18" Wheel Upgrade: not that easy...

[Blackstridaaustria]

Hi Googleg,

welcome to Stridaforum!

I’m sorry to hear about your troubles, doing the same upgrade a few months ago I had no problem, but my Strida’s are 5.2, they seem to have a different snubber.

I guess your snubber looks like this:

http://picasaweb.google.co.uk/Human.Amp/StridaTech#

(Pictures by Human Amp)

This is the 5.2 snubber:

Do you see the difference?

@Googleg

I tried to adjust the belt tension but I simply could not manage to unscrew the screw under the bike ! I even twisted two screw drivers… Crazy !! Is there a special thing I should know to unscrew this thing ?

For my opinion the belt seems to be to loose.
To adjust belt tension please refer to pic 7 of Human Amp’s Picasa album, and look here:
[url]Adjusting belt tension?]

At first, you have to loosen the big groove nut with the correct tool (doing this by a hammer and a drift punch might damage the groove nut), then you should be able to loose the tension bolt with a 6 mm Allen key ( you actually used a screwdriver ?).
Typically the tension bolt is fixed by Loctite glue.

Thanks for your pictures, I noticed something strange on them:
As far I know, brake discs are usually marked with a rotating direction arrow (like a tyre).
You will find that arrow on the Strida front disc, the rear disc is not marked (!).
So, looking at your pictures, I think you mounted the rear disc the wrong way…

Here is some additional information from Hongkong Strida Club http://www.hkstrida.org/:

@STRIDA HK

We have the freewheel tool, but not the industrial strength equipment required to remove it. The freewheel is installed at the factory with an industrial strength pneumatic drill and is not easily removable. A proper bike shop (which we aren’t) may be better equipped to do this operation.

@Amuro Lee

strida.us
7. Keep belt tension as low as you can tolerate ! This improves efficiency and reduces wear.
On bikes without rear belt snubber, I run the belt tension so the weight of my arm (average) presses the belt to approx 2-5mm of the bottom tube – this means that in the wet setting off / up hills the belt can occasionally ‘pop’ over a tooth.
On bikes with a snubber the belt can have same (low) tension and belt will not ‘pop’.
8. On bikes with a rear belt Snubber; the snubber bearing should have a small gap, (approx
0.25mm) between it and the belt. So the bearing does not continuously turn with the belt
(occasionally high spots on the belt may turn the bearing momentarily – which is OK). The snubber works by ONLY stopping the belt rising out of the teeth under high loads, most of the time it is clear of the belt. To adjust the snubber gap, carefully slacken the lock nut and fixing bolt (v tight), and then the Bearing position can be adjusted, then re-tighten - Also see strida.com web site for more info.

D) More FAQ’s

1. Snubbers
   Question: “I Have a friend who is a good mechanical engineer, & he wonders why the “snubber” bearing is placed effectively at the centre of the rear sprocket rather than at the point where the belt starts to wrap around the sprocket?”
   Answer: This is a good question. The mechanical engineer is theoretically correct - the ideal theoretical position for the snubber would be at the at the start of the belt wrap. But this would restrict the bottom tube movement when folding, (ie when lowering bottom tube to the ground). Also I did some testing and found the position of the snubber
   around the rear pulley made marginal difference, to the effectiveness of the snubber - I think this is because when belt teeth jump, they ALL rise up over the pulley teeth together, so a snubber position is less critical than theory suggests. It certainly works 100% on Strida … Interesting factoids …
   Strida (and car cam shaft belts) are reinforced with Kevlar for super strength.
   However kevlar is a weird material with a reverse co-efficient of thermal expansion (ie unlike most materials, it gets longer as it gets colder and vice versa).
   In the early days of the Strida I didn’t realise this - so in the winter when I was testing early belt systems I’d set up the tension perfectly (in the warm workshop), BUT when testing it seemed to get loose, back in workshop it was OK … It took a lot of head scratching to work this out .
   Lotus cars 1st introduced snubber in the 1970’s when they were developing their 1st belt drive cam shaft engines … which used to jump in cold Canadian mornings - and wreck the engines … but their snubber where crude - did not have bearings and just forced the belt to stay engaged. Snubbers, especially with bearings are very neat because they do not touch the belt in normal use, only when the belt is about to slip - they allow the belt
   tension to be reduced and so improve efficiency and wear.

Best regards