78' CB750 Front Swap

Cody.linhart said:
With what my numbers are looking like, I'll need to do a new stem and triple tree to get some decent offset. That and some new bearings and I'm off to a good start!


Sent from my iPhone using DO THE TON
Click to expand...

What's your plan for a front wheel?
Narrow glide?


Sent from my iPhone using Tapatalk
 
This is a subject that should be a fully acceptable mod by now... haters gonna hate ;D

Find the stock geometry and hold to it as close as you can. if your going to go race the bike your probably gonna loose, the mod is a great mod for cruising and some mildly aggressive riding with better turn in, more grip and braking than the frame is designed for so plan to gusset or weld in knife gussets (L V T shape steel plates) and you can grind it back to look stock after welding in.

Get advice from someone who has done the swap or like I said hold geo and don't lower the front without lowering the back...R6 setup would of been better... R6 clamps after 08 have a 40mm offset 24/96 R&T so very steep and pushing the limit on trail nearing 4 inches the forks are about 15mm longer than the R1
 
Tune-A-Fish said:
This is a subject that should be a fully acceptable mod by now... haters gonna hate ;D

Find the stock geometry and hold to it as close as you can. if your going to go race the bike your probably gonna loose, the mod is a great mod for cruising and some mildly aggressive riding with better turn in, more grip and braking than the frame is designed for so plan to gusset or weld in knife gussets (L V T shape steel plates) and you can grind it back to look stock after welding in.

Get advice from someone who has done the swap or like I said hold geo and don't lower the front without lowering the back...R6 setup would of been better... R6 clamps after 08 have a 40mm offset 24/96 R&T so very steep and pushing the limit on trail nearing 4 inches the forks are about 15mm longer than the R1
Click to expand...

He is good on offset if he keeps to 17's, and I think the numbers are negligible for the swap. Tune I don't think this bike is for seriously aggressive riding, more of a joyride from what I gather. It's doublful the frame is ever going to see intense stress.
 
The frame is less concern. It's the stator cover he should be worried about. That's what will hit the ground before he ever reaches the chicken strips. These motors are really wide. The stator cover hits at the outer edge of the strips in stock trim.
 
deviant said:
The frame is less concern. It's the stator cover he should be worried about. That's what will hit the ground before he ever reaches the chicken strips. These motors are really wide. The stator cover hits at the outer edge of the strips in stock trim.
Click to expand...

So you have done this mod? Learn your bikes limits, this never was a moto GP bike and never will be. Have you raised yours up so you can get your shoulder slider down yet? lol If I was gonna race club I would remove the stator and run a series of litho's and run a Dewalt sticker lol

All of the old 70/E80's bikes have the stator out in harms way and why the mini crash was designed... I ride Harley's and the floorboards toss sparks all the time not because I don't know the bikes limits but because I like the sound lol

Get off your horse on this one... lots of ways to raise the R1/6 mod and not break the bank hell I just had a top clamp made that raised my GSXR front for the KZ1R right back to stock for under $200 my rake and trail are now mac daddy... I got a stem from Devin and pushed it in myself saving there too... you cant send a stock front end off to be rebuilt with progressive springs, new stanchions,, build the brakes up with double disks from an F and even come close to perf and cost.

Sorry Eric but... All the haters of USD's should just not do it and shut the fuck up 8)
 
I don't understand the stator comment, a fraction of an inch of fork length, and a less that a half inch if wheel radius ( a 120 tire up front has a larger sidewall) results in less than .75 of an inch difference up front. You really see that as a make or break for lean angle? I bet in reality it's less 5°, and no "Sunday rider" would be the wiser to the difference.
 
jag767 said:
I don't understand the stator comment, a fraction of an inch of fork length, and a less that a half inch if wheel radius ( a 120 tire up front has a larger sidewall) results in less than .75 of an inch difference up front. You really see that as a make or break for lean angle? I bet in reality it's less 5°, and no "Sunday rider" would be the wiser to the difference.
Click to expand...
The whole premise of the thread was: any advice on what needs to be considered to go with the swap. That's one of the things that should be considered. So is exhaust placement. As is preload, compression and rebound. Is there enough room in the fork adjustments to get where it needs to be?. There may be other things that we haven't brought up. If that's all the difference, then my point about the stator is moot and I accept being wrong and we move on. No hate and every hope the swap is a good one. But, I've also ridden a lowered CB750, so I have at least an inkling of how poorly they respond to it. It's a wide, heavy pig. It needs a little extra muscle in it's legs to act right- Sunday rider or not. Maybe the R1 or R6 are the only legitimate swaps for these bikes that don't negatively effect handling.
 
deviant said:
The whole premise of the thread was: any advice on what needs to be considered to go with the swap. That's one of the things that should be considered. So is exhaust placement. As is preload, compression and rebound. Is there enough room in the fork adjustments to get where it needs to be?. There may be other things that we haven't brought up. If that's all the difference, then my point about the stator is moot and I accept being wrong and we move on. No hate and every hope the swap is a good one. But, I've also ridden a lowered CB750, so I have at least an inkling of how poorly they respond to it. It's a wide, heavy pig. It needs a little extra muscle in it's legs to act right- Sunday rider or not. Maybe the R1 or R6 are the only legitimate swaps for these bikes that don't negatively effect handling.
Click to expand...

I'm sure the cartridges could be replaced with a stiffer setup if indeed they cannot be adjusted enough, however I doubt that is needed. It's highly unlikely to ride any worse than stock, might wind up a bit better depending on the rear suspension that goes with it. Generally speaking, newer suspension is much improved from 1970's tech.
 
You assume he is leaving the bike stock, but its stripped down to the frame right now The aluminum rims alone make a big difference. I bet the bike is 50 pounds lighter when he is done with it.
 
deviant said:
I'm not assuming anything. It's funny how people can accuse and criticize others of making assumptions while making assumptions themselves. Just putting data down that someone building a bike might want to consider, especially when they're making suspension choices. I don't want to assume the guy is 150 lbs or 300 lbs, either. But it's something to consider when making these decisions. How heavy are the USD forks compared to stock? I know at least two of the bikes I converted, the USD was heavier. Where's he losing the weight? How much does a CB750 engine weigh? Or the frame? Where exactly is he going to drop 50lbs, because that's a lot of weight to lose? That's nearly 10% of the total mass. People are also suggesting he gusset the frame too, which adds weight. It was suggested that he match an R6 swingarm with the R1 front end. Which is heavier? A CB 750 has a 5 gallon tank, how many gallons is the R1. We haven't mentioned wet weight yet. 6 lbs per gallon.
No, but rims are a factor in the handling characteristics of a motorcycle. They also factor into how much breaking power he needs to stop the bike. No one has gotten into the part about converting to dual rotor. But ya know, no one has offered any thought as to what the unsprung weight actually is, either. Obviously, a 1978 CB750 could only be improved on braking, even if he goes with one floating rotor and dual pot caliper. Just a thought.

I bring up concern over lowering a motorcycle and now I'm a hater of USD shocks. I provide a weight comparison, and now I'm making assumptions about what the OP is or isn't going to do with his motorcycle. Sorry fellas, just bringing up things that someone building a motorcycle should consider when converting the entire suspension; or building in general.
Click to expand...

You're turning this into a pissing contest. Anyone can easily go through every component of every system and cast doubt, that's not a sign of knowledge, just fucking annoying. So go ahead and question everthing on the bike, by the time you're done he'll be riding the fuckin thing.

Seacrest out.
 
clem said:
Out of curiosity, what are the trail numbers for the stock 19" and a new 17" wheel with this new setup?

Sent from my SAMSUNG-SM-G920A using DO THE TON mobile app
Click to expand...

stock cb750 trail is 4.49"

r1 fork length with a 120/70/17 tire is 3.79" if custom triples are used to match stock offset.....or 4.99" if using the r1 stock triples. none of which accounts for any change in neck angle from the reduced tire diameter with the 120/70/17 tire. I wouldn't call this "close"

to match stock trail with the 17" tire and not accounting for any minute difference in neck angle, 38mm offset would be identical to stock geometry with the r1 front end.

This is why I "overcomplicated" my previous post. Because I've done this over a dozen times and do the math for each individual bike/project before just tossing parts on that look cool.

additionally, those bringing up the difference in weight from a cb750 and an R1.....once the bike is mocked up to how it's actually going to be when finished, it's not hard to weigh it and call racetech to talk spring rates and fork oil weight/amount. They're actually extremely helpful folks.
 
focusinprogress said:
stock cb750 trail is 4.49"

r1 fork length with a 120/70/17 tire is 3.79" if custom triples are used to match stock offset.....or 4.99" if using the r1 stock triples. none of which accounts for any change in neck angle from the reduced tire diameter with the 120/70/17 tire. I wouldn't call this "close"

to match stock trail with the 17" tire and not accounting for any minute difference in neck angle, 38mm offset would be identical to stock geometry with the r1 front end.

This is why I "overcomplicated" my previous post. Because I've done this over a dozen times and do the math for each individual bike/project before just tossing parts on that look cool.

additionally, those bringing up the difference in weight from a cb750 and an R1.....once the bike is mocked up to how it's actually going to be when finished, it's not hard to weigh it and call racetech to talk spring rates and fork oil weight/amount. They're actually extremely helpful folks.
Click to expand...

Here's a novel concept, instead of everyone having fun explaining what's wrong, fucking explain how to make it right by the simplest means. And if you can't explain it simply, shut the fuck up, because you have no idea what you're talking about (paraphrasing Einstein).
 
I believe part of the equation was answered in previous posts when it was said to get triple clamps with the correct offset. I guess we could nominate jag676 as DTT mechanic of the month and fly him to the OP's house to do the install for him.
 
when are the dic pics going to start so y'all can get this over and done with
 
You must log in or register to reply here.

DTT Light or Dark

  • DTT Light
    • www.jadusmotorcycleparts.com
    www.lostapostle.ca/
    www.sparckmoto.com

    Spread the Love

    Back
    Top Bottom