How low of a gear for Reedy MVP?

[ImprezaWRC]

I've got an HPI RS4 Rally. I'm running a 27T pinion with a 90T spur. I'd like to know how low of a pinion or spur I can go without disaster while running a Reedy MVP. My final drive ratio is 2.1, and I run the car both onroad and especially, off. My highest gearing info would be helpful too.

Also, I usually only change pinions, but I would like to know the ropes of changing spurs too. I'm finding it difficult to understand; if I go lower on a spur, do I compensate on the pinion? Why does HPI only include spur options as low as 85T? Does that mean that my car can't gear down to 70-something teeth? I don't get it....any help would be appreciated though.

Kind Regards,

Impreza

[k-thib]

I don't know if this will help you, but my friend ran his off-road buggy with a green machine3. He switched to a MVP and had to gear down a few teeth. The motor will never stay cool. Even if you have it geared real low, it will get very hot.

[Nairb]

Yeah, that's the truth. Mike Reedy himself said they were'nt concerned with efficiency when they designed the MVP. They have pretty low efficiency, and hence, they get hot.

[Grizzbob]

Very true, I have 3 of them , & even the one I use in my 1/12 scale car(on 4 cells, usually lets motors stay at room temperature) gets pretty warm after a run. As for gearing, it really depends on how its set up. If it's been tuned for lots of top end, then stick with a small pinion(can't give an exact one, don't know nearly enough about your particular situation), but they can also be set up for torque. One of mine(in my TC3) is now running very similarly to a P2K(I did a lot of tuning on it), but with a bit more top end, so I gear it about the same as a P2K, & it's starting to fly..... :)

[Grizzbob]

By the way, Imprezza, I don';t see how any touring car chassis can have a final drive ratio of 2.1:1. Most of them have an outdrive ratio of at least 2:1, which means when you figure out the ratio between the spur & pinion, you multiply that number by your car's outdrive ratio to get your final drive. So, for example, my TC3 has an outdrive ratio of 2.5:1, which means if I use a 100 tooth spur & a 30 tooth pinion, my final drive would be 8.3:1(100 div. 30, x 2.5 = 8.3333:1)..... :)

[ImprezaWRC]

Thanks for the help, guys.

Grizz, the only thing that it says in my manual is that my final drive ratio is 2.1, so I don't know. They could have misprinted. They also said that the pinion packed with the kit was a 31T, but looking at the pinion, it is a 30T. Who knows....

[noobie]

You can try narrowing the brush on the MVP. take .140" off each side. should increase torque and reduce overheating problem. You can check out rcvehicles.about.com for more info,especially in the "ask big jim about motors" thread.

I am going to try it tonite for the first time, but there are many people who have responded with very positive results trying this trick.

[Grizzbob]

Ok, I'd say that 2.1 is the outdrive ratio of your car, so with a 27 tooth pinion & a 90 tooth spur, your final drive ratio is 6.9999:1, & that is pretty tall for any stock motor save for the P2K(& it's still a bit tall even for that), I can easily see motors like the green machine 3 getting fried on it....

[Grizzbob]

Oh, & for an MVP, well, I'm not sure. It's still a very new motor, I don't know how it'll react to overgearing, except for a lot of heat(MVP's seem to get hot no matter how you gear them), but for now I wouldn't gear one any higher(if as high) as a P2K.... :)

[KerryG]

You can adjust by either changing the spur or the pinion. For every tooth you change on the pinion it is the equivilant of changing three teeth on the spur. So you can change the pinion for a drastic change and the spur for fine tuning.

[ 07-05-2001: Message edited by: Administrator ]

[Nairb]

I don't agree that you can make a blanket statement about the relationship between pinion and spur gears - "For every tooth you change on the pinion it is the equivilant of changing three teeth on the spur." That will be different with different size spurs. Just use your trusty calculator to figure out ratios and you won't have to think about it any further.

[ 04-20-2001: Message edited by: Nairb ]

[ImprezaWRC]

But, does that mean that I can go with any spur I want? Could I use a 27T pinion, and down into the seventies for my spur? HPI only gives options for the mid-eighties through the mid-ninties.

[KLKLRL]

i use a mvp on a losi xx cr 84t spur 26 t pinion the motor does get very very hot but i have never had any truble out of it i have geared it to a 23t pinion all it did was slow it down did not help on the heat at all one thig i can say it that to clean it regular with all the air holes it gets dirty real easy but for a stock motor i have been very happy with it maby i should try a heat sink on it so that my .02 cents hope it helps
been running it for 1 month

[Grizzbob]

In general, ImprezaWRC, yes, you can use any spur that you want, as long as it fits the mounts & you can get the gears to mesh. You may get to a point, though where you be more limited in which pinion you can use that'll reach the spur, or it may go the other way, a huge spur may limit how large a pinion you can fit in there. Beyond that, go ahead & try whichever ones you like..... :)

[ImprezaWRC]

Thanks again, folks.

Kind regards,

Impreza