Understanding Chassis a little more

Goatie said:

Why is it that race bike set ups have more trail than the road bikes? I would have thought you would want to have a race bike steer as quickly as possible to get it in a turn fast? Am I missing something counter intuitive? Like a stability issue?

You have explained the basic geometry well.

I would add that it is more important to set the geometry first than the clickers and springs. Well I suppose spring weight will have an effect on geometry so I suppose set sags and spring weights then dial in the geometry, then ride it and fine tune with clickers

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Hi Guys, great questions, so let me get to them in order received. I'm a bit pissed as I spent about 45minutes writing the thread, and it logged me out. When I logged in, it disappeared.

There are many factors that racebikes must consider. Remember, they are much lighter and have less rotation mass to aid in stability like street bike. Also, trail is important to them as they are running a all rates of speed, at all given angles. But trail is only as good as the rest of the bike. Stability comes in many forms, and a racebike is a compromise of sorts.

The bikes steering is an affect of rake. The less the rake, the faster the bike will feel it wants to fall into the radius. Though rake does affect trail, racers change their triples for that very reason, to regain the lost trail from steepening the rake. Stability is also based on wheelbase, but it also depends on what type of stability you are looking for. As an example, a chopper will be extremely stable in a straight line, however is about as stable as you on one ice skate in sand, while the fat lady is on your shoulders singing the Titanic song. This is due to weigh bias and why you don't see Big Dogs racing.

I agree as springs are more part of chassis than suspension.

A more forward weight bias will aid in turning, due to roadholding capabilities the extra trail brings to the table, along with the extra weight on the front tire.

IdZer0 said:

+1 on that question

The way I understand geometry, trail is like the length of a rudder. I understand it adds stability and decreases needed steering input, but I don't understand how it solves the 'running wide coming out of corner' problem form instance. An issue that everyone is 'solving' by using reduced offset triples (i.e. increased trail).

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This takes me to the running wide question. Extra weigh on the front does several things. More Feel, larger contact patch, less load transfer to the rear, resulting in less squat effect. The more the bike squats, the less weight on the front tire. This increases your bikes' wheelbase, increasing the turn radius in relation to the bikes' lean angle. result: wide.

I would say though that wheelbase is more like a rudder, as the longer it is, the more longitudinal stability you have.

Many guys, when changing their triples tend to inadvertently change other factors that aid in roadholding and stability.

First off, by adding the lesser offset triples, you have three main changes:

1. More Trail = more Roadholding, due to larger contact patch.

2. Lesser Wheelbase = less lean angle at a given turn radius.

3. More Forward Weight Bias = better feel anti-squat effect, allowing for better acceleration out of a turn.

The other factors involve have more to due with proper adjustment of the chassis. Most riders that add the triple clamps usually adjust the rear ride height taller. This moves more weight to the front, lessens the wheelbase slightly more and increases the CofG height, allowing for faster transitions.

Lastly and most important, with chassis set up there is no perfect numbers. It is always a compromise, and always negotiated at different tracks. This is why I developed the adjustable triples and not a static unit. (shameless plug for me)

I hope this helps guys, and feel free to contact me any time.