Gearing help for beginner

[joatham]

Hi, I've just finished building my Mission ST, but I'm very confused about the gear ratios, and what size pinion and drive gear I should use.

I'm running a core 27 turn motor, and will be racing on a fairly small carpet track, and I've driven off roaders but never the touring cars.

Is there a golden rule as to what size pinion and belt pulley to use? I've put the 17 tooth pulley on the belt drive, mainly because I've lost the 20T :( but I don't know what size pinion I should get.

Can anyone advise me, or point me to a good article on the net explaining what all the different ratios of pinion and drive pulley actually do? Thanks

[MarkB]

Hi John,

Welcome to the Mission and touring car racing.

The theory of gearing doesn't differ between off road and on road too much. Want more top speed = a bigger pinion, want more duration and accelleration = a smaller pinion. Where I suspect you're struggling is a staring point.

You say a small carpet track - how small? Tell me the longest stragith length and typical 27-turn lap time (if you know it!), and we should be able to give you a good place to start.

The 17-tooth pulley is like using smaller pinions - great for indoor smaller tracks like yours. The 20-tooth pulley is like using bigger pinions - hence its all we use on larger outdoor tracks.

Cheers
MarkB

[joatham]

Hi Mark, you're quite right about the starting point, I just want somewhere to start from and then I can tweak it if it's too fast/slow for me. I thought the 17T pulley would be the best, but it's good to have that confirmed..

The clubs we have looked at are Grays and Southend, looks likely that we will be joining Grays. I'm not sure the length/width of the track, but I think it's about 30x40 feet, with the longest straight normally along the longest length (I'm not that great at judging sizes though, it's 5 rolls of carpet wide it that helps :- - see http://www.neilmoorman.co.uk/grccc/pics/24.JPG for a pic which gives some idea of the size) the lap times with stock 27T motors range from about 10.5 sec for the fastest to 27.0 sec for the slowest drivers.

John

[mark barord]

John are you using foam tyres?
If so you will need to think in terms of mm/rev.
At Grays I usually run around 25/89 but with a 20t pulley on my BRM motor (which is the same as the Orion Core).
The tyres were 58mm in diameter which equals 28.44mm/rev.
This was with 2000's and I was coming off with about 40% left in the cells and I won!

[Bonny]

typical good stock laps at gryas and southend is 9.9 seconds
straighhts vary but at southend about 9 m
and grays about 7m
but the tracks usually have fast infield section

JOHN on my tc3 i used to gear up 1 tooth or 2 from grays to southend

i have only used my mission once at grays and once at southend

[joatham]

Yep mark. I will be using foam tyres, and an Orion Core stock motor. Thanks for the heads-up on the track size Bonny, I was close with my guesstimate but perhaps over-estimated by a few feet!