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Author Topic: Riley Dobbs Special build.  (Read 534 times)

sjc56

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Riley Dobbs Special build.
« on: 17 November 2020, 05:50:11 pm »
After setting out full size on some MDF board, I’ve started cutting some plywood  to form the tub and seat. These will be used as templates, but as this car is off set I’m going to make it wider and going to add a few inches to the wheel base.
I have been watching a lot of YouTube ck racing and notice most seem to suffer from under steer. Although I have never driven a ck, but do have over 20yr experience racing two stroke karts  like 100cc in the mid 90s then Rotax max/177/125 icc to F100, so I reckon ck’s seem very similar to karts and suffer the same problems.
As there seems to be no specific regs, I intend to build a fairly stiff chassis and work from there building in some adjustments. I believe one rear wheel is free running this is probably to create a diff effect, karts have both rear wheels fixed but deal with the solid axle in a different way.
Does a free running wheel not create issues under braking especially trail braking on corners, please let me know if I’m wrong (always willing to learn).

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RhysN

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Re: Riley Dobbs Special build.
« Reply #1 on: 17 November 2020, 08:52:20 pm »
You are correct about the braking, and depending on how freely the wheel runs the opposite pull under power, for the very few that still use one heel drive.

synthpunk

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Re: Riley Dobbs Special build.
« Reply #2 on: 17 November 2020, 09:54:30 pm »
Hiya!
Do most people run with drive to both wheels with a solid axle then? Or use a diff of some sort like the perrless? I meant to ask what the score is about finding back axles with keyways- are they a go kart part, or somethin to farm out to someone with Serious Tools?
Cheers!
Rich

StefanN

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Re: Riley Dobbs Special build.
« Reply #3 on: 17 November 2020, 10:18:34 pm »
Hiya!
Do most people run with drive to both wheels with a solid axle then? Or use a diff of some sort like the perrless? I meant to ask what the score is about finding back axles with keyways- are they a go kart part, or somethin to farm out to someone with Serious Tools?
Cheers!
Rich
Yes go-kart axles.   Gemini Karts supply them.

Solid or not solid rear axle.   At the last Stretton meet, 3 ck's outperformed all the others by a country mile - Bill's Maserati and Chris's ERA (both 1 wheel freewheeling) and Jim's Dodge (a diff).   The rest of us were examining the edges of the track as we battled huge understeer in the wet.

Adrian has been experimenting with a "limited slip freewheel" that shows promise:  http://www.cyclekartsgb.com/tech-forum/limited-slip-freewheel/.  You'll find a similar but different design on the French cyclekart forum http://www.cyclekart-fr.com/forum/index.php?page=post&ids=5480.

sjc56

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Re: Riley Dobbs Special build.
« Reply #4 on: 18 November 2020, 11:00:01 am »
Hi Rich,
 yes all karts racing in MSA, now Msuk, run with both wheels keyed and bolted tight  to a one piece axle (no diff). As you know when turning any corner the inside wheel will follow a different curve than the outside wheel, because they are fixed together by the axle, the kart will try to go straight, this causes the kart to push on (or under steer) There are a few things you can do to combat this, two main things are chassis design and adjusting the front end camber/caster, in my opinion caster is more important.

There is also a relationship between front end track width and back end width, for instance if the back has too much grip compared to the front that will also cause under steer. In kart racing we call this ‘balance’.
This is a vast subject which should include every thing from how the engine delivers power  to driving style and where you place the kart on the track, especially if you only have 6.5 hp. Out of interest two stroke karts like Rotax produce about 29hp. F100 100cc about 34hp both weighing in at around 160kg

There are plenty kart axles out there that I reckon would work for a CycleKart, they range from 25/30/40/50 mm. 40 and 50 are hollow and come in a range soft to hard, a 50mm will bend easier than a 40mm, 30 mm comes in both hollow and solid, 25 mm are solid, all have key ways cut in them. Look at kart shops like Dartford karting/KKC karting.
Word of warning if you see one on e’bay it is probably bent, but you do see axles with other bits on it like brake disc and carrier and sprocket carrier, which may be worth buying.

Chris Brown

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Re: Riley Dobbs Special build.
« Reply #5 on: 18 November 2020, 12:18:55 pm »
The majority of cyclekarts use 25mm axles. One thing that is different from karts is grip, we run narrow treaded tyres, so the back end will break away more easily. I went down from a 120 modern tread tyre to a 3.00 more of a block tread on the Morgan as I had too much grip initially.

synthpunk

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Re: Riley Dobbs Special build.
« Reply #6 on: 18 November 2020, 04:36:56 pm »
Ace! Some excellent information here gentlemen, cheers!

I must admit that I’ve looked at Gemini Karts website lots of times, but only the stuff listed under the Cyclekart menu, never the rest of the shop... certainly some very useful stuff in the main shop!