Wheel size change affecting gear ratio

[WebDog]

I moved from 1.9" to 2.2" wheels on a Kyosho Outrage. I have 32 pitch
gears. Originally the car had an old reedy stock motor. Now it has a
Lightspeed stock motor. (hopped up Epic motor) I used to use a 15
tooth pinion. I'm not sure how many teeth are on the spur gear but
there are so many other gears I wouldn't know what to do with that
number anyway. Regardless, the spur gear can't change. I'm wondering
what range I should be looking at for pinion size as far as the wheel
and motor change. Would a 10 tooth pinion be way to far of a drop?

Thanks,

WebDog

[V_Tach]

About a 12 or 13 tooth pinion will return you back to your original final
drive ratio based on some quick math. Of course different model tires have
different circumferences so it is a rough estimate. A 10 tooth pinion would
be a significant difference even with the new wheel size. With the 10 tooth
pinion you would lose a bit of top-end speed and gain more wheel spinning
power.

V_Tach



"WebDog" <webdog@austin.rr.com> wrote in message
news:3E826F47.4000506@austin.rr.com...
> I moved from 1.9" to 2.2" wheels on a Kyosho Outrage. I have 32 pitch
> gears. Originally the car had an old reedy stock motor. Now it has a
> Lightspeed stock motor. (hopped up Epic motor) I used to use a 15
> tooth pinion. I'm not sure how many teeth are on the spur gear but
> there are so many other gears I wouldn't know what to do with that
> number anyway. Regardless, the spur gear can't change. I'm wondering
> what range I should be looking at for pinion size as far as the wheel
> and motor change. Would a 10 tooth pinion be way to far of a drop?
>
> Thanks,
>
> WebDog
>

[chuck_steak@nospam.com]

In article <3E826F47.4000506@austin.rr.com>,
WebDog <webdog@austin.rr.com> wrote:

>I moved from 1.9" to 2.2" wheels on a Kyosho Outrage. I have 32 pitch
>gears. Originally the car had an old reedy stock motor. Now it has a
>Lightspeed stock motor. (hopped up Epic motor) I used to use a 15
>tooth pinion. I'm not sure how many teeth are on the spur gear but
>there are so many other gears I wouldn't know what to do with that
>number anyway. Regardless, the spur gear can't change. I'm wondering
>what range I should be looking at for pinion size as far as the wheel
>and motor change. Would a 10 tooth pinion be way to far of a drop?
>
>Thanks,

you really need to know how much bigger the tire is, not just the wheel.
If the tire is the same size, (outside diameter)
then you don't need to change anything.
if the tire increased in diameter, the same as the wheel, (.3") more than
likely dropping one tooth would be enough. if your new motor is supposed
to be a higher revving motor, AND your tires are taller,
then you could try dropping two teeth...

I only do oval racing with direct drive,
but the gear thing is just math..
the theory would be the same on any car.

I was assuming that you have a transmission with a 2:1 gear ratio, and
like a 50 tooth spur gear.( I have NO idea what off road stuff is)
But I'd bet it was close to that..

If it were me, I'd try two teeth smaller, then if that didn't heat
up your motor too bad, try one tooth.. The worse thing you can do is overheat
your new motor on the first run... always better to go conservative at first.

if you want to get technical..

what you are toying with is called 'roll out' gearing.
it refers to how far your car rolls, per motor revolution.
it's very important in on road type racing, where your tires
can wear considerably.

roll out = tire circumference/gear ratio

gear ratio = spur gear/pinion gear.
if you have a transmission:
Gear ratio = spur gear/pinion gear X transmission ratio

Very basic formulas.
Just use algebra and a calculator to solve for the unknown.





Dan
----------------------------------------------
Never kick a cow flap on a hot day........

[Divrdan007]

>Subject: Wheel size change affecting gear ratio
>From: WebDog

>I moved from 1.9" to 2.2" wheels on a Kyosho Outrage. I have 32 pitch
>gears. Originally the car had an old reedy stock motor. Now it has a
>Lightspeed stock motor. (hopped up Epic motor) I used to use a 15
>tooth pinion. I'm not sure how many teeth are on the spur gear but
>there are so many other gears I wouldn't know what to do with that
>number anyway. Regardless, the spur gear can't change. I'm wondering
>what range I should be looking at for pinion size as far as the wheel
>and motor change. Would a 10 tooth pinion be way to far of a drop?
>
>Thanks,
>
>WebDog

I would try running with the new wheels first, before making any gear changes.
The new wheels are only 3/10th's of an inch larger in diameter. You will get
more top speed from them, with the same gearing you have. That may not be a bad
thing... depending on the track & the surface you're running on.
If the car is REALLY sluggish off the line & outta the corners, I would drop
the pinion size one tooth at a time till you're satisfied with the results.
Pinion gears are pretty cheap, you should have a few extras (of different
sizes) in your box anyway.
Good luck.
Let us know the outcome.

[V_Tach]

"Divrdan007" <divrdan007@aol.com> wrote in message
news:20030327131614.23247.00000005@mb-cu.aol.com...
> >Subject: Wheel size change affecting gear ratio
> >From: WebDog
>
> >I moved from 1.9" to 2.2" wheels on a Kyosho Outrage. I have 32 pitch
> >gears. Originally the car had an old reedy stock motor. Now it has a
> >Lightspeed stock motor. (hopped up Epic motor) I used to use a 15
> >tooth pinion. I'm not sure how many teeth are on the spur gear but
> >there are so many other gears I wouldn't know what to do with that
> >number anyway. Regardless, the spur gear can't change. I'm wondering
> >what range I should be looking at for pinion size as far as the wheel
> >and motor change. Would a 10 tooth pinion be way to far of a drop?
> >
> >Thanks,
> >
> >WebDog
>
> I would try running with the new wheels first, before making any gear
changes.
> The new wheels are only 3/10th's of an inch larger in diameter. You will
get
> more top speed from them, with the same gearing you have. That may not be
a bad
> thing... depending on the track & the surface you're running on.
> If the car is REALLY sluggish off the line & outta the corners, I would
drop
> the pinion size one tooth at a time till you're satisfied with the
results.
> Pinion gears are pretty cheap, you should have a few extras (of different
> sizes) in your box anyway.
> Good luck.
> Let us know the outcome.


3/10th of an inch difference in diameter may not sound like much but it is
about a 14% difference which can result in a significant difference in the
circumference of the tire. This however doesn't mean that there might not
actually be a performance improvement without changing the pinion gear
depending on the original setup. Trial and error and small changes are a
good recommendation as noted, pinion gears are inexpensive and it can be a
pleasant learning experience experimenting. Preferences can be an
individual choice depending on what one is looking for.

V_Tach