top speed 114mph, What the F&*(?

[latexeses]

When I had the 920 Virago, top speed was 118 at redline. That was with one person or two. It never seemed to mind the extra weight either. The two person speed had to be reached within one good breath. The closer the bike got to 118 the harder it was to take a breath. There was a really strong compression that occured around my midsection. SQUEEEEEZE!

[MindWebs]

hmm..

you have to turn the throttle all the way...

Thanks ya, i don't think i have a problem there.
i'm too heavy handed as it is. every time i leave work i turn left out of the lot
and promply powerslide the rear till i'm about a 1/2 inch off my pipes. and headed down the road right where i want to be.
(the details are according to an experienced GSXR600 rider behind me)
(she slides real nise!!) this is on dry clean pavement, just so you know.

i rode an xt500 for about 4 years, i drive better slideways then normal

so it's a consensios that my motor ain't quite right...

that's what i wanted to know.

Thank you gentlemen!!
Webs

[TADracer]

Checking my math

My statement above that A 79 special with the 16" rear wheel numerically should do 170 is based on the numbers only and not what the machine will actually do. So checking my rough math (which I admit is not a strong point) works out like this.

16" rear wheel with tire conservatively is a 20" diameter times pi = 5.25 ft. per turn.
8500 RPM redline factored for the .882 overdrive in 5th = 9637 driveshaft RPM at redline reduced by the 3.3 to 1 final gear ratio = 2920 wheel turns per minute. Middle gear is a 1:1 ratio so is not considered.
2920 x 5.25 = 15330 feet per minute.
15330/5280 ft. per mile = 2.9 miles per minute x 60 minutes = 174 MPH numerically.

So, unless there is some reduction between the crankshaft and the transmission that I am not aware of, I think my statement is correct. However, there is no way an 11 will even come close to this because of the power drain as speed increases. But 130 is obtainable with a bike that is in good tune

[trbig]

My XJ has the same setup with a 16" rim, and when I had the original final drive, I took it to @ 8k... wouldn't quite get to redline... and I was a lot closer to 130 than I was 170.

I'm guessing something isn't right with the math somewhere.

Tod

[Trainzz]

My 2 cents

I have. uhmmmm..., "heard" that a 1980 xs1000 special will do 135+ on highway 54 between Kingman and Wichita KS, with 1500 rpm left in the bank.

Now understand that this is only hearsay, I wouldn't have any first hand knowledge of this act of speed atrocity. Not me, nope.

BTW, just thinking, I need to go see if I can find the do-rag I misplaced in that area a few weeks ago.

[petejw]

I was just going thru some of my old tech stuff and came across the formula
for road speed, its in metric, here it is........

using the specs that TAD gave the wheel diam i used is 500mm
and the top gear ratio i used is 1:1 i know our bikes arent that but it was easier to work out.

RPM; 8500
Top gear ratio; 1:1
Final drive; 3.3:1
Wheel Dia; 500mm (20")

Cir: 2 x (R)Radius x Pie(3.142)
=2 x 250mm x 3.142
= 1571mm
cm = 157.1
= 157
m = 1.57
km= 00157

Axle RPM = 8500 divided by final drive 3.3
= 2575 rpm

road speed = wheel circ x axle rpm
= 00157 x 2575
= 4.042 km/m x 60
= 242 km/h or 150mph.

so theoretically the bike could get to 150mph
but that was using the 1:1 top gear ratio.

Hope this helps.


also found a formula for air flow cfm if any is interested.

[TADracer]

Dis goood land, dis America!

This is so much more fun than talking politics?

So Pete bears it out. 150 mph at 1:1 driveshaft speed. Factor in the 11.8% overdrive in 5th and voila! 167.7 MPH. Realistically our machines will never come close to that speed but it shows what potential is there if you have a big pair and alot of $$$.

There is probable clutch slippage at high speed as wind drag gets higher, scrubbing off some top end. Also our motors probably reach top power way before the redline and then the curve begins to taper off. There is probably a bunch of other parasitic stuff going on as well and our gauges are really not that accurate. When our tach says 8500 or our speedo says 130, how do we really know its not more....or less? So in reality 130 or 135, maybe touching on 140 is about it for a street 11.

But it is fun to just know the possibility.

[trbig]

Still saying that's wrong. I don't know where the thread is, but this math has all been done and posted and discussed before... a couple of times. Seems I remember redline was figured something like 142mph, but that very few of the bikes can get to redline in 5th. As I said... I've been really close.. within 500rpm.. and it's nowhere near the speeds you guys are saying. Maybe at 10k rpm... but not 8500.

Tod

[Shuriken]

i rode an xt500 for about 4 years, i drive better slideways then normal

so it's a consensios that my motor ain't quite right...

+1

I ride an XL500.... having experience sliding a dirt bike around and constantly spinning the tire in the dirt has made me a better rider on the street....

Have you seen "the speed thread" ? Can't vote anymore but it will show you what a well-tuned 11 will do:
http://www.xs11.com/forum/showthread.php?t=5198

You gotta' have decent compression and the right jetting. I had an 80g that smoked when starting and running. Compression was only like 90-110psi but I ran it down the road 120mph one time.

[crazy steve]

Actually, if you do all the math and use the correct tire diameter of 25.3 inches, you'll come up with a 'calculated' top speed of 134 mph at 8500 rpm. This is for a 16" wheel; you guys with 17" wheels would be good for a bit more.

Remember, you have multiple reduction gears in these bikes. The 'primary' ratio is 1.657 (engine to clutch), then the trans at .882 (5th gear), then the trans output at .936, then the middle drive at 1.056. Multiply all these out, and you end up with a 'driveshaft to crankshaft' ratio of 1.44.

Look like Yamaha hit the gearing right on the nut. I suspect that the 141 mph indicated that I saw was probably a bit optimistic on the speedometer's part...

'78E original owner

[petejw]

The numbers might not be spot on,
but the formula is.

[Ivan]

Actually, if you do all the math and use the correct tire diameter of 25.3 inches, you'll come up with a 'calculated' top speed of 134 mph at 8500 rpm. This is for a 16" wheel; you guys with 17" wheels would be good for a bit more.

Remember, you have multiple reduction gears in these bikes. The 'primary' ratio is 1.657 (engine to clutch), then the trans at .882 (5th gear), then the trans output at .936, then the middle drive at 1.056. Multiply all these out, and you end up with a 'driveshaft to crankshaft' ratio of 1.44.

Look like Yamaha hit the gearing right on the nut. I suspect that the 141 mph indicated that I saw was probably a bit optimistic on the speedometer's part...

'78E original owner

Who pays attention to that redline. Mine has faded over the years and looks more like a suggestion than anything.

[MindWebs]

suggestion sounds right.

that's what the red line is. It's a suggestion not a rule.

i'm sure the manufacturer has a reason for it...

but if you cause damage to the engine your not "IN TUNE" with your machine
it WILL tell you when enough is enough, before damage happens(by 1/10sec or so).

any way it really wasn't the calculated MPH i was looking for, i am familier with the Drag to HorsePower problem.

i was just wondering what some of you gents thought, 114mph seemed low to me, and it appears that my engine isn't tuned quite right yet.

so, back to the man cave with a few new tools in hand, Timing light and ignition trk tester (found it at harbor freight item#93795) don't have a clue if it will tell me S%& but i thought i'd give it a try for $4.99

i still have to replumb the gas lines with plastic and rebuild petcocks.

to many projects to little money....

[tw1980]

80 special with stock FD reads 5000 rpm @ 72 mph.Assuming that my speedo and tach are remotely close to being correct,that looks to me like 144 mph @ 10,000 rpm in 5th gear.My guess is most of these bikes won't achieve 10,000 rpm in 5th gear unless they have some serious mods.

Terry

[DGXSER]

Before I swapped out my FD, I know 5,000 rpm equated to about 70 mph on my speedo and I also recall calculating that based upon other tach and speedo readings I do not remember anymore in 5th gear that 7k was roughly 110 mph. Now, having said all that, I alos figure my speedo is off by at least 5mph low, maybe more. So, I am certain that 110 was at least 115. Soo, based upon that, at least, assuming the ratio stays consistant, then 8500 rpm would be about 145 mph.

Reality is my speedo stops at 85 and anything above is just "dang that was fun, who gives a s*&t what the number was anyway" speed .