Tire and Gear

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Wilkersonbj

Member
Trying to understand gearing in relations to rpms. Race a track 2 weeks ago my son won and was fast. Turned green plate motor 6500 and hint tires spit on. Raced this week and left gear the same and could not get motor to turn over 5000. Did not change gear throughout night cause was unsure which way to go, was running a 15/64. Come feature time he kept up with other karts just mottor wasn't turning hard enough.

Also, had tires prepped soft a ready to go track turned a little slick and rubbered up in spot what can u do prep wise to help with that track change, only had the one set of tires with me.
 
Wilkersonbj said:
Trying to understand gearing in relations to rpms. Race a track 2 weeks ago my son won and was fast. Turned green plate motor 6500 and hint tires spit on. Raced this week and left gear the same and could not get motor to turn over 5000. Did not change gear throughout night cause was unsure which way to go, was running a 15/64. Come feature time he kept up with other karts just mottor wasn't turning hard enough.

Also, had tires prepped soft a ready to go track turned a little slick and rubbered up in spot what can u do prep wise to help with that track change, only had the one set of tires with me.
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This was the same track ? You prepped tires differently going into the race ?
 
I'm afraid you've got more problems than a gear ratio change can help. One tooth, plus/minus, on the axle is worth about 100 RPM on the top plus/minus.

Just guessing, you may have a leaking head gasket, a valve that is sticking open, a plug that is going bad etc. etc.

When ever we were having troubles with the KT100, the first thing we reached for was a compression gauge. Check it often!! That drop in RPM, if true, sounds like, to me, something serious is going wrong.
 
Camshaft could have gone flat, could have galled the rod to the crank journal, valve springs gone bad, valve lash way off, and the one thing I hear of from time to time, over oiling the air filter and /or air filter plugged with dirt/oil.....
 
Valve guides worn out, piston rings worn out, bad fuel, exhaust pipe gasket burned up...so many possibilities....
 
There is little you can do prep wise . Wipe with methanol is about it and its not much . Borrowing a different set of tires would be best .
 
Tracks change from week to week... Just because one gear set and setup worked one week doesn't mean it will work the next time... But a drop of 1500 rpms sounds like there are more issues than gears and setup...
 
What was the temp of the motor after the race. Was it well over 450, if so that will explain a lot. Kart could have been locked down dragging the motor down with it and you will never turn the RPM's you want. Then again it could be a problem mentioned above.
 
Is this a clone? Turning 6500 RPM's on a green plate is up there. I'd check the plug for fouling. Did you flush the fuel and clean the carb? Are you using a tach that shows you the RPM's for each lap? Did your driver keep up all the way around the track or catch them in the corners and fall back on the straightaway?
 
Motor was fine. I do believe it was more of a kart being locked down all the kids were having a problem getting rpms up. He was staying with them all the way around.

Really trying to understand kart gearing and is there anyway once you have a set of yellow Vegas that are set for a wet hammer down track is there anything I can to do when track turns slick to that sett of tires.
 
General gear changes to increase RPM'S is to run a smaller front sprocket or larger rear sprocket. I believe most people try to stay with a 5 tooth range on rear gear (58-62 or 60-64) and adjust the front sprocket accordingly.
Peak RPM is good to know but you don't always have to chase it. RPM drop compared to lap times compared to peak RPM can provide some insight as well.
 
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