R100gs- 4 pot caliper mod

[barny]

Hi all

I have just bought a R1100RT front LH caliper and was wondering if anyone who has carried the same mod and rebuilt their caliper happened to have a spare set of seals/rebuild kit remaining from their installation. I am happy to split the cost down the middle + postage, before I go down the avenue of buying a full set and having half unused myself.

I have already gone with the HE disc, braided hose, TRW pads and rebuilt standard caliper (stage 1) but would like to try the 4 pot to compare (stage 2)

regards
Barny

 

[ChasF]

I have had a K1100 4 pot caliper on mine with the standard disc and standard 13mm master cylinder. I would say that the braking performance is about the same as the OE caliper but the feel is more wooden.

 

[Beemerboff]

I tried the six pot conversion on my GS and a my G/S came with a four pot and the results results were similar to Chas's.

Part of the problem is in the leverage in the bell crank lever itself - modern radial master cylinders have twice the mechanical advantage.

The other is the ratio , MC to caliper and few alternative calipers improve this. A 12 mm M/C will.

So you end up with the same pressure being applied to a larger pad, which reduces the contact pressure in pounds per square inch and results in little to no gain and the braking force.

Modern HH pad materials need to get hot to work their best and the larger lightly loaded pads run cooler so it is easy to actually go backwards, and some have found that the stock G/S caliper actually work better than the four pot.

Nice flexible Teflon brake lines will usually remove the wooden feeling at the lever and give a bit more feel, and they are easy to find, usually with a protective / decorative SS mesh sheath over the Teflon.

 

[ianboydsnr]

I had a modern four pot from a k1200 on mine, With the standard disc, worked pretty well.

 

[cookie]

I had a 4 pot on my R100PD, it was almost as hopeless as stock. I fitted HE 320mm disc and stock caliper, which is a decent improvement, but in no way modern standard of braking. TBH if it was, you'd twist the puny forks out of the yokes anyway

I've ridden my friend's G/S with stock disc and 6 pot billet caliper and that was surprisingly good. Possibly slightly better than my G/S with HE kit.

 

[Beemerboff]

Actually, the R100 GS has a pretty decent set of stout forks, and with a set of HPN inserts perform as well as most current ADV bike forks, particularly if you have them dialed in with a stock GS Ohlins at the rear.

It is the G/S which has the puny unbushed 36mm fork with the piss weak flat top plate, but even they can be upgraded with a billet top triple, a SJ type tubular lower brace, and nice soft springs matched with a soft 400 lb spring on an Ohlins at the rear.

That billet six pot probably has six small pads on each pot, the old six pots with one large pad are history, for a good reason.

I have a well worn 320mm floating disk my G/S and as a replacement I am in the process of modifying a 320mm ten spoke wave floater intended for a KTM to suit the stock G/S centre .
Should work out around a third of the cost of the HE kit, as I already have the bracket to relocate the caliper, and I think wave floater will work better too.

 

[cookie]

You can stick whatever inserts you like inside them, but that will do nothing to stop them flexing and twisting when an effective single disc brake is applied hard.

 

[Beemerboff]

The GS is a soft roader, and was fitted from the factory with a 90 mm wide 70/30 semi off road tire.
If you use the bike as it was intended and fit similar tires , or indeed any 21" tire they simply wont have enough grip to flex the GS forks , which incidentally are only 1mm smaller than the forks fitted to Moto GP bikes.
So perhaps you should be better writing to Ohlins and Marzochi and telling them they don't know what the are doing,I am certain they would be interested in your special knowledge, but make certain you enclose all your engineering calculations which show that they are wrong!

 

[ChasF]

The GS is a soft roader, and was fitted from the factory with a 90 mm wide 70/30 semi off road tire.
If you use the bike as it was intended and fit similar tires , or indeed any 21" tire they simply wont have enough grip to flex the GS forks , which incidentally are only 1mm smaller than the forks fitted to Moto GP bikes.
So perhaps you should be better writing to Ohlins and Marzochi and telling them they don't know what the are doing,I am certain they would be interested in your special knowledge, but make certain you enclose all your engineering calculations which show that they are wrong!

So what causes the bike to lurch violently to the right when I really slam the brake on - the tyre squeals but doesn’t normally lock. I’ve always thought it was the forks flexing.

 

[mikeyboy]

I would say fork flex,
A decent bridge yoke would sort but worth checking the bushes etc first

 

[Beemerboff]

My GS has a six pot, EBC HH pads, Kyoto disk, a 11mm master cylinder, and a SJ cast lower brace on the 42mm forks, and with Mitas E 08s I dont detect any lurch to the right under full braking.

Not that I have much call for emergency braking anyway, in traffic free South Australia.

As Mikey said, your problem is probably elsewhere, worn fork bushes, wheel bearings, steering head bearing, or your frame may have a slight twist.
Or a combination of any or all of the above.

The unbushed 36mm forks on my well braked and braced G/S have done 460,000 hard km and are understandably a little worn, but if there is any pull to the right it is small enough that I automatically compensate for it, so to me it is not noticeable.
But it probably does happen.

 

[ChasF]

I would agree that a better fork brace may reduce the effect of heavy braking on the forks, but to suggest that the great long, gangly forks don’t flex because they’re similar in diameter to forks used in motoGP is daft.

 

[solidstate100]

dont forget Moto GP bikes are all USD forks, which is a fundamentally stiffer set up than ancient long travel off road type forks. Just sayin...

 

[Beemerboff]

Why don't you guys spend a little time on google and find out something about Moto GP forks and suspension in general.
FWIW Moto GP forks are designed to flex , they are the only suspension when the bike is 55 degrees over!

At the performance level of road bike forks , at any given performance level USD forks are heavier and more expensive to make than RWU forks.

The spring / damping cartridge is functionally identical in both, and you still just have two tubes sliding over each other.

There is no intrinsic reason why USD forks are any stiffer - remember that a pound of alloy steel is stronger than a pound of aluminum alloy.

Apart from at the extreme end of the performance spectrum USD forks are just a gimmick for the ill informed and the gullible, and the have been very successful in that regard.

 

[cookie]

The GS is a soft roader, and was fitted from the factory with a 90 mm wide 70/30 semi off road tire.
If you use the bike as it was intended and fit similar tires , or indeed any 21" tire they simply wont have enough grip to flex the GS forks , which incidentally are only 1mm smaller than the forks fitted to Moto GP bikes.
So perhaps you should be better writing to Ohlins and Marzochi and telling them they don't know what the are doing,I am certain they would be interested in your special knowledge, but make certain you enclose all your engineering calculations which show that they are wrong!

That is truly a standout post, even considering the the tosh you usually come out with.

Comparing airhead forks to MotoGP forks. Outfuckingstanding!

 

[ianboydsnr]

My G/s forks twist more than slow me down,

I will make a fork brace, or add a second disc, or both at some stage.

 

[ianboydsnr]

Why don't you guys spend a little time on google and find out something about Moto GP forks and suspension in general.
FWIW Moto GP forks are designed to flex , they are the only suspension when the bike is 55 degrees over!

At the performance level of road bike forks , at any given performance level USD forks are heavier and more expensive to make than RWU forks.

The spring / damping cartridge is functionally identical in both, and you still just have two tubes sliding over each other.

There is no intrinsic reason why USD forks are any stiffer - remember that a pound of alloy steel is stronger than a pound of aluminum alloy.

Apart from at the extreme end of the performance spectrum USD forks are just a gimmick for the ill informed and the gullible, and the have been very successful in that regard.

Surely the reason is that the thinner part of the forks is at the top on rwu forks and at the bottom on usd forks, ergo they flex less, because they are clamped by the thicker bit.

 

[mikeyboy]

I would agree that a better fork brace may reduce the effect of heavy braking on the forks, but to suggest that the great long, gangly forks don’t flex because they’re similar in diameter to forks used in motoGP is daft.

These bikes are 20,30 years old.you really cannot make a comparisment to anything modern,
The whole design is basic,it’s carrying a massive amount of unstprung weight,
The damping cannot be tuned to any degree.
The spring rate can be changed but,,,,,,
If you want to really improve stuff you have your work and wallet on a work out.

 

[mikeyboy]

Why don't you guys spend a little time on google and find out something about Moto GP forks and suspension in general.
FWIW Moto GP forks are designed to flex , they are the only suspension when the bike is 55 degrees over!

At the performance level of road bike forks , at any given performance level USD forks are heavier and more expensive to make than RWU forks.

The spring / damping cartridge is functionally identical in both, and you still just have two tubes sliding over each other.

There is no intrinsic reason why USD forks are any stiffer - remember that a pound of alloy steel is stronger than a pound of aluminum alloy.

Apart from at the extreme end of the performance spectrum USD forks are just a gimmick for the ill informed and the gullible, and the have been very successful in that regard.

Whilst I’m not going to get into an argument with you boff,
If you pick up a set of usd forks from something modern they are noticeably lighter than old stuff.
Physically bigger but lighter.
Then we get to wheels,,hmmm carbon fibre?
Tyres hmmmmmm.
So we get to the flex,,,,
The whole reason forks got bigger was to increase the ridgitity but not the weight due to increased diameters and thinner wall diameter.
There’s a whole lot more to talk about if you wanted but what’s the point?

 

[Beemerboff]

Cookie, the only comparison I made was the size, and if you are numerically challenged 43 mm is actually quite close to 42.

If you look at the current 200 hp superbikes very few have forks greater than 43 mm, and they will put considerably more strain on their forks than a 50 something horsepower airhead.

It is a simple fact that for any given strength RWU forks are lighter than USD forks.

There is an excellent article in the August issue of Roadracing World and Motorcycle Technology which traces the development og Moto GP frames and suspension.
It was written in conjunction with Kalex and Ohlins, and if you can access a copy you will find that the key is controlled flex , there is no particular merit in rigidity for rigidity's sake.

And no slight intended Mikey, the first rule of business is is finding out what you customers want, and giving them it., no profit in telling a man with money he is asking for the wrong thing.

My GS has been repeatedly tested against USD forked frankenbikes, and on every occasion the combination of stock forks with HPN inserts and an Ohjlins with the stock #80 whatever spring has proven to be superior to any alternative - HPN and Ohlins know what the are doing!

There is actually no such thing as a spring which is progressive to any meaningful degree, for any meaningful time, so Cookie, don't feel alone, there are plenty of others who would call them selves suspension experts taking a lot of tosh about suspension too!