I was speaking with my engine builder and he said im gearing too high and should gear for peak power.
He suggested that I should aim for 14200-14300 for my TM R1, vs my 15,500. My engine quite happily revs that high.
Also to consider is that im 15-20kg overweight too.
I’m down on top speed on the main straight by 3/4 km/h. Its also quite a tight tecnical track.
The issue I also face is getting the gearing to suit certain corners without dropping out of the powerband.
So what gains more time? I know this is testing based. I plan to get a couple of days out next week. But I was planning to spend more time in building a database for my jetting and carbs, along with testing castor.
One tool I look at is an rpm histogram. You want to optimize your track time / distance spent in the peak of your torque / power band. If you see that the histogram is shifted to the left (lower rpm) a bit, drop a tooth or two. If the histogram is shifted to the right (higher rpm), add a tooth or two.
We are running single speed stuff…so may not apply the same for shifter?
Gearing is always a tradeoff. I tend to prioritize mid-corner RPM over outright straightaway speed. That said, if you’re hitting 15,500 down the longest straight then you would certainly go faster down the straight with taller gearing. If your engine likes to rev then I would target 15,000 and go from there. A ratio change of 0.050 would yield around a 600 RPM change, and about 3 mph more for the same RPM. Example here would be going from a 16/24 (1.500) to a 16/23 (1.438).
Running a shorter ratio can help balance out being over the weight limit, but I’m with your engine builder that it creates more emphasis on the need for peak power.
Have you looked at your data to see your minimum RPM in the slow corners?
This is the universal truth. One exception can be your starting position in a race. If you’re way at the back and need to pass a bunch of driver you might add a tooth to the rear in a shifter. Most don’t bother though.
In terms of peak power, yes in the sense that you want to spend as much time at peak power as possible over the course of a lap. But that will often mean having to overrev. Put simply is a compromise between speed of the slowest turn and the length of the longest straight.
Yes and track layout may dictate that too. You do want to spend most of your time in the powerband if you can, but a track might have some wonky super tight corner or something and that might change your philosophy on gearing. If you are lugging the engine with low RPM because that’s where you spend most of the time on a track, you might got mobbed in the one tight hairpin or lose so much time in that one corner it offsets what you gain in the rest of the track.
As others have said, the stop watch is a good metric. I am usually looking to get off all the corners that lead onto straights as fast as I can, so I will often sacrifice top speed for being in the right place in the power getting off those crucial turns.
A gear that has you 1mph ahead all the way down the straight except right at braking is going to be quicker than one that reaches a higher top speed but takes longer to get there.
One thing you can do is go one step taller and one step shorter on the gearing, and see if the speed increases or decreases speed in the same way as the gearing would suggest, or if it goes the other way. TThhat should tell you which direction to move. en of course, it’s stopwatch…but by checking gearing vs speed, all things equal, it will tell you what tradeoff you are making. The LKE I’m running, as an example, tends to like a little shorter gearing than other engines and I can get same or higher mph as it stretches higher in RPMs and I gain a little in the leading to the straights, so shorter gearing actually means faster top speed (compared to my prior TM baseline). But every engine has its tune, so depending on what porting/advance/compression etc you have, your engine may like one solution or the other. I know it’s a non-answer
