Air Shock Info... for an unusual use....
jimcroisdale
Posts: 11
Hi all,
Really hoping to get some help from the community on the subject of air shocks. I'm building a 4 wheeled vehicle - a gravity racer - and the design currently has a rear subframe that pivots off the main frame. We need a shock to do the business of keeping it all in check.
The completed vehicle will weight 250kg all in, and will be a 50-50 weight split front and rear. Unusually, the shock will be mounted at the rear of the car, so the sequence will be pivot > axle > shock, and the shock will be mounted pretty much straight up and down.
We want probably around 25mm total movement at the wheel, including the static sag (7.5mm at 30%). As the shock is mounted approx as far away from the axle as the axle is from the pivot, this will give a shock travel required of 50mm, with 15mm static sag.
Given these numbers, where would you start?
Jim
Really hoping to get some help from the community on the subject of air shocks. I'm building a 4 wheeled vehicle - a gravity racer - and the design currently has a rear subframe that pivots off the main frame. We need a shock to do the business of keeping it all in check.
The completed vehicle will weight 250kg all in, and will be a 50-50 weight split front and rear. Unusually, the shock will be mounted at the rear of the car, so the sequence will be pivot > axle > shock, and the shock will be mounted pretty much straight up and down.
We want probably around 25mm total movement at the wheel, including the static sag (7.5mm at 30%). As the shock is mounted approx as far away from the axle as the axle is from the pivot, this will give a shock travel required of 50mm, with 15mm static sag.
Given these numbers, where would you start?
Jim
0
Posts
viewtopic.php?f=10004&t=13071316&p=19980317#p19980317
Sorted the wheels out yet?
What's unusual about shocks at the rear. My cars all have rear shocks, and front shocks.
There is no secret ingredient - Kung Fu Panda
London Calling on Facebook
Parktools
retired 9.6kg Carrera Kraken
The Carrera Hardtail combined thread - come on all you Carrera's!
The Sons Scott Genius RC20 build
The road in Canada where the new car will be running is getting a little more rutted as time goes by, so we want a little more compliance than the types of chassis that have run there before. Canada is a long way to ship a car to find out that the winter has screwed the road so bad that it's too rough for a rigid chassis.
I thought it was unusual cos it's a car, and this is a bike forum :-) Also, I think the placing of the shock is a bit unusual, but perhaps not so much.
Jim
My initial assumption is that because air shocks are adjustable for pressure, we'll be able to tune these to suit our car in a way that may not be the case with springs. Does that sound reasonable?
https://www.youtube.com/watch?v=F8k-VC6pUnI
Yes, but don't forget that the shock will also have rebound damping (and maybe compression damping too). That will stop the rear wheels bouncing up and down like a pogo stick. If you ride an mtb you will know exactly what I'm talking about.
A Basic Monarch R would do the job and can be picked up from £150 new or about £30 used.
With mid tune compression https://www.bike-discount.de/en/buy/roc ... 63EALw_wcB
retired 9.6kg Carrera Kraken
The Carrera Hardtail combined thread - come on all you Carrera's!
The Sons Scott Genius RC20 build
Thing is, my ratio would be more like 1:2, so I think it will be a case of finding a shock that can me made soft enough, not hard enough, even though the car will be 250kg all in, and a bike might be 110kg with rider. This is why I thought an air shock would be most suitable as I can just let the air out until it's right - damping etc aside.
Because of that, i thought one shock may be better than two?
MTB and rider = 110kg
Weight on back end 55kg
3:1 shock ratio
= 165kg on the shock
Car and driver = 250kg
Weight on back end 125kg
1:2 shock ratio
= 62.5kg on the shock
See my point though?