Rake angle and grip

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Taffy
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Rake angle and grip

Post by Taffy »

the steering head angle (also known as the 'RAKE') is still very conservative on Sidecars.
at the extreme angles of steering lock, LESS tyre is in contact as the wheel leans over. so for a right hand bend the tyre has least grip when on full lock. the less rake and steeper the steering headstock = the more grip you get at full lock.

for example (figures are examples only)
23d head angle (typical solo)
straight ahead 100%
half lock 90%
full R/H lock 60%

and then a steeper angle of say
15d head angle (speedway type)
straight ahead 100%
half lock 95%
full R/H lock 75%

the contact area is more central to the tyre allowing the suspension to work better rather than working the tyre wall on one side.

in the past, to try this steeper rake angle, folk on solos have cut a wedge out of the underside of the frame or taken a little wedge out and welded it into the gap in the top half of the frame. doing this would:
1) change the wheelbase - a few mm - not too important here but anything over say: 15mm is too much.
2) it alters the weight distribution and puts way more on the front - the weight distribution/spring rates etc = all gone to pot
3) trail (the distance the tyre sits behind the steering pivot point as it would strike the ground - this is shortened making the steering less stable.

for sidecars, with a few extra holes drilled at the base of the leading link fork to send the wheel backwards - this is no problem, and backed up if you have one by an eccentric wheel spindle we can get the trail just right again.

what's required is to weld and add metal into the front of the frame between the main frame and the headstock. this would steepen the steering head up from say 27 degrees to the (say) 23 degrees and thus keeps the front wheel in exactly the same place on the *ground.

In recent years in order to get the rider forwards the continentals have been placing their handlebars well ahead of the crown nut which causes a weird steering sensation and eventually prohibits you from doing it anymore and after this you can't put them (and therefore the rider's weight) any further ahead. a dead end for development...

however, if you make the steering headstock steeper by moving the steering head away by say 60mm to steepen the rake, then take the bars from 60mm in front of the crown nut to a position on top of it, you - the rider, start from the same riding position as before. Just go look at a trials bike with the steep rake and the bars are behind the crown nut! you then have room to move the handlebars forward (with the rider!) again if it helps for weight distribution comfort and control etc.

the rider's seated position is controlled by his comfort and angle to the bars. even on the face of a sloped seat, if the bars go forwards 60mm, the rider will sit further forwards increasing the weight over the front wheel. downward pressure on the front tyre will give a more grip.

add the two together: contact area and pressure and you have more grip on the front.

some figures to work with and why:
well, working through the angled headstock: the wheel spindle is luckily a quarter of the way between the ground and the top of the headstock on the steering line. true the wheel spindle is ahead of this line but we still use spindle height as a fulcrum.

aiming to move the headstock forwards a distance of 68mm overall, we start by rotating the top of the headstock 51mm and rotate through 4 degrees. this means that with using the spindle as a fulcrum that the point that the ground trail has lost 17mm. ask your son or daughter: they'll explain! the 'point on the ground' which is the line straight through the middle the steering stem as if drawn with a lazer.

there is also a point on the ground below the middle of the front wheel spindle. yes it is the bit the tyre sits on! but when measuring the distance this point is compared to the one through the headstock is your 'ground trail'.

the reason I'm using the steering axis lines meeting at the same height as the spindle is that when we discuss trail it is necessary.

so, so far we needed 68mm to weld on a new headstock but have gone only 51mm remember?

well to keep the same trail we should have to move the wheel back 17mm and we don't want to do that so we weld the headstock 17mm further forwards at the same new angle of 23d and THAT becomes the 68mm!

this makes it 68mm ahead of the old headstock which is roughly the size of a headstock tube! :-D :-D

so now the headstock angle is 23d (from 27d), it has rotated forwards 51mm, been moved forwards 17mm at the same new angle and now we have the wheel 17mm ahead of where it used to sit.

the pivot point of the front arm needs to be the same height off the ground as before as well.

the above will change the rake by just under 4 degrees. from say 27 to 23 etc. 15 degrees and less are possible but the headstock moves too far away from the rider. one step at a time though, after all you don't know whether you'll want to sit forward again.

here is a heavily changed photo, way more than 68mm at the top of the headstock:
Image

note;
lilac line = the old headstock angle
yellow line = the new angle but look where the line strikes the ground. wheel needs to be on this for zero trail but this would shorten wheelbase
blue line = headstock shunted forwards at same angle to yellow line so the wheel has the same ground trail wheel has now moved forwards though from where it intersected the yellow/lilac/red to the light blue/red intersection.
swingarm must move back on the pivot holes until the wheel spindle is back on the yellow/lilac/red point.
wheel spindle/wheelbase finishes where it started.

white line = wheel spindle position. + and - trail starts here
red line = changes made on the plain of the wheel spindles


if you want the engine forwards, the rider forwards for grip on corners, get the steering head forwards and then you can plonk the rider further forwards to do it?

tests on solos have proven that it is the amount of trail you have that gives stability and not the rake. after all: the coffee trolley wheel works vertically (zero rake) doesn't it? :thumb:

some photos added 9/10/13:
this is Steph Parr and Josh Haynes. Photo by Ann (thanks!). all photos Wakes Colne September 2013 British Round.

I've not used the wheel spindle as a fulcrum as described above this time but simply used ground trail. wherever the steering point would strike the ground then the wheel stands on it for 'zero' trail. simple!

nice photo gives a nice side on shot. IF the outfit runs zero trail he appears to have 30d headstock. I've marked the lines. Orange line through the headstock is the rake. the line down from the wheel spindle meets the orange line so it is zero trail. if the front wheel was back a bit it would be positive trail. we don't put the wheel ahead of it.... I think!
Image

with a bit of trickery the head angle is now 15d but the wheelbase has been dramatically shortened. no good.... we have negative trail. very bad. if you stop a tea trolley and then push it back the opposite way what happens to the wheels....yeh....yug! :shock: :shock:
Image


so we extend the headstock forwards but at the same angle as above. now we have zero trail again! lilac line is the old 30d, white line is the new 15d

the rider needs arms like an Orang-Utan at this point but everything else can go forwards now. does the rider want to sit further forwards? the only extra weight in the chassis is in the additional spine length in the frame.
Image

regards

Taffy
Last edited by Taffy on Tue May 31, 2016 8:58 pm, edited 6 times in total.
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Re: Rake angle and grip

Post by Taffy »

Image

in the above photo the wheel doesn't leave the centre line because it has 'zero trail', even though it is nearly on full lock.

if any of you have, do run, or used to run with lots of trail, the wheel would now have been say an 1" further back and therefore 'offline'. (in this case, as you view it - 1" nearer the sidecar wheel)

on a right hand turn, as above, the front wheel would be nearer the middle of the outfit and on a left hand bend, it would be outside the outfit (the other way). i exagerate slightly....

was there any benefit in the handling when you had lots of trail? (just that not the fact that it was stiff to steer etc) anyone?

Taffy
Last edited by Taffy on Mon Sep 08, 2014 12:40 am, edited 1 time in total.
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Re: Rake angle and grip

Post by BANKSY »

You need to get out more mate!!! :dontknow:

Speak to Kevin at KHR, he knows about angles and building bikes!! :phone:
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Re: Rake angle and grip

Post by Taffy »

cheers Banksy

I understand it, I just need feedback.

I get out alright - it's called shed time! :lol: :lol:

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Re: Rake angle and grip

Post by Dave Tye »

Kevin Hollister is indeed the man with Frame building and angles for steering, I also seem to recall Mr. Mallows running a VMC with extended headstock back in the late 90's/early 2000's sometime.

Dave
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Re: Rake angle and grip

Post by Taffy »

Dave Tye wrote:Kevin Hollister is indeed the man with Frame building and angles for steering, I also seem to recall Mr. Mallows running a VMC with extended headstock back in the late 90's/early 2000's sometime.

Dave
maybe, just maybe, someone has a side on shot of this outfit?

well this is my take on it as regards steering

rider's have reduced the trail to make the machines easier to man-handle and fair enough! but have a look at the mechanics of it and see if there is a new way forwards

on the left in the image below is what we have now. the dot in the middle is the point through the middle of the stem to the contact patch of the tyre. easy to turn, wheel never leaves the centre line of the 'bike'.
Image
the image on the right is what the tyres would look like with trail. further back and moving well offline, harder to steer - but only as you are right now! think unicycle on the left and think tea trolley wheel on the right. to bring that wheel forwards for the same wheelbase the headstock needs welding further forwards - the front end shunting forwards in effect. but that is with the present rake. now pretend you're looking at this from the tread blocks of the rear tyre? as it is right now, with no trail, it points at the front tyre and always driving at it, so it is in effect helping to create understeer because at the point where the front tyre goes over on to its edge the rear tyre is driving into it!


so read on
let's just concentrate on a right turn on a UK set-up. now look at the diagram below and on the left, how the rear wheel is pointing into the middle of the front wheel. The middle left diagram shows the rear wheel driving infront of the front wheel. steering is at 31 degrees.
Image
in the middle right shows the tyre contact points are still on the middle line (thin brown) but look what has happened to the chassis (zig-zagged black line) you can see that the rear wheel is driving ahead of the front wheel. try and imagine where the chassis is in the first diagram then where it is in the second and then the third diagram. they look similar but the one the middle right shows the chassis is already turning right 'deflecting' the drive from pushing the front tyre into a skid. steering at 31 degrees and the chassis is over 7 degrees here.

on the right the steering is straightened by 7 degrees to 24 degrees. so 7 + 24 is the 31 degrees and same steering as the first diagram. 7 degrees saved. firstly though these aren't exact figures and indeed are more than you can expect, they are done for explanation. if seen above, the act of turning is 'rotating' and the rear wheel is now working against rotation of the outfit but you WILL get more grip on the front and as I'm always being told, sidecarX riders skid steer and this will help.

under acceleration the steering will want to straighten up because the headstock/frame rams ahead of the contact patch which straightens up the steering (ever pushed a bicycle by the seat starting with a twisted steering? push the seat and it straightens up). under braking it'll be harder to turn in.

the chassis has turned a few degrees into the corner compared to the contact patch of the front and rear tyres and therefore the steering won't need turning as far. for example, if you want to turn 10 degrees and the chassis has turned 3 degrees of them then you only now need to turn the steering 7 degrees from the line ahead of the chassis.

the diagram below describes it better than i can.
Image

standard photo
Image
below though, is a very exagerated view of an outfit with more trail. I simply shoved the wheel back a collosal 3". but you get my drift (ouch!) :kick:
Image

so why do I mention it?
well it seems that two things need to be done at once. less rake by moving the headstock forwards and steepening the steering. but also to go back to having trail - quite a bit of it.

there are two ways of creating lighter steering:
firstly, conservative rake angle and zero trail = what you have
but, there is a second way
TO HAVE A STEEP RAKE, LIKE A BICYCLE, LIKE A SPEEDWAY BIKE, once this is done you can then add trail and still the steering isn't too heavy. below is the effort you have to put in...on the left what you have to do with the steering right now. on the right the effort if you have a steeper rake. high (middle) to low (L & R) = no effort and vice-versa.
Image
think of a Hardly Davidson if you've sat on one with their 'kicked out' front ends, the steering slams down to full lock and takes a huge effort to pick up. you aren't steering the bike, it's called weight lifting damn it man! so if you go to a steeper head angle this won't happen!

if you could get the rake steeper, more trail and power steering from some other form of racing (take away the weight of a steering damper as no longer needed) where could you go with this? 19" tyre for a start.... I could add many more but one thing at a time right?

with a Husaberg engine weighing just 30KG and a rider weighing say, 90KG, it is the rider that needs to move forward and back and not so much the engine. the engine should be in a position that gives the rider to add or subtract equally to its weight. until now the engine has been as far forwards as possible but what if the rider made the general balance overall allow the engine to move back slightly?

presently, you are sitting behind these camel humps but we have to hope that soon fuel cells won't be an issue and riders can move freely. each frame manufacturer is slowly giving the sidecarX boys the room to move that the solo riders have taken for granted for 15 years now.

weight
the extra steel is NOT in the cradle part of the frame, merely in the extension along the spine of the frame and well worth it too. it could also lead to the rider forward, the engine back, the swing arm shorter and this being from a solo.
SidecarX swingarm with 65cm centres = 11.5KG
solo swingarm with 61cm centres = 4.5KG
all this 7KG for 5cm?

I've held these views for the 5 years I've been involved in watching this superb sport, probably the best motorsport I've ever and will see. I hope someone will have a go at some of this, I think you need to try the first thing and if it works then chase the second etc.

In the stock car racing I follow there has been a rush to little rake, heeps of trail and power steering. it's like watching a tea trolley with a steering wheel :lol: remember you are turning the chassis while the wheels stand still - very weird to watch as the cars wiggle sideways across the front.

sometimes to go in the right direction 2 or 3 other things may have to be sorted. in isolation, the above might get a good kicking but if someone works out how X, Y and Z need to be changed then they may have something. in a sport that is so open and visible though there seems little reward for innovation when all you need do is wait and copy...

regards

Taffy
Last edited by Taffy on Sat May 09, 2015 6:07 pm, edited 4 times in total.
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Re: Rake angle and grip

Post by Taffy »

No input from anyone?

over your heads?
talking balls?
all been done before?
are you all sworn to secrecy?

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Re: Rake angle and grip

Post by papsck »

Around year 2000 the vmc didn't turn to well for racing in the uk it was more suited to dutch tracks.I had made eccentric steering head bearing cup collars,so what you had then was taper roller cones with same as orginal internal diameter but smaller outside diameter and the cup outside diameters where smaller than orginal and then an ecentric collar same outer diameter as orginal cup that the new cup would sit into.This transformed the bike but cant remember the angle change.
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Re: Rake angle and grip

Post by JohnPannell »

we're sidecar racers..... we cant read....! :hammer: :sofa:
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Re: Rake angle and grip

Post by peter logan »

Taffy I have followed your many interesting and well engineered comments regarding sidecar set up and geometry, if I had the cash to set up a business you would be the first man I would have on my design team, you certainly know your stuff !! Unfortunately I assume most of the people who read this forum are drivers and passengers who probably don't understand about steering geometry, they just buy them and ride them.
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Re: Rake angle and grip

Post by Taffy »

well at least we're all alive and kicking!

I know a fair bit about this but I didn't race sidecars so I don't have that experience to fall back on.

I hope I haven't spoken down to anyone but laid 'how it works' out and everyone is a little wiser! what I would like to see is a good team with a second outfit try some of this but we shall see....

part of me wants to start ScX at the age of 53 but I'm well aware that any success would be 10th instead of 17th at a Clubman's round and frankly wouldn't prove a thing to anyone.

I have a few more "why on earth"s but best to focus on this right now. It seems the steering is the fundamental weakness in this.

what you really want is adjustability and the ability to go forwards and back. alas head angles are the one freekin area where 'welded up remains welded up'!

If anyone is at all interested and they'd like a chat, then please get in touch, I'll help anyone and free of charge just as I did for a certain race team from Kent :lol: :lol: :lol: :lol:

one last point: while the leading teams get given a great deal of their technology by working with the top people that want to help and give info, it is NOT risky stuff! nothing is chanced!championships are lost on one single DNF!!!! this stiffles progression! they can't take the risks!

this means that infact it is down to some of the lesser lights to have a go at it. Norman and Stuart will be very conservative about what they do and the old racing expression is: "eye, all well and good, and I'll have a look at it when it beats me/the world champion uses it - until then it can bu**er off!".

these guys don't have time to fail! they have sponsors who will leave them after even one disasterous season. therefore you shouldn't look to Stuart Brown etc to do this first. in some respects, one of the better GP teams should be paying towards a 'junior' team to test this stuff. you test and improve until the better team has a go and remember "the stop watch never lies!"

To recap on what I think the benefits are:
more grip at extreme angles of steering
that moving the headstock 4"-6" further forwards will allow the rider that or slightly less if you want so 3"-6"
the extra weight on the front cornering will allow the engine back 2"
which allows a solo swing arm weighing 1/3 of the sidecar SA
try some trail, perhaps only 1" and see if this improves times and if the rider isn't worn out by it.
with this much extra grip at full turn it is also a chance to explore 19" wheel and tyre
with the headstock forwards, bars in front of the crown nut, the rider can get further forwards
the front top railing to the sidecar can also move a long way forwards, this puts the radiator even further out of the triangle? however the raditor, panel and frame don't all have to be together on the same vertical plane.
there will be an area below the headstock and behind that can take the fuel tank. this then allows the rider to slide up to the nose of the bike and lowers the C of G.
Image

all measurements in imperial are done to confuse Johnie Foriegner! :lol: :lol:

regards

Taffy
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Re: Rake angle and grip

Post by Taffy »

here's some stuff I drew up

this shows the 'slew' you presently get, every kilo you stick in the sidecar adds to this 'slew' on acceleration and the problems with braking as well. note that at present the radiator is outside the triangle. not good except when spinning up the rear tyre when leaving lefts?
Image


but below, I've put the radiator in my prefered position which weighs down the rear wheel at all times. note; some radiator fans (in red). the reason I've done this is because we have to think 'afresh' as of this year Li-On batteries are down from £125 to £50 and weigh just 500 grammes while putting out double and treble the old acid batteries, so from now on you can indulge in anything electrical you want, rev counters, shaving points you name it! the radiator is tipped over and behind the present plastic screen with holes. with rad fans less rad area is needed.

the exhaust runs underneath it. again, the weight of the exhaust is back and would be under the rad and some heat shielding if I could. it's good enough when shorter for solos so why not?

probably not legal but I'd have open mesh floor and the panel for the adverts would be set back 3 feet and infront of the passenger at roughly the height of his balls! :kick:

total weight loss in the sidecar section?

anyway, the idea is that the passenger would go back to leaning over the seat with his chest. in the long run the reason is (as you'll see at the bottom) that he has more energy to arrive in the right place and on time. if you want to go quicker you've gotta move people around quicker!
Image


I watched Stu Brown and Luke Peters at Canada Heights three years ago and as they came over the table top away from the lagoon the sidecar slewed the whole outfit hard left every lap, I moved to see it more clearly and put it down to the sidecar swingarm being too short for the travel it was being asked to carry out - a bit like the present leading link forks but at least they have time to react by going backwards into the bike - the sidecar wheel doesn't.

so this is simple enough: the sidecar swingarm pivot is right on the very front edge. the diagonal arm down from behind the rider's bum would flatten out over the present footpad in the corner and therefore act as part of the footpad on the front corner for the passenger. I'd probably make the swingarm have two converging arms joining at the wheel hub for extra rigidity now that it is longer. next step: lay the shock nearly flat and, using a bell crank, compress the shock as it lays sideways under where the present radiator has been?

note all these ideas have lowdown weight except the rad. but see the bottom one for that.
Image


now , if Rolf Biland had done a ScXer!
note how the front wheel is to the left of the track of the 'bike' part and the rear wheel is to the right, this is still a two track and not a three track vehicle!
with the front wheel now to the left and trail built in right handers will be quick!
note the engine is a Husaberg. obviously the best you can get and made with British and Swedish sidecarX teams in mind! :whistle: :whistle: it is inside the sidecar. the fuel cell is now where the engine was for that new buzz word: mass centralisation'.
the rider I figured would sit in line with the front wheel but that is where my lack of knowledge shows...out on the right or where he is? figured he'd like to sit behind what he's steering at least!
sidecar wheel now set further back than conventional.
passenger zone is now to stay at the rear of the outfit and weigh down the outfit by being a solid lump and not a hinged person outside the chassis. sorry if this is dull.
rider now rides right against the inside of the corner scraping the passenger wheel against the inside markers, rule of thumb: passenger stays within the bodywork so the rider knows where he is!
exhaust in old spot but not where I'd like it really I want the silencer under the rad.
Image

two drawings I did for Millards in 2009 of a closed and sealed cooling system. this rad has a wedge shape under the belly forcing cool air into the wedge and to rise evenly along its length up and out. the fans pull the heat UP. this has a low mass and heat dissappates about 40% quicker from a flat surface. the mud can't turn all those corners....
Image

positioned where your present battery boxes are - but you knew that!
Image

the drawings aren't the best but you get the idea. the plastic conduit is from a Volvo lorry. radiator in the triangle, low down, pressurised airbox heat leaving easily. I'd probably let the air straight in the font now and just have a load of cubicle walls ceiling and floor to stop the dirt.

well you'll be pleased to hear that that is it. I've nothing left in the cupboard and there won't be any more. I have a 45d footplate idea but that'll wait and that is it...

well, what about that lot?

Taffy
Last edited by Taffy on Mon Sep 08, 2014 12:58 am, edited 2 times in total.
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Re: Rake angle and grip

Post by shaun »

Taffy, I have tried most of your geometry ideas at some stage, and have some knowledge of what is good or not in motocross. Whilst some of your ideas could work in roadracing, they would not be as beneficial in motocross. You seem to be trying to improve the sidecar going round right turns, but, if you lengthen the sidecar swingarm you are undoing all the work you mentioned in your earlier posts regarding head angles etc. The most important geometry you should be focussing on is the relationship of where the rear and sidecar wheels are positioned. I don't want to freely give away my knowledge on here but am willing to have a chat with you behind "closed" doors to exchange ideas!!
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Re: Rake angle and grip

Post by Sos »

Hi Taffy
Maybe you could explain the following for me - last May I did a toughish enduro on my wht outfit which was set up for mx with a 20" front wheel and the front fork loop bolted through the middle hole of three.
I usually use a 21" front wheel in the back hole (closest to engine) on my vmc and it's spot on for enduro riding - bike handles fantastic and is easy to ride even in the most extreme of conditions.
Anyway with the 20" front I found the steering very very heavy on some parts of the track - especially so when negotiating some very slow technical parts of the track such as awkward rock steps, weaving through tightly spaced trees and climbing out of deep ruts. Two or three times when the steering was on full lock and the bike at a standstill due to having to change rut/line or waiting for a run at a clear track, it was almost impossible to turn the handlebars back to the centre!!! I've never come across this problem before when using a 21" front wheel and front forks in sand setting!!!
Reading what you've written on trail and rake here I'm trying to figure out whether the smaller diameter wheel and fork setting would cause the steering to be so stiff - riding 75 miles of mud, ruts and forestry going using this setting beat me up far more than anything I've ridden on the vmc before and that includes some super tough extreme enduros - why would that be? (ok I know that renewing my gym membership, staying off the beer :beer: and cutting out the cakes would help!!!!!)

What do you think Taffy?
Gad hi gal hi!!!
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Re: Rake angle and grip

Post by Taffy »

Hello Aled

you changed the trail Aled somehow and this was after all, two different outfits so let's start by always getting the amount of trail right: this is what went wrong somewhere! I think you went to negative trail, like pushing a tea trolley from the opposite end and trying to keep the wheel in front of the axle....not good!

if the 21" on the back hole was nice I would think you had zero trail at that point but either way that is the "sweet spot". best to get on a bit of flat and level concrete (I know you got flat bach, but have you got level? :-D ), lift the sidecar wheel using a nice chap to hold it or suspend it on rope a teeny bit off the ground so there's no friction from the chair wheel when you go from left to right lock. pump the front and rear tyre to 30PSI so it sits on a 'point'.

that done you need to turn from straight ahead onto say the left lock. put something down by the frame rails like the little V stand you use for a car axle stand or to hold the sidecar wheel up etc. have it 1mm from the frame. then straighten the steering up and measure the gap.

if you have 'zero trail' it should still be 1mm. if you have trail like the tea trolley wheel then that gap will grow. if it gets to 20mm-30mm then you clearly are way off!

this is my take on the 20" problem
pump your 20" and your spare 21" to 40psi and then put the spindle half through both together, then put packers under the 20" tyre till the pair stand up straight. the thickness of your packing is your height difference.

so fitting the 20", the front end dropped by that amount; say - 5mm or so I'm guessing and steepened the head angle compared to 'before'. that brought the 'hypothetical line' through the steering stem and where it points at the ground back. it brought it back a couple or so millimetres behind where the tyre contacted with the ground. that means that your tyre was ahead of the zero trail at negative trail!

then you put the arm forwards as well by some 10mm on top as well pushing the tyre even further ahead! the arm is the main culprit. below is the problem exagerated. it's not 4" in real life OK?
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I know you couldn't put the arm back any further because they were on the back holes but back is what was required when fitting that 20". so, I think you had no trail so you were riding with the tea trolley wheel turned around the wrong way!

when changing either way between 21" and 20" wheels
everytime you change wheel sizes you must always measure from the ground with a tape measure up to a point and get the outfit back to that point (see the white arrow below), the chassis must sit at the same height. a good place is to have a centre punch mark on where the triple clamps on a solo would be (red dot below). a good manufacturer gives you fresh holes to just re-bolt the shocks so you can lower/jack the front to the same height but you can also adjust using the pre-load castle nut on the shocks. it's not ideal though.
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arthur waltons outfit, made by KHR is just brilliant for this. just a pair of pinch clamps (photo courtesy of ann). if you change wheels and want the outfit to sit in the same position you just adjust the clamps.

I would do all these measurements in the yard, with a clean outfit so you get to swap wheels and bolt holes etc and then record it in a little book. you should have high and low bolt holes to peg the arm into. then when you are at the meeting, if you ever change you simply do exactly what you have written down, no more and no less.

so for example
21" wheel = shocks in upper bolt hole (lower the front of chassis). arms in the 'up and forwards' holes (front wheel forwards)
20" wheel = shocks in lower hole (raise the front). arms in 'back and down' holes (front wheel backwards)
to be honest with you, bolt holes aren't accurate enough. everything should be on rotating eccentric bushes.

below is a diagram to help
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the reason the arms go in high and low holes isn't to so you get half-way holes! nope, it is so that the arm stays at the same angle as before to keep your anti-dive the same. so here is a view from the nearside. if you don't have it - you should!
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you may think a 5mm drop with the 20" wheel isn't a lot but it creates a tipping motion so there is more dive with the 20" wheel. on its own the 20" wheel creates more dive, more trail, more wight on the front which means not only did the front drop 5mm with the change to 20" but it will drop more because the springs sank!

teams could have a set of industrial scales off ebay for £30-£50. you then learn the difference changing from 20" to 21" etc and back makes.

so using the arms you can keep the trail the same. the shocks should be compressed the same as before so the preload on the 20" set up needs more and the 21" is less. the actual 5mm lost when dropping to a 20" should be done with the shock mounting points but is appears the designers don't leave this facility - why?

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now; Copy, paste on plain paper, remove photos, print, visit the workshop, experiment!

and start keeping records!

regards

Taffy
Last edited by Taffy on Sun Apr 27, 2014 12:45 pm, edited 2 times in total.
I don't want a works bike I just want their address book! :?: :?:
here is a link to the SMCA web site for ya! http://smcagb.moonfruit.com/ :-D
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