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 'inventor' 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 up to 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.