Crank shaft HP

John, very interesting tire clamp drag not detectable. Will have to chew on that for power lost guessitmates.

Shrapnel that low 26 lb chart is what I set my rear tire when big rocks or soft sod to cross and have found that low rather dangerous on harsh power leans as tire distorts and wallows similar to a flat. I don't think 5 hp tire drag in out size and pressure tires realistic, maybe half that with say 32 and above PSI. If someone would stick a electric engine in place of crank shaft with couple guage on we would know for sure.

Maybe it is more sensitive to tire pressure than to load. As stated earlier, PM me and I can send you reference as well as spreadsheet model if truly interested. Keep in mind that this scenario of 5 hp is at what, 150 mph. I seem to recall most Norton dyno pulls are at around 80 mph.

Dances with Shrapnel said:

Interesting observation there "pommie john". The above numbers are for a specific set of conditions (air pressure, load and speed) so your conditions are more than likely different (heavier bike, different air pressure, speed?). So if you were doing a dyno pull in the 50 MPH range you would expect to see a 0.5 HP difference; not much.

In your case, my hunch is that what you lost on rolling resistance with the bike cinched down tighter was equal to what you lost to wheel slip (power loss) on drum when loosened it up. Compound this with an assumed lower MPH dyno pull and it would all get lost in the wash.

It stands to reason that tire deformation is work and the faster you spin (or do work) the greater the power required.

Click to expand...

Yeah you could be right about tyre slip Vs deformation.
I was surprised and had to eat humble pie after telling the dyno operator he'd strapped it down too tight

It was a fourth gear run and on the BM that's somewhere around 120MPH at peak rpm.

Here's some more scuttle butt on tire effects and dyno read outs. Also mentions first dyno run will be a handfull of hp less than other done once fully heated. I don't know but would be a fun if destructive day to test different tire factors.

http://www.jamesrussellpublishing.biz/m ... pipes.html
A lot of bikers are being ripped off by repair shops charging money for dynometer runs. Don't be fooled. Most riders do not need any dynometer measurements or adjustments. Did you know that by changing the air pressure in the bike's tire can raise or lower they dyno horsepower output? Also, just by tightening or loosening the bike to the dyno will do the same? How much change? Ten percent differences that's what. So that increase in power you are getting on your dyno print out may be fabricated figures to make you believe you gained power when you gained nothing at all.

In configuring Peel I had to ponder the fuel heating flows so got familiar with cfm and fuel mass per horse power btu wattage/min.

Its written it takes 140-150 cfm of proper mixture to make 100 shaft horse power.
Rational guessimates by builder of Peel's 920 10.5 CR drag cam JMS stuffed Dreer head kit unboosted is 80's rwhp or low 90's at crank. Huh assumes 10-ish hp drive train drag. Just found this simple engine calculator to plug in Peel with 100% V.E. to get 130 cfm mixture inhaled = 87 hp so reasonable ballpark way to talk about shaft power. We've plenty of examples that imply best engines put out like 10-11+ shaft hp per 100 cc's which lands within ballpark bounds above. So if fuel flow monitored then another way to estimate power output. Again this is a basic calculator there are scads beyond this down to the mach #'s predicted by also imputing port and valve and cam timing data. Peel better damn well pack in over 100% V.E. naturally or will be pissed about Norris D cam.

http://www.mez.co.uk/mezporting/enginepower.html