Third Bearing in or Not?

[Christopera]

I am running an R31 in TAG with a Leopard. Tires YHC 10psi. Axle D. 2.5 spacer in on the front with standard freeline hubs. Standard medium rear hubs. 55inches wide. Long front bar installed and .5 added caster. High ride height front and rear. All lead mounted low.

The kart turns in well and is free off corner exit. However, I need the kart to rotate slightly more mid corner. This is true for both high speed and low speed corners. For example if I don't enter the corner very precisely I often find that I am unable to reach the apex due to what is a very slight second and third quarter understeer. On high speed corners it often developes into a third and fourth quarter understeer.

I have run the kart with less rear weight and this only made the understeer worse. The kart would lift very quickly and lean on the outside front tire at which point the kart would begine to understeer drastically. After adjusting weight rearward the kart became considerably more ballanced but i still fight this slight tighntness of the kart.

I have also tried lower ride height on the rear and the kart lacks "side bite" and fails to take a strong set. My opinion of the kart was that it was slower and times agreed.

Should I move weight further rearward or remove the third bearing to see if this doesn't free the rear up slightly? Current weight distribution is 57.2 rear and 42.8 front.

Keep in mind that I am looking for maybe two or three tenths, not anything huge.

[Chris Lobaugh]

Which R31 do you have? It would be worth a test. Run with the middle bearing in for 10 laps pull in the pits, remove the bolts and then run it again. The D 2.5 might be a bit soft still, so, if the problem gets worse with the middle bearing out try narrowing the rear of the kart a 1/4" per side at a time. If that helps, but, you still need more try going to an M. You might need to add another .5 degree of caster as well.

[Christopera]

I believe it is an '07 R31 (perhaps SE, i don't know how to tell) with 50mm axle. We started with the F axle which I think comes standard. We tried the D with no real change so just stuck with it. You are thinking stiffer might work better?

Steering is direct on turn-in and the kart is pretty close during high speed direction changes. I have considered more castor but haven't felt like like it really needed it. Occasionally the kart will hop a touch, which is another reason I avoided extra castor.

I am starting to think that slightly more rear weight and then perhaps some more castor might do the trick. I guess i really just need to hit the track and try these few things.

[Chris Lobaugh]

On the outside of the left bearing hanger there should be two letters after the frame size which will tell you what year the kart was made. If you have two front torsion bars it is either an 07 or 08. In '07 Birel added an extra 2 degrees of caster for a total of 17 degrees static caster. Does the hop start in the front or is it only the rear. If the front hops you probably need to add caster. If the rear hops it is because the axle is too soft.

[Christopera]

Alright, well I will test these few things next time out. Which might be Daytona. Who knows.

Thanks for the help.

[RPMotor]

You might try more air pressure. I probably would run 12- 14 with YHC