Just wondering...

[trbig]

I have the 750 final drive on my bike. On a last little ride with Vincer and Bigfoot in Talihina, I took off on a straight-away. I got to 7500 RPM in 5th where it hit the wall. Anyone know how to figure how fast it was? I've got the stock speedo... so when Vince pulled up and asked how fast I went, I just shrugged and said 85!

I just put the motor together last week with honed cylinders and had done @ 700 miles on it. I figured I was just trucking it home anyway and I had the 1179 piston kit waiting on me when I got home... so thought I'd see if it would hold together or blow up. ??? Dang thing held together. Held it at top speed over a minute, but I guess it got put together OK. I just need to figure out why it's doing the James Bond smoke cloud when I first take off...

Anyway.. didn't know if anyone knew what the gearing of the 750 final drive does at the rpm ranges.


Thanks.

Tod

[planedick]

On mine it's...

I also have the 750 final, but Pathfinder can't get 7500 I don't think. In my case it's 50 mph at 3000 rpm and each 500 rpm is 10 mph more, so doing the math makes 7500 rpm is 130 mph. I have fairing, bags etc and weak center cylinders so Pathfinder hits the wall at around 120 - 125 mph. Pathfinder likes freeway running at 5000 rpm which is 90, seems to run the smoothest there.

[stoked]

lol, this is exactly why I never need to do this gear swap. To much temptation to see how fast it would go. By the way, what color is your smoke?

[trbig]

I have the fairing and bags also, but have never done a compression check on it yet. I haven't synched the carbs either so I'm sure between the rings not seated and the carbs not set quite right, I can cure a lot of the problem there. It may be a mute point though. I had planned on building this other motor with the 1179 kit and keeping it in reserve for when I needed it, but the temptation may be too great. I just got back from taking the cylinders down to get bored. I'm using the 78 cylinders since the gasket they sent doesn't have the part for the YICS tube and that would eventually let dirt and crud settle in that tube. I have blocked the ports anyway on the head.


I thought I remembered seeing something to the effect that @ 8 grand in 5th was 140. I know this dropped between 7-800 rpm at 70mph when I put the final drive on, so thought it may be a little faster than that. Oh well. Not bad for pushing a fairing, bags, and a 260 pound guy through the air.

LOL.. HippyDave and I went to leave the Talimena trail after the ride and head to town with everyone. Dave came up (Instigator that he is.. ) and revved it a bit wanting to race. So... I rip the throttle back, and in the evening light, I can really see the cloud billow behind me. When we got to town, Dave said that he saw the cloud I left and took off though it, then missed second gear really bad... finally crunching it into gear. He said he was pretty sure we really impressed everyone with that! lol.


Tod

[jimboreeno]

Check you speed

If you wanna know your actual speed... carry a handheld GPS if you have one or can borrow one. Velcro it on the bars or whatever. Reset the stats and take off. The GPS will measure your max speed. Also, if you dare to look, it will measure your speed as you ride.

[planedick]

Radar

We have radar signs around here. Just drive by one and it will tell you your speed. Just look at your speedo for verification or calibration purposes.

[trbig]

Radars are exactly what I don't want to be clocking me!

I don't run the bike like that on main roads where these signs may be. I just thought there would be someone who knew the gear ratio and could tell me. Thank you though.

Tod

[pggg]

So 50mph at 3000, 100mph at 6000, 75mph at 4500, pretty much perfect but any taller is a waste of time, and the only way taller gears will get you faster is with super-strong tailwind and a long long hill

[fredintoon]

Hi trbig,
there ain't no wall, at least not a new one. With the 750 final drive you effectively have a 3 speed tranny with two overdrives. When in the new 5th gear the motor just don't have the power to push the bike any faster. Most bikes will go faster with the tranny one gear below the highest even when geared stock and the 750 final drive just exaggerates the phenomenon.

[trbig]

Yeah, I noticed earlier in the year when Hobbyman and I were running them top speed... that I didn't go any faster in 4th or 5th. It had the same top end... it was just easier on the motor in 5th gear. 4th gear sounded almost identical in engine pitch to his 5th when he rode next to me.

This video is terrible in quality. I didn't realize how bad and shaky it was. I was leaning my left arm on the handlebar and holding the camera, so every little bump translated into the camera. It was actually a smooth ride. This was a nice cruise through the hills from Honobia, OK to Talihina, OK this last weekend at 55-60 mph. At the end is where I made this top speed run. I also had to use a video editor to get it down to under 5 minutes and it killed the sound. It was originally 15 minutes long.

Anyway... here it is. If it's too bouncy for you, just fast forward to the last minute and a half or so.


Honobia Cruise


Tod

[planedick]

Bad math

pggg, looks like your math is off some.

50 @ 3000
60 @ 3500
70 @ 4000
80 @ 4500
90 @ 5000
100 @ 5500
110 @ 6000
120 @ 6500
130 @ 7000
140 @ 7500
150 @ 8000

Of course being analog and somewhat unsteady it isn't a precision measurement, but close.

The radar signs are not cops or ticket writers. They are a way to get people to slow down. Usually near school zones. There is one near me in a 40 mph posted zone so in order for it to show me my actual speed I need to go over 40 mph. I go 50 and it shows my actual speed then flashes "Slow down". Sometimes they place a portable system (on a trailer) in problamatic areas.

[pggg]

bad maths

Er.. if doing 3000 at 50mph, then you should be doing 6000 at 100mph... sounds to me like the 750 drive IS overgeared after all, or else planedicks' speedo is toast - 120mph at 6500 is waaay overgeared...

[trbig]

120mph at 6500 is waaay overgeared...

If that's the case... then my bike REEALLLLYY likes being overgeared. It loves the 70mph at 4K, and I don't find myself looking for another gear like I used to. My clutches on the other motor I was running with it are all still well within spec... so...

I guess everyone is entitled to their opinion!?


Tod

[planedick]

Love it...

I just love the overdrive and I was also always looking for the next gear. PGGG, go through that again and remember that each 500 rpm adds 10 mph, so 3500 = 60, 4000 = 70, 4500 = 80, 5000 = 90, 5500 = 100, 6000 = 110. I don't know where you got that 6000 = 120.......?

[MAXIMAN]

Using a standardized gear reduction equation ...with the 750 ratio ...at 7500 you should have been doing about 134.86 mph.

That can vary some with the tire you're running. Buty I think it pretty much proves the old adage it doesn't matter how ya gear it... the top speed is dictated by power and aerodynamic drag.

134 is about what the stock 11 would do with stock gearing.

BTW here the formula:

MPH = (rpm/fdr)(Do*pi/12)(60/5280)

or

MPH = (rpm/fdr)(Do*.00297)

Where Do - Overall Diameter of your tire inches
fdr - final drive ration

fdr is top gear ratio x primary ratio x secondary ratio

PS: Patrick is like a potato chip. Whatever he says you can take it with "several" grains of salt. hahahahaha...damn I 'm funny!