Front Fork Dive

[leswaller]

Wirespokes
Got back home last night, first job this morning was to check the sag. The difference between fully extended and me sitting on the bike is 2.5"
What is the next step please?

[Barry]

Les

The simple rule for Laden sag is that it should be 28 - 33% of total fork travel and no more.  On your /5 with a published travel of 8.19" that's 2.29" to 2.7" so you are in the middle of the acceptable range which suggests the spring rate and preload are about right. You did this wearing full riding gear and took account of any stiction by averaging the measurements first by stroking the forks up and then down before taking the reading ?

Incidentally for an R45/R65 the published fork travel is 175mm or 6.89"  My laden sag measurement comes out at 26% with the stock springs which is a little low. It's beacuse I'm a lightweight at 150 lbs so there's not much I can do about that except put on weight but that would make the bike slower so it's definitely not an option to be considered.

It would be interesting if anyone else has taken sag measurements and could post their results together with the weight they admit to.

[leswaller]

Barry
Thanks for the information, so it would appear that the spring sag is ok. How then can I stop the nose dive. Incidentally the 2.5 inches was the average of a number of measurements varying from 2.3 to 2.7. I had the gear on, applied the front brake then pushed the bars up and down a few times between each measurement

[nhmaf]

How much oil are you running in your forks at present?
It seems that you could first try running a slightly greater amount (reduces amount of air space in fork tubes) and/or try a slightly heavier weight oil - like if you are using 5W oil you could try 7.5W, or if already at 7.5W, add another 30cc or so?   I don't think that you'd want to go as high as 10W in those forks, but maybe.

[tvrla]

So now we know you've got the correct springs for your weight.

I don't know if other springs are available that will possibly cut down on the dive, yet give you the same amount of sag.

Those are good suggestions about trying a little more oil per leg (decreasing the air space) and stiffer oil if that doesn't do it. Keep in mind that different brands of fork oil aren't the same - one's five wt may equal another's 7.5 wt. There are no standards they stick to.

After that, I'd try cartridge emulators. They help a lot!

Or, just don't use the brakes.   It's wonderful how those forks soak up the bumps!

[leswaller]

Thanks Nhmaf and Wirespokes.
I put Silkolene 7.5 oil in from the local BMW garage when I  changed it and there is 300 ml in each leg. Any comments on this please?
I have been doing a bit of lateral thinking and wondering if brake grab would cause the same symptoms?

[tvrla]

Yeah, don't grab the brakes and the front end won't dive!!!  

[nhmaf]

Hmm.  My manual shows for the /5 forks that 280cc per leg is normal.  You are already a bit over that, but you could perhaps go another 20-30cc I would think - definitely do use a rod/stick to measure the fluid height because you definitely want some air to remain in the tubes!   You've already verified that the sag (laden) of the bike is within spec, so the springs aren't totally kerflumpt.   If you put stiffer springs in there you will have a much stiffer, less compliant ride overall.

IT could be  that some of this is also just "the nature of the beast" - BMW did put those long travel forks for soaking up the bumps, and the /5 bikes were, I think, the introduction of the "gummi-kuh" terminology.

[leswaller]

wirespokes - not the grab I had in mind  
any thoughts on the other type of grab causing the initial drop
nhmaf - thanks I will try a little more oil and measure air height carefully. Any suggestions on minimum air height?

[Bob_Roller]

The problem with fork compression, is when the front brake is applied, there is a weight shift forward on the bike .

When the brake is applied the front wheel and the lower fork leg slow down, the rest of the bike is still moving at the same speed, the fork compresses as the rest of the mass of the bike tries to drive itself into the lower fork, the spring compresses to 'absorb' that energy and the fluid in the fork is forced through the metered holes in the damper assembly to 'release' that energy in a slowed down manner  .  

Try using your rear brake, you'll notice you don't get much, if any front fork 'dive', or compression .

It sounds like emulators are pretty much you're only real solution to your fork compression .

You have to remember that your bike is probably an early '70's era machine, nothing real high tech about it .

Unless you want to spend a fair amount of time, effort and money and in the end the results may not be what you want after all, pretty much accept the bike the way it is .

They're 'farm implements' after all !!!!!!

[Ed Miller]

After that, I'd try cartridge emulators. They help a lot!

Have you (or anybody else) fitted those to an R65 yet?  I wouldn't even know which ones to order.

I don't use my brakes very much either.

[tvrla]

I know of some emulators that cost about $50 and one of these days I'll try them. I've got them bookmarked somewhere - Mike's Yamahas or something like that. They're for a 650 Yamaha, but guys have used them in the larger beemers successfully.

[mrbindc]

I too have excessive dive and I'm looking at new fork springs for my R65.  So far I've seen OEM, Progressive, IKON and Wilbers.  Does anyone have any experience with the aftermarket brands?

Thanks!

[Bob_Roller]

I've got the Progressive brand springs on my '81 R65 I really didn't notice much of a difference in ride quality or handling in my opinion .

I changed them in '07 with 78,000 miles on the OEM springs, the original springs were about an inch shorter than they should have been when I removed them .

Personally, I don't think I would spend too much money trying to improve an R65 in the suspension area, it's an entry level bike that was meant for utilitarian usage and one up back roads cruising  .

[Barry]

Mike's Yamahas or something like that. They're for a 650 Yamaha, but guys have used them in the larger beemers successfully.  

Certainly the cheapest emulators I've seen by some margin.

http://www.mikesxs.net/products-19.html#products