Bad vibrations

[Hajuu]

Hey guys

I've just finished my second build a few days ago, and its already got probably 100km on it.

However i've just started noticing something, there is seemingly suddenly a LOT of vibration. Maybe i'm just going faster than I imagine but it doesn't feel like im going any faster, it just feels unbelievably vibratey.

So much so that it's almost unusable at its max speed as the handlebars are very hard to hold onto.

 

[motorpsycho]

the rims could be bent, tires could be out of round or have flat spots in them, wheel bearings could be loose, headset bearings could be loose...there are a lot of things that will cause a vibration.
yes, tires can be out of round, even when brand new.

 

[Hajuu]

Hm, i'm not familiar with that phrase 'out of round'. Does that mean like, isn't propperly round?

If I take the bike to a bike workshop what are my chances of getting the rear wheel tuned with all this kit on the bike?

 

[professor]

Really, this is simple stuff that you can do.
Go to youtube and punch in bike rims or something like "Lacing rims" and learn to do truing. All you need to do is buy a spoke wrench and they are very inexpensive.
Make sure your motor is tied down good. Plus check what Motorpsyco said.

 

[Al.Fisherman]

One of the first things one should do before anything else after choosing a bike is to flip it over and spin both wheels. I've bought 3 NEW bikes and not one of them were the wheels true. I now do it in the store to see how bad it is and choose a different bike. To true a wheel is very easy but at times can run ragged. A very bad out of round wheel (notice I'm talking WHEEL) can take some time to true up. There are a number of sites that take you through the process of truing a wheel on the internet. Now for out of round...both the wheel and tires can be out of round. The best way to check this is first true the wheel WITHOUT the tire, once the wheel is true install the tire and spin. A out of round tire will while spinning look like the tire is moving up and down while looking at it from the tread. Today, out of round tires are not as common as many years ago, and I'm talking when I was 15-16 and we used nylon (auto) tires. Back then to true a out of round tire they would mount the tire, balance it (No spin balance back then just bubble balance) and shave the high tread off the tire.

 

[Hajuu]

Some good tips there, i'll check it out - I do also feel a kind of slight 'bump bump bump' at high speeds if I put weight on the seat (rear wheel) instead of the pedals, but it's very slight.

Thanks for the tips anyway, i'll let you guys know how I go.

 

[motorpsycho]

actually, semi truck tires can be out of round (and i'm not just talking about re-caps or re-treads either)
I have seen brand new semi truck tires so badly out of round that they will shake the whole truck bad enough to make the driver think he has a busted axle, bad wheel bearing or a bent rim.
Bicycle tires can also be made out of round like al said.
yes, this out of roundness used to happen qhite often on the old bias ply nylon tires. but today we have nice radial tires, and i don't thin it happens too often with those.
But most semi truck tires and bike tires are not as sophisticated as radial car tires are, so there could be some casting /molding mistakes here and there. I don't think bike tires need to be made with the tight tolerances that car tires do.
after all, most bike tire mfg's probably think " the bikes that these tires are going on wil never see over 10-15 mph, so a little wobble won't hurt."

 

[Al.Fisherman]

after all, most bike tire mfg's probably think " the bikes that these tires are going on wil never see over 10-15 mph, so a little wobble won't hurt."

Same thing with the wheel itself...at 10-15mph you'd never realize the wheel itself isn't true. Kick it up some and it's very noticeable especially when someone is following you. I'd suspect this would raise all kinds of heck with the bearings over a period of time.

 

[Hajuu]

On a side note, I realised the simplest solution for the time being (going to attend to it propperly today now I have some time off) was some big foam handlebar mounts, big enough even to go over the throttle.

The vibration at max speed on a flat (WOT - not gaining any more speed) was at times so unbearable to my hands that at one point I actually believed myself to have a fractured knuckle/finger it was so sore. (all good though).

I'm thinking some additional vibration is being caused by;

1. After about 100km, the mounting bolts have come slightly loose
2. As a side effect/possibly always, the engine may have twisted a few degrees, making the chain not mesh with the gears propperly
3. A slight wobble on the wheel caused by either a buckled rim or 'out of round tyre' as you guys are saying, exadurated by speed - possibly also causing a partial rub with one side break pad unnoticable at such speeds.

Going to attend to it today as best I can.

The main thing that sucks is its all in the handlebars, the seat is quite comfortable still

 

[Hajuu]

Currently im thinking of taking the following steps:

1. Add on some very thick foam handlebar grips, with some weatherproof but removable glue.

2. Add thin rubber under the flat handlebar mount bracket and the seat post mount all the way along the inner tube (if it will fit!).

3. True up the motor alignment, add another set of rubbers (2x) to the engine mounts and tighten all mounting bolts

4. Give the clutch and chain a really good greasing/oiling.

5. Mix some fresh fuel with a racing 2 stroke oil (currently inadvertently using a lawn mower 2stroke). (Will this/Could this have an effect on vibrations?)

6. Grease and repack wheel bearings, retighten, check tyre rim for buckles and attempt to fix as possible, check tyre is not out of round.

Any other happy time generating vibe tips appreciated!