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Hinckley Classic Triples 885cc Classic Styled T3's: Legend, Thunderbird, Thunderbird Sport & Adventurer.

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Old 11-29-2012, 06:25 PM   #1 (permalink)
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quick question about fork preload

I just recently picked up some racetech springs, and wanted to know what would get me to the ball park area of the previous preload of my stock setup.

If i cut the spacer tube they provided so that it would stick out of the top of the fork about half as much as the stock ones did (the spring rate is slightly 2 times more than the original spring), would that give me about the same amount of preload? they included a bunch of preload washers so i can add and remove to fine tune it, but i want to get as close to the original preload as possible.
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Old 11-29-2012, 09:07 PM   #2 (permalink)
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When you sit on the bike the springs push back with exactly the amount of force required to counter the weight of you and the front end of the bike. If you match the old ride height with the new springs, they will have the same preload.
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Old 11-29-2012, 10:45 PM   #3 (permalink)
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All preload does is raise the ride height. Race tech gave you spring rates stock, and what they recommend with their springs, your weight and your bikes weight. Then you set your front end "sag", which for spirited street riding is usually in the 25-35 mm range (firmer to softer).This is done with the preload height. Stock, your sag is probably in the 35 to 45 mm range, which produces a Cadillac ride, but it sucks if your looking for better handling. It's kind of a trial and error sorting, but the result is great. tommyturbo2
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Old 11-30-2012, 05:46 AM   #4 (permalink)
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I can see what the idea is re the spring rates & length of spacer exposed, tho' the length that the cap screws into the top needs to be added in as well?

This, in theory (assuming the 2x rate ratio applies) would get the preload force (forks off the ground) back to where it was. But when the weight of bike & rider bears on the fork, the higher spring rate of the Racetech springs (presume linear?) will determine the sag length. So to achieve a given sag a more complicated calculation is needed, knowing the actual weight load proportion of bike & rider on the front end.

However, this calculation is further complicated by the fact that the original springs are dual rate & the transition point not precisely known.

In the end, it's probably a case of trial & error to get a sag figure in the desired range, but less spring preload is definitely what will be needed.
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Old 11-30-2012, 06:40 PM   #5 (permalink)
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must have been dumb luck but I nailed it first try!!

HUGE improvement. I noticed a difference just backing it out of the garage. So I guess taking half of the original preload away worked! I'm going to put fresh oil in tomorrow, I know i got a little crud in the forks from swapping the old and new ones out. Handling seems by far better. Slow and high speed turns are much more controlled. I get just the right amount of brake dive, so i know im not going to be doing any endos! For $70, you can't beat that. I got lucky getting them for that cheap. Some one ordered them about 5 years ago and never picked them up, and the sales rep was about to send them back, so he gave them to me for cost! Can't wait to do some mountain riding, especially since the weather has been so nice down here.

Last edited by 303frost; 11-30-2012 at 06:43 PM.
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