Am I really fat or is my suspension buggered?

[upanddown22]

I weight 13st 7lb ish, but I'm constantly bottoming the forks on my Honda City Fly out under heavy breaking.

A garage recently replaced the oil seals but I have no idea how the forks were before they did the work as I'd only just got the bike. I'm guessing the springs are just buggered but before I go out and buy some new ones is there anything else that could make it really easy to bottom the forks out?

Also if I do replace them, should I replace with stiffer springs (if they're available?)?

Sorry for yet another post about my broken bike, I don't think she's seen much love

[Kickstart]

Hi

How much forks compress depending on a few things. Firstly the spring strength but also spring preload and also the air gap above the fork oil (as the forks compress the air gap gets smaller, and the air acts as a spring).

The grade of fork oil also makes a difference to how quickly the forks compress but ultimately not to how far they compress. If you use thicker oil you just slow down how quickly they compress.

Easiest is probably to use a couple of suitable size coils on top of the springs to act as preload and / or add a small amount of extra oil to each fork to reduce the air gap (do not add too much as if is possible the seals will blow).

All the best

Keith
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[upanddown22]

Thanks Keith, thats interesting about the air compressing. Sounds like it's worth checking that there is the correct amount of oil in there.

Any suggestions on a suitable coil to increase the preload? How much should I be looking to add?

[Kickstart]

Hi

Not sure on the City Fly, but probably some 2p pieces, or maybe old 10p pieces. Try a couple on top of each spring first.

Fork oil levels are normally measured from the top of the fork, with the spring out and the fork full compressed. Some makers give a figure for oil level, some for oil quantity and some for both. The level is the important bit.

I think the City Fly should have an air gap of 140mm, but not sure what oil it is meant to use.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[upanddown22]

[Kickstart]

Hi

All that is changing is the preload, so a limited amount it can achieve but it is cheap and fairly easy.

Coins are just convenient size disks to sit on top of the springs.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[Teflon-Mike]

Constantly bottoming the forks under heavy breaking.....

As kick suggests, upping the pre-load and firming up the damping is probably a worth while thing to do.
Little bikes tend to have pretty squidgy suspension to begin with.

But!

Probably more helpful to back up and ask WHY you are braking that hard so often you find it a 'problem'.
Braking is not a helpful thing to do.

OK, so it saves you running into the back of things, BUT every time you brake, you are dumping kenetic energy you've given the bike by accelerating, into the brakes, for them to dissapate as heat.

This is not good for MPG, becouse that energy had to come from burning fuel.

Its also not goood for safety. Heavy braking loads the tyre and uses most of its available grip to slow the bike down. This soes not leave much grip spare for steering or leaning.

Its also not good for service life. Loading the tyre under braking, normally puts far more force on it than you can get from cornering or acceleration. So it will wear out faster.

Not only will the tyre wear out faster, soo too will the brake, and the syspension, and the steering bearings all carrying thier share of that load.

If you are nose diving the bike a lot, I suspect that you are probably not riding very predictively, and reacting at short notice to the actions of vehicles ahead of you, rather than riding more predictively, looking further up the road, leaving a bigger gap, and giving yourself room and time to respond, so that you dont have to do so much on the brakes.....

basically when the car infront's brake lamps come on, you have already backed off and slowed down, and given yourself a bit more space, so you dont have to brake so hard, as you'll have been wathing up the road and predicting what that car is going to have to slow down for.

Are you a reletively new rider? Are you by any chance an existing car driver?

Riding to a forshortened horizon is a particularly common thing with riders coming from a reletively long time in cars, but a common newbie 'thing'.

Not saying its all 'your fault', but shifting the event horizon forward a bit, and trying to ride more progressively, predictively and smoothly, is always a good thing, and it could give your forks an easier time.

There might not be a lot wrong with them, especially if they were serviced by a dealer when you got the bike, and have the right springs and right oil and the correct amounts in them.

Though, on a hard worked newbie bike, that has had prebiouse owners bottoming them out the whole time, they MAY be a bit 'soft' from over work. In which case, adding pre-load or fork oil, wont solve the problem. Might compensate a bit, but the fundemental will be that the spring has lost its temper.

If you have a manual, and strip teh fork, it will give the 'free' length of the spring when removed from teh fork, which you can measure with a tape-measure.

It should also give the spring rate, which can be measured by measuring the compressed length under a known load / force.... or putting the spring on a work-bench hanging a coat hanger wire through it off teh top coil, and a 5l can of water (5Kg, or 50N) on the wire hanging out the bottom under the bench and measuring how much it comresses.... though it can be a bit hit and miss, as the spring out of teh fork will try and bend and wobble, and with that sort of load wont compess a huge aount and the accuracy wont be great, but might give an idea.....

Or you can just buy new springs and give it a go......

But, as a start, I'd have a think about your riding....... even if teh forks ARE duff... biggest improvement to ANY bike is to fit a better rider.........
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[upanddown22]

[G]

[upanddown22]

Update: Finally managed to look at the springs yesterday. Service limit is 579mm and my spring measured about 586mm but I can't work out which way the service limit is meant to be?!

Also put in 5 2pence coins, doesn't seem to have made a huge difference. Unfortunately I didn't get a chance to check the oil level.

[DrDonnyBrago]

[upanddown22]

[Kickstart]

[upanddown22]

[Kickstart]

Hi

Trouble with checking the level is that the normal tool to set the level is a syringe connected to a straight tube. Set the tube length to the air gap, over fill the forks (compressed with no springs in them) and suck out the excess. When the level drops so the tube can't suck out anymore then the level is right. Put the springs back in and put the caps back on. As you can see the process relies on having too much fork oil in there to start with.

If the tube is straight and kept parallel with the fork sides and in the middle then the forks can be a bit of the vertical when doing this (ie, in place in the bike).

Dry the fork springs off before putting them back in.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[upanddown22]

[Kickstart]

Hi

Think I would be tempted to get the relevant tool (cheap enough) and some fresh fork oil of the right grade and just change the oil (hopefully there is a drain screw at the bottom of the forks).

You never know what someone has done to the suspension before you owned the bike. Our ZZR600 had very dodgy handling when we got it which finally turned out to be thicker than stock fork oil.

All the best

Keith
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