70 section rear tyre

Corvus · Post by **Corvus** » Wed Jul 17, 2013 5:41 pm

I wonder how the rockster A arm conversion affects the anti dive properties? As well as the geometry under suspension compression?

Would it tend to send wheel travel (locus) more forwards or more backwards? Or is this effect mitigated by changing shock absorber length?

conkerman · Post by **conkerman** » Thu Jul 18, 2013 12:02 pm

The other option is buy a fireblade.

The R1100 is OK, it just needs a bit of muscle to make it turn. Try an old 955i Daytona, they really are a heavy old barge to turn in

slparry · Post by **slparry** » Thu Jul 18, 2013 12:36 pm

conkerman wrote:The other option is buy a fireblade.

The R1100 is OK, it just needs a bit of muscle to make it turn. Try an old 955i Daytona, they really are a heavy old barge to turn in

Paging Hayden to the house phone

Motocod · Post by **Motocod** » Thu Jul 18, 2013 3:07 pm

conkerman wrote:The other option is buy a fireblade.

The R1100 is OK, it just needs a bit of muscle to make it turn. Try an old 955i Daytona, they really are a heavy old barge to turn in

Wash your mouth out young man!

I'll probably never buy a Fireblade - except perhaps an early Urban Tiger one as a future classic. It's never been my way to buy "conventional" bikes, and I quite enjoy owning something different and a bit unusual. It might sound a bit daft, but purely because it's not as good as a GSX-R1000 is quite appealing to me - I like the fact that you've got to work at it a bit. Ok, reading that back it makes me sound a bit odd, but you know what I mean, right?!

Nik

Motocod · Post by **Motocod** » Thu Jul 18, 2013 3:09 pm

Corvus wrote:I wonder how the rockster A arm conversion affects the anti dive properties? As well as the geometry under suspension compression?

Would it tend to send wheel travel (locus) more forwards or more backwards? Or is this effect mitigated by changing shock absorber length?

What I'm wondering is whether you have to use the Rockster shock too? Can anyone confirm this please?

To answer your question, I think the simple answer is that by lowering the shock mount means the front of the bike is lower, effectively pitching it forward. Giving the same effect as dropping the yokes down the forks on a conventional front end. Steeper steeting angle = faster steering. That's my impression, but someone who's been paying attention better than me might be along shortly to point out the error of my ways!

Nik

Corvus · Post by **Corvus** » Thu Jul 18, 2013 5:07 pm

Motocod wrote:
Corvus wrote:I wonder how the rockster A arm conversion affects the anti dive properties? As well as the geometry under suspension compression?

Would it tend to send wheel travel (locus) more forwards or more backwards? Or is this effect mitigated by changing shock absorber length?
What I'm wondering is whether you have to use the Rockster shock too? Can anyone confirm this please?

To answer your question, I think the simple answer is that by lowering the shock mount means the front of the bike is lower, effectively pitching it forward. Giving the same effect as dropping the yokes down the forks on a conventional front end. Steeper steeting angle = faster steering. That's my impression, but someone who's been paying attention better than me might be along shortly to point out the error of my ways!

Nik

Hi

Thanks for reply. This kind of thing seems to bore most people to death, but I find it fascinating. Because Telelever has seductively conventional (ish) looking forks it is so easy to assume the same rules apply as they do to telescopics. They don't, generally. At least not as I interpret things anyway.

Whether lowering the shock mount to make the front sit lower will steepen the steering I'm not sure. I definitely would be skeptical about that. For one thing the wheel moves upwards in vertical fashion, maybe even slightly forwards, as the suspension compresses. Plus the steering pivot points move in relation to each other as the A arm swings through its arc of travel. This plays havoc with rake and trail.

I made the assumption that by using a shorter A arm, but leaving the top yoke alone, should "steepen" the steering. But it would also change the way the front wheel moves (the locus of the wheel spindle), which in turn would change the anti dive effect.

No?

Surely just shortening the front shock would move the A arm further into its normal arc of travel. How this would change the rake and trail I'm not sure. Maybe Telelever keeps a reasonably constant rake and trail as it moves? We'd need someone with a cad machine to tell us. Or else a patient person armed only with a set of compasses and graph paper. Hee Hee.

Give me the measurements and I'll do it.

Motocod · Post by **Motocod** » Fri Jul 19, 2013 9:22 am

Ironically, I'm sat at a CAD machine right now...

I think we're thinking the same thing, fundamentally. Steepening the steering angle, and producing a faster rate of turn. Would be interesting to compare the geometry of the 1100S with the Rockster - they seem more or less mechanically identical save for the front swingarm.

Nik

slparry · Post by **slparry** » Fri Jul 19, 2013 10:18 am

http://forums.pelicanparts.com/bmw-r110 ... lever.html

Boxermed69 · Post by **Boxermed69** » Fri Jul 19, 2013 10:19 am

How about a modified 11S front wishbone? A few of us have one. Some of us might get around to fitting it some time...

. Plenty of positive comments about this mod, and related discussion. Do a search on here.

Mike.

Motocod · Post by **Motocod** » Fri Jul 19, 2013 1:15 pm

slparry wrote:http://forums.pelicanparts.com/bmw-r1100s-r1200s-tech-forum/555807-r1100s-10mm-shortened-telelever.html

That's a good read, thank you. So the question is, is there anyone in the UK that's done this wishbone mod, and would they be prepapred to do another one?

Nik

slparry · Post by **slparry** » Fri Jul 19, 2013 1:18 pm

I may be wrong but I seem to recall someone here doing it at one time

Corvus · Post by **Corvus** » Fri Jul 19, 2013 4:08 pm

Motocod wrote:Ironically, I'm sat at a CAD machine right now...

I think we're thinking the same thing, fundamentally. Steepening the steering angle, and producing a faster rate of turn. Would be interesting to compare the geometry of the 1100S with the Rockster - they seem more or less mechanically identical save for the front swingarm.

Nik

The top yoke "method" is definitely different. Like all the high bar models (as opposed to clip ons), the stanchions are pivoted at the top, with the yoke centre pivot being rigid.

Not read the pelican link yet. Will do soon.

Cheers.

Corvus · Post by **Corvus** » Fri Jul 19, 2013 5:02 pm

Re pelican link.

I can see what has been done. So, I go back to my post higher up. What effect does this have on the anti dive properties? It must change it.

In theory it should also need a different spring rate as the leverage is a different value. Mind you, theory and practice are two different things!

I'm not being a party pooper here by the way. I think it's great that someone has had the know how and balls to carry out the mod. I'm just inquisitive as to how other things around it change. As they surely must have.

Presumably then, the rockster must use a shorter A arm too?

nab 301 · Post by **nab 301** » Fri Jul 19, 2013 7:30 pm

All here, rockster arm and all...

viewtopic.php?t=13910&postdays=0&postorder=asc&start=0

Corvus · Post by **Corvus** » Sat Jul 20, 2013 9:19 am

[quote="nab 301"]All here, rockster arm and all...

Thank you for that. You're a tolerant lot on here, thankfully.

If anyone could be generous enough to help me get my head around this.

I've read the linked thread, albeit a bit quick as there's a lot to read, trying to isolate the important bits, which seem to come from r550s.

So the rockster arm is not shorter after all, but has a lower bottom shock mount. I can clearly see how a shorter arm will steepen the rake, but, taken as a separate issue and not in conjunction with the shortening mod, I'm struggling to see the advantage of lowering the shock mount. Yes, this will alter the angle struck between top and bottom steering pivot points very slightly, but will this definitely steepen the rake? Will it also shorten the available travel on the forks? It should increase overlap, which is a good thing. And amongst all this no one seems to have mentioned anti dive.

Does the A arm point below or above horizontal in the static position? With std set up.

Has anyone considered a different top yoke position? Admittedly this would be a lot more involved on the bikes with the r1100s type yoke, but would allow you to steepen the rake and keep a longer A arm setting.