You will hear a lot of people say "Gearing down gives you more bottom end and gearing up gives you more top end".

This is not correct.

Most standard quads are sold with an appropriate gearing for their general design purposes. If you are doing something different that is other than what the OEM considered the general user would, then you may want to change your gearing to suit. Or if you have modified your machine, ie. Increased the engine output, then too, you might want to change your gearing.

If you ride most OEM quads full throttle in a straight line on a hard-pack flat surface, they will probably only just run out of legs and start bouncing off the rev-limiter. Some seem to hit it quite early and could be geared up from stock if you want to a bit go faster. Others top out at right near the rev limiter anyway, and probably wouldn't go much faster even if they had the gears to do it.

Say you are doing 115kmh and just hitting the rev-limiter in top gear and you think your trusty steed might be capable of more. Two things happen if you decide to gear up.

One, your engine is now pushing through a taller gearing and you are multiplying your torque to the real axle by a smaller number (final drive ratio) before it gets to the ground. On this point, it is worth considering that you will now need some extra power just to do the same speed you were before.

Two, if your bike does have the extra power you thought, you will push a higher top speed before you hit the same factory rev limiter. In this situation you might go up on the gearing again. If you do it is most likely you will get to a point where you are not hitting the rev limiter any more and most likely losing out on top speed.

So why is the above statement untrue?

Most quad racers that race on dirt will take off in 2nd gear because this gives them their fastest launch even though it is obviously a higher or taller gear. Once you are moving you simply need to be in the best gear to put the most power to the ground at what ever speed you are doing. It does not matter if this gear is called 1st 2nd 3rd 4th 5th or even 6th (if you have one).

Some owners of quads with six gears say I was doing 120kmh in 5th! And I still had another gear to go... imagine how fast it would go it 6th? Truth is... most often ‘slower' because the gearing is too tall. Most modern cars will go faster in 4th than they will in 5th, because 5th is too high for max speed. A classic case of where gearing up made the car go slower (in that gear). They keep it up there because it is a cruising gear and some emissions are measured in grams per 100km, so less engine revs keeps that down too. So there are reasons to gear high, like cruising and economy, but as a performance thing you really need to have a proper look at how often you actually go that fast.

But anyway, let's get back to quads... If you have done ‘the big 3' mods or any other modification that increases your power... Chances are that gearing higher than standard might be appropriate.

How high?

If your engine mods mean you are making 10% more power than the factory ever did... then a 10% gear up might be a good place to start. You should consider that gearing up will increase the gaps between gears (wide ratio) and will reduce your ideal gear ratio choices for different hills and corners etc. So you might be revving in 3rd or chugging in 4th etc, where a lower geared quad will have smaller gaps between gears, and you won't have this problem as much. Gearing down lower than standard will reduce top end because you will most likely bounce of the rev limiter well before your top speed and run out of gears, but you might be significantly quicker around an MX track with better gear selection for the job (close ratio).

I have geared speedway quads up to a theoretical top speed in 5th of 170kmh when the bike would only be raced at 88kmh.
In this example, I wanted a higher 1st gear to take off in, less gear changes and run the track in 3rd (so 3rd was effectively my top gear).
But as one of the fastest bikes on a speedway track, it would not pull top gear in a straight line down the beach.
In this case, gearing up made the bike significantly faster for the job.

I should add that the quad could still chew up most other trail quads in 4th gear when they were in 5th or 6th down the beach, because top speed is dependent on the actual gearing and not the number written in front of the gear.

There are other examples where MX racers are doing the opposite and taking off in 3rd gear, for max acceleration to get the holeshot, and sometimes they do.
They do not gear down for more bottom end, and in fact they never use their lower gears on the track.
They might gear their quad down, but select a higher number gear to go faster... in their application.

As far as the above statement is concerned, when I'm playing chains and sprockets...

I gear my DS450 down to race MX with a top speed of 110kmh and gear it up to race speedway at only 88kmh.
In both situations track times and therefore acceleration is improved.

So it is much more fair to say that changing your gearing does not effect your acceleration.
Only acceleration in top gear... but then you could just change back a gear and accelerate even harder if you wanted to.

Only your engine power and how you use it effects your acceleration.

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