Author Topic: Help me research/understand front end swap stuff (XS650) (Read 10248 times)

Scott S · « **on:** February 04, 2015, 01:14:38 PM »

I've been doing a lot of reading and searching the forums, but I have a rudimentary understanding of this geometry stuff. My eyes start to cross after a while.....information overload.

I have a '75 XS650 and I'd like to upgrade the front end. I have access to a good machinist, welder and a friend that's an engineer. But I need to narrow down the choices a bit, first.
I've seen several GSXR swaps, but they're shorter and alter the geometry a good bit. Ideally, I'd like to find something that DOESN'T require re-raking the neck.

Here are some stock XS650 specs:

Tire size: 26.1"
Rake: 27 degrees
Offset: 1.938"
Fork Length: 29.5"
Tree rake: 0.0 degrees
Trail: ~ 3.9 - 4.47 (I'm seeing two numbers....maybe different between early and later models?)

I've found some CBR 600RR forks. They're traditional (not USD). They're 45 mm, vs. 34mm for the '75 XS.
Online, I've found the CBR has a rake of 24 degrees and trail of 3.7".

I've asked the seller for fork length, steering stem length and a rough measurement of the offset of the triples (stem to triple distance).

The rake and trail of the two bikes seem close, at least with the measurements I have. How big a difference is three degrees when it comes to suspension geometry? Is that, like "Really close and ought to work great!", or is three degrees suicidal? Will it be a twitchy tank slapper or ill handling pig?

I'm not set on USD forks. Traditional but modern and beefy are fine. Can someone help me sort through the myriad charts and info online and suggest a set of forks/triples that are a good starting point? I don't mind mixing and matching. Bonus of the upper triple has handlebar mounts.

calj737 · « **Reply #1 on:** February 04, 2015, 02:07:21 PM »

If you seek traditional forks but want improved handling, install cartridge emulators, a fork brace, and a steering damper. Lots less expensive, uses your existing forks and retains all current geometry.

Scott S · « **Reply #2 on:** February 04, 2015, 02:52:52 PM »

Just received this about the CBR forks:

Length: 28.5"
Steering stem length: 7" from top of bearing seat to bottom of lower bearing seat.
Offset: 1" offset of steering stem

Those measurements "seem" very close to the XS650, but are they? In terms of steering geometry? Is this one a close match to start with?

Scott S · « **Reply #3 on:** February 04, 2015, 02:53:51 PM »

Quote from: calj737 on February 04, 2015, 02:07:21 PM

If you seek traditional forks but want improved handling, install cartridge emulators, a fork brace, and a steering damper. Lots less expensive, uses your existing forks and retains all current geometry.

Except that the 34mm forks are wimpy and there aren't emulators available for them. I may do a spacer, some HD oil and a brace but, ultimately, I'd like to do a swap. Just because.

FunJimmy · « **Reply #4 on:** February 04, 2015, 08:12:42 PM »

Scott,

This isn't all that different than the R6 fork upgrade I did on the Cafe Interceptor. What I see with your numbers is additional trail which increases stability at the expense of agility. Let's see if this makes sence. 1" shorter fork length is equivalent to approx 1° steeped rake (head angle) which = less trail, but the reduced offset of the CBR triples will provide additional trail countering the loss accrued from the shorter forks. In the end you will still have more trail that before which is most stable at speed and less likely to tank slap.

Retro Rocket · « **Reply #5 on:** February 05, 2015, 01:45:08 AM »

Quote from: FunJimmy on February 04, 2015, 08:12:42 PM

Scott,

This isn't all that different than the R6 fork upgrade I did on the Cafe Interceptor. What I see with your numbers is additional trail which increases stability at the expense of agility. Let's see if this makes sence. 1" shorter fork length is equivalent to approx 1° steeped rake (head angle) which = less trail, but the reduced offset of the CBR triples will provide additional trail countering the loss accrued from the shorter forks. In the end you will still have more trail that before which is most stable at speed and less likely to tank slap.

+1, plus, don't compare bikes with different rakes when trying to work out trail, 3 degrees difference in rake dramatically reduces trail, as does lowering the front end as Jim touched on. If you aim at keeping trail at around 4 inches you should have a nice stable ride. I have a trail converter that will help you with the guess work, PM me your email address and i'll send you a copy, all numbers in the converter can be change to suit your measurements and rake, that way at least you are getting a handler on which way things have to go to achieve a good result......

Scott S · « **Reply #6 on:** February 05, 2015, 03:40:02 AM »

Thanks, FunJimmy and Retro Rocket! FunJimmy, I was kinda hoping you'd chime in. So...the parts I listed are a pretty OK start?
I can find charts showing fork diameter and length of various bikes. I wish there was something similar with triples. That way I could mix and match to get the desired results.

Retro, I'll PM you.

FunJimmy · « **Reply #7 on:** February 05, 2015, 05:49:04 AM »

Ya, it would be nice to have a triple tree data base that's for sure. Retro's Trail Converter will be good for this. Start by inputting your stock measurements, then change only the triple offset. This will tell you how much additional trail the triples provide. Next change is fork length. Shorter forks will reduce trail. If this final trail measurments is to high you may need to look for triples with more offset.

Retro Rocket · « **Reply #8 on:** February 05, 2015, 03:09:44 PM »

Cognito Moto have hubs and adjustable triple clamps to make this all easier, they aren't cheap but they are excellent......

http://cognitomoto.com/collections/fork-conversion-parts/products/gsxr-adjustable-offset-triple-tree-conversion-45mm-50mm-55mm-60mm

faux fiddy · « **Reply #9 on:** February 06, 2015, 02:56:20 AM »

Here's is one i found a long time ago that deals with triple clamps.

http://www.ohiocaferacers.com/OCRStemSizes.pdf

And this is the one I found it just now that has other links.

http://www.dotheton.com/forum/index.php?topic=5669.0

Scott S · « **Reply #10 on:** February 06, 2015, 12:23:13 PM »

Retro Rocket.... I can get that calculator to open but it won't let me enter any numbers.

Right now, after doing some reading, I'm leaning towards FZR 600 front end. It uses the same bearings (or at least has the same upper and lower stem size) as the XS650.
They're 38mm forks and have lots of options for upgrades if I ever wanted to go that route. They use dual piston Sumitomo calipers and the discs have the same pattern as the XS (though you have to use spacers to align them).

Rake is 25 degrees vs. 27 degrees for the XS650.
Trail is 3.7" vs. 3.9"

Best part is, I can use an XJ600/Seca II top triple and get handle bar clamps. It bolts right up and they're cheap on eBay, as is the entire FZR front end.

FunJimmy · « **Reply #11 on:** February 06, 2015, 02:00:15 PM »

Quote from: Scott S on February 06, 2015, 12:23:13 PM

Retro Rocket.... I can get that calculator to open but it won't let me enter any numbers.

Right now, after doing some reading, I'm leaning towards FZR 600 front end. It uses the same bearings (or at least has the same upper and lower stem size) as the XS650.
They're 38mm forks and have lots of options for upgrades if I ever wanted to go that route. They use dual piston Sumitomo calipers and the discs have the same pattern as the XS (though you have to use spacers to align them).

Rake is 25 degrees vs. 27 degrees for the XS650.
Trail is 3.7" vs. 3.9"

Best part is, I can use an XJ600/Seca II top triple and get handle bar clamps. It bolts right up and they're cheap on eBay, as is the entire FZR front end.

Scott,

I might be misreading your post but are the rake and trail figures listed above, a comparison of the FZR600 motorcycle to an XS650? If so, this is not a relevant comparison. Rake is a factor of your frame's head tube angle and can only be changed marginally by lowering the forks in the triples or installing longer rear shocks. Trail is effected primarily by the triple offset.

Scott S · « **Reply #12 on:** February 06, 2015, 02:35:59 PM »

Well, those are just numbers I found online. The FZR swap has been done a few times on the XS 650 forum and it's one of the simplest I've found so far.

Retro Rocket · « **Reply #13 on:** February 06, 2015, 03:25:23 PM »

Hi Scott, I just opened the email I sent you and the trail converter works..? I've sent this to quite a few people and it works for them too..
Click on the box that you want to change the value in and you'll see the box change, you then type in the value or measurement to suit, don't try and back space out the existing numbers, just type in the new ones.

You can not compare numbers from another bike with different rake, different triple clamp offset and different wheel sizes, all these factors are critical in determining the final trail number, so coming from a different bike means nothing, as all these measurements are different, This is a fact and you need to change your understanding of how front end geometry works... Just remember, most of the front end conversions i've seen done on the internet are NOT DONE correctly, they are a mash up of parts or the parts from a different bike just stuck onto a new bike

Scott S · « **Reply #14 on:** February 06, 2015, 07:33:01 PM »

I get a notice saying that my Office subscription has expired, so that's probably why I can't get the calculator to work.

And you're right: I don't have a complete understanding of how this all works. I mean, I know what rake, trail, etc., all mean. I understand that the neck of one bike may have a different rake of another. That triples have different offsets. Fork lengths and assembled height make a difference. I get all that. Rudimentary, but I get it. That's why I started this thread.
But what I don't get are how to take the numbers I find online and extrapolate them between two bikes. I've Googled and searched forums and looked at charts and bearing swaps and so on.
I can't always find the information I need online, such as a particular models fork length or neck rake.

How can I find the numbers I need to compare, say, the FZR 600 to the XS650? If someone can help me by plugging this stuff in I would greatly appreciate it.

FunJimmy · « **Reply #15 on:** February 06, 2015, 08:28:57 PM »

Scott,

Forget all the other donor bike out there. All you need to know is the XS650 geometry. Got it? Now consider what effect on the XS650 geometry a slightly shorter fork will have. Figure that our first and get a clear understanding of it. Ok, so now you know what a slightly shorter fork will do to your bike. Regardless of the donor bike the forks came off.

Next calculation will be the offset of the considered triple trees. Compare the effect of different offsets as they relate to your XS650 geometry. Regardless of the donor bike the triples came off. Understand? Consider other triples with the same fork diameter to achieve the best compromise. You don't have to use the triples for the same bike the forks came off as long as the fork diameter is comparable.

Retro Rocket · « **Reply #16 on:** February 06, 2015, 08:55:44 PM »

I just bought a set of 41mm forks for one of my bikes, I measured the free standing length of my stock forks then started looking for forks with a similar length, when I spotted the forks I was interested in on evil bay, I sent a message to the seller asking him if he could measure the free standing length for me, which he did, the forks I bought were 5 mm longer than my stock forks so I bought them as I can work with that, i'll just drop them 5 mm through the clamps. I decided, based on the stock K model geometry, that I wanted a 1 inch longer swingarm, which will add a little stability at the rear, to match that at the front I would like a little more trail than stock, I used the converter I sent you to give me around 4 inches of trail and it gave me the offset I need. Do you know anyone with Microsoft Office on their computer..? That calculator makes it easy, taking out all the guess work...? You really can't compare anything until you know what rake trail and offset your yammy has, then those same numbers from the donor bike, its very rare that a straight swap can happen if you want to retain the stock handling traits. Can you download a trial version of Office< I still use office 2007, ..? Keep asking questions mate, thats what we are here for..

This says its a free version of office 2007 if you are interested,

http://getintopc.com/softwares/productivity/office_2007_download/

This one is a trial version, 60 days....

https://2acc1-downloads.phpnuke.org/en/c63172/microsoft-office-professional-2007

bwaller · « **Reply #17 on:** February 06, 2015, 09:21:59 PM »

Scott, just as a rule of thumb figure 1 degree change of rake for every inch up or down, front or back. For example if you lower the front an inch for shorter forks, rake is reduced to 26d. Consider this is for a wheelbase of 55.5". I'm not sure what the wheelbase is for the XS650?

The CBR is fairly typical for sportbike rake/trail of that era. With my recent experience in steering head angles I think it wouldn't hurt the XS at all to lower the front a bit if that's what you want. Just decide what fork you want to use and keep track how the front height changes. As the guys mentioned forks can sit proud of the top clamp and give you adjustability that way too. Then finally by whatever means (calculator) determine the clamp offset you need to settle into that 3.75-4" of trail.

I should have read your whole thread, hope I'm not duplicating.

Scott S · « **Reply #18 on:** February 07, 2015, 04:49:49 AM »

OK, here's what I've found so far:

Wheelbase: 56.5" (1,435mm)
Weight: 467lbs
Tire size: 26.1"
Neck Rake: 27 degrees
Fork length: 29.5"

Tree rake: Now I'm confused on this. I find measurements of 0.0", but there's obviously and offset on the triple tree; in relation to the steering stem and the centerline of the hole the forks pass through. I find an "OFFSET" number of 1.938". Are they referring to the tree rake?

Trail: Again, I find two numbers.... 3.9" and 4.47".

I found this diagram, too.

Scott S · « **Reply #19 on:** February 07, 2015, 04:55:45 AM »

Wait...I think I get it.
The triple tree has no rake of it's on. The forks run on a plane parallel to the steering stem. The offset is 1.938", meaning they sit that much "forward" of the centerline of the steering stem.
The rake is 27 degrees and comes completely from the angle of the steering head on the frame. The triples don't add/subtract any additional rake.

bwaller · « **Reply #20 on:** February 07, 2015, 06:51:42 AM »

Right on Scott.

Here's something to consider. This was raced by Mick who did well with it. Denis is also a friend of mine and has done some stuff for me and is a real craftsman. Don't hesitate to ask him if you have any inkling...

http://cmrracingproducts.blogspot.ca/2014/07/for-sale-to-good-home-vrra-championship.html

Scott S · « **Reply #21 on:** February 07, 2015, 07:31:36 AM »

A friend helped me put the XS650 and FZR numbers into the calculator. I do NOT know the FZR tree rake, if any.
That said, we came up with:
XS650 trail: 4.47" or 112.91mm
FZR600 trail: 3.92" or 99.58mm

Scott S · « **Reply #22 on:** February 07, 2015, 07:43:07 AM »

The XJ600/Seca II top triple has handle bar mounts and is a direct bolt on for the FZR. That's how a lot of the FZR guys add handle bars.

Is it safe to assume that the entire triple from the Seca II would work with the FZR conversion? Or better to go with the FZR lower?

FunJimmy · « **Reply #23 on:** February 07, 2015, 08:11:26 AM »

Quote from: Scott S on February 07, 2015, 07:43:07 AM

The XJ600/Seca II top triple has handle bar mounts and is a direct bolt on for the FZR. That's how a lot of the FZR guys add handle bars.

Is it safe to assume that the entire triple from the Seca II would work with the FZR conversion? Or better to go with the FZR lower?

It's safe to assume that the entire Seca triple trees would work.

Are you sure these fork options are worth the effort?
They're basic, non-adjustable forks. If I where going to this ammount of effort I'd look for fully adjustable forks. There are some nice (cheap) Triumph Daytona front ends on FeeBay. Daytona forks are 43mm so triples from other manufactures are an option too.

Scott S · « **Reply #24 on:** February 07, 2015, 10:27:18 AM »

Hell....it was hard enough for me to figure out these numbers. Start adding in triples from other manufacturers and stuff...
I actually enjoy research and shopping around, but for some reason this stuff just makes my eyes cross.

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Author Topic: Help me research/understand front end swap stuff (XS650) (Read 10248 times)