ESE's works engine tuner

[Pumba]

I remember a post that went something like a pit bike shock of around the right length was put into the delta ????
my memory is a bit fuzzy

No that was the FXR frame he had

[bucketracer]

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Tony Foal on motorcycle chassis and suspension:- http://www.tonyfoale.com/Articles/index.htm

Motorcycle Chassis Design and Construction and Other Technical Topics:- http://www.eurospares.com/frame.htm

[F5 Dave]

Yeah ideally as Henk says chain life & grief on the sprockets is a concern, as they found out in the early days of long travel dirtbikes, one could lose a chain pretty easily if it was that far away esp with wildly changing travel you can go from too tight to waay too loose. You will see modern MX bike with the sprocket virtually running against the sw plastic it's as close as possible on tall gearing.

Also this can bear the chain heavily on the swingarm. Rollers cost power if in the way (on the power side of the chain) & a small amount when on the trailing side. Any sideways or parallelism issue will be magnified & the 'whip' on the chain will cause drag or derail at worst.

The height relative to the pivot can produce pro or anti squat issues, yes on a small engine not such a drama, but a seriously too low sprocket will pull the rear down as it straightens the chain over the slider on top of the pivot.

That being said there are compromises & you can get away with a bit, it's just when you go beyond that there are problems. My 50 is further away than I wanted & I have to run the chain a little loose, but it is still ok. Engine weight forward is less of an issue on a small bike. but the bigger the bike the more the issue. I'd say the 250 is pretty big (long esp). Shortening it would make that issue go away.

[TZ350]

Chambers measuring the spring rate. The spring is being held in a plastic pipe and the ram of the press has a long pin fitted to it so the spring cant escape.

Chambers used a set of scales to measure the pressure on the spring and for every 10kg.... ie at each point 10-20-30...........50-60kg he would measure the amount the spring was compressed, this seemed to work pretty well.

A dual wound Honda RS125 spring measured at 0.60kg/mm and 0.72kg/mm and 85mm total fork travel

The dual wound FZR spring measured out at 0.45kg/mm and 0.71kg/mm and 130mm total fork travel

We also made some longer dog-bones to lower the bike but did not like the resulting angle of the suspension rocker and the swing-arm pivot bolt is still 50mm higher than the RS chassis.

Pumber has come to the rescue and helped us out with an original FZR shock which is shorter than the unit we have now, we will see what can be done with that next.

[gatch]

Would it be at all possible to cut the top shock mount and relocate it, higher in the chassis ?

Keeps the linkage ratios all the same etc. Then maybe make up some ally plates to mount the engine lower to keep sprockets and pivot in line ?

I guess then that would increase the steering head angle even more..

Maybe I'm just talking shit, haha.

[SS90]

OK, So now we have progressed on to Tony Foals' work...... and in doing so, we have somehow managed to overlook that the plenum idea was never completed.

Do you still have your Karate suit and Guitar in the wardrobe?

[Yow Ling]

OK, So now we have progressed on to Tony Foals' work...... and in doing so, we have somehow managed to overlook that the plenum idea was never completed.

Do you still have your Karate suit and Guitar in the wardrobe?

If you are that interested why not copy Thomases work and fit it to a Vespa, you can post your findings here.

[SS90]

What exactly is Thomas's work.... we only hear from Teezee (and his halfwit inbred delinquents), I can best some up this thread with " And now for something completely different"

[SS90]

If you are that interested why not copy Thomases work and fit it to a Vespa, you can post your findings here.

Is that better?... this thread was dying a death...now we can go back to the "old School" shit talking!

[SS90]

.

This is Thomas a Vietnamese race mechanic, you know that place where they have all those hot 50's and 125's are big bikes.

Thomas, ESE's Race Team's Tuner is fettling number 9. adjusting the port timing for Taupo.

Its hard to see but he has taped a degree wheel to the magneto flywheel so he can mark out the exhaust port height he wants.

None of this raise the port 3.5mm for a gazillion HP nonsense. He knows what timing he needs and sets the crank position there before marking the port and then doing the hells death port job that we all dream of.

You should see him setting up a carb. Talk about pain staking, he starts with a main jet so big the bike floods at about half throttle (apparently this proves the oriface of the needle/needle jet combo is big enough) and then he slowly step by step works back until it runs clean.

Most people start at the bottom with a carb and work up, He starts at the top and works backwards.

Never seen him blow one up. But then he is intelligent with the throttle and does not ring its neck when the engine is in distress.

Boy o Boy am I Looking forward to Taupo.

.

Pure genius........... I'll give Thomas €1000 Euro if he starts contributing.

My favourite bit is "Hell's death port job"........ you can't buy that kind of humor!

("Raise the port timing buy 3.5mm for a gerzzillion horse power")...Fark, now that is comedy!)

[speedpro]

I'm pretty sure my FZR chassis has the stock shock fitted. I certainly have not swapped it and the preload adjuster looks like a standard FZR style. On the minimum preload setting the sag as measured was in the ballpark as suggested by RT. The front forks are a real mixture of bits and I'm not sure which springs are fitted but they are FZR250 of some sort and with the cutdown preload spacers, again not sure from which model, they also have close to ideal sag settings as per RT. I only have to compress the springs about 5mm to start screwing the fork caps on. The basic suspension on a 3LN FZR is about right with a bucket engine in or at least it can be adjusted to be. I have no idea of spring rates but that didn't stop me getting the sag right.

[TZ350]

Hi Speedpro, we value your suggestions and now have two FZR250 chassis, our problem is that one had been fitted with a shock that looks like a FZR250 but is 20mm longer and the bike rides much higher than the std one we got from ShellRacing.

Also the ShellRacing FZR had the "progressive" part of the front springs cut off. We are newbies to chassis work and are looking at everything in an effort to understand what we have got and how it compares to the best handling bikes we have on the team, the RS/GP125's.

One of the things we have learned is, that springs, that are commonly called progressive are in fact dual wound and have two distinct spring rates.

For a spring to be "progressive" the coils at one end would have to be wound closely together and then progressively further apart. And when measured under load should require a progressively grater load to compress them. The FZR and RS front springs had two distinct compression rates.

The FZR and RS front springs have about a quater wound close and then the rest of the spring is wound with a coarser pitch without a progressive transition between the two sections.

Read about springs here:- http://www.worksperformance.com/html...rate_desc.html A Progressive spring is not the same as a Dual-Rate Spring. A progressive-wound spring is similar to a dual-rate in that it has an initial and final rate. The drawback of a progressive spring is that the crossover point is not adjustable. How the spring is wound determines the characteristics of the spring. This type of spring is wound with a varying pitch, as opposed to a constant pitch used in linear rate springs.


I can see this suspension bizz all getting very complicated, and quickly.............

[TZ350]

Would it be at all possible to cut the top shock mount and relocate it, higher in the chassis ?

Keeps the linkage ratios all the same etc.

I think the theory is right but technicaly it's difficult for me to do.

[gatch]

I think the theory is right but technicaly it's difficult for me to do.

Its sorted then, build a chrome-moly chassus tube frame. Easy

[TZ350]

Talks about Harley’s but the ideas apply to any bike.

Excerpts taken from:- http://www.calsci.com/motorcycleinfo/Suspension.html

When we think of bumps, we think of large and small bumps. However, your suspension does not see things like this. To your suspension, there's square edged bumps and rounded bumps. The key to understanding how your suspension works is that small, square edged bumps are harder to handle than large rounded bumps. The shape of the bump is more important than the size.

Springs typically come in three types: straight wound, dual rate, and progressive wound.

Most shocks have a small amount of compression damping, and a much larger amount of rebound damping. This is what you really want: the shock moves easily when it is compressing to absorb a bump, then slowly lengthens to release the energy stored in the spring.

Because of this, while compression damping is very important to dirt bikes in general and supercross bikes in particular, compression damping is not very important for street bikes - unless you routinely hit 4 by 4s on the freeway, or drive in Manhattan.

Rebound damping happens after the bump is all over. If there were only one bump in the whole world, rebound damping rates could be set very high, and the spring energy could be dissipated very slowly. Of course, on real highways you're likely to hit another bump in a short time, so the rebound damping must be chosen to allow the spring to uncoil quickly and get ready for another bump.

For rebound damping, we just want to slow down the spring as it releases its energy. It is not so important exactly how this is done. If there is not enough rebound damping, the bike feels loose and disconnected from the road. In extreme cases, bumps may produce a waterbed like wave action in the bike. If there is too much rebound damping, the suspension may pack down: you hit another bump before the suspension recovered from the last bump. After several bumps in a row like this, your suspension may be nearly bottomed out and unable to respond.

Many dirt bikes also have complicated rebound damping systems with several different sized holes and literally dozens of spring washers. Even on dirt bikes, there is no evidence that these complicated systems are either useful or necessary. On street bikes, a simple velocity squared hole works fine, as long as the hole size and oil are correctly chosen.

Since the forks get shorter when you hit a bump, all forks are effectively air-assisted. Because of this, it is important to get the oil level set correctly when you change your fork oil, or the spring rate will be wrong.

Forks have an additional problem - flex. Because they are almost three feet long, relatively small forces on the front wheel can cause the forks to flex and the front wheel to wiggle side to side, even while the handlebars are held firmly.

On compression, the fork spring is compressing and storing energy. The Rebound Washer is pushed by the fork oil up against the upper stops. These stops have holes in them to let oil through. Oil is collected in the pocket between the Damping Piston rod and the fork tube. Also, oil flows through the Compression Holes, up the centre of the Damping Piston rod, and out the piston. The size and number of the Compression Holes determines the compression damping.

During rebound damping, the Rebound Washer is forced by the fork oil down against the lower stops. These lower stops form a seal. The oil trapped between the Damping Piston rod and the fork leg must travel through the Rebound Hole, down the Damping Piston rod, and out the Compression Holes. Since the Rebound Hole is much smaller than the Compression Holes, the rebound damping force is almost completely controlled by the size of the Rebound Hole and the oil thickness.

Your forks can be modified by changing the fork springs, changing the fork oil, and drilling new and/or larger holes in your damper rods. If modified correctly, your forks can work extremely well.

Excerpts taken from:- http://www.calsci.com/motorcycleinfo/Suspension.html