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how to calculate shock spring rate #542844
05/13/14 4:43 am
05/13/14 4:43 am
Joined: Oct 2012
Posts: 75
Chiangmai Thailand
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Hoghead Offline OP
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How to calculate the rear spring rate for a T-140 Bonnie?

YSS can give me any range of spring I want, however they seem clueless here in Thailand about how to do the calculation

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Re: how to calculate shock spring rate [Re: Hoghead] #542846
05/13/14 6:08 am
05/13/14 6:08 am
Joined: Dec 2004
Posts: 9,071
Scotland
kommando Online content
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Go to the IKON site and look up the part number for the T140 rear shock, then download their pdf on the make up of each shock by part number and see what spring they fit which hopefully will be one of their progressive springs. Adjust if required.

Re: how to calculate shock spring rate [Re: Hoghead] #542856
05/13/14 8:24 am
05/13/14 8:24 am
Joined: Oct 2012
Posts: 75
Chiangmai Thailand
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Hoghead Offline OP
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Thanks and I do not why I did not think of that. The rates offered are:
Solo rider 84-146 lbs/in
With Pillion 95-174 lbs/in

That is a very wide range and I would prefer a spring for my weight and riding style rather than the one size trying to fit all approach of a progressive spring. I always ride solo and at best might rarely carry a 15Kg tail bag

Interestingly Ikon state that the spring "may" hit the chain guard up to 1978 and it can "safely be moved".
It seems that YSS can fit an offset eye(s)to mitigate any chainguard clearance issues

I still would like to be able to calculate the proper rear spring rate
Front spring calculators are available from both Racetech and Sonic but I cannot find anything for the rear

Re: how to calculate shock spring rate [Re: Hoghead] #542859
05/13/14 8:54 am
05/13/14 8:54 am
Joined: Dec 2004
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kommando Online content
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The wide range is because the springs are progressive not single rate, so the 84 to 146 one starts out on initial movement as a 84lbs/in spring, then as the close together parts touch the spring stiffens until over the last part of the travel it is a 146lbs/in spring. I find that works very well on a solo bike, responsive over smooth roads and no bottoming out on rough.

If you want a single rate spring look in the T140 Factory manual, it lists the spring rates.

Re: how to calculate shock spring rate [Re: Hoghead] #542982
05/13/14 9:26 pm
05/13/14 9:26 pm
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Posts: 75
Chiangmai Thailand
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Hoghead Offline OP
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I understand the concept of progressive springs. I do not agree is that this is better than a linear rate spring suited to the bike + rider

Progressive springs are an attempt at a one size fits all solution so that the manufacturer can offer a single item to cover all conceivable applications. Consider the 50 Kg solo rider and the 2 x 100 Kg twinkie eaters with their luggage. A progressive rate spring is the only way to offer a single product but not the ideal solution for either rider.

The factory spring is a similar compromise at 100 lbs/in

Presuming that the factory had an "average" rider in mind, it would indicate that the Ikon is far too oversprung

I still would like to know how to calculate the ideal spring rate for my weight and riding conditions

Re: how to calculate shock spring rate [Re: Hoghead] #543026
05/14/14 3:33 am
05/14/14 3:33 am
Joined: Jul 2009
Posts: 3,549
Vic. Australia
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I think factory spring rate on the rear varied between 88lbs/inch and 145lbs/inch,depending on model.
I'm not keen on double rate springs or progressive springs.I wouldn't even say they're "one size fits all".I see them as more like one size that only fits one weight of rider.Any adjustment of ride height to suit different rider weight will also affect how much of the travel happens at the soft rate and how much is left at the harder rate.A small adjustment to ride height could see you having half as much travel at the soft rate.

At least with a single rate spring,you can adjust pre-load and ride height and still have the same spring rate throughout the full travel.

I like to set the ride height so that 30% of travel is used up with the normal weight of rider etc on the bike.If it bottoms out occasionally in severe circumstances,the spring rate is about right.If it never bottoms out,it's too hard and you're not taking advantage of your possible suspension travel.

I could be using the 84/146 springs,but I'd have dig through records to be sure.It seems OK.I know they offered the same spring for XR Harleys.

Re: how to calculate shock spring rate [Re: Hoghead] #543478
05/15/14 11:52 pm
05/15/14 11:52 pm
Joined: Oct 2012
Posts: 75
Chiangmai Thailand
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Hoghead Offline OP
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I usually set mine at 25% of the total suspension travel when using a linear rate spring so we are in the same ballpark.

Now if I only knew how to calculate the ideal spring rate for my weight and riding conditions I would be set. YSS here in Thailand where they have their factory is stunningly incompetent when it comes to answering a technical question.

Last edited by Hoghead; 05/15/14 11:53 pm.
Re: how to calculate shock spring rate [Re: Hoghead] #543817
05/18/14 12:06 am
05/18/14 12:06 am
Joined: Oct 2012
Posts: 75
Chiangmai Thailand
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Hoghead Offline OP
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A shameless bump in the hope that someone knows how to calculate the spring rate as the 2 manufacturers I have spoken to are not helpful in the least

Re: how to calculate shock spring rate [Re: Hoghead] #543825
05/18/14 1:46 am
05/18/14 1:46 am
Joined: Aug 2011
Posts: 416
OZ
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OZ
Ask this bloke, he supplied custom set-up YSS units for my Daytona so he would be able to help you with it.

http://www.suspensionshop.org/VIEW.php#searchview

davy

Re: how to calculate shock spring rate [Re: Hoghead] #544182
05/20/14 1:43 am
05/20/14 1:43 am
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Posts: 75
Chiangmai Thailand
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Hoghead Offline OP
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He will sell me the shock but naturally enough will not tell me how to calculate the rate

Re: how to calculate shock spring rate [Re: Hoghead] #544191
05/20/14 3:53 am
05/20/14 3:53 am
Joined: Aug 2011
Posts: 416
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OZ
Cross him off your Christmas card list then smile

davy


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