Gravity sidecar, anyone?

Bookmark and Share

I'm planning to build a new downhill vehicle to run for fun and, if we can get enough interest and get race organisers to make room for it, competitively as well.

Basically, the idea is to put a sidecar onto a BMX frame to make a gravity sidecar.

Anyone care to take me on?

Posted In

Gravity Sidecars

With all the debate going on already about cartie racing rules and differences of opinions regarding what constitutes a level playing field in cartie design; the idea of starting gravity sidecar racing is bound to open up another can of worms. As for the challenge I can say with confidence that A.B.C. gravity racing is up for anything provided the rules and venue are clearly set out before construction starts.

G'wan, G'wan, G'wan. Smile

peasnbarley | September 16, 2009 - 21:13
scottishcarties's picture

OK - so lets write some

OK - so lets write some rules then. I don't have anywhere to run it yet, except possibly as a demo at a few events next year. However, having mentioned it to a few people while at Belchford last weekend, I'm sure there will be enough interest to get it moving.

So - rules. Starter for 10;


  • Sidecar outfit will have a front wheel, a back wheel and a sidecar wheel.
  • The front wheel must steer.
  • The rear wheel must be directly behind the front wheel.
  • The sidecar wheel may be on the left or the right of the front and rear wheels.
  • The spindle of the sidecar wheel must not be further forward than the spindle of the front wheel nor further backwards than the spindle of the rear wheel.
  • At least two of the wheels must have its own independent brake system.
  • Sidecar outfits are to have the top half of the rear wheel covered on both sides and the inboard side of the sidecar wheel covered over.
  • The unladen weight of the sidecar outfit must not exceed 75Kg.


  • Driver must sit astride the line between the front and rear wheels.

Other rules? Dimension limits? Wheel sizes? Fairings allowed?
scottishcarties | September 16, 2009 - 22:09

Sidecar rules

Gravity Sidecars. I think if the outfits were to use measurements close to the current Belchford rules say 2000mm max wheelbase 1500mm max width 75kg weight limit. The passenger must play an active part in maintaining vehicle stability during the decent.
Anonymous | September 17, 2009 - 17:15
scottishcarties's picture

European rules

It seems that the Commission Europeenne de Course de Caisses a Savon (European Soapbox Racing) already have some sidecar rules;

(Gravity sidecar is class C5)

Max length - 2500mm

Max width - 1200mm

Min wheelbase - 700mm

Max dry weight - 100Kg

Max wheel diameter - 500mm


scottishcarties | September 16, 2009 - 23:50
scottishcarties's picture

This is what I had in mind

This is the sort of thing I had in mind. I think gravity sidecar should be based on an existing bike rather than a chassis built from scratch.


A gravity sidecar in action


Sorry for the multiple posts.

scottishcarties | September 17, 2009 - 08:35

That all sounds and looks

That all sounds and looks great going by the photographs. Can I ask why you think any Gravity Sidecar should be based on an existing bike rather than a chassis built from scratch?
peasnbarley | September 17, 2009 - 12:16

Yip Yip Yip, the cheats are

Yip Yip Yip, the cheats are keen for this. I can see slammer MK4 getting put into production asap. Who has big enough balls to lets some else steer their faite down the cairn o'mount???
Anonymous | September 17, 2009 - 12:57

I think you have more chance

I think you have more chance of getting a passenger than me.

Dont see why basing a machine on an existing bikes have to be used, either. I think most builders are more than capable of building a complete machine, especially those that took part at Cairngorm. Its not the frames that break its usually wheels.


azuma | September 17, 2009 - 21:37
scottishcarties's picture

gravity sidecar rules

I'm planning to get my son trained up as ballast. (His mum doesn't know this yet...)

As for the "built on an existing bike" idea, I was thinking that the vehicle ought to take the form of a recognisable bike and sidecar combo, with the bike part at least looking as though it would function as a proper bike should the sidecar be detached (although I'm not proposing that the car should actually be detachable). I thought it would make it less intimidating to newcomers if they could easily see the basis of the vehicle being something that they already have languishing at the back of their shed, rather than the "three wheeled sled" affair similar to the current F1 sidecars (which are not even vaguely motorcycle based).

I'll admit it's just a prejudice though and I'm sure that existing teams would have no trouble building on from scratch using (e.g.) minimoto parts.

Anyway - I'll draft up a set of rules over the weekend and publish them here for comment. In the mean time, check out this video (taken a few years back at Scammonden Dam, on the M62 between Rochdale and Huddersfield).

scottishcarties | September 18, 2009 - 09:11
scottishcarties's picture

Gravity Sidecar Rule - First Draft

OK - I've attached a first draft for the Gravity Sidecar rules [clicky for download].

Please reply here to comment. 

scottishcarties | September 18, 2009 - 10:16

Rules sound good to me.

Rules sound good to me. Think you may need to add the wording Passenger needs to play an active role in the decent. Possably run 2 classes one for BMX based and one for prototype F1 style outfits???????. Im starting my build plans already.
Anonymous | September 18, 2009 - 16:11

I think rule 7 regarding the

I think rule 7 regarding the passenger needs a bit of tweeking?
peasnbarley | September 18, 2009 - 21:28
scottishcarties's picture

Sidecare passenger rules

Oops - cut and paste error there. Yes that does need tidying up.


Driver must sit or kneel astride the line between the front and rear wheels.

The passenger must be positioned to the side of the driver and should be able to lean out of either side of the sidecar.To this end, the vehicle must be equipped with a suitable facility for the passenger to hold on when leaning out.

The driver's torso and the passenger's body must be visible from above at all times. The use of transparent materials to evade this rule is not permitted.



scottishcarties | September 19, 2009 - 09:27

sidecar building

Well, I hope you are nearly finished with the rules because we hope to have our outfit done by the end of the weekend. I think we ought to try and persuade Geoff and the Applehead lot to run a sidecar class at Cadwell. Dick (Belchford)
Anonymous | September 19, 2009 - 10:06
scottishcarties's picture

I think the basics are

I think the basics are pretty much right already (dimensions, etc), so you should be pretty much OK to start building now. I expect any changes now will be clarifications and plugging loopholes.

I'm not sure about the 100Kg weight though - that's lifted from the European rules, but I think there might be a case for keeping the weight down below that to - say - 75Kg.


scottishcarties | September 19, 2009 - 14:56

Why 50kg

You say "I think there might be a case for keeping the weight down below the European rules to - say 75kg" and we seem to end up at 50kg without actualy making a case for that weight? I only ask because just taking a shot at an arbitory weight might/will restrict creativity and inovation. If there is a good reason to hit on 50kg then fine.
Anonymous | September 20, 2009 - 11:37
scottishcarties's picture

Sorry - my mistake for not

Sorry - my mistake for not being clear. 50KgF is the force that the brakes must be able to hold against.

I think we ought to try to keep the weight down though, and 100Kg does seem quite a lot for a gravity sidecar outfit (no need for rollbars, etc, remember). 75Kg should be pretty easy to achieve, I'd have thought.

[edit] I've uploaded a new draft of the rules which, unless there are any major objections, will be the first version.

scottishcarties | September 21, 2009 - 08:03

Gravity sidecar rules - First draft

Stephen, Dick & I are keen to have a go - we've already found a BMX bike and Dick's looking for his angle grinder as I write. I have had a quick look at the rules and like what I see. I just wonder whether the brakes at 50kg lateral load would be adequate, bearing in mind the additional weight of a passenger - the all-up weight of the device would be approximately 150% of the weight of an average soapbox and driver combo. Not convinced that driver and passenger should have to wear leathers, as the speeds we will achieve are similar to what I do on a racing pushbike with next to no protection in the event of a spill. I have permanent scars on elbows and knees but can live with them. I do however accept that a decent helmet should be worn I am not sure whether the rules should prevent someone building from scratch or not - as they are drafted I think this is an option and I suspect most people would dabble with a bike conversion anyway to see what works before embarking on anything more complex and expensive. We hope to have something together to play about at Cadwell.
Anonymous | September 19, 2009 - 11:01
scottishcarties's picture

I reckon 50Kg ought to be

I reckon 50Kg [edit: clarification - 50KgF brake test] ought to be enough. Remember, with more weight on board you'll be able to brake harder without locking up. But I guess we'll do some testing of our own soon and might revise that figure.

As for protective clothing - there might be a case for leaving that up to individual race organisers, as strictly speaking it's not related to the actual design of the vehicle. I can see that the requirements for gear on (say) a gentle grass slope with top speeds around 20mph might be somewhat different to somewhere like Cairngorm where you'll be doing close to 60mph and only inches from the tarmac. I think it'd be difficult to make a case in a risk assessment for considering lycra shorts to be adequate Personal Protective Equipment (PPE).

The PPE rules in the draft are copied from the rules we used for Cairngorm Soapbox Extreme, which were in turn based heavily on the IGSA Rules for Luge and G-Bike PPE.

scottishcarties | September 19, 2009 - 15:15

Would love to get on and

Would love to get on and build an outfit, but with the other things going onat the moment it may not happen in a hurry. What I do have though is a pile of bikes including at least 3 BMX bikes minus wheels,(for obvious reasons) mountain bikes (better handlebars for getting down low rather an the tall BMX bars) kids bikes etc. If anyone is interested in some stuff let me know, I'm sure I could sort out a pile of bits for a smallish amount of cash, swap, donation etc etc.
azuma (not verified) | September 19, 2009 - 22:04

Just to confirm that Azuma

Just to confirm that Azuma put up the post regarding the bikes - forgot to sign in at the time DOH!. If anyone is interested drop me a line and I will see what I have got.
azuma | September 20, 2009 - 00:07

Cadwell sidecar

Team Black & White will be TRYING to get a a sidecar ready intime for cadwell if they are pemited in 2010.
Anonymous | September 20, 2009 - 19:58
scottishcarties's picture

Sidecar rules - second draft

I've just uploaded the second (and, with luck, final) draft of the gravity sidecar rules [clicky for download]. The main changes are;

  • Dropped max dry weight to 75Kg.
  • Clarified driver and passenger position rules. 
  • Clarified rules on fairings, steering and hand holds for the passenger.
scottishcarties | September 21, 2009 - 09:43

B&W Racing

Hi there, Paul from B&W Racing here. Yes Mick is right when he says we will be trying to get a sidecar ready as soon as possible. As usual we have lots of (mainly off the wall) ideas but I'd just thought I'd add my 2p to the regulations discussion. My first reaction was to build a device based on the theories of F1 and F2 motorcycle sidecars, check out our friends Barry and Ellie Yes I know it looks nothing like a motorcycle but thats the way motorcycle sidecars have developed over the years and they perform very well (does help when you have 220+bhp of course) And it appears that other people have gone this route too with their gravity sidecars. The pictures here of people with their noses 3 inches from the ground look awesome. If the regulations that are settled upon pretty much dictate that every gravity sidecar will look like a bmx bike with a tea tray attached to one side will it not look a bit boring? Remember, for those who were at Belchford, we were the daft ones who tried to build a 4 wheel steer cart that weighed more than the Ark Royal - so we like to think 'outside the box' - pun not intended, well actually I think it may have been ;-) Whatever happens, we'll build something that fits the regs but I personally would like to get the COG down as low as possible. But then we've already realized we used the wrong wheels on our cart so I want to make sure we get the right ones for the sidecar and that could well dictate a more 'established' design.
Anonymous | September 24, 2009 - 09:47
scottishcarties's picture

current rules allow either approach

The current draft rules allow either approach - either "BMX + scaffolding" or "0HP F1" design. I think we may eventually need different classes, but for the time being we should be OK with what we've got to get things kicked off.

Those pictures are great. I think they are carts built to the CECCAS rules. They have several classes, and I think the first picture that come up on your link is a C7 "Carrioli" class two man cart. If you scroll through the pics you'll soon see a few sidecars though, and you're right - that's just the kind of thing we want to see!

We'll have to see if we can tempt some of these guys to come over here. Or maybe take them on on their own turf!

BTW - I've been in touch with the organisers of Border Bogies and I'm optimistic that we'll be able to do something sidecar-ish in 2010, although it might be a demo run. You've got to come to Border Bogies, not least because it's held in Denhom which, as I'm sure you already know, was Hizzy's home town. We'll aim to include sidecar in Cairngorm 2010 too.

scottishcarties | September 24, 2009 - 10:18


Is anyone planning on having a sidecar at Cadwell in Aurgust?. If you are and need an idiot for balast I mean a Passenger im available as I think Paul will be out of the country working and the Black & White cart has yet to be repaird. Then again I might knock together a BMX based one and get a friend roped in.
Anonymous | September 27, 2009 - 08:29
scottishcarties's picture

Best check with the

Best check with the organisers first to see if they'll allow it.

My plan is to build a sidecar over winter and have one ready to run next year. I won't be able to get one ready in time for Cadwell as they are insisting on rollbars this year, so I now have to do some major work on the two carties I'm planning to bring down.Yell Wouldn't mind a shot on your sidecar if you get it built though.

scottishcarties | September 27, 2009 - 15:26

I thought you used to have a

I thought you used to have a roll bar for the ferret. Did you not have one for a previous Cadwell meet?
azuma | September 27, 2009 - 19:48
scottishcarties's picture

I did have one, but I took

I did have one, but I took it off earlier this year. I bust a gut putting one on for Cadwell last year, as I was also going to need one for Belchford. However, there were at least two carties running at Cadwell 08 without any form of roll bar, and one of them actually won the event.

We were discussing standardising the rules and lowering the technical requirements to make it easier for new teams to get involved on the UKGSA forum earlier this year, and one of the suggestions that came up was to re-introduce a rule from the original Goodwood set that would allow carties without rollbars to take part. Belchford adopted this idea, and it was also included in the rules for Cairngorm Soapbox and Border Bogies. I decided then that I wanted to get the Ferret back to the original concept, which was for a low, light and minimalist cartie, so out came the angle grinder and off came the roll bar. It's a real shame that Cadwell hasn't been able to make the same move, but I understand they have to comply with the requirements of the circuit owners. I do think it's a bit OTT though, as Cadwell is about as safe a course as you could possibly want and the speeds involved are not particularly high. Cairngorm, Belchford and Denholm are all longer, and much faster courses.

scottishcarties | September 28, 2009 - 11:05
scottishcarties's picture

Gravity Sidecar Rules - Final

I assume we're all fairly comfortable with the second draft of the rules, so I've re-published them as the first version. In summary;

  Maximum overall length - 2500mm

  Maximum overall width - 1200mm

  Minimum track width - 700mm

  Maximum wheel diameter – 550mm

  Maximum weight of vehicle and ballast - 75kg

  Rigid chassis only - no variable camber wheels

  Fairings allowed, but cannot fully enclose driver or passenger

Clicky here for downloading of the full document.

scottishcarties | October 11, 2009 - 11:46
scottishcarties's picture

BMX is to Gravity bike what BMX Sidehack is to Gravity Sidecar?

I had a go on Belchford Ahead's gravity sidecar at Cadwell the other day, and really enjoyed it. This is definately a goer for a new racing class!

Their outfit was basically a chopped and stretched BMX with a platform welded on the side. I must admit that when I was originally thinking about it I had a more conventional BMX based design in mind with the donor bike remaining almost unmodified except for removed chain, rear sets and flat or dropped bars. I thought I'd have to build it myself, but have just discovered the "BMX Sidehack" have been around for ages, and are currently undergoing something of a renaissance. Just google for "BMX Sidehack " and you'll find dozens of articles and pictures. I think this one is really tasty.

scottishcarties | November 23, 2009 - 16:51

outfit started

Hello, just to say I have sent my plans of to the blacksmith to weld his magic , will se how it goes i have based my idea on a minimoto sidecar as i used to race them . I have used the head stock from a minimoto and wheels maybe to small ? but it will have discs on all wheels , will get some photos of build , not a single bit of BMX used , OLD GOTH RACING .
Anonymous | February 16, 2010 - 12:40
scottishcarties's picture

gravity sidecar options

Mini-moto parts is definately and option. e.g. This one. A lot of the european sidecars use mini moto parts too.I reckon it could work really well.

Gravity Sidecar

scottishcarties | February 17, 2010 - 10:37


Anonymous (not verified) | April 2, 2010 - 14:47
scottishcarties's picture

Great news! Can't wait to see it

That's really good news. Looking forward to seeing how it turns out. Mine is still in it's component form, but should start taking shape soon.


scottishcarties | April 2, 2010 - 15:45

Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.