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Author Topic: Gemini karts front axle + funbikes pit bike wheels axle size options  (Read 1958 times)

synthpunk

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So im planning to get a geminikarts front axle for my riley build, with a set of yokes and stub axles welded on. Along with some 17 inch Funbikes pit bike wheels. Hurrah!

But....

What size stub axles do i need? 15mm, or change the bearings and go to 17mm? And most importantly, what length stub axle of the two options? Would i need 62mm or 70mm?

Do i need anything else apart from the adaptor plates that Gemini also do?

Tanks in advance,

Rich.

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StefanN

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Hi Rich,
I'd say go for 17mm stub axles.  That's what I've been using and they seem to hold up well.  The bearings are pretty inexpensive too.    Marek's front axle also has 17mm stub axles and has 6 deg of caster, 10 deg of king pin inclination and the stub axle at 10 deg to the yoke for zero deg camber.  I can't remember what length stub axle we ordered but hopefully one of us will be able to measure that for you tomorrow.

StefanN

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Stub axles photos below from Marekís Delage (pit bike wheels)
« Last Edit: 05 December 2020, 09:11:42 am by StefanN »

synthpunk

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Aces, cheers!! Iíll get me credit card out then.... ;c)

Graham Hill

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For clarity, the 70mm stub is to suit pit bike wheels. 62mm is to suit honda wheels.

RhysN

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Or get the longer ones anyway, then you can have a play with spacers, and the facility to swap wheels at some time.

synthpunk

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Aha! Cool!
Does the track width increase with the pitbike wheels? Im sort of assuming yes, but not by much. Maybe 8mm?

Ive seen some Honda innova wheels that look pretty good. I might try a pair on the back end.

StefanN

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I don't think the track width increases with the pit bike wheels necessarily, and I suspect most set-ups are slightly different anyway.

synthpunk

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Cheers for all the responses and info chaps!
I ordered one this afternoon, thats one further step forward on the riley.
Anyone got any advice or sources for axle clamps for bolting it to the springs?
Cheers!
Rich

RhysN

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My suggestion for clamps is to use U bolts and a square plate on the opposite side. There is a decision to be made whether it's spring under, or over the axle. You do need to have some system to stop the axle rotating once you have established the castor you want. Don't forget a centre bolt too.
I use a hole saw in an off cut of chassis tube and then cut them in two, ironically I deleted the photo from my computer just yesterday. Here's a "back of an envelope" sketch which might help.

synthpunk

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Brilliant, thanks for that!
Iím going to betray my ignorance here, but can someone please explain the centre bolt to me? Iíve done some googling, which has lead me to learn that they are very important in multi leaf springs but google has been less informative about single leaf springs.
Does the bolt get bolted through the axle? Or is it merely there to use as a locating pin and the head fits through a hole in the mounting plate? Or does it get bolted to the mounting plate? Duhhhh....

Iíve got some glass drill bits for drilling through the carbon springs. Health and safety: donít do this indoors or without a mask/dust extraction, as itís really hecking bad for lungs.

Tanks in advance for any answers, cheers!
Rich

StefanN

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Itís a locating pin (or bolt) to help keep the axle in position longitudinally on the spring.   Some use them, some donít.

RhysN

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As Stefan has said the centre bolt  to locate the axle on the spring longtitudinally. Otherwise you are relying totally on clamping pressure.
 Secondary function is that it fits snugly in the hole in the spring, and helps to eliminate spring breakage across the hole. And for the doubters, yes there have been known breakages of springs (not in the UK but elsewhere).

synthpunk

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This is what im worried about- these carbon composite springs are basically a stab in the dark. Id like to minimise being quite on the very sharpest edge of bleeding edge technology if i can help it. I know that on the adult sizes of these springs, they do have a hole drilled in the middle. Theyre about the same width as this, just longer and thicker. The heavy set of CF springs i have are 68 vs 36kg strength, and are the same length and width but are a few mm thicker. They are bolted to the stilts via 5mm high tensile hex (cap head) bolts. Im planning on enlarging the holes to at least 6mm for attaching to the eyelets im fabricating.

Oh yeah- thats another thing- what size bolts do you chaps use to secure your springs? M8? M10?

So to summarise your excellent info and my current thoughts:
Drilling holes in CF is difficult, id better be be bang on centre.
A centre bolt is probably a good thing
I should probably find something to practise drilling on first. Maybe one of the 68 springs.
I should have a really really good long sit and think about all of this...

RhysN

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What format are you using for the springs? I mean semi elliptic, quarter   ?
I would suggest that the centre bolt merely locates, not clamping it. Then use either U bolts, square or round, to clamp them to the axle and spread the load. Perhaps if you gave us a sketch of your thoughts some suggestions might be given for you to consider.