This spreadsheet I'm working on calculates the relationship between engine RPM and final road speed. I've taken the standard running setup (gears, sprockets and tyre size) from the workshop manual.

I figure there are three types of speed: theoretical speed - calculated by ratios, registerd speed - estimated by speedo & actual speed - best measured by GPS?

I've set it up to show what speed the rear wheel will be doing at a particular RPM in any gear, it is also easy to change the ratios, say -1 on the front sprocket to see what happens.

Can anyone think of any reason other than the working radius of the tyre that would have any effect on the bikes speed relative to engine RPM's?

The reason I ask that question is because by my calcs, the bike should be moving at 100kph or 62.5mph when the tacho shows 3,849rpm - but that's not true, it's closer to 4,000rpm.

I hope I don't explode anyones brain with this...

 

Drag? Road friction?

 

TRI, good one!!!!!
ambient temp, air density,wind direction,original bike break in, engine oil -type, wt., level, quality, clutch slip, chain lubed, chain/sprocket - quality/size/type/adjustment/ alignment,Tire size, age, wear pattern, brand,pressure, wheelbearings, fork tune, oil wt., level,wear/ stiction, gas tank level, quality/temp of gas, jetting,float level air cleaner, type and clenliness, exaust, can/ clenlyness, bike clenliness, waxed. Original factory assembly tolerences, cam age/index,camchain wear /adjustment, Ignition specs., plug heat range, age, type, brand, factory, day of assembly, variations in componant quality/assembly technique. How close to the equator, and direction of travel,road temp... I could get padantic!!!!!!!! Clean and free, Ripp'n

 

Considering that there is a hard mechanical connection between all the parts of the bike (assuming no clutch slip..thanks rippn) the only place where you'll find a change is tire diameter growth at speed, effectively changing your ratios (think crinkle wall low presssure drag tires during warm up). I would say that this is minimal, but whether it is .01% or 3% is anyones guess. Then again, tire wear will make your tire smaller than you think changing the ratio the other way.

I just saw something in a magazine where the speedo error may change at different speeds. By the same thought there could be Tach error (like the new R6) you are dealing with. If you are worried about 151 rpm out of 3849 rpm, that is 4% error, is this with the stock tach or some kind of diagnostic equipment/dyno, all your numbers may be suspect depending how you measure them and what your eyeballs actually see and how your brain interprets the results (paralax and whatnot).

Depending on what you are really looking into and how far, you could be out of the powerband too, where the motor simply isn't spinning fast enough to make enough power to get through the air, or it ain't spinning fast enough to make torque to get through a smooth start. I would if I were you, skip everything but the theoretical speeds, calculated by ratios, keep in mind that your bike will be drag limited on the top end most likely and wheelie limited on the start and somewhere in the middle you'll get the info you need.

My brain still seems OK, but I haven't tried to stand up yet.

 

I believe you can eliminate all parasitic factors and draw a direct correlation between tire RPM at the contact patch and road speed. That, I believe will be the only function that should not change and all 3 should match within some degree of accuracy. Only calculation that should change this will be error of measurement and how fast the diameter of tire changes (wears out). If you enjoy the mathematical exercise, go for it. My question: What would be the practical application of this data? If memory serves correctly, SportRider Magazine did a spreadsheet and made it available based on Engine RPM, Gear Ratios and HP Dyno data. All of this data culiminated in a graph with nice curves that allowed a rider to determine optimum shift points.

 

Theres a program you can dl on the honda cr forum, called easy calc I think, its pretty good but I couldn't bring myself to trust it too much as theres so many diff things can effect speed.On my 89 Hurrican iget 100km/h at around 4-5.

 

I guess the point is to understand what is happening between the pistons and tyre in more detail...

Rippn, that is one hell of a list but missed the point... all of those things except slipping the clutch vary power and load on the engine, but are not relevant for the straight out mechanical connections, you almost exploded my brain though!

Mixing Jay and Fish, I'm thinking it would be possible to relate the length of the contact patch at stop, and at speed to different radii, and then relate them to the tyre rotation for a continuously varying factor

That could also be related to tyre wear... interesting.

But yeah, the only application I can think of is what happens when you change sprockets and/or gearing, and that is a really easy calc to do without a mother spreadsheet... so the only reason now is I like to play with excel in my spare time!

 

Glad we got to the point.


1) Its a Tire not Tyre.
2) What do you mean by continuously varying factor?
3) If you really want to explode your brain, calculate the tire expansion due to Centripetal Force, Stretch due to Torque applied at the friction surface, AND vary that with heat and it's effect over time...if you like to play with Excel.

 

Just because Americans can't spell, doesn't mean the rest of the world follows suit...
In the Queens English Oxford dictionary, you'll find: tyre (US tire) • noun 1 a rubber covering, typically inflated or surrounding an inflated inner tube, placed round a wheel to form a soft contact with the road.

Sadly, there's no right and wrong spelling with such an insane language as english... I guess that's what happens when you steal words from every other language! But enough about philosophy...

My interpretation of a continuously varying factor is a number that changes with respect to TYRE RPM such that things like you mentioned in 3) are accounted for in the actual speed.

 

Y'all got too much time on your hands. Get out and ride!! [sm=happy046.gif]