Topic: Shock Lengths

[Alldatjazz]

Hi all. I've been rebuilding a 1982 Nighthawk 650, and have been having a tough time finding information regarding aftermarket shock Lengths for this bike.

I've been reading alot about motorcycle geometry etc, and raising the rear up/lowering the front for a cafe style positioning. Any insight into what lengths I should be looking at?

All the information I typically come across is for much more common bikes, unfortunately. The length adjustability on most units also seems pretty minimal, so I'd appreciate if someone could offer me a bit of insight into this.

[BenelliSEI]

I have no experience with your Honda model, but get pretty nervous when folks start altering the “stance” of their bikes by adjusting ride height at one end or the other...... if looking for replacements, measure your old shock length (usually at the centre of the mounting collar, both ends). Also, measure that same dimension when you are sitting on the bike. Your replacement should give you that same dimensions.

[Alldatjazz]

Thanks for the input! Yeah I hear alot of bikes turning to "tank slappers" from too high of a rear end etc. That's why I've been reading alot about geometry (rake,trail, wheelbase etc) of different styled bikes and how they interact with each other. Unfortunately I don't have a ton of real world experience with riding a bunch of models so it's a bit difficult for me to predict. It's quite a bit different than car geometry which is cool.

Unfortunately shocks are sold in small adjustability increments (350-360MM as an example). So it's really a p.i.t.a to approximate.

[Jimcg]

One thing to remember and probably obvious to most,  but at the same time easy to forget, is that small increases in shock length gives different raise at the wheel than you might think at first, as they are mounted in front of the axle and in a leaning angle. If the shocks had been mounted vertically and straight above the axle it would have been easier to calculate. The small adjustability increments you talk about might be more than enough.

The original ones on my CB650Z could be disassembled, so I inserted a nut under the top mounting eye and a collar under the spring which gave me the height I wanted. Even if that's not the solution you want to end up with it could be a cheap way to try out how a small raise affect handling and looks (pics in my project thread) before you spend money on new ones and might get disappointed, as I did.

/Jim

[Alldatjazz]

Thanks Jim that's some nice advice. Unfortunately it's winter here so no riding capabilities at the moment. I was gonna do the old wood block mock up trick to find the length I wanted, but I'm worried about potentially messing up the rideability/geometry. I'm more concerned with that than purely aesthetics, but it's difficult to find people with experiences with this particular model

[Don R]

 Read up on rake and trial, it's interesting but a math problem for sure. I recently asked about different offset triple trees on a cb750 F vs K of FB and ended up reading about it as the answers came in. It turned out I had it backwards and the F forks made more trail rather than less.

[Alldatjazz]

Don- I've read allot about Rake, Trail etc and have been trying to compare the numbers to all sorts of bike manufacturers models (including wheelbase, ride height etc) just to make sure nothing is crazy out of whack. It's been extremely tedious though. I'm trying to find a build calculator of some sort.

The odd part on this bike is the rake/offset. I can see why people do GSXR fork swaps on them. I'm tempted to do it also at this point.

[Don R]

https://www.facebook.com/marketplace/item/272606891463390/?ref=search&referral_code=marketplace_search&referral_story_type=post&tracking=browse_serp%3A1d1ddad2-166c-4fd0-93fd-b3cdf15ec0f9

[Don R]

 Honestly, in the 70's guys did ridiculous things with these frames and still rode them on the highway, lowering blocks, extended forks, crazy handlebars, sissy bars 4 feet tall, forward controls, slipping the front tubes through the trees, cut frame tubes, etc.