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#Post#: 13014--------------------------------------------------
tyre pressures
By: EARWIG Date: April 7, 2025, 12:21 pm
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I have been testing my newly built kart on a local industrial
estate road. It is a wide tarmac road.
In a straight line and weaving about the steering feels fine -
at around 30 - 40 mph I can take my hands off the wheel.
However making a U turn at the ends of the road the front wheels
tend to want to keep going forward in a slide.
I have to slow right down to get round. That was with low
pressure in the tyres. With 30psi it was worse as it wanted to
do the same thing but judder.
I would be interested to know what tyre pressure most karts have
in the fronts.
kind regards
Bri Jones
#Post#: 13018--------------------------------------------------
Re: tyre pressures
By: NewbieNick Date: April 7, 2025, 11:44 pm
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Hi Bri, don’t know about all the others but I have mine at 16 on
grass & 30 ish on tarmac.
Are you driving both back wheels?
Cheers Nick
#Post#: 13019--------------------------------------------------
Re: tyre pressures
By: Jimr1999 Date: April 8, 2025, 12:56 am
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If your axle is keyed both wheels, it will tend to make the car
under steer into corners, which on grippy surfaces, would fit
what you are describing. Some just key one wheel and have the
other (Usually the inner if we are given a clockwise,
anticlockwise track direction) free wheeling. This gives less
drive but helps with under steer.
Some just learn to invoke over steer and slip the inner wheel
around the corners go kart style (Counterintuitive leaning)
Others use a differential and that changes the dynamic again.
My tyre pressures vary from surface to surface but not less than
15 psi and not more than 22psi. (I have a Differential on mine)
JimR
#Post#: 13020--------------------------------------------------
Re: tyre pressures
By: EARWIG Date: April 8, 2025, 1:57 am
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OK thanks for that - I am driving both wheels - I may experiment
with one.
Without major surgery I don't have the option of s diff - we
will see
regards
Bri
#Post#: 13021--------------------------------------------------
Re: tyre pressures
By: EARWIG Date: April 8, 2025, 2:29 am
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Just a thought -
does the freewheeling back hub merely spin on the axle and does
this generate a lot of heat -0 or am I overthinking it ?
Bri
#Post#: 13022--------------------------------------------------
Re: tyre pressures
By: Jimr1999 Date: April 8, 2025, 2:44 am
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Depends how you have done it Bri.
Most of us replace the bearings in the hub with oilite bushings
and run the axle through the hub. The burr on the keyway around
the oilite bushings needs a little softening to prevent wear.
Have a look at the design on Stefan's Bugatti build journal...
HTML https://cyclekartsgb.createaforum.com/build-journals/bugatti-type-37-build/
JimR
#Post#: 13023--------------------------------------------------
Re: tyre pressures
By: jay pratt Date: April 8, 2025, 4:50 am
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Hi Bri, I run a locked rear axle and on tarmac/concrete i run 15
front, 30 rear, as Jim mentioned you have to induce oversteer on
tight corners to help. In my head running fairly hard at the
back helps to break the traction. When I drive around the street
I find that a small amount of throttle when turning at low speed
helps to reduce understeer, very counter intuitive but it works.
Hope that helps.
#Post#: 13026--------------------------------------------------
Re: tyre pressures
By: jon.pearce Date: April 8, 2025, 2:03 pm
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I am in agreement Jay,
I am running 18 and 25 and with a live axle, its better to have
some power on even for slow corners.
Understeer is greatest when you bowl into a corner and lift off
completely !! Tons of fun !!!
#Post#: 13027--------------------------------------------------
Re: tyre pressures
By: EARWIG Date: April 8, 2025, 3:08 pm
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Thank you everyone for the input - I have plenty to think about
and experiment with it.
cheers for now
Bri
#Post#: 13028--------------------------------------------------
Re: tyre pressures
By: uncantim Date: April 9, 2025, 8:14 am
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Hey Bri
I run a solid axle for all the reasons above, I think the
positives outweigh the negatives.
The one thing I will add, however, is a single-wheel drive
set-up means you only have single wheel braking, and that, my
friend, can be a white-knuckle ride, especially when wet. I
tried that when I first built my kart, it had the same effect as
a really good laxative. Suffice to say, I've run a solid axle
ever since and always keep a spare pair of pants with me when
cyclekarting.
Hope that helps
T
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