Geartronics - Suzuki TRE description

If you are the rider of any of the big Suzuki sport bikes, it's highly likely that you will have heard of the so-called
'TRE' modification.

The internet abounds with information and discussion of this simple modification, much of it speculation, some
of it just plain wrong! There is a huge band-wagon of would-be entrepreneurs established around the world,
each of them attempting to cash in on the hype. Here I will attempt to explain what the TRE modification is and
dispel some of the myths surrounding it.

First of all, TRE stands for 'timing retard eliminator'. This was a phrase coined by the US 'inventer' of the
modification. I personally don't like the term 'retard' because it implies that the ignition timing is retarded, which
certainly isn't the case! To be correct, it should be described as less advanced - not the same thing at all. The
modification only applies to Suzuki motorcycles with fuel injected engines. This includes most of the later
GSXR and all Hayabusa models. In common with all modern engine ECU's, the fuel injection computer used
by Suzuki is a fairly complex piece of hardware. However, the Suzuki unit goes one step further than most of
the competition, both car and bike, in that it provides gear dependant mapping. That is to say, the various fuel
and ignition settings are modified to account for the differing conditions that the engine experiences in each of
the 6 gears. There are several reasons for doing this, one of which is to 'sanitise' the power delivery of these
extremely responsive engines. What Suzuki has done is to 'soften' the response in the lower gears under light
throttle conditions. This makes the bike less on-off in response to the throttle and makes them easier to ride at
low speed in traffic. It therefore follows that the electronics is holding back some of the potential of the engine.
The way in which the throttle response is softened is to hold back on some of the ignition advance given to the
engine - an easy way to cut power. It's highly likely that the fuel settings are also altered to benefit fuel
economy and/or emissions. The effect of the gear dependant mapping is evident in the first 4 gears at throttle
openings of upto 50% and at all engine speeds. The effect on 1st gear being more than that of 2nd etc.

So, how does the ECU 'know' which gear is selected? Simple, the gearbox is fitted with a gear position sensor.
Actually, sensor is not the correct way to describe it, it's more of a switch. Anyway, the switch presents a
different resistance to the ECU, depending upon which gear is selected. The ECU 'measures' this resistance
and uses the appropriate map settings which are programmed into its memory. These map settings cannot
easily be altered because they are 'burned' into the chip during manufacture, however, we can 'fool' the ECU
into thinking that a different gear is selected to the one that actually is! If we disconnect the gear position switch
and hard wire a fixed resistor into the loom, we can force the ECU to use whichever map we desire. Clearly, we
don't want to use the 1st gear map because this has the least amount of ignition advance. Likewise we don't
want 2nd, 3rd or 4th either. On the face of it, it would seem obvious to use the 6th gear map as this will certainly
have the optimum fuel and ignition settings. However, the later bikes have their top speed restricted by limiting
the maximum engine revs in 6th gear. So, 5th gear is the one to go for, because it has optimised settings and
doesn't have a speed restriction imposed.

The resistance presented to the ECU when 5th gear is selected is 6800 Ohms. If we cut the sensor wire and
replace the switch with a 6.8K resistor, the ECU will always use the 5th gear map regardless of which gear is
selected - including neutral. This can present problems on some bikes and riders have complained of poor idle
quality and poor hot starting performance when a fixed resistor is fitted. This prompted some people to offer
what they described as an 'active' TRE. This only set the 5th gear map when a forward gear was selected. The
neutral map remained unchanged. The Geartronics remote display unit incorporates the active TRE for use
with Suzuki gearboxes.