[Del]

I weigh 195 pounds when dressed and my bike came stock with a 500 lb spring with a 1.5 inch stroke. When I sit on the bike I feel like I am generating way too much sag.

I searched the forums and found nothing and I searched Google and found math problems.

Is there a simple chart anyone knows about or simple guidelines to figure out what spring I should get?

 

[chicodude]

This is a very rough estimate http://www.mojo.co.uk/index1.htm

 

[Del]

This can't be right:

 

[chicodude]

I think it meant 105, cause that's what I got the 4 times I tried it with your #'s

 

[binary visions]

105? That's so light, it doesn't even make sense. edit: seems to be a Firefox problem, chicodude. IE gives me the right numbers, but FF does not.

Let's crunch the numbers here so you can at least see where that's coming from and don't make silly guesses like 105 being accurate

You want your bike to sag about 30%, give or take, so you want it to sag about 0.5" of your stroke.

Spring weight is measured in the number of pounds it takes to compress the spring 1". So, with a leverage ratio of 3.33, and your weight being 195, you're exerting almost 650lbs of force on your bike when you sit on it. That's why your 500lb spring seems soft - even a 650lb. spring would compress one full inch when you sat on your bike, which is still too much sag.

Now, unfortunately, that's not the whole story, because your bike isn't perfectly linear. Not only is your bike not linear, but these days, your shock probably isn't linear either, if it's an SPV shock. So... it's a little bit of a crapshoot. The 1050 sounds like it's not too far off, though. 3.33 isn't exactly a light leverage ratio... a large number of bikes are at 3:1 or lower.

How much sag do you get when you sit on your bike?

 

[chicodude]

105? That's so light, it doesn't even make sense. edit: seems to be a Firefox problem, chicodude. IE gives me the right numbers, but FF does not.

Let's crunch the numbers here so you can at least see where that's coming from and don't make silly guesses like 105 being accurate

You must be talking out of your ass, I have a 95 pound spring on my bike....

 

[binary visions]

The one glued on the top of your saddle doesn't count.

 

[Del]

The one glued on the top of your saddle doesn't count.

Ouch!

I am looking into figuring out my leverage ratio. The bike in question is a Preston FR, if anyone happens to know off the top of their head. I think Sir Crackien may have told me during a ride but I can't remember. I emailed Transition but they could take several days to respond.

I am going to borrow a ruler from work today and attempt to scientifically measure the sag. I have two six-packs of Anchor Octoberfest beer in the fridge so I can't promise an accurate reading!

 

[chicodude]

What the hell does antimony's bike have do do with this?





You disgust me.

 

[davep]

Ouch!

I am looking into figuring out my leverage ratio. The bike in question is a Preston FR, if anyone happens to know off the top of their head. I think Sir Crackien may have told me during a ride but I can't remember. I emailed Transition but they could take several days to respond.

I am going to borrow a ruler from work today and attempt to scientifically measure the sag. I have two six-packs of Anchor Octoberfest beer in the fridge so I can't promise an accurate reading!

Not sure where the confusion about the ratio comes from. Your transition get either 100 or 120mm of travel (roughly 4 or 5") out of a 1.5" stroke shock. As B.V. mentioned your leverage rates on this bike are quite high (not a good thing). At 4", the ratio is 4 / 1.5 = 2.666. At 5", the ratio is 5 / 1.5 = 3.33 = BAD for a bigger guy.

There are several spring calculators out there but they are all just an educated guess. Try http://www.tftunedshox.com/springcalc.htm and http://www.mojo.co.uk/springcalc.html and you will see a variation of 950 - 1050 lbs depending on shock type and frame. for this type of frame, your sag should be about 25% - 30% or .375 - .45 inches. Giving a sagged measurement of 6.05 - 6.125 from center of bolt to center of bolt.

I would HIGHLY suggest that youset your frame to the 4" travel setting to keep the ratio below 3.00 and your spring weight realistic.

 

[Del]

I would HIGHLY suggest that youset your frame to the 4" travel setting to keep the ratio below 3.00 and your spring weight realistic.

Thanks - this is some interesting information. Why do you recommend keeping it on the 4' setting? In other words, how does this affect the ride?

 

[bjanga]

A lower ratio means that you can run a lighter spring and have better sensetivity. Ratios above 3.00 tend to be hard on shocks.

This is what I understand, at least.

 

[binary visions]

Thanks - this is some interesting information. Why do you recommend keeping it on the 4' setting? In other words, how does this affect the ride?

Well, you understand how a leverage ratio works, right? In the 4" setting, you're putting less stress on the shock - 2.66:1 instead of 3.33:1. In this particular case, your ideal spring weight is very high, so keeping it in a lower leverage ratio will both reduce the stress on the shock, and will improve your problem with the spring being too light.

You'll probably still want a heavier spring, but you could try putting it in the 4" setting and seeing if your sag is right. It probably won't be. For ideal sag, your shock should compress about .5" when you're sitting on it.

 

[Del]

That's a little disappointing that to get the most out of the bike I need to set it to a lesser amount of travel. But I guess it's not too bad. I don't often do big drops and I rode hardtails before this. I still feel a little let down though. I'll definitely try a stronger spring as soon as I have a little cash to throw down and I'll try the 4" setting in the meantime.

 

[binary visions]

Well, hey, if you want to throw a heavy spring on there, it might be fine in the 5" setting. Also, I don't know what shock you have, but an SPV shock like a Swinger or a DHX will allow you a little more leeway, since you'll be able to ramp up the bottom out resistance. You're still stressing the shock a lot, though.

It's not great advice now of course, since you have the bike, but next time you're shopping for a bike, try to get the longest shock stroke for the amount of travel. For estimation purposes, rear wheel travel divided by shock stroke is your easiest way to estimate leverage ratio, and you want to keep it at or under 3:1. The further under, the better, especially when you start getting in the 200lb. rider range.

 

[Del]

It's a 4 Way Swinger that I have on now.

Ultimately, I need to lose some weight

 

[Del]

Here's what Kevin from Transition said after I emailed them:

On 9/12/06, Transition Bikes <tech@transitionbikes.com> wrote:
Hey mike, you need a 650lb spring for sure, that would be perfect. Have your shop call us to get one. We have them in stock. When you ordered it we were probably out of 650's because we normally send out 550's or 600's as the base spring. - kevin

I had asked him for the leverage ratio on the frame but he didn't supply that information. It's odd they would make a frame with such a high leverage ratio as to make the 5" travel setting not feasable for someone around 200 lbs, which in my opinion is not that heavy for an adult male.

 

[partsbara]

the frame has 120mm travel yeah ??? about 4.7"s of travel... stroke of shock is 1.5"s...

leverage ratio is 3.13 / 1