Home Forums Tech Talk Spindles: Can someone help me understand the variables

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    • #46898
      Samir Shah
      Participant

      My son had an off in practice, hit a barrier, and has bent his spindle (and tie rod). I replaced the tie rod, and hammered the spindle arm back down, but the arm has also bent horizontally, needing more tie rod length.

      So it will need to be replaced. I was told its a 12 degree spindle, and it has 2 ackerman holes, and has a17mm arm.

      It turns out that the good one on the other side only has 1 ackerman hole, so they are not identical, and I should probably replace them both. And I have no idea which one of the 2 is an original for the kart, although they both seem to be Birel spindles.

      The kart is a old suspected Brazilian Birel R31, and I certainly don’t need the expense of Birel parts unless there are benefits to doing so.

      Can someone walk me through the variables involved in choosing a spindle, and what impact they might have on handling?

      I have no problem going aftermarket or used to save money – the kart only needs to function, not look good (it doesn’t anyway).

      If anyone has some good used spindles, contact me too please.

      Thanks, Samir.

       

    • #46939
      Walt Gifford
      Participant

      The only thing you really have to worry about is getting a set of spindles that will put your camber straight up in about the middle of your adjustment range. 12 degree king pin is pretty much standard these days so, a cheap after market set should work.

      Gif

      FAA certified jet engine and aircraft technician,
      Nicholson Speedway class champion 2001,
      Yamaha KT100 Service Center,
      41 years karting experience

    • #46999
      Samir Shah
      Participant

      Thanks. Will look around for aftermarket spindles. I managed to repair my kart at OVRP – they had a spare for the one I damaged, but that was just luck – at another track I might have been SOL, and I should get a pair of spares.

      Any benefits to 25mm over 17mm spindles? Which application is better for a Junior karter in an full size chassis (Birel R31)? Thanks.

    • #47027
      Gary Lawson
      Participant

      Ackerman settings could change drastically if you put a spindle on that has a different tie rod location. Sounds like you already didn’t have the right stuff on it to begin with though. The correct solution is to find out what the kart is and find out what spindle it’s supposed to come with.

    • #47050
      Samir Shah
      Participant

      The kart is a Birel R31, but it appears to be a Brazilian made import, and is slightly different than the US ones, that came in with a direct drive Parilla Sudam 125. For example, it uses KG nerf bars, and Freeline front nerf bars wont fit it. The spindle C is smaller than the one on a US R31 that I looked at. So anything is possible with this. The kart is full of Birel parts though – gas tank, steering, braking system, etc but there is no chassis plate, no information about year, and tie rods are the only spot with information – they say Freeline Sudam!

      There is no information out there that I can find about what angle the kingpin is set at for ANY Birel R31s, or whether they changed over the years, or if they were all the same, and therefore no information about what the spindles should be. And in any case, the Brazilians could have done anything.

      Birels in general came with both 10d and 12d, and the Birel dealer that I took it too (at OVRP) just wanted to look at the old one and replicate that (ie 12 degrees). It seems to work, and my son is fast, but I want to be sure that it is optimized.  The owner at OVRP is fantastic, super nice and very helpful and kind, and gives me great prices, but openly admits he is not technical. He might have the part I need for the Birel, but I need to know what I want. He will hunt for parts that might work, but at the end of the day I have to know what I want. And they don’t know anything about Leopards – they are a Rotax track.

      I therefore need to go back to first principles, and measure things myself.  Thus, in this thread, I am looking to learn what this number means – 12 degree spindle – and figure out whether it is appropriate for my kart. I am NOT mathematically or mechanically challenged, and have all sorts of race car engineering books from when I campaigned an Alfa GTV6 in time trials, but none of them cover kart engineering, and I’ve not found the right books yet for karting. Would recommend any suggestions there too.

      I appreciate the wealth of experience on this forum, and have been learning a lot from the archives. I wish there was a search function.

      I have been climbing a very steep learning curve over the past few months of kart ownership, and we are testing and racing every weekend till the end of May, at new tracks that my son has to learn, and are scrambling to get this kart reliable and setup so we can do reasonably well at 2 upcoming regionals – NJ Sprint Series at Millville, and F1 Gearup at Englightown – so I need to do all the work on the kart during the week, get parts in, and repaired before the next weekend.

      I apologize for the bombardment of questions about a plethora of topics, but as I mentioned, its been a steep learning curve, and the kart is getting better and faster and more reliable everytime. I don’t have the budget for a tuner, and in any case there are no kart shops, (let alone 2 cycle experts) or even engine builders nearby.

      So I have to do it all myself, gleaning information from the internet, and from the kindness of forum members that share their knowledge.
      Thanks again for all your help.

      Samir

       

       

       

    • #47059
      Steen Carstensen
      Participant

      The 10 or 12 degree is the angle between the kingpin/bolt and the spindle i.e. a 10 degree will give you 2 degrees more negative camber.

      The 25mm spindle is of cause stiffer than the 17mm, but is also supported by a 10mm kingpin, as compare to 8mm for the 17mm.

      Hope this helps.

    • #47086
      Samir Shah
      Participant

      Aha. So, since I have 12 degree spindles in there, if I measure my camber, and its close to zero (or less than 2), I will know if I have the ‘correct’ spindles for the way the kingpin C brackets are mounted in the chassis, is that correct?

      Thanks Steen. I think that’s what I was looking for.

      Samir.

    • #47104
      Walt Gifford
      Participant

      Yes, that’s right as I mentioned in my post above. I wouldn’t be too concerned about the ackerman effect of the steering arms as long as it’s the same on both sides. Most of the ackerman effect is caused by the pitman arm on the steering column anyway. Ackerman sets a different radius for each wheel but it’s main function is to help make a height difference on the front wheels which can mostly be dialed in with caster. I’ve never heard of anyone tuning with ackerman and I would bet all modern aftermarket spindles would be pretty darn close to what you had before.

      Gif

      FAA certified jet engine and aircraft technician,
      Nicholson Speedway class champion 2001,
      Yamaha KT100 Service Center,
      41 years karting experience

    • #47127
      Steen Carstensen
      Participant

      Samir, I had to correct my post with regards to the 10 and 12 degrees spindles, less angle,  i.e. 10 vs 12 will give more negative camber.

    • #47139
      Gary Lawson
      Participant

      Ackermans main purpose is to increase to out when turning. Casters main purpose is to change wheel height when you turn.

    • #47154
      Walt Gifford
      Participant

      I reject your reality and substitute my own.

      Gif

      FAA certified jet engine and aircraft technician,
      Nicholson Speedway class champion 2001,
      Yamaha KT100 Service Center,
      41 years karting experience

    • #47206
      Samir Shah
      Participant

      Can you verify my understanding: To get more jacking at the inside rear, I would need more castor – ie kingpins angled towards the driver.

      Would one ever run different caster on each side? Since the tracks are counterclockwise, you need jacking on left side, rarely on right.

      Would making the rear axle stiffer help in jacking the inside rear wheel?

      Thanks, Samir.

    • #47211
      TJ Koyen
      Moderator

      Samir,

      Yes, more caster = more jacking in the rear.

      We never run off-set caster side to side.

      Stiffer axle will absorb less of the weight transfer and jack the inside rear quicker, but it will also set down the rear wheel quicker too. Too stiff of an axle and you risk the kart setting down too early and being flat on exit. Too soft of an axle and you risk the kart not reacting quick enough.

      Driver/Coach/Wrench : Innovative Performance/Exprit
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