Need Suspension Help '16 Street Triple Rx - Page 2 - Triumph675.Net Forums
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post #11 of 20 Old 10-11-18, 11:11
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Originally Posted by Plasmablaster View Post
Yes, I agree with that. But I wasn't talking about damping and feel in general - I was talking about getting feedback near the traction limit under braking (my bad for not having cleared that out). I found out that it was braking traction information that I had a lack for whereas cornering traction information was about the same. It was all about braking. It has an easy explanation: Braking is a longitudinal force that bends the forks backwards - turning creates a lateral force that is mostly handled by the telescopic function of the fork stanchions and the axle (so admittedly damping is more important here). There's a video by Keith Code that shows extreme flexion of a fork under extreme braking, and loss of traction - you can actually see the fork tubes bending and unbending as traction is gained and lost in quick succession. As I understand it, "information", when it comes to braking and fork flexibility, comes from tiny such loads/unloads of the fork that functions essentially like a forward-backward spring: as braking force is applied it bends, and at the moment traction is lost it unbends - then it gets loaded again etc. I'm pretty sure that very tiny such cycles create this feeling of "uneasiness", before the ultimate loss of traction occurs.

Anyway, a cartridge system supposedly offers more information and I experienced the opposite so the difference HAS to come from the increase in stiffness.

The fork I put on the SV was the "classic" modification of a 1997 GSXR 750 USD fully adjustable cartridge fork. Indeed the donor bike was heavier. Still, the springs were soft (actually softer than those I had previously installed in the stock fork) and damping plenty adjustable. The suspension worked like a dream: after some adjustments it became supple yet very controlled so it being wrongly sprung/valved for the bike is out of the question.

What is perhaps interesting about this modification, is that braking traction increased to an amazing +10/15%. Same wheel (had caliper brackets machined), same tyre... yet braking force was higher but the limit of adhesion was not felt as much! I had lots of opportunities to test this behavior, (some of them not planned!) and it was always the same. Another thing I noticed and is obviously due to the different damping curve, was that if I applied the brakes abruptly the bike would lose traction. With the old fork it didn't matter - I could slam the brakes, the bike would dive and brake. The cartridge forced somewhat more gradual application of the brakes.

Ultimately, I can not and so I do not claim that I know exactly what part of the lack of braking traction feel was due to stiffness and what part due to different damping characteristics. But I've ridden more than 20 bikes in my life, 4 of them pretty hard, and there's no way someone can persuade me that that lack of feel was only due to damping difference or mal-adjustment. As I told you, I am very careful and sensitive abou tall things suspension and the SV was fine with that fork. Besides, remember all the talk on the MotoGP world about how chassis stiffness alters feedback? So as the fork is in reality part of what connects the wheels and the rider together, it wouldn't be sensible to overrule fork stiffness as regards to information influx to the rider right?

Another thing for consideration: I remember from the SV650 forum I used to hang out at, many people who raced SVs and had the opportunity (class rules allowed it) to upgrade the fork, eventually got rid of USD forks altogether and instead installed cartridge systems in the stock fork (Matris was a company that offered them) as "the stock conventional fork offered more feedback". I was amazed to read that as I thought that stiffness would be imperative when racing yet still... those people did that.


To close my rant, I've come to understand that those now ubiquitous USDs, especially the 43s on bikes like Ducati Monsters are purely for looks and bling factor. It's the internals what matters the most - cartridges provide infinitely better ride quality. Conventional forks with adequate quality cartridges can be perfect for the street and maybe better in some cases.

Im not going to argue about this in someone elses thread but ill say this. Your feel starts with damping and spring rate, If you didnt have any damping or movement you wouldnt feel anything. I can tell you right now that damping 100% effects feel/feedback, is it the only thing? No. But it is very important. Just because the damping is adjustable does not mean the flow is correct for the weight of the bike, the oem valve is designed for a certain amount of movement and flow, the adjustment for a lighter smaller bike may not fall in range of that oem valve.


Your comments about abruptly braking vs smoothly braking is the key, you changed the dynamic of the bike including geometry and your riding style needed to change to support it. You reduced the spring rate because the hydraulics were better at damping then the stock setup which will also change how the bike feels. I just went through this after installing a DDS cart kit into my 675r. I had to re learn how to brake, but im now faster and more confident with the front end.


Dont bother comparing what you see/hear in motogp vs what you have between your legs right now, they are so far apart its comparing apples to planets.You are doing a disservice to yourself by not allowing anyone to persuade you with a proper argument behind it. Thats how you learn new things and push yourself further.
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post #12 of 20 Old 10-11-18, 19:17
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Originally Posted by tottenham12712 View Post
Im not going to argue about this in someone elses thread but ill say this. Your feel starts with damping and spring rate, If you didnt have any damping or movement you wouldnt feel anything. I can tell you right now that damping 100% effects feel/feedback, is it the only thing? No. But it is very important. Just because the damping is adjustable does not mean the flow is correct for the weight of the bike, the oem valve is designed for a certain amount of movement and flow, the adjustment for a lighter smaller bike may not fall in range of that oem valve.

Your comments about abruptly braking vs smoothly braking is the key, you changed the dynamic of the bike including geometry and your riding style needed to change to support it. You reduced the spring rate because the hydraulics were better at damping then the stock setup which will also change how the bike feels. I just went through this after installing a DDS cart kit into my 675r. I had to re learn how to brake, but im now faster and more confident with the front end.

Dont bother comparing what you see/hear in motogp vs what you have between your legs right now, they are so far apart its comparing apples to planets.You are doing a disservice to yourself by not allowing anyone to persuade you with a proper argument behind it. Thats how you learn new things and push yourself further.

Well, I'm not feeling I'm arguing, I'm just discussing, I don't have the need to persuade anyone, and given some good arguments I don't have a problem in changing opinion - I've done it may times in the past. It's all in the spirit of a gentlemanly exchange of opinions, nothing more. Just because we are disagreeing doesn't mean there's an argument. After all that's what the forum is all about isn't it? Having said that of course, I've got to return the "disservice" comment as it works both ways: we actually both have arguments, not just you.


So, about our talk, what you say about damping and dynamics has merit, and not only do I agree on the different dynamics due to the different damping characteristics but I also have an understanding behind the technicalities of it. What you don't know however, (although I mentioned it) is how well the suspension (the GSXR fork) worked on the SV. It did move and it did damp, properly and controllably. (By the way I didn't change the springs until well later - my first experiences came with the stock springs which were softer than the SVs - which were aftermarket. Eventually I changed them to harder ones but there was no fundamental change in braking dynamics or feel apart from the bike diving less). There's no way of course to persuade you about this, it's just my word.

What I said about MotoGP is about a general principle that applies to all machines with wheels. All conventionally-sprung motorcycles (and MotoGP are such since they have telescopic forks) work on the same principles as the physics that affect them are the same. Stiffness equals less feel and I've been reading this throughout my 18 years on motorcycles and reading about them. If I remember well, Tony Foale in his true Bible "Motorcycle Handling and Chassis Design" mentions it. Truly amazing book, found many answers to issues I had and still have*. I also remember a story when Mick Doohan had total lack of feel from his NSR front (don't remember the year) and his championship was on the line. What they did, (he and Geremy Burgess) was to remove two mounting bolts from the engine, to allow more flex into the chassis and... voila the miracle happened (I think it's somewhere in his biography: "Mick Doohan: Thunder from Down Under"). Even cars are governed by the same principle: a flexible chassis gives more feel to the driver, I've also heard this many times. And... after my experiments and trying various bikes I've been persuaded myself too. I had an AX-1 once, a 250cc trail bike with road tyres... it was so goddamn flexible that when I got to the SV I felt like there was no information whatsoever. It took me about 6 months to learn how to "listen" to the new bike. And guess what: They both had damping rod forks - simple holes for the oil to get through, with very similar damping characteristics. The difference with the USD fork is that I never got to learn how to listen to it. It just never spoke enough under braking.

The bottom line is that if you disagree with my advice against the OPs willingness to purchase a 43mm fork due to my claiming it gives less feel then I don't have a problem but I'm standing by my opinion with the asterisk of not being able to tell the exact extent to what stiffness alone is responsible for that lack of feel I experienced.


*One of the most bizarre issues I have experienced that Foale explains thoroughly, is why on slippery asphalt when the bike is tipped-in somewhat abruptly, it may lose front wheel traction momentarily, although it has just started leaning. The answer lies in the gyroscopic force applied on the tyre plus the rotating inertia of the motorcycle - the two combined create a momentary heavy lateral load on the tyre which goes away after the bike has leaned to some degree. There's even a graph showing the escalation of this lateral load. There's an abrupt "spike" before the load falls and then gradually climbs as the bike continues to lean further.

Last edited by Plasmablaster; 10-11-18 at 19:31.
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post #13 of 20 Old 10-11-18, 19:32
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Quote:
Originally Posted by Plasmablaster View Post
What I said about MotoGP is about a general principle that applies to all machines with wheels. All conventionally-sprung motorcycles (and MotoGP are such since they have telescopic forks) work on the same principles as the physics that affect them are the same. Stiffness equals less feel and I've been reading this throughout my 18 years on motorcycles and reading about them.
There might be 1 or 2 people on this forum that are sensitive enough and can lean a bike over far enough to feel the fork tubes flexing. Most of what you're feeling when leaned over is tire flex, with some suspension travel mixed in since forks still do work at normal track day or club racer lean angles.



Like @tottenham12712 says, don't bother comparing to GP bikes. Some of the theory is universal, but a lot of it is lost at our riding levels and on our bikes. I will say that with my old SV (also with a USD GSXR front end), at my max lean angle, I did notice the swingarm flexing a little, but look how flimsy it is compared to the frame and GSXR forks.



Good example of Doohan's engine mount bolts though. GP teams have gotten more sophisticated since then, but only a little. Now they change the engine mount bolts' torques, as well as lengthening or shortening the frame spars by the radiator, or in Suzuki's case, making them out of carbon fiber of varying lengths and thicknesses. Another common practice to adjust flex is to wrap parts of the frame in carbon, which is even allowed in WSBK. Check out the third edition of MotoGP Technology by Neil Spalding. Sounds like it'd be right up your alley. What surprised me most was how much of the frame tuning is simple trial-and-error, and how often the engineers still get it wrong.
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post #14 of 20 Old 10-11-18, 19:39
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Originally Posted by MGFChapin View Post
There might be 1 or 2 people on this forum that are sensitive enough and can lean a bike over far enough to feel the fork tubes flexing. Most of what you're feeling when leaned over is tire flex, with some suspension travel mixed in since forks still do work at normal track day or club racer lean angles.
Oh come on guys. I clearly stated that it was only under braking (in a straight line or slightly leaned) that I experienced this lack of feel and that leaning and turning traction feel wasn't affected much. I could feel the uneasiness of the front when well-leant over - what I couldn't feel was the imminent loss of traction under increasing braking force.


I'll definitely check that book by Spalding, thanks for the lead. Yes, it amazes me to see how they are still mostly in a trial-and-error state. Foale states clearly that many parts of handling physics have not been clarified yet... and it is obvious isn't it :)
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post #15 of 20 Old 10-11-18, 19:40
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I was referring more to the SV guys you talked to who said they prefer the RSU forks but anyway...check out that book. Seriously.
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post #16 of 20 Old 10-11-18, 19:47
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Originally Posted by MGFChapin View Post
I was referring more to the SV guys you talked to who said they prefer the RSU forks but anyway...check out that book. Seriously.

OK no worries.



I'll do that. Foale's book is excellent too. There is so much stuff in there - for example a detailed analysis of all forces acting on the bike when powersliding. Also, detailed force analysis showing the slip angle of the tyre on the asphalt - did you know that it's almost impossible to have turning force without some -minuscule even- slippage?
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post #17 of 20 Old 10-11-18, 20:38
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Check out the third edition of MotoGP Technology by Neil Spalding.

Off topic but I got to ask: Is the 3rd edition significantly better than the 2nd? The 2nd is the only one I can find at the moment at a (kind of) sensible price.
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post #18 of 20 Old 10-12-18, 02:12
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Off topic but I got to ask: Is the 3rd edition significantly better than the 2nd? The 2nd is the only one I can find at the moment at a (kind of) sensible price.
I bought the 3rd edition for around $100 from the UK. Expensive as hell for a book, but there are some really fascinating tidbits that actually contributed to my 4 second improvement at the track this year. Much cheaper than any race school.

I havenít read the 2nd edition but I see it was published in 2010. That puts it pretty far out of date; the 3rd is from last year and includes info on seamless transmissions, Michelins vs Bridgestones, and a few other updates in that 7 year gap.
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post #19 of 20 Old 10-12-18, 06:16
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there are some really fascinating tidbits that actually contributed to my 4 second improvement at the track this year.
I've always thought that linking theory to practice, i.e. ideas to the real world makes us wiser. 4 secs in a year for a rider as experienced as you... must have been a revelation.

I found the 3rd edition for about 60$ including shipping so I pulled the trigger. Thanks again for the lead.
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post #20 of 20 Old 10-12-18, 06:28
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Your picture shows you have the 108mm Nissins as fitted to the 2006-08 Daytona and Street Triple R 2008 onwards depending on country. So they will fit the Daytona forks you mention. Your yokes would just need machining out to 43mm and away you go. But you still have shitty forks. So what I would do is give the forks a dam good service with springs that match your weight and riding style and play around with the oil height. You can buy a much better compression adjusters that actually work and can be changed with ease.
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