Rear Shock Absorber Upgrade - Best to Worst

GregZ wrote:

floivanus wrote: Yeah, I knew you had the lesters on the restored one, my jealousy apparently made me forget you have multiple running clones though. Much better pic to boot.

The repro z1 shocks just as crappy as the OEMs? If they are my H2 will get something else instead.

You might have been referring to this photo while I restoring.........and damn it looks good problem is my ADD is so bad I dont know what the hell doing most of the time

Well I was over when it was in that shape, but lesters aren't my cup of tea. But that bike when it had the spokes and that 4 into 1 was plain sexy.

never mind

kaw-a-holic wrote:

Kidkawie wrote: If you ever worked on a $20k shock, if there is such a thing for bikes, even A kit Pro Ircuit units costs less, you would look at those Ebay shocks and laugh.

He wasn't referring to a 20K motorcycle shock. They were purpose built off road shocks for racing. Chris only does what he does because he is a member of another motorcycle forum and guys were asking about RFY shocks so he bought a set tore them down and gave his opinion. Guys them asked him to rebuild them. Due to the price point and so many guys building budget bikes he has rebuilt/upgraded quite a few of them. He is just offering information gentlemen. Take it or leave it. Members here are always asking about RFY shocks, I do not believe you will find anyone more knowledgeable about them than Chris. If you think they are junk don't buy them. Mine ride just fine. I have not had a chance to put a lot of miles on this set but I can say that the upgraded set by Chris versus the stock set I bought a few years ago ride better.

Hi Jon
I for one love to add knowledge to my KZ brain cells and Shocks and suspension are near the top of my want list.
When you speak to Chris please invite him to keep posting on KZR and share his knowledge with us here.
Thanks
Dave

Due to close proximity of the lower shock mount to the chain guard on the 750/4 model, both Progressive and Gazi have an offset eyelet on the bottom to improve clearance. These shocks are larger around than the stockers so the offset eyelet seems like a good feature to me. I'm not familiar with other KZ bikes but they also may have a similar concern. Both Gazi and YSS list the piston diameter on their spec sheet and I think (generally speaking) larger is better. So a large diameter shock body with offset eyelet seems like an attractive package to me. Gazi Sport X fits the bill only they are quite spendy. If I can find a set for $500 or so I'll pull the trigger.

Nessism wrote: What size is the piston and the shaft on those RFY shocks? I'm also curious about the inner workings of them. Maybe this is an incorrect supposition, but typically products like this start out as knockoffs of some well known product. What shocks are they similar to in terms of valving and general construction?

The piston size is right around 1.25" (31.75mm). The shaft size is 12.2mm. You are correct that these are obvious knockoffs. It's not clear what model of shock that they copied exactly, but the internals resemble many different brands including Fox and Ohlins. The have a simple piston, but use a short stack of shim both for heave and rebound. They however are not what I would consider a high flow piston, but that's to be expected really.

Kidkawie wrote: If you ever worked on a $20k shock, if there is such a thing for bikes, even A kit Pro Ircuit units costs less, you would look at those Ebay shocks and laugh.

Wasn't a bike shock. Rather, it was for a racing car. The $20k units were the okay units, the $30k units are the good ones. Five way adjustable with blow-offs and inertia controlled slow speed heave. Neat stuff. I wouldn't want to be the engineer (or team of) attempting to make them work though.

Nessism wrote: Due to close proximity of the lower shock mount to the chain guard on the 750/4 model, both Progressive and Gazi have an offset eyelet on the bottom to improve clearance. These shocks are larger around than the stockers so the offset eyelet seems like a good feature to me. I'm not familiar with other KZ bikes but they also may have a similar concern. Both Gazi and YSS list the piston diameter on their spec sheet and I think (generally speaking) larger is better. So a large diameter shock body with offset eyelet seems like an attractive package to me. Gazi Sport X fits the bill only they are quite spendy. If I can find a set for $500 or so I'll pull the trigger.

Piston size is directly correlated to the amount damping force you need. The amount of damping force required is based on the amount of weight bouncing on a given spring rate. The reason this Gazi model uses a large body and piston is because it's an emulsion design. Emulsion pistons generally are easier to tune with when they are large, but also sometimes require greater surface area. Emulsion designs work the oil into a forth, and frothy oil generates less resistance than oil held in liquid state. So to get a similar amount of damping force as a gas separated shock you need a bigger piston.

There are a few downsides to large body shocks. 1) Pistons have more surface area and generate greater friction on the inside surfaces of the shock body, 2) They take up more space. 3) They can be heavier.

There are a few benefits of the larger body. 1) They have more surface are to dissipate heat, a major concern with emulsion shocks. 2) Can be more robust.

GregZ wrote: I have been reading this thread and thought I would ad my two cents if it's worth that. I have restored many Z1's and as a purist always used original shocks. They suck period!!! even the repo's. The best absolute upgrade you can do on your old kz is upgrade to a modern rear shock. I Never had a good "progressive "shock, Hagon shocks are pretty good and might buy a set for my next bike. The best are old koni special D's I had a set rebuilt by the konimon and you wont believe the difference they make on a bike. Expensive but worth every penny.
You can go to Hagon usa and get a good set for kz900/1000 $219 worth every penny just get the SS slime line's

my two cents
here is my every day bike , ride with konis

A Progressive shock exists as a brand, but progressive damping force generally is frowned upon for road conditions. Make sure that you separate the two factors here. Progressive brand shocks are not the same as progressive damping force. In fact, for road conditions (and most dirt conditions) digressive damping force is preferred. This means that you arrive at a point in the damping curve where as piston speed is increasing, i.e. over sharp edge high amplitude bumps, that damping force decreases. This means that wheel will move over the bump rather than force the bike (platform) to move as well. Progressive spring rates create the same issue and again are generally not preferred up until the point that you are attempting to deal with chain pull and other anti-squat forces.

"In fact, for road conditions (and most dirt conditions) digressive damping force is preferred."
That is an interesting point, Chris. That is what I have always been told, and in fact, I believe the opposite is true with springs. That is, for a road-going bike, a progressive (not the brand) spring that is initially light will allow the suspension to work easily over small irregularities, providing a smooth ride, but will increase resistance over large irregularities to prevent bottoming.

TexasKZ wrote: "In fact, for road conditions (and most dirt conditions) digressive damping force is preferred."
That is an interesting point, Chris. That is what I have always been told, and in fact, I believe the opposite is true with springs. That is, for a road-going bike, a progressive (not the brand) spring that is initially light will allow the suspension to work easily over small irregularities, providing a smooth ride, but will increase resistance over large irregularities to prevent bottoming.

Progressive springs (or progressive wheel rates) are preferred for a number of reasons. Remember, for rear suspension with linkages you can actually have a straight rate spring but build progressive wheel rates using the various linage geometries. With twin shock bikes, you don't have this option. So in an attempt on racing machines to combat chain pull progressive springs sort of became the go to fix for a long time. And on street bikes progressive springs are liked because they give you a best of both world scenario. You can ride alone and have a fairly plush ride, but when you load up and you aren't necessarily sitting on the bump stops either. It was a good compromise in that sense. However, for the best performing suspension (for racing, etc.) we find that straight rate is more often preferred today. Squat/Anti-squat/chain pull can be adjust in other ways, thusly it is better to get away from a suspension compromise in their name. As far as I know RaceTech and some others no longer push their progressive springs (for rear suspension).

Thanks for all the awesome info Chris. I have not knowledge to speak of when it comes to suspension.

Nether do I.
All I can say is I'm not into racing and the series 12 Progressives with heavy springs work fine for me.
The only problem I have is they are wider at the bottom were they hit the chain guard and cause it to twist a little.
I have a chrome chain guard off a LTD that I'm going to try next.