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Old 04-24-2005, 10:26 PM   #1 (permalink)
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I realize that setting race sag is not done as much with ATVs as it is with dirt bikes, but I also know there are a lot of really smart people on this site, with a wealth of experience in setting up race suspensions, so here is my question:

When setting race sag, and dialing in an aftermarket suspension, when do you know that you will need a higher than stock rate spring (or lower than stock rate for that matter). Take for example a YFZ that has 9" of rear suspension travel:

In choosing the correct spring for my Ohlins rear shock, I want about 25mm of static sag, and about 75 mm of total sag. So, ... if I have 25 mm of static sag, but 125 mm of total sag, and the spring length (preload) is within spec, then I need the optional stiffer spring, right? I weigh just over 220 lbs.

So is this the correct way to determine if a stiffer spring is needed? Am I on the right track? Are my numbers correct? Thanks for your help.

Katoom.
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Old 04-25-2005, 10:16 AM   #2 (permalink)
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I'm not sure about those numbers bieng correct or not. You're on the right track. First you should figure out your precentages for static sag and race sag. I myself like 25 percent static and 40-45 percent race sag. Set your race sag first and then if your static sag isn't within the percentage that you want then you need to change out springs or make a crossover adjustment. Make sure when setting race sag that you compensate for gear or wear your gear while you're setting race sag. Check and make sure that you don't have too much stiction in the suspension before you start setting sag. When I set sag I always will push down slowly on the quad and then release it slowly, then take a measurement and the do the samething going up. Then split the difference of those two measurements. I do it this way because of normal stiction in the suspension components.
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Old 04-25-2005, 01:38 PM   #3 (permalink)
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I agree with TBD. I also run 40% race sag but i don't run a stock shock. I don't think a stock shock and it's 9" of travel can handle 40% sag. However, i pay little attention to static sag. Static sag has alot to do with what rear shock you are running. It will be different for every brand of shock even when the springs are set up spot on. Axis and Elka live spring settups will never have the same static sag as the PEP's for example as their first spring has enough tension to keep the quad off the crossovers without a rider on board, but will have nearly the same race sag. As for choosing different springs, I always wait to see how the shock responds on the track before making any assumptions.

According to your numbers, 125mm is 4.9" of sag. That about 55% sag which is way too much on a stock shock, but you are running an Ohlins. I would bet that your Ohlins offer at least a little more travel than a stock shock. Most after market shocks offer around 10-11" of travel with the stock linkages, so thats gonna change your calculations. 125mm of sag with 11" of travel is 45%, which is close. I like it to be 40%, so a few turns on the preload ring will raise ya up a tad, and you should be fine with the spring you have.

On another note, most times I set ride height up according to frame height. I run 7 1/4" at the rear of the frame and 7 1/2 at the front. It just so happens that with my shocks, or with an Axis, pep, or elka settup, it works out to about 40% race sag.
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Old 04-25-2005, 03:58 PM   #4 (permalink)
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Good point on the frame height measurements, I hadn't even thought about that. Back to garage with tape measure in hand ...
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FMF Q2 exhaust; Ohlins suspension; T-9 Bajas; iRazrs.

2005 KTM 525 MXC: Stock, no mods needed.
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Old 04-25-2005, 05:15 PM   #5 (permalink)
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Quote:
Originally posted by Katoom@Apr 25 2005, 11:58 AM
Good point on the frame height measurements, I hadn't even thought about that.* Back to garage with tape measure in hand ...
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Old 04-25-2005, 07:10 PM   #6 (permalink)
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yeah but the front of the yfz 450 frame tapers up 3".
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Old 04-26-2005, 02:10 PM   #7 (permalink)
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Thanks for the help everyone. I used the information here to set up both ATVs and the bike. It looks like the ATVs will be ok with just preload adjustment, although I will need new springs for both ends on the bike. This site is great, keep it up.

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FMF Q2 exhaust; Ohlins suspension; T-9 Bajas; iRazrs.

2005 KTM 525 MXC: Stock, no mods needed.
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Old 04-26-2005, 07:29 PM   #8 (permalink)
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You do not measure from the front of the frame, Granddragon, i know you know this, but it sounded like tuklugs doesnt. You measure right under the engine mounts for the front ride height, and measure under the footpegs for the rear ride height.
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Old 04-26-2005, 11:50 PM   #9 (permalink)
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i have my quad set up at 2" ride height for mx. is that too high.
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