la_strega_nera
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Re: Scrub Radius, Wheel Track and Coil Overs

Post by la_strega_nera »

Load through the shock mounting points is higher than spring loads anyway...
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Re: Scrub Radius, Wheel Track and Coil Overs

Post by Duk »

Mats wrote:MR depends on rife height, I suspect you did your measurements with the wheel off and the suspension in full droop?
MR measurements were with the LCA at horizontal without the TB installed but with the shock absorber there to get the angle.
Do you calculate a different MR Mats?
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Re: Scrub Radius, Wheel Track and Coil Overs

Post by Micke »

Don't worry about Mats. He's just being a smart ass :twisted:
Anyway as you just want to get into the ballpark it's not the las decimal that counts.

The values I've used are
315 mm effective length
250 mm to shock mount
17.5 deg shock inclination.

In my new LCA's I make 3 fastening positions for the shock. This way I can easily soften the suspension for rain by changing the MR.
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Re: Scrub Radius, Wheel Track and Coil Overs

Post by Maurizio »

I have the same MR from my calcs.

Edit: Micke's typing is faster :lol:

What Mats is saying is that the MR is changing, as your suspension moves, your lower arm runs trough a circle segment. In theory the tb setup has no linear stiffness.
Plus the top off your shock stays in the same place, so your helper spring changes also in angle wrt the forces.

The difference though is an second order effect and gets less if you stiffen up the suspension, so for hobbyists neglect-able :lol:
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Re: Scrub Radius, Wheel Track and Coil Overs

Post by Mats »

Just remembered that my car is maybe not the perfect datum either... :lol:
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Re: Scrub Radius, Wheel Track and Coil Overs

Post by Duk »

Micke wrote:Don't worry about Mats. He's just being a smart ass :twisted:
No, I don't believe you :P :P :P

Any way, has anybody any input about the effect of the scrub radius? Especially the effect of reducing the scrub radius?
I've read some stuff about how the scrub radius effects the braking behavior when the left and right wheels are on surfaces with different grip levels, but what about steering feel???

By the way, cheers to you die hards that entertain my mental wanderings :mrgreen:
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Re: Scrub Radius, Wheel Track and Coil Overs

Post by Micke »

A moderate increase in scrub radius is OK. In the 116 I'd say up to ET about 10 or so is still good to drive.
I once had some (I think Mirafiori) rims with huge ET. Probably negative. CAr was very heavy to turn and sensitive to braking surfaces.

My 5 ct conclusion is that if you want to widen the car from stock it's a good idea to so something about the scrub. As long as you keep within stock fenders probably not worth it.

Then only the hubs wont help at all. As long as you want the tire in the position it is (as far out as possible) only the position of the upper and lower ball joints can do the trick.

Then again if you make the LCA much longer you will reduce the scrub radius. But your KPI will go to hell. So you need a new UCA as well.
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