Rear scrub raduis

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johnny99
1
Joined: 09 Apr 2009, 19:28
Location: Killucan Westmeath Ireland

Rear scrub raduis

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Folks, I am in the design phase of a single seater very similar to a D Sports Racer. I have most stuff covered, but I cannot find much info on rear scrub radius. I believe it's not too important but I would like to hear the inputs of people on this forum.

John

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Tim.Wright
330
Joined: 13 Feb 2009, 06:29

Re: Rear scrub raduis

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It's not really critical in terms of any steering effects but it does affect the split of the longitudinal forces between the wishbones and toe link.

Do you have a picture of the proposed design?
Not the engineer at Force India

johnny99
1
Joined: 09 Apr 2009, 19:28
Location: Killucan Westmeath Ireland

Re: Rear scrub raduis

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No not yet Tim, just geo I want to meet without too much compromise. I hope to collect 2 sets of Formula Renault or F3 wheels when I get time in the next week or 2 and design around. Picking up a GSXR 1000 engine this weekend.

John

Greg Locock
233
Joined: 30 Jun 2012, 00:48

Re: Rear scrub raduis

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You could use it to modify your toe in and out under braking and accelerating, but if everything is rigid (it isn't) then it has very little effect on anything. I don't think I've ever seen it discussed and I know I've never been asked to calculate it.

Having said that, I have been asked to look at its sideview counterpart, the mechanical trail. This obviously interacts with the lateral compliance of the suspension to give toe effects under lateral loads, and is quite important in your understeer budget, although subjectively using too much rear compliance steer results in nasty steering feel.

johnny99
1
Joined: 09 Apr 2009, 19:28
Location: Killucan Westmeath Ireland

Re: Rear scrub raduis

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Ah Greg, now I have more thinking to do, mech trail on the rear, never thought of that. With my budget maybe I should go with zero of each and when it's working well, do some changes then.

John

Jersey Tom
166
Joined: 29 May 2006, 20:49
Location: Huntersville, NC

Re: Rear scrub raduis

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I would indeed start with zero of both unless you're really clever with compliance tuning.
Grip is a four letter word. All opinions are my own and not those of current or previous employers.

Greg Locock
233
Joined: 30 Jun 2012, 00:48

Re: Rear scrub raduis

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Definitely the place to start, and once you've done that you'll probably never need to change it.

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