osiris Posted June 21, 2013 Report Share Posted June 21, 2013 HI guys! I am happy to share my own expirence of designing the rack in order to move a trial bike out a city on a small car like BMW 116i. I bought the standard tow bar (250$) and have mounted it (30$), bought some raw steel such as angle 30mm*3mm, plate 3mm, square tube 30*60*3mm, square tube 30*30*3mm and something else i needed i found in my garage (plus 100$). Then i've welded this construction previously calculating and evaluating its safety and reliability. Finally, i mount this item on the tow bar. It's slightly hard to load the bike on but it is possible to do by myself (bike weight is 69 kg). I fix the bike by the heavy cable and the buckle. Also i fix the bike's pegs with 10cm bolts into the rack's stell angles. It seems that bike is much longer then the width of the car. However, it is just 10 cm longer then the gabarit. I was testing it for 3 weeks and it really works awesome. There are no problems. I drove the car up to 140 km/h. You know that here in Russia a lack of flat roads (we say there are no roads just directions, it is true). Mostly i have to limit the speed down to 10-20 km/h on holes. I would honestly recommend this bike rack if you don't have enough place on the car park to stand a trailer. I save up to 100$ a month on parking. Quote Link to comment Share on other sites More sharing options...
osiris Posted June 21, 2013 Author Report Share Posted June 21, 2013 oh sorry for my English Quote Link to comment Share on other sites More sharing options...
billyt Posted June 21, 2013 Report Share Posted June 21, 2013 (edited) Osiris I appreciate your inginuty, engineering and design. A word of caution........ When you mount a trials bike to a steel platform like that vie the skid plate, engine every little bump that the car sees (and could be many per your description of the roads) will get transfered into the gear box, engine area. This mounting was tried for regular dirt bikes i.e. mounting it by its bash plate instead of the wheel and suspension. The results where not to kind to the transmission and engine after a while as the shock was messing up shifting an even cracks in the cases. Why not run a channel across the back and mount it by the wheels? There are many different ways of designing and building the bike rack transporters I have attached a picture (click on picture to see the whole picture) of how it designed and built my bike rack. The front wheel lock pivots down to allow the front wheel to go forward and then pivots up and locks in the upright position. The bars are drawn back vie the tie downs to the centre member drawing the bike back to the pivot upright taking all loads off the suspension when transporting. Many other little tricks it does that can not be seen by this picture. Edited June 21, 2013 by billyt Quote Link to comment Share on other sites More sharing options...
osiris Posted June 21, 2013 Author Report Share Posted June 21, 2013 billyt, thanks! Some photos of the Russian directions: I agree that if i had used the base for the bike's wheels it would have presented more damping. But we have to realize that the same long and massive construction adds +35kg vertical weight to convey to a tow bar. And it is hardly possible to be putted in a car if it nessesary (we have just a small 1-serie BMW but not a framed 4x4). I think that my rack can not damage the engine because the vehicle has its own damping system which absorbs a lot of wave energy. Only time will help to determine whether my solution is perfect or foo ) Quote Link to comment Share on other sites More sharing options...
billyt Posted June 21, 2013 Report Share Posted June 21, 2013 (edited) I dont understand I fully appreciate that you have a car chassis. BUT you are still putting the weight of the bike on the back of the car regardless. My channel is made out of aluminuim and hardly and extra 35Kg. I doubt it even weighs 5Kg (aluminuim channel). You can drill big holes along its length and lighten it even further if you wish. When you hit a bump the bike will go up and then come down on the plate and with the plate. The mounting plate to bash plate relationship is critical. At least have a BIG piece of rubber in between them. Cheers Edited June 21, 2013 by billyt Quote Link to comment Share on other sites More sharing options...
osiris Posted June 21, 2013 Author Report Share Posted June 21, 2013 billyt, my system is ready to absorb the fluctuatings. It is not so solid and hard. There are no rubber inside but the system of arms and metal's features are slightly movable. Your (common) solution is much better but more massive at the same time. Aluminium costs a wee bit more then steel and here it seems impossible to find an aluminium tube or plate on the local market. My solution easily works adding my own upon the bike which stands on the place. Quote Link to comment Share on other sites More sharing options...
billyt Posted June 21, 2013 Report Share Posted June 21, 2013 (edited) You seem technical competent but material challenged and doing the best with what materials have available. If you feel confident then go for it. The bike may be fine and the car may be fine. My point was to draw your attention to what some others who have mounted a bike this way have experienced. Why did you mount it so high, is it so that you can see the license plate? Cheers Edited June 21, 2013 by billyt Quote Link to comment Share on other sites More sharing options...
furse Posted June 21, 2013 Report Share Posted June 21, 2013 I know racks have been around for years and I have used one many times, but most towbars are limited in there down force weight less than what your bike will weight. It is tow bar for pulling not sitting 70kg on, check what the spec says on your towbar, Ive justed fitted a towbar to my van and the down force was 65kg max. Quote Link to comment Share on other sites More sharing options...
laser1 Posted June 21, 2013 Report Share Posted June 21, 2013 A few strips of rubber or even wood will help dampen the road vibrations transmitted to you bike. Quote Link to comment Share on other sites More sharing options...
billyt Posted June 21, 2013 Report Share Posted June 21, 2013 (edited) Furse, I agree. Most class III tow hitch receivers are rated for 300Ibs tongue weight and 6000 tow weight. Most people design/build their motorcycle carrier based on a class III hitch. Class 1: up to 2,000 lbs. GTW up to 150 lbs. TW Class 3 : 5,000 - 6,000 lbs. WC 300 lbs. TW Osiris car hitch is not a class three as it only look like class one which is a 1.25 inch or 32 mm receiver. A class one is limited to a tongue weight of, according to the chart 150lb. I think his car can handle the towing capacity, but in this case he is not towing, the tongue weight not so much as he has it sticking out perhaps one foot and so there is leverage and a bending moment so it is no longer just the weight of the bike it is the weight of the bike multiplied by the length of the horizontal metal arm sticking out. There will also be a lot of rotational movement as the bike rocks on its centre vertical arm due to how high it is on the upright arm. All this on a piece 30x30mm" square tubing? You can see in his pictures that the back end of the car is sagging under the tongue weight. If the roads area as bad as he says in Russia then he has made a very low car even lower to the ground, add in a ground that is very rough and the potential for hitting a ground obstacle even greater. Osiris, is the car a manual or automatic, are you driving off the road onto the dirt with this set up to the riding area? Cars and trucks are rated for tow capacity by two main things. Tongue weight: is determined by how the weight at the back on the tongue in a straight vertical line in how it affects steering (by lowering the car at the back subsequently pointing the nose up and affecting steering by making it light in the front end). How it places extra burden on the suspension. How the chassis or bracket is designed to handle the extra load on the welds of the hitch etc. Tow Capacity: is determined by the cars/truck chassis, brakes and transmission. The chassis must be able to handle the extra load and the brakes and transmission must be capable of stopping the extra load. Osiris, We are trying to help you avoid damaging that really nice car and nice Sherco. Maybe we can send you some aluminum channel if you cant get it over there? Can you post some close up shots of the towing platform from different angles without the bike on it? Edited June 22, 2013 by billyt Quote Link to comment Share on other sites More sharing options...
copemech Posted June 23, 2013 Report Share Posted June 23, 2013 I think this may well work out, as he seems to have tested it already. Due to the fulcrum arm behind the rear axle, it will obviously sag the car, but the car will absorb the shock as compared to a simple trailer rig with little or no suspension bashing the bikes bottom . If the upright arm to the platform is solid and does not sag, as compared to a hollow tube structure, he should be ok. If it starts sagging I would worry! Quote Link to comment Share on other sites More sharing options...
osiris Posted June 25, 2013 Author Report Share Posted June 25, 2013 Why did you mount it so high, is it so that you can see the license plate? precisely! I know racks have been around for years and I have used one many times, but most towbars are limited in there down force weight less than what your bike will weight. It is tow bar for pulling not sitting 70kg on, check what the spec says on your towbar, Ive justed fitted a towbar to my van and the down force was 65kg max. yes, the towbar has 70 kg down force limit but it is only to the ball which has been demounted. The base uses 8mm metall. A few strips of rubber or even wood will help dampen the road vibrations transmitted to you bike. I will do it later. However, i prefer to find flat roads which we also have here Some additional photos: Quote Link to comment Share on other sites More sharing options...
osiris Posted June 25, 2013 Author Report Share Posted June 25, 2013 I realise my rack is not ideal. But it was made quickly and works perfect as a result. It has to be painted asap. I designed it feeling the forces, which can be applied, by the ends of my fingers. I finished Samara State Aerospace University (rocket engines) and got 4 of 5 score on the material resistance course. It was very difficult and comprehensive course when about 30% of our group have been expelled. I hope whole expirience i got in there helped me to achieve great results constructing this rack. Quote Link to comment Share on other sites More sharing options...
billyt Posted June 25, 2013 Report Share Posted June 25, 2013 Osiris I think you designed this very well considering the limitations you where faced with. At the end of the day it is your car, your bike, and your design. If it works for you then give it a good powder coat and show it off and use it. Just keep an eye on transmission issues or small cracks, it may take a while if they appear at all. Quote Link to comment Share on other sites More sharing options...
b40rt Posted June 26, 2013 Report Share Posted June 26, 2013 The rack looks excellent, it's the bit it's connected to that I would have concerns about. A tow ball is round, so twisting forces are not transmitted to any great extent, in this design it may be an issue. Quote Link to comment Share on other sites More sharing options...
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