Track day feedback

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Fast Eddie

Fast Eddie

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I had the Trident Hunter out at Cadwell t’other day.

I’ve only done 2 track events this year, but packed in quite a few sessions and laps.

I’m really chuffed with the bike, it starts first time, goes around the track unreasonably quickly, then ticks over like a Honda in the paddock afterwards!

For those interested in such things, the motor is an 850, JS rods and high comp pistons, approx 0.040” squish, JS#1 cam and followers, Comstock ported RH10 head, FCR carbs, Tri spark ign, Norvil belt drive.

Despite the stock gearbox being fine most of the time, I do think that 5 speeds and the extra strength of a TTI box would be wise for the track. It’s when changing down rapidly that the wide ratios of the stock box are felt the most.

Although I have Falcon shocks and Lansdowne fork dampers, something is still not quite right as I have a juddering on fast corners (notably Charlie’s and Chris curve at Cadwell). This requires further investigation.

I’ve a few mods planned for winter, but we’ll have to wait n see how many I actually get done!
 
re; "Although I have Falcon shocks and Lansdowne fork dampers, something is still not quite right as I have a juddering on fast corners (notably Charlie’s and Chris curve at Cadwell). This requires further investigation."

what grade fork oil and how much are you using in each leg?
 
160ml of 15 wt. Previously 160ml of 10wt.

Also dialled in a little more damping

Forks now feel much better overall, just a judder on certain bends. And I'm not even sure this is the forks. Need to check through all basics first of course.
 
Are you feeling the limitations of the frame/swingarm/ISOs? The tires that you have are, probably, sticker than the racing rubber worn by Norton "back-in-the-day"

If you are shaping 45 degree cuts on the outside of your boot souls with shocks and forks never dreamed of by Norton suspension designers, then you are transmitting much higher loads to, and through, the frame.

Have you gusseted the frame?
 
Main frame is stock, swinging arm has Norman White cotter pin mod, new AN Vernier ISOs, running at approx .002”, Comnoz rose joint head steady. Forks have Lansdowne internals and shocks are Falcon. Avon Roadrider front and rear.

There is zero ‘hinge in the middle’ feeling at all. It turns in faster than I think it should. It shakes its head occasionally when accelerating hard over bumps, but seems to settle down quickly.

I have thought about a Seeley Chassis, but having sat on a few, I know I’m too big. A Manx rep chassis would be a better fit.

But I’m loath to lose the ISOs! I think the lack of vibration is a great boost to reliability. So on balance I think I’ll stick with the stock frame.

If I change anything, I might send the forks to Maxton. I also suspect I might benefit from stiffer rear springs. And I might fit a steering damper... for the psychological benefit.

At the end of the day, I might have all these modern aids at my disposal, but I’m not pushing even close to the limits of Williams, Croxford, et al. At my (low) skill level, I don’t think the frame will ever be the real bottleneck !
 
Sounds like tires (stiffness), tire (inflation pressure) and damping/spring rate. Anything else you can do to reduce unsprung mass is always helpful.

Is the juddering in the curve(s) with neutral throttle, hard driving out of curve on the throttle or trail braking/rolling into the corner(s). Have you played around with body position to see if there's any change?


Keep in mind (from what I have read) that there are distinct viscosity differences between several brands of fork oil of a given "oil weight"
 
Good questions Dances.

For reference, the judder was bad enough to make me van the bike at Mallory, but with new fork oil and slightly firmer settings it was only mild at Cadwell.

What do you mean by tyre stiffness? Too stiff / not stiff enough??

Pressures: I’ve tried at Avon recommendations and 2 PSI less. No change.

Body position: didn’t really try differences with this.

Where / when: in the middle of long fast corners, on trailing throttle and when exiting under gradual acceleration.

Fine under braking, and fine at speed in a straight line (which rules out wheel balance).
 
Not enough rebound damping can lead to front end chatter, patter or judder. Probably some other terms that can be used. There is a wealth of info on the interweb. Might see u on the track one day. One Seeley is ready, other is waiting on parts. Do u do classic bike track days only or just any old?
 
I think you’re right Steve. There’s a bit more left on the Lansdowne adjusters which I can try. Trouble is, I’ve got no more track days booked this year and these issues just don’t show up on the road. I might try and get some more track time in Sept / Oct. If you are going to any, let me know.

I’m open to any track day, but these days there are plenty of classic based ones which are just more enjoyable, so that’s what I end up doing most of.
 
I hadn't really thought about looking at classic bike track days until you mentioned it earlier. Found one next week at Castle Combe, of course got something else planned!! For sure will pm if I get anything organised.
 
Nigel, when I was setting up the race bike, I also had a few front end issues similar to yours.
I also have the Lansdowne inserts with the original single disc on the RHS.
I am running 18" rims,Avons front 90/90/18 and rear 110/90/18 , softer compounds than for road use, available in the Road Rider range.
I tried different weights of oil and put up with it for a couple of seasons until I found that it was sideways run out on the front rim.
The problem showed up on the bigger sweeper corners with neutral throttle openings, problem went away under brakes and when back on the throttle.
There was bugger all run out, but enough to create problems under race conditions.
Does it do it punting hard on the road or just during track days!
Regards Mike
 
Fast Eddie said:
Good questions Dances.

For reference, the judder was bad enough to make me van the bike at Mallory, but with new fork oil and slightly firmer settings it was only mild at Cadwell.

What do you mean by tyre stiffness? Too stiff / not stiff enough??

Pressures: I’ve tried at Avon recommendations and 2 PSI less. No change.

Body position: didn’t really try differences with this.

Where / when: in the middle of long fast corners, on trailing throttle and when exiting under gradual acceleration.

Fine under braking, and fine at speed in a straight line (which rules out wheel balance).
Click to expand...

Every style and model of tyre has it's own stiffness characteristics; I was thinking along the lines of mainly sidewall. Nothing you can do but deal with it and tune around it.

It's smart to check some of the obvious things such as - are things all fastened tight, no broken components, no bent components (rims), tires running true and balanced, fork bushes have little to no slop, etc but it really sounds like front end tuning (spring rate and damping). From your observations it does not seem to occur under braking which is a good thing - not sure of what to make of that other than geometry changes and the forks are laterally stiffer (nested inside).

In the past when I used AVON super venoms on the Commando racer I would usually start cold with 28 psi front and 32 psi in the rear. That was a pig of a heavy bike (compared to the Seeleys) yet I was probably weighing in just under 1/10th of a ton back then. With the Seeley at say 280 lbs and Dunlops I start with pretty much the same air pressure bias. Unfortunately I now weigh over 1/10th of a ton. Add insult to injury in that I occasionally weigh closer to 1/10th of a long ton.
 
Mike, I haven’t checked the wheel for run out, it’s a good point and I will check it out.

BTW, I tried your pipe out on the last track day as I intend to run it with the new mota, which I hope to get in it next year.

So, I spent this afternoon making hybrid cNw and FEss rear sets. It’s always surprising how something that looks so simple can take so long. Do one job... find another... repeat...!

Track day feedback
 
Examining your tyres can tell you a lot about what's going on (apparently). When I was doing regular track days a few years back I spent a lot of time looking at my tyres and comparing to photos from the web. If I remember correctly lifting on the trailing or leading edge of the cross grooves gave an indication of too much or too little damping.
Correct pressure is crucial, get it wrong and you have a set of trashed tyres in no time at all!
 
Well I sure hope I did not give the impression on being learned on this matter. Strictly an amateur.
For what it's worth, they look okay, nice balance front and back, maybe running a smidgin on the warm side. But what do I know!!
 
Speaking of heat, I rode about two hours yesterday. Upon return, sitting on the bike off the stand, I bounced the front end with the brake on.
Hard not to notice that it seemed a good deal more compliant both C and R than when I headed out. Perhaps the straight weight fork oil
does indeed thin out and effect the operation of the dampers.
 
Fast Eddie - do you get the pattering when the bike is cold and hot - might shed some light based on Onder's observation.

Suggest starting a track day log book that lists such things as track conditions, cold tire pressure F/R, post session tire pressure F/R and any observations such as track temp, how hard you were driving the bike and bike behaviour. The log should also include fork oil brand, volume and weight, unladen sag F/R, laden sag F/R, front C/R damper settings, etc. You get the idea. On the other hand you may get lucky with a simple change or two and can forego the log book but a log book is a handy thing when you step away from things for a while and don't necessarily recall particulars.

Is this bike also used on the streets - I am speculating here but maybe the tire wear pattern has been biased to the center and this is contributing to your problem in some way.

Hard (for me at least) to judge things by just looking at a tire. I can say you have more tire lean to go but other bits may likely start dragging first.
 
Never ride any bike without a hydraulic steering damper. If you get into a crashing lock to lock tank slapper and don't let go of the bars quick enough and grab the tank to stay on , you might be flicked over the front of the bike.
 
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