RE Sidecar Design

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Hi Folks,

Well it time to pick your brains once again. Its looking like first on the build schedule is going to be a sidecar (needs to be done for boxing day). Even trying to persuade my wife to be the passenger although she would prbably do a better job of racing...Anyway back to the point.

Looking at the sidehacks etc on the net i was wondering where the sidecar wheel should be for stability and speed. Parallel to the rear or mid point between that and halfway down the bike. Also is there any real difference in speed between 16" and 20" wheels as i can get my hands on a pair of 16" bmx's (complete bikes). I quite like the idea of small donor bikes to keep the centre of gravity low especially if i stretch them a little.



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scottishcarties's picture

sidecar stuff

We're all pretty new to the gravity sidecar lark, as this is the first year they've been raced in any numbers.

Conventional wisdom from powered sidecars is that the sidecar wheel is at the mid point between the front and the rear. That doesn't seem to work so well for unpowered sidecars though and can produce some balance problems as you don't have the benefit of a dirty great engine to help keep it the right way up.If you put it too far forward, it makes it quite easy for your passenger to lift the front wheel off the ground by leaning back. Which rarely ends well.

Also, if it is anywhere other than level with the rear wheel, it will scrub to a greater or lesser degree on corners.

I've got mine about 10cm forward or the rear wheel. The bike wheels are 20" and the sidecar wheel is 18", for no reason other than they were the wheels I had to hand. After running it as basically a stock BMX with an outrigger for the first two races I chopped and streched it for Belchford and it felt much more stable. Putting some ballast underneath the sidecar helped with that too. Pics here and here.

The main advantage to using 20" wheels as opposed to 18" or 16" is that you get a much better choice in tyres for 20". Also, availabilty of strong wheels is better.

scottishcarties | September 27, 2010 - 22:27


Thanks for the advice.

Might hold out for the 20" frame that also on offer. I think we will see if i get it right when we do a few test runs, good and hilly round here. I was hoping to run a tube from the crank of one frame to the crank of the other one cut down (for side car) assuming the bikes have the same frame height. Plan being to form the main strength for the side car. Notice the use of "normal" brakes on yours were they up to the job? Thinking of also breaking the sidecar, wheel might allow for quicker turning around the sidecar side.....maybe.. just thinking of the chicane courses......

Its all getting a bit addictive!

Cheers again.

Shutz | September 28, 2010 - 22:13
scottishcarties's picture

The stock brakes that came

The stock brakes that came with the BMX weren't really good enough, although we did use them for the first two races. The bike was prtetty cheap and the quality of the brakes wasnt great. I changed them out for Belchford and they were much improved. I put decent MTB V brakes on and, more importantly, used aluminium brake levers that didn't bend like the stock plastic ones. I also took out the gyro. The V brakes seem pretty much OK. I might put a disk brake on the front, but that's only to make room for some clip ons.

I've only seen one sidehack with a brake on the sidecar wheel, and I don't think they've been brave enough to actually use it at speed. Maybe as skill levels and knowledge increase we'll see crews using differential brakes to help with cornering, but at the moment I'm happy if we cross the finish line the right way up.

Not sure what your plans for the car are - a chunky bit of tube brace linking the bottom brackets should be strong, but I'd still put the passenger's kneeler board well below that to keep the CoG as low as you can get it.

scottishcarties | September 29, 2010 - 20:51

Differential braking allowed

Differential braking allowed on sidecars, but frowned upon for carties - now that will start the tongues wagging!!

You're right though its nothing you want to try unless you are supremely confident with the braking characteristics and your monkey.



azuma | September 30, 2010 - 19:02


Just got hold of the two 16" bikes, both in good nick and the kids now want them!!! Never mind eh..

 To try and clarify......

Plan is to remove the rear triangle from one frame which will then allow the remainder  to swing down creating a greater rake angle and lowering the ground clearance. The other frame will have the headstock and the crossbar and other tube removed. the rear frame can then swing down to match the clearance of the other frame. these can be now joined up giving a stretched and raked frame as low as you want. the crank tubes will be used to support the car.

Will have a look at MTB brakes got hold of one of these lying about. Cheers for the tip.

Seen some after market 16" wheels and what looks like decent smooth tyers as well. Just in case these go belly up. 

We will see if the braking on the car offers any improvement in the corners...might be a laugh after seeing the comments.

Might even make a start at weekend if the weather holds.....

Shutz | September 30, 2010 - 20:02

Sidecar construction

As one of the pioneers of sidecars in the UK, I have to say that despite racing in a few places this year we are still learning the ropes.

I think the advice you have received about the basic geometry for your outfit  is sound - we started with the chair wheel about 1/3 of the way toward the front of our stretched BMX based outfit, but moved it rearwards to reduce the tyre scrub in corners.  This doesn't seem to have had any detrimental efffect on stability.  We also reduced the head tube ange to create greater trail than the standard BMX frame to make the thing more stable in a straight line.  As a team we weigh about 160kg and the machine is about 40kg.  We have  good quality, but cheap V brakes on either end of teh bike , operated by metal levers and these seem to provide ample stopping power - after all you can only use as much force as your tyres have grip.  We also have a simple caliper brake on the chair (which we haven't dared to use at speed) which is operated by the monkey.

We have lots of development planned for the winter, but the basic geometry of the machine is likely to remain pretty much unaltered.  We do not ballast at the moment, as we are still a bit wary of over-stressing our wheels and more weight compromises braking on courses where you have to slow down for sharp corners.  The weight of the monkey alone seems to be plenty to keep all the wheels on the ground.

Having raced at Dalby against soapboxes, we think that with a bit of development we will be at least as fast as the carties on most hills and as a bonus we both get to enjoy all the runs.

Good luck with your build - I'm looking forward to racing you next year.

Organ Grinder

Organ Grinder | October 7, 2010 - 14:01

Cheers for that I've now got

Cheers for that I've now got pretty much most of the bits, been begging old bikes of every one i know to try and keep the cost down for a first attempt. I reackon a weekend should pretty much get a rolling chasis sorted. But with the selection of bikes i have don't know whether to use the 16" inch wheeled BMX (which i reackon would look pretty smart) would need stretching (was going to join 2 together but the daughters claimed one!) the 20" inch wheeled mountain bike (turn the frame upside down) or a ladies mountain bike and fit the 20" forks so i can run the 20" wheels. would make a reasonable length and with it being a ladies one its easy to create a low ride position..... will need to have a ponder over a brew...Undecided
Shutz | October 14, 2010 - 20:43
mollydog's picture

my sidecar build

hope to be at cadwell,pull to bits, any advice welcome

mollydog | May 2, 2011 - 22:22
scottishcarties's picture

sidecar design

It's hard to tell from the picture, which is quite wee, but I think you might find the riding position quite upright. I'd suggest trying to drop the bars as far as you can.

Also - put  a load of ballast under the outrigger as close as possible to the sidecar wheel to improve stability.

There's a picture of the current incarnation of our sidehack below (click on it for a bigger version). More pictures are here.

Sideweasel Gravity Sidecar


scottishcarties | May 4, 2011 - 11:29
mollydog's picture


how/where do you load pics to this forum, help
mollydog | May 10, 2011 - 11:42
scottishcarties's picture

adding images to

I'm afraid you can't upload images directly, but you can embed images from other photo sharing sites such as flickr, photobucket, picasa, etc. Just click on the "Insert/Edit Image" button above (Insert/edit image) and enter the address of the image you want to insert in the "Image URL" field.
scottishcarties | May 11, 2011 - 12:13
mollydog's picture

better pic

sidecar mrk 1 

a few mods since this pic,, mudg shaped with handle

mollydog | May 30, 2011 - 09:35
scottishcarties's picture

sidehack thoughts

Seems quite a high and relatively upright position, and the bars are a quite high. I've gone for clipons and rearsets to get nice and flat. Lower riding position made it feel more stable to me too.

Nice wide bars mean you will probably get away without a steering damper, although I suspect you'll find it a nicer ride if it has one.

Sidecar wheel looks to be about midships. That's normal for powered outfits, but I'm not sure it works so well for gravity sidehacks as it can give balance problems and will scrub on corners. 

Have you tried it out? How does it handle?



scottishcarties | May 31, 2011 - 19:06
mollydog's picture



thanks for the comments

will be testing soon, will let you no.

mollydog | June 14, 2011 - 09:30

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