ESE's works engine tuner

[TZ350]

I'm pretty sure my FZR chassis has the stock shock fitted. On the minimum preload setting the sag as measured was in the ballpark................ I have no idea of spring rates but that didn't stop me getting the sag right.

Ok from what I have read recently, spring rate is about having enough umph to push the weight of the wheel back down, on the other side of a bump and preload is about holding the weight of the bike and rider up.

The ideal is to have the bike and rider sail along flat and level with the wheels bobbing up and down as they roll over the lumps.

The big thing is, spring rate is associated with the unsprung weight of the suspension and wheel, not the weight of the bike.

The heavier the wheel and unsprung part of the suspension the stronger the spring needs to be.

Pre-load is about supporting the weight of bike and rider at the 1/4 - 3/4 position of suspension travel.

To get the smoothest ride, one wants the lightest wheels and unsprung suspension parts possible. Because the lighter suspension and wheels means you can use softer springs.

But a bike with the same weight wheels and suspension parts like a FZR250 turned into a Bucket, although some 30 kg's lighter it still needs the original spring rate to control the wheels.

But I can see other issues here with changing the ratio of unsprung weight to total weight of rider and bike by swapping the engine out for a lighter one.

There will be less reactive force in the lighter chassis/engine/rider combo to help store energy in the suspension spring as a wheel rolls over a bump.

This means there is less umph to keep the wheel in contact with the road on the other side of a bump and the lighter sprung mass will get flung around more as the wheels try to compress the suspension springs.

You will know what I mean if you have ever ridden in an empty ute with over load springs and then again with a load in the back. The heavier the load the smoother the ride.

Trying to understand all of this hurts my head.......... but fits with what you have told me...

[TZ350]

From:- http://www.gostar-racing.com/informa...ion_set-up.htm

1 - Front compression
This is when you want your front compression to control the "nose down" effects of braking so it turns in to corner properly

2 - Front rebound
You have let go of brakes, adjust front rebound so that the front forks extend at a controlled rate allowing you to keep your line.

3 - Rear Compression
You want the rear end to squat a bit as you apply the power.

Make sure that the rear rebound setting keeps the rear wheel in contact with the road.

A very easy to follow guide to suspension setup:- http://www.gostar-racing.com/informa...ion_set-up.htm

[TZ350]

I just knew it was going to get complicated, from YSSUA the suspension people:-
http://www.yssusa.com/suspension_problems.html

The result of a too hard rear spring ratio is that the bike gives easy turning into corners but creates traction problems. Too soft rear spring ratio gives good traction in acceleration, but tends to under steer in the entry of a corner and will give the front a light feel. The result of a too hard fork spring ratio shows in the bike with good under braking, but creates under steer and feels harsh in corners. A too soft spring ratio gives easy turning into corners, but creates over steer and can cause the front to tuck-under or dive under braking.

What’s “Spring Ratio” ?????? for goodness sake…….

[Henk]

I assume they are talking about the spring constant. I wouldn't get too worried about it. It should be possible to get ballpark numbers for static sag at both ends offf the interwebs. I know that for dirt bikes we used to work with about 10 - 20 mm without rider and 65mm with rider as a start point. 5 and 20 feel about right for my FXR.
I haven't got too worried about this with the bucket since the suspension isn't being asked to deal with two foot whoops and wheelstanding over logs and the power and weight involvled aren't that great. I'd get the ride height about right at the rear if you can, and then try and get the front end sorted, you can do this by feel and messing about with oil levels and weights when you have the sag right, again I'd be looking for about 20mm sag with the rider on board. Then start in on the rear end if you find that you are having issues. I'm not convinced that a bucket is going to be making enough power to start overwhelming the suspension and tyres unless things are so far out that the rear end is almost rigid.

I am by no means a great suspension tuner and have gone with things that feel about right to me and that might not suit everybody since I prefer to have my suspension a bit soggy anyway after years of dirtbikes with 12 inches of travel.
The fact that I'm not that fast also helps the suspension.
If you can get the delta frames close to ballpark they are likely to be beter than the standad frames you are going away from in any case and one you have them working you can start zeroing in on gains.
Suspension tuning can be as much of an art as engine tuing I think you'll find as evident by the fact tat there are people that make their living doing nothing else.

[Skunk]

5 and 20 feel about right for my FXR.
I haven't got too worried about this with the bucket since the suspension isn't being asked to deal with two foot whoops and wheelstanding over logs and the power and weight involvled aren't that great. I'd get the ride height about right at the rear if you can, and then try and get the front end sorted, you can do this by feel and messing about with oil levels and weights when you have the sag right, again I'd be looking for about 20mm sag with the rider on board. Then start in on the rear end if you find that you are having issues. I'm not convinced that a bucket is going to be making enough power to start overwhelming the suspension and tyres unless things are so far out that the rear end is almost rigid.
Suspension tuning can be as much of an art as engine tuing I think you'll find as evident by the fact tat there are people that make their living doing nothing else.

I think you're right with just about everything in that post. As you say - get it in the ballpark and go from there as every rider will want a different setup.

[TZ350]

How do you do change the stock springs, spring rate?

How do you do change the stock springs! Spring rate? YOU CUT THEM SHORTER! But not without calculating how much! to get from .72 kg/mm to 0.9 kg/mm the calculation is rather strait forward surprisingly! Just figure out the percentages!

0.9 minus .72 divided that by .72 = 24% holy moly!!!

you need to cut off 24% of the coils to get a 0.9 spring rate? Or you could just settle for 0.8 kg/mm or 10% cut off!

From:- http://www.vfrdiscussion.com/forum/i...-spring-rates/

[Henk]

Never got into the cutting things down game as with dirtbikes it was the right shock to start with. If you can't get the static sag to line up both loaded and unloaded with the preload adjustments available it's time for a different spring. About the only real mod we ever had to make was to lower the ride height on a couple of bikes for my wife and we did that with longer dogbones in both cases. We did throw springs in as well but cutting coils off? I'm not sure I'd want to go there.

[Buckets4Me]

Never got into the cutting things down game as with dirtbikes it was the right shock to start with. If you can't get the static sag to line up both loaded and unloaded with the preload adjustments available it's time for a different spring. About the only real mod we ever had to make was to lower the ride height on a couple of bikes for my wife and we did that with longer dogbones in both cases. We did throw springs in as well but cutting coils off? I'm not sure I'd want to go there.

this is buckets not motorX welcom to our world

[TZ350]

Now the boys have given up on the GP chassis they are getting right into building new bikes and engines.........

They are working on two Honda RS125 chassis, two Yamaha FZR's and an Aprillia RS125 chassis.

It's all to try and keep those FXR's honest.

Now that we have some good engines and chassis next seasion and the TRRS should be interesting.

[F5 Dave]

Cutting down springs is a known procedure, its been disscussed here many times. Getting them straight flat edged is tricky & they need to be to avoid jamming the spring heavily against the inner tube. Also making sure you don't have a coil bind situation requires care.

With the FZR you have removed a lot of weight replacing the engine & no road fairing/lights etc. On the other hand yams of that era always had light front springs. The first post form the Harley site is twaddle, but what you'd expect & probably fit for purpose considering the intended audience. Henk, I thought you'd had KDXs? Front springs on those were pretty light & responded well to some stiffer springs (mind you my one was a 91, but the later ones apparently too).

[Buddha#81:Me]

Now the boys have given up on the GP chassis they are getting right into building new bikes and engines.........

They are working on two Honda RS125 chassis, two Yamaha FZR's and an Aprillia RS125 chassis.

It's all to try and keep those FXR's honest.

Now that we have some good engines and chassis next seasion and the TRRS should be interesting.

Seems alot of effort to keep a single mass produced cheap form of racing honest? hehehehe

[F5 Dave]

Yeah but have you ridden a GP on the track? They're dreadful. Seriously a better option would be to buy one of these regularly exploding FXRs & jam the engine in that.

[TZ350]

Seems alot of effort to keep a single mass produced cheap form of racing honest? hehehehe

OkeDoke your right.....but...........so there..........and...................

[Buddha#81:Me]

OkeDoke your right but...........so there..........and...................

Bwahahahahahaha!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!

[Henk]

Henk, I thought you'd had KDXs? Front springs on those were pretty light & responded well to some stiffer springs (mind you my one was a 91, but the later ones apparently too).

Dead right, the fork springs on the KDX were light, but then when the rider is around the 50 - 55 kg mark they are about right, whacked in a softer spring at the back and longer dog bones and all was good, bike came with gold valves fitted in the front and it works well set up like this its regular rider.