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Andrew Hsieh
Joined: 25 Sep 2005
Posts: 18
Location: United States, California, Tustin
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 Posted: Wed Apr 05, 2006 7:55 pm Post subject: Gearing for autox |
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Hey all,
I am having a diliemma for gearing in autocross. Previously for autox, I was using a 16/26 (1.625) ratio and was only able to use 4 gears for that particular track. The motor seemed like it pulled pretty well even though the gearing seemed too "tall" for the course.
For the next event, I decided to use a 15/26 (1.73) gear and I think I was able to use all 6 gears, but the motor seemed like it didnt pull as well because I was running through the gears so damn fast. Also the kart was more of a handful to drive since the gearing was so short.
1) So which type of gearing would be faster?
2) Do you usually gear so that you can use all six gears for the course?
(It seems like I paxed higher overall with the shorter gearing, but then again there are too many variables to make that an accurate comparison.) |
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Larry MacLeod
Joined: 28 Sep 2005
Posts: 299
Location: United States, Michigan, Ypsilanti
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| Posted: Thu Apr 06, 2006 3:16 am Post subject: Re: Gearing for autox |
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| Andrew Hsieh wrote: | 1) So which type of gearing would be faster?
2) Do you usually gear so that you can use all six gears for the course? |
Assuming your engine is built like the other shifter kart engines I've driven, then you are potentially much faster using the shorter gearing. However it does take just a little more precision in gear selection to do it properly.
And yes, I always change gear to match the course. I've used as short as a 15/28 for local events and even some Pro Solos. And my engine is built accordingly (all top end).
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F125 #196
Old Birel/ hodgepodge Honda CR125
Lefty Funk
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Andrew. james
Joined: 30 Jul 2005
Posts: 245
Location: United States, Georgia, Atlanta
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| Posted: Thu Apr 06, 2006 5:23 am Post subject: |
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| I usually go to a slightly taller gear than is needed if it's raining. It helps me stay in control. |
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Vic Madrid
Joined: 26 Oct 2003
Posts: 192
Location: United States, Maryland, Catonsville
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| Posted: Thu Apr 06, 2006 8:31 am Post subject: |
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any advice on the best way to change the drive gear (the small one)? Do you remove the seat, so that you can hold the gear w/ the chain and the rear axle, or do you remove the motor and just use an impact wrench? (how do you torque if properly?)
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- Vic
- SCCA/WDCR F125 #54
- 2006 Tony//Kart Krypton 125 |
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Andrew. james
Joined: 30 Jul 2005
Posts: 245
Location: United States, Georgia, Atlanta
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| Posted: Thu Apr 06, 2006 9:36 am Post subject: |
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| Vic Madrid wrote: | | any advice on the best way to change the drive gear (the small one)? Do you remove the seat, so that you can hold the gear w/ the chain and the rear axle, or do you remove the motor and just use an impact wrench? (how do you torque if properly?) |
I do neither, I take the chain off put the motor in gear and remove the bolt with an wrench. I tighten it the same way. |
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Larry Andrews
Joined: 13 May 2002
Posts: 2848
Location: United States, California, SC Mtns
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| Posted: Thu Apr 06, 2006 9:36 am Post subject: |
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| Vic Madrid wrote: | | any advice on the best way to change the drive gear (the small one)? Do you remove the seat, so that you can hold the gear w/ the chain and the rear axle, or do you remove the motor and just use an impact wrench? (how do you torque if properly?) |
I use a 10" long 12mm double box wrench and just fish it in there with the intact kart on the ground. Loosen the bolt, then remove the chain and everything just comes right apart. Installation is reverse of removal. |
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John Denman
Joined: 19 Jul 2001
Posts: 4846
Location: United States, Texas, McKinney
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| Posted: Thu Apr 06, 2006 10:41 am Post subject: |
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My motor has a ton of power and a real wide powerband. Normally I run a 16/26 and just leave it there.
Higher ratio gearing may help on the launch if you don't have the grunt to pull off but part of that also has to do with the alacrity between the clutch & throttle.
Lower ratio gearing keeps you in lower gears which have a higher span between gears; You can see the spans in the Gearmaster XL File . Click on the CR 125 Tab to see the ratios vrs speeds. Enter the sprockets and RPM characteristics of your motor and you'll get the speeds for the shiftpoints.
With an OEM Ignition curve there isn't as wide of a powerband so you'll probably do better with a higher ratio.
The other point is where you're shifting. If you find yourself shifting in a turn, that may not work the best. It really hurts on turns leading into long straights. Thats where Data Acqusition is really helpful to balance the ratio to allow the best overall shift points.
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John Denman
Producer for RTMP
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Vernon Head
Joined: 21 Jul 2001
Posts: 455
Location: United States, California,
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| Posted: Thu Apr 06, 2006 5:24 pm Post subject: |
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| I have to agree with Larry. Shorter gearing is usually faster for me. My powerband is pretty narrow, also. About the worst thing that short gearing can do is make you run out of revs on the longest straight. Compared to missing the powerband, even by a little bit, that isn't so bad. I've listened to the guys who say tall is better because you shift less. That's true once you build up some speed, but autocross courses usually have really short straights and lots of tight turns. |
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Alan Sheidler
Joined: 09 Aug 2001
Posts: 471
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| Posted: Wed Apr 12, 2006 11:04 pm Post subject: |
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| Andrew. james wrote: | | Vic Madrid wrote: | | any advice on the best way to change the drive gear (the small one)? Do you remove the seat, so that you can hold the gear w/ the chain and the rear axle, or do you remove the motor and just use an impact wrench? (how do you torque if properly?) |
I do neither, I take the chain off put the motor in gear and remove the bolt with an wrench. I tighten it the same way. |
If you have a helper, have the engine in 1st gear and use the brake to hold the rear axle while on a stand. Otherwise you can just wrap your right arm around the RR tire and reach under the chassis with your left. I use a ratchet with a 6-point deep socket, as that is what fits for my frame spacing. Others may use box-end wrenches, etc. Some guys swap out the honda hex-headed bolt for one with a socket head and use an allen wrench or hex key. You may have to move the shift lever to the "upshift" position to get on the bolt.
Remember, failure to tighten will lead to separation of the sprocket from the countershaft, and a lot of damage can be done by the flailing chain!
Loosen your engine mount and slide the engine back before taking off the sprocket. With a good J-lever, there is sufficient space to pass the sprocket out and replace it with a different one, and never have to remove the chain. Impact? Only if gorilla arm and loctite were used to install. Torque wrench? Nah. Just tighten it using a standard length wrench or ratchet. Don't use a breaker bar! Also, that big dished washer is essential. Concave side towards the sprocket, please.
Alan |
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Brian Garfield
Joined: 04 Apr 2004
Posts: 667
Location: United States, Maryland, SKCA Racing!
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| Posted: Thu Apr 13, 2006 6:27 pm Post subject: |
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I used an cordless impact, but I have an older one that doesn't put out that much power. In fact, I always have to break things loose with something else usually. But it worked great for this, so I didn't have to hold the wheel or anything.
Is there a standard amount of links on a chain per teeth added? The way I've temporarily set mine, I'm not sure I've got enough links to go to a bigger axle gear.
I simply want to change from the 15/25 to a 26, with room to go to a 27. How many links should I add to the chain?
The other problem is that I don't want to have to move the motor too far forward, which is why I'm looking for more precision in choosing the number of links.
Oh yeah, I can't slide the motor back further to allow for more slack, the heim hits the chassis...
Brian |
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Larry MacLeod
Joined: 28 Sep 2005
Posts: 299
Location: United States, Michigan, Ypsilanti
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| Posted: Thu Apr 13, 2006 6:44 pm Post subject: |
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| Brian Garfield wrote: | Is there a standard amount of links on a chain per teeth added? The way I've temporarily set mine, I'm not sure I've got enough links to go to a bigger axle gear.
I simply want to change from the 15/25 to a 26, with room to go to a 27. How many links should I add to the chain?
The other problem is that I don't want to have to move the motor too far forward, which is why I'm looking for more precision in choosing the number of links. |
You're always going to have to do some engine movement to get it properly tightened.
To make it easier with smaller engine movements (like what you're aiming for) I carry two different length chains. When I use my 15/27 or 15/28 I use the chain that's 1 link longer. For 15/25 and 15/26 I use the shorter one. I guess that makes a 2 tooth change in the back roughly equal to one chain link.
But the two chain method is simple enough that I can change to any gears between runs at a solo.
Any gear that's taller than a 15/25, I go to the 16 tooth front gear. Again, I have two chain lengths to choose from when setting up those combinations (16/26 or 16/25).
LM
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F125 #196
Old Birel/ hodgepodge Honda CR125
Lefty Funk
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Brian Garfield
Joined: 04 Apr 2004
Posts: 667
Location: United States, Maryland, SKCA Racing!
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| Posted: Thu Apr 13, 2006 6:49 pm Post subject: |
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| Larry MacLeod wrote: |
You're always going to have to do some engine movement to get it properly tightened. So I carry two different length chains. When I use my 15/27 or 15/28 I use the chain that's 1 link short. For 15/25 and 15/26 I use the longer one. I guess that makes a 2 tooth change in the back roughly equal to one chain link.
LM |
Did you mistype? If you have more teeth, you should need the LONGER chain, right? A 15/27 or 28 should require MORE teeth than the 15/25 or 26.
I plan on carrying several chain sizes, that's what I have now, but none are as long as I need.
I have room to move the motor, but just enough for chain tention right now, not enough to change gears, I think.
Brian |
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Andrew. james
Joined: 30 Jul 2005
Posts: 245
Location: United States, Georgia, Atlanta
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| Posted: Fri Apr 14, 2006 5:35 am Post subject: |
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| I carry an extra master link I can add real quick if I need a longer chain. |
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Larry MacLeod
Joined: 28 Sep 2005
Posts: 299
Location: United States, Michigan, Ypsilanti
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| Posted: Fri Apr 14, 2006 6:14 am Post subject: |
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| Brian Garfield wrote: | | Did you mistype? If you have more teeth, you should need the LONGER chain, right? A 15/27 or 28 should require MORE teeth than the 15/25 or 26. |
You must've responded so quickly that my quick edit didn't make it to you. See above.
LM
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F125 #196
Old Birel/ hodgepodge Honda CR125
Lefty Funk
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Rick Brown
Joined: 14 May 2003
Posts: 38
Location: United States, California, Lake Elsinore
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| Posted: Tue Apr 25, 2006 3:59 pm Post subject: |
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Rick Brown
SCCA F125
03 Tony Mitox - Honda Stock Moto
Last edited by Rick Brown on Wed Aug 23, 2006 12:25 pm, edited 1 time in total |
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