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Message started by paulmarshall on 08/07/14 at 14:04:56

Title: Lowering the Front
Post by paulmarshall on 08/07/14 at 14:04:56

To all cafe racer builders what is the recommended amount to lower the front forks and still remain functional. Is leaving 1.5-1.75" of travel not enough?
http://www.chopcult.com/forum/showthread.php?t=7129

Title: Re: Lowering the Front
Post by Spamy on 08/07/14 at 14:29:43

I think I lowered mine 2 inches and it works out great.

I would hesitate to put a bigger spacer in there just for the fact that it is a serious PITA to put the forks together like it is.

The spacer makes it so that you have to compress the entire assembly in the bike while you try to start the threads on the caps.

Also I think its 3/4" aluminum conduit works perfectly as a spacer. Light weight, strong enough for the job and wont rust.

Title: Re: Lowering the Front
Post by paulmarshall on 08/07/14 at 14:42:10

Thanks Spamy. I like the way Braveteacher went and think I might do the same using 40mm PVC.
http://i1300.photobucket.com/albums/ag91/PaulMarshall1977/23ac2a98-a3e5-4ab8-a1aa-3d41dbf72bb5_zpsd8787821.png?t=1407447981
Braveteacher I hope you dont mind me posting your pics? Please let me know and I will remove it.

Title: Re: Lowering the Front
Post by Spamy on 08/07/14 at 14:54:47

The PVC may be fine, I would just be afraid of it degrading with the fork fluid and either deforming, dissolving or cracking.

But perhaps after the year or so that he has used it he may have feedback about its performance.

Title: Re: Lowering the Front
Post by verslagen1 on 08/07/14 at 15:30:16

4E6D7C70641D0 wrote:

Cut off several slivers and drop it into a jar of old fork oil.
take one out every so often and compare.

Title: Re: Lowering the Front
Post by paulmarshall on 08/07/14 at 15:34:31

746770716E6365676C33020 wrote:

[quote author=4E6D7C70641D0 link=1407445496/0#3 date=1407448487]The PVC may be fine, I would just be afraid of it degrading with the fork fluid and either deforming, dissolving or cracking.

But perhaps after the year or so that he has used it he may have feedback about its performance.

Cut off several slivers and drop it into a jar of old fork oil.
take one out every so often and compare.[/quote]
That is a excellent idea thanks Verslagen. That way if I see any signs of deterioration I can quickly remove and replace them with a alloy one.

Title: Re: Lowering the Front
Post by Michael L on 08/07/14 at 15:57:28

You can use steel if you want, they are soaked in oil inside. Also the rods are made of steel, so they wont be grinding on Them if you choose to use steel. I would make them out of aloy or steel, preferebly aloy, it's quite a long dis/assembly process..

And yes, no more than 2 inches.

Title: Re: Lowering the Front
Post by paulmarshall on 08/07/14 at 16:19:16

516E2B282D2D1D0 wrote:

Thanks Michael ;)

Title: Re: Lowering the Front
Post by Dave on 08/08/14 at 06:36:27

I was not satisfied that installing 2" spacers would leave enough fork travel, and some reports from folks who have done that complain of a rough ride.

I used a different set of fork yokes with clamps on the top and bottom, so that I could just drop the fork tubes in the yokes. I did install a 1/2" spacer, and that allows a bit more pre-load to account for the weight shift forward. Adapting the fork yokes from another bike (1980 RM400) was a lot of work - as the spacing between the fork tubes was narrower and I had to shorten the axle spacers, narrow the brake disc mounting surface, make a new fender mount, etc.

I think you could adapt a bottom yoke for use on the top of the bike, and that would give you the ability to have clamps on top. You would need to cut off the existing stem, then drill it to fit onto the top of the existing stem. If you are using clip-on handlebars, you don't need to worry about how to mount the handlebars. I converted one of these bottom yokes for someone on this site to use on top......but he has never reported that he has used it.

I made my spacer from steel. I would think the PVC would not have any problems dealing with the oil - but was concerned that with repeated pounding it would eventually deform.

Dave

Title: Re: Lowering the Front
Post by Spamy on 08/08/14 at 08:24:29

Do those caps work ok that way Dave? I notice you dont have the 10 mm spacer that is build into the stock top triple. I imagined that the o-ring seal would be into the threads without that spacer.

Therefore you actually have 1/2 inch spacer + 10 mm deeper cap equaling closer to 3/4 or 1 inch.

Title: Re: Lowering the Front
Post by Michael L on 08/08/14 at 12:04:20

775445495D240 wrote:

The way that works, is that by the top caps being 10 mm more down, it only gives 10 mm more preload, not lowering. You could actually chose to only add 2 inches of preload, and keep the forks the same length, or matter of fact, make the forks LONGER, by ~1 inch.

Have anyone noticed when their fork was not modified, that when you leaned the bike to the left on the sidestand, that the fork would stretch aproximately 1 inch, and when you sat on the bike again it would fall back down that 1 inch.. The first set of spacers I used was 1 - 1/5 inch, and it didn't seem that the fork was lowered 1 - 1/5, but that was because the fork would naturally drop down the same length as my spacers. But then when I sat the bike on the sidestand again, it didn't stretch anymore. So if you wan't to lower the fork by lets say 2 inches, you actually need to make spacers that are a bit longer than 2 inches, to acomodate for the ~1 inch, that the natural weight of the front, will press down the forks.. IF you measure from the standpoint from when the bike is ridden, and not when it's on it's stand that is..

Title: Re: Lowering the Front
Post by Dave on 08/08/14 at 12:35:53

My fork tubes are raised up in the top triple clams 1.5"....so it lowers the front end 1.5". That is one of the reasons I used the RM400 triple trees, the other reason was to reduce the offset between the steering stem and fork tubes....which increases the trail. The photo in the post above shows the fork tubes projecting above the top triple clamp by 1.5".

The 10mm is not an issue - the top caps are tightened into the threads and they really didn't do any lowering or preloading. The rubber O-rings seal between the nut and ID of the tubes. Since that photo was taken I placed some rubber O-rings in the gap just to make it look more finished. There isn't any need to take the time and machine a 10mm spacer......I have been riding the bike this way for 4,000 miles, and it works fine.

The other 1/2 inch of lowering and the additional pre-load comes from the spacers I built from steel. They don't allow the fork tubes to rebound fully - which then causes the existing spacers at the top of the springs to compress the spring an extra 1/2 inch when the to caps are installed. The RYCA method uses 2" spacers.....I used 1/2".

Dave