Running a TAG in F125

Jeff Grossman · Joined: 11 Feb 2005 Posts: 4

So, of course I am not looking to win, but if I was were to run a TAG kart in the F125 class, what would be a good gear ratio setup? As a reference the engine is a Mortori 7, turning it up to 15K RPM's, with power between 9K and 15K, and right now I am running a 11 main, and 85 sprocket.

richard watson · Posted: Sun Jan 07, 2007 5:26 pm Post subject:

Jeff,

I think most people run 15/27 on their shifters. This gives a top end around 72-73 mph for a CR 125.

Richard

Vernon Head · Posted: Sun Jan 07, 2007 10:59 pm Post subject:

I used to run 10/87 on my Parilla 125 at Sears Point, getting a peak of 16.4k rpm. This was beyond the powerband, but gave me better low end. Some other drivers were twisting theirs above 17k. I don't know if your motor can do this, but for autocross you can get away with higher revs because of the short time you're out there.

Michael Long · Posted: Mon Jan 08, 2007 7:27 pm Post subject: Gearing

I run a TaG with a PRD Fireball 125, Margay chassis in F125 & in karting events in Houston, Austin, Katy, & soon to be doing Waco, TX. also.

With PRD (15,100 max rpm) running a 10T primary is not easy..due to crank diameter..I run an 11T primary & a 92T secondary. I also have the newly released Horstman clutch just for PRD's and it allows me a 6,000 rpm stall speed on the clutch.

The 92T works great with an 11T... an 88 - 92 works great on a 10T. Best advise is to run the gear that gives you just over peak torque / HP at you fastest point / speed area. Then if need to change for a better lower end due to coming out of corners you can add secondary teeth. That WILL affect you overall top speed thou.. Also you style of driving with also play a role in your final decision. Given those basic gear configurations... say an 88, 90 & 92T secondary & a 10 & 11t primary..just paly around a little & final with a combo that YOU feel most comfy with...

Bill Hall · Joined: 30 Dec 2006 Posts: 25

Back in the day when I ran a KT100 I would just keep adding teeth to the secondary gear a taking lap times until I started to slow down then I worked on the chassis and then back to gearing. I also kept a gear ation chart in my toolbox to use for recording my final ratio.

Here's one /www.sckarting.com/gear_ratio_chart.htm

also as a rule of thumb one tooth on the primary is like three teeth on the secondary.

good luck

Bill
_________________
Hey it's fast to me....

Jeff Grossman · Joined: 11 Feb 2005 Posts: 4

Thanks for all the input!

My 10/85 allows a top speed of 61MPH and so we'll see what happens in the corners, with the power band of the Motori.

Larry Andrews · Posted: Tue Jan 09, 2007 11:54 pm Post subject:

Hey Jeff...been a while...hope that you and your son are doing well.

Anyway, you should be fine with the TaG setup but you just might need to gear for a bit more speed. I usually got to around 70-75 on the faster CSCC courses in my kart, rarely much below 65 top speeds. Dono how the lack of shifting will affect the ultimate observed top speed, but I bet it'll take a bit longer to get up there as compared to a shifter.

Not sure if you know that Eric Nelson has a shop - www.seventh-gear.com

best, la

Ihor Bilyy · Posted: Sun Apr 29, 2007 12:22 pm Post subject:

Aren't you scrubbing asphalt with 92t?
I'm trying to avoid anything above 87t.

Daniel Morency · Posted: Thu May 17, 2007 3:11 am Post subject:

I've run as high as 99 teeth. I make up high density poly sprocket guides. Cut it out at 10.25 dia with a jig saw, don't worry if it isn't perfectly round, it will be quickly. Right now we run 10 to 95 with our KT-100's the plastic lasts a looooong time with a 95 tooth rear.

Dan

Jeff Grossman · Joined: 11 Feb 2005 Posts: 4

Probably also helps to have a height adjustment on the rear axle. My Gold kart only has one setting.

My experience with the kart out here in So Cal was interesting. Gearing wasn't so much of an issue, as was tire selection. Most everyone is running MG Greens for autocross, of course. I was just on a set of practice YHC's, and fortunately the So Cal courses are typically 60 sec courses. So for the first 2/3's of the run, there was no traction what so ever. The last 1/3 was always fun, but since we intermix the F125, and cars, the tires would get cold again, by the next run. So tire selection, and keeping heat in the tires was a larger issue than gearing for me.

I'm going to try it again in the summer months, and see if the 90+ air tempratures helps keep some heat in the tires.

Daniel Morency · Posted: Thu May 17, 2007 1:19 pm Post subject:

height adjustment? it isn't the chassis that is the problem, the chain and sprocket try to dig into the pavement! what matters is how the tire diameter, usually about 10.5 inches vs the 11 on the sidewall, compares to the sprocket diameter with the chain wrapped around it. A 99 tooth #219 sprocket is about 10 inches (# teeth x .098 + the chain that extends past the teeth) That's why we use the 10.25 inch plastic protector. my 95 tooth is 9.31 inches + the chain

Dan