Try refreshing the page to ensure you are enjoying the latest version. I tend to make endless edits and corrections over time. Forgive the sometimes off-topic nature of my blog these days. Walking and enjoying the countryside are vital to my physical and psychological fitness and sense of well-being. They combine to undo the damage caused by an occasional excess of cycling. And, may even stave off another rant! Though I can't promise anything. My long-suffering wife, "The Head Gardener," refers to me as the Imelda Marcos of saddles and saddlebags. She is usually right about almost everything. So it may well be true.


9 Mar 2010

Longstaff Trike Conversion

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Trike conversion sets were usually made by exactly the same frame builders as their more famous trikes. Sometimes, independent frame builders would buy axle sets from the trike specialists to make up complete trikes to customer's orders. The trike axles and matching hubs are the most difficult part to do well. This meant that the loyal fan of a particular frame builder could obtain a unique trike to his own, individual ideas. Often with fancy lugs or other details thought essential to one's personal mount.

An old, 23" "racing" bike converted to a trike using the Longstaff, trike conversion set. The front forks on this machine were bought secondhand with caliper brake bosses already fitted. The forks are moved over to each new bike frame I find, along with the trike conversion set. Perhaps the geometry isn't ideal this time but I'm getting borderline shimmying for the very first time since I started using this conversion set. Perhaps the new frame is just too flexible? Though the frame worked fine as a bike. It felt light, quick and responsive without being at all twitchy.

The odd thing is that front fork trail should have been increased by the lower attitude of the bike frame with the trike axle passing through the rear triangle. The centreline of the trike axle is 1" above the rear drop-outs and 2" forwards of the usual bike axle position. This results in a 38" trike wheelbase against 40" as a bike. No wonder the chainline is sensitive!.

Fork trail should actually increase slightly as the bike is being tipped downwards at the back by 1". On smooth or rough surfaces, even at only 10mph, the shimmy is just noticeable. I'm not riding any differently and everything is fastened well and tightly. I checked carefully in the interests of my continued longevity! On downhill speed runs need my hands need to rest well forwards on the front of the tri-bars to keep things steady. Though I certainly haven't hit violent and uncontrollable, front end wiggles yet. Not like I did after I steepened the head angle on my long wheelbase recumbent! The trike just feels slightly unstable all of the time. At all speeds, on all surfaces, but most noticeable on rough patches of tarmac. Where the road has been repaired badly. Though it certainly doesn't feel particularly unsafe.

Here's a useful article on the subject of shimmy problems:

Dave Moulton's Blog - Dave Moulton's Bike Blog - High Speed Shimmy.

I have noticed that even modern trikes have a lot of rake on the front forks. They all seem to sport a nice bend to the tips of the forks. More like "granny" bikes of yesteryear, if anything. The trike builders must know something I haven't yet discovered for myself. I'll see if I can find a similar pair of forks in my collection to see if this helps. I expect they'd be more comfortable on my bumpy local lanes into the bargain. Except that the article seems to suggest that I will reduce trail to zero with such a pair of forks:

A rough drawing of the present steering geometry of my trike. (lines made with Photofiltre)
I measured the head angle with a large protractor on a greatly expanded version of the image above at 73 degrees with plenty of trail. So there should be no real problem here.

Problem solved! I checked the tightness of the head bearings by applying the front brake and rocking the trike backwards and forwards. The head bearings had freed up since assembling the forks to this new frame. I managed a few deliberately experimental miles and it seems completely stable now. I even managed to ride hands-off at 15 mph for a few hundred yards on a smooth main road with little camber. Even going round a bend was possible without touching the handlebars. The trike automatically seems to follow any slope and requires much leaning and arm waving to overcome the camber. Then it suddenly heads off to the other lane and has to be brought back again! Naturally there was no traffic while I was playing the clown.

The moment I start pedalling the trike veers sharply off to the right towards the verge. This is largely to be expected with one wheel drive (OWD) since I live on the Continent where everybody drives on the right side of the road.  The effort I put into the rear left wheel is trying to rotate the whole trike in a circle to the right. This turning tendency is further exaggerated by the road camber. As soon as I stop pedalling the trike holds a straight course.

BTW: The red saddle in these images was not at all 'comfy' and I've since gone temporarily back to my Brooks B17 again. The red one is just too curved across the back and puts intense pressure where it didn't ought. While the Brooks is much more comfortable the rivets are sticking out all over the place after twenty years of abuse. The danger is that the nasty rivets will tear holes in my delicate cycling shorts. So I'm now working my way through my box of saddles again trying to find the perfect fit. That's the advantage of buying recycled bikes. They come with everything still attached. Chainwheels, cranks, wheels, brakes, gears, levers, handlebars and saddles, of course. The whole lot!

An update: I set a heavy steel bar upright in a portable workbench with the bottom end resting on the ground. Then used the bar as an anvil to reset the old Brooks rivets with a small tack hammer. The heads of the rivets were allowed to rest flat on the smooth, top face of the bar. One rivet had to be turned and crimped with pliers before being fitted back though its hole in the saddle metalwork. Some of the riveting on the underside had broken away over the years. Allowing the rivet to escape from its hole in the metal frame. Now all the rivets are flush with the leather again and my shorts are no longer in danger of snagging. On the first ride it felt soft but uncomfortable until I tightened the tension bolt to put some shape back into it. On the next days ride I hardly noticed I was sitting on anything until I passed 15 miles on the bike computer. The following day I forgot I was even sitting down. Comfort at last!

Another view of the "converted" trike. Only the white axle, stays and rear wheels constitute the conversion set itself. Note the "full sized" 700 x 23 HP tyres on slender, light alloy rims and multiple dérailleur gears. These features are what tends to separate the "sports" tricycle from the disabled tricycle. Very low rolling resistance and light weight are vital for serious mileages at relatively high speeds in all terrains. With the narrow tyres pumped rock hard such a trike can be used for time trialling, or even a rare massed start event, with average speeds well up around 25-30mph (40-50kph).

This is my Longstaff conversion set shortly after unpacking the parcel kindly sent to me by my brother in the UK. It had belonged to a neighbour of his who was suffering from increasing ill health and was no longer able to ride. He also had a Longstaff trike but that was not for sale.

The telescoping, adjustable stays are shown in the foreground. Unfortunately the hex socket of the Allen screws, which are supposed to clamp the telescoping sections, are worn out. So a really secure grip on the sliding chromed sections isn't possible. I am thinking of replacing these screws. Well, this simple modification was quick, easy and worked perfectly. I bought some high quality, hex socket, stainless steel M5 x 16mm screws and stainless steel, Nylock nuts to match. An M5 x 0.8 tap was run through the clamp bosses to clean up the threads before fitting the new screws. The original screw thread were very similar in diameter but had a much smaller M4 hex socket in the head. The M5 Allen key is a nice fit in the new screw heads. Which allows much more torque to be applied ensuring good clamping pressure on the adjustable stays before snugging the locking nuts up tight. Stainless steel is tough and avoids rust but should ideally be lubricated prior to assembly to avoid seizure over time.

How to cheat and use a strong steel clamp to fix the trike conversion seatstays onto the seat post when there's no old-fashioned, saddle post clamp, through-bolt handy. I tried "everywhere" to buy such a clamp and then found one in my own bike junk box.

My Longstaff tricycle conversion fitted in place on a donor bike frame. Note the duplication of seat stays which looks a bit untidy and adds to the overall weight of the converted machine. The spacers on the drop-out fixing bolts ensure a reasonable chain line. This is a major problem with these conversion sets since they force a very short wheelbase on the converted machine. When fitting the conversion set in place the axle is literally passed right through the rear stay triangle before being bolted in place. The axle can only be pushed backwards as far as the inside of the rear stay triangle will allow. Usually hitting the inner parts of the rear drop-outs just between the meeting point of the seatstays and chainstays. Back in the distant past, when 5 speed blocks and single chainwheels were the norm, it wasn't a serious problem. With triple chainwheels and 9 sprocket blocks the chain gets badly bent out of line between chainwheel and rear sprocket. So the longer the rear end the better with these older trike conversion sets. Otherwise you could find yourself changing gear far too often just to keep the chain quiet.

The answer to this problem may be to invest in a later model of the Longstaff trike conversion. Scroll down Shelley Gautier's blog to see a later example of the Longstaff trike conversion set. This fits behind the rear drops-outs of the donor bike frame.

http://roadtolondon2012.wordpress.com/new-race-trike/


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Short arms, clamped to the chain stays, ensure the whole axle assembly doesn't rotate around the drop out fixing bolts. A great improvement over the older version which passed through the bike's rear triangle!

Here's Geoff Booker's TRYKIT version of a very modern trike conversion. Again the axle is arranged behind the rear drop-outs of the bike frame to which it is attached. In this case a single arm and chainstay clamp are provided.

http://myweb.tiscali.co.uk/trykit/Conversion%20Axles/index.htm

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Since these later conversion sets place the axle behind the rear drop-outs they ensure a longer wheelbase than the original bike frame. Greatly easing chainline problems. Since the axle isn't raised, relative to the drop outs, the steering geometry of the frame is unchanged. The later design also provides plenty of extra heel clearance for those with large feet. Before finding this latest bike frame, I had fitted the conversion to a short wheelbase, 23", racing bike frame. My heels of my size 10s (45s) hit the axle on every turn of the pedals and made the trike completely unrideable! Oh dear! (sans expletives!) The chainstays on this frame measured one inch shorter than the other frames I'd used before that. So be very careful in your choice of bike frame to match with your older, trike conversion set!

I tend to swap the conversion set to each new (better) bike frame as I add another to my collection. Used bikes are incredibly easy to obtain in Denmark and are often found in council recycling centres and private flea markets. A fiver equivalent (£5GB) is often enough to secure a decent (but usually cosmetically tired) sports/racing bike like that shown attached to the conversion here. I understand that the police also hold regular sales of unclaimed bicycles but haven't investigated this particular source yet.

The parallel-sided stub axle with hexagon end to ensure drive to the matching hub. A captive screw in the hub screws into the female thread in the axle end. Holding the wheel firmly in place. The wheels hubs on this trike conversion are self-extracting simply by unscrewing the captive, wheel fixing screws with a matching Allen key. There is nothing magical about this but it is a really clever and elegant solution to wheel removal. A captive washer presses hard against a screw-in steel cup in the outer surface of the small flange, alloy hubs. A neat and lightweight idea which saves using a hub extractor. Greasing the stub axles before wheel fitting helps to avoid a firmly stuck wheel hub and the risk of a stripped thread on the fixing screw. As nearly happened to me until I dismantled the hub cap and used a crank extractor to pull the hub off.

A trike conversion set usually has a slightly different arrangement of reinforcing tubes than a real trike. These curved tubes are essential to stop the axle casing from folding up in the middle under the loads placed upon it. The design of the tubes and exact form of the chain stays varies by maker. Though the semi-circular, looped reinforcing tubes at the centre of the axle are a fairly common feature of all of them.

This conversion set has a one wheel drive (OWD) fixed wheel boss. I have since fitted a wide ratio freewheel gear block to this adaptor instead of the fixed gear sprocket. The threads are identical but much shorter in a fixed wheel bicycle hub (or this trike adaptor boss) but quite safe in normal use. Geoff Booker at TRYKIT makes an adapter for older trike axles if you'd like to bring your own machine right up to date with a modern Shimano gear block. Note that the kit consists only of the left and right parts in the image below. The "drum" part in the middle is the freehub which you have to provide yourself. Either borrowed from a recycled wheel or purchased from a bike shop. ((From £20 and upwards)

http://myweb.tiscali.co.uk/trykit/General%20Gallery/pages/16%201wd%20Shimano%20cassette%20body%20and%20Trykit%20adaptor.htm

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The conversion set axle has to be mounted securely onto an ordinary bike frame so needs strong (but adjustable) attachment points to fit the bicycle rear drop-outs. On this particular set some rather heavy steel bars are brazed onto the axle itself. The chromed cross bar (in the image above) is further strengthening for the heavily loaded centre of the rear axle of a trike. These heavy parts are absent on a "proper" trike rear axle since the axle can be brazed directly to the frame's chain stays. This offers not only greater strength but much lighter weight of a trike over a trike conversion. If you like how a conversion feels and take your triking seriously then I heartily recommend seeking out a proper trike for its lightness and far more lively feel. In the UK there are usually secondhand trikes seeking a new home as their owners age or give up cycling for some reason. Or Geoff Brooks at TRYKIT will build you a brand new one at a price.

The lightweight wheels which came with my trike conversion. Longstaff alloy hubs with beautiful Alesa rims and stainless steel spokes. I consider these light aero rims as pretty as they get for a trike.

A close-up of the Longstaff hub showing the captive, hex socket, fixing screw and black metal, screw-in, steel cup insert. This cup ensures easy, wheel, self-extraction simply on undoing the central Allen screw. The cup itself can be unscrewed with circlip pliers (or similar) in case of emergencies. For instance a stripped wheel holding screw or a firmly stuck hub requiring the use of a hub extractor tool. Fortunately the cup thread is identical to a normal cotterless, crank extractor. Thus saving the purchase of a specialised tool which will only be used very rarely if you remember to grease the stub axles.

Since no braking surfaces are required on rear trike wheels the lightest of track racing rims can be used. These are by the Belgian firm Alesa and beautifully light. The tyres are 700 x 23 Bontrager RaceLite available in a range of brightly coloured treads. I love these tyres! They are easily fast enough for me. with fairly low rolling resistance, but seem immune to punctures. At least so far. My previous Michelin and Continental HP tyres punctured at least once a week on the flint and thorn strewn lanes around my home. I was puncturing on almost every ride at one time! I almost gave up riding bikes out of sheer frustration with mending endless punctures. I even stopped wearing cycling shoes and took to wearing narrow trainers on my trike because they were so much easier to walk home in! The shed was filling up with patched inner tubes! There was no room left for my bikes. I was terrified of going any distance beyond an hour's walk back home. Happily I haven't had a single puncture since fitting these Bontrager tyres. That's over a period of several years now.


Who's that fat bastard?
Posing with newly arrived conversion on my Claud Butler. 
Prior to regular rides.

The rear axle bearings on earlier trikes used standard bottom bracket cups and cones. These were fine when first fitted and well greased but can become noisy after a while. Later axles use pressed-in, rubber sealed, journal bearings with circlips to retain them. I wouldn't like to speculate which design offers the least friction but journal bearings seem to be maintenance free in ordinary use. I lift each wheel occasionally to give them a spin to check for odd noises or increasing friction. No problems so far.

While the majority of trikes are single-sided (one wheel) drive some older trikes were fitted with differentials. Differentials have the problem that they send all the power through a slipping wheel. Completely ignoring the one with lots of grip. A newer device invented by George Longstaff uses a sprocket block adaptor with twin sets of pawls and ratchets to allow independent two wheel drive. This is supposed to make riding in the wet, or on gravel, much easier. Wheel spin can be a real problem with the lightly loaded rear wheels of a lightweight trike when pedalling hard uphill. Particularly when sprinting out of the saddle. Which throws the rider's weight well forwards and off the already lightly-loaded back tyres. It is usually best to remain seated and twiddle up hills.



Longstaff 2WD assembly

The drive with a double freewheel type  2WD trike is always to the slower wheel. Which is usually the one on the inside of a turn. Should wheelspin become a problem with one particular wheel then drive is instantly and automatically transferred to the other wheel with this clever system. This ensures grip under most conditions as the pawls will rapidly take it in turns to drive the wheel with grip. Though both wheels are only driven equally when riding in a dead straight line. Which is actually quite possible on a trike. Totally unlike the gently weaving course of a bicycle as the rider automatically balances the machine by leaning or steering first one way and then the other. As examination of a wet bicycle tyre track on a dry road will clearly show.



Trykit 2WD conversion on a Longstaff trike.

The beautifully machined Trykit 2WD "innards" are shown below. The pawls, bearings and spacers fit inside the freehub housing to accept a standard cassette. Unlike the Longstaff no specially manufactured tools are required to dismantle the 2WD assembly or to change sprockets. Nor does it rely on obsolete parts or outdated sprockets. Useful advantages for those wishing to save weight and have the freedom to select different cassettes to provide the correct gears for particular tours or races. A fast time trial on a flat course would favour completely different gears to a tour of the Lakes or Snowdonia for example.


Geoff Booker of Trykit has further developed the twin pawls, two wheel drive axle within the dimensions of a modern sprocket block carrier. (freehub) The TRYKIT 2WD system provides an ultra-lightweight design suitable for racing or touring. It allows modern gear blocks with a large number of sprockets to be used on almost any trike. Shimano and Campag versions are offered. Geoff, who is a highly successful trike racer himself, also offers a range of trike axle conversion sets and complete trike, tandem trike and bicycle frame-sets and even complete machines. Here is his excellent website:

Lightweight Racing and Touring Tricycles and Conversions

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I am regularly tempted to braze my conversion set onto one of my old bike frames to make a "proper" trike. My only fear is that, should I mess up the brazing, I will end up with no trike at all to ride. All bikes and trikes require very accurate building jigs to ensure alignment. It is this aspect which puts me off attaching my conversion set permanently to a bike frame. I also know that sod's law applies. The week after I finished the brazing I'd probably find a much better and lighter bike frame to replace the junk frame I'd just used.

So I would still prefer to try and obtain a used trike from the UK where most of them reside. I do have some experience in brazing having built a long wheelbase recumbent for myself back in the 80s. Plus a few smaller projects since then. This recumbent bike was made using a dirt cheap, "turbo", propane-butane cartridge gas torch and one burner of my wife's gas cooker turned on full for the heavier work like brazing the bottom bracket. An evil misdeed which I have never been allowed to forget in moments of marital distress!

Do *NOT* be tempted to copy this design without using a much more relaxed head tube angle! This one really liked to shimmy downhill! It was very noticeably faster on the flat compared with my racing bike of the time. Hill climbing was its other Achilles heel. That, and turning in the width of a road. Oh, and finding storage space for it at home and at work.

It was absolutely fine, as first built, but the pedal reach was just a little too much for me with no adjustment built in. So I decided to shorten the front end and then reattach the head tube.. In doing so I inadvertently steepened the head angle and only then did the violent shaking begin at higher speeds. An examination of similar, commercial, long wheelbase bikes shows relaxed head angles and extreme fork offsets are popular. Back then there were very few recumbent bikes to copy and no internet to find them even if they existed.

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