Steering Geometry

[MatthewBasaraba]

There has been lots of discussion on this topic, so rehashing everything is kind of BUT recently I had made a post with my spindles and was shot down by its angles.

Now I have had several people point me to THIS site for geometry of Castor, Camber and Acker.

Quote on Castor..."In practice, many people settle for angles between 20 and 25 degrees."

Quote on Camber..."Generally this angle is between 10 degrees and 12 degrees, and to allow the wheels to stand flat on the floor, is offset by a similar angle on the stub axle."

So I built mine with 20 degrees of Castor and 10 Degrees of Camber. The statement replied to me is, with 20 degrees of Castor this kart will never turn. I made reference to the site posted and never got a reply. IMO, if you are going to shoot something down, bring some facts and offer advice from experience on how it SHOULD be.

Since this person has failed to follow up, can anyone offer insight on why this was wrong and what to do to improve it?

Picture of my spindle plus fixture.

 

[redsox985]

I do not know about how these ideas change steering, only what these online sites say. Now, I prefer this site. IMO, it is one of the best places for kart info because it is interactive and contains so many topics.

 

[Kaptain Krunch]

Quote on Camber..."Generally this angle is between 10 degrees and 12 degrees, and to allow the wheels to stand flat on the floor, is offset by a similar angle on the stub axle."

That quote describes KPI (king pin inclination) not camber. Generally i would suggest 0* of camber for your average go kart.

Quote on Castor..."In practice, many people settle for angles between 20 and 25 degrees."

Those angles are a little steep, i'd say somewhere in the 10-15 range max, the 20* you used would definitely make it a little harder to steer.

Personally i'd say somewhere in the 10-15 range for both castor and KPI, i used 12 and 12 on my kart IIRC

 

[MatthewBasaraba]

SITE it says Camber, I am just repeating what it says. I dont care what it is called as long as I have the angles correct, Camber/KPI or whatever people want to call it.

I will reduce the castor angle to around 10 I guess. I will need to redo my fixturing.

So apparently this site doesnt show camber, I thought the only one that people leave at zero is toe.

Matthew

 

[Doc Sprocket]

Ah, Kaptain, you beat me to the punch! So... What he said...
Camber refers directly to the vertical angle of the tire, expressed in degrees + or - perpendicular to the road.

You should care what it's called. Having a confusion in terminology leads to misunderstanding, and errors.

You could theoretically have a 10* KPI angle, and a -2* Camber angle. This is where the terms must be clearly defined. In this example, the kingpin sits 10* off the vertical, YET- the tire sits only 2* off true vertical. This example would be attained by cutting the end of the axle tube at 80* before welding the spindle bracket on. Then, you would attach the spindle to the bracket NOT at an opposite 80* angle, but at 82*. Everything attached, this would give you a KPI of 10*, AND -2* of camber. See what I mean?

Positive camber is when the top tof the tire tilts outward from the vehicle, negative camber is when the top of the tire tilts inward.

Having a little bit of negative camber will improve cornering traction. Having the right combination of caster, camber, and KPI will load up the inside tire in a turn, greatly improving cornering.

There is a lot more to proper steering geometry than this, and the ideal caster, camber, and KPI angles will differ between vehicles.

EDIT- A had a peek at the site link you provided. Their definition of camber is very simply wrong. Camber refers to the orientation of the tire (spindle), and NOT the kingpin.

 

[redsox985]

Is there a way to calculate needed caster, camber, and KPI or are certain amounts better for different applications?

 

[devino246]

I thought the only one that people leave at zero is toe.

Matthew

Actually, you need a little toe in to help with steering.

 

[Briang701]

The best advise I can give you is to either get your hands on some suspension design books or visit Locost usa dot com and reads through some of the threads in the suspension section, there is a huge amount of good info there.

A wise man once told me suspension is nothing but compromise, you have to decide which factors are important to you.

 

[Doc Sprocket]

The numbers vary by application, which goes hand-in-hand with the above comment. What works well on asphalt is not likely the best choice off-road. There are some very complex formulas for figuring this stuff out, or you can just start with good base values and tweak. Generally, the KPI is directly correlated to the scrub radius. Ideally, you should be able to draw a straight line through the kingpin, and that line should extend right to the centre of the tire's contact patch.

 

[Briang701]

The numbers vary by application, which goes hand-in-hand with the above comment. What works well on asphalt is not likely the best choice off-road. There are some very complex formulas for figuring this stuff out, or you can just start with good base values and tweak. Generally, the KPI is directly correlated to the scrub radius. Ideally, you should be able to draw a straight line through the kingpin, and that line should extend right to the centre of the tire's contact patch.

 

[MatthewBasaraba]

Ok so my spindle has 20 degrees Castor (going to reduce this some, was just going by the numbers given), 10 degrees KPI and since I am welding the the stub axle perpendicular to the frame, 0 degrees of Camber.

Your vertical statement threw me off a bit but I see now that you meant 2 degrees off perpendicular to the frame or 82 degrees from the Kingpin perpendicularity which now makes perfect sense.

What I meant about 0 degrees of toe is, that I wouldnt figure this into the spindle, this can be adjusted by the tie rod end in and out.

Thanks everyone to your replies, this is what makes this community what it is.

Matthew

 

[Doc Sprocket]

Good stuff!