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Author: Subject: Request for Baseline Suspension Numbers for Light Weight Vehicles
woodsy144

posted on 1/9/19 at 11:34 AM Reply With Quote
Request for Baseline Suspension Numbers for Light Weight Vehicles

Hello Team,
I am starting to model some front and rear uprights. To assist i would like to see what sort of baseline suspension numbers people have used and are happy with.
I understand there is going to be differences based on weight distribution, components used, peoples preferences etc etc etc. But I would like to see whats out there and the range.
I am looking for numbers for, but not limited too
- Camber
- Caster
- Caster trail
- KPI
- Scrub Radius
- Ackerman
- Roll Centres
- etc etc etc

Thanks

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G13BLocost

posted on 2/9/19 at 11:19 AM Reply With Quote
Hello,

What's your end goal? What are you trying to build?

Cheers
Josh





Between Building Robots, Building Cars, Playing D&D and Walking Dogs, I have no time at all!

Long time car builder and ex-F1 engineer; no silly questions please.

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woodsy144

posted on 4/9/19 at 05:23 AM Reply With Quote
Similar to the Warner R4, exo bike engined vehicle.

90% road, 10% track

Build a fun vehicle that can go on club drives and events. A bit of track blast.

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Sam_68

posted on 4/9/19 at 10:52 AM Reply With Quote
If it's mid-engined, you could do worse than use the Lotus Elise as a baseline.

Front suspension
roll centre height 30mm
travel 50mm bump / 60 mm rebound
camber gain in bump 0.31 degrees per inch
frequency 90cpm
KPI 12.0 degrees
Castor 4.25 degrees
Trail 4mm
Scrub radius 10.5mm

Rear suspension
roll centre height 75mm
travel 50mm bump / 70 mm rebound
camber gain in bump 0.45 degrees per inch
frequency 98cpm

Personally, I focus very heavily on keeping the geometric roll centres absolutely fixed (to within a couple of millimetres both horizontally and vertically) relative to the sprung mass... simple reason being that the roll centre height influences diagonal weight transfer when cornering, so if your roll centres are moving around, so are the loads at the individual tyre contact patches.

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woodsy144

posted on 4/9/19 at 10:46 PM Reply With Quote
quote:
Originally posted by Sam_68
If it's mid-engined, you could do worse than use the Lotus Elise as a baseline.

Front suspension
roll centre height 30mm
travel 50mm bump / 60 mm rebound
camber gain in bump 0.31 degrees per inch
frequency 90cpm
KPI 12.0 degrees
Castor 4.25 degrees
Trail 4mm
Scrub radius 10.5mm

Rear suspension
roll centre height 75mm
travel 50mm bump / 70 mm rebound
camber gain in bump 0.45 degrees per inch
frequency 98cpm

Personally, I focus very heavily on keeping the geometric roll centres absolutely fixed (to within a couple of millimetres both horizontally and vertically) relative to the sprung mass... simple reason being that the roll centre height influences diagonal weight transfer when cornering, so if your roll centres are moving around, so are the loads at the individual tyre contact patches.


Hello Sam,
Can you please confirm the scrub radius is +10.5mm, ie on the inside of the contact patch, not outside.
Due to the light weight nature of the car, I was thinking negative scrub, to assist with stability under braking due to the toe in nature

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G13BLocost

posted on 5/9/19 at 05:21 AM Reply With Quote
Why not just use toe to control stability? This is the classical method, or are you planing on having a lot of suspension compliance? You do say your going to be using this as mainly a road car.





Between Building Robots, Building Cars, Playing D&D and Walking Dogs, I have no time at all!

Long time car builder and ex-F1 engineer; no silly questions please.

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Sam_68

posted on 5/9/19 at 07:08 AM Reply With Quote
Negative scrub radius has a reputation of leading to very 'dead' feeling steering.

It also obviously requires a lot of KPI to physically package it.

As above; use toe in to give sufficient stability. But in any case, I'm assuming you're building a fairly hardcore sports car, not a Jaguar/Aston Martin style GT, so you'll be looking for steering feel and responsiveness, at the cost of some straight line stability?

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