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Overthinking alert - ‘resting’ height of suspension
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Author:  shakes [ Fri May 07, 2021 5:46 pm ]
Post subject:  Overthinking alert - ‘resting’ height of suspension
I’m keeping myself distracted and also driving 4hrs a day at the moment, apologies for the waffle. A question for the cleverer folk.

A random though I had, is there a specific ratio of up to down travel. And where the car should sit into that?

IE a shock has 300mm of total travel. And an example of 1/3rd up travel and 2/3 down. So set your spring/ride height to where the shock sits 100mm into its travel.

Have I thought about this the right way? I assume this changes for rally, to crawling to track and across suspension designs.
Where would I go to read more on this?
Author:  Gwagensteve [ Sat May 08, 2021 8:29 am ]
Post subject:  Re: Overthinking alert - ‘resting’ height of suspension
Good question Shakes

Very conventional 4WD wisdom is 50% up and down, but that's a way to end up with an excessively tall car if you keep adding lift as you add travel.

A stock Sierra has more droop than compression in the front and more compression than droop in the rear at rest because the rear sees more change in load than the front.

As you point out it's more about use. increased speed = more requirement for compression travel

Even then, in offroad racing, it's not that clear cut -
Very high travel off road cars (i.e trophy trucks) will run around 1/3 compression 2/3 droop (with ~36" of total travel) - but that's still 12" of compression, but buggies are limited in travel by having CV joints in the rear (independent suspension) so they tend to run more compression than droop, maybe they're close to 50/50 with around 24" of total travel in the rear.

I'd say rock crawling is such a niche application it's almost unhelpful to talk about as there is almost no allowance given to speed. Ultra4 is a more realistic application of suspension design.

As I alluded to in my first comment though - the examples I'm giving are where the whole chassis is designed around a suspension outcome. For those of us working within stock parameters we largely have to deal with what the factory dishes up.

there's a number of books along the lines of "fundamentals of suspension design" intended to help chassis builders set up (typically circle track) cars
Author:  MrRocky [ Sat May 08, 2021 10:13 am ]
Post subject:  Re: Overthinking alert - ‘resting’ height of suspension
On rocks ive found with less than a 1/4 uptravel can work well with the car resting on the bumpstop however if you are doing anything other than crawling you will want a bit more than this or alternatively some more absorbtion in your bumpstops
Author:  fordem [ Sat May 08, 2021 10:22 am ]
Post subject:  Re: Overthinking alert - ‘resting’ height of suspension
I just wanted to suggest that "resting on the bump stops" should perhaps not be considered the upper limit of compression travel - I believe it's not uncommon nowadays for manufacturers to use "progressive bump stops" that are designed to compress providing an increase in spring rate as the suspension nears the end of travel.
Author:  shakes [ Wed May 26, 2021 2:35 pm ]
Post subject:  Re: Overthinking alert - ‘resting’ height of suspension
fordem wrote:
I just wanted to suggest that "resting on the bump stops" should perhaps not be considered the upper limit of compression travel - I believe it's not uncommon nowadays for manufacturers to use "progressive bump stops" that are designed to compress providing an increase in spring rate as the suspension nears the end of travel.


I'll pretend to be smart and ad that as body twists, diff's get pivoted off bump stops etc. There is more travel. Most bumps are rubber and compress too.

Thanks for the answers, helped when I needed to keep busy.
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