Karting1.co.uk

[328isport]

Hi all,

quick question, i was suffering a little bit from axle hop yesterday at Rye, it was a very hot day and the track did feel very grippy so i'm reluctant to make too many changes as it was quite minor but want to know the first couple of things i should try. My understanding is this happens from too much grip. Is upping the rear tyre pressure slightly likely to help? i was considering this or bringing the rear hubs in slightly, but as it only really started to happen in the afternoon i didnt get a chance to make any changes. I had earlier in the day narrowed the front end slightly which made a massive difference to oversteer on corner entry, in short there was none, which increased my confindence and therefore my pace, so i wonder whether i was trying to carry too much speed also.

My kart is a TKM Extreme, TWS frame with OTK parts, new age maxxis, no torsion bars, ali rims, bumper, pods, stays all done up tight.

[Sam19]

iv been told that to avoid "hopping" you can add seat stays but it completely depends on what sort of corners its happening on

sam
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[T.J. Koyen]

Narrowing the rear track will make the kart hop more. Hopping usually occurs two ways:

Either you're too soft and the axle is flexing and rebounding in the corner,

OR

You're too stiff and you're overloading the outside tire and it's losing traction, then gripping, then losing traction again then gripping.

I usually find that my hopping occurs from being too stiff or having too much mechanical jacking. So narrowing the rear would only compound that problem.

Sometimes the hop can come from tire pressure too. If you are too low on pressure and the sidewall gets flexing and rebounding that can cause a hop. It would be a quick easy change to go up by 1 or 2 psi and see if that helps the problem.

I would start by widening the rear slightly or taking out caster or narrowing the front slightly.
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www.OKTANEVISUAL.com - custom helmet paint and graphic design

[Jinder]

What tyre pressures are you running? My only experience with the modern Maxxis tyres is at Clay, where the sweet spot (for me) on a mild day is 11-12psi. 11.5 was where I was quickest last Fri. I'm not sure if this would also apply at Rye House, always worth taking advice from other TKMers at the track.

If tyre pressure makes no difference, I'd try widening your rear track...mark your hubs' current positions, and move each out by 10mm at first. Do a run, see if it feels better and adjust accordingly. You'll eventually find a sweet spot in between hopping and a loose back end (which you'll get with too wide a track).

Hopping can cost you quite a bit of time in a TKM if it's happening on the exit of slow corners, due to the lack of low-end grunt and the bogging down effect that hopping causes. For example, Clay is a relatively high-speed track with one hairpin corner which is effectively the only slow section of the track. Most TKM runners at the track run a sprocket somewhere between 73 and 75, so getting a smooth exit from the hairpin is vital to avoid getting mired in the torqueless low-rev end of the powerband. I was having horrendous hopping problems there, and was bogging down like hell. After widening the rear track by 20mm each side, I found .5sec almost instantly. Admittedly, my adjustments were more extreme than most would require, as I'm very tall and have some centre of gravity issues accordingly.

How is your self-starting going by the way? I'm still not there yet, but getting closer, thankfully I'm free of back trouble at the min so am enjoying working on my starts whilst I can! I've found putting an extended bush on my steering column and raising the steering wheel boss up the column by one hole has made leaping in a little easier now-I tend to not kick the airbox off and land on my knees in the seat now!
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Sr. TKM #25 at Clay Pigeon.
www.jinderracing.com

[nowysz6]

If you have some shorter hubs, give them a try. They'll let the axle flex a little more and should let the inside rear stay unloaded more easily. If you can't do that, try taking the bolts out of the 3rd bearing on the axle and replace them with cable ties (unless you already have them out).
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[328isport]

Cheers for the responses guys, really useful, i'll look at widening the track when i'm next out, i was out at a newly resurfaced track yesterday which was very grippy, again it only happened to a minor degree and sometimes when i know i was pushing too hard, so i think a slight change should solve it, it's tricky as i'm running OTK bearing carriers (only 2 for TKM), OTK hubs with a Gillard M axle and Gillard rims, with a chassis from neither manufacturer so don't have any real reference as such.

As far as tyre pressures goes, just to check this is to be adjusted when the tyres are cold/cooled down? as if i'm running 11.5psi i know its probably more like 15psi on the circuit?

Jinder, starts are going good, i went out on my own on Friday so had no choice! i had had some sucessful practices beforehand though so was confident i could do it if not first time. I'm still not getting it first time everytime but practice makes perfect as they say! One thing i would say now that i'm nailing the starts alot of the time is the buzz from doing it all yourself is awesome, i have a smile on my face just pulling out of the pits which i imagine wouldnt be there if i had a clutch!