gearing

[slow coach]

Just a quick Question

mmpr got my head round this ok, my question is this how can you use the same mmpr for say a 13 turn motor and a 10 turn surely there would have to be a gearing difference, all i have read about modified racing is you aim for about 36mmpr and there doesnt seem to be any allowance for the number of winds in the motor?

Over to you lot

Jason ???

[Dave Treacy]

As I understand it, you need to gear in a range for mod of somewhere between 35-40 MMPR. This will depend on motor wind, timing, track length, driving style etc.

I generally start at the low end (35 MMPR) and if I don't dump, start going up from there

[jason]

Jason,

I normally run a Fantom 12x1 Ti in my 12th car at large tracks I have geared as high as 44mmpr but at a small track like Milton Keynes run this motor at about 39-40mmpr.
For a 13t motor I would go a couple of mm higher and for an 11t acouple of mm lower.

35-36mmpr is really 9 & 10t teritory.

All the above is based on running 3300's and you must be gentle with the throttle in the infield.

Hope that helps

Jason B

[MattW]

Yeah you wouldn't want to gear "all mods" on about 36mmpr. That is about where i would gear a 9x2.

[KRob]

If I was to drop a wind on the motor (ie go from an 11 turn to a 10 turn),
I would look at lowering the mmpr by about 1.5.

[Martin P]

sorry to but in but whats mmpr??? ???
People keeps using it and i dont understand what it means? ???

[MikeS]

Martin, I am fairly sure that this subject has been covered before, but here it is for you.

MMPR in plain English means: Millimeters per revolution
Where MM refers to the distance the car will move forwards for one Revolution of the motor armature.

It is also sometimes referred to as MPR or "roll out".

It is a universal way to describe the gearing of a car, as it takes into account the motor pinion, spur gear, internal transmission ratio and tyre diameter, which means it can be used across different makes of car and with different diameter tyres.

It would generally be easier for you to use a chart, or calculator that produces the same charts to work it out. The Corally 1/12th cars come with a large number of pre-printed roll-out charts at the back of the manual. There are also a number of gear ratio calculators around the web (including on my own RCLab UK web site) you just need to check that it produces MPR, MMPR or Roll-Out charts, as some do not.

The calculation for 1/12th scale cars is easier, since the internal transmission ratio will be 1:1 for all makes of cars since they are direct drive - the spur gear is actually mounted on the rear axle.

[jason]

Martin,
If you can't get it from Mikes post I'll run through it at the weekend.

Jason