Topic: Front end "hop" at 35 mph.

[Inkscars]

Ok, I've been riding my bike near daily since june 4th. All of my modifications were complete before then and it did not do it for the first 200-300 miles.
Forks through trees about 2 inches, hard tail, new tires, wheels where trued and a couple spokes were replaced when he trued, mounted and balanced my new tires.

At 35 I experience a front end hop, if I speed up to 40, it stops, if I slow down to 30 it stops.
Sometimes it gets a little scary. 
So, I have no idea how much air is supposed to be in there. lol I know that's stupid. How much to you guys run in a 19" with an inner tube?
Other options or causes for this "hop"? It's an up and down sensation. It doesn't not jiggle my bars or wobble, if i watch the tire.
I can probably take my wheel back down to the fella that did the work, but he's a geezer and everyone in town says he's the best.
When I had it done I asked him what kinda condition the wheels were in and he said " very good considering their age, not even bent.
What kinda impact would I have had to have to bend a front wheel on this thing? I've hit some small potholes but, nothing that made me say " oh no! now my wheels bouncing!"
So, Maybe my forks are low on oil? Maybe I need new front springs? Maybe My wheel didn't get trued or balanced properly?
I come to you, because... well you know more than me.
TIA

[mlinder]

Check tire pressue. Proper pressure is listed on the tire itself. If that doesn't fix it, take it back to wheel guy for a re balance.

[Inkscars]

I looked I didn't see it. Stupid cheng shin. 
Thanks.

[mlinder]

I looked I didn't see it. Stupid cheng shin. 
Thanks.

Which cheng shin is it?

[Inkscars]

THe black and round one.......
I'm just kidding it's a nice tire....
Hang on lemme look on my old ebay stuff.

[Inkscars]

Well the seller quit selling the cheng shins because they "decided to stop importing" them
but on my email (from 11/08) says 100/90/19 "k673"

[mlinder]

Well the seller quit selling the cheng shins because they "decided to stop importing" them
but on my email (from 11/08) says 100/90/19 "k673"

well, pressure should probably be somewhere in the neighborhood of 30. Go check what you have it at.

[Spanner 1]

With respect, the correct tire pressure is noted on the tire and max. load sticker on the rear fender.....if not there then in the manual.....I can tell you it should be 28 psi, tho' !
Any psi # on the tire will be a max. psi the tire is rated for, not anything to do with the bike..

[mlinder]

With respect, the correct tire pressure is noted on the tire and max. load sticker on the rear fender.....if not there then in the manual.....I can tell you it should be 28 psi, tho' !
Any psi # on the tire will be a max. psi the tire is rated for, not anything to do with the bike..

Spanner, some of the tires are whacky and don't do as well at the honda recommended tire pressure. For instance, I run the avons at about 25 or 26, but run cheng shins a couple psi higher than rated by the manual. The dunlops I run even lower than the avons. All this, of course depending on the bike and load. It kinda gets all over the place, from bike to bike.

[MCRider]

Well the seller quit selling the cheng shins because they "decided to stop importing" them
but on my email (from 11/08) says 100/90/19 "k673"

Agreeing with mlinder in general. Once you've changed the original bikes setup, and tire brand and size, the recommended tire pressure can no longer be valid. With your modifications you're into a trial and error zone. But rather than being driven by your personal preference you're being driven by the tire. Not good.

To me the tire should perform satisfactoriy within a wide range of tire pressures. My Clymer manual says stock is 26psi. I've always run something higher 28 to 30. From there up to 85% of the max on the tire should be a good range.

Makes me think something may have happened INSIDE the tire. Cheng Shin does not have the best of reputation, though in general probably Ok for less than performance applications. Personally i wouldn't use one for any reason other than to keep the rim off the ground.

So if after experimenting with tire pressure, and realizing as you sy it didn't do it at first, you didin't change anything and now it does it, Iwould suspect the tire, internal ply separation or something like that.
PS: Such a problem may not show up on a truing stand or a staic balance stand. Only when it gets rolling. I'd save up and pop for a premium tire, Bridgestone or Avon, etc. Look around, you can find them on sale.
PPS: there may be a reason they decided to stop importing them
PPPS: I think its a DOT requirement that a max PSI/load number be printed on the tire. It won't be with the size markings, but somewhere else.

[Spanner 1]

Well, I've never gone lower pressure  on front tires...scared of stress on the side walls as the tire 'flattens' out on contact with the pavement and the rotating sidewall 'bulge' created, or am I just too anal !?

[Inkscars]

Thank you spanner, I understand. Although I asked a completely ridiculous question, I work In a shop and I understand that It SHOULD have these specs on the tire.
No offense taken and I appreciate your input.
I just didn't see it, and I thought maybe someone could say " WTF are you thinking putting 28 lbs in that!!"
It does look a bit low. It's supposed to rain at some point today, so I didn't ride into work as I do not get a break, I figured better dry, than wrecking.  
I will look for the 2 levels, If it doesn't have it, I will check pressure, if it IS low, I will increase to 28, drive, and then 30, drive. I hope that's all the issue is. All the consumer ratings on this particular brand when I bought it were maxxed out for the price of the tire.
I had been building my bike and just needed new rubber and figured any new rubber is better than no rubber.
Ok so after some more investigation, I found my actual reciepts and not generic fleabay invoice.
My front tire is a KENDA 100/90/19 k673 and my rear is a cheng shin 130/90/17 c907.

[mlinder]

Well, I've never gone lower pressure  on front tires...scared of stress on the side walls as the tire 'flattens' out on contact with the pavement and the rotating sidewall 'bulge' created, or am I just too anal !?

Again, it's depended on the tire and bike for me, spanner. I've had tires on bikes that at honda recommended PSI, did not have quite as much grip as I'd like, so I drop the pressure a couple pounds. And, with the cheng shins, since they aren't grippy anyway, I found the ride comfort was a bit better at higher PSI, now and then.

[754]

Could be:

Rim was trued for sideways, but not up & down.

Fork oil too light

Fork slider wear (common)

Tire balance

Tire not seated, or tire itself untrue

Combinations of the above..

[Inkscars]

Thanks 754. If air doesn't  make a difference. I will go to fork oil. If low I will add, if full, I can put a heavier weight, if that doesn't change it, I will be inspecting the soundness of the tire, and then last worst case scenario, take it back to the tech.

[754]

block it up, spin the tire, watch it carefully.. if it has up & down, changing the other wont cure it.

If it dont spin easy, bonk the caliper..

[Bodain]

My guess is it's really and up and down bounce... Your wheel is not round but rather oval. Odd that it would stop at slight greater speed..

Put the bike on centerstand. Now jack up the front of the to where the front wheel just a frogs hair off the ground. Give it a spin. If it's not round. You will know in a hurry. The high spot will drag the floor.

[Alan F.]

Hi Ink, I've got a few questions on your hardtail setup. Do you just have struts bolted up? Do the ends of your struts have a tight fit on the mounting points or are they rubber mounted? Does anyone else think that the rubber mounts on the swingarm aren't quite up to the task of supporting the load that solid struts exert upon them? New bushings there may be better up to it.

But how's your swingarm bushings? Does anyone think that a little play in there could cause this hop?
-Alan

[Inkscars]

Hi Ink, I've got a few questions on your hardtail setup. Do you just have struts bolted up? Do the ends of your struts have a tight fit on the mounting points or are they rubber mounted? Does anyone else think that the rubber mounts on the swingarm aren't quite up to the task of supporting the load that solid struts exert upon them? New bushings there may be better up to it.

But how's your swingarm bushings? Does anyone think that a little play in there could cause this hop?
-Alan

They are struts.
They seem to have been machined specifically for a honda mount because they have no room for up and down or side to side movement on the upper shock bolt. There aren't any rubber bushings.
I'm not sure how to "check for swingarm play" however when I had it apart i did try and teeter it back and forth and it didn't have any significant weird range of motion.
I suppose I could just get some if it comes to it. I believe there is a fella on the forums that makes them just for ours bikes, right?

[754]

I doubt any slop on the back , will translate into hop on the front..

[WFO]

Could be:

Rim was trued for sideways, but not up & down.

Fork oil too light

Fork slider wear (common)

Tire balance

Tire not seated, or tire itself untrue

Combinations of the above..

I have ran into tires that have factory defects or blems that can't be seen.

[alltherightpills]

I suppose I could just get some if it comes to it. I believe there is a fella on the forums that makes them just for ours bikes, right?

That'd be Hondaman.

[Alan F.]

I doubt any slop on the back , will translate into hop on the front..

Don't mind me, I've just finished Tony Foale's second book for the third time.

This guy wound up finding a flat spot on his front rim... http://forums.sohc4.net/index.php?topic=52789.0

Concensus here was front wheel bearings... http://forums.sohc4.net/index.php?topic=52983.0

Here's an interesting solution... http://forums.sohc4.net/index.php?topic=10608.0;all

Check out reply #14... http://forums.sohc4.net/index.php?topic=17978.0

[andy750]

I had the exact same issue only my hop was at 40mph...up or down of this and it was gone. It was tire pressure in my case as Mindler suggested. I am running Bridgestone BT-45s and had used 28psi up front. Tire was rated for 40psi max. I went for 32psi and hop went away and bike handled a lot better (since cruising speed around town/back roads is 40 mph).

I check tire pressure all the time...I one of the unlucky ones who always gets a puncture so I have become paranoid. I must be on 7 front tire and 2 rear tire punctures now (over 7 years, +35,000 miles). Checking tire pressure can sometimes give you a heads up that a tire is going down.

cheers
Andy

[Alan F.]

I've done some searching and there are plenty of other cases where the source of the front end 'hop' was located at the rear of the bike.  From rear sprockets that were out of round, chains with tight spots, swingarm bushings, worn out rear shocks, too aggressive rear shocks, wrong fork oil, clogged orifices in the fork dampeners, misaligned forks, bent triple trees, cracked triple trees, steering bearings too tight, steering bearings too loose, steering bearing races notched, flat spots on tires, flat spots on rims, tubeless type tires not seated correctly, bits of inner tube trapped under tire bead, a variety of spoked wheel specific issues, wheel bearing issues, axle issues, spacer issues, and frame issues. 

Since your most apparent mod is the rear struts, I'm thinking that your front end is reacting to the change in resonant frequency they made by exhibiting this vibration in the speed range you're noticing it.  Fork oil is where my search points me.  Have you changed it or is it old and original? Maybe go heavier or lighter than what's in there now... if you've changed it.

And be sure your forks are nicely aligned too, there's a Hondaman trick out there somewhere that roadracers used to align the forks, something about loosening certain things up and pogo-ing the front end up and down with the tire on the ground, then re-tighten the loosened things in a particular order... maybe he'll chime in...
Good Luck.
-A