For those interested in top speeds I think we need to do the math.
Looking at Mylap it shows "Best Spd" of around 90mph for juniors!
This is of course not quite right and in fact is the average speed in km/hr around the 1.247km circuit when completed in around 50 secs.
For top speed we need to look at engine revs.
For an engine reaching top revs of 12,350 with standard tyres on (circumference of 900mm) and gearing of 13 (pinion) and 83 (sprocket) I think the calculation would be:
12,350 x 13 / 83 x 0.9 x 60(mins per hour) / 1000(meters per km)
Answer to that one is 104.45km/hr
Pretty good when your **** is only half inch off the floor guys!
Anyone can check my theory please?!

That sounds about right Geoff.

Here's a lap from Sepang last weekend in my Rotax Senior:


Top speed of 109.3kph on that lap. I think highest was 109.8kph last weekend. The speed is taken off the front wheel.

In lay-down big track racing I think rotax karts reach somewhere around ~ 160kph

yea math. i like this.

i also check what ratio to achieve a desire top speed
ex: 14,069 x 0.9 x 60 / 1000 / 109.3 = 6.95
around 83~84 / 12. about right mikko?

what D2 circumference anyway?

mikko, do u rev at 14 flat or you do go above?

Well a bit off ... with that calculation change the tyre circumference to about 863mm to get about there with the gearing .



14,2 pretty much as high as it goes. On tracks with bumps I've seen 15,000 + .

I think it's bullshit that you can reach 160km/h on the straight on a Rotax.Maybe coming down a hill with no brakes would do that.KF1 which is much faster hardly reach 130km/h on European Tracks.

Hi there karting,
I said:

Take note of the bolded part.

This is what lay-down karts look like:


This is an example of a big track:

Geoff,

Yes, i noticed that too and dismissed that from the result sheets......


Mikko,

I have to agree that my own data logger shows a top speed of 106kph for sepang - ROK engined, hard tyre compound.. and speed read off the rear wheel.

So 109 for a max is not unreal although for the D2 tyre.


Yes, the lay down karts are mighty fast ( dunno exact top speed ) and the use large tracks......and that means for CARS...er mr "karting". Do a google search or read the Ekartingnews Forum....

Yeah 109 should be about right.. the only variance should be from if the tyre circumference changed since I measured it .

Any reason why you have your speed sensor on the rear? Or do you have one on the front as well?

Our MyChron says top spead of 105km/h in the Juniors Round 1 Final, but we were off the pace. Our data also shows us we were probably 2 teeth too many on the rear sprocket

Mikko is right a rotax will reach speeds of around 160 kph geared correctly on large circuits. I was racing 125 cc super karts 30 years ago and doing speeds of 210 kph on car circuits these were yamaha yz motor cross engines and heavily modified, they were replaced with Rotax engines with gear boxes and doing the same speeds so the rotax engines without gear boxes as we race would achieve around 170 given the right gearings and big track. Lay down karts were very popular in those days to reduce wind resistance. i will try and find some of my old photos to post.

Your very first post and this is what you come up with. I admire your social skills and your uncanny ability to dash off a reply without first reading the post you are replying to.

Brilliant!

Only have one speed sensor.....

Why the rear? well, it shows where my wheelspins are....from poor throttle control! and how I brake....

I use hard compounds.....which is another reason to observe the above.


Sorry for off topic but why the recommended front from Unipro? ( their manual did not suggest rear at all....)

Cheers!

Rotax max senior engines are used in a class in superkart clubs in Australia.

They place the full aerodynamics on these karts and look just like any other superkart.



See the link

http://www.superkart.org.au/classes.asp

Started a new thread on wheel speed sensors.

anyone know Mojo D1 rear tyre circumference?