Short fork conversion on gen 1 Vmax

[kai_Zna]

Hi! I am new to this forum, and live in Norway. I was not happy with the performance of the original fork/brakes of my 88' Vmax, either in handling, high speed stability or braking. Being used to sharp handling and braking on my streetfighter, owned and ridden for 22 years, it was a too big step down. I loved the bike, with is distinct character, though! Modifying is a part of the fun. I got hold of a TL1000S USD fork with a custom top yoke with lowered upper fork clamps, designed for a Vmax. However, I wanted to use the original 18'' front wheel, as a modern 17'' looks to small compared to the bike, in my opinion. The short fork gives a steeper steer angle, hence reduced trail. However, the offset in the yokes was less for the new fork, hence increasing the trail somewhat. It was very exciting to test the new geometry, whether the trail was balanced between high speed stability and agile handling. I am very happy with the result, and will never go back to original. I like the compact "locomotive look", and stance, as well. With 18'' front wheel and short fork, there will be clearance problems with the radiator. I had to modify, to get the radiator as close to the frame as possible. I even had to make a little dent in the bottom of the radiator, it is indeed a tight fit when the fork strokes all the way. Sleeves for adapting the Vmax front axle to the bigger axle holes in the Suzuki fork also had to be made. Brakes with 320 mm Galfer discs from a R1, and 4 pot calipers from a Suzuki GSXR600 are performing very well combined with the Vmax brake pump. So there are parts from 4 different bikes in this front end!. I must make fender brackets for the original front fender this winter. I guess it is a far easier route to take a complete fork assembly from a FZR1000, as they are quite long, and come with decent brakes. I have restyled my bike with a cast aluminum headlight nacelle from an old HD FLH. Probably the first Vmax in the world looking like this It is fun when people think they have found a slow bobber to play with... The hardtail conversion with self designed machined aluminium struts, is another surprise. It is very fun to ride actively with this bike now, as opposed to earlier. I guess the combination of high rubber profile 15'' rear wheel and original mid controls is the key to success, to get sufficient comfort. I am using this bike most days for travelling to work, about 50 miles in total. I enjoy it, it is not a journey of pain. If someone told me, i wouldn't believe how well this hardtail conversion works. I thought it as all show and no go, and that I would go back to rear suspension after a couple of trips... I guess part of the technical explanation is that with struts, the rear subframe acts as a rigid brace for the original swingarm, making a torsionally stiff structure for attaching the rear wheel to the bike. So maybe a well designed brace of the original swingarm, is what it takes to make the Vmax handling much better? Now I can ride hard with no worries, and change track in the middle of a turn, or brake, without inducing wobble. And it is stable on the straights. Sounds to good to be true, but this is my experience.

 

[Fire-medic]

You win the "Going My-Own Way" award. Bottom line, you had an idea, you did it, and you're happy with the results.

I'm older, I need the rear suspension, my back is showing evidence of deterioration of cartilage after my 'many-years.' I have a complete FZR 1000 front end I bought, sitting, I haven't bothered to mount it because I found that a series of mods made a huge difference in the feel of the bike. The changes involved both the front and the rear suspensions.

In 'the old-days,' the chopper guys would use a 5.10" X 15" rear wheel with their rigid frames, and run really-low tire pressures (20 p.s.i.) in a 90-series profile 'balloon' tire. They got their rear suspension from the volume of air in the tire carcass. Low aspect ratio tires, and their wide wheels weren't yet available. For a historical perspective on the emergence of wide tires and low-aspect ratio construction, look at Mickey Thompson's Indy car entry.

The #1 change which makes the most-difference, in my experience, is to go to radial tires, you can get a modified rear wheel, and use a narrow front radial tire on the OEM front wheel. The important thing to-do is to have the same tires f & r. By that I mean, from the same manufacturer, and with the same tread compound. You want the f & r to 'stick' similarly, because if you don't, you'll end-up with all-sorts of weird handling issues. Also, different radial tires have different construction, and mixing different construction tires can make your bike downright unsafe! Some radial tires have a 'Zero-degree' construction, where the warp plies are at 90 degrees to the tire circumference, while other tires have oblique angle warp plies, where the wrap from the tire circumference is at say, 30 degrees. This greatly affects the way the tire handles, when you mix the two construction types, and not in a good way!

A brand-new pair of premium bias-ply tires (bias-ply tires being VMax OEM) has a smaller degree of difference to a pair of radial tires, at legal operating speeds. However, at speeds easily achieved in even only third gear, the differences in handling characteristics quickly appear, favoring the precision of the radial tires over bias-ply tires, especially evident in curves. Put 1,000 miles on the bias-ply tires, and their handling difference compared-to a set of radial tires becomes even-more noticeable. This is my own experience. The way you ride your bike may-not reveal the differences I've experienced. I tend to-ride 'enthusiastically,' and I probably see that red oil light flicker every time I put the key in the ignition.

AT the rear, I use a pair of Progressive Suspension shocks, I think the OEM shocks aren't that-bad, remember they have preload and damping adjustments, so if you're ighter, don't run the preload too-stiff, and try the lightest damping, and experiment with the settings from there.

In front, again, the replacement of a radial tire for the OEM bias-ply makes a huge difference in precision. The stock rim needs to be about an inch wider to allow the 'spread' of the radial tire bead to properly-assume the correct stance for the radial tire carcass to provide optimum dynamic characteristics.

There afre several other mods for the front end. New springs, for one. Race Tech offers straight-rate springs selected for your riding style and your riding weight, while the venerable Progressive Suspension variable-rate springs become stiffer as the spring compresses. They can also alter the ride height up to a maximum 2".

Cartridge Emulators or RICOR inserts provide a better damping than the old-style fork damper rods the VMax front fork came-with.

A fork brace helps reduce twisting of the downtubes under load, keeping 'em parallel to each-other.

Braking is a 'whole-'nother issue. Going to the 1993-'07 43 mm downtubes/sliders/triple trees allows use of sportbike calipers, as-used on the '93-'94 FZR 1000 (Sumitomo six-piston/three opposed pairs), or the YZF calipers used on 600/750/1000 bikes before the debut of radial calipers. Some had steel pistons, some were aluminum pistons, the aluminum pistons, though they are thicker metal, are reported to provide better performance. You can also contact Sean Morley for his Tokico six-piston kit, available for either the early (1985-1992) or the later (1993-'07) downtubes/sliders/triple trees.

You're not-using a front fender, no-way could I do that here in south Florida, where we have >60 inches (152+ cm) of rain a year.

A question, what exhaust are you using? Are they bolt-ons, to the stock f & r downtubes? I see the OEM exhaust ribbed collars, so I suspec that you have OEM header pipes and some-sort of aftermarket bolt-on where you are eliminating the OEM resonator and megaphones. Was that something you did, or was the bike wearing that when you acquired it? Is your bike a fully-operational VBoost? Could you show us pics of the exhaust underside, so we could see exactly what your exhaust is? Thanks.

The H-D massive nacelle is certainly distinctive, and you've arrived at a combination of mods which works for your needs. Thanks, for showing us, another way-'round.

 

[kai_Zna]

You win the "Going My-Own Way" award. Bottom line, you had an idea, you did it, and you're happy with the results.

I'm older, I need the rear suspension, my back is showing evidence of deterioration of cartilage after my 'many-years.' I have a complete FZR 1000 front end I bought, sitting, I haven't bothered to mount it because I found that a series of mods made a huge difference in the feel of the bike. The changes involved both the front and the rear suspensions.

In 'the old-days,' the chopper guys would use a 5.10" X 15" rear wheel with their rigid frames, and run really-low tire pressures (20 p.s.i.) in a 90-series profile 'balloon' tire. They got their rear suspension from the volume of air in the tire carcass. Low aspect ratio tires, and their wide wheels weren't yet available. For a historical perspective on the emergence of wide tires and low-aspect ratio construction, look at Mickey Thompson's Indy car entry.

The #1 change which makes the most-difference, in my experience, is to go to radial tires, you can get a modified rear wheel, and use a narrow front radial tire on the OEM front wheel. The important thing to-do is to have the same tires f & r. By that I mean, from the same manufacturer, and with the same tread compound. You want the f & r to 'stick' similarly, because if you don't, you'll end-up with all-sorts of weird handling issues. Also, different radial tires have different construction, and mixing different construction tires can make your bike downright unsafe! Some radial tires have a 'Zero-degree' construction, where the warp plies are at 90 degrees to the tire circumference, while other tires have oblique angle warp plies, where the wrap from the tire circumference is at say, 30 degrees. This greatly affects the way the tire handles, when you mix the two construction types, and not in a good way!

A brand-new pair of premium bias-ply tires (bias-ply tires being VMax OEM) has a smaller degree of difference to a pair of radial tires, at legal operating speeds. However, at speeds easily achieved in even only third gear, the differences in handling characteristics quickly appear, favoring the precision of the radial tires over bias-ply tires, especially evident in curves. Put 1,000 miles on the bias-ply tires, and their handling difference compared-to a set of radial tires becomes even-more noticeable. This is my own experience. The way you ride your bike may-not reveal the differences I've experienced. I tend to-ride 'enthusiastically,' and I probably see that red oil light flicker every time I put the key in the ignition.

AT the rear, I use a pair of Progressive Suspension shocks, I think the OEM shocks aren't that-bad, remember they have preload and damping adjustments, so if you're ighter, don't run the preload too-stiff, and try the lightest damping, and experiment with the settings from there.

In front, again, the replacement of a radial tire for the OEM bias-ply makes a huge difference in precision. The stock rim needs to be about an inch wider to allow the 'spread' of the radial tire bead to properly-assume the correct stance for the radial tire carcass to provide optimum dynamic characteristics.

There afre several other mods for the front end. New springs, for one. Race Tech offers straight-rate springs selected for your riding style and your riding weight, while the venerable Progressive Suspension variable-rate springs become stiffer as the spring compresses. They can also alter the ride height up to a maximum 2".

Cartridge Emulators or RICOR inserts provide a better damping than the old-style fork damper rods the VMax front fork came-with.

A fork brace helps reduce twisting of the downtubes under load, keeping 'em parallel to each-other.

Braking is a 'whole-'nother issue. Going to the 1993-'07 43 mm downtubes/sliders/triple trees allows use of sportbike calipers, as-used on the '93-'94 FZR 1000 (Sumitomo six-piston/three opposed pairs), or the YZF calipers used on 600/750/1000 bikes before the debut of radial calipers. Some had steel pistons, some were aluminum pistons, the aluminum pistons, though they are thicker metal, are reported to provide better performance. You can also contact Sean Morley for his Tokico six-piston kit, available for either the early (1985-1992) or the later (1993-'07) downtubes/sliders/triple trees.

You're not-using a front fender, no-way could I do that here in south Florida, where we have >60 inches (152+ cm) of rain a year.

A question, what exhaust are you using? Are they bolt-ons, to the stock f & r downtubes? I see the OEM exhaust ribbed collars, so I suspec that you have OEM header pipes and some-sort of aftermarket bolt-on where you are eliminating the OEM resonator and megaphones. Was that something you did, or was the bike wearing that when you acquired it? Is your bike a fully-operational VBoost? Could you show us pics of the exhaust underside, so we could see exactly what your exhaust is? Thanks.

The H-D massive nacelle is certainly distinctive, and you've arrived at a combination of mods which works for your needs. Thanks, for showing us, another way-'round.

You are right, I wasn't copying another bike when assembling "Locomotive" Thank you very much for a brilliant reply, filled with valuable information! No question about that, good progressive rear shocks, and modern 17" radial tires front and rear, will certainly objectively be far better. Especially when ridden to the limits on a track. I have ridden my Yamaha TRX850 streetfighter actively on the street with such a setup for 22 years. (Lots of winding roads in Norway, due to the mostly rocky terrain) The geometry of that bike as original was a bit "lazy", until I shortened the trail by putting on a shorter fork from a early Yamaha R6. Much sharper and more playful handling, yet still stable at 130 mph, and no need for a steering damper. My front tyres usually lasted about 3200 miIes, rear tires 3700 miles, give or take 500 miles. Funny, but front tires always lasted less than rear tires. However, I didn't always have exact same tires front and rear, without big issues. Very few ride tires to the grip limit on the street, I don't. I actually built the Vmax to try to cure my habit of speeding, I didn't expect it to be so fun to ride. So I got a bike that is perfectly OK to cruise at 45 mph, but it is undramatic to ride at 110 mph, and fun to ride actively on twisty roads...so actually, I was not very successful... My humble understanding of this "case", my modified Vmax, is that I have been lucky and hit some sort of a very unlikely "sweet spot". Hardtails is out of fashion for a reason, and they will not start using them in MotoGP... Hardtail is not an invention. But it is surprisingly fun to ride with it on the street, and surprisingly not to harsh. My main subject with this post was that replacing a front end is not so dramatic, and can actually produce very good results. And modifying is fun! There are a lot of good parts out there, with impressive engineering behind them all. But of course we must have in mind, by doing so, we take the role as designers. As I showed a picture of the modification, I had to mention the hardtail conversion. That was not the main subject. But it is an interesting find, though, the massive change in stability by "bracing" the swingarm with the rear of the main frame. No matter how sophisticated twin shocks you use, they will not be able to help a twisting swingarm much. I had read about rigid engine mounts, and aftermarket frame reinforcement bars. On my bike, I feel no need for these modifications now. So welding on a brace on the original swingarm, may cure a lot of handling issues? What is the experience in the Vmax community with reinforced aftermarket swingarms? The nacelle is just a design idea, two cast aluminium design icons brought together, the nacelle and the scoops. And it gave the bike a name; "Locomotive", as it reminds me about old Di3 diesel locomotives. Custom brackets for the front fender will be made this winter, it is too impractical to go fenderless. But the problem is at least less at higher speeds. This is really a great forum, there is a lot to learn about these fascinating bikes. As I see it, the spirit of the Vmax is not limited to 100% original bikes. It can actually be distilled. The exhaust is a Cobra 4-4 aftermarket slip ons, present on the bike when I bought it. The original downpipes is kept. Cobra is good on sound and vision ( not to noisy, nice sound ) But as I have read elsewhere on this forum that the original 4-1-2 muffler actually give more power, the days of the Cobra is about to end. My bike is all about going against the stream, so I will put on the original mufflers again. There are so many fuel to noise converters around... Having a bike with the original exhaust system is pure anarchy... When tuning more later, I will accept to loose some top-end power, by not installing a free flowing aftermarket muffler. I will put my emphasis on increasing torque in the midrange. It is a V-boost model, but the original controller is dead. I am waiting for a new from micromachines.com. I am looking forward to the first testrun! Very interesting that you have a FZR1000 front sitting. As far as I have investigated, this should be a convenient swap. With the old FZR 1000 forklegs being significantly longer than the modern superbikes of today. What is the difference in length of the original Vmax fork, and the FZR 1000 forklegs? Any other real obstacles to this conversion?

Regards,
Kai Ingvald Flateland

 

[Fire-medic]

Hooo-boy, are you in for a surprise! When you replace those pretty-but crappy-performing Cobra 4/4's, you're gonna wonder why in He-double-hockeysticks anyone would ever-think that they're a good idea! The difference in performance being better from returning to a stock exhaust is considerable! I don't know what exhausts you're thinking of running, the OEM exhaust has a lot of engineering going into it. It's heavy, but so-what? The metal is thick, as-is the chrome. They're quiet, and durable, they last a long time. It really comes-down to what you want to-spend, and what you can find for-sale. I suggest posting your possible choices on here, and see what types of input you get, before a purchase.

Congratulations on deciding to ditch the Cobras. If you go to a stock exhaust, changing your main jets 1 or 2 sizes smaller should make it run even-better, as you're probably very-close to sea level, Mikuni 150 or 147.5 (smaller #=smaller jet) will provide you with a crisp throttle response, and there is no comparison in performance between the Cobra 4/4 system and even the stock megaphones.

 

[kai_Zna]

Hooo-boy, are you in for a surprise! When you replace those pretty-but crappy-performing Cobra 4/4's, you're gonna wonder why in He-double-hockeysticks anyone would ever-think that they're a good idea! The difference in performance being better from returning to a stock exhaust is considerable! I don't know what exhausts you're thinking of running, the OEM exhaust has a lot of engineering going into it. It's heavy, but so-what? The metal is thick, as-is the chrome. They're quiet, and durable, they last a long time. It really comes-down to what you want to-spend, and what you can find for-sale. I suggest posting your possible choices on here, and see what types of input you get, before a purchase.

Congratulations on deciding to ditch the Cobras. If you go to a stock exhaust, changing your main jets 1 or 2 sizes smaller should make it run even-better, as you're probably very-close to sea level, Mikuni 150 or 147.5 (smaller #=smaller jet) will provide you with a crisp throttle response, and there is no comparison in performance between the Cobra 4/4 system and even the stock megaphones.

Thank you very much! Yes, this forum is a very valuable source for information. I learnt here that the Cobras had to go. I love the look of the Cobras that came with the bike, but I have sourced a original exhaust that will replace them. Heavy indeed, but the whole bike is heavy. Probably better to run more, and ride more enduro, if weight saving is an important issue... More power and less hassle with the police is a good combination. I still have to look out for police though, with more power... Thank you for your tips! I have decided on the challenge to increase torque and mid range power, with the original exhaust. I am after real life improvements, not bragging figures. Higher compression and adjusted squishband is a possible route. How about increasing flow by ditching Y-piece on filterbox and install K&N? Will that only give a minimal effect on high RPM, which nevertheless is limited by the original exhaust?

 

[MaxMidnight]

To brace or not to brace that is the question. I guess what you are trying to achieve is a machine that can go round corners better than the riders ability allows or the sort of riding they do?

Another question is what is the pecking order of improvements, i.e. what will give the biggest bang for the buck/ euro/ pound?

IMO solid mounts are relatively cheap compared to the other options and gives a solid framework (pun intended) for the other components to interact through.
In addition to the mounts gussets can also be added around the swinging arm mounts.

Bracing the swinging arm will reduce flex but by how much I have no idea.

There are various examples out there, an example is below plus the drawing are attached.



You can also add a ring into the drive shaft tube to give additional support.



Whilst the 15" OE tyre may offer some form of suspension I wouldn't think the 17" I have would do so well.

 

[kai_Zna]

To brace or not to brace that is the question. I guess what you are trying to achieve is a machine that can go round corners better than the riders ability allows or the sort of riding they do?

Another question is what is the pecking order of improvements, i.e. what will give the biggest bang for the buck/ euro/ pound?

IMO solid mounts are relatively cheap compared to the other options and gives a solid framework (pun intended) for the other components to interact through.
In addition to the mounts gussets can also be added around the swinging arm mounts.View attachment 73148

Bracing the swinging arm will reduce flex but by how much I have no idea.

There are various examples out there, an example is below plus the drawing are attached.

View attachment 73151

You can also add a ring into the drive shaft tube to give additional support.

View attachment 73152

Whilst the 15" OE tyre may offer some form of suspension I wouldn't think the 17" I have would do so well.

Thank you for a very interesting reply! The goal is always to improve the bike so the rider becomes the limitation That is safer as well, being able to quickly change direction without inducing wobble is never a bad feature. We don't have to use the improved capacity to increase overall speed. The trellis brace solution certainly look heavy, but very rigid. And it is a relatively easy job to do, that don't require access to machining, hence no potential for alignment problems if done wrong. Round tubes are a very stiff structure, so the weight can be reduced by using relatively limited wall thickness. The trellis looks a bit over engineered, thus more complex than really required. A brace loop of round tube, with soft transitions and good stress distributing transitions between the members, with two supports near the pivot axis of the swingarm, will do a very good job. And the effect increases fast, when the distance between the loop and the pivot axis increases. Obviously within reasonable limits, to avoid loss of ground clearance This is my opinion, based on my work as a mechanical engineer. I also agree from a engineering point of view, that making the motor a stressed member by adding stiff engine mounts, is an effective way of vastly increasing overall stiffness of the frame. But my surprising experince is that with a torsionally stiff rear end, the chassi performs very well even with the original rubber engine mounts. Indicating that focus should be kept on the swingarm. Again, thank you for nice pictures of several options!