind up the suspension. And when they have a stel sleeve through them that always becomes unbonded in a very short period. In used cars I have scrapped that crap time and time again,, and had to weld up pick up points as well. If your mechanic sugests it, sack him. Rubber is the only reliable medium for those bushes.

[GSpeedR]

I'm a bit over the bolts and rod ends in bending objection, if you know what your loads are you can design accordingly.

Yes, but I think we would all agree that particular part would need a re-design.

[kikiturbo2]

Rubber is the only reliable medium for those bushes.

I really like how some suspensions have clearly diferentiated type of bushing depending on location... For example, on my EVO, rear lateral links use well protected spherical bearings... while longitudinal ones are rubber..

[Magoo]

I do not like the ball joint retention either. Depends solely on the hoop strength of a short length of tube. Good luck with that.

[kikiturbo2]

I do not like the ball joint retention either. Depends solely on the hoop strength of a short length of tube. Good luck with that.

exactly... plus, there is a bending moment on that left weld during braking and when hitting a pothole..

[Magoo]

The excessive adjustability is an interesting feature, recalls the adage: there is a limit to what can be accomplished with intelligence, but with stupidity the potential is infinite.

[gruntguru]

We are not seeing any suggestions for the lateral G's. GSpeedR gave us 1.5G for pavement which I assume is a figure for sedans - GE open wheelers would more than double that.

A quick and dirty calculation for a 1/4 mile (400m) circle and a laptime of 11 seconds (something a sprintcar can do on dirt) gives a latacc of 2G (can someone check my calcs). Clearly, speedway tracks are not circular so the latacc in the tighter corners will be even higher.

Edited by gruntguru, 21 November 2012 - 22:57.

[Lee Nicolle]

G Forces are just a number in this case. A speedway sedan is often all twisted up and bucking over ruts and holes. Bitumen is generally far easier on equipment. And they have a heap of scrub radius adding to the loads.
A sprinter is beam axle front and rear. Normally a 3" chrome moly front axle with 125thou wall, though some use 95 thou. Hanging on 1"OD alloy radius arms with alloy heim joints. Far more fragile than a sedan

[GSpeedR]

We are not seeing any suggestions for the lateral G's. GSpeedR gave us 1.5G for pavement which I assume is a figure for sedans - GE open wheelers would more than double that.

I missed the detail in the original post that he was asking about dirt tracks. I was speaking about stock cars on huge 2.5mi ovals (in a restricted format)...maybe some specifics about the racecar and the track would help us give better numbers. It sounds like Lee Nicole has a better idea of what he's describing that I do.

[Magoo]

If you look at the catalog page for the control arm, it's designed for an IMCA Modified. This is a specific U.S. racing series which cars run on mainly dirt and some paved oval tracks in the quarter to half-mile range. These cars are relatively heavy (2800 lbs) big and large (especially by global motorsports standards) and often run on very rough, torn-up tracks (since they are the cars tearing them up).

As with many limited, club/sportsman type racing series, a convoluted set of rules has evolved over the years. This in part is why this component is so funny looking -- it must bolt up to an original-spec frame location, accept a production car ball joint, and the adjustability is built in as a workaround for the other issues. In other words, it's a fairly specific application. If you are doing something else you can surely find something better. If you had a pair laying around that's one thing, but you wouldn't pick these.

[gruntguru]

G Forces are just a number in this case. A speedway sedan is often all twisted up and bucking over ruts and holes. Bitumen is generally far easier on equipment. And they have a heap of scrub radius adding to the loads.
A sprinter is beam axle front and rear. Normally a 3" chrome moly front axle with 125thou wall, though some use 95 thou. Hanging on 1"OD alloy radius arms with alloy heim joints. Far more fragile than a sedan

But far lighter too.

[bigleagueslider]

At first glance, that arm does NOT appear to be acceptable for road-car use. Threaded bolts used in single-shear and rod-end used in a member that experiences bending (the rod axis on the LS member is not parallel to the axis between the UBJ and the rod-end spherical). It might be usable in the IMCA series since the loads will be reduced significantly from a larger US stock car...in fact it is likely a bad design mandated in the rules. US stock cars will typically see roughly 1.5G's laterally (body-fixed coordinates) at the "super-speedway" tracks (Daytona, Talladega), where they are restricted to roughly 190-195mph. Unrestricted, they could obviously reach much higher corner speeds and thus higher G's, but that has not been the case for many years.

I would agree that this A-arm is not well designed. Putting bolts or the threaded portion of a rod end in bending is never a good idea. But it is an upper A-arm, so it is not subject to the same loading as the lower A-arm. The guys that sell these components and the guys that buy these components probably don't have any understanding of sound mechanical design principles.

[Fat Boy]

Is it pretty, no. Has it undergone FEA work or 'engineering' per say, no.

Can it probably take a hell of a lot more abuse that any of us would give it credit for? Yep. This this is the evolution of Lord-only-knows how many miles and failed attempts. Dirt cars are things that I don't claim to know much about, but I bet if it's bolted on the car it's made for it can last quite a while doing it's job in a satisfactory manner.

Cave men brought down their share of Mammoths, too.

[Magoo]

Is it pretty, no. Has it undergone FEA work or 'engineering' per say, no.

Can it probably take a hell of a lot more abuse that any of us would give it credit for? Yep. This this is the evolution of Lord-only-knows how many miles and failed attempts. Dirt cars are things that I don't claim to know much about, but I bet if it's bolted on the car it's made for it can last quite a while doing it's job in a satisfactory manner.

Cave men brought down their share of Mammoths, too.

[Grumbles]

I would agree that this A-arm is not well designed. Putting bolts or the threaded portion of a rod end in bending is never a good idea. But it is an upper A-arm, so it is not subject to the same loading as the lower A-arm. The guys that sell these components and the guys that buy these components probably don't have any understanding of sound mechanical design principles.

That sounds a little harsh, I'd be surprised if there weren't some sharp guys racing on dirt. They probably realize that car parts, like everything else, don't normally have to be perfectly engineered, they just have to be good enough. And that even imperfect designs can be entirely adequate (albeit a little heavy) if properly proportioned.