Author Topic: Mod XR / GP Gearing  (Read 9532 times)

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Offline Nkaratzas89

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Mod XR / GP Gearing
« on: April 23, 2015, 11:58:23 am »
Hey guys-

Have my Mod XR mower all buttoned up but some people have been saying that its too slow for the class, it has a 5 to 3 pulley ratio to a Peerless 700 and a 12 to 48 sprocket ratio. I used an app on the Iphone for finding a top speed, and it goes about 36 MPH.

So What I want to know, is how does that speed/ratio sound? Too slow?

Any feedback would be great!

Thanks
Nico
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Offline PJG56

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Re: Mod XR / GP Gearing
« Reply #1 on: April 23, 2015, 12:28:17 pm »
What gear are you using in the transmission?
36mph sounds real fast for GP  - modxr!
Paul Guptill  (oppy) #238modX
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Offline Nkaratzas89

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Re: Mod XR / GP Gearing
« Reply #2 on: April 23, 2015, 04:35:40 pm »
What gear are you using in the transmission?
36mph sounds real fast for GP  - modxr!

We'll see how she goes with the 6" front pulley - I'll post a new topic once she's running with it on!  :D
Nico
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Offline mowdivator

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Re: Mod XR / GP Gearing
« Reply #3 on: April 23, 2015, 11:31:43 pm »
To find your true final out put ratio take and put a make on the flywheel then put one on the side of your tire while the rears off the ground put in the gear your plan on racing in mine is 3rd turn the flywheel by hand and count how many turns of the flywheel to 1 full turn of the tire my GP is around 5.5 to 1

Offline Nkaratzas89

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Re: Mod XR / GP Gearing
« Reply #4 on: May 02, 2015, 09:35:22 am »
To find your true final out put ratio take and put a make on the flywheel then put one on the side of your tire while the rears off the ground put in the gear your plan on racing in mine is 3rd turn the flywheel by hand and count how many turns of the flywheel to 1 full turn of the tire my GP is around 5.5 to 1

Okay thanks! I will do that shortly
Nico
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Offline Jeff McKelroy

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Re: Mod XR / GP Gearing
« Reply #5 on: May 06, 2015, 02:20:05 pm »
Where do you find you're at your slowest? On exit of the turns?

Offline Nkaratzas89

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Re: Mod XR / GP Gearing
« Reply #6 on: May 11, 2015, 08:57:01 pm »
Where do you find you're at your slowest? On exit of the turns?

mostly on the straight aways is when I get beat, so I just invested in a larger trans. sprocket (12T) from an 8T so that should help, and still give me some good pull out of the corners. Now with the 12T it should do 32 MPH, it used to only go around 27-28 MPH in 3rd
Nico
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Offline PJG56

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Re: Mod XR / GP Gearing
« Reply #7 on: May 11, 2015, 09:23:40 pm »
mostly on the straight aways is when I get beat, so I just invested in a larger trans. sprocket (12T) from an 8T so that should help, and still give me some good pull out of the corners. Now with the 12T it should do 32 MPH, it used to only go around 27-28 MPH in 3rd

Where did you race?
Paul Guptill  (oppy) #238modX
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Offline Jeff McKelroy

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Re: Mod XR / GP Gearing
« Reply #8 on: May 19, 2015, 12:22:58 pm »
Throw away your "Top Speed" factoring. That's what is getting you into trouble.  Rarely on any track will you ever hit your top speed. Look at your figures, then look at the times on the Nationals race results. Your best bet is to have a final drive ratio (that's all your pulleys and sprockets factored together) at or near 5.0:1 and adjust from there. GP gearing is a delicate balance of torque and chassis dynamics. You can have the correct gearing, but lose forward momentum if handling is poor.

Offline Nkaratzas89

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Re: Mod XR / GP Gearing
« Reply #9 on: May 19, 2015, 09:14:56 pm »
Where did you race?

My friend has a dirt track thats 10th of a mile and we tested it out there, Bartlett this summer, and hopefully more ARMA races in the future!
Throw away your "Top Speed" factoring. That's what is getting you into trouble.  Rarely on any track will you ever hit your top speed. Look at your figures, then look at the times on the Nationals race results. Your best bet is to have a final drive ratio (that's all your pulleys and sprockets factored together) at or near 5.0:1 and adjust from there. GP gearing is a delicate balance of torque and chassis dynamics. You can have the correct gearing, but lose forward momentum if handling is poor.

Okay, I agree.

How do you find the final drive ratio?

I have a 5 to 3 on pulleys - 12 to 32 on sprockets - and ill run in 3rd gear 20/30 on the gear set.

Thanks!
Nico
Nico
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Offline Nkaratzas89

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Re: Mod XR / GP Gearing
« Reply #10 on: May 20, 2015, 10:58:41 am »
My bad its a 25/25 gear set in 3rd gear!
Nico
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Offline PJG56

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Re: Mod XR / GP Gearing
« Reply #11 on: May 20, 2015, 12:19:59 pm »
Final ratio =4.7999999 -------in short 4.80
Paul Guptill  (oppy) #238modX
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Offline Nkaratzas89

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Re: Mod XR / GP Gearing
« Reply #12 on: May 20, 2015, 12:51:03 pm »
Final ratio =4.7999999 -------in short 4.80

Do you think that's too high? Or should that work out for a 1/10th mile track like BBR?
Nico
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Offline more4les

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Re: Mod XR / GP Gearing
« Reply #13 on: May 20, 2015, 01:00:16 pm »
That's tall. 5.00 to 1 - 5.50 to 1 is where we run on 1/10th mile tracks depending on the radius of the corners. Tighter corners require shorter gearing,

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Offline PJG56

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Re: Mod XR / GP Gearing
« Reply #14 on: May 20, 2015, 02:51:36 pm »
Do you think that's too high? Or should that work out for a 1/10th mile track like BBR?

That track carries a lot of speed thru the corners, plus you don't weigh much,i would stop trying to overthink this and try what you have!
Paul Guptill  (oppy) #238modX
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