Topic: swaping front end and rear end?

[Ouch]

I have been searching on here for a while information on swaping out a  front end and swing arm and have found lots of great info....but what escapes is the..."i did my research and found the correct ones I need not to mess up the ride..."

Question?....what is needed to know when starting a swap?.....what math angles?.......what is needed to keep in mind when doing this?.....what is dangerous to do(ie stretch the swing arm too long kills turing ability, it is like turing a cadilac on 2 wheels)....what is need to be researched?...if this goes good then this tread can be to refenece to when others want to to a swap

thanks for the input

[crazypj]

Generally, if you don't know what your doing, keep stock angles and offsets.
 Fitting just about ANY modern front end without having custom machined yokes is going to have a major effect on handling. (different offset affects trail, different height may affect rake)
You can take a mediocre handling bike and make it downright dangerous with all new 'sport bike' components that work fine to 200mph,( on a bike designed for them)
There is quite a lot of information online, spend some time reading about rake, trail, of-set, CoG, etc
 

[Ouch]

http://www.rbracing-rsr.com/rakeandtrail.html

http://www.thompsonchoppers.com/tech_tips.asp

http://www.streetchopperweb.com/tech/0602_stcp_american_suspension_rake_and_trail/index.html

Here are some great articles and calculator i found on this subject... it explains; Rake, Trail, offset, diameter, Fork length...what and how to keep the bike , when doing mods, in a safe area of measurements to be ridable...not a death machine 

[FunJimmy]

I don’t have any experience swapping out swingarms from modern bikes, so I’ll leave that to those who have, but up front isn’t as mysterious as it might sound.

Unless you’re donor forks and triple trees are way off the stock dimensions, you’re not going to make the bike unsafe to ride. Keep the triple offset as close to the stock offset and the fully extended fork length within ½” of the factory forks and the bike will behave just fine. Modern sport bike triple trees typically have less offset than the stock Honda triples from the ‘70s. Less offset will increase the amount of trail, which in turn will increase high speed stability, at the expense of agility. A small loss of agility in favor of stability isn’t a negative compared to the performance advantage of fully adjustable modern suspension.

[Stev-o]

What exactly are you trying to accomplish? If you're trying to make the CB a modern sport bike, I recommend selling it and buying a crotch rocket!

[Ouch]

....lol.....thanks for the advice, and ur right the cb will never be a modern sport bike....besides that u have any info to help in keeping mods safe?

What exactly are you trying to accomplish? If you're trying to make the CB a modern sport bike, I recommend selling it and buying a crotch rocket!

[Retro Rocket]

What exactly are you trying to accomplish? If you're trying to make the CB a modern sport bike, I recommend selling it and buying a crotch rocket!

You won't like mine then Steve....

[Stev-o]

What exactly are you trying to accomplish? If you're trying to make the CB a modern sport bike, I recommend selling it and buying a crotch rocket!

You won't like mine then Steve....

I bet I would, but you never post pics!

Plus you have a little more bike experience than the OP.

[Retro Rocket]

What exactly are you trying to accomplish? If you're trying to make the CB a modern sport bike, I recommend selling it and buying a crotch rocket!

You won't like mine then Steve....

I bet I would, but you never post pics!

Plus you have a little more bike experience than the OP.

Pics soon mate, was talking to my engine builder yesterday and also looking at a 150HP Australian Champion cb750 race bike, yep, thats 150HP....

[splitt]

Understanding rake and trail is the most important thing to understand when it comes to modifying front suspension geometry. Make sure that you have positive trail. (think grocery cart wheel) However, too much positive trail will make the steering behave slow. Too little positive trail will make the front end twitchy and could cause a tank slapper. If you're using the stock rake angle, I'd keep the trail as close too stock as possible and use move the forks up and down in the triple trees to make minor adjustments.

[Ouch]

Understanding rake and trail is the most important thing to understand when it comes to modifying front suspension geometry. Make sure that you have positive trail. (think grocery cart wheel) However, too much positive trail will make the steering behave slow. Too little positive trail will make the front end twitchy and could cause a tank slapper. If you're using the stock rake angle, I'd keep the trail as close too stock as possible and use move the forks up and down in the triple trees to make minor adjustments.

Splitt...thanks..question? what effect will putting a longer swing arm in have on rake, trail, offset, CoG...or is that only a question that will be answered once a different swing arm is in?

[OldSchool_IsCool]

With a sidecar rig, it's easy to swap front end and back end.  Just go into a left turn too hot and grab a fist full of front brake.  You'll swap ends in a hurry! LOL  Done to the extreme, you can swap top end for bottom too.

[Ouch]

With a sidecar rig, it's easy to swap front end and back end.  Just go into a left turn too hot and grab a fist full of front brake.  You'll swap ends in a hurry! LOL  Done to the extreme, you can swap top end for bottom too.

 

[crazypj]

Pics soon mate, was talking to my engine builder yesterday and also looking at a 150HP Australian Champion cb750 race bike, yep, thats 150HP....

 That's gotta be expensive on primary drives, cranks and cases?

[Retro Rocket]

Pics soon mate, was talking to my engine builder yesterday and also looking at a 150HP Australian Champion cb750 race bike, yep, thats 150HP....

 That's gotta be expensive on primary drives, cranks and cases?

Thats one of Rex Wolfenden's bikes PJ, he's been building these things for quite a while now and they are very reliable, they have the hivo chains that the Boldor's use. They look relatively stock from the outside but there's a ton of work on the inside....

[splitt]

Splitt...thanks..question? what effect will putting a longer swing arm in have on rake, trail, offset, CoG...or is that only a question that will be answered once a different swing arm is in?

A longer swingarm will not affect rake (neck angle) and trail. I assume that CoG is center of gravity. If your swingarm remains parallel to the ground (like stock) and you are staying with the same seat height, the CoG should remain the same.

Lengthening the swingarm will make the bike turn slower, but it will be more stable at high speed. That's why the Suzuki Hyabusa is stretched out lke it is. It also will require more rider input to attempt to turn on an equal radius. Shortening the swingarm will make the bike turn quicker but lose high speed stability.

By offset, are you referring to offsetting the tire so that you can run a wider rear tire?

[Retro Rocket]

By offset, are you referring to offsetting the tire so that you can run a wider rear tire?

I would say he is referring to trail changes caused by different triple clamp offset.....

[splitt]

Ahhh!!!  I didn't put that one together.

Offset trees work alright, but you are usually limited to a couple different angles. There are a few machinists out there who have custom made there own offset trees to a desired angle.

The advantage of offset trees is that you can rake the forks without altering the frame.

Just make sure that you understand what your rake and trail measurements are and where you want to them to be, before you go out and slap offset trees on your bike. Don't become one of those statistics that wanted to quickly build a cool, low dollar custom bike, then ended up in either a hospital or morgue.

[FunJimmy]

Offset trees work alright, but you are usually limited to a couple different angles. There are a few machinists out there who have custom made there own offset trees to a desired angle.

The advantage of offset trees is that you can rake the forks without altering the frame.

The reference to offset in this discussion pertains to the overall fork offset of the triple trees and is not referring to a different offset between the top and bottom triples as used by some of the chopper dudes.

The concern about overall triple offset is the effect that it has on trail measurements.

When swapping front fork assemblies from modern motorcycles to ‘70’s era Hondas the difference in overall fork offset of the modern unit is generally less than the stock Honda SOHC component. This reduced fork offset of the modern fork assembly will increase the amount of trail and alter the handling characteristics of the motorcycle.

[crazypj]

Splitt...thanks..question? what effect will putting a longer swing arm in have on rake, trail, offset, CoG...or is that only a question that will be answered once a different swing arm is in?

A longer swingarm will not affect rake (neck angle) and trail. I assume that CoG is center of gravity. If your swingarm remains parallel to the ground (like stock) and you are staying with the same seat height, the CoG should remain the same.

Lengthening the swingarm will make the bike turn slower, but it will be more stable at high speed. That's why the Suzuki Hyabusa is stretched out lke it is. It also will require more rider input to attempt to turn on an equal radius. Shortening the swingarm will make the bike turn quicker but lose high speed stability.

By offset, are you referring to offsetting the tire so that you can run a wider rear tire?

Ahhh!!!  I didn't put that one together.

Offset trees work alright, but you are usually limited to a couple different angles. There are a few machinists out there who have custom made there own offset trees to a desired angle.

The advantage of offset trees is that you can rake the forks without altering the frame.

Just make sure that you understand what your rake and trail measurements are and where you want to them to be, before you go out and slap offset trees on your bike. Don't become one of those statistics that wanted to quickly build a cool, low dollar custom bike, then ended up in either a hospital or morgue.

 You really sound like your recycling something you Googled, without actually understanding anything your spouting forth.
 Your first reply is so dumb as to be meaningless. If you REALLY want to help, stop trying to kill people

[Retro Rocket]

Offset trees work alright, but you are usually limited to a couple different angles. There are a few machinists out there who have custom made there own offset trees to a desired angle.

The advantage of offset trees is that you can rake the forks without altering the frame.

The reference to offset in this discussion pertains to the overall fork offset of the triple trees and is not referring to a different offset between the top and bottom triples as used by some of the chopper dudes.

The concern about overall triple offset is the effect that it has on trail measurements.

When swapping front fork assemblies from modern motorcycles to ‘70’s era Hondas the difference in overall fork offset of the modern unit is generally less than the stock Honda SOHC component. This reduced fork offset of the modern fork assembly will increase the amount of trail and alter the handling characteristics of the motorcycle.

Thanks Jimmy.....

[Ouch]

correct me if I am wrong...not too proud to admitt if i am....

Front fork swap......when dong a front fork swap choose a set up that keeps the rake and trail as close to stock as possible so not to alter the ride unless that is the goal

Rear swing arm...lengthing the swing arm gives greater straight riding stability but takes away from sharp turning and shorting the swing arm takes away from straight riding but adds to turning

 

[Retro Rocket]

Thats about it mate. The offset on the triple clamps on a K 750 is 60mm , the F's have a 50mm offset, i am going with the 50mm offset. An inch or maybe 2 is all you need at the rear if you must go longer, the 750's have a reasonably short swing arm so an inch or 2 won't change things too much and should add a bit of straight line stability any longer and it will slow handling down a bit. The later model K's had a slightly longer arm.

[Ouch]

Thats about it mate. The offset on the triple clamps on a K 750 is 60mm , the F's have a 50mm offset, i am going with the 50mm offset. An inch or maybe 2 is all you need at the rear if you must go longer, the 750's have a reasonably short swing arm so an inch or 2 won't change things too much and should add a bit of straight line stability any longer and it will slow handling down a bit. The later model K's had a slightly longer arm.

Thanks Retro....any other advice you can think of please add it!?!

[Retro Rocket]

Well i am using spoked wheels with mine so make sure everything lines up properly and also check the weight of the bike you are sourcing a front end off and compare it to your bikes weight, you may have to buy new springs. I have a GSXR43mm right side up front end with progressive springs, the beauty of the more modern fronts is the amount of adjustment for rebound and damping. Also use good quality rear shocks. the rear shock angle can be changed as well, a lot of guys racing 750/4's here move the top shock mount forward an inch or 2, apparently it improves the rising rate of the shock. I was looking at a couple at the weekend just like that....