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HPV grasshopper rear wheel offset ?

Posted: 19 Feb 2019, 11:33am
by NUKe
HPV wheel offset Grasshopper

At the weekend I needed to fix a slow puncture that I had been putting up with for a while (very slow). Wheel out tyre off so I decide to check and true the rear wheel at the same time. Put the wheel in the trueing Jig and noticed the rim was offset to the left by about 3mm to 4mm, more than enough to be noticeable, I bought the bike second-hand so no history for the wheel, and not knowing whether it has been replaced or rebuilt in the past, I assumed this was wrong I centred it and trued it up. Now in hindsight I am wondering if this was done for a reason. The lower chain tube in 1st catches on the tyre slightly, but always did (just enough to make a noise (in a gear I hardly use), but it did before , I had assumed this was due to the derailleur which I have a replacement for but was waiting for the next time I replace the chains to do. Anyone any idea is the wheel deliberately off set . I am beginning to doubt myself. its the SRAM Dual drive 24 hub.

Re: HPV grasshopper rear wheel offset ?

Posted: 19 Feb 2019, 11:37am
by [XAP]Bob
ICE trikes are offset to make the wheel strength symmetrical.

Don't need to dish a wheel at the rear of a trike (heck, it doesn't even need to run the middle of the two front wheels )

So I'd guess that it was built centred between the flanges, not the OLN.

Re: HPV grasshopper rear wheel offset ?

Posted: 19 Feb 2019, 1:51pm
by Tigerbiten
Next time the wheel out, straight edge down the centerline of the trike and measure the distance to the dropouts.
If the dropouts are symmetrical then the wheel really wants to be built centered.
It then all depends on the clearance between the tyre and the frame if you can get away with off-setting the rim to one side.

But I also rode for over a year on a trike which had a slight sideways bend to the mainframe after a slight crash while on tour.
Downhill around a bend and hit a patch of mud on the road which equalled very little steering or brakes so bounced a front wheel down a cornish bank for a few feet.
The extra sideways force due to the weight of the trailer was enough to twist the frame under the seat.
There was no difference in handling or tyre wear even though the back wheel was no longer in line with the center of the frame.
The only noticeable difference was the handlebars were no longer parallel with the cross frame when cycling a straight line.
So having the back wheel centered is not vital.

Luck .......... :D

Re: HPV grasshopper rear wheel offset ?

Posted: 19 Feb 2019, 1:54pm
by [XAP]Bob
IIRC the wind cheetah has it quite substantially offset by design.

Re: HPV grasshopper rear wheel offset ?

Posted: 19 Feb 2019, 2:15pm
by UpWrong
Surely a grasshopper rear wheel should be dished as normal so rim is centred between dropouts.

Re: HPV grasshopper rear wheel offset ?

Posted: 19 Feb 2019, 2:25pm
by Brucey
on a lot of trikes the rear wheel is less dished than 'it should be' which is actually a not too bad compromise; the wheel sees high lateral loads and the adverse effects of excessive wheel dish are worse than normal. Anytime the wheel is not in the centre the loading is uneven and the machine wants to turn slightly on a perfectly flat road. But real roads are not perfectly flat and on average a machine that wants to turn slightly rightwards on the flat is not so bad, it fights the camber that exists on most roads. Some designs have an offset in the frame so that an offset wheel (where the rim is better centred over the spoke flanges ) gives perfect track.

cheers

Re: HPV grasshopper rear wheel offset ?

Posted: 19 Feb 2019, 3:05pm
by UpWrong
The grasshopper is a bike. Maybe the rear wheel came from an Ice trike.

Re: HPV grasshopper rear wheel offset ?

Posted: 19 Feb 2019, 3:06pm
by [XAP]Bob
UpWrong wrote:Surely a grasshopper rear wheel should be dished as normal so rim is centred between dropouts.

I don't know if the GH dropouts are centred on the vehicle (or the desired rear wheel position).

ICE trikes have an offset rear triangle, so that a conventional wheel is undished in use (i.e. spoke lengths and tensions are the same each side), which helps provide additional lateral strength.

I currently run a normally dished rear wheel, which means that my tyre doesn't quite line up with the mudguard, but it's close enough..

One of Mike Burrow's latest two wheelers had the wheels offset, and that apparently rode just fine.

Re: HPV grasshopper rear wheel offset ?

Posted: 19 Feb 2019, 3:58pm
by NUKe
Thanks guys ,
Firstly I don’t think that there is an offset in the rear dropouts, Easily measured and I will check next time I take the wheel out, although the tyre seems to line up with the mudguard better now.
My wheel is now centred to OLN, suppose it could have been centred on the Flanges, athough it was dished beforehand or at least the spokes were slacker on the driver side. The question is why had somebody in the past done it that way, The only reason I can come up with it might have been done to give the rear mech a bit more room as it is a small wheel. I have got admit I realigned without thinking about it. It was afterward I wondered if there was a reason for it.

Re: HPV grasshopper rear wheel offset ?

Posted: 21 Feb 2019, 3:25pm
by firedfromthecircus
No mention of offset in the manual that I can see.

ftp://ftp.hpvelotechnik.com/anleitungen ... kes_en.pdf

Re: HPV grasshopper rear wheel offset ?

Posted: 21 Feb 2019, 4:18pm
by pjclinch
[XAP]Bob wrote:One of Mike Burrow's latest two wheelers had the wheels offset, and that apparently rode just fine.


The 8-Freight has an offset rear, the point being that you don't need to split the main frame tube so it's stronger/lighter. The rear wheel just attaches to the main frame spar. It doesn't make it awkward to ride AFAICT.

I imagine the same may well go for the Windcheetah trike.

Pete.

Re: HPV grasshopper rear wheel offset ?

Posted: 21 Feb 2019, 4:31pm
by NUKe
firedfromthecircus wrote:No mention of offset in the manual that I can see.

ftp://ftp.hpvelotechnik.com/anleitungen ... kes_en.pdf

I had come to the same conclusion. But thanks for looking
Since My original post,
I realised something was rubbing in first gear, not a gear I use day to day, this was the derailleur catching on the rim, this didn’t happen prior to realignment of the rim. I can see the derailleur is bent in slightly, I have a new one ready to go on as it seems to be mech which is causing it rather than the hanger(new one order to be sure) , so my intention is to fix it by replacing the mech. But the question is did a previous owner re-dish the wheel to accommodate the mech?
Edit
All resolved fitted a new rear mech.