Small clearance

[Alan85]

Hi everyone!

We’ve made a chopper. Its clearance must have been 5,5 inches, but, with a man of 175 lbs on, the clearance is only 3,5 inches. Do you think it’s gonna be enough? It’s comfortable enough to ride it; it’s set very low; but I haven’t run over any obstacles on the road yet.

Is 3,5 inches clearance going to be enough for a chopper?

Thank you a lot!

[Rogerborg]

90% complete, eh?

Clearance from where, to where?
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[Riejufixing]

Pictures?

[owl]

ebay link?

get to the chopper!

[A100man]

A decent chopper should have at least 6 inches surely?
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[Skudd]

If you went round the speed humps by me 18" wouldn't be enough.
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[stinkwheel]

So it's not a hardtail? I've seen lowriders with that much ground clearance but they were always hardtail lowriders.

If it goes from 5.5" to 3.5" when you sit on it, what's going to happen when you go over a bump?
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[Evil Hans]

[Evil Hans]

[skatefreak]

How good are you at avoiding speed bumps/pot holes

[Rogerborg]

[Teflon-Mike]

Oh-Kay.. we are all assuming you are talking 'ground clearance'

You say that it has 3&1/2 inches with rider on board; 5&1/2 inch without...

Lets start there; Old rule of thumb for setting up suspension is thatyou should have aprox 1/3 of the total suspension travel in 'droop', and 2/3 of the travel in compression.

So.. lets say you have 6inches of suspension travel, that would give you 2" in droop, 4" in compression... with the rider on board. When the rider gets off, suspension will uncompress, but there's still the weight of the bike on the wheels, so whatever you measure between rider and no rider, isn't 'all' the droop, only a part of it; to find out how much droop you have you would ned to put a jack under the bike and lift it until the wheels are 'just' on the floor but there's no weight compressing the suspension...

From your suggested 3&1/2inch, unloaded and 5&1/2inch loaded ground-clearance measurements, you have at least two inches of droop travel.... so, by guide, you aught to have at least 4inch of compression travel above that.... that would give a total travel of around 6-8inches plus...

Yamaha Diversion, has 110mm of total rear suspension travel, 140mm total front suspension travel. 4&1/3 inch rear, 5&1/2 inch front.

Using that as a guide for a typical road-bike; 6" of travel would be on the higher side; you might get that sort of travel on a dirt bike but it would be a bit more than we'd expect for a cruiser; the XV535 only has 3&1/2in at the back, though it does have 6in at the front, but I suspect that is the travel of the longish and heavily raked forks rather than the vertical axle travel of the wheel, which is likely more like 4in.

This then begs suggestion, that if you get 2in plus change in travel between loaded and unloaded, the suspension is PROBABLY rather on the soft side...

A cruiser would possibly have softer suspension, but, that would tend to be via softer damping, the springs still need to hold the bike up, and they can't be that much softer to do it.

So, it begs the suggestion, that the ground clearance is probably not the first thing to tackle... get the spring rates a bit closer to ideal first, or even without any bumps the thing will be bottoming out, and neither be comfy, nor handle particularly well... even for a chopper!

NOW... 3&1/2inch of clearance, with rider. Thats just one notional dimension... and doesn't tell us much. We need get into the realms of aproach angles, departure angles and 'break-out' angle, as well as overall length, and wheel-base.

These are more pertinant to 4x4's than bikes; as they tend to have bodywork infront of the front wheel and behind the back; on a bike all you have is a mudguard following the tyre, and on a dirt bike, that probably doesn't start or stop much beyond the vert top of the wheel. On a cruiser/chopper, particularly at the back, it may come a lot lower, but its likely still pretty close to the axle, and you'd need to do a pretty big wheelie to get the back mudguard to ground!

More relevent bit is the break-out angle, which is the gap between the wheels. Imagine a very long low-rider chop going over a big speed-bump; front wheel reaches it, and goes up the hump; it rides over the hump and is probably back on the level before the back wheel even reaches it. Now if the road-hump is 3inch high, and you have 3&1/2 inch of clearance under the engine cradle... you 'should' have 1/2 inch of space between top of hump and bottom of bike whilst it does it. Imagine a Mini-Moto, with incredibly short wheel-base and probably even less ground clearance trying same... now the ground clearance probably isn't as much as the hight of the hump, BUT, because front wheel doesn't come off the hump before the back gets on it... because of the very short wheel-base, it doesn't necesserily 'belly-out' on it. Your long Chopper, though, MIGHT.

Even though the nominal ground clerance is more than the height of the hump; as the front strikes the hump, the suspension will compress; as the wheel ramps over the hump, the suspension will 'recover', but then as the wheel reaches the other side, it will be inclined to compress the suspension again. Same will happen when the back wheel reaches, ramps and departs the hump. NOW how much ground clearance you may measure, is rather accademic; its how much ground clearance you have, LESS how much the suspension compresses, at each end, as it strikes and departs the hump.

Go over the hump very very slowly... less the suspension will be inclined to compress, more of your measured clearance you have, less likely you are to ground. Go over it flat out.... more likely the suspension to compress, more likely you are to ground.

As stock, the Yamaha XV535 Virago has just over 6" of claimed clerance (no rider), The XJ600 Divvy, just a tad less than 6"... You 'say' your chop has about 5&1/2inch unloaded, so its probably not far off typical.... and it's probably got 'adequete' clearance at that for most road use... IF you dont go charging road-humps too fast!

BUT... back to top... difference between clearance when unloaded and when loaded, DOES imply that you are using up more compression travel with rider-weight at rest, and the spring rate is just too soft.... so road-humps asside, you ARE more likely to have something that wallows and bottoms all over the place, and handles horribly, even as choppers and cruisers go, road-humps or no!

Also remember when picking your spring rates to allow for not just rider wight, but potential all-up weight, or rider plus a potential passenger, plus an anticipated luggage.
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[Riejufixing]

[Rogerborg]

[WD Forte]

pertinent Mike, pertinent
I'd have used applicakle meslef of corse.......
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[Teflon-Mike]

[Evil Hans]