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Discussion Starter · #1 ·
Ok, I was reading the specs on some bikes and ran across these words. If you know what they are please tell me what they mean and what exactly they do. Also, what should I look for when looking at these?

1. Rake / Trail


2. Compression Ratio


3. Bore X Stroke
 

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Rake/Trail is (if I recall and translate correctly) something with your front tire.
Rake is the angle your forks are set (not sure about this though),
Trail is the difference between the center of your wheel above ground and the contact patch of your tire.

Compression Ratio-
When the piston moves up, and the valves are shut, the air/fuel mixture in the cylinder is compressed.
12:1 Means: you have 12x the atmospheric pressure than your surroundings.

Stroke X Bore = Displacement.

Stroke is how much the piston moves up and down, Bore is the width of your cylinder. As you may recall from school, space is area * height.
To calculate the area, you need also the number Pi for bore is only the diameter.
 

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What do you need these numbers for?

Stroke X Bore e.g. affects the tolerated rpms of your bike-

A 600 supersport has a large Bore and small stroke, so it revs higher.

A Harley hardly revs, for it has a huge stroke and small bore.

Rake/Trail affects handling and stability, in various means.

Compression ratio determines which fuel you need.


You don't need the numbers.
Rake/Trail manifests in handling so you better ride a bike instead of looking at the numbers (they are not everything that affects handling anyway).

Stroke X Bore you won't change- so don't look at it. Instead look at the torque curve (most important), powercurve and the redline.
That tells you more about how the engine will feel like.

Compression Ratio you might want to check to see if the piston rings still seal- maybe after 60.000kms or so. Before that look in your manual what fuel you bike runs on.
 

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[ QUOTE ]
specialsymbol said:
Compression Ratio-
When the piston moves up, and the valves are shut, the air/fuel mixture in the cylinder is compressed.
12:1 Means: you have 12x the atmospheric pressure than your surroundings.


[/ QUOTE ]
I don't think that is correct, the 12x the atomopheric pressure than your surroundings...maybe your saying the same thing as (since im tired whild reading this) that the volume inside the combustion chamber when the piston is at BDC (bottom dead center) of its rotation is 12 time greater than the volume inside the combustion chamber when the piston is at TDC (top dead center) of its rotation. I don't think it has anything to do with pressure per say, just how much the gas/air is being compressed ya know. Then again maybe its the same thing as you were saying.
 

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First of all.... Google is your friend.

1. Rake / Trail - Rake is the angle of the forks with respect to vertical. The smaller the angle (nearer to vertical, generally termed "steeper") the easier it is to turn the bike. A bike that is easier to turn is also generally less stable.

Trail - draw a line down along the forks and extend it to the ground in front of the rear tire. The distance between this point and where the front tire touches the ground is trail. Trail is the lever arm that when combined with the force of the front tire on the road, generates the torque that makes the front wheel want to go straight. It's related to trail... in general terms a steeper rake produces a smaller trail number.

2. Compression Ratio is the ratio of combustion chamber volume to total volume.
R = (volume displaced + combustion chamber volume) / combustion chamber volume

Compression ratio is one measure of the efficiency of an engine. The relationships are fairly complex but generally, higher compression ratio = higher power output for a given engine size.

3. Bore X Stroke - Bore is the diamter of each piston. Stroke is the linear distance the piston moves from top to bottom. These are used to calculate the displacement of an engine. Volume displaced = pi/4 * stroke * bore^2
 

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[ QUOTE ]
1slowF3 said:
Compression Ratio is the ratio of combustion chamber volume to total volume.
R = (volume displaced + combustion chamber volume) / combustion chamber volume.

[/ QUOTE ]
That sure is a much easier way of saying it lol
 

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But what does he need this information for? Is there anything you can do with it?
 

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[ QUOTE ]
specialsymbol said:
But what does he need this information for? Is there anything you can do with it?

[/ QUOTE ]

What does he need this information for? I've no idea.

What can he do with it? If you're a racer or designer then these things mean something to you. For the rest of us there are many, many other factors that go into the total package of chassis response and power output. So other than just to compare one bike to another in very general terms and perhaps feel a bit more knowledgeable... not much? :crazy:
 

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Discussion Starter · #12 ·
I was just wanting to know what they meant. I always saw those terms and numbers on a spec sheet for a bike, but I had no clue what they were for. Thanks for all the help guys
 
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