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Suspension - A Racer's View

The following is the text of an article prepared for the British magazine 'Racer' but unfortunately not printed after a change of ownership of that magazine.  John Cornwell (JS) is a personal friend, he rode the Sigma Supermono to victory at Daytona in 1988 (for more info on that particular adventure have a look at the first few episodes of 'Racer Road' ). He is also a full time Ohlins suspension technician responsible for the Ducati Works teams at World Superbike. What follows is a discussion between friends on the way bike suspension works. I hope you find it as interesting to read as I found it to be involved in.

Neil Spalding (NS)

NS

What is the difference between a race bike and a road bike as far as suspension is concerned?

JC

The main difference is that the street bike rider needs to have a little bit of comfort regardless of whether or not you are a sporting rider. It's not not very much fun if you ride the bike for 10 minutes and you can't sit on it anymore because its too sore.

What you look for when you are converting a standard motorcycle it into a race bike is two things; the characteristics of the bike and rider. Now there are some riders out there that prefer to have their racing bikes behave more towards the street side of things and there are those who prefer to have their motorcycles set up towards what we would consider a full on race set up.

For example that there are some motor cycles that benefit from not having so much weight on the front, there are three examples right off the bat: the Ducatis, and both the R1 and R6. They are already really biased to the front even as a street bike and they don't need any more.  The R1 is specifically a razor sharp handling motor cycle and by and large one of the biggest things that you find when trying to take an R1 to it's limit is that the front is awfully soft. We need to do something with that so that the racer can actually approach the limit of the front tyre with some confidence.

NS

What do you mean when you say soft though - soft as in springy? or soft damping?

JC

Soft as in springy mostly and this also contributes to the ability of the motorcycle to handle sharp - it turns in really good and seems to hold the line really well. However it is at the expense of confidence building, the R1 is scary to ride fast, really hard, as a standard bike. Man it's like wow you got to be some sort of hero because it's not always very user friendly on the racetrack. It turns in too fast, it reacts too quickly, when the thing starts to move around it doesn't move around with any predictability, things happen really quickly with it.  It starts to shake it's head, it snaps the bars out of your hand, you can get into trouble so fast with it. There is no confidence building in there at all.

NS

So what can you do to try and calm that down?

JC

For the track you stiffen up the front, definitely, springs, oil level, and the damping side of things because the front fork seems to be under damped in both directions. The one thing that Anders (Andersson) has found works really well is to go from standard oil to 10 weight, that seems to help quite a bit with the standard set up.  Bump spring rate up a long way, it comes standard with mid 7 (ie 0.7Nm) springs and we've ridden the thing with 9 / 9.5's and it's nice, much nicer.

The 748 on the other hand is in the opposite direction, it's sprung really stiffly in front, but the Ducati is also the kind of motorcycle that doesn't pitch, it doesn't do a lot of weight transfer, it's a more neutral handling and stable platform to start with. This is one of the things most street bike riders have trouble coming to terms with. It is the ability for that motorcycle to be a neutral confidence building, flowing type of a motorcycle but, to me, the 748 when it's ridden to it's limit is just too stiff on the front.  Having said that a guy like Casoli goes even harder with the front and to me this is a characteristic of the rider because even on a 996 race bike he runs harder fork springs than anybody else that I know.

NS

So, to go back to your original point, it's a characteristic of the rider, of Casoli, to like the front end stiff?

JC

Oh yes, he wants to brake late and he wants to have heaps and heaps of feedback through the handlebars so he knows exactly where the front wheel is, what it's doing, what bumps it's hit, everything. He doesn't care about suppleness or being able to go over bumps, it's more important that he knows he has a direct connection between his hands and the front tyre.

NS

When you change the springing on the front, ie if you have a stiffer spring, the axle is effectively held further out you presumably need more fork leg protruding to get the chassis attitude back to where it started?

JC

If you were to look at the numbers, you've changed the trail of the bike.  Your stiffer fork springs let the bike brake harder and into the corner, to get back to the actual relationship between the front trail of bike you've had to jack the rear up and tuck the front back in.

NS

Right. So really all I'm trying to do is get back to where the original chassis designer had the chassis but with a stiffer front end.

JC

Yes

NS

So what was the original chassis designer after?

JC

He was after a balanced bike, one with very little weight transfer, a non pitching motorcycle. He wanted something that was neutral in any position like on it's side, under-braking or accelerating, he didn't want that bike rotating around the centre of gravity.

NS

I hear people complaining that a given bike will not 'hold a line', if it isn't holding a line what is actually happening?

JC

It could be too much weight on the front, push, or too little. As the rider is turning it in he's chasing the front, actually pushing the front wheel sideways, perhaps because the rear is too high.  It is possible that the rider will equate push with not holding the line, the solutions for that one would actually make the problem worse.

 It's a problem with many riders, especially inexperienced riders who don't have thenecessary experience. They have never actually had anybody that sat down with them and tried to understand exactly what they are trying to describe.

You almost have to have that guy's language. I have two riders I work with, they both speak different languages even though in both cases it's English!  It's taken Slick (Bass, Fogarty's mechanic) six years with Carl to understand when he says he's having a lot of trouble holding the line. Because Carl rides the front very hard so as soon as you drop the back, or do whatever you have to do to get some weight off of the front, you get a change.

If you were to listen as an uneducated person you'd say ok we need to raise the rear, we need to make the rear stiffer, we need to soften up the front etc. then you are just making it worse, exacerbating the problem. This is something so personality affected that it takes 3-4 years of working with the guy to actually try to get a handle on what that person is trying to tell you.

Most of the mechanics, tuners and suspension guys don't have time to go and watch the bike in the corners and on the race-track so you have to rely on the information that the rider gives you and then make a judgement call, you go ok he's now having trouble holding the line.  We have several options: first of all we make it have less off-set, secondly we raise the back; or stiffen it so that it doesn't slide or turn in or whatever. The rider goes out and rides around and comes in after 10 laps and says it's no better in fact I think it might be a bit worse. Right away you recognise 'oh it's worse' or he says that he's not as comfortable or the lap times are not as good or whatever, then you run to the other direction before he's forgotten the feeling.

After half an hour or whatever we send him right back out and see how it works. That's the thing with testing, seat time may play such a big part because it gives the rider the confidence and it also gives the rider an opportunity to actually feel so many different things on the motorcycle, there's no pressure. He doesn't need to win a race so he can think about what's happening.  At a race meeting that is so difficult, to do a really fast lap time it takes a 110% of your concentration and you don't really have time to think about what's actually happening because you're concentrating i.e. I know I'm having trouble with this corner but I'm just gonna hold on and I'm gonna force it in there - that's what happens. Then you get off the race track and the only thing you can think of is that every lap meant I had to push that thing into that corner and hang on for dear life and you don't understand why.

NS

I always get confused people talk to me about straight rate race springs and progressive springs and I consider things like oil level.  I understand that a progressively wound spring can overload a racing tyre if you're already on the limit not a nice thing to happen however nice it might be on the road - if oil level introduces a progressive element why isn't that as bad?

JC

Because its only affecting the wheel travel of the tyre towards the very end of the stroke, in the last 20 mm of stroke of the fork the oil level has much more affect than anything else. But the effect is really light, if you didn't have a bottoming problem before and you put 10 mm of oil in it, you are not really gonna notice it.

You want to be able to use as much of the stroke as possible in the front fork however, on the flip side, in the rear, you don't really want to use all the stroke.  The more wheel movement you get in the rear creates pitch which under acceleration off a corner can cause you to run wide.

NS

How does the pull on the chain affect the rear suspension?

JC

There are some race tracks where you want the bike to have some chain-force or some anti-squat so as the thing comes off the corner, and as you roll it up the chain actually pulls the swing-arm down a bit as it accelerates and it doesn't try to tuck the front or run-wide. As the swing arm comes up it actually holds it's line a lot more because the swing-arm is either in a neutral position or it's actually being pulled down as is pulling the bike.

NS

So you're looking for a balance of the spring and the chain and that is really a fine line that you're heading for.

JC

Yes especially on a Ducati, 1mm is a lot on a Ducati for some reason. My feeling is that it's got an eccentric on it so when you change the ride height and stuff there are rocker changes so the leverage ratio changes on the shock absorber a little bit, there's a lot of little things that actually take place there.

For instance if you make the swingarm 10 mm longer, as you would if you reduced the teeth on the rear the rear sprocket, you have more leverage working on the spring and therefore it gives a softer feeling. On a Ducati you would need a full half kilo heavier spring to get you back close to where you were.  The best way to check that is once you get everything set up on the bike you put the bike on the ground and check the static sag, because you've got a longer wheel base all of a sudden you've got more static sag.  So we add some pre-load to it to get it back to where we were.  Now we test it, and the rider complains it seems to sit down a little bit at the rear, and of course the linkage angles have changed so the shocks moving slower, feels softer and with less compression. It is virtually impossible to change only one variable

NS

You often see guys in pit lane bouncing bikes up and down - why?

JC

It's a security blanket, it's like oh you close the compression clickers two clickers and you bounce it up and down the rider will go ok that's cool!  But more often than not they get a feel for that kind of a thing. 4-5 compression clicks can always be felt, you have to be aware of the effects of what you are doing though, when I change the re-bound clicker I also have to adjust a little bit on the compression.

NS

So you go up, say, two clicks on one and down one on the other to get yourself back to where you are. Is it actually two and one?

JC

No it depends on where the needle is in the oriface or what size oriface is in the shock so it's more of a feel thing, that's a thing that comes with time. I find the biggest mistake that a lot of people make is that they by-pass steps, they just push on the bike, and close the compression adjuster 3 clicks or 2 clicks whatever and then they push on it and think it didn't feel very different.  Then they close it up 2 more but it still doesn't feel that much different so they close it 6 clicks and go out and ride on it. All of a sudden things are a handful and they can't understand why. It's because they didn't think that the paddock and the race track are 2 different worlds and pushing on the motorcycle is not really an effective method of checking for damping, spring rate, re-bound damping you name it.

The biggest mistake people make is when they push on the motorcycle and they think the way the bike comes up is too fast - so they end up screwing the re-bound in a long way to get the control that they want in the pits. then they go a ride the motorcycle and it does all kinds of weird things, it doesn't hold the line anymore, doesn't absorb bumps, or it shags the tyre real bad.

Then they come in and say there is something wrong with the shock absorber, it's got all these problems; you check it and the re-bound is in 6 clicks from where we set it .  Why is it in 6 clicks? - oh because I was pushing on it in pits and it was coming up too fast.  Oh did you push it with you on the motorcycle - no, well then that's the first thing to do because it will come up slower with you on the bike. The second thing is did'nt you ride it with the click position where it was.  Well no.  Why not?  Because it was too fast in the pits.  Well you don't know that until you ride it, it is two different worlds, you have to actually physically do something and go and ride it and get an impression.

NS

 .and take it to it's limits, where you've got to be to test.

JC

It's difficult to do sometimes, a lot of people don't like riding 110% every time they get on a race track but then again that's why there's people like factory riders and then there's the rest of us.

Jonathan Cornwell won the Canadian 250 Grand Prix Class Championships twice. Won the Canadian Dirt-track Championship at least 4 times and finished in the top 10 in the U.S. Championships 4 or 5 years in a row, best finish there was fourth.  Jon also raced in 3 250 Grand Prix in the early 90's out of the back of a Toyota pick-up. He still races when he is off Ohlins duty with a fourteenth in the Daytona Supersport race this year as well as competing in several US Dirt track races.

Jonathan Cornwell won the Canadian 250 Grand Prix Class Championships twice. Won the Canadian Dirt-track Championship at least 4 times and finished in the top 10 in the U.S. Championships 4 or 5 years in a row, best finish there was fourth. Jon also raced in 3 250 Grand Prix in the early 90's out of the back of a Toyota pick-up.  He still races when he is off Ohlins duty with a fourteenth in the Daytona Supersport race this year as well as competing in several US Dirt track races.

 © Neil Spalding 1999. All rights reserved

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