Narrowing Rear Track

Pete Schaible · Posted: Mon Apr 30, 2012 3:21 pm Post subject: Narrowing Rear Track

I have been running around 53.5-54 inches in the rear with 90mm rear hubs. I got a set of 115's looking for more rear grip but I can only get to a minimum width now of 54.25 will the extra hub width compensate for a wider rear track? Also if i needed to go narrower with the 115's is it ok to cut a little off each end of the axle? I know many guys are running long hubs and a narrow rear. How does everyone else do it?

Jason Vehige · Posted: Mon Apr 30, 2012 4:20 pm Post subject:

Don't cut the Axle...!!! Try different widths to find the big hub's happy spot... And it may be wider than you would think. Narrower does not always = more grip.
_________________
Jason Vehige

08 Gillard Charlotte / SGM sl204
05 Vanspeed Sirio / SGM sl204

Larry MacLeod · Posted: Mon Apr 30, 2012 4:44 pm Post subject:

It sounds like your hubs are cast with a "cap" of sorts on the end. I had a set of these once. I replaced my rear hubs with ones that I could remove the cap, and slide inward on the axle so the axle actually sticks through my wheels.

I agree with Jason, don't cut the axle. But if you know someone with a vertical mill or something, maybe you can get that "cap" chopped off your hubs so they willl slide easily onto the axle.

As for width, on my ~14 year old chassis I regularly run 53-54" wide. But if you aren't getting enough grip when running narrow, then try other methods like adding seat struts. I have 2 on each side of my kart. Also, add a rear bumper bar if you don't already have one, or make sure its tight.

If none of that works, check your front setup. Too much front caster could make the rear feel squirly.

Larry
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F125 #196
Old Birel/ hodgepodge Honda CR125
Lefty Funk
Detroit Region

Pete Schaible · Posted: Mon Apr 30, 2012 5:06 pm Post subject:

I am running a 50mm rear axle, I don't think you can find open end hubs because of the wheel studs.
I have another set of wheels that is slightly narrower with the same offset. With them I would be able to get back to 53.75 but I am not sure if that would have the same effect as moving the hubs in or if I am just cheating my measurement. I am still trying to learn this whole tuning thing.

Larry MacLeod · Posted: Mon Apr 30, 2012 6:14 pm Post subject:

Pete Schaible · Posted: Tue May 01, 2012 12:38 pm Post subject:

I am running 2 seat struts per side. Max height front and rear. 60% rear weight. Mostly the issue is corner exit. When I went narrower I had more grip out of the corner but no stability in the slalom. So I am trying to get more rear grip while not going too narrow. Not really having a chance to test before the autocross I want to make sure I am not shooting myself in the foot by going .5 wider in the rear to use the longer hubs.

Larry MacLeod · Posted: Tue May 01, 2012 4:52 pm Post subject:

Pete Schaible · Posted: Tue May 01, 2012 6:11 pm Post subject:

I think playing with seat height will be my next experiment. The Philly region has some really good karters so I am up against some very tough competition. I am not as good behind the wheel as they are so I need every bit of speed through tuning I can get Very Happy

Tom Reynolds · Posted: Wed May 02, 2012 12:39 pm Post subject:

Also try reducing front caster and or testing wider front track width. Also do you have a rear stiffener bar and is it adjustable? What about rear axle ride height?

Pete Schaible · Posted: Wed May 02, 2012 1:33 pm Post subject:

Rear bar is in and vertical, rear ride height is at max. I think the question I really have is how big an effect does hub length have vs. track width. Perhaps the only way to know is to run it this Sunday and find out.

Tom Reynolds · Posted: Wed May 02, 2012 1:36 pm Post subject:

What's your total weight in kart? Which rear axle? Which chassis?

Christian Hubbell · Posted: Wed May 02, 2012 5:56 pm Post subject:

Brian Garfield · Posted: Tue May 08, 2012 9:11 pm Post subject:

Do you have the hardest axle you can get? If not, start there. IMO, it's MUCH better to get the hardest axle and have to remove grip in other ways. If you have never seen rear hop from too much grip, find that first, and it's likely you'll get closer to that with a Hard axle.

Brian

Pete Schaible · Posted: Wed May 09, 2012 5:54 pm Post subject:

Brian that is kind of what I am looking for. My thought was get to the point of too much grip and then loosen it up a bit so I know I am not leaving anything on the table. Right now I am running a 04 Swiss Hutless Vinto with K9B.

Kart and I weigh in around 335 (too much cheeseburger) I am at max ride height front and rear, rear bar in full stiff. rear bumper with cross bar. 4th rail in but no bolts in it, 60 % rear weight, and 115mm rear hubs with a rear width of 54 1/8 is the narrowest I can get. Swiss hutless Hard axle and 2 seat struts on each side . Seat is a little above flush with the bottom of the chassis. I have yet to get any hop. Aside from raising the seat some I don't really know what else I can do to gain more grip. I wasn't a big fan of going too narrow, When I was at 53.5 rear width it was scary in the slaloms. The rear would slide bad through the slalom.

Brian Garfield · Posted: Wed May 09, 2012 6:00 pm Post subject:

Some chassis don't behave typical of the norm. In those cases, you just have to try some extreme changes...one at a time.

One thing you haven't talked about is your actual position to upright with the seat. Many karts that come from Road Racers or Sprint Racers are laid back much more than needed for Solo.
You want extreme weight transfer if you're not getting grip. Try sitting your seat as upright as possible, that would be a good start.

BTW, you aren't trying to tune with old tires...are you?! You need to do this with NEW tires, if not brand new, at least 20 runs or less.

Brian