Tire Shrub ???

FABRICATOR

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Yes, unequal length does make most of the camber change. It is also influenced, to a lesser degree, by the positioning of the arms. As Porter said, side scrub won't cause binding in the dirt. The only way side loading would be induced is if you dropped the car several feet straight down. Even then it's not much. It must also be remembered that the tires are rolling.

Re: "OK, some think side scrub is important and some don't?
Is the total weight of the vehicle a factor? Light weight rear engined vs a heavy mid/front engine?"

I would say it's proven that side scrub isn't very important. The weight debate affects all aspects and components of a vehicle. As mentioned in my previous post, there are some fast class 1 and 10 cars that have equal length arms, that are scrubbing vigorously. They are usually so wide and light that camber is not relevent. The heavy trucks need all the help they can get for stability, handling, and strength. Some camber change is always used, especially as the wheel goes up. Another factor that you did not mention is available power. The more power you are applying to the ground, the less all that matters.

<font color=orange>The best ideas are the ones that look obvious to the casual observer.</font color=orange>
 

ntsqd

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Yea, I didn't mention the incurred bumpsteer of that design nor did I mention it's other major faults, but I did say "Don't go there." Anyone who's ever driven a Morgan will know why........

TS

I used swerve around my halucinations, now I drive right thru them.
 

MNotary

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"They are usually so wide and light that camber is not relevent."

Please explain.

When does excessive camber change induce excessive loads?

At 20in of travel, which parameters are the most critical to reduce?

Measured at 10in. down and 10in. up.
Camber-down 3.5deg up 1.1deg
Side Scrub-down 1.6in. up 1.1in.
Scrub radius 3.8in.
Caster 6.9deg
Caster trail 1.5in.
Bump Steer down .12deg toe in up .042deg toe in out Get alot of small "zigzags" through the cycle.
Fore/Aft .4in. forward down 1.375in aft up
This all on a A-arm suspension program.
 

MNotary

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And speaking of centrifugal forces. If the camber is changing it loads the tie rod. The steering loads the heims on the arms.
 

FABRICATOR

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Re: "Please explain."
Explain what? This is common existing stuff. These cars basically have no camber change and plenty of scrub. They are also plenty fast. There is a picture of one in another thread. It might just be a coincidence... but these are usually the ones with aluminum spindles.

Re: "When does excessive camber change induce excessive loads?"
When it causes a large, fast spinning wheel to quickly deviate from the plane it is spinning on. This is because of the very strong gyroscopic effect. This can be more detrimental than the alleged scrubbing.

Re: "At 20in of travel, which parameters are the most critical to reduce?"
Bump steer, bump steer, and also bump steer. Those "zigzags" are probably from your program. Scrub radius may be excessive. However everything you show is affected by application, tire size, and vehicle weight, just for starters. They also must be considered is a dynamic sense because most of them are not fixed as many "engineers" often assume.





<font color=orange>The best ideas are the ones that look obvious to the casual observer.</font color=orange>
 

MNotary

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I didn't get what you meant by camber not relevant. It is not relevant because there is no camber change...ok...got it. Aluminum spindles??? They are built with different king pin and stub angles?

"When it causes a large, fast spinning wheel to quickly deviate from the plane it is spinning on. This is because of the very strong gyroscopic effect. This can be more detrimental than the alleged scrubbing." Going with the idea that the sprung weight is proportional to the build strength, could you give me a number?

From my previous post, the bump steer change on the way up is toe IN.

"They also must be considered is a dynamic sense because most of them are not fixed as many "engineers" often assume." Dynamic as in the suspension travel or in the "flex" of all the parts?
 

FABRICATOR

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Sorry, you're right, I left a word out and was referring to camber change.

Re: “Aluminum spindles??? They are built with different king pin and stub angles?”
Not really, what I was saying is that they are usually used with equal or nearly equal length arms. The spinning plane moves in and out but does not deviate much from vertical; therefore low stress.

Re: “Going with the idea that the sprung weight is proportional to the build strength, could you give me a number?”
Proportions or ratios are the key to all of the engineering and are the biggest kept secrets. Also, a lot of them are just not known. This is one area where computer tracking and analysis could be extremely beneficial. A number is not that simple. There are too many variables involved. It is highly affected by unsprung weight, wheel travel, and the design of the rest of the car.

Re: “From my previous post, the bump steer change on the way up is toe IN.”
If you’re going to have it, that is the way it should go.

Re: “Dynamic as in the suspension travel or in the "flex" of all the parts?”
Partially in the suspension travel but mostly in what the rest of the car is doing. Often the A-arms or their axes are not mounted perfectly parallel in any direction. This changes things throughout the travel. As far as what the car is doing; a TT, for example, in the fast forward, braking, or turning mode is hardly level. There are several degrees of angle there to add or subtract from the static numbers. All front end values work around the tire-to-ground contact patch. That patch moves around a bunch in nearly all directions This all results from the combination or ratios of power to weight, sprung vs unsprung weight, wheel travel, CG, and weight transfer. The dynamic numbers are the ones being put to the ground.

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BA_DirtDriver

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Re: “From my previous post, the bump steer change on the way up is toe IN.”
If you’re going to have it, that is the way it should go.

This would result in oversteer when cornering. Wouldn't you rather have a little understeer? If that is the case toe out on the way up would be easier to drive.
 

FABRICATOR

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Toe-out is in the same boat as positive camber and is never good. You can get away with a little in the wheel down position because traction is poor anyway. Toe-out makes the car wander, especially up the sides of any trail or road. This happens in the rear also. The target is zero at times of high traction. That is why axles have a static setting with a small amount of toe-in. Toe-in will waste some power and rubber but will provide a higher degree of vehicle control compared to toe-out.

<font color=orange>The best ideas are the ones that look obvious to the casual observer.</font color=orange>
 

ntsqd

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If you're driving on pavement and you need the car to be more reactive to cornering input, then you may want to run a little toe-out and possibly monkey with the Ackerman.
Toe-out makes a vehicle 'darty', it will follow seams (or ruts) in the roads and just generally be squirelly. And not in a good way. Probably not what you want in handling characteristics when landing the 35' jump...........

TS

I used swerve around my halucinations, now I drive right thru them.
 

BA_DirtDriver

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Ok, makes sense in an off-road app. Next question most people are building the lower links at or near wheel centerline. What is the advantage of this? Also lets look at this picture and do a little on the fly analysis. For our analysis lets assume that the cars body roll and overall attitude is 100% from turning. I am sure this is not the case, but if it were whats going on with the suspension.

Bret

PS I am not making insinuations about the builder or designers here just a case study for fun if anyone is interested. That is also why I chose the cornering assumption since a static picture can in no way tell us all the loads that the vehicle is seeing.
 

ntsqd

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By placing one arm very close to the wheel CL you reduce the mass required in the other arm. By choosing the lower arm you get a larger travel path radius since the nearest arm dominates the travel curve. So the system acts more like a TIB except that the upper arm gives you a more desirable camber curve than the TIB's camber curve.

The truck in your attachment has parallelogram or very nearly parallelogram front arm geometry. Notice that both tires are still straight up and down relative to the body.
If there were a camber curve both tires would be closer to rolling flat on the ground. By going with geometry like that in the pic you are giving up tire contact patch in corners. My guess is that this truck understeers a lot. If the driver prefers to drive with the throttle and the brakes that's OK. If the driver wants it to drive more like a slot car and less like a WRC car then the front geomtry will likely need to change drastically.

TS

I used swerve around my halucinations, now I drive right thru them.
 

ntsqd

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Adding roll stiffness ("more roll/sway bar") to an axle decreases cornering traction at that axle. So if you add roll stiffness to the front it will understeer even more. If you add it to the rear it will be easier to kick the tail out with the throttle.
Swaybars should be used to fine tune, not correct basic problems.

TS

I used swerve around my halucinations, now I drive right thru them.
 
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