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Author Topic: BUMPSTEER MEASURING
teofragoso
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Posts: 7
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Post BUMPSTEER MEASURING
on: September 1, 2014, 09:58
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Hi;
I´ve been measuring the bumpsteer and I wonder wether the possitive figures are toe-in or toe-out?, for example: if I have +0.1mm is that toe-in and if I have -0.1mm is it toe-out?. I think this is important to avoid toe-in in bump (bump-oversteer). Thank you, and again, congratulations for all these apps. They are awesome!
cheers.
racingaspi-
rations.co-
m
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Post Re: BUMPSTEER MEASURING
on: September 1, 2014, 10:14
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Hi teofragoso,

A negative value is toe-in, a positive value is toe-out. You will also need to multiply the value by the length of the steering arm on the upright to get the true value.

Imagine drawing a line perpendicular to the kingpin to the steering arm / upright connection. The length of this line is what you will need to multiply by.

Regards,
Huw
teofragoso
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Posts: 7
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Post Re: BUMPSTEER MEASURING
on: September 1, 2014, 12:59
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ok, I see. What doesn´t make sense to me then (if I have to multiply the value by some number) is that then the value that the calculator gives can´t be in millimiters?, because if I multiply 0,1mm by 100 mm (say this is the tie rod end to KP distance) then the bumpsteer would be 10mm, which is too much. I´ve been measuring the bumpsteer on the car (same geometry as in the model) with the gauge and it was 0.3 mm toe-out in full bump, so something does not match?
thank you for your help.
racingaspi-
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m
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Post Re: BUMPSTEER MEASURING
on: September 1, 2014, 13:37
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Sorry, I meant to calculate the change in toe-in/toe-out angle you would need to factor in the length of the "tie rod end to KP distance".

The toe-in/toe-out distance will be different depending on where you measure it. The kingpin is the centre of rotation as far as steering goes. The calculator measures a 0.1mm difference in steering 100mm from the kingpin. If, on the car you where to take the measurement 300mm from the kingpin then the change would be 0.3mm.

Just a thought for why the values might be different.

Regards,
Huw
teofragoso
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Posts: 7
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Post Re: BUMPSTEER MEASURING
on: September 1, 2014, 13:45
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OK, I understand. So the calculator is using 100 mm as reference (what a coincidence!) I think on my car the real "tie-rod to KP distance" is something like 130 mm so I would need to multiply 0,1 mm by 1,3 as correction factor, which gives 0,13 mm if I´m not wrong. this makes sense to me. thank you for your help. It is really appreciated!
racingaspi-
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m
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Post Re: BUMPSTEER MEASURING
on: September 1, 2014, 14:29
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I was only using 100mm as an example. The calculator doesn't store the "tie-rod to KP distance" yet so unfortunately you have to manually calculate what the change will be if you want it to be at a specific distance from the kingpin - for example: the front edge of the tyre.

If you know "tie-rod to KP distance" (which you do) you can use it to calculate the change at different points across the tyre.

So in your case your "tie-rod to KP distance" is 130mm. The calculator displays a 0.1mm change. Assuming you want to calculate the change at the outer edge of the tyre and your tyre radius is 390mm (example).

Multiply 0.1 by 390/130 = 0.3mm

Regards,
Huw
teofragoso
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Posts: 7
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Post Re: BUMPSTEER MEASURING
on: September 1, 2014, 14:42
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ok, understood now.
thanks again.
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