I'm running ZX7R forks and an Ohlins rear shock on my MC21.

The fork length is 29inches, compared with the MC21 standard of 28" (correct me if wrong). I have dropped the front end 20mm through the clamps so it roughly matches the original front, and have the rear shock at max ride height.

My question is: What is the best geometry balance for the NSR? I have heard that dropping the front by 15mm over standard is good, but does this take into account standard or increased rear ride height?

I have ridden it with max rear height and full height on the front and it was good, but felt like there was something missing, hence dropping it down on the front and asking the question of knowledgeable people.

Also if it helps, I'm using Bridgestone 250GP slicks.

You're in for some fun - Im working thru similar set up myself at the moment.

The slicks raise the front by 8mm and the rear by around 12mm over standard tyre sizes. So overall your c of g is now higher and possibly more forwards than previous.

Dropping just the front or trying settings that 'work' for the NSR won't really work. It's not really an NSR anymore.

Work through it methodically to find what works for you.

Do you know if the ZXR forks have changed the offset of the forks / front axle at all?

It doesn't hurt to try in regards to lowering the front ride height. Try 5mm at a time and see what you get for results. I would say rear first but you're maxed there.

greggo wrote:You're in for some fun - Im working thru similar set up myself at the moment.

The slicks raise the front by 8mm and the rear by around 12mm over standard tyre sizes. So overall your c of g is now higher and possibly more forwards than previous.

Dropping just the front or trying settings that 'work' for the NSR won't really work. It's not really an NSR anymore.

Work through it methodically to find what works for you.

Do you know if the ZXR forks have changed the offset of the forks / front axle at all?

Thanks Greggo. Good point there. It's true that it's not a true NSR anymore, but reference points for setup are handy.

Thanks for the tyre measurements. I am using an RVF 3.5 front wheel though, was your 8mm for a 3.0 inch front wheel? The rear is the standard Magtek 4.5, so your 12mm is probably accurate there.

The ZXR triples have approx. 35mm offset (will need to confirm that when I get home - it may be slightly less at around 32mm). So my theory was to get a general setting close to what is know to work for the chassis, then make changes from there.

For example, if I wound down the rear ride height by 12mm to what would have been the max height with stock tyres, then dropped the front approx. 32mm (ZXR forks already 24mm longer than NSR), would I achieve the same rake and wheelbase of the NSR with standard forks and an ohlins rear shock?

I know that the trail is not so simple to correct, though reducing the rake further could balance that right?

Does anyone have the MC21 standard rake, trail, wheelbase and offset figures?

Or would adopting a standard fork length with max ride height on the rear (seemingly accepted as a good set up with stock tyres - and stock offset) be fine, given the larger tyre on the rear is likely to tip the bike forward and reduce the slick-induced rake and trail?

Though yes, the centre of gravity will be fractionally higher this way.

According to the data posted in the "Specifications" section:

Rake: 23 degrees 15 minutes
Trail: 87 mm
Wheelbase: 1340 mm

No data is presented for offset however, sorry.

r/
Dave

Looks like the offset for an MC21 (and I would assume MC28) is 35mm, which conveniently is the same as the ZXR750.

That means with standard tyres I could lower the front to match the NSR forks and it would match the original balance of the bike.

So, that being said, any suspension experts care to comment on the question of their ideal (for track/race) geometry setup (with an adjustable ride height shock)? And maybe any opinions on the affect the slicks have? Greggo?

Might help others with a ZXR conversion too (think the 400s are the same).

Cheers!

If you use a u.s.d ZXR front end try if possible to go for the 'R' model for the 750 or 'SP' for the 400. As they have an additional adjustment in the form of a dial located on the same casting the axle goes through and face backwards. On the standard fork there is just an unmachined plug in the casting.

On older ZXR750 front ends i've seen, sometimes the chrome worn through, so i'd check that before buying it as some of these front ends are over 20 years old. Not sure why the chrome fails, it may just be natural wear.

The spring rates will be completely wrong, regardless of playing with the dampening.

I'd be interested in the weight difference between ZXR and NSR forks, both in terms of sprung and unsprung mass.

I think at the time (early 90's, or 89 onwards for the 400) these fork represented a major leap forward, and this contributed to ZXR's reputation of being planted at the front.

Still for the amount of time it takes to change the front end over i'd spend the extra money and get later model front end with radial brake calipers even if it is mainly for aesthetics reasons and also i suspect the later the model year the easier you may be able to find something off the shelf to resolve the spring issues.

Dannyvirk wrote:If you use a u.s.d ZXR front end try if possible to go for the 'R' model for the 750 or 'SP' for the 400. As they have an additional adjustment in the form of a dial located on the same casting the axle goes through and face backwards. On the standard fork there is just an unmachined plug in the casting.

On older ZXR750 front ends i've seen, sometimes the chrome worn through, so i'd check that before buying it as some of these front ends are over 20 years old. Not sure why the chrome fails, it may just be natural wear.

The spring rates will be completely wrong, regardless of playing with the dampening.

I'd be interested in the weight difference between ZXR and NSR forks, both in terms of sprung and unsprung mass.

I think at the time (early 90's, or 89 onwards for the 400) these fork represented a major leap forward, and this contributed to ZXR's reputation of being planted at the front.

Still for the amount of time it takes to change the front end over i'd spend the extra money and get later model front end with radial brake calipers even if it is mainly for aesthetics reasons and also i suspect the later the model year the easier you may be able to find something off the shelf to resolve the spring issues.

I agree with everything you just said, no doubt a newer model front end would be much smarter.

However, the bike came with the Kawasaki forks and triples, which cost me nothing to keep. A little bit of work on the caliper brackets was required, but in all it was a lot cheaper to keep it on. Plus surprisingly the offset/trail etc can be kept pretty much as standard (slicks notwithstanding). I also keep the NSR brakes running on a 3.5 inch RVF wheel with the 296mm rotors. Ok they are not super modern, but it keeps the 'time piece' look while still being much better than standard. I think maybe I have spent about $400. Not too bad but it would have been much more to do it from scratch. No doubt a newer front end would be much smarter there.

Thanks for the good ZXR specific advice about the forks. Mine are pretty much mint on the chrome so I am lucky there, but I must have the base model ones as there is no dial adjustment where you say. What did this adjust specifically?

The forks have been resprung (again not by me) but I suspect that they are still too hard. Even so, I've been amazed at the stability and response from these forks when really pushing the bike hard. A test day is what I need to see what my next move is with the spring rate. The ZXR forks have a heap of available travel (which is maybe best not fully used) so it will be a case of adapting the setup to the lighter weight