Enlightenment needed, My 82 Maxim road test!

[MerlinDudley]

My 82 Maxim, road test, claims a top speed of 88.4 mph? and yet the road test on the 82 Seca (which uses the same engine) has a claimed top speed of 107.8 mph. Can anyone explain the discrepancy of almost 20 mph, between the two? as both use the same engines, and the overall gearing is supposedly the same, despite the extra gear, on the Seca?

This has been puzzling for a while now, I have asked at a couple of local Yamaha dealers, and they were of no help whatsoever! As they didn't seem interested in old models, all they wanted to do was to try and sell me the latest R1! So any help to settle this little conundrum, for my own peace of mind, would be much appreciated!

Merlin

 

[xschris]

The seca also runs a 18" rear wheel. There may be some other carb jetting or cam differences. I also think there was a turbo version of the seca model also. But that may have been for the 650 models.

 

[Jeff0133]

I've Taken the two engines appart a Maxim and a Seca and the weights on the Seca crankshaft are lighter,( the weights on the crankshaft are smaller).
Maybe this explains some of the difference although in my opinion it would show more on acceleration rather than top speed...

 

[MerlinDudley]

I agree with you there Jeff! That would only account for a quicker acceleration, but that wouldn't account for the shortfall, on topend speed. From what I have been able to find out, is that on at least one year, the Seca, sprocket rato's were changed, however I don't know if this was for quicker acceleration, for about town use, or for topend performance? as I can't find out any more information, about these one off year change!

Merlin

 

[Jeff0133]

Maybe going +1 front , -2 rear would get more top speed?...from what i've read here somewhere, that drops the rpm at top speed around 500...theoretically giving 500 rpm to go, but then the trade-off is ...I think...less acceleration getting there...
My cafe build will get -1 front, +2 rear....with the 6 speed seca engine....making for max acceleration, but the trade-off will be less top speed, but my bike makes 140-150 kmh (85-90mph) right now with the stock set-up ie maxim engine and gearbox,stock airbox and jetting, stock sprockets.
Looking to build a lighter/faster(acceleration wise) cafe city bike so top speed can be sacrificed for acceleration.
Even then I think i'll be able to get around 130 kmh (80 mph)...which is quite enough on this bike...

 

[xschris]

Running a 18" rear wheel (seca) will drop your rpm's by about 500 over a 16" wheel. This is what happened with me when I went from a 120/90 16 wheel to a 110/90 18. The seca also uses a 18" front wheel where the maxim has a 19". Smaller wheel = less rotating mass.