Scrub, KPI, spindle balance
Scrub, KPI, spindle balance
(OP)
Hello. I've re-read the relevant bits of RCVD and looked through my pile of prints from your discussions. Let me tell you what I think is true and I hope you will give me your thoughts.
My car has SLA front and rear I am lowering it by moving both the front and rear, top and bottom outboard pivots down vertically relative to the hub centres. I will do this by remaking the front and rear uprights. My concern is mainly with the effects this will have at the front.
Currently it uses: 3deg castor, 9deg KPI, 100mm spindle length and has 53mm positive scrub radius, all measured wheels straight ahead. Due to the proximity of the lower outboard front pivot to the brake disc, then as the pivot moves down so either the spindle length must grow, or the KPI reduce and scrub radius increase.
To maintain a constant spindle length, I calculate the KPI must reduce to 5.6deg and the positive scrub radius will increase to 71mm.
I have gathered from my readings that a 2:1 KPI:castor is a good guide, I wonder if for a road car you would agree?
What do you all think about the balance of these existing features and the best choice of the ones to move to?
Thank you, Colin.
My car has SLA front and rear I am lowering it by moving both the front and rear, top and bottom outboard pivots down vertically relative to the hub centres. I will do this by remaking the front and rear uprights. My concern is mainly with the effects this will have at the front.
Currently it uses: 3deg castor, 9deg KPI, 100mm spindle length and has 53mm positive scrub radius, all measured wheels straight ahead. Due to the proximity of the lower outboard front pivot to the brake disc, then as the pivot moves down so either the spindle length must grow, or the KPI reduce and scrub radius increase.
To maintain a constant spindle length, I calculate the KPI must reduce to 5.6deg and the positive scrub radius will increase to 71mm.
I have gathered from my readings that a 2:1 KPI:castor is a good guide, I wonder if for a road car you would agree?
What do you all think about the balance of these existing features and the best choice of the ones to move to?
Thank you, Colin.
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RE: Scrub, KPI, spindle balance
RE: Scrub, KPI, spindle balance
My interest is in how others viewed the balance of srub, KPI and spindle as now and how they could be moved.
I have tried without much success to find data for a range of current road cars to see where castor and KPI sit.
RE: Scrub, KPI, spindle balance
RE: Scrub, KPI, spindle balance
I had thought about tyre roll as the car uses old style tall tyres and may well, for all I know, loose its srub when cornering hard.
I'm sure I've seen either people on here or somewhere similar talk about this 2:1 ratio of KPI:castor, can't remember where I picked it up from though.
My inclination at the moment is to keep the spindle length as is and reduce the KPI and let the scrub grow. Not had the jig made yet so still time to change mind, will see.
Thanks again, Colin.