Author Topic: Indespension Spring  (Read 204 times)

StefanN

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Indespension Spring
« on: 19 Jan 23, 12:34 pm »
In the search for cheaper springs I experimented with an Indespension leaf spring - mainly because they are about the right size and reasonably priced.  The cost has gone up now to £38 but still not crazily expensive and discounts might be available.

https://indespension.co.uk/1200kg-7-leaf-spring-eye-to-eye

I dismantled the spring to get the long leaf from the pack.  It's about 585mm (23") eye to eye, 50mm wide and approx 6.85mm thick.  The camber from the eye down to the outside of the spring is 78mm. 

Deflection with 83.2kg (183lbs) was 14.5mm   (would be higher if no friction between eyes and workbench).  That’s a spring rate of 320 lbs/inch

I cut 9mm off each side with a 1mm cutting disc.  I burned through 4 cutting discs (£3.50) and it took less than an hour.  By doing long cuts rather than concentrating in one spot, the spring didn’t get much above warm to the touch so the heat treatment won't have been changed.

Deflection at 32mm wide = 24mm  = Spring rate 194 lbs/inch

Switching to metric
CK + driver approx 180kg
say 35:65 weight distribution gives 63kg on the front.

As a transverse spring this would deflect about 18mm at rest
Or 9mm as a pair of longitudinal springs.

The eyes are a bit oversize (visually).

I hope we might be able to test the spring out on a cyclekart.
« Last Edit: 19 Jan 23, 12:36 pm by StefanN »

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Ian L

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Re: Indespension Spring
« Reply #1 on: 20 Jan 23, 01:08 pm »
Stefan, I was thinking what else uses light springs and than had a thought - pony carts! - see attached pic. I have dropped him an email and he had come back already asking for some pics and dimensions of what we want. Please can you kindly do a sketch and take a pic of your set up and I will go back to him. Many thanks. Ian

Ian Fletcher

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Re: Indespension Spring
« Reply #2 on: 20 Jan 23, 06:24 pm »
Thanks Stefan for posting all the dimensions and resultant spring rates. I will be looking at building a second cycle kart as soon as my current project (class 7 classic trials car) is finished. The new CK will have a transverse fron t leaf spring and I will be looking for about 120 lbs/ inch spring rate, so.I now have good idea from your measurements.  I am currently thinking about making my own leaf springs and bolting on the eye ends as the loads are lower on A CK

StefanN

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Re: Indespension Spring
« Reply #3 on: 20 Jan 23, 07:25 pm »
Stefan, I was thinking what else uses light springs and than had a thought - pony carts! - see attached pic. I have dropped him an email and he had come back already asking for some pics and dimensions of what we want. Please can you kindly do a sketch and take a pic of your set up and I will go back to him. Many thanks. Ian
Hi Ian,
They look interesting.  There’s a drawing on this post https://cyclekartsgb.createaforum.com/where-to-get-stuff/leaf-springs-492/msg3894/#msg3894
Can I suggest you have a word with Graham Hill as he and Chris Loader are working on sourcing springs and it would be good to feed your findings into that effort. 

Ian Fletcher

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Re: Indespension Spring
« Reply #4 on: 21 Jan 23, 06:20 pm »
You can buy spring steel cheap on eBay, etc. so was thinking annealing it, then shaping a d drilling, then getting it tempered.  Rather than forming the eye ends was going to weld some tubes to tangs and then bolt onto the end.  Just an idea at the moment, but expect to do some proper investigation in Spring (no pun intended) 🤣

RhysN

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Re: Indespension Spring
« Reply #5 on: 23 Jan 23, 07:38 am »
If it's any help, the calculated rate on the front of Dave (Bentaxle on the US site) Maserati 250F is 160 lbs/inch (per side), he says that works well.
« Last Edit: 23 Jan 23, 08:08 am by RhysN »
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