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13" Suspension Setup
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Author:  WasabiPimpNinja [ Thu Aug 16, 2018 3:43 pm ]
Post subject:  13" Suspension Setup

Hi All,

I'm in the process of setting up a car on 13x7 rims with 175/50R13 tyres. This will be a track/hill climb car only, it is not registered and won't be driven on the street. Currently on GAZ Coilovers all round, all the normal adjustable bits front and rear, and a rear Anti Roll Bar. The car is in the process of having a full 6 point cage welded in as well.

When setting up 13" rims, is the only real difference the reduced Camber front and rear? Or are Toe and Castor also different from a 10/12" setup?

Just need a general starting point for the car so I can experiment from there.

Cheers,

Author:  fuzzy-hair-man [ Sat Aug 18, 2018 5:36 pm ]
Post subject:  Re: 13" Suspension Setup

An article in mini magazine years ago suggests the following starting point for a road sport and trackday car on 13" wheels :


For race the suggestion was :
3 degrees castor, 1.5 to 2 neg camber front, 0 to 0.5 neg camber rear, 1/16 to 3/32 toe out front, zero toe in rear.

Author:  WasabiPimpNinja [ Mon Aug 20, 2018 12:38 pm ]
Post subject:  Re: 13" Suspension Setup

Cheers fuzzy-hair-man!

That's a bit more front camber than I was thinking but we'll see how it looks on the alignment machine.

Also interesting it calls for Zero Toe on the rear, I would have thought 1/16" toe in as minimum..

Cheers,

Author:  fuzzy-hair-man [ Mon Aug 20, 2018 6:20 pm ]
Post subject:  Re: 13" Suspension Setup

The toe in on the rear was factory it seems a bit of a safety tolerance thing to make sure they didn't get toe out as that has dramatic effects towards oversteer I'm told. If you know your rear toe then zero toe becomes acceptable as factory there's no way to adjust except
Those are a starting point so feel free to modify to your tastes...

Author:  simon k [ Tue Aug 21, 2018 1:18 pm ]
Post subject:  Re: 13" Suspension Setup

fuzzy-hair-man wrote:
The toe in on the rear was factory it seems a bit of a safety tolerance thing to make sure they didn't get toe out as that has dramatic effects towards oversteer I'm told.


not really 'dramatic'... toe-in at the back promotes understeer, toe out at the back promotes oversteer, but it's not like the car is constantly trying to spin itself around. It just feels like the car is more willing to turn when you start to feed in some steering

If you think about the outside wheels when going around a corner, they're the ones doing the work...

So, when turning right, the wheels are like this:

rear toe in - the car will turn less for a given amount of steering input - the rear wheels resist the turn-in
/

/


rear toe out - the car will turn more for a given amount of steering input - the rear wheels assist the turn-in
/

\


The rear toe-out picture is the way *most* four wheel steering cars work. The rear wheels turn the opposite direction to the front wheels to help the car go around the corner. I once borrowed a 4WS Honda Prelude and it was great fun when turning right on roundabouts, once I got used to how it turned much sharper than I expected for the amount of steering input I was giving it. I kept bumping up the inner curb.

I say *most*, because I gather some cars at the higher price range (Mitsubishi GTO I think) actually change the direction of the rear steering at higher speeds. At low speeds the rear wheels turn in the opposite direction to make maneuvering easier, but at higher speeds the rear wheels turn in the same direction as the front wheels to lessen the direction change from small steering inputs - basically making the car more stable, but it doesn't turn in to a corner as well (but to turn in to a sharp corner you'd have slowed down enough for the steering to change modes and help you turn blah blah)

Author:  WasabiPimpNinja [ Tue Aug 21, 2018 3:25 pm ]
Post subject:  Re: 13" Suspension Setup

Some good points to consider here.

I think I'll baseline with 0 Zero Rear Toe and if I find the need for turn in adjustment or if the rear tyres aren't keeping temp I'll look at adjusting the toe.

Cheers

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