August issue - backsliding again?

[YellowDuck]

Article on the press launch of the Triumph Sprint GT reads like a travel log. Interesting I guess, but how about some information about the bike itself? No tech bar provided (grrr....), but even worse, don't you think an article about this particular bike should mention, somewhere, oh, I don't know...how many FRICKIN' CYLINDERS it has????? And of the three photos of the bike, two are from precisely the same angle.

C'mon. I know the goal is to distinguish the magazine by being all artsy fartsy, but it's still a motorcycle magazine isn't it?

And just to get me more wound up, in the same article Uwe trips into one of my pet peeves, stating that he "firmed up the ride" by adding rear preload. Wouldn't it be nice if someone writing an article about testing a motorcycle, or perhaps the magazine editor, or maybe even the copy editor, had some notion of how motorcycle suspensions actually work?? Adding preload just extends the shock - it doesn't in any way firm up the ride.

I'm a fan of CC, have been for many years, and likely always will be...but every now and again.....

[Rocking Couple]

This caught my eye yesterday.

Neil said it in the Aug issue's Timeline:
"One of these days I'm going to show up on someone's doorstep and we'll have it out - editor to reader - in person, and you'll have no computer to hide behind."

Love it! And unlike so many internet threats (although to be clear, my quote of Neil's was of a dream he had apparently, not a conscious thought) this time he knows where you live.

As for your comment, YD, "how many FRICKIN' CYLINDERS it has?????" I think to be fair to Uwe, on page 38, 2nd paragraph in, we can infer that the usual engine config has been passed down thru the generations as displacement increased, that being an inline triple. Or rather, I guess he did rely on the assumption that readers would know the Sprint has been famous for its use of inline triples for years. Granted, to an entirely ignorant reader, they wouldn't have known. I guess if the piece was enough to whet one's appetite on the GT, then they'd find out after researching the bike a little further.

And with a bit of digging, I found this on pg 40. "Although the engine is unchanged from the ST...snip"
Also.. "The GT has sacrificed sexiness (the ST's underseat trio of exhausts....snip"

He did comment on lack of turbulence off the WS, but I still like to hear more details about the need for ear plugs. Admittedly almost all bikes require 'em. I think moto mags should include a rating system of earplug requirement for average height riders. List their torso height and a scale of 1 to 10, with 10 really needing the hearing protection.

Example, average 5'9" rider with a 32" inseam, on a 2004 EX250 - can ride in relative comfort without any plugs at all, would get a 1 or a 2. (I've heard this also about many old nakeds fitted with a Rickman type fairing) An 01 VFR gets an 8. New ST's get a 9. Your average naked, a 5 or 6.

[yzf1000jon]

The earplug rating is interesting, but given the hundreds of helmets out there it would be very difficult to apply. The buffeting comment really also applies to specific riders, but is interesting in a relative sense.

Adding preload doesn't extend the shock, it compresses the spring, or "pre-loads" it (you can compress a spring alot until it binds, but can't extend a shock beyond its design limit). When the sag isn't correct the bike can wallow or bottom, adding preload compensates for weight and puts the suspension in the proper portion of it's travel. It may not have "firmed" up the ride, but if the bike behaves better, and reacts to the bumps correctly, it's difficult to describe it using other words.

[YellowDuck]

Adding preload doesn't extend the shock, it compresses the spring, or "pre-loads" it (you can compress a spring alot until it binds, but can't extend a shock beyond its design limit). When the sag isn't correct the bike can wallow or bottom, adding preload compensates for weight and puts the suspension in the proper portion of it's travel. It may not have "firmed" up the ride, but if the bike behaves better, and reacts to the bumps correctly, it's difficult to describe it using other words.

The last part of what you said is correct, but the first part isn't. Adding "preload" only compresses the spring more in the situation where there is no sag at all - for example, if you have the shock right off the bike and so it is fully extended under spring pressure.

And if you don't think that adding preload extends the shock, then you have never made a sag measurement before and after adding preload. How do you think the bike is going up if the shock is not extending???

Once there is enough weight on the shock to move it from the fully extended position (i.e., there is some sag, and there had better be a bit of sag under bike weight alone, and 20 to 30 mm of it with you on the bike), then adding preload just raises the bike up, by extending the shock. The spring itself will still be compressed exactly as much as it needs to be compressed to support whatever weight is on it, which hasn't changed. That's why adding preload does not compress the spring. It just changes how much the shock is extended with the same amount of spring compression, by pushing the top of the spring farther down the shock body. Yes, adding preload helps to prevent bottoming, but not because the spring is compressed - it prevents bottoming because in resting state you are starting with the shock more extended, so you have more positve shock travel available.

More importantly, the amount the shock moves for any given force (i.e., the "firmness") will be exactly the same regardless of the amount of preload (except in the extreme, never-happens-in-the-real-world case of zero sag), because the spring rate is not affected by the preload setting.

The only qualifier to this is that adding preload (because it extends the rear suspension) does change the front-to-rear weight distribution somewhat, and also changes the linkage ratio on a progressive suspension (but usually in such a manner that the net effect is to make the ride less firm, not more so).

Trust me, I am right on this and you are wrong. Don't feel bad about it because it has got to be the most common misconception in the world regarding suspension tuning - in my experience, fewer than 20% of riders have any clue about it. Please please please don't argue it further until you have read some good material on it - say, Kevin Cameron's book, or maybe Andrew Trevitt's.

[yzf1000jon]

Read Camerons, and just finished Trevitt's (happy fathers day to me). We are kinda saying the same thing in different ways. If you are tightening a fastener what part do you tighten? I'd say the nut, you'd say the bolt. It's tomatoe/potatoe. How would you quantify the difference when you ride a bike with the preload backed way out and it handles like poo, then crank preload up and it feels tight and controlled? There aren't good terms to describe it well, and the general riding population understands "firmer". Instead of just criticizing, try correcting, what should he have said?

And if the first part of what I said was incorrect, how do you extend a shock beyond it's design limit? Because if I did, it'd be wrecked.

[YellowDuck]

I already answered your questions, if you read what I wrote carefully.

The difference in feel between a bike with too little rear preload and correct rear preload is due to a) reduced chance of bottoming, b) increased rear ride height and therefore sharper steering geometry, c) increased weight distribution towards the front wheel, and d) operating the suspension at a different point in its travel, where the linkage ratio (ratio between shock compression and vertical bike movement) is different.

It is, emphatically, NOT because the spring is more compressed. It only has more compression in the case where it is fully extended. In any other case (i.e., every case that matters), the spring is compressed essentially the same, since it is supporting the same amount of weight. (I only say "essentially" because items c and d above affect that a little bit.)

Think of it this way: if the spring must compress 40 mm to support the weight of the bike and you, and it has 10 mm preload (fully extended), then the spring will compress a further 30 mm to hold up the weight. If you add an additional 10 mm preload (for a total of 20), then it must compress an additional 20 mm to support the weight. But, the total spring compression is the same, regardless of the preload setting. Increasing the preload just results in the shock being in a more extended state with the spring having that same amount of compression. Accordingly, the ride height will increase by the product of the additional preload and the linkage ratio.

I never claimed that you could extend a shock beyond its design limit, but you would have to add enough preload to extend the shock *to* its design limit (i.e., to the point of zero sag) before adding additional preload would increase spring compression. And that is not a normal or useful setting, obviously.

[yzf1000jon]

So if I had 50mm of rider sag, and could raise my rear ride height to compensate (I can) the bike would handle just the same?

[YellowDuck]

Yes, because adding the ride height would also extend the suspension, so you would be at the same linkage ratio.

The practial problem of course is that if you had 50 mm sag you would still be in danger of bottoming out the shock, no matter how much ride height you added. Also, 50 mm sag is a good indication that the spring is too light for you, so the bike is not going to work right no matter how much preload or ride height you add. So, the scenario you paint is not realistic, but still, yes, if you don't bottom the shock then adding ride height gives you the same result as adding an equivalent amount of preload. You end up with the same geometry ***and the same spring compression***.

The big misconception is that adding preload somehow results in a spring that is more compressed (and therefore "firmer") while you are riding. It simply ain't so. It just makes it so you need more force to bottom out the shock, because the starting point is higher up in the shock's travel.

[stan wagenaar]

Sag bad, firm good. Mmmm...firm, rounded, perky...oops, sorry! A little off topic!

[Rocking Couple]

The big misconception is that adding preload somehow results in a spring that is more compressed (and therefore "firmer") while you are riding. It simply ain't so. It just makes it so you need more force to bottom out the shock, because the starting point is higher up in the shock's travel.

I am still struggling with these scenarios, yet I have studied this all a bit myself.

But I know that if you put a coil spring in a vise that has the ability to measure psi, as you compress the spring the psi will go up.

I was always under the impression that that is why progressive rate springs by the likes of HyperPro are used. They allow the suspension to work in an ideal area of shock working travel with respect to linkage variables etc.

[YellowDuck]

Progressiveness just means that it takes more force to compress the suspension the same amount as you move it through its travel. On rear suspensions that is usually accomplished through the linkage - it is designed so that mechanical advantage of the swingarm on the shock declines as the suspension compresses - that is the change in the linkage ratio. At the top of the suspension range, the bike might drop 2 mm for every 1 mm of shock movement (linkage ratio = 2), while nearer the bottom it might be only 1.5 mm of bike movement for each mm of shock movement. This change in the linkage ratio has the same effect as if you were increasing the spring rate as the suspension compressed.

(Note that this also means that as you increase preload and the rear of the bike rises up (i.e., the suspension extends), the linkage ratio is affected such that the ride gets slightly *softer*, not firmer as most people think).

The other way to get progression in the suspension is to use rising rate springs, so that it actually takes more and more force to compress them the same distance as the suspension compresses.

Some rear suspensions use both rising rate linkages and progressive springs in combination.

[Battleax]

Indeed the preload is simply a ride height adjuster, up until the point that the shock or fork is fully extended, a situation not achieved while sitting on the bike.
The last thing you want is for the suspension to bottom out, or worse top out. So preload is used to set ride height so that aprox. 1/3rd of the suspension travel is used up while sitting on the bike.
If, while sitting on the bike someone cranked up the preload the forks and shock would simply extend and raise the bike. Now if you could keep cranking up the preload till the forks and shock topped out (with you sitting on the bike) then further increase in preload would begin, only then, to actually compress the spring, however no bike will top out while you are sitting on it so that won't happen.

Of course, on a side note, rising rate linkages are designed to operate best in that 1/3rd (aprox) sag range, and altering ride height front vs rear will have steering effects which may or may not be noticeable.

Now to be more specific, preload is not so much used to alter ride height, but to keep the bike in it's ideal range regardless of load carried.

[TimP]

This is fascinating, YD, so thanks for the lessons.

I understand your points about extension and wonder how this is relates to the hydraulic rear preload adjuster on my BMW (big knob on a small reservoir under the seat - turn it in to increase preload, out to decrease). Does it achieve shock extension/retraction (preload) simply by increasing/reducing fluid volume inside one end of the shock? Is this the functional equivalent to the external reservoirs on, say, Ohlins shocks?

[Battleax]

This is fascinating, YD, so thanks for the lessons.

I understand your points about extension and wonder how this is relates to the hydraulic rear preload adjuster on my BMW (big knob on a small reservoir under the seat - turn it in to increase preload, out to decrease). Does it achieve shock extension/retraction (preload) simply by increasing/reducing fluid volume inside one end of the shock? Is this the functional equivalent to the external reservoirs on, say, Ohlins shocks?

The hydraulic preload adjuster you find on BMWs, and Ohlin shocks is completely separate from the shock and it's internal fluids, dampening functions, or the shocks external reservoir.
It is simply a unit mounted on top of the shock that pushes on the spring just as a manual ramped adjuster would do, only it uses a hydraulic piston to do so.

[yzf1000jon]

Now if you could keep cranking up the preload till the forks and shock topped out (with you sitting on the bike) then further increase in preload would begin, only then, to actually compress the spring, however no bike will top out while you are sitting on it so that won't happen.
It can if you have a company such as Race Tech send you incorrect springs and then deny that what is happening is possible (even they say I can't be topped out with these springs). True, I (260lbs sans gear) should have sag with 1.00kg/mm fork springs, while sitting on the bike, but they remain topped out even then. And I have yet to work out a less than expensive solution.

[Battleax]

It can if you have a company such as Race Tech send you incorrect springs and then deny that what is happening is possible (even they say I can't be topped out with these springs). True, I (260lbs sans gear) should have sag with 1.00kg/mm fork springs, while sitting on the bike, but they remain topped out even then. And I have yet to work out a less than expensive solution.

Jon if your forks are topped out while you are sitting on the bike then something is terribly wrong, and of course the bike can not be ridden, you'd be tank slapping regularly and the banging of the fork would be catastrophic.
Even with the fork preload cranked fully down you should not be topped, certainly not with a 260 lb load.
RaceTech does know their stuff so possibilities are...
There is a spacer in the fork that shouldn't be there, maybe Racetech uses a longer spring with a correspondingly shorter spacer.
The spring is for a bike with a longer fork, maybe a different year YZF and they sent you the wrong one.
You'll have to remove the spring and measure it's uncompressed length then ask Racetech what it should be. This is the only way to confirm.
Your forks should settle about 1.75 inches from full extension to when you're sitting on the bike.
Obviously the the first thing to do is to get the stock springs back in so you can ride, which you' must have done.

[kml]

it has got to be the most common misconception in the world regarding suspension tuning


Ain't that the truth.... :D


cheers
ken

[Kootenanny]

Getting back to the original post here...is CC backsliding? I just got the August issue, and I haven't read it yet, but I will say the cover is nowhere near as good as the July issue!

[YellowDuck]

Well, aside from my pet peeve about suspension preload, my other beef was the lack of technical information in the Sprint GT first ride report. Mentioning the basics of the engine configuration is mandatory in my opinion. It's just like another of Uwe's reports a year or so ago - it was a cruiser model (Yamaha I think), and nowhere in the article did it mention if the thing was liquid or air cooled!

I am not saying that I want CC bike reports to obsess over all of the technical minutia and leave out the more sensory aspects of what the bike is like, but geez louise if it is an article about a machine then surely some base level information about the mechanical configuration is warranted!

Please just bring back the tech sidebars and all would be well on that front. Then at least I could go back to whining about the lack of dyno graphs, instead of asking questions like "how many valves per cylinder"? or "wet or dry clutch"?

[Kootenanny]

Well, I finally did read the article YD posted about in the op of this thread. And yeah, it's a bleedin' travelogue. Scotland sounds like a great place to take a motorcycle vacation...no reason to rub it in, Uwe! Ok, so you get paid to travel to Scotland and ride around the countryside on a brand-new bike...how nice for you. About the bike, though...;)