Mph

monster · 10 Apr 2005, 10:11 (Ref:1274513)

Please could someone tell me the calculation to working out Mph with relation to the revs,gearing and tyre size

Alex Hodgkinson · 10 Apr 2005, 14:03 (Ref:1274723)

Quote:

Originally Posted by monster

Please could someone tell me the calculation to working out Mph with relation to the revs,gearing and tyre size

"Blue Peter" style, you need;

- Rear tyre circumferance
- Maximum RPM
- and your gear ratio written F:R, eg. 10:83.

Multiply your RPM by (your front gearing/rear gearing)

eg. 19,250 x 0.120

Now you've got how many times per minute your rear wheels will rotate at that RPM.

Now get your rear wheel circumferance in KM and multiply it by the value you now have, and then multiply that by 60 to get KM/h.

x0.6 to get MPH.

Gore · 10 Apr 2005, 14:06 (Ref:1274724)

I guess it's just a case of taking the number of times the engine revolves, dividing through by the gearing to find how many times the wheels revolve, then multiplying by the circumference of the wheel to find distance covered:

Road speed = engine RPM * gearing * wheel circumference.

For instance, at 16,000 rpm, 12:70 gearing and six inch wheel diameter(including tyre), road speed would be:

16,000 * (12/70) * (6*pi) = 51,701 inches per minute

51,701 * 60 minutes / 63,360 inches per mile = 49 mph.

[Note that the parameters above are guesses; in particular, where I race we can't change the gearing, so I don't know what a realistic final gearing would be]

monster · 10 Apr 2005, 16:31 (Ref:1274797)

Sorry being really thick ,could one of you kind fellows work it out for me
13,000 revs
12/86 gearing
Wheel circumference 84cm

Gore · 10 Apr 2005, 17:13 (Ref:1274828)

I make it 91.4 kph, or 58.5 mph.

Are you sure about your wheel circumference, though? 84cm implies diameter of 27cm, which sounds pretty big for a kart to me--although I don't have a tyre to hand to measure.

monster · 10 Apr 2005, 17:22 (Ref:1274835)

Many thanks ,wheel circumference i measured with a flexilble measure(wifes tape out of her needle work box)

speedy king · 10 Apr 2005, 21:09 (Ref:1275030)

What kart is it you race? and what track was that?

monster · 11 Apr 2005, 07:15 (Ref:1275241)

Hi,i have just started karting,my local track is Blackbushe and i have only done one test session in a rotax max.

DSM · 11 Apr 2005, 13:22 (Ref:1275477)

13000 rpm x 12 teeth / 86 teeth = 1814 revs per min of the tyre. 84cms = .00084km so 1814 x .00084 = 1.524 km per min or 91.43km per hour, 56.8mph. (The conversion is .621 miles to the k).
You realise you've opened a can pf worms here? Just wait for all the mail from the guys who will swear their ROTAX does 100MPH+ everywhere!!!!!

Alex Hodgkinson · 11 Apr 2005, 13:27 (Ref:1275481)

yup, that's gonna come soon isn't it?!

yelodwg · 11 Apr 2005, 15:27 (Ref:1275589)

Monster,

You can also try this program: http://www.muller.net/mullermachine/...re/gearsel.zip

and possibly this one (I haven't used this one, so am not certain if it can do the MPH conversion): http://www.nacoma.cc/kartsmart.htm

Tom Stephens
www.kartfinder.com

monster · 11 Apr 2005, 17:05 (Ref:1275683)

Quote:

Originally Posted by DSM

13000 rpm x 12 teeth / 86 teeth = 1814 revs per min of the tyre. 84cms = .00084km so 1814 x .00084 = 1.524 km per min or 91.43km per hour, 56.8mph. (The conversion is .621 miles to the k).
You realise you've opened a can pf worms here? Just wait for all the mail from the guys who will swear their ROTAX does 100MPH+ everywhere!!!!!

Having not driven any where else do not know what revs or gearing you can pull round the other circuits.So where is the longest straight or quickest entry to a slightly shorter sraight ,in other words where is the highest top speed achieved ,also where is quickest average lap speed found.

speedy king · 11 Apr 2005, 18:13 (Ref:1275727)

The fastest circuit with the longest of straight(ish) areas would be Three Sisters i think. Would be pulling about 80mph maybe a tad more, but the gearing would be alot less, maybe 80 or so in a Snr Max, generally the things dont tend to rev above 14,000RPM maximum i don't think. Mine is reving at about 13,200 at the end of the Ellough straight, on 12/89, reaching mid to late 70's

speedy king · 11 Apr 2005, 18:14 (Ref:1275728)

Blackbushe is a very short twisty circuit ive hear with not very long straights. Only heard that as the people who bought my Junior Max from last year are practicing there in Mini Max and they wanted information on how it should be geared

REALIST · 11 Apr 2005, 19:00 (Ref:1275762)

Quote:

Originally Posted by speedy king

The fastest circuit with the longest of straight(ish) areas would be Three Sisters i think. Would be pulling about 80mph maybe a tad more, but the gearing would be alot less, maybe 80 or so in a Snr Max, generally the things dont tend to rev above 14,000RPM maximum i don't think. Mine is reving at about 13,200 at the end of the Ellough straight, on 12/89, reaching mid to late 70's

That's interesting. Working on the above formula, which looks correct, that would be a top speed of 90kph or 56mph, not mid to late seventies.
Those revs on that gearing would need a tyre diameter of about 14" to achieve 75mph, which sounds like a big kart tyre!!
How did you calculate that top speed Speedy?

Alex Hodgkinson · 11 Apr 2005, 19:04 (Ref:1275769)

Yeah 3 sisters claim to be the quickest kart circuit in england, which I can believe. Incidentally it's also one of the the slowest circuits bikes race on in england.

We pulled about 93 there when tested a kart in Super Libre trim.

speedy king · 11 Apr 2005, 19:33 (Ref:1275796)

Quote:

Originally Posted by REALIST

That's interesting. Working on the above formula, which looks correct, that would be a top speed of 90kph or 56mph, not mid to late seventies.
Those revs on that gearing would need a tyre diameter of about 14" to achieve 75mph, which sounds like a big kart tyre!!
How did you calculate that top speed Speedy?

MyChron 3, displays 74/75/76mph depending on how i exited the previous corner. Those revs are not exact, just what i see to remember seeing them around. I'll take a look either this evening or tomorrow at the data i have from the circuit