Lowering 750C

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Lowering 750C

Postby Rob@TZP » 10 Sep 2017, 03:25

Hi Guys - So glad the forum is back.
So....if I want to lower the back end of my 750 by an inch or so, what would you say? It would just be changing the shock/spring set-up right? Any suggestions on what to get? I'm no peg-scraper so I don't think dropping the ass a touch will be my undoing.... :D
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Re: Lowering 750C

Postby Freddy » 10 Sep 2017, 05:33

Rob@TZP wrote:Hi Guys - So glad the forum is back.
So....if I want to lower the back end of my 750 by an inch or so, what would you say? It would just be changing the shock/spring set-up right? Any suggestions on what to get? I'm no peg-scraper so I don't think dropping the ass a touch will be my undoing.... :D


You did ask ......
Simple answer, No! Raise it by an inch if anything.

Dropping it an inch will significantly reduce ground clearance. You may not be a regular 'peg scraper', but I'd be willing to gamble if you check the ends of the foot peg feelers they won't be in pristine condition. They will have scraped the ground at some point. All you need is to be coming down a steep hill, hard on the brakes, sitting in a 'classic' style, into a reducing radius corner with a 'negative' road camber and I'll guarantee a Zephyr 750 will drag the inside peg. I know one such corner where it'll always happen unless I hang way off to reduce lean angle.

And don't take 'dragging hard' parts on a motorcycle lightly as you often see on internet forums. It is a big deal, because you can't tighten up your line further. Whatever the arc you're on when the peg starts dragging, is the arc you'll be on through the remained of the curve (or less as you stand the bike up in fright). That's probably going onto the wrong side of the road, or off the road edge. View dragging hard parts as a potentially life threatening situation. You are planning to increase that risk. Question: Why do cruiser riders crash so much in corners?? Answer: poor ground clearance.

Also, by dropping the arse of the bike you'll increasing the rake angle of the front forks. Effectively making the bike into a mini version of a Captain America chopper. This may make it slightly more stable in a straight line, but will make it harder to turn into a corner. It will also have a tendency to run wider in a corner than if the suspension was set correctly.

Also, a Zephyr doesn't have all that much rear end suspension travel, and will bottom out. If you drop it an inch, that 1 inch less travel it will have.

OK, now you know the pitfalls. If you still want to proceed, why not simply reduce the rear preload to the minimum? If your are average weight, on the minimum preload settings the rear suspension should be way down in its travel.

P.S. If you are wanting to lower the bike because of being very short, lower the front an equal amount to keep the geometry of the bike correct by also dropping the forks an equal amount through the triple clamps.


You did ask for opinions ......
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Re: Lowering 750C

Postby Rob@TZP » 10 Sep 2017, 06:19

Yep I did ask for opinions and I appreciate them! I've taken your advice and reduced the pre-load on my springs to almost nothing. I'll see how that goes. I've looked at the chain tensioner flip to lower it and it's already sitting down. Reason for wanting the drop is my ducks' disease lol.
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Re: Lowering 750C

Postby Stu » 10 Sep 2017, 09:26

I'm with Freddy... I've lifted the back end on the last four bikes I've owned. The first thing I did with the Zephyr when I got it home was rotate the eccentrics to lift the back which helped. I've since fitted slightly longer shocks. Haven't ridden it yet!

Can't claim I do it for clearance, normally to improve geometry. After experimenting, I often end up dropping the front a bit as well... dropping forks through yokes. This improves turn in and makes it more neutral in the turn, at the expense of a bit of stability. Most older bikes are set up slow steering and stable, which I find gives a tendency to run wide.

Having said that, the bike in my avatar was written off 2 minutes after that pic was taken due to running out of clearance and levering the rear wheel off the ground. It's not fun.

If you need it lower, can't you take some foam out of the seat?
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Re: Lowering 750C

Postby Rob@TZP » 11 Sep 2017, 01:47

Good idea. I might look at that first!
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Re: Lowering 750C

Postby Larry02ACR » 11 Sep 2017, 06:23

Rob@TZP wrote:Good idea. I might look at that first!


I highly recommend it as a first option. It's what I did with my KX250 (37"+ seat height!) so that I could ride it in the trails (enduro) instead of MX with it.

Being able to dab a foot in a slow technical section is vastly preferable to dropping and stalling the bike and having to kick start it in odd, recalcitrant situations...
- Larry
1990 Zephyr 550, 1978 KZ400, 2004 KX250
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Re: Lowering 750C

Postby Freddy » 11 Sep 2017, 07:26

Freddy wrote:P.S. If you are wanting to lower the bike because of being very short, lower the front an equal amount to keep the geometry of the bike correct by also dropping the forks an equal amount through the triple clamps.


I probably should clarify something ...... if you were to check the front rider sag of a typical Zephyr I'd be willing to bet it would be excessive. Soooooo, if you were to give the bike excessive rear rider sag to lower it, I'd first calculate how much excessive rear sag it's got. Then I'd measure the front rider sag, see how much excess its got, and if the 2 excesses are about equal, then you wouldn't need to alter the front. The bike would now just have the correct 'attitude' (think that's the right term) that the factory intended.

The suspension on a Zephyr 750 should compress from fully extended when the rider in riding gear sits on it, 30mm in the rear (measured between the rear axle and a vertical point on the chassis), and 40mm in the front (measured by using a cable-tie on the inner fork tube).

P.S. And if anyone wants to know if they have strong enough fork springs in the front, the amount the front should sag just under the weight of the bike alone, after the rider sag has been correctly set should be 24-28mm. If there is materially less than this number the springs are too weak. If materially more, the springs are too strong. This calculations will only work with linear type springs (standard in the C1 - C5 models I believe).
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Re: Lowering 750C

Postby ZR468 » 15 Sep 2017, 02:20

I am very happy with the ride height of my ZR750. It is low. I can flat both feet with my running shoes on. My inseam is 29-30". The chain tensioner is set at the highest point which is the lowest ride height. The seat has been shaved down by an inch by the previous owner. The rear shock preload is set at Notch #2. Acccording to the owners manual, notch 2 is for 150lb rider with no gears. I am 170lbs. The rear sag is perfect for me, 30% of the shock travel.
Kenny
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Re: Lowering 750C

Postby Rob@TZP » 01 Oct 2017, 00:54

Well, for what it's worth you were right @freddy.
Cruising through some northern NSW roads minding my own business I not only scrapped a peg, but scrapped the side stand as well. The bike skidded about 2 foot at the rear and then corrected nearly highsiding me - I was lucky I held it and there was a flat run-off spot.

.......Ok, so maybe I wasn't 'cruising' lol but you're right - I wont be lowering the bike anytime soon as I didn't feel that far lent over (there was a touch of -ve camber in the corner). This was the most dramatic 'educational experience' I've had to date (only been riding 2 years) and I intend to learn from it.
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