How Much Should I Shim A 3rd Gen Shock?

I know that you can't use the regular washer method to shim a 3rd gen shock... Luckily Jamie has said he will attempt to adapt a 929 shock to fit the 3rd gen mounting style. He has offered to add some lengh to increase rear height. The question is, how much should I have him raise the effective length of the rear shock? I have read as many threads as I can find refering always to 4th and 5th gens. It seems that 6mm is the typical adjustment.

What is everyones best guess then for the 3rd gen? Is the geometry more laidback than 4th and 5th? Do you think 10mm would be a nice improvement in response buy still allow use of the centerstand and not create chain issues? Unforturnately this mod will be permanent and cannot be changed once the shock is modded.


FYI I have raised the forks 5mm and had a noticable positive impact on the steering feel.

it is entirely possible to over do it there, if you already raised your forks leave it at that, shimming the shock on top of that will have you fumbling around at slow speeds and having a weird countersteering feel at speed. You can always reverse the forks, lowering the front and rasing the back will take too much wieght off the back tire and you will be fishtailing around on the brakes and not getting enough drive out of corners, and possibly tank slapping. If you like the way it feels now leave it at that. I assume of course you set the sag before you started doing all these mods?

HispanicSlammer, Jan 8 2007, 10:59 PMit is entirely possible to over do it there, if you already raised your forks leave it at that, shimming the shock on top of that will have you fumbling around at slow speeds and having a weird countersteering feel at speed. You can always reverse the forks, lowering the front and rasing the back will take too much wieght off the back tire and you will be fishtailing around on the brakes and not getting enough drive out of corners, and possibly tank slapping. If you like the way it feels now leave it at that. I assume of course you set the sag before you started doing all these mods?

Thanks for that warning. Noted.

Suppose I wanted to put the front end back to factory settings. what would be the rear shock shim height to get me back to this point? Are geometry adjustments to the front and rear interchangeable? Would 5mm rear shim get me back to where I am now?

Thanks

Oh, yes I set sag every year. This old suspension is just no fun to think about any more.

You have to consider the leverage ratio of the suspension linkage.

It runs something near to 2:1.

So if you lengthen your shock 5mm, you will effectively gain ~10mm ride height out back.

I thought it was close to 3:1, but am 100% positive on that one.
Anyway, you can't just increase eye to eye distance of the new shock and, taken the leverage ratio, calculate how much the rear is raised without taking into account the springrates of both shocks. Or does the cbr shock take the vfr spring?

From what I have read, raising the rear is preferable to lowering the front.

V4 Rosso, Jan 9 2007, 12:24 PMOr does the cbr shock take the vfr spring?

They are within 4% of each other IIRC. 15.3 vs 16

FWIW, I bought the tail riser from thurn which claims to raise the rear ride height by 33mm (really about 20mm), and that really seemed to put more life back in the bike. If you wanted, the most cost effective way might be to buy another stock shock linkage(looks like this) http://cgi.ebay.com/Honda-VFR-750-90-93-TA...tem270078106368 and simply shorten it by 6mm. When I compared the thurn unit to my stock unit, the eye to eye length was the only substantive diference. Any quality welding shop should be able to handle the mod for you and I figure the cost would be around $50-$80.

If you decide to do this, pm me and I'll put a caliper on the part and give you exact numbers for the stocker versus the modified unit.