I ran my first race this weekend and was warmly welcomed by a [not nice word] who thought he was more deserving of the apex I was already at. Anyways. Now I get to ask fun questions like “How much axle runout is ‘acceptable’”? I’m currently at about 20thou (+/- 0.010"), and I do not know what I was at before getting punted. There was a noticeable vibration afterwards, but I still went to set a PR during the final (where I also finished ahead of said punter who got sent back a few places because of the wreckage he caused). I am still trying to narrow down where the source of the vibration is, and I do know my chain tension was tolerably uneven prior to the race. So I don’t think my axle was truly PERFECT beforehand, I just never measured its runout until today. Is there a general guidance that applies here? It seems pretty even left and right, so I am inclined to accept it, but I don’t won’t to get it all put together and still have an issue next time I go out.
I typically shoot for <0.005" of travel on the indicator per side.
Where are we measuring the runout?
I am measuring the OD of the axle inside and outside of the hub keys. I redid my measurements and I think I am close to 5 thou on the right but definitely 25 thou on the left. I could visually see the tire having some runout at the track and eyeballed it at 1mm which gets me to 40 thou, so it is all adding up to a bent axle.
I moved the hub from the bad side to the good side and measured runout on the surface of the hub to be 8 thou. I can pretty much rule the hubs out, so next I just need to check the wheels to see if I need to add one of those to my Mondo shopping cart as well.
Eyeballing via the tire isn’t going to be of much use, as the tires and wheels will both deform slightly over time. The hub I would worry about even less, unless you notice damage to the hub face where it meets the wheel.
I measure the runout at the farthest point I can manage from the center of the chassis. Usually there is some meat outside of the keyway, but if you’re running a cut axle you may have to measure inside of the keyways.
Usually small bends can be corrected with a large dead-blow hammer. I slide an old hub over the axle first so as to prevent the end of the axle from getting deformed.
Yeah, I only mentioned eyeballing because it was my first clue as to where to look for the vibration.
And also yes, I was measuring at the farthest point from center. My axle isn’t cut, so I had a good surface outside of the keyway. I have a trusty deadblow and tried that trackside, but my sprocket carrier is also bent, at least somewhat contributing to my uneven chain tension. The carrier/axle is deformed just enough I cannot get it off the axle, so it isn’t a bad time to just go with a new carrier and a new axle together.
If after the incident you didnt change tyres - I would first check are the tyres in balance. One might be deformed or cord is broken etc. On my karts tyres will give vibrations if not balanced.
Btw the tyres will rotate in use, by few minutes - they need rebalancing now and then. I use white marker pen and paint a line to the rim and side of the tyre
Second that has caused me vibrations is the rear floating disc. If the mounting hardware is worn out the disc can move radially. Its a quite big piece of cast iron that has lot of inertia
Nearly all of the runout has been traced to the axle. The tire might not be perfect, but the axle is much worse.