Camber for inner wheel 1

[sierra4000]

Hello!
my thoughts now
What is the requirement camber for inner wheel when racing cornering?

For example, when the outer wheel works well on 1 DG negative?
This means that the inner wheel require 1 DG positive camber?
or is different recommendation?

This achievable with macpherson's


Thank you
Radek

 

[GregLocock]

MacP limits your options with camber. Roughly speaking it would be nice if the tires were parallel in front view when cornering, but if you look at the F&M data for your tire you might want to change that a bit to account fr load transfer and the difference in steer left to right.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

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[sierra4000]

Thank You Greg,

Can you explain this please? : you might want to change that a bit to account fr load transfer and the difference in steer

this means :inner less load = smaller positive camber will better?

 

[BrianPetersen]

Most of the loading is on the outer tire. Unless the center of gravity is exceptionally low compared to the track width, it's pretty likely that the loading on the inner tire will be so low that the camber is not meaningful.

Look at Formula 1 cars. They run static negative camber and have a front suspension design that almost keeps the wheel camber the same (very nearly parallel upper and lower links in front view) and have exceptionally high roll stiffness, and exceptionally wide tires (by road-car standards) that ought to be very sensitive to camber. Yet the inner wheel is leaning the "wrong" way because of the geometry that they use. If it was meaningful, they would do something about it, but they don't.

Get your front suspension so that it's stable on straightaways (both wheels equally loaded) and so that the outside front wheel does the right thing when cornering, and let the inside front wheel do whatever it wants to do as a result.

Lots of front engine rear drive cars lift the inside front completely off the ground during hard cornering. What effect does the geometry have in that situation??

 

[GregLocock]

I don't know. Look at the data for a few tires and draw your own conclusions.

Thinking about it I expect evenness of wear is more important than max Fy, in which case the graphs won't help much.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

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[dynatune]

The "ideal" requirement for camber during cornering is "in general" to compensate for the roll angle in order to keep the contact patch as ideal as possible to the ground. Said simply: if you would have a typical 2° of suspension roll for your type of car you would be looking to compensate for that value. If you run a static negative 1° of camber you would have to compensate on the outside wheel still a remaining 1° and at the inside wheel a 3°(see below later). Typically a McPherson does not have huge camber gains (about -15°/m in heave which roughly equals -0,15°/°roll) which would mean that on the outside wheel you would recapture 3 x -0.15° = -0.45° camber due to roll movement. Let's assume 0.5°. This would leave a remaining 0.5° to be addressed. Your steering system does also increase negative camber with steer angle on the outside wheel (up to a certain lock angle) and one can say that for a rule of thumb for a typical 4 degree caster, 8° KPI steering system the amount of negative camber with 15° wheel angle is about -0,5° extra on the outside wheel. So in high steering lock corners you are arriving at a total camber to road angle of: (2°roll -1°static -0,5vert/roll -0,5°steer) = 0°. So your outside wheel is about correct.

Now bear in mind an important fact: On the outside wheel King Pin Inclination and Caster counteract each other in creating negative camber, however on the inside wheel the do work beautifully together creating Positive camber ....

For the inside wheel you should be recovering 1° more since your static negative camber hurts works in the same way as the roll angle. McPherson suspensions do increase their camber gain in rebound more than in compression (long story). This means that the positive camber recovered in roll will be around 0,75°. The Steering system will however (due to caster and KPI) recover more than twice as much which is about 1,25° positive at about 15° wheel angle. Having found 0.75° and 1,25 ° positive camber at the inside wheel at high lock steering angles one arrives at the following numbers for the inside wheel: (-2°roll - 1° static + 0,75°vert/roll + 1,25°steer) = 1° negative. This means your inside tire still is running with negative camber angle relative to ground but since it is the inside tire it is of lesser importance. If one would like to change this the options are limited:

1) changing static negative camber .. this will hurt the outside tire which is the more important one
2) making camber gains in bump/rebound more significant (which unfortunately many times affects roll center heights and movements)
3) play with KPI & Caster angle layout. Here one needs to bear in mind that what is good for the inside tire is bad for the outside

Usually these kind of trade off studies are done with suspension kinematic programs. It is as you might have guessed not a simple task but all the more rewarding if it works. Food for thought.

Cheers,

dynatune,

http://www.dynatune-xl.com

 

[sierra4000]

Thank you gentlemens!! very informative for me


Cheers Radek

 

[dynatune]

We want you to win races .....

 

[sierra4000]

Thanks ,
I really appreciate it!

Dynatune,
we can say:
There are the typical values ​​(approximately) Caster and KPI for camber -0.5-1 DG and 2 DG body roll ?(for crossply tire)

as a starting values for my tuning and test


For example those 4 and 8 DG of what you say?
what relationship Caster vs KPI?

(racing seat leon has about -3,5 camber,9 caster,13 KPI for radial tires-very approximate values)

Radek

 

[dynatune]

Typically a (modern)McPherson type Strut is designed to have around 4° of caster and 8° of King Pin. On racecars like the Seat the King Pin increase comes basically from package reasons in order to fit racing brakes, increase track width and permit wider tires whilst the increase of caster is for the reasons that I explained earlier in order to gain camber with steering lock. The static camber of -3,5 degree is a typical value for a low aspect ratio slick tire (between -2,5° and -4° usually)

The relationship between Caster and KPI is that as I explained on the outside wheel the two work against each other (caster creates negative camber on the outside wheel with steering angle and KPI creates always positive camber with steering lock) and on the inside wheel the work together creating both positive camber angle with steering angle. The ratio is about 1 to 3. Explained: for every degree of KPI at 15° steering angle the camber changes 0.1° (always versus positive values) and for every degree of Caster the camber on the outside wheel becomes 0.3° degree more negative and on the inside wheel 0.3° more positive.

So the seat leon at 15° lock will change it's camber setting (due to steering effects only):
Ouside Wheel KPI : 13 * 0.1 = + 1.3°
Outside Wheel Caster: 9 * (-0.3) = -2.7°
Total = -1.4° Camber extra due to steering

Inside Wheel KPI: 13 * 0.1 = + 1.3°
Inside Wheel Caster 9 * (+0.3) = +2.7°
Total = +4° Camber due to Steering

Remains the camber due to body roll but that should be max 0.5°. Again all of this is more or less approximated.

Hope this helps understanding

Cheers

Dynatune,

http://www.dynatune-xl.com

 

[sierra4000]

I read about 10 times!!
hopefully I understand correctly

it means that
my KPI (resulting from packages reasons like for example wheel width and required scrub radius)is compensated caster angle (for required maintaining wheel camber)?

it means that
more KPI=more caster requirement ?

of course
more KPI =more lifting effect?

I understand correctly?

 

[sierra4000]

so for example
If I have now my sierra KPI 11 DG (small KPI is always better?)caster 7 DG and static camber -1 DG
then at 15 DG steer I will change have

in +1,1 out+1,1 (KPI effect)
in +2,1 out - 2,1 (caster effect)
in -1 out -1 (st.camber)

total camber without body roll effect in +2,2 DG and out -2 DG

if body rolling 2DG - will change

+0,75 in and -0,5 out caused due to roll movement - but -2 DG roll

remaining in +0,95 and ou -0,5 (of course also there will small help anti dive)

calculation is correct? I understand CORRECTLY?


I can improve a little change in static camber (for example -0,5 DG)
or is better caster change?

 

[dynatune]

Yes, as far as I can follow it is correct. It is important to know that caster angle and King Pin Inclination angle do interact on suspension characteristics. The matter is far from simple - but that is the fun part -and soon you will be able to have a tool that does all that for you. I am putting the final hands on a software tool that should allow you to investigate by yourself the world of suspension kinematics.
Whether static camber or caster is better ? .. I would always go for caster since it is beneficial in cornering. The only disadvantage is steering torque increase (and compliance feel, but who cares..). You as a 4x4 guy need to stay attend to the caster offset at wheelcenter for torque steer issuer. If you were a RWD you could go to 10° of caster with a lot of caster offset ....

 

[sierra4000]

OK,

provided that on the basis of tire temperature(for example at skidpad)
I find that the best camber on outer front wheel(For example, - 0.5 DG)
I should try to be close to this value (using the caster setting)at different angles steering and different body roll ?
(For example, - 0.2-0.8 DG)?

or is better get more negative values (For example, - 0.4-1 DG)?

how much sensitive(generally) crossply racing tire for camber deviation ?(grip loss)

how much scrub radius is good for 10 inch wide tire?