Forks & brake caliper mounts

A general question for anyone who has swapped out the forks; the bottom fitting on the GRiSO Showa forks is for the Brembo radial mounted brake calipers.

If you swap out the forks for another set, maybe a different manufacturer but the bottom mount is for radial brake calipers are the mounting bolts going to be specific to the brake caliper manufacturer & model or is there a 'standard' dimension ?

Put another way; if you want to swap out the forks from another bike to upgrade the GRiSO's Showa's. Do you have to fit whatever brake calipers went with those forks ? Or can you change out the lower fitting from the Showa's to the replacement forks ?

If you're looking at the Aprilia line of machines & considering swapping out the forks is that the beginning of the project that leads to replacing the brakes as well ?


Hey it's cold, the bikes in the shed, it's Friday & I'm enjoying a beer or 3. So just wondering / dreaming..

There are several things to consider but generally speaking if the forks you are using come off a bike with 320mm discs then the calipers will be fine.

There are a few other things to consider though.

If you look at the front of my bike f'rinstance.....

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You'll notice that it has a different mudguard. That's because the Guzzi mudguard mounts aren't different to those on the RSV-4 which is what the forks came off. Making up some little mounts to make it work is easy enough but I just opted to go full wanker and get a CF guard because I could!

Now the forks are also slightly wider at the bottom yoke and slightly smaller at the top. This required boring of the bottom yoke and the manufacture of some shims for the top. Once again not a big deal but it's something you should be aware of. The Showas used on the GRiSO are the same diameter top and bottom.

Why did I do this? Slightly greater rigidity mainly, although that is scarcely a problem with the Showas. The Matris internals swapped straight over so that wasn't an issue and partly it was because I'm a wanker and like gold forks!

I also had a set of Ohlins I was going to play with but at the end of the day I on sold them to another Gheto dweller. Just let it be said I'm happy with the way my bike handles. I'd like a longer rear shock with a slightly lighter spring but that can wait for its next rebuild when I'll get Laurie to extend it a bit.

Pete

The Showa 43mm fork are a good base to start from, with proper internals (like Matris) they can be made equal to or even better than a set of Ohlins.

Chances are, if you buy a set of forks off a better (?) bike, it will likely be a sports bike that is approx 50kg lighter than a GRiSO. You will definitely need new springs.
Also, there is no guarantee the damping will be suitable to your needs, a re-valve may be required.

But I like gold anodized too. Problem with the Bellagio is fork length so I ended up with silver 43mm Showa's off a MultiStrada 1000DS

Thanks all.

Ghezzi, Usedtobefast made a comment that has stuck with me; about getting a set of Showa's from a cbr 600 r and working with that on the bench. Going the Racetech route, new springs & a kit with a variety of shims & a chart indicating for a race set up use this shim stack, for a sport tourer use this set up etc.

This gives you the option to still have a ride able machine & yet figure out different combinations.

Which is appealing to me as with kids, a business, a house & property to maintain & I'm slow. All too often I don't get back to a project for months.

Ebay has a variety of Showa forks which surprised me at how resonable the prices go for. Of course you don't know if they have just been swapped out for others or are damaged.

Most Guzzi's have longer forks than sports bikes.
You would have to measure their lengths from axle to top.
I found the Multistrada 1100 forks were same length as the Bellagio stock forks.
When a Multistrada 1000 DS front end was up for grabs on ebay, I checked the specs for both model Ducati's.
Everything appeared the same but the 1000 DS forks were actually 20mm shorter. I had already lowered the front 13mm via changing front wheel sizes.

My Aprilia RS500 = 720mm
Multistrada 1000 DS = 780mm
My Bellagio (stock) = 800mm

I would target a 2006 or 2007 Suzuki GSXR 600 or 750 fork. Length is 738 mm (29"), center line of axle to top fork cap. What's a GRiSO? (Yes too lazy to go to the garage, lift bike and measure. )

That's if you want your "experiment away" fork.

Took a quick look at US eBay Motors, several on there, $250, $320, $350, $400, and on and on.

One set had Ohlins internals, one had Racetech valving.

If you look at it as a self paced mechanic class ... you pay $250 ish, plus whatever kit you are going for, plus seals, bushings, oil, heavier springs?, etc.

I've been tempted to do that and compare to my el'cheapo self revalved stockers.

Here's a link to some of the technical videos that I've been watching to learn more;

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A bit geeky on occasions but gradually the fog of incomprehension is lifting.

Nobleswood wrote:

Here's a link to some of the technical videos that I've been watching to learn more;

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A bit geeky on occasions but gradually the fog of incomprehension is lifting.

Thanks Nobleswood, This is a great source of suspension tuning info

Happy to share

He does talk a lot about track type tuning which is academically interesting for me. But I’m searching for the videos that cover riding on ‘goat tracks’

Keep posting your inspiring race pics; always good to see in our northern winter.

Here's one more for you;

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Titled 'fork manipulation & fork geometry' which relates to where this thread started for me ; what are you doing to the rake & trail when you change forks.

Got to measure the GRiSO forks, front end off the ground, center of axle to top of red fork cap ( not the top of the nut, top of the lip ) Right fork 738mm. Left fork 736mm.

So that would be the same figures as for the GSXR 750 / 600  2006 - 2007 year models.

How can you find the specs for the fork length on different bikes ? I haven't had much success looking that up.

I have my GRiSO & 2004 V11 Sport up on blocks at the moment & was thinking of replacing the damper rod Marzocchi's, on the V11, as we have been discussing, with the GSXR forks. Measured the fork length just now at 775mm.

Nobleswood wrote:

How can you find the specs for the fork length on different bikes ? I haven't had much success looking that up.

Easy, wonder on down to the local used bike lot with a tape measure in hand.
You only need to assist 'topping out" of the fork by lifting the right bar with one hand, measuring the fork with the other.

Hadn’t thought of that

The Suspension guy had me ‘roll’ the GRiSO up onto the kickstand to get the free length. That had a few ‘puckering ‘ moments!

Nobleswood wrote:

...The Suspension guy had me ‘roll’ the GRiSO up onto the kickstand to get the free length. That had a few ‘puckering ‘ moments!

I watched a guy on a crotch rocket do that once. Pulled head first into the curb, lowered the side stand, got off the bike and leaned it into himself until both wheels were off the ground, pivoted the bike 180° on the kick stand and settled it down facing the street. Freaked me out. I kept waiting for the side stand to snap like a broken bone.

Crotch rockets are light and well balanced, do it all the time.
Try it on a Harley and you're likely to blow ya phoofoo valve.

Pete,

Did you note the free length of the RSV4 forks of yours & the year ?

Watching the Dave Moss video on Rake & trail he made a comment that I've been wondered about. He's saying that within the same tyre rated size there is quite a difference in circumference & hence diameter. Now considering that we talk about dropping or raising the forks to change how the bike steers into a corner, by reducing or increasing the rake, often by mere milimeters. The change in tyre, sorry tire, diameter is going to have a similar effect.

This is probally only going to be noticable to those guys with a dedicated track bike but I was wondering if anyone had noticed, experienced that ?

tyre
/ˈtʌɪə/

noun

noun: tyre; plural noun: tyres
a rubber covering, typically inflated or surrounding an inflated inner tube, placed round a wheel to form a soft contact with the road.


tire
/ˈtʌɪə/

noun: tire; plural noun: tires
a corruption of the word tyre, used in the USA and Canada.

A change from tired tyres to new tyres will give an increase in diameter/circumference, but the average sphincter couldn't tell the difference. A front tyre change would actually raise the front ride height, increasing both rake and trail, making the steering slower.

The big improvement will be in the profile, giving the opposite feeling of the bike steering quicker or tipping into a corner easier and smoother.

Back in 2007 I bought a new Ducati that came with Pirelli Rosso whatevers (?). When I changed to the then just released Michelin Pilot Power 2CT's, the tyre tech said. "Be careful, it will turn in a lot quicker with that tyre".

The numbers were still 120/70/17 on the sidewall, to the naked eye it didn't look no different, but bloody hell, first round-a-bout it stumbled for the gutter like a drunk.

I suspect all performance street tyres now have a similar contour to their profile.

So the change in rake /trail from increase or change in diameter is small enough that it can be negated by the profile on a fresh tyre.

Your bike will always feel better for numerous reasons with a new set of tyres, however;

As this thread is more about changing forks (and possibly triple clamps), the possibilities are endless.
How long is a piece of string?

General rule of thumb (IIRC) with your average sports bike (short wheelbase):
1. Raising the rear ride height by 30mm (measured vertically from rear axle), will decrease the rake by 1 degree.
2. Lowering the front ride height by 25mm (moving forks UP through the triple clamps) will decrease rake by 1 degree.

2019 Panigale V4R - rake of 24.5* and 100mm trail (narrow handlebars)
GRiSO ................ - rake of 26.3* and 108mm trail (wide handlebars)
Street Triple 675R. - rake of 24.3* and 95.3mm trail
Bellagio .............. - rake of 28.0* and 95mm trail (with 18" front wheel). These are theoretical figures taken off the design board, and are equal to the suspension being fully topped out.

Dropping 6 lines on the GRiSO forks I hear does wonders for the turn in. I estimate rake to be 25.8*

My experience is all with the Bellagio, my changes were calculated using Tony Foales suspension kinematics program and then physically measured using digital building trade equipment.

By using a modified Matris R (GRiSO) rear shock, rear ride height was increased approx 60mm.
Changing to a 17" (BST) front wheel lowered the front 13mm, and pulling the stock forks up through the clamps also by 13mm.

Rake was measured at 25.something* (static sag plus Bellagio's longer wheelbase compared to sports bikes would account for less than a 3* reduction in rake). However, trail was now like 72mm. Steering was very light and it should have shaken its head like a rabid Pitbull on a kitten, but Bella always behaved and never got out of shape.

Bellagio triple clamp offset measured 65mm (centre of steering to centre of forks). My research led me to believe Multistrada 1000 DS 43mm Showa inverted forks were the same length, and the T/C offset was only 36mm. But when the forks turned up they were 20mm shorter and 2kg lighter. Other things to consider were the different thickness of the top triple clamps. So I ended up with a total drop in front height of 31mm.

Rake is now in the low 25* region and trail about 105mm. Steering/turning is super fast for a Guzzi, aided by the carbon fibre wheels, but I prefer the feel of lighter steering with less trail. All up, it is on par with a Triumph 675 Street Triple R, for change of direction in the twisties. Bella is 200kg wet.

I just changed my signature to this quote from Ghezzi & Brian;

Cheers Ghezzi

Found this;

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&

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The beautiful part of Guzzi being such a small manufacturer is, they rarely request a parts supplier to make unique and specific, generic items such as brakes and forks etc.

Guzzi would seek out the cheapest components available from say Brembo.
320mm discs for example, have been fitted to Ducati, Aprilia and also Guzzi for years.
It turns out the same Brembo part # is used from the 916 thru to some of the current model Ducati's.
Same diameter, same offset, same bolt pattern leads to wheel designs that may have different spoke patterns and made of lighter alloys, but the wheels will use the same hub design for discs, wheel bearings, axle etc.

These same wheel/disc combo dimensions require fork designs from either Ohlin or Showa, to have the same caliper mounting locations and axle hole size. And so the mass production (cheap) cycle continues.

Fork tube outer dimensions (triple clamp holes) may vary, and stanchion tube lengths WILL vary, but many of the other dimensions will be compatible with a whole range of other brands and models.

I have a 2009 Bellagio fitted with;
Matris shock for a GRiSO, no biggy there, just longer.
Brembo calipers off a Ducati 998R. These are the greatest caliper for axial mount forks, they have individual pads per piston and give exceptional bite,power and feel.
BST front wheel for a 1999 Aprilia RS250 (same as all Ducati from that era) except its 3.75" x 17"
later came a Ducati Multistrada 1000DS forks and triple clamps, BST wheel and 998R calipers still fitted perfectly.
R1 Yamaha radial (Brembo) master cylinder.
Currently looking at a mudguard off the new Kawasaki Z1 replica to suit the Showa forks for a retro look.

Each wheel fitting may have required slightly different axle spacers and I had a new triple clamp centre bolt made as there was no compatibility between lengths and steering heads bearings.

I have always found the easiest way of researching compatibility is to take my tape measure and vernier calipers down to the local bike shop and ask the manager if I can measure some of his 2nd hand stock.

Starting point for me was measuring the distance between the discs, then google research .........

Yesterday took the forks up to Jake my suspension guy. He's been good enough to agree to work on the suspension & teach me as he goes. Having someone look over your shoulder is not always appreciated but so far so good.

The forks surprised me by how good they were internally; no sludge, nothing worn or corroded. The oil was relatively clear & didn't smell.

The spring was linear, I had assumed it was going to be a progressive version with a top out spring.

There were no markings on the spring to give a clue to it's strength. I know from setting the sag I need a stronger spring. Sonic springs online chart recommends a 0.95 kg/mm spring as I weigh 83 kg & am not an aggressive rider, ie don't brake hard.

So trying to find what the spring rate is currently I came up with this;

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The space between the upper nut & the lower on the threaded rod was 30mm. Turning on the scales set it to zero & then when I pushed the bar & spring down to the lower nut I got a measurement in kg's. Did this 20 times, did some calculations & came up with a figure of 0.866 kg/mm.

I knew the OEM springs were considered soft but this soft ?

More on the valving soon.